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PRINCIPLES OF HEATING

A practical and comprehensive treatise
on Applied Theory in Heating.

By WILLIAM G* SNOW,

Member

American Society of Mechanical Engineers.
American Society of Heating and Ventilating Engineers*

NEW YORK
DAVID WILLIAMS COMPANY

239 West 39th Street

7 it
?

Engineering
Library

PRINCIPLES OF HEATING.

PREFACE.

While the title of this book may not be sufficiently compre-
hensive, it perhaps expresses, as nearly as may be done in a few
words, the contents of the following pages. These are largely
made up of a collection of articles by the author, which have ap-
peared from time to time during the past few years in the Metal
Worker, Plumber and Steam Fitter.

These contributions have been supplemented by reprints of
articles relating to heating prepared by other writers.

Included in this work are the results of tests made by the
author on heating apparatus and systems, together with numer-
ous original tables and charts which he has found to be of prac-
tical use in the solution of heating problems.

Considerable space is devoted to a collection of articles on
Vacuum and Vapor systems of heating, in view of the amount of
interest manifested of late in this 'class of apparatus.

Special stress has been laid on the application of the heat unit
to the solving of heating problems.

It is hoped that by the aid of the complete table of contents
and the index persons interested in the subject treated will find
the data contained in the following pages convenient for refer-
ence.

BOSTON, 1907. WILLIAM G. SNOW.

The work has been revised, rearranged, and added to in
1912.

W. G. S.

271689

TABLE OF CONTENTS.

CHAPTER I.
HEATING POWER OF FUELS, BOILERS AND COMBINATION HEATERS.

PAGE

The Heat Unit - 7

The Heating Power of Fuels, etc 8

Efficiency of Boilers and Coal Consumption 8

Computing Grate Surface on a Heat Unit Basis 10

Heating Surface in Boilers and Furnaces 10

Hot Water Combination Heaters 1 1

Dome Heater 12

Ring Heaters 12

Vertical Slab Sections 13

Pipe Coil Heaters 14

Types of Combination Heaters 15

CHAPTER II.

GAS, OIL AND ELECTRICITY vs. COAL, AND THE CAPACITY AND FUEL
CONSUMPTION OF HOUSE HEATING BOILERS.

General Discussion 16

Electric Heating 20

The Capacity and Fuel Consumption of House Heating Boilers 2 1

How Compute Size of Boiler 22

Rate of Combustion 22

Amount of Fuel for a Season 23

CHAPTER III.
HEAT GIVEN OFF BY DIRECT RADIATORS AND COILS.

Notes on Heat Emitted by Direct Radiators , 27

Heat Given off by Indirect Radiators 30

Computing Indirect Radiating Surface 31

vi Table of Contents.

PAGE

Heat Given Off by Heaters Combined with Fans 34

Cast-Iron Radiation for Use with Fans 36

Temperature of Air Required to Heat Rooms by Indirect Radi-
ation 36

Size of Aspirating Heaters or Coils 37

CHAPTER IV.
THE Loss OF HEAT BY TRANSMISSION, COMPUTING RADIATION.

Computation of Heat Losses and Radiation 44

Computing Direct Radiation on the Heat Unit Basis 46

The Boiler Horse-Power and Radiating Surface Required to

Heat Isolated Buildings 53

Size of Heaters with Blower Systems 54

Relative Loss of Heat from Buildings Having the Same Cubic

Contents 56

Transmission of Heat through Concrete 58

CHAPTER V.

HEATING EQUIVALENTS, SPECIFIC HEAT, HUMIDITY, THE HEATING AND
COOLING OF AIR, ETC.

Convertibility of Heat and Mechanical Energy 60

The Mechanical Equivalent of Heat 60

Conservation of Energy 60

Heat per Horse-Power. 60

Latent Heat of Vaporization 61

Specific Heat and the Heating and Cooling of Air 61

Cooling Air - 63

Evaporation and Humidity 64

Actual and Relative Humidity 66

Cooling and Conditioning Air 66

Cost of Increasing Humidity 67

Expansion of Air and Absolute Temperature 67

Velocity of Air in Flues 69

CHAPTER VI.
HEATING WATER.

Heating Water by Submerged Steam Pipes » 72

Hot Water Generators 73

Boiling Liquids in Vats 74

Table of Contents. ' vii

PAGE

Heating Small Swimming Pools , . .... 75

Heating Large Swimming Pools , , , . 77

Amount of Steam and Size Boiler Required 77

Amount of Steam Pipe Required 78

Size Boiler Required 78

Tank Heaters 79

Water Backs and Gas Heaters 81

Coils for Heating Water 83

CHAPTER VII.
CAPACITIES OF PIPES FOR HOT WATER HEATING.

The Flow of Water in Pipes 85

Volume of Water to Supply Radiators 86

The Velocity in Hot Water Heating Pipes 87

Radiating Surface Supplied by Pipes of Different Sizes 87

Pipe Sizes for Indirect Heating 89

Sizes of Risers 90

Radiator Connections 91

Elbows and Bends 92

Expansion Tanks 92

CHAPTER VIII.

THE FLOW OF STEAM IN PIPES AND THE CAPACITIES OF PIPES FOR STEAM
HEATING SYSTEMS AND FOR STEAM BOILERS.

A Comparison of Formulas 94

Application of Factors to Table XXV 95

Resistances to the Flow of Steam 96

Effect of Condensation 98

Steam Flow With More than 40 Per cent. Drop in Pressure. ... 99

Relative Capacities of Pipes 99

Sizes of Steam Heating Mains 102

Sizes of Risers, One-Pipe System 104

Sizes of Risers, Two-Pipe System 105

The One-Pipe Circuit System 106

Pipe Sizes for the Two-Pipe Vacuum System of Steam Heating. 106
Comparison of Different Methods of Determining the Size of

Steam Mains to Supply Radiating Surfaces 108

Low Pressure Heating Mains 113

Sizes of Main Steam Pipe Connections with Boilers 116

Sizes of Steam and Exhaust Pipes for Engines 117

Effect of Back Pressure on Simple Automatic Engines. 119

viii Table of Contents.

PAGE

Effect of Back Pressure on Compound Engines 119

Counteracting Back Pressure by Increased Boiler Pressure 120

Steam Heating in Connection with Condensing Engines 120

CHAPTER IX.
MODIFIED SYSTEMS OF STEAM HEATING.

Two-Pipe Vacuum Systems 122

The Air-Line Vacuum System 126

Absence of Back Pressure 127

Steam to Operate the Ejector 129

Heating with Radiators at a Relatively Low Temperature 130

The Positive Differential System of Steam Circulation 130

Fractional Valve Systems of Steam Heating 131

Gravity Return Vacuum Systems 133

Advantages Claimed for the Mercury Seal Vacuum System. ... 135

Comparison with Hot Water Heating 137

Suggestions to Fitters for Installing Gravity Vacuum Systems. . 137

Vacuum Air Valve Systems 138

The Vapor System of Heating 139

Advantages Claimed for the Vapor System 146

The Atmospheric System of Steam Heating , 146

CHAPTER X.
HOT WATER HEATING BY FORCED CIRCULATION.

Central Hot Water Heating Plants 151

Hot Water Heating by Forced Circulation 1 53

Evans-Almiral Hot Water Heating System 156

Volume of Water Required for Hot Water Heating Service 159

Hot Water Heating by Forced Circulation 160

Hot Water Heating in the South Station, Boston 162

Hot Water Heating for Mills 163

Steam vs. Hot Water for Central Heating Systems 166

CHAPTER XI.
CENTRAL STEAM HEATING PLANTS AND MILL HEATING.

Central Steam Heating Plants 169

Central Power and Heating Plant for Government Buildings. . . 172

Data on Central Station Heating 179

Exhaust Steam for Heating Purposes 180

Table of Contents. IX

PAGE

Explanation of High Value of Exhaust Steam 182

Exhaust Steam Heating 183

Heating Versus Condensing 184

Some of the Factors that Affect the Cost of Generating and

Distributing Steam for Heating 185

Heating Systems for Mills 190

The Use of Steam from the Receiver of Compound Engines for

Heating Purposes 191

Receiver Steam 192

High Pressure Steam Heating 193

Relative Economy of High and Lojv Pressure Heating 193

CHAPTER XII.
THE STEAM LOOP.

The Steam Loop, by W. C. Kerr 195

The Steam Loop, by James Mackay 202

CHAPTER XIII.

NON-CONDUCTING COVERINGS. MISCELLANEOUS TABLES AND FlJR-

NACE TESTS.

Teasts of Steam Pipe and Boiler Coverings by C. L. Norton,
of the Massachusetts Institute of Technology, for the

Mutual Boiler Insurance Co., 1898 205

Steam Pipe Covering and its Relation to Station Economy 207

Economic Values of Steam Pipe Coverings 209

Chimney Flues _. 212

Tests on the Rate of Combustion in Furnaces and the Velocity

of Air in the Pipes 213

A Cold Day Test 214

Data on Size of Rooms, Pipes, and the Flow of Air 214

Other Tests 216

Advantages of Air Supply at Relatively Low Temperatures. ... 217

CHARTS.

A.RT

I. Ratios for Direct Steam Radiating Surface in Rooms with
Two Sides Exposed Toward the North and West, with
Glass Surface Aggregating 20 per cent, of Total Exposure. 47
II. Ratios for Direct Steam Radiating Surface in Rooms having
only One Side Exposed Toward North and West, with
Glass Surface Aggregating 20 per cent of Total Exposure. . 49

X ~ Table of Contents.

CHART PAGE

III. Ratios for Direct Hot Water Radiating Surface, Open Tank

System, in Rooms with Two Sides Exposed Toward the
North and West, with Glass Surface Aggregating 20 per
cent, of Total Exposure $I

IV. Ratios for Direct Hot Water Heating Surface, Open Tank

System, in Rooms with only One Side Exposed Toward the
North or West, with Glass Surface Aggregating 20 per

cent, of the Total Exposure 52

V. Space Heated per Boiler Horse-Power in Isolated Buildings

under Conditions Stated 53

VI. Showing Approximate Boiler Horse-Power Required to

Heat Buildings having Various Cubical Contents 55

VII. Showing Size of Steam Mains According to Different

Rules m

VIII,

TABLES.

TABLE

I. Summary, Giving Ratings for Different Classes of Com-
bination Heaters 15

II. Summary of Tests of Various Steam Radiators at Sibley

College 29

III. Loss of Heat from Pipes 30

IV. Heat Units Given off per Square Foot per Hour from

Indirect Pin Radiators Having 40 per cent. Prime
Surface — Steam, 5 Pounds Pressure, Entering Air

o degree F 31

V. Approximate Velocity of Air in Flues of Various Hights 42
VI. Loss of Heat through Brick Walls of Approximately the

Thickness Stated 43

VII. Loss of Heat through Stone Walls, Rubble or Block

Masonry 43

VIII. Loss of Heat through Pine Planks 43

IX. Loss of Heat through Windows and Skylights and
through Outside Walls of Frame Construction,
Expressed in Heat Units per Square Foot of Exposed

Wall per Hour 44

X. Loss of Heat, Expressed in Heat Units per Square Foot
of Surface per Hour, through Partitions, Floors and
Ceilings Separating Warm Rooms at 70 Degrees from

Cold Rooms at 40 Degrees 44

XI. Increase in Heat Losses Due to Special Conditions 44

XII. Thermal Conductivity of Concrete 58

XIII. The Weight of Mixtures of Air Saturated with Vapor

per Cubic Foot at Different Temperatures 62

Table of Contents. xi

TABLE PAGE

XIV. The Weight of Water Vapor per Cubic Foot of Saturated

Space at Different Temperatures 65

XV. The Approximate Volume to which One Cubic Foot
of Air at o Degree will Expand when Heated to the
Temperatures Stated in the Table. Volume of Air at

o° = i Cubic Foot 68

XVI. The Weight of Dry Air per Cubic Foot at Different

Temperatures 69

XVII. The Approximate Velocity of Air in Flues of Various

Heights 71

XVIII. Volume and Weight of Distilled Water 87

XIX. The Capacity of Mains 100 Feet Long, Expressed in the
Number of Square Feet of Direct Hot Water Radiating
Surface they will Supply with the Open Tank System,

when the Radiators are Placed in Rooms at 70° F 88

XX. The Capacity of Hot Water Heating Mains Expressed
in the Number of Square Feet of Direct Radiating

Surfaces Supplied 89

XXI. The Capacities of Pipes Expressed in the Number of
Square Feet of Indirect Hot Water Radiating Surface

they will Supply with the Open Tank System 90

XXII. Comparison of Ratings for Hot Water Risers 90

XXIII. The Capacities of Risers Expressed in the Number of

Square Feet of Direct Hot Water Radiating Surface
they will Supply on Different Floors 91

XXIV. Capacity of Expansion Tanks '. '. . . 93

XXV. Showing the Weight of Steam in Pounds that will per

Minute through Straight Pipes 100 Feet in Length. . . 95
XXVI. Factors to be Applied to Table XXV for Other Gauge

Pressures than 5 Pounds 95

XXVII. Factors Applying to Table XXV for Other Drops in

Pressure than i Pound 96

XXVIII. Factors for Other Lengths than 100 Feet 96

XXIX. The Resistance at the Entrance of Pipes Expressed in
the Number of Feet of Straight Pipe that would
Produce the Same Resistance as that at the Entrance 97

XXX. Equation of Pipes _... ....... 100

XXXI. The Amount of Ordinary Cast Iron Radiating Surface
that may be Supplied by Pipes of Different Sizes,
100 Feet Long, with 5 Pounds Initial Gauge Pressure 101
XXXII. Direct Radiator Tapping 104

XXXIII. Capacity of Up Feed Risers, One-Pipe System 104

XXXIV. Capacities of Up Feed Risers, Two-Pipe System 105

XXXV. Circuit System. Pipe Sizes and Approximate Safe

Capacities 106

xii Table oj Contents.

TABLE PAG»

XXXVI. Return Pipe Capacities for Two-Pipe Vacuum Systems. 107
XXXVII. Diameter of Pipe and Number of Square Feet Supplied. 112
XXXVIII. Size of Main Steam Pipes for Boilers of Horse-Poweer

Stated 117

XXXIX. Sizes of Supply Pipes for Steam Engines 118

XL. Sizes of Exhaust Pipes for Steam Engines 118

XLI. Showing Steam Pressure and Vacuum and Corresponding

Temperature , 136

XLII. The Number of Hours of Different Degrees of Tem-
perature During a Ten-Hour Working Day and on
Sundays and Holidays During an Entire Heating

Season of 200 Days 156

XLIII. Record of Steam Requirements in Central Heating 171

XLIV. Heat Losses in One Fourth Mile of Protected Steam Pipe 175

XLV. Heat Losses in One-fourth Mile of Hot Water Pipe 177

XLVI. Pressure Required to Distribute Water through One-
Fourth Mile of Pipe 177

XLVII. Effect of Exhaust Steam Utilization on Compound

Engine Economy 192

XLVIII. Data of Pipe and Boiler Covering Tests 205

XLIX. Partial Components of Different Covering Materials. . . . 205
L. The Saving, in Dollars, Due to the Use of Various

Covers 206

LI. Loss of Heat at 200 Pounds from Bare Pipe 206

LII. Comparison of Pipe Covering Tests 208

LIII. Composition of Coverings (Brill) 209

LIV. Minimum Temperatures Recorded in Various Parts of

theU. S 211

LV. Wind Velocity 212

LVI. The Approximate Grate Surface or Fire Pot Area for
Chimneys of Various Sizes and Hights, Based on
a Rate of Combustion of 5 Pounds of Hard Coal per

Square Foot of Grate Surface per Hour 212

LVII. Area of Fire Pot in Square Feet 212

LVIII. Anemometer Tests. Furnace Tests 215

LIX. Flue Velocities. Furnace Heating 216

LX. Space Occupied by Anthracite Coal per Long Ton 217

CHAPTER I.

HEATING POWER OF FUELS, BOILERS AND COMBI-
NATION HEATERS.

THE HEAT UNIT.

What the pound is to the grocej, and the 2-foot rule is to the
carpenter, the heat unit should be to those engaged in heating and
ventilating work. It is their unit of measurement and is the com-
mon sense basis of all heating calculations. Briefly stated, a heat
unit, is the amount of heat required to raise the temperature of I
pound of water i degree F.

To make practical use of the heat unit one must become famil-
iar with the heating power of fuels, the loss of heat through walls

Trie. METAL WORKER

Fig. 1. — Horizontal Tubular Boiler.

and glass, the heat emitted by radiators and many other facts bear-
ing on the subject. It is hoped this information will prove useful
to those who wish to know the " whys and wherefores " of heat-
ing calculations and are not content to blindly follow " thumb
rules," which may be good enough for small work, but for large
undertakings are apt to give very unsatisfactory results and bring
a serious loss to the contractor. A good grasp of the " heat unit
basis " gives one confidence to attack and the ability to solve al-
most any heating problem that may arise.

"&'*'•'•'•' Principles of Heating.

THE HEATING POWER OF FUELS, ETC.

Anthracite coal has a theoretical heating power of about 14,200
heat units per pound of combustible. With 10 per cent, ash and
noncombustible matter, I pound has a heating power of about
13,000 heat units. The smaller the coal the greater the percentage
of ash, 16 per cent, or more being not uncommon with the smaller
sizes.

Coke, like anthracite coal, consists almost entirely of carbon
and has about the same heating power.

Good bituminous coal has a heating power of about 13,000 to
14,000 heat units per pound of combustible.

About 2.Y-2 pounds of dry wood have the same heating power
as a pound of coal.

Taking a fair average, 25,000 cubic feet of natural gas, or
40,000 cubic feet of illuminating gas, are equivalent in heating
power to a ton of coal. A cubic foot of ordinary illuminating gas
has a heating power ranging, as a rule, from 600 to 700 heat
units.

The heating power of I pound of crude petroleum is about
21,000 heat units, the refined oil, or kerosene, having a heating
power, in round numbers, of 27,000 to 28,000 heat units.

Electrical heat units are: I kilowatt hour equals 3412 heat
units; I watt hour equals 3.412 heat units; I heat unit equals
0.293 watt hours.

A person gives off about 400 heat units per hour, an ordinary
gas burner approximately 4,000 heat units and an incandescent
electric light of 16 candle-power about 190 heat units.

EFFICIENCY OF BOILERS AND COAL CONSUMPTION.

To determine the probable coal consumption in a heating boiler
one must assume a certain efficiency. It is of interest in this con-
nection to discuss briefly the efficiency and coal consumption of
high pressure boilers of the types shown in Figs, i and 2, and to
show the application of the heat unit in solving problems of
this nature. A boiler horse-power is equivalent to 33,305 heat
units per hour; hence 3 pounds of combustible per horse-power
is equivalent to 11,102 heat units out of a possible 14,000 in
round numbers, representing an efficiency of about 80 per cent.
With 4 pounds of combustible per horse-power these figures

Heating Power of Fuels. 9

would be reduced to 8,326 and 60 per cent, respectively, the latter
conforming more nearly to ordinary working conditions than
does 80 per cent. Suppose a boiler evaporates 9 pounds of water
per pound of coal containing about 16 per cent, ash ; then i pound
of coal will contain only about 5/6 pound of combustible, or the
evaporation will be equivalent to about n pounds of water per
pound of combustible. To evaporate I pound of water at a tem-
perature of 212 degrees F. into steam at the same temperature
requires about 964 heat units ; hence the evaporation of 1 1 pounds

Fig. 2. — Water Tube Boiler.

of water by I pound of combustible is equal tp 10,604 heat units
per pound, or approximately 76 per cent, of the theoretical amount
of heat in the coal.

Such an efficiency may be obtained under well managed high
pressure boilers, but smaller cast iron heating boilers, illustrated
in Figs. 3 and 4, will with the less skillful attendance given them
have hardly more than 60 per cent, efficiency. In other words,
we would not be likely to transfer from the fire to the water in
the heater more than 8,000 to 9,000 heat units per pound of coal.

The distinction between coal and combustible must be -kept in
mind, the latter being only the burnable portion of the fuel.

Principles of Heating.

COMPUTING GRATE SURFACE ON A HEAT UNIT BASIS.

A knowledge of the heat utilized per pound of coal burned ai
the total loss of heat from a building, the latter to be comput
as described later, gives a convenient basis for determining t'
size of the heater, irrespective of the total radiating surface, (
which the size is commonly based. If each pound of coal burn*
gives up to the water in the heater 8,000 heat units ; dividing t!
total heat loss per hour from the building by 8,000 gives tl
weight of coal that must be burned. The grate surface is th<

THE METAL WORKI*

Fig. 3. — Sectional Cast Iron Boiler with Vertical Sections.

determined by dividing the weight just computed by 3 to 4 fc
small boilers, 4 to 5 for those of medium size, and by 5 to 7 fc
large sized boilers. These figures represent permissible rates c
combustion, expressed in pounds of coal burned per square fcx
per hour in house heaters.

HEATING SURFACE IN BOILERS AND FURNACES.

The proper grate surface is only one element to be determine*
It is equally important to see that the heater selected has tli
proper amount of heating surface well located. As to the amour
of heat absorbed per square foot of heating surface, the sma

Heating Power of Fuels.

1 1

boilers mentioned commonly have only 10 to 15 square feet of heat-
ing surface per square foot of grate, the medium sizes 16 to 20,
and the larger ones 20 to 25. These proportions, with the rates
of combustion stated, give from 2,000 to 2,200 heat units absorbed
per hour per square foot of heating surface.

Hot air furnaces commonly have 15 to 20 square feet of heat-
ing surface to each square foot of grate. Taking the average,
iJJ/2, and a 5-pound rate of combustion, the heat emitted per

square foot of heating surface would be — — = 2,400.

This figure is, of course, only approximate, the kind and location

THE METAL WORKES

Fig. 4. — Sectional Cast Iron Boiler with Horizontal Sections.

of the heating surface making some portions more effective and
others less so than the average. The heat given off varies also
with the rate of combustion, but not at all in proportion to it.

HOT WATER COMBINATION HEATERS.

At best it is difficult, in a combination system of heating, to
secure a proper balance between the hot water and hot air. Much
depends on the proper rating of the coil or special casting used
for heating the water. A number of tests made by the writer on
various types of these heaters have established ratings which may
safely be used in proportioning systems of this kind. In making
the tests, radiators were arranged so that the total amount of sur-
face connected with the heater could be nicely regulated to de-

Principles of Heating.

termine the total radiating surface that could be maintained at an
average temperature of about 160 degrees for hours at a time
with an even fire and an ordinary rate of combustion.

DOME HEATER.

A dome shaped cast iron section, of the general type illustrated
in Fig. 5, proved capable of maintaining an average temperature
in the flow pipe of about 160 degrees when supplying approxi-
mately 15 square feet of radiating surface to each square foot of
heating surface. A great increase in capacity was noted when
the fire was bright on top, the heater then being subjected to the
direct rays from the burning coal. At other times it was merely

FLOW,

DOME WATER HEATER
Fig. 5.— Type A.

RING WATER HEATED

Fig. 6. — Type B.

surrounded by hot gases. The rating given is that under average
conditions during an eight-hour run.

RING HEATERS.

A fire pot having a cored space 4^2 inches high by about I
inch wide extending around the entire circumference, as shown
in Fig. 6, was next tested. Three tests, each of about eight hours'
duration, showed this type of combination heater, having a total
of 5 square feet of heating surface, to be capable of heating to
an average temperature of 170 degrees, the water in the flow pipe
connected with 250 square feet of direct radiation. This is equiva-
lent to a capacity of 50 square feet of direct radiation to every
square foot of heating surface in contact with the fire. A combi-
nation of the ring and the dome shown in Fig. 7, has the heating
capacity stated in Table I.

Another combination heater of a similar type, shown in Fig. 8,

Heating Power of Fuels. 13

was tested, the cored portion of the fire pot being 8 inches high,
or about two-thirds the depth of the fire. Three eight-hour tests
proved these heaters capable of heating the water in the flow pipe
to about 1 60 degrees when connected with approximately 300
square feet of radiation. This heater had nearly twice the surface
of the one previously described, yet the radiating surface carried
was only about 20 per cent, more and was not so hot. Only about
30 square feet of radiating surface was supplied per square foot of
heating surface exposed to the fire. The rapid falling off in ef-
ficiency was due to the chilling effect on the fire of so large a body
of water, necessitating more frequent attention than with the

COMBINED RING
DOME HEATER

Tig. 7.— Typo C.— A Combination of A and B.

DEEP RING
WATER HEATER

Fig. 8. — Deep Form of Type B.

other combination heaters tested. The average rate of combustion
during the tests was about 3^ pounds of hard coal per square
foot of grate surface per hour.

In each of the three series of tests the drop in temperature
between the flow and return pipes was, on an average, about 20
degrees and remained nearly uniform throughout.

VERTICAL SLAB SECTIONS.

Some makers who use vertical hollow cast iron slabs in con-
nection with brick lined furnaces rate them as high as 75 square
feet of radiating surface per square foot of heating surface. This
rating is 50 per cent, greater than the highest one stated
above. With a brisk fire there is no question that a square foot

14 Principles of Heating.

of heating surface in direct contact with the fire will carry at least
75 square feet of heating surface, but it seems hardly wise to

PIPE COIL
WATER HEATER

Fig. 9. — Type F.

reckon on its doing so right along, in view of the kind of attention
commonly bestowed on furnace fires.

PIPE COIL HEATERS.

Coils of ij4 or i ^2-inch pipes, as shown in Fig. 9, make an ex-
cellent form of heater to combine with furnaces, especially if ar-
ranged so that the lower portion may be either above the fire or
buried in it, according to the hight at which the fire is carried,

Fig. 10. — Auxiliary Heater for Combination Heating.

thus giving a ready means of regulating the temperature of the
water ; since the coil, when in contact with the fire, is about twice

Heating Power of Fuels. 15

as effective as when the fire is kept several inches below it. Pipe
coils, when suspended above the fire, may be rated to carry from
20 to 25 square feet of radiating surface per square foot of heat-
ing surface, and say, 30 to 40 square feet when arranged as de-
scribed, the lower strand of the coil to be in contact with the fire.
Single coils placed in the fire will carry at least 50 square feet of
surface per square foot of coil.

Work installed on the basis of the figures above given has

Fig. 11. — Disk Heater for Com- Fig. 12. — Overhanging Type of Auxiliary

bination Heating. Heater.

proved satisfactory under the practical working conditions found
in dwellings :

TABLE I.
SUMMARY, GIVING RATINGS FOR DIFFERENT CLASSES OF COMBINATION HEATERS.

Rating expressed in the number
of square feet of direct radia-
ting surface, which may be
kept at a temperature of 160
degrees per square foot of
heating surface in the corn-
Description, bination heater.

A. — Cast iron sections suspended above the fire. 15 to 20

B. — *Cast iron sections in contact with the fire 40 to 60

C. — A and B combined 25 to 35

D. — Pipe coil suspended above the fire 20 to 25

E.— Pipe coil buried in the fire. 50 to 60

F. — D and E combined 30 to 40

* Capacity decreases as the depth of the surface in contact with the fire is
increased, since the deeper the section the greater the chilling effect of the
water on the fire and the harder to keep up the latter.

TYPES OF COMBINATION HEATERS.

Several common types of combination heaters on the market
are shown in Figs. 10, n and 12.

CHAPTER II.

GAS, OIL, AND ELECTRICITY vs. COAL, AND THE

CAPACITY AND FUEL CONSUMPTION OF HOUSE

HEATING BOILERS.

The question sometimes comes up whether to use gas or oil,
instead of coal, for heating purposes. On a heat unit basis, we
may not expect to utilize more than 8,000 to 9,000 units from each
pound of coal burned. Comparing this with gas having a heating
power of about 700 heat units per cubic foot, and assuming that
75 per cent, of the heat is transferred to the water in the heater,
we have 525 heat units utilized per cubic foot of gas burned.
From a ton of coal there would be utilized 2,000 (Ibs.) X
8,500 (heat units, as a maximum) — 17,000,000 heat units. This
amount divided by 525 gives 32,400 cubic feet, or the equivalent
amount of gas in heating effect. This volume of gas, at $i per
1,000, would cost more than five times as much as a ton of
coal at $6 per ton having the same heating power. Of course,
the great advantages possessed by gas over coal are the absence
of dirt and the ability to instantly turn on or shut off the heat.

The following statement by B. T. Galloway,* who made a
number of experiments on oil and gas heating, is of interest :

" Oil (and by this material we mean the refined product, kero-
sene) may be dismissed with a few words, as, after many trials
with numerous devices, it is found to be impracticable as a means
of heating water or generating steam. In all of our experiments
oil and gas were used to heat water circulating either in pipes or
ordinary radiators. Taking an ordinary heating plant, say with
a radiating capacity of 500 to 1,000 square feet, oil, when burned
in the boiler with any of the so-called hydrocarbon burners, would
be beyond the means of the ordinary house owner. The cost of
heating 500 square feet of radiation, using kerosene oil and the
best devices we have been able to secure or make, would be about
three times as great for oil as compared with anthracite coal,
provided coal was selling at $6 per ton delivered in the cellar, and
oil at 10 cents per gallon delivered in the same way. Then the

* See "Heating Experiment? with Oils and Manufactured Gas," by B. T. Gal-
loway, in The Metal Worker, Plumber and Steam Fitter, October 17, 1903.

Gas, Oil and Electricity vs. Coal.

labor of handling oil, watching the burners and keeping the ap-
paratus in order is fully as great as that connected with putting
on coal and taking out ashes. Furthermore, we have never seen
an oil device that could be entirely trusted, as experience with
them shows that, when least expecting it, they go wrong, and fire
and explosion follow unless great care is observed. The utiliza-
tion of oil, therefore, as described, is hardly to be recommended.

" There is one method of utilizing oil, however, which is
worthy of further trial and consideration — viz., that of adopting
as a burner the ordinary blue flame oil stove, of which there are

Fig. 13. — Type of Electric Radiator.

several kinds on the market. The burners for these stoves can be
bought separately. They have a gravity feed, and will run indefi-
nitely with little care and attention.

" It was found that boilers made for coal with their arrange-
ments for cinders, drafts, etc., were poorly adapted for the use of
a fuel as costly as gas. Only a small portion of the efficient heat
units in the gas could be utilized, the rest going up the chimney
or being lost in overcoming the resistance offered by the iron and
in other ways. With specially constructed boilers, and by such
we mean those where the flame of the burning gas can be brought
into direct contact with a large surface of some metal like copper,
much more effective results can be obtained than where ordinary
boilers made for coal are used. Types of such boilers are to be
found in those used for automobiles containing either a large num-
ber of small copper tubes or consisting of series upon series of

1 8 Principles of Heating.

copper coils through which the circulating water passes. Even
with such devices, however, it has been found impracticable to
sufficiently heat the water from a central plant, except at a cost
considerably more than that of coal at ordinary prices. In actual
practice the cost of the gas would be about double that of coal,
the price of the latter being estimated at $6 per ton, and the for-
mer at $i per I, OCX) cubic feet, 22 candle-power. Of course, in
this case there is no coalman to bother with, no ashes to take out
and no trouble in regulating the apparatus with the proper de-

Fig. 14. — Luminous Electric Radiator.

vices at hand. Theoretically, and practically too for that matter,
there is no reason why a householder could not light his burner
in the autumn and the apparatus would do the rest, until it was
time to turn the gas off in the spring. By means of properly ad-
justed regulators, the gas would be fed to the burner in sufficient
amounts to maintain a uniform temperature in the room above.
With gas at present prices this method of heating would be prac-
tically prohibitive for many, notwithstanding its advantages."

Extracts from an article by Donald McDonald on " Domestic
Heating by Gas "* seem worth repeating here :

* See " Domestic Heating by Gas," Donald McDonald, in The Metal Worker,
Plumber and Steam Fitter. October 24, 1903.

Gas, Oil and Electricity vs. Coal. 19

" Where the gas is the only source of heat and the room is
occupied as a bed chamber it is much better, although somewhat
more expensive, to use a closed heater provided with a good flue,
Such a heater must, however, meet many very rigid conditions ;
otherwise the flue connection will be worse than useless. First of
all, the flue must be so open and must run so high that a down
draft through it will be an impossibility. A few seconds of down
draft, carrying with it a load of carbonic acid and nitrogen, will
put out the fire, and the flue becoming cold, the down draft will
continue and the apartment become full of gas. No flue at all is

Fig. 15. — Non-Luminous Electric Radiator.

much better than this. The stove must also be so constructed that
no more air is drawn through it than is necessary to burn the gas,
otherwise there will be a great waste of heat up the chimney. .

" The amount of air required to burn the gas, if it is cooled to
300 degrees before it reaches the chimney, will only carry away
with it about 5 per cent, of the heat. Closed stoves, however, as
generally constructed, send up the chimney anywhere from 20 to
80 per cent, of the heat produced by the gas. Any device which
sends a part of the products of combustion up the chimney and
the rest of it into the room is simply folly. The part which reach-
es the chimney is no better and no worse than the part which is

2O Principles of Heating.

put into the room, and unless care is taken to send all the products
of combustion up the chimney it is much more sensible not to
send any of them.

" I have seen and heard many learned discussions as to the
question of whether a luminous flame or a blue flame produces
the most heat. Nearly all salesmen and dealers of gas stoves will
insist that the particular burner which they are advocating pro-
duces a great deal more heat than any other burner. Of course,
any chemist or any engineer knows that if the combustion is com-
plete and all the products of combustion escape into the room to be
heated, the room receives all the heat due to the combustion of the
fuel, and no amount of ingenuity can increase this i per cent. If
the combustion is not complete the odor will be so vile that no
one will tolerate it. In other words, in this class of stoves the
efficiency is almost always 100 per cent., and need not be con-
sidered at all in selecting them."

ELECTRIC HEATING.

To determine, on the heat unit basis, what it would cost to heat
a room with electricity by means of an electric radiator, or heater,
as shown in Fig. 13, let us suppose, for example, that it is desired
to know the cost of heating a corner room, 14 x 14 x 10 feet, ten
hours per day under average weather conditions. With, say, 20
per cent, glass surface, the equivalent glass surface, corresponding
to the exposure, would be (20 per cent, of 280 square feet = 56
square feet) + [% X (280 — 56) =56 square feet] = a total
of 112 square feet of glass; wall surface being rated as one-fourth
as much glass surface. One hundred and twelve square feet
of glass X 85 heat units per square foot an hour for 70 de-
grees difference in temperature X 1.25 (the factor for northwest
exposure) = approximately 11,900 heat units per hour.*

A certain allowance must be added for quickly warming the
contents of the room, apart from the transmission loss above com-
puted. To do this it is convenient to add to the computed loss of
heat through walls and windows a number of heat units equal to
at least one-third the cubic contents; in this case 1-3 X 1,960 =
653 heat units. This combined with the 11,900 heat units pre-
viously computed, gives a total of 12,553 neat units per hour.

See page 43 and following for a fuller discussion of computation of heat

Gas, Oil and Electricity vs. Coal. 21

Electric current, when metered, is charged for on the basis of
watt hours, a heat unit being equivalent to 0.293 watt hour.
Therefore, 12,553 neat units would be equivalent to 3,680 watt
hours ; or, to heat the room ten hours in zero weather by electricity
would require 36,800 watt hours.

The average amount, during the heating season, would proba-
bly not exceed, for a ten-hour day,^— X 36,800= 15,800 watt

hours, approximately. Ten cents per 1,000 watt hours is a not
uncommon rate for such service ; and at this price the cost to heat
the room ten hours per day in average weather would be $1.58, a
prohibitive cost.

With coal, such a room, with a 50 square foot steam radiator,
would, in zero weather, allowing 250 heat units per square foot of
radiating surface per hour and 8,000 heat units per pound of coal,
take only 50 (square feet) X 250 (heat units) X 10 (hours) -f-
8,000 = 15.6 pounds of coal, costing, say, 5 cents.

Electric heating is bound to be expensive in comparison with
steam, if the exhaust from the power plant goes to waste, since
about 90 per cent, of the heat of the steam passes away with the
exhaust from the engines. With, say, 75 per cent, boiler efficiency,
10 per cent, engine efficiency on a heat unit basis and 85 per cent,
on a mechanical basis (that is, allowing 15 per cent, for friction)
and 90 per cent, dynamo efficiency and 95 per cent, line efficiency,
we have for the combined efficiency of boiler, engine, dynamo and
wires: 0.75 X o.io X 0.85 X 0.90 X 0.95 = 5.45 per cent. The
efficiency of a direct steam heating system would probably be as
high as 55 to 60 per cent., or, say, 10 times that of the electric
heating system.

THE CAPACITY AND FUEL CONSUMPTION OF HOUSE HEATING

BOILERS.

Manufacturers' boiler ratings vary so- widely that it is worth
while for contractors to compute the capacities themselves and
not trust implicitly the figures given in the catalogues. The basis
of computation should be the grate surface and the rate of com-
bustion. In house heating boilers of medium size not more than

22 Principles of Heating.

5 pounds of coal should be burned per square foot of grate surface
per hour. As to a 5-pound rate being a fair maximum to assume,
it may be compared with horizontal tubular boiler practice in
which, with easy firing, a 10 to 12 pound rate is common. Such
boilers have 33 to 40 square feet of heating surface per square foot
of grate, whereas common sizes of house heating boilers have,
roughly speaking, 16 to 20. Hence, with half the heating surface
the rate of combustion should be proportionally lower in order
that the heat may be as well absorbed. This would give a 5 or 6
pound rate for house heaters.

HOW COMPUTE SIZE OF BOILER.

To ascertain the size of boiler necessary to supply a given
amount of direct radiation, say, 1,500 square feet, for example,
including the surface in mains, first multiply the total surface by
the heat given off per square foot per hour. With hot water, in
the case taken for illustration, this would be 1,500 X 150 = 225,-
ooo heat units. Assuming 8,000 heat units to be utilized per pound
of coal burned, each square foot of grate, with a 5 pound rate of
combustion, will give to the water in the boiler 40,000 heat units
per hour. Therefore the grate surface required will be 225,000 -r-
40,000 = 5.62 square feet.

RATE OF COMBUSTION.

The rate of combustion should not exceed 5 pounds for boilers
having, say, not over 6 or 8 square feet Q| grate surface.

Boilers with two or three times as large a grate are generally
cared for by a paid attendant, in which case there is no objection
to burning coal at a faster rate. Such boilers generally have more
heating surface in proportion to the grate than the smaller ones,
hence the increased output of heat will be readily absorbed and
the boiler will be just as economical as a smaller one burning coal
more slowly.

Small boilers with 10 to 15 square feet of heating surface per
square foot of grate should be rated to do their work on a 3 to 4
pound rate of combustion, corresponding to about 160 to 210
square feet of hot water radiating surface per square foot of grate.

Medium size boilers, with 16 to 20 square feet of heating sur-

Gas, Oil and Electricity vs. Coal. 23

face to I of grate, should be based on burning 4 to 5 pounds of
coal on each square foot of grate per hour, corresponding, in
round numbers, to 210 to 260 square feet of hot water radiation
per square foot of grate.

Large size boilers with 21 to 25 or more square feet of heating
surface per square foot of grate may be rated on a coal consump-
tion of 6 to 7 pounds per square foot per hour, or even a trifle
higher rate, where the heating surface is ample, corresponding
approximately to 320 to 370 square feet of hot water radiation
per square foot of grate. With steam radiation giving off, say,
250 heat units per square foot per hour, the same grate would
carry only 150-250 = 3-5 as much surface as with hot water radi-
ation.

The maximum night rate, when a boiler is expected to run
at least eight hours without attention, should not exceed 4
pounds, equal to 32 pounds of coal burned on each square foot of
grate in that length of time. With the 4-pound rate of com-
bustion assumed, a fire one foot thick would burn about half
through during the night, leaving an ample quantity of uncon-
sumed fuel on the grate to readily ignite the fresh fuel added
in the morning. With a higher rate of combustion a thicker fire
would be necessary. Too great a depth, however, would inter-
fere with the draft.

One of the essentials in a house heating boiler is a fire box
of sufficient depth to permit carrying a good deep fire. Thin fires
require too frequent attention. Avoid boilers with grates of ex-
cessive length, owing to the difficulty of properly handling the
fire.

AMOUNT OF FUEL FOR A SEASON.

To compute the season's coal consumption in a house is, as
heating men know, a very uncertain problem. The radiating sur-
face or the grate area may be taken as a basis. If the boiler is
properly proportioned for its work, so that the maximum rate of
combustion need not exceed that stated above, the amount of coal
required may be computed most readily by basing it directly on
the grate surface. With a climate like that in many sections of
the northeastern part of this country, where the heating season is

24 Principles of Heating.

of about seven months duration and the average outside tempera-
ture during that time is not far from 40 to 45 degrees, the aver-
age rate of combustion will be, roughly, from \y\ to ij4 pounds
per square foot per hour.

Take, for example, a boiler of medium size, in which the coal
is to be burned no faster than a 5 pound rate in zero weather.
Assume the heating season to last 200 days, or 4,800 hours.
With an average outside temperature of, say, 45 degrees, the aver-
age rate of combustion, based on the difference between the indoor

and outdoor temperatures, will be only — X 5 = 1-79 pounds.

Making allowance for the lower temperature maintained at night
brings the average rate down to about 1.68 pounds. This, with a
boiler having 4 square feet of grate surface, gives 4 X 1.68 X
4,800 = 32,256 pounds, or about 16 tons for the season.

If the estimate be based on the radiating surface instead of on
the grate area, we may assume, for example, a house heated by
1,000 square feet of direct radiation, including mains as a part of
the surface.

Using the figures previously stated — viz., 150 heat units per
square foot of direct hot water radiating surface and 8,000 heat
units utilized per pound of coal, we have 1,000 X 150 -f- 8,000 =
1 8.8 pounds per hour in coldest weather. The average hourly con-
sumption, with an outside temperature of 45 degrees, would be

^ X 18.8, and the total for the season of 4,800 hours— X 18.8
70 70

X 4,800 = approximately 32,200 pounds. This would be reduced,
owing to the lower temperature kept up at night to, say, 15 tons.
With indirect radiation, reduce to approximate equivalent di-
rect radiation by multiplying by not less than 1.6. Some boiler
manufacturers recommend multiplying by 1.75. Expressed in
another way the computation just made, based on hot water radia-
tion, gives about 40 pounds of coal per season per square foot of
surface in radiators, allowing 25 per cent, for mains. With steam

2^0
radiation the coal required would be — §— X 40 = about 70

pounds.

It may be well to repeat that the above computations apply only

Gas, Oil and Electricity vs. Coal. 25

to properly proportioned systems. If a boiler is known to be
small for its work a higher average rate of combustion must be
assumed and vice versa.

There is no economy in having a boiler so large that the fire
must be checked by opening the feed door or running with a very
low rate of combustion.

With a pair of boilers it is better to run one at its maximum
rate until the second one is needed rather than run both with
drafts checked nearly to the limit.

CHAPTER III.
HEAT GIVEN OFF BY RADIATORS AND COILS.

Repeated tests have shown the amount of heat given off by
ordinary cast iron radiators per square foot of heating surface
per hour per degree difference in temperature between the steam
or water in the radiator and the air surrounding same to be about

I t t t

OUTLET SCREEN

"RADIATOR

MARBLE FRONT

INLET SCREEN

FRONT ELEVATION I \

ELEVATION ,

PLAN

'HE METAL WORKS*

Fig. 16. — Plan and Front and Side Elevations, Showing Method of Concealing
Radiator with Marble Wainscoting.

1.6 heat units. With this as a basis a steam radiator under 5
pounds pressure, corresponding to 228 degrees, surrounded by air
at 70 degrees (neglecting the difference in temperature between
the air near the top and the bottom of the radiator), will give off
(228 — 70 degrees) X 1.6 heat units per square foot per hour =
253, commonly taken as 250. With hot water at an average tem-
perature of 160 the heat given off is (160 — 70) X 1.6 = 144,
commonly taken at 150.

Heat Given Off by Radiators and Coils. 27

These are good average figures to use. If we go into the sub-
ject closely we note that low radiators are more effective than
high ones and those of single column pattern are more effective
than deeper radiators, since they radiate their heat more freely
and air will circulate around them to better advantage.

Wall radiators and coils of pipe are still more effective, over-
head coils, with pipes side by side, giving off more heat per square
foot than those on walls with the pipes one over the other. The
advantage in the location of the latter, however, more than offsets
the greater efficiency of those placed overhead, as is common in
mill heating. Coils may be based on 300 to 350 heat units per
square foot per hour with low pressure steam, and wall radiators
on about the same amount. Concealed radiators, like the one
illustrated in Fig. 16, give off practically no heat by radiation,
but heat the room by heating the air passing over them — that
is, by convection. Such radiators should therefore be rated to
give off not more than 200 heat units per square foot per hour,
depending on the hight and arrangement.

NOTES ON HEAT EMITTED BY DIRECT RADIATORS.

Professor Carpenter, in Vol. I, Transactions A. S. H. & V. E.,
states : " The capacity for heat transmission increases at a much
higher rate than the difference of temperature. The efficiency of
the radiator will be greatly increased by increasing the steam
pressure or by forcibly bringing the air in contact with it. The
heat emitted per hour under different conditions by the same
radiator was found by tests to vary about 15 per cent., this varia-
tion being largely due to a difference in temperature and also to
changes in velocity of air passing over the radiator.

" With radiators of the same form, but of different heights, the
lower the radiator the more efficient. In the case of a Royal
Union radiator 17 inches high, with practically the same amount
of heating surface as another 37 inches high, 50 per cent, more
heat was emitted by the low radiator. The radiator coefficient
for a difference of temperature of 150 degrees is usually about
1.6 heat units; that for a 2-inch horizontal pipe 3.8 heat units;
i-inch pipe, 5.7 heat units.

" Radiators with one row of tubes are much superior to those
of the same kind with two or more rows of tubes. The fact that

28 Principles of Heating.

low radiators are more efficient than high ones would indicate that
the tubes in the high radiators are too closely placed ; that the air
in its passage upward reaches nearly its maximum temperature in
a short distance and from that point upward absorbs but little
heat/'

. The average of many tests on ordinary cast iron radiators ap-
pears to confirm the figure of 1.6 heat units per square foot an
hour per degree difference in temperature as a fair one to use.

Tests made by the City Engineer of Richmond, Va., on several
types of radiators commonly used, gave results ranging from 1.43
heat units to 1.81 heat units per square foot an hour per degree
difference in temperature. The average of the tests on five dif-
ferent makes of radiators was 1.68.

Monroe, in his book on " Steam Heating and Ventilation "
states : " The writer found that under the conditions in his test-
ing plant the 38-inch, 2-column cast iron radiator gave out 1.6
heat units per square foot per hour per degree difference of tem-
perature, with an average difference of 147.5 degrees."

He states that " within the limits of ordinary radiator practice
with steam temperatures from 212-230 degrees, and mean air
temperatures from 40-70 degree, the coefficient of 1.6 will not
vary more than 9 per cent, due to the difference in temperature
between the steam and air. The radiator which has the most open
space around its surface and the largest uninterrupted exposure
to the surrounding air will give out the most heat per square foot
under the same conditions. In compliance with this rule, other
things being equal, narrow radiators are more effective than
wide ones and low ones than high ones. Professor Cooley found
that a single coil of horizontal pipes set side by side gives out 40
per cent, more heat per square foot than a two column cast iron
radiator under the same conditions."

In the " Plumbers' and Fitters' Pocket Book," published by
the International Correspondence Schools, 1905, a statement is
made that the heat units emitted per hour per square foot of sur-
face per degree difference in temperature amounts with 90 degrees
difference (which would correspond approximately with hot
water heating conditions), to 1.41 for radiators 40 inches high,
1.7 for radiators 24 inches high, 1.62 for single column radiators

Heat Given Off by Radiators and Coils.

40 inches high, and 2.22 for those 24 inches high. The figures
taken in the same order for over 160 degrees difference in tem-
perature corresponding practically to steam heat conditions would
be 1.66, 1.98, 1.88 and 2.59.

The Fowler & Wolfe Mfg. Co.'s catalogue gives a summary
of tests as follows :

TABLE II.

Summary of Tests of various steam radiators made at Sibley College, Cornell
University, by Messrs. Camp, Woodward and Sickles, mechanical engineers, under
the direction of R. C. Carpenter, M.S.C.E., M.M.E. (This summary is the aver-
age of several consecutive tests made on these several radiators.)

A standard
A stand-
ard hight
cast iron
Standard
hight 3-
column cast

These tests were
all made in
the same closed
room under even
temperatures
and under same

F. & W.
wall radia-
tor. Stand-
ard 7-foot

radiator

hight radia-
tor made of 1-
inch wrought
iron pipe at-

with loops tached to cast

conditions. section tested, iron radiator.

*B. T. U. heat radiated
per hour per square
foot of actual surface.
Per degree difference
in temperature 2.325 1.732

B. T. U. heat radiated per
hour per rated
square foot of sur-
face. Per degree dif-
ference in tempera-
ture 2.400 1.712

Steam condensed per
hour per actual
square foot of heat-
ing surface. Pounds. 0.351 0.236

attached
to base.

1.705

1.594

0.239

iron base
3 rows wide.

1.643

1.266

0.182

A stand-
ard hight
cast iron
2-column
radiator.

1.319

1.266

0.182

* B.T.U. — British thermal units, or heat units.

Reference is made in the Heine Safety Boiler Co.'s catalogue
to the average of four experiments on the condensation in uncov-
ered pipes which showed with an average steam pressure of 5
pounds gauge, 2.236 heat units per square foot per hour per I
degree F. Other tests showed a loss of 2.812 for bare pipe.

Mr. A. R. Wolff gives 250 heat units per square foot per hour
for ordinary cast iron radiators with steam from 3 to 5 pounds
per square inch, and recommends about 60% of this amount for
hot water heating.

The results of a number of radiator tests are given in Mills's
book on " Heating & Ventilation," Vol. II., page 335. The heat

3O Principles of Heating.

emitted from cast iron radiators, according to these tests, ranges
from 1.4 for certain types of cast iron radiator, to 2.38 for single
column wrought iron tube radiator. Heat given off by horizontal
pipes is as follows : i-inch pipe 2.73 ; 2-inch pipe 2.3 ; 3-inch pipe

2-33-

The following figures are taken from " Steam in Covered and
Bare Pipes," by Paulding:

TABLE III.

LOSS OF HKAT FKOM PIPES.

Tempera- B. T. U.

Temperature ture per square

Name of Size of pipe, of steam. of air. foot per hour

experimenter. Inches. Deg. F. Deg. F. per 1 deg.

Barrus 2 325.2 56.6 3.01

Barms 2 365.4 63.2 3.25

Barrus 10 365.3 73.6 3.18

Hudson-Beare 3.53* 358.0 67.0 3.10

130 pounds 2 354.7 80.1 3.13

Jacobus 2 300.6 71.2 2.78

Brill . . 8 344.5 75.5 2.71

* Actual outside diameter.

Since the heat given off is roughly proportional to the differ-
ence in temperature between the steam and the air in the room,
radiators placed in rooms to be heated to a temperature lower
than 70 degrees, say 50 degrees, will give off with radiators at

228 degrees ~ — g _ . X 250 heat units = about 280 heat units.

In this connection it may be well to remark that in computing
boiler capacity one must remember that catalogue ratings are
based on the radiators being placed in rooms at 70 degrees. The
radiation must be reduced to equivalent surface when surrounded
by air at 70 degrees temperature.

It has just been shown that in rooms at 50 degrees the radi-
ators give off 280 heat units, against 250 heat units in 7o-degree
rooms ; hence, a boiler rated for, say 2500 square feet will carry

only X 2500 = 2230 square feet if the rooms are to be

heated to only 50 degrees.

HEAT GIVEN OFF BY INDIRECT RADIATORS.

Indirect radiators of the pin or similar type, with extended
surface, arranged somewhat as shown in Fig. 17, give off heat not

Heat Given Off by Radiators and Coils. 31

only in proportion to the difference in temperature between the
steam and the surrounding air, but in proportion (though not di-
rectly) with the volume of air coming in contact with them.

The tests made some years ago by John H. Mills have been
frequently quoted by writers on heating and ventilation. The
writer has reduced these tests to a zero basis for the entering air,
the data being given in the following table.

TABLE IV.

THE HEAT UNITS GIVEN OFF PER SQUARE FOOT PER HOUR FROM INDIRECT PIN
RADIATORS HAVING 40 PER CENT. PRIME SURFACE. STEAM, 5 POUNDS PRES-
SURE ; ENTERING AIR., 0 DEGREE F.

Velocity in feet per
minute between 10
square foot sec-
Cubic feet of air per Heat units t i o n s, having %
hour passing over given off per hour square foot air space
each, square foot of per square foot of between each two
heating surface. extended surface. sections.

100 370 50

200 540 100

300 700 150

400 850 200

500 1,015 250

600 1,175 300

700 1,330 350

800 1,500 400

It is common to assume about 400 heat units to be given off
per square foot an hour from ordinary indirect pin radiators with
low pressure steam. Short vertical flues mean low velocities ;
higher ones give an increased air flow.

The table shows that where a good velocity between the sec-
tions may be secured their effectiveness is increased and less sur-
face is required.

COMPUTING INDIRECT RADIATING SURFACE.

To illustrate the use of the table, suppose we have a room
20 X 30 X 12 which it is desired to heat by indirect radiation and
change the air every 12 minutes — contents equals 7200 cubic feet.
With 5 changes per hour 36,000 cubic feet must be supplied.
The heat loss by transmission, with two sides exposed, would be
about 24,000 heat units per hour. The loss by ventilation would
be 36,000 X i/4 (J/4 representing the heat units carried away
by each cubic foot of air escaping from a 7o-degree room, with
outside air at o degree) = 45,000. Adding these, the total heat
loss is 81,000 heat units per hour. Assuming 400 heat units per

32 Principles of Heating.

square foot of radiation per hour gives a trifle over 200 square
feet of surface, or a ratio of I to 36 cubic feet. With 36,000 cubic
feet per hour supplied the air admitted to the indirect radiators
would be 36,000 -.- 200 — 1 80 cubic feet per square foot (neglect-
ing the difference in volume between air at 70 degrees and at o
degree). The table shows that with 200 cubic feet per square
foot per hour 540 heat units are given off ; hence we should expect

Fig. 17. Indirect Radiator Connections.

that with 1 80 cubic feet about 500 heat units in round numbers
would be given off, in which case only 81,000 -r- 500 = 162
square feet would be necessary. One must always be certain that
the air space through the groups of radiators is considerably in
excess of the area of flues connected therewith. The rule to allow
2 square inches of flue area to the first floor, i^ to the second
floor and i/4 to the third and fourth floors is simple, and gives
good results in dwelling house work when the radiation is prop-
erly proportioned. That is just the difficulty, however, for in case
of a mistake in the radiation a second mistake follows in the flues.

Heat Given Off by Radiators and Coils.

Taking il/2 square inches of flue area per square foot of indi-
rect radiating surface as a fair average for a house, a bench or
stack of loo square feet would have flues aggregating 150 square
inches. The flue area between the sections would be about 480
square inches, or over three times the flue area ; thus, common
practice dictates that the velocity between the sections of pin radi-
ators shall be only about one-third that in the flues. The rule to
make the indirect surface 50 per cent, more than the direct radi-
ation that would be required may be shown on a heat unit basis
to be very nearly true under certain conditions. For example,

THE METAL WORKER

Fig. 18.— Blower System Heater.

take a corner room 16X20X10 = 3200 cubic feet, the heat
loss from which is 14,400 heat units per hour. With direct steam
radiation rated at 250 heat units 14,400 -f- 250 = 58 square feet
would be required. Now, to heat the same room by indirect radi-
ation at 400 heat units per square foot, the air to enter the room
at 1 20 degrees, with o degree outside, about 86 square feet would
be required, computed as follows :

One cubic foot of air at 120 degrees weighs 0.068 pound. Its
specific heat is 0.238, therefore the heat units brought in by a
cubic foot of air at 120 degrees is 0.068 X 120° X 0.238 = 1.94.

Principles of Heating.

Of this only -3 — is available to offset the loss of heat by trans-

120

mission, the other ' — escaping with the air leaking out at 70

120

degrees temperature.

5Q
1 20

X i-94 = 0.810 heat unit. To make

good the loss of 14,400 heat units per hour by transmission 14,400
— 0.810 = 17,800 cubic feet of air per hour at 120 degrees must
be supplied. Each cubic foot brings in 1.94 heat units; total
equals 17,800 X i-94 = 34>5oo heat units, which divided by 400

THE METAL WORKER

Fig. 19. — A Heater for Blower Use.

gives 86, an amount almost exactly 50 per cent, in excess of the
direct radiation required. ,

HEAT GIVEN OFF BY HEATERS COMBINED WITH FANS.

It is not uncommon to secure an emission of 1500 to 2000 heat
units or more per square foot of pipe coils when zero air is enter-
ing the heater at a velocity of 1000 to 1200 feet per minute, meas-
ured between the pipes and the steam is 2 to 5 pounds gauge
pressure. See Figs. 18 and 19.

The heat given off per square foot by supplementary heaters
or reheaters, as shown in Fig. 20, with which air at, say, 50 to
70 degrees from the main tempering coils comes in contact would
be not far from 1000 to 1200 heat units in the case of low pres-
sure steam. The velocity of the air and the depth of heaters —

Heat Given Off by Radiators and Coils.

that is, the number of coils of pipe they contain — have much to
do with their efficiency, which depends chiefly on the steam pres-
sure. Assuming a main tempering coil arranged to have the air
blown through it by a fan or blower, as in Fig. 21, or to have the
air drawn through, as shown in Fig. 22, to give off 2000 heat
units per square foot per hour, what amount of surface would
be necessary to raise the temperature of 30,000 cubic feet per
minute 70 degrees from zero?

Since one heat unit will raise the temperature of approxi-
mately 50 cubic feet of air from o degree through i degree, to

CA9WQ — \

SUPPLY HEADER

RETURN HEADER I

Fig. 20,— Supplementary Heater or Reheater.

THE METAI WORKER '

Pig. 21. — A Fan Blowing Air through Heater.

raise 30,000 X 60 = 1,800,000 cubic feet per hour 70 degrees,

1,800,000 X 70
would require - ~7~ ""= 2,520,000 heat units, which could

be obtained by using a heater of

2000

— I^6o square feet, or

about 3600 lineal feet of i-inch pipe.

2 6 Principles of Heating,

CAST-IRON RADIATION FOR USE WITH FANS.

Cast-iron radiation made up in large sections and of a design
to give prime surface in place of the extended surface so long in
vogue with indirect radiation is now largely used in connection
with fans.

These sections are more easily handled than large coils and
may be arranged in a variety of -ways to suit the space at one's
disposal. Manufacturers' catalogs relating to this product give
an unusual amount of valuable engineering data.

Fig. 22. — Fan or Blower Drawing Air through Heater.

TEMPERATURE OF AIR REQUIRED TO HEAT ROOMS BY INDIRECT

RADIATION.

It may be desired to predetermine the temperature that must
be secured at the air inlet to warm a room.

Take a corner schoolroom, for example, 28 x 32 x 12, with
30 per cent, glass and exposed north and west.

The equivalent glass surface, rating the wall as equivalent to
one-quarter as much actual glass surface, will be 342 square feet.

The heat lost through same per hour will be 342 X 85 X 1.25
= 36,340 heat units. (1.25 being the factor for N. or W. ex-
posure.)

With the standard air supply to a 5o-pupil room of 1500 cubic

Heat Given Off by Radiators and Coils. 37

feet per minute the loss of heat by leakage — that is, by the re-
moval of air through the ventilating flues — will be 60 X 1500
X i/4 (since i^ heat units are removed by each cubic foot of
air escaping from a room at 70 degrees when the outside
temperature is at o degree) = 112,500 heat units per hour. Total
heat loss equals 148,840. To make good the loss of heat through
walls and glass the 90,000 cubic feet of air per hour supplied to
the room (the volume being based on /o-degree temperature)
must be superheated above the room temperature an amount
equivalent to the 36,340 heat units transmitted through walls and
glass.

The weight of 90,000 cubic feet of air at 70 degrees is about
90,000 X 0.075 — 6750 pounds. The specific heat of air is 0.238
— that is, one heat unit will raise the temperature of about 4
pounds of air I degree.

Therefore, 36,340 heat units would raise the temperature of
36,340 X 4 = 145,360 pounds of air i degree, or would raise the
temperature of 6750 pounds of air ; 145,360 -f- 6750 = about 22
degrees.

That is, the air would have to be superheated at least 22
degrees above the room temperature of 70 degrees to maintain
the room at that temperature under the conditions stated — viz.,
with a change of air about every eight minutes. As a matter of
fact, with the indirect system there is a considerable difference
between floor and ceiling temperatures in high studded rooms,
which means that if 70 degrees is to be maintained near the floor
a considerably higher temperature must be maintained above,
with a consequent increase in the loss of heat by transmission;
therefore, instead of 92 degrees, as above computed, based on an
average temperature at walls of 70 degrees, the inlet temperature
would probably have to be kept at not less than 100 degrees in
zero weather, especially if the windows were not tightly fitted.

SIZE OF ASPIRATING HEATERS OR COILS.

To compute the size of heaters or coils to be placed in venti-
lating flues, as shown in section and elevation in Figs. 23 and 24,
to produce an aspirating effect in a system of ducts, as shown by
plan and elevation in Figs. 25 and 26, we may proceed as follows :

Principles of Heating.

Suppose it is desired to remove 3000 cubic feet of air per minute
from a room. Knowing the size and hight of the flue, for ex-
ample, 10 square feet area and 40 feet high above where the coil

TM6 METAL WORKED

Tig. 23. — Section through Vent Flue, Showing Aspirating Coil.

Fig. 24.— Elevation on Line A B of Fig. 23.

is to be placed, look up the flue velocities in Table XVII — the
excess of temperature over that outdoors that must be maintained
in the flue to produce the required velocity. In this case the
velocity must be 3000-7- 10 = 300 feet per minute, and the ex-
cess temperature required, taken from Table XVII, is 20 degrees.

Heat Given Off by Radiators and Coils.

J_L

nig

1 1 i

o > z

!6=S

« \\

1 ^

x r-

|||l|||||

TTTH

(l_

vLJ

1
1

[

4° Principles of Heating.

To heat 3000 cubic feet per minute 20 degrees would require

3000 X 60 X 20

— — — = 65,454 heat units per hour (55 representing

o j
the number of cubic feet of air heated i degree by i heat unit).

With an aspirating heater made up of ordinary pin radiators,
giving off, say, 400 heat units per square foot of extended sur-
face per hour, and this would be a fair allowance, the surface
required would be 65,454 -f- 400 = 163 square feet. The sections
should be coupled together with extra long nipples.

One should always compute the air space through heaters to
make sure it is ample.

The free area between the sections of the heater should be at
least 20 per cent, greater than the flue area, to allow for the in-
creased friction of the air in passing over the pins or extended
surface. A temperature rise of 20 degrees in the ventilating
flues to produce an aspirating effect would require the use of very
large heaters and coils, or radiators. It is therefore seldom that
a temperature rise of more than 10 degrees is provided for.

This means that a 4O-foot vent flue proportionel to handle the
required volume of air with a 2O-degree excess of temperature in
the flue over that outdoors will work without the assistance of
a coil up to 50 degrees outside temperature. If the outdoor air
is 60 degrees then 10 degrees of the 20 degrees excess is provided
by the air entering the vent flue from the room at 70 degrees, the
balance, or other 10 degrees, to be furnished by the aspirating
coil.

Should the weather reach 65 degrees outside the excess in the
flue would be 15 degrees, and a slight falling off in flue velocity
would take place, this falling off increasing as the outside tem-
perature approaches 70 degrees, when windows may be opened
and ample natural ventilation secured. When possible it is far
preferable to use a fan in place of aspirating coils to produce the
desired removal of air. Positive results are secured and the air
may be handled at less cost.

It is impossible as a rule to install pin radiators in flues just
above the ventilating registers in rooms without cutting down the
flue area too much. The radiators must therefore be placed in
the attic.

Heat Given Off by Radiators and Coils.

42 Principles of Heating.

More radiation must be used, however, since the chimney
effect of the flue is decreased the nearer the top the aspirating
heater is placed.

TABLE V.

A table giving the approximate velocity of air in flues of
various heights will be found on page 71.

Where small volumes of air are to be removed coils or lines
of pipes may be used to advantage in place of cast iron radiators,
care being taken not to block off too much of the flue area. Such
coils may be computed on a basis of 600 heat units or more per
square foot per hour, depending on the flue velocity.

CHAPTER IV.

THE LOSS OF HEAT BY TRANSMISSION, COMPUTING
RADIATION, HORSE POWER REQUIRED FOR HEATING.

The following tables have been computed from data presented
in a series of articles on " German Formulas and Tables for Heat-
ing and Ventilating Work," by Prof. J. H. Kinealy, published in
bound form, pocket size, $1.00. The values given include those
for a greater variety of building materials than the writer has
seen published elsewhere. The values for glass and brick work
agree pretty closely with those commonly used in this country.

TABLE VI.

LOSS OP HEAT THROUGH BRICK WALLS OF APPROXIMATELY THE THICKNESS STATED.

70 degrees inside, 0 degree outside.

Thickness of wall, inches 8 12 16 20 24 30 30

Heat units per square foot per hour. .24 21 18 16 14 12 10

Tables showing the relative transmitting- power of solid brick
walls and those with air spaces about 2.4 inches wide show that
those with the air space transmit about 15 to 20 per cent, less heat
than the solid walls. This applies only to walls, say, 8 to 16 inches
thick. With thicker walls the saving due to an air space is much
less.

TABLE VII.

LOSS OF HEAT THROUGH STONE WALLS, RUBBLE OR BLOCK MASONRY.

70 degrees inside, 0 degree outside.

Thickness of wall, inches 12 16 20 24 28 36 44

Heat units per square foot per hour.. 31 27 25 21 19 17 14

The values given are for sandstone ; about 10 per cent, should
be added for limestone.

TABLE VIII.

LOSS OF HEAT THROUGH PINE PLANKS.

70 degrees inside, 0 degree outside.

Thickness of planking, inches 1% 2 2*4 3

Heat units per square foot per hour 21 18 16 14

* A. R. Wolff's values for brick walls closely approximate those given except for
8-inch wall, which he states is 29, and for 4-inch wall is 46 B. T. U. per sq.ft. per
hour 70 degrees difference.

44 Principles of Heating.

TABLE IX.

LOSS OP HEAT THROUGH WINDOWS AND SKYLIGHTS AND THROUGH OUTSIDE WALLS
OP FRAME CONSTRUCTION'., EXPRESSED IN HEAT UNITS PER SQUARE FOOT Or
EXPOSED WALL PER HOUR.

70 degrees inside, 0 degree outside.

Heat units

per

square foot
per hour.

Single window 77

Single window, double glass 43

Double window 32

Single skylight 81

%-inch sheathing and clapboards 20

%-inch sheathing, paper and clapboards 16

Professor Kinealy states : " These can hardly be considered
much more than rough approximations on account of the uncer-
tainty due to leakage."

TABLE x.

LOSS OP HEAT, EXPRESSED IN HEAT UNITS PER SQUARE FOOT OF SURFACE PER
HOUR, THROUGH PARTITIONS, FLOORS AND CEILINGS SEPARATING WARM ROOMS
AT 70 DEGREES FROM COLO ROOMS AT 40 DEGREES.

Heat units.

Ordinary stud partition, lath and plaster one side only 18

Ordinary stud partition, lath and plaster both sides 10

Ordinary lath and plaster ceiling separating unheated space from heated

rooms 18

Floor, single, thickness % inch, warm air above and cold space below :

(a) No plaster beneath joists 13

(b) Lath and plaster beneath, joists 8

Floor, double, thickness 1% inches, warm room above and cold space below :

(a) No plaster beneath joists 9

(b) Lath and plaster beneath joists 5

The heat losses stated in the tables are to be increased as fol-
lows, based on the practice of different German engineers:

TABLE XI.

Per cent.

For northeastern, northwestern, western or northern exposure 20 to 30

For rooms 13 to 14% feet high 6%

For rooms 14% to 18 feet high 10

When the heating is continued during the day only 10

When the building is allowed to become thoroughly chilled at night 30

When the building remains for long periods without heat 50

COMPUTATION OF HEAT LOSSES AND RADIATION.

To illustrate the use of the German values given, suppose it
is desired to compute the amount of steam radiation required to

Loss of Heat by Transmission. 45

heat a corner room 14 x 16 x 10 feet, exposed to the north and
west, located below a heated room and over an unheated room;
floor to be double, with under side of floor joists lathed and plas-
tered; outside walls 12 inches, brick; glass 20 per cent, of the
exposure, equal to 60 square feet, net wall equaling 240 square
feet:

Heat losses :

Wall, 240 X 21 heat units 5,040

Glass, 60 X 77 heat units 4,620

Total 9,660

Heat loss X exposure factor = 9,660 X 1.25 12,075

Heat loss through floor, 224 X 5 1,120

Total heat loss 13,190

Direct radiating surface is equal to the total heat loss divided
by heat given off per square foot of radiating surface — viz. : 250
heat units, or 13,190 -r- 250 = 53 square feet, giving a ratio of
about i square foot to 43 cubic feet of space. It will be noted
that no allowance has been made in the above example for air
leakage. Professor Kinealy points out that the German engineers
appear to make no allowance for this item, except as taken into
account by the percentage addition for exposure. Some engi-
neers in this country allow for the accidental leakage by assuming
a certain rate of air change, say once an hour, for all rooms.

In large rooms having little exposure in proportion to the
contents the loss of heat due to leakage, based on an hourly rate,
is often as great as that through the walls, if not greater, which
would call for more radiation than is found necessary in practice.

The question of leakage is an important one and requires good
judgment for its proper determination. In preference to making
a fixed allowance for leakage, based on the cubic contents, the
writer has found it more satisfactory to consider the leakage to
be sufficiently allowed for by the exposure factors of 1.25 for
north or west and 1.15 for east, especially when using factor 77
or 85 for glass, and to make a separate allowance for the effect
of the cubic contents on the heating of a room by adding to the
loss of heat by transmission an amount of heat equal to the cubic
contents in feet multiplied by 1/3 for room with two exposures,
and the cubic contents multiplied by 2/3 for rooms with one
exposure. This allowance will be found sufficient to provide for

46 Principles of Heating.

reheating where the rooms are allowed to become somewhat
chilled at night.

The reason for making a greater allowance for reheating in
the case of rooms with one exposure than of those with two ex-
posed walls is that the rate of transmission is somewhat greater
per square foot through the single exposed wall having three
partition walls radiating heat to it than through the same wall
area of a corner room having only two interior walls radiating
heat to the outer ones.

Furthermore the three inside walls on account of their greater
surface, require more heat to warm them in a given time than
do the two inside walls of a corner room of the same size, there-
fore, in order that corner rooms and single exposure rooms shall
heat in approximately the same time, a greater allowance for
reheating should be made for the latter.

COMPUTING DIRECT RADIATION ON THE HEAT UNIT BASIS.

Perhaps the most time consuming operation in connection with
the work of the heating engineer or contractor is the computation
of radiating surface. Innumerable rules have been devised, good,
bad and indifferent, but the subject appears to have simmered
down to the simple proposition that if the wall and glass surface
and the required air change are known the heat losses due to
transmission and leakage may be readily determined, and this total
divided by the heat given off per hour per square foot of radiating
surface gives the amount of radiation required.

The German values for the heat transmitting power of various
substances of different thicknesses have been widely used since
they were first introduced by A. R. Wolff. Tables or charts
giving these values may be found in Kent's " Mechanical Engi-
neers' Pocket Book " and in many trade catalogues. Values
closely approximating these have been stated. The French values,
based on the investigations of Peclet and introduced by Profes-
sor Carpenter, are in some cases considerably lower than those
just mentioned, his value or coefficient for glass being 70, Wolff's
being 85. Furthermore, Carpenter assumes a certain air change
per hour by leakage in rooms heated by direct radiation, whereas
Wolff provides for this loss by adding a certain percentage to

Loss of Heat by Transmission.

RATIOS 1 TO

g §

CHART I.

Ratios for DIRECT STEAM Radiating Surface in Rooms with TWO SIDES
EXPOSED Toward the North and West, with Glass Surface Aggregating 20
Per Cent, of Total Exposure.

For northeast corner rooms use ratio 5 per cent, greater than given by chart.

For southwest corner rooms use ratio 10 per cent, greater than given by chart.

For southeast corner rooms use ratio 15 per cent, greater than given by chart.

48 Principles of Heating.

the heat losses through walls and glass. Of course, where the
leakage is great, as in rooms provided with ventilating flues, it is
allowed for independently.

Admitting that the wall and glass surface affords the best
basis on which to compute the radiating surface, it frequently
happens in a contractor's office that insufficient time is given in
which to lay out the work on this basis and prepare a bid. In
house heating work especially some shorter method must often
be used for the reason stated. In such cases an experienced man
may be able to hit pretty close to the mark by " thumb rule," but,
while quick, this method is a rather rough one.

Some simple method that will give reasonably accurate results
that may be quickly arrived at is needed by many contractors.
The author prepared, and has for several years used, the accom-
panying charts, Nos. I and 2* for computing direct steam and 3
and 4 for direct hot water radiation, the curves representing the
mean or average of the German and French values with these
modifications :

To the heat loss through walls and glass, based on German
values, has been added a certain amount to allow for reheating
the air in the rooms in case they should become chilled.

To the heat losses by transmission, computed on the French
basis, has been added an amount representing the heat units es-
caping by a leakage of air equal to the contents of the room once
each hour.

The tables are based on a glass surface equal to 20 per cent,
of the total exposure. This the author has found to be a fair
allowance ; some rooms may have more than this amount, but an
excessive glass surface is readily detected in inspecting plans and
may be allowed for by adding to the radiating surface given by
the chart an amount of radiation equal to about one-third of the
excess of glass surface over the 20 per cent, on which the charts
are based.

For example : If the total exposure is 40x3 square feet and the
glass surface 120 square feet, or 40 square feet in excess of the
glass surface based on 20 per cent, of the exposure, 13 square
feet, being one-third of 40, should be added to the radiation com-
puted by the chart.

Loss of Heat by Transmission.
RATIOS i TO

O oo

CHART 2.

Ratios for DIRECT STEAM Radiating Surface in Rooms Having Only ONE

SIDE EXPOSED Toward North or West, with Glass Surface Aggregating 20

Per Cent, of Total Exposure.

Curve 1 is for rooms having length to width as 2 to 1, with short side exposed.
Curve 3 is for rooms having length to w'dth as 2 to 1, with long side exposed.
Curve 2 is for square rooms with one side exposed.
For rooms with east, south or southeast exposure use ratio 10 per cent, greater

than chart.
For rooms with southwest or northeast exposure use ratio 5 per cent, greater

than chart.

SO Principles of Heating.

Chart No. I shows a curve from which the proper ratios of
steam heating surface to cubic contents may be determined for
rooms with two exposed sides. The curve was computed for
square rooms. Rectangular rooms of good proportions, however,
have but little more exposed wall surface in proportion to their
contents, and unless they are unusually long and narrow the ratio
given by the chart may be safely used. The contents expressed
in thousands of cubic feet is stated on the lower line and the
ratio of radiating surface to contents is given in the vertical line
at the left of the chart.

Example : What radiating surface should be used in a corner
room 16 x 19 x 10 feet, having 3040 cubic feet? Just to the
right of the 3000 line is a point representing the contents of 3040
cubic feet. Note where a line drawn vertically through this point
would intersect the curve. In the left hand column this point of
intersection is the ratio sought. The ratio in this case is about
i to 47. The contents (3040) divided by this ratio gives 63
square feet of direct radiating surface.

Chart No. 2, for rooms with one exposure, contains three
curves, one for rooms with sides in the proportion of 2 to I (24
x 12 feet, for example), having the long side exposed; one for
similar rooms with the short side exposed and one for square
rooms. Obviously it makes a great difference whether the long
or the short side of a room is exposed.

For rooms having sides in the proportion of 1^2 to I (i5x
10 feet, for example), with the long side exposed, compute the
contents and proceed as explained in connection with Chart No.
I, selecting a point in Chart 2 midway between curve 2 and curve
3 on the vertical line corresponding with the contents. The
proper ratio will be found in the left hand column opposite this
midway point.

With rooms like the one described, but having the short side
exposed, select a point midway between curve I and 2.

Example : What amount of steam radiating surface is required
in a room 12 x 18 x 10 feet, having the 12-foot wall exposed?
Contents 2160 cubic feet. On Chart 2 follow up the line represent-
ing the contents to a point midway between curves I and 2, then
out horizontally to the left hand column. The ratio there found is

Loss of Heat by Transmission.

RATIOS 1 TO

8 8

ffiK

CHART 3.

Ratios for DIRECT HOT WATER Radiating Surface, Open Tank System, In
Rooms with TWO SIDES EXPOSED Toward the North and West, with
Glass Surface Aggregating 20 Per Cent, of Total Exposure.

For northeast corner rooms use ratio 5 per cent, greater than chart.

For southwest corner rooms use ratio 10 per cent, greater than chart.

For southeast corner rooms use ratio 15 per cent, greater than chart.

Principles of Heating.

RATIOS 1 TO

& 8 ft S

CHART 4.

Ratios for DIRECT HOT WATER Heating Surface, Open Tank System, in Rooms
with Only ONE SIDE EXPOSED Toward the North or West, with Glass
Surface Aggregating 20 Per Cent, of the Total Exposure.

Curve 1 is for rooms having length to width as 2 to 1, with short side exposed.

Curve 3 is for rooms having length to width as 2 to 1, with long side exposed.

Curve 2 is for square rooms, with one side exposed.

For rooms with east, south or southeast exposure use ratio 10 per cent, greater
than chart.

For rooms with southwest or northeast exposure use ratio 5 per cent, greater
than chart.

Loss of Heat by Transmission.

about i to 72, and the radiating surface 2160 -f- 72 = 30 square
feet.

With this explanation of charts No. I and No. 2 for steam
heating, the use of charts No. 3 and No. 4 for hot water heating
will be readily understood without further examples.

THE BOILER HORSE-POWER AND RADIATING SURFACE REQUIRED TO
HEAT ISOLATED BUILDINGS.

It is of interest to compute on a heat unit basis the boiler
horse-power necessary to heat buildings under the conditions
stated in connection with Chart 6.

-T-16000-

--140(X

- -12000

XXX)

btsooc

CUBIC CONTENTS

CHART 5.
Space Heated per Boiler Horse-power in Isolated Buildings under Conditions Stated.

Chart No. 5 shows by the curve the increased space that may
be warmed per boiler horse-power in large buildings over that
in smaller ones, since the former have less exposed surface per
unit of contents.

Chart No. 6 is based on buildings ranging in size from 100,-
ooo to 1,000,000 cubic feet and in hight from 20 to about 60 feet,

54 Principles of Heating.

according to the size. The buildings are assumed to be rectan-
gular in plan, the length being twice the breadth in each case.
The glass surface is assumed to be one-third of the total expo-
sure; the equivalent glass surface of the roof is taken as one-
tenth the total area of same. An allowance for reheatinsr the

buildings was made equivalent to an amount of heat that would
raise a volume of air equal to the contents 20 degrees in one hour.
This amount of heat would not actually raise the temperature
of the air in the building that amount in the time stated, since
the walls and machines or what not in the rooms must have their
temperature raised as well as that of the air, and would absorb
a large portion of the heat. The greater the amount of material
in the rooms the less will be the fluctuation in temperature with
intermittent heating, since the machinery or goods that become
thoroughly warmed during the day, when surrounded by air at,
say, 60 to 70 degrees temperature, store up heat which is given
off during the night or at times when steam is shut off.

For direct radiating systems the charts will be of service in
checking roughly the boiler horse-power required. They apply
only to buildings exposed on all sides under the conditions stated
as to glass surface, exposure, etc. For other conditions due allow-
ances must be made.

On the basis of, say, 85 square feet of radiating surface per
boiler horse-power, mains and risers to be computed as radiating
surface unless covered, the horse-power indicated in Chart No.
6, multiplied by 85, gives roughly the square feet of radiating
surface necessary for buildings of contents stated. For exam-
ple: A building of 200,000 cubic feet requires 20 horse-power,
per chart No. 6 = 20 X 85 = 1700 square feet of radiating sur-
face, a ratio of approximately i to 120 cubic feet. For 400,000
cubic feet, radiating surface = about 33 X 85 = 2805, giving
a ratio of i to 143 cubic feet, and so on.

Of course, the above is to be considered as only a rough ap-
proximation. The figure 85 is perhaps too conservative. For ac-
curate work the wall and glass surface must be computed.

SIZE OF HEATERS WITH BLOWER SYSTEMS.

With the blower system the inleakage of cold air will be some-
what diminished by the pressure in the rooms maintained by the

Loss of Heat by Transmission.

fan. This pressure is scarcely measurable, however, and its effect
in preventing inleakage of cold air will be neglected in this dis-
cussion. With air supply at 140 degrees and building at 70 de-
grees, half the heat supplied is carried away by the air escaping
at 70 degrees, the other half being lost by transmission through
walls, windows and roof. Under these conditions twice as much
heat is necessary as with direct radiation.

If the frequent change of air incident to the blower system
is necessary, or if ample exhaust steam is available, well and

r80

-4J

CUBIC CONTENTS

CHART 6.

Showing Approximate Boiler Horse-power Required to Heat Buildings having Various

Cubical Contents.

good ; otherwise the loss of heat over direct radiation is a serious
one.

Since a building with the blower system, under the conditions
stated, taking air from the outside, will require twice as much heat
as with direct radiation, the boiler horse-power shown in Chart
No. 6 must be doubled; for example, a building of 200,000 cubic
feet will require about 2 X 20 = 40 horse-power, and on the basis

5 5 Principles of Heating.

of 50 lineal feet of i-inch pipe in the heater per horse-power, a
not uncommon allowance, a 2000 lineal foot heater would be
required.

With other conditions than 140 degrees, 70 degrees and zero,
as. stated above, greater or less boiler horse-power would be re-
quired with lower or higher inlet temperatures, respectively. A
much higher inlet temperature than 140 degrees is not to be
generally recommended. With the blower system the heater
pipes, with low pressure steam and ordinary velocities of air
between them, are generally rated to give out 2000 heat units or
more per square foot an hour, or, say an average of 600 heat units
per lineal foot of i-inch pipe, corresponding to 55 lineal feet per
horse-power.

RELATIVE LOSS OF HEAT FROM BUILDINGS HAVING THE SAME
CUBIC CONTENTS.

The relative loss of heat from buildings having the same con-
tents, but of different forms, is shown in the diagrams ABC and
D of Fig. 27, each of approximately 125,000 cubic feet. Let each
have glass equal to one-sixth the exposure, the equivalent glass
surface of walls to equal the area of wall surface divided by 4, and
let i square foot of roof be considered equivalent to one-tenth
square foot of glass; the equivalent glass surface of each build-
ing is as stated under the different figures. Since the cubic con-
tents is the same, the loss of heat would be roughly propor-
tional to the equivalent glass surface in each. Long, low build-
ings require less horse-power per 1000 cubic feet than those more
nearly cubical in form.

Building D, which is high in proportion to its floor area, would
take considerably more horse-power per 1000 cubic feet than
those represented by A, B or C.

The loss of heat by leakage of air would be greater in high
buildings like D than in low ones like B and C, as they have a
greater flue action involving greater leakage and have more wall
surface in proportion to their contents than those shown in A,
B and C.

Loss of Heat by Transmission.

03 H

p. -I

f! J.

58 Principles of Heating.

TRANSMISSION OF HEAT THROUGH CONCRETE.

Tests made by Walter Kennedy on transmission of heat
through concrete, published by the Armstrong Cork Co., Pitts-
burgh, showed for 4-inch concrete (1-3-5 mixture) a transmission
of 25.5 and 26 B. T. U. per square foot per degree F. difference in
temperature for 24 hours.

Figuring the loss per hour as is common in heating calcula-
tions, these values are equivalent to a trifle over 1.06 B. T. U. per
hour per square foot per degree F. difference in temperature for
concrete 4 inches thick.

From "Some Thermal Properties of Concrete," by Charles L.
Norton, of the Massachusetts Institute of Technology, the fol-
lowing extracts are taken, with the permission of the National
Association of Cement Users:

Professor Norton says the thermal conductivity is that prop-
erty which determines how rapidly heat will travel through a
substance. He states that there is very little data to be found as
to this important property of any of the common materials of
engineering and such data as are to be found are not at all con-
cordant. As to the conductivity of concrete or its variations with
temperature and with composition, practically nothing has been
known.

Professor Norton's tests may be tabulated as follows:

TABLE XII.
THERMAJ, CONDUCTIVITY OF CONCRETE.

Temp, hot Coefficient B. T. U.

side of plate, Mixture. per 1° F. per square foot

degrees F. 1 inch thick per 24 hours.

95 Stone concrete 1-2-5 150

122 Stone concrete 1-2-4 76 to 114

Not tamped
95 Cinder concrete 1-2-4 56

The specific heat of concrete is stated to be slightly less than
either red brick or firebrick. It is stated by Professor Norton
that steel transmits heat 75 to 100 times as fast as the densest of
stone concrete.

Loss of Heat by Transmission. 59

It is of interest to note the far greater conductivity of stone
concrete than of cinder concrete, as given by Professor Norton.
Kennedy's values for transmission through concrete 4 inches
thick show a transmission for 70 degrees difference in tempera-
ture of about 75 B. T. U. per square foot per hour. This rate,
it may be noted, is about twice as great as that for brick of the
same thickness, the rate for the latter being that taken from a
chart originally introduced into this country by the late A. R.
Wolff and deduced from German values. These German values,
by the way, are in pretty close agreement with those presented
in this treatise, transformed into English units from the German
by Professor Kinealy.

Table VII, page 43, shows a rate of heat transmission for
stone walls to be about one and one-half times that for a solid
brick wall of the same thickness.

In the absence of definite available data relating to the
actual heat conductivity of concrete it is the author's opinion
that an assumed rate of heat transmission through stone concrete
of twice that through brick, as given in Table VI, page 43, is
not very wide of the mark.

Doubtless actual tests will soon bring this matter of heat
transmission down to a definite basis.

CHAPTER V.

HEATING EQUIVALENTS, SPECIFIC HEAT, HUMID-
ITY, THE HEATING AND COOLING OF AIR, ETC.

CONVERTIBILITY OF HEAT AND MECHANICAL ENERGY.

"The formal statement of the first law of thermodynamics is :
Heat and mechanical energy are mutually convertible, and heat
requires for its production and produces by its disappearance a
definite number of units of work for each thermal unit. The
mechanical equivalent of heat is designated by J."

THE MECHANICAL EQUIVALENT OF HEAT.

"The amount of mechanical work which is capable of gener-
ating one unit of heat is called the mechanical equivalent of heat.

The mechanical or dynamical equivalent of heat is the num-
ber of units of energy or work to which one unit of heat is equiv-
alent. The unit of work is the foot-pound, i.e., the amount of
work required to raise one pound one foot. It has been deter-
mined experimentally that one heat unit (B. T. U.) is equivalent
to 778 foot-pounds."

CONSERVATION OF ENERGY.

The following law, which is a statement of the doctrine of
the conservation of energy, holds for all known forms of physical
energy : "The total energy of any body or system of bodies is a
quantity which can neither be increased nor diminished by any
mutual action of these bodies, though it may be transformed into
any of the forms of which energy is susceptible." — Maxwell.

HEAT PER HORSE-POWER.

Whenever mechanical work is done heat is given off. Thus,
the heat due to the running of machines in a shop assists in the
warming of the room. A horse-power is 33,000 foot-pounds per
60

Heating Equivalents, Specific Heat, etc., of Air. 61

minute. For each mechanical horse-power expended in whatever
manner in factory, shop or elsewhere, 33,000 -j- 778 = 42.4 heat
units are given off. A mechanical horse-power hour is equal,
then, to 2545 heat units per hour, an amount equal to the loss of
heat through over 30 square feet of glass, or that given off by 8
to 10 square feet of direct radiation.

LATENT HEAT OF VAPORIZATION.

"The latent heat of vaporization is the number of thermal
units required to convert the unit mass (or weight) of a liquid
at a given temperature into saturated vapor at the same temper-
ature. At any pressure below the critical temperature, a sub-
stance may be converted wholly into saturated vapor by heating
or cooling to the temperature of the boiling-point corresponding
to that pressure. It is found experimentally that the heat of
vaporization varies with the temperature at which the conversion
from liquid into saturated vapor takes place. Hence the neces-
sity for the introduction of the temperature restriction in the
above definition."

The evaporation of water, a question which comes up in the
consideration of air washers, involves an expenditure of heat.

The heat quantity expended in evaporation is very nearly

1092 B. T. U. — 0.7 (t° — 32°)

per pound of water evaporated at t° F.

Latent heat, commonly expressed in B.T.U., is the heat which
disappears when a liquid is changed to a gas, as water to steam
or water to aqueous vapor.

This heat again comes into evidence when the steam or vapor
is condensed back to water, as when steam is condensed in a
radiator, for example, or as when moisture is condensed from the
atmosphere.

SPECIFIC HEAT AND THE HEATING AND COOLING OF AIR.

Different substances vary greatly in the amount of heat they
must absorb to raise their temperature a given amount. The quan-
tity of heat that must be imparted to a body to raise its tempera-

62 Principles of Heating.

ture i degree in comparison with that required to raise an equal
weight of water I degree is known as the " specific heat " of the
body. Thus, the specific heat of air is 0.2375 (generally taken as
0.238) — that is, only about one-fourth as many heat units are re-
quired to raise I pound of air i degree as would be necessary to
raise i pound water the same amount. The specific heat of water
varies slightly, but this need not be taken into consideration ex-
cept for scientific work.

To determine how many heat units are required to heat a given
volume of air a stated number of degrees the quickest method is
probably to multiply the volume in cubic feet by the degrees rise in
temperature and divide the product by 55, this number represent-
ing approximately the number of cubic feet of air at 70 degrees
that will be raised i degree by one heat unit. One cubic foot of
dry air at 70 degrees temperature weighs 0.0747 pound, or i

pound occupies 13.4 cubic feet. One heat unit will raise ~

pound of air I degree, equal to 4.2 pounds of air i degree. Since
i pound of dry air occupies 13.4 cubic feet, i heat unit will raise
4.2 X 134 cubic feet i degree = 56 cubic feet; 55 cubic feet is
commonly used in making approximate calculations. On pre-
cisely the same basis it will be found that i heat unit will raise
approximately 50 cubic feet of air at zero through i degree, zero
air weighing 0.0864 pound to the cubic foot.

TABLE XIII.

THE WEIGHT OF MIXTURES OF AIR SATURATED WITH VAPOR PER CUBIC FOOT AT
DIFFERENT TEMPERATURES.

Weight in Weight in

Tempera- pounds of Tempera- pounds of

ture. — F. 1 cubic foot ture. — F. 1 cubic foot

of dry air. of dry air.

0 . 0.086379 92 0.070717

12" . 0.084130 102 0.068897

22" 0.082302 112.. . 0.067046

32" 0.080504 122 . 0.065042

42" 0.078840 132 0.063039

52" . 0.077227 142" ' 0.060873

62" 0.075581 152 \ 0.058416

72" '.'.'.'.'.'... 0.073921 162 0.055715

82'.'.'.".'.'. 0.072267

See Table XVI, page 69, for weight of dry air per cubic foot
at different temperatures.

Heating Equivalents, Specific Heat, etc., of Air. 63

COOLING AIR.

When the volume of air to be cooled is small, ice is generally
used, each pound in melting absorbing about 142 heat units. Sup-
pose, for example, it is desired to know the weight of ice that
must be melted to cool 60,000 cubic feet of air per hour from 90
down to 80 degrees, the water from the melted ice to be dis-
charged at 62 degrees temperature :

Heat units.
1 pound of ice, in melting, absorbs 142

1 pound of water, when warmed from 32° to 62°, absorbs 30

Total heat units absorbed 172

The effect of condensing the moisture in the air "must be allowed for, about
1000 heat units being given off per pound of moisture condensed.

One cubic foot of air at 90 degrees weighs 0.072 pound. Hence
60,000 cubic feet will weigh 4,320 pounds. Since the specific heat
of air is 0.238, the number of heat units that must be absorbed by
melting ice to cool this weight of air 10 degrees will be 4,320
pounds X 10 X 0.238 = 10,250 heat units, approximately. Since
i pound of ice melted and the water raised to 62 degrees absorbs
172 heat units, 10,250 -f- 172 heat units will be required, equal to
about 60 pounds of ice per hour to cool 60,000 cubic feet of air 10
degrees F.

The ice would be most effective if it were crushed into small
pieces so that the air would come in close contact with it. This,
unfortunately, would seriously retard the flow of air, owing to
the increased resistance over that when large cakes are used. With
the latter arranged in properly constructed racks and provision
made for retaining the water until its temperature has increased
to within 20 or 30 degrees of that of the air, good results have
been obtained ; but practically one must expect the amount of ice
required to exceed considerably the theoretical weight based on
the volume of air cooled, since there are losses by transmission
through surrounding partitions, walls, etc.

For large systems mechanical refrigeration should be used. It
may be said in a general way that in small plants the consumption
of i ton of coal is sufficient to produce 7 to 8 tons of commercial
ice. The actual ice making capacity of a machine is only 50 to 60
per cent, of its so-called ice-melting capacity, which is expressed
in tons capacity in 24 hours — that is, a 3O-ton machine means a

64 Principles of Heating.

refrigerating capacity in 24 hours equivalent to that produced by
the melting of 30 tons of ice. The machine would produce, how-
ever, only 15 to 1 8 tons of real ice in the same period. For cool-
ing air with a refrigerating plant, brine at, say, 8 to 12 degrees F.
would be circulated by pumps through coils over which the air
would be required to pass.

Unfortunately, the cooling of air does not make it agreeable.
Its relative humidity is increased, which makes it less capable of
absorbing moisture or perspiration from the body. Therefore
the air should be dried by passing it over trays of calcium
chloride, which has a great capacity for absorbing moisture, or it
may be slightly heated after the chilling process to reduce its
humidity.

It is unwise to cool the air in a room on a hot summer day
more than about 10 degrees F. below the outdoor temperature,
since to do so makes the room feel chilly to one entering from the
outside.

When air is cooled down to the dew point, latent heat appears,
due to condensation of moisture, and this is to be taken into con-
sideration in cooling problems.

EVAPORATION AND HUMIDITY.

To moisten air water must be evaporated or steam must be
injected into it. In either case about 1,000 heat units are necessary
for the evaporation of I pound of water or the making of I
pound of steam. Water evaporates very slowly when exposed in
still air, the evaporation per square foot from a water surface in
contact with still air at 70 degrees having a relative humidity of
40, being about 1-40 pound per hour. The rate of evaporation
rapidly increases with an increase in temperature or the passage
of air across the surface of the water. The capacity of air to
absorb moisture increases rapidly with its rise in temperature —
e. g., air at 70 degrees can absorb about four times as much
moisture as air at 30 degrees, as will be seen by referring to
Table XIV:

Heating Equivalents, Specific Heat, etc., of Air. 65

TABLE XIV.

THE WEIGHT OF WATER VAPOR PER CUBIC FOOT OF SATURATED SPACE AT DIFFERENT

TEMPERATURES.

Weight of Weight of

Tern- vapor in grains Tern- vapor in grains

perature. per cubic foot. perature. per cubic foot.

0 0.54 50 4.09 = 4 appro*.

10 0.84 60 5.76

15 0.99 = 1 approx. 70 7.99 = 8 appro*.

20 1.30 80 10.95

30 1.97 = 2 approx. 90 14.81

40 2.88 100 19.79 = 20 approx.

1 pound avoirdupois = 7000 grains.

Approximately 1000 heat units are required to evaporate 1 pound of water.

The amount of heat and fuel necessary to moisten air is not
generally appreciated. To illustrate this point take the amount of
heat required to moisten air entering a furnace at 30 degrees, with
a relative humidity of 65, so that a relative humidity of 50 will be
maintained in the rooms kept at 70 degrees. Assume that 50,000
cubic feet of air per hour passes through the furnace : One cubic
foot of saturated air at 30 degrees temperature contains, approxi-
mately, 2 grains of moisture, and with a relative humidity of 65
would contain 1.3 grains. Each cubic foot of air at 30 degrees
expands to 1.08 cubic feet when heated to 70 degrees. One cubic
foot of saturated air at 70 degrees contains about 8 grains of
moisture. With 50 relative humidity I cubic foot of 7o-degree
air would contain 4 grains.

The amount of moisture that must be supplied by the evaporat-
ing pan in the furnace is the difference between 50,000 cubic feet
per hour X 1.08 X 4 and 50,000 X 1.3. The difference equals
151,000 grains, or 21.6 pounds per hour.

Since about 1,000 heat units are required to evaporate I pound
of water, 21,600 units per hour are absorbed, equal to the heat
utilized from the burning of 2,^/2 pounds of coal.

If an attempt is made by specially provided means to raise the
relative humidity in the room to, say, 50, in cold winter weather,
the moisture will condense on the windows and they will become
frosted.

A relative humidity of about 30 is said to be about as high
as one can secure without trouble from condensation on single
windows in severe winter weather.

66 Principles of Heating.

ACTUAL AND RELATIVE HUMIDITY.*

By actual humidity (A.H.) is meant the weight of water
vapor in a given unit volume of space or air as the number of
grains contained in a cubic foot of air.

By relative humidity (R.H.) is meant the ratio in hundredths
between the quantity present in that volume of space or air and
the quantity it would contain if saturated.

Actual humidity remaining constant, relative humidity is deter-
mined by temperature.

Dew Point. — When the humidity of any space is raised to satu-
ration it may be said to have reached the saturation point, as any
excess of vapor must be precipitated in fog or dew.

When the temperature of any given space is lowered to such
a point that the contained vapor saturates the space, that satu-
rating temperature is called its dew point.

It is pointed out in pamphlet W. B. 235, treating of humidity,
etc., by C. F. Marvin, and published by the U. S. Department of
Agriculture, that a false notion is widely prevalent that air has a
certain capacity for moisture. It is pointed out that the presence
of moisture in a given space is independent of the presence or
absence of air in the same space except that the air retards the
diffusion of the vapor particles. It is more correct to say that
the space is partly saturated with moisture.

COOLING AND CONDITIONING AIR.t

"The cooling of 10,000 cubic feet of air a minute, or 600,000
cubic feet an hour, from 95 to 80 degrees would require an
abstraction of heat from it which would melt 1,150 pounds of
ice. But air so cooled would be more uncomfortable and danger-
ous than the hotter air of 95 degrees because of its excessive
humidity. To remove the excess of moisture by cooling would
require an additional extraction of heat, varying with the tem-
perature and relative humidity of the outside air, equal to the

* From S. H. Woodbridge's Technology Notes.

t Extract from Professor Woodbridge's Report on the Ventilation of the U. S.
Senate Chamber, dated December 14, 1895.

Heating Equivalents, Specific Heat, etc., of Air. 67

melting of from 600 to 1,000 pounds of ice, or a total refrigerat-
ing effect of about i ton of ice an hour.

Either of two methods may be followed for making the
treated air salubrious and agreeable. The whole quantity of air
cooled may be brought down to so low a temperature as to precip-
itate the necessary moisture for drying it, and then warmed
again by artificial heating to the temperature and dryness essen-
tial to comfort ; or a part only of the air may be so sharply chilled
as to remove the weight of moisture necessary to insure dryness,
and this chilled and dried air may then be passed on and mixed
with the untreated part, resulting in the drying and cooling of the
entire volume of air. . . .

By means of modern mechanical refrigerating appliances from
15 to 20 tons of refrigerating effect may be realized from i ton
of coal, and such cooling and drying as is above mentioned could,
therefore, under the best working conditions, be had by a fuel
expenditure of from 150 to 200 pounds of coal an hour."

COST OF INCREASING HUMIDITY.

The statement is sometimes met with that air may be humidi-
fied without extra cost, that is, that a saving may be made in the
loss of heat by transmission through walls and glass sufficient to
offset the cost of adding moisture to the air. The saving in heat
by transmission is due to the lower room temperature that may
be maintained with a relatively higher humidity, than the temper-
ature that would be necessary to produce practically the same
degree of comfort when the air in the room is of the low relative
humidity common in heated buildings during the winter.

This statement may easily be proven to be false, a much larger
amount of heat being used up in evaporating the water to secure
the increased humidity than is saved by the lessened transmission
through walls and glass, due to a lower room temperature.

EXPANSION OF AIR AND ABSOLUTE TEMPERATURE.

Air expands and contracts with changes in temperature ac-
cording to a known law — viz., for each degree rise or fall in
temperature from 32 degrees F. air expands or contracts V491

Principles of Heating.

of its volume at that temperature. If a cubic foot of air be
heated through 491 degrees from 32 degrees, or to 523 degrees,
it will double in volume. On the other hand, if a cubic foot of
air be cooled through 491 degrees from 32 degrees, or to 459 de-

grees below zero, it will theoretically contract ^— of its original

bulk, or will entirely disappear. This point, 459 degrees below
zero, or more accurately 459.4 degrees, is known as absolute zero,
and is the point from which the expansion of air is reckoned in
determining its relative volume at different temperatures, the
volume being proportional to the absolute temperature. For con-
venience in making ordinary calculations 460 degrees F. below
zero may, with sufficient accuracy, be considered absolute zero.
Hence the absolute temperature of a body is equivalent to 460 de-
grees plus its Fahrenheit temperature. Suppose, for example,
we wish to determine how much space i cubic foot of air entering
a furnace at o degree F. will occupy when heated to 140 degrees
F. Since the volume varies in proportion to the absolute tempera-
ture, we have :

Absolute temperature of air at 0°F= 0° +460° =460 \ Volume at 0° is to volume at
Absolute temperature of air at 140°F = 140° -j- 460° =600 J 140° as 460 is to 600.

Hence, volume at 140 degrees =- X volume at o degree; vol-
ume at 140 degrees =1.3 cubic feet.

TABLE XV.

THE APPROXIMATE VOLUME TO WHICH 1 CUBIC FOOT OF AIR AT 0° WILL EXPAND
WHEN HEATED TO THE TEMPERATURES STATED IN THE TABLE. VOLUME OF AIR
AT 0° =1 CUBIC FOOT.

folum
)egree
10. .
20

e when heated to —
s. Cubic

feet.
.02
.04
.06
.09
.10
.13
.15
.17
L.20
L.22

Volume when heated to —
Degrees.
110

Cubic feet.
— 1 24

120

... — 1.26

130. .

40^

140

— 30

150

... — 33

200

— 44

300

— 65

400.

— 87

. — ]

500

— 2 09

100.

Heating Equivalents, Specific Heat, etc., of Air. 69

TABLE XVI.

THE WEIGHT OF DRY AIR PER CUBIC FOOT AT DIFFERENT TEMPERATURES.

Weight of a

Temperature. cubic foot

Degrees F. in pounds.

0 0.0864

12 0.0842

22 0.0824

32 0.0807

42 0.0791

52 0.0776

62 0.0761

72 0.0747

82 0.0733

92 0.0720

102.. . 0.0707

Weight of a

Temperature. cubic foot

Degrees F. in pounds.

112 0.0694

122 0.0682

132 0.0671

142 0.0660

152 0.0649

162 0.0638

172 0.0628

182 0.0618

192 0.0609

202 0.0600

212.. . 0.0591

VELOCITY OF AIR IN FLUES.

The velocity of air in a flue is governed by its hight and the
difference between the inside and outside temperature. Suppose
we have a flue I square foot in area and of hight h, .
represented in Fig. 28. ||

The air in the flue is balanced by a column of T
colder outside air of hight H, leaving an unbalanced
force represented by the hight (h — H), tending to
produce a velocity at the base of the flue equivalent
to that developed by a body falling freely through
a distance represented by the hight (h — H).

The velocity acquired by such a body, neglecting
friction, is expressed by the equation

v = V

(a)

Here v = velocity in feet per second, g = the
acceleration in feet per second due to gravity, = 32.2 j
feet, h = the hight through which the body falls — |
in this case represented by (h — H). 3

Now let

Fig. 28.— Flue

o;0=the weight per cubic foot of outside air. Diagram.

«V=the weight per cubic foot of air in the flue.

t0 =the absolute temperature of the outside air = Fahrenheit temperature + 459.4°.
if =the absolute temperature of the air in the flue = Fahrenheit temperature + 459.4°.

70 Principles of Heating.

We have seen that the velocity at which the air enters the base
of the flue is expressed by

"=V 2 g (h-^H) (b)

Now since the columns of air represented by h and H balance each
other we have weight of column h = weight of column H; or,

hwF — H w0 (c) hence H = -—? ^

The density of the air, or its weight per cubic foot, varies inversely

as the absolute temperature ; hence we may substitute for — , -~

w0 l F

rr*

equation (d) becoming H = h — (*)

Substituting this value of H in (b) we have

Now the weight of air leaving the flue must be equal to the weight
of air entering — that is,

Velocity of air leaving flue X WF = velocity of air entering
flue X w0 ........................................... (g)

Velocity of air leaving flue =

velocity of air entering flue X WQ

Or, since the weight varies inversely as the absolute temperature,
Velocity of air leaving flue =

velocity of air entering flue X T

7^ ~ ................. (.*/

±0

Equation (/) gives the velocity of the air entering the flue, hence
Velocity of air leaving or passing through the flue =

Allowing 50 per cent, for friction, and substituting the value of g
= 32.2, the Velocity in feet per minute in the flue is

from which the following table is calculated :

Heating Equivalents, Specific Heat, etc., of Air. 71

TABLE XVII.
THE APPROXIMATE VELOCITY OF AIR IN FLUES OF VARIOUS HIGHTS.

Outside temperature 32 degrees. Allowance for friction 50 per cent, in flue one square

foot in area.

Hight

of , Excess of temperature of air in the flue over that outdoors. ^

flue. 10° 20° 30° 40° 50° 60° 70° 80° 90° 100° 120° 140°

Feet. Velocity of air in feet per minute.

5 77 111 136 159 179 199 216 234 250 266 296 325

10 109 156 192 226 254 281 306 330 354 376 418 460

15 133 192 236 275 312 344 376 405 432 461 513 565

20 154 221 273 319 359 398 434 467 500 532 592 650

25 173 248 305 357 402 445 485 522 560 595 660 728

30 189 271 334 390 440 487 530 572 612 652 725 798

35 204 293 360 423 475 527 574 620 662 705 783 862

40 218 311 386 452 508 562 612 662 707 753 836 920

45 231 332 408 478 538 597 650 700 750 800 887 977

50 244 350 432 503 568 630 685 740 790 843 935 1030

60 267 383 473 552 622 690 750 810 865 923 1023 1125

70 289 413 510 596 671 746 810 875 935 995 1105 1215

80 308 443 545 638 717 795 867 935 1000 1065 1182 1300

90 327 470 578 678 762 845 920 990 1060 1130 1252 1380

100 345 495 610 713 802 890 970 1045 1118 1190 1323 1455

Since the volume of air in cubic feet per minute discharged
by a flue equals the velocity in feet per minute multiplied by the
area in square feet,

volume volume

Velocity = Area = — : — —

area velocity

Example: Find the area of a flue 20 feet high that will dis-
charge 3000 cubic feet per minute, when the excess of tempera-
ture in the flue over that outdoors is 40 degrees.

Opposite 20 in left-hand column and under 40 on upper line is
the number 319, representing the velocity in feet per minute. The
volume 3000-^-319 = 9.4 square feet, the required area. In esti-
mating the effective hight of a warm-air flue from a furnace, con-
sider the flue to begin 2 feet above the grate.

CHAPTER VI.
HEATINQ WATER.

The question frequently comes up how to determine the heat-
ing surface required to heat a given volume of water a certain
number of degrees in hot water storage tanks or generators,
as shown in Fig. 29. The proportions of feed water heaters in
connection with boilers give a basis for such calculations, these
heaters of the closed tubular type having 1-3 to j£ square foot
of heating surface per boiler horse-power.

HEATING WATER BY SUBMERGED STEAM PIPES.

Taking the greater amount as a basis, j£ square foot of heat-
ing surface is expected to heat about 30 pounds of water per hour
from, say, 50 to 200 degrees, that is 30 X 150 = 4500 heat units.
In other words, a square foot is rated to transmit 9000 heat units
per hour. .

Suppose the exhaust steam pressure is 2 pounds, correspond-
ing to a temperature of about 220 degrees, the average water
temperature is (200 + 50) -r- 2 = 125 degrees, making the aver-
age difference in temperature between the steam and the water
220 — 125 = 95 degrees. Hence the number of heat units trans-
mitted per square foot of heating surface per hour per degree
difference in temperature is 9000 -r- 95, or about 100 heat units
in round numbers.

Low pressure steam coils surrounded by air at 70 degrees
give off only about 2 heat units per degree difference in temper-
ature per hour, whereas when immersed in -water they condense
steam per degree difference about 50 times as rapidly — a strik-
ing fact.

To take a practical example, suppose it is desired to compute
the heating surface in brass pipe required to. raise the tempera-
ture of the water in a 4OOO-gallon tank from 70 degrees to 160
degrees in two and one-half hours with steam at 5 pounds pres-
sure. The given number of gallons is equivalent to 4000 X 8 1-3
(number of pounds per gallon) = 33,333 pounds. The increase

Heating Water.

in temperature is 90 degrees. Total number of heat units re-
quired is therefore 33,333 X 90 = 2,999,970. The number of
heat units required per hour is thus approximately 1,200,000. The
average difference in temperature between the steam and water
is 228 — 115 = 113 degrees. Since I square foot of heating sur-
face with i degree difference between the temperature of the
steam and water gives off approximately 100 heat units per hour,
with 113 degrees difference approximately 11,300 heat units will
be given off in an hour, and 1,200,000 -r- 11,300 = 106 square

-™P MUDBLOwLT

Fig. 29. — Hot Water Storage Tank Heated by Steam

WATER rNLET
THE METAL

feet, the area of the heating surface required, which is I square
foot to approximately 37 gallons capacity.

HOT WATER GENERATORS.

Hot water generators, so-called, otherwise known as coil boil-
ers or hot water storage tanks, commonly have about I linear
foot of i -inch pipe to each 5 gallons capacity — that is, about I
square foot of heating surface to each 15 gallons capacity. Such
boilers are commonly assumed to be capable of heating their con-
tents at least once an hour from, say, 60 to 1 60 degrees.

To heat 300 gallons per hour, for example, 100 degrees would
require the expenditure of 300 X 8 1-3 X 100 = 250,000 heat
units (81-3 representing the approximate weight of i gallon of
water in pounds). With a coil based on the proportions stated,
I square foot to 15 gallons capacity, the heating surface is 20
square feet and the heat emitted per square foot per hour would
be 250,000 -T- 20 = 12,500 heat units.

With steam at 228 degrees and average water temperature at

74 Principles of Heating.

no degrees the difference is 118 degrees; the transmission per
square foot per hour per degree difference is 12,500 -i- 118 =
106 heat units.

A hot water generator of even moderate size when heating
the contents once an hour condenses an immense amount of steam.
Take, for example, one of, say, 300 gallons capacity. To heat this
volume from, say, 50 to 160 degrees requires 300 X 81-3 X no
= 275,000 heat units. The condensation of i pound of steam at 5
pounds pressure gives off 954.6 heat units ; therefore nearly 300
pounds of steam would have to be condensed in an hour, equiva-
lent to about 10 boiler horse-power, or the consumption of 35
to 40 pounds of coal.

In office buildings and apartment houses at certain periods
the volume of water drawn from the hot water generator is equal
to a per hour rate many times in excess of the average per hour
requirements throughout the day. The generator, or hot water
storage tank, must be made large enough to meet these demands,
just as a storage battery is used to carry an electric plant through
certain periods of overload. The steam coil in the generator then
has several hours in which to make good the sudden large drafts
that occur at intervals.

BOILING LIQUIDS IN VATS.

It is a well-known fact that when water is heated in an open
vessel to the boiling point, 212 degrees F., its temperature cannot
be increased. If more heat is applied it simply causes the water
to boil more rapidly. The amount of heat required to evaporate
i pound of water at a temperature of 212 degrees into steam at
the same temperature is, neglecting decimals, 966 heat units. This
is known as the latent heat. The same number of heat units are
given up by the steam when it is condensed back into water.
For example, an ordinary heating coil condensing about 1-3
pound of steam per square foot per hour gives off a little more
than 300 heat units, or about one-third of the latent heat in a
pound of steam.

In computing the amount of coil necessary to evaporate a
given amount of water in a stated time proper allowance must
be made for the latent heat necessary to evaporate the water after

Heating Water. 75

sufficient heat has been applied to bring it to the boiling point.
Since the heat given off by the coil depends on the difference in
temperature between the steam inside and the water outside one
should have 20 to 40 pounds steam pressure in order to provide
a reasonable excess of temperature in the steam over the water.
For boiling thick, heavy liquids considerably more heating sur-
face is necessary than for boiling water, on account of the more
sluggish circulation. The difference in the specific heats also
enters in.

HEATING SMALL SWIMMING POOLS.

Hot water generators fitted with steam coils, as shown in Fig.
29, are sometimes used to heat small swimming pools, the water
being admitted to the latter through concealed pipes placed near
the bottom.

When connected with a gravity return system of steam heat-
ing no more attention is necessary with regard to maintaining
the proper amount of water in the steam boiler than if the steam
coil in the hot water generator were a large radiator, since the
condensation returns to the boiler, provided the generator is lo-
cated well above the water line.

To compute the size of coil required with this method of
heating take, for example, a pool 12 x 30 feet in plan and 5 feet
in average depth. Its contents, 1,800 cubic feet, multiplied by
62^, the number of pounds i cubic foot of water weighs, gives
about 112,500 pounds to be heated.

Suppose the water to be continuously changing at the rate of
one complete change every ten hours, equivalent to 11,250 pounds
of water per hour. If the water in the street mains is at, say, 50
degrees, and that in the pool 75 degrees, 11,250 X 25 — 281,250
heat units must be supplied per hour.

It has been pointed out that i square foot of heating surface
in the generator will give out about 12,500 heat units per hour;
therefore 281,250-^12,500 = 22.5, or about 22 square feet of
coil would be necessary when using steam of, say, 5 pounds pres-
sure. On the customary basis of i square foot of heating sur-
face to 15 gallons capacity, 22 square feet of surface would cor-
respond to a 33o-gallon boiler, which, from experience, the writer
has found gives good service under the conditions stated.

Principles of Heating.

fMfeL

s;'
^l~p^

Heating Water. 77

HEATING LARGE SWIMMING POOLS.

For heating large pools one of three methods is commonly
used:

1. Steam is admitted directly to the water in the pool through
one of the devices on the market for muffling the sound.

2. Steam coils are submerged in the pool.

3. The water is made to circulate through a boiler or heater,
as shown in Fig. 30, the pool being practically a huge expansion
tank.

AMOUNT OF STEAM AND SIZE BOILER REQUIRED.

The amount of steam that must be admitted to heat the water
in a pool will depend on the volume, the temperature and the
time in which the heating must be done.

Take, for example, a pool 20 x 80 feet, with an average depth
of 7 feet, equal to 11,200 cubic feet, in which the water is to be
heated from the street temperature of, say, 50 degrees, to a tem-
perature of 80 degrees during a period of ten hours. Water
at the street temperature weighs approximately 62^2 pounds per
cubic foot; therefore 11,200 cubic feet of water to be raised 30
degrees in ten hours will require a number of heat units per hour
equal to

11,200 X 62.5 X 30 -f- 10 = 2,100,000 heat units.

Suppose the steam be admitted at low pressure, say 5 pounds.
One pound at that pressure will supply 955 heat units when con-
densed, and the water, in cooling from 228 degrees, the tempera-
ture of the steam at 5 pounds pressure, to 80 degrees, will give
up 148 heat units more, making a total of 1,103 neat units per
pound. This figure is contained in the total number of. heat units
required about 1,903 times — that it, 1,903 pounds of steam must
be condensed in one hour.

The boiler capacity required is equal to 2,100,000 -f- 33,305
(which is a boiler horse-power expressed in heat units) =63
horse-power. The above makes no allowance for the loss of heat
by evaporation — a subject previously discussed — nor for losses
through the walls or the bottom of the tank.

78 Principles of Heating.

AMOUNT OF STEAM PIPE REQUIRED.

To ascertain the amount of steam pipe required with steam at,
say, 5 pounds pressure, the pipes to be placed around the tank
in recesses near the bottom, other conditions to be as stated above,
proceed as follows: The average difference in temperature be-
tween the steam and water is

/ 50 + 80 \
228 — ^ /= 228 — 65 = 163 degrees.

The discussion of feed water heaters showed that it is approx-
imately correct to reckon on 100 heat units being given off per
hour by the steam to the surrounding water per degree difference
in temperature. Hence, with 163 degrees difference, we should
expect to transmit to the water 16,300 heat units for each square
foot of brass pipe installed. If galvanized wrought iron pipes are
used we should expect to get only about 70 per cent, of the heat
stated above, or 11,410 heat units per square foot per hour.

The total heat units — viz., 2,100,000 — divided by 11,410, gives
184 square feet, or about 368 linear feet, of i^-inch pipe that
would be required to meet the conditions stated. If the water
were to be heated in a shorter time proportionately more surface
would be required.

The above computations have as a basis the heat given off by
the pipes or tubes in feed water heaters where the circulation of
water is comparatively rapid. With coils submerged in tanks
the movement of water over them is sluggish and the heat is
taken up from the pipes less rapidly, hence it is wise to add 25 to
50 per cent, to the computed amount of pipe according to its
location to allow for this sluggish circulation.

SIZE BOILER REQUIRED.

If a boiler is to be used, as in the third method mentioned, the
amount of coal to be burned, the size of the grate and the size of
the boiler may be determined as follows :

The total number of heat units required per hour, as computed
above, is 2,100,000. Assuming that i pound of coal will give up
in this case 9,000 heat units, since the boiler will be more efficient
than usual, due to the cooler heating surfaces, the coal required
will be 2,100,000 -T- 9,000 = 233 pounds per hour. With a regu-

Heating Water. 79

lar attendant at least an 8-pound rate of combustion per square
foot of grate surface per hour may be safely assumed. The grate
surface therefore should be 233 -r- 8 = approximately 30 square
feet.

The water in the boiler being only 80 odd degrees instead of,
say, 228 degrees, with 5 pounds pressure, less heating surface is
required, in proportion to the grate area than with ordinary heat-
ing boilers to give the same efficiency. Assuming, as a rough ap-
proximation, that the average temperature of the gases in the
boiler or heater is 700 degrees, the effectiveness of the heating

surface in the two cases would be in the proportion of— =?

700 — 228

-- 52? ; that is, only about 472 -j- 620 = 76 per cent, as much
472

heating surface per square foot of grate would be required in the
boiler used for heating water to 80 or 90 degrees as would be
needed in ordinary low pressure boilers.

The gist of this is that a heater for the purpose stated could
have an abnormally large grate in proportion to its size and still
be economical in the use of coal.

TANK HEATERS.

Tank heaters are commonly rated by manufacturers to heat
one-half to three-fourths as many gallons of water per hour as
the number of square feet of direct radiating surface they will
supply ; that is, a heater with a grate 20 x 24 inches connected as
shown in Fig. 31, would be rated to carry, say, 600 square feet of
radiating surface, or to heat 300 to 450 gallons of water per hour.
Manufacturers fail to give the temperatures from and to which
the water is heated, but for apartment houses and the like the tank
temperature should be kept as a rule at about 160 degrees. There-
fore the water must be heated on an average at least 100 degrees
above that of the city supply.

It is a simple matter to show on a heat unit basis that a much
greater expenditure of heat is necessary to raise 300 gallons —
that is, 2,500 pounds — of water 100 degrees than to supply 600
square feet of radiating surface, the heat losses being 250.000
and 90,000 respectively. Therefore tank heaters are commonly
overrated. This fact, however, seldom becomes apparent, as the

Principles of Heating.

large capacity of the storage tank enables the heater to heat the
water at night, or when little water is drawn, so that time and
storage capacity help out the overrated heater.

If one knows approximately the number of gallons of water
that must be heated per hour to a given temperature from that of
the city supply, the size heater may be readily determined on the
heat unit basis. For small heaters, having, say, not over 2 square
feet grate surface, the rate of combustion should not exceed 3
pounds per square foot of grate per hour. Larger heaters may

Fig. 31.— Tank Heater Connections.

be rated to burn 4 to 5 pounds or even more with frequent atten-
tion.

Example: What size will be required to heat 75 gallons per
hour 90 degrees? The product: 75 (gallons) X 8 1-3 (number of
pounds of water in one gallon) X 90 (the temperature range),
gives the number of heat units involved. Dividing this product
by 3 (number of pounds of coal burned per square foot of the
grate per hour) X 8000 (the number of heat units utilized per
pound of coal) gives 2.3 as the number of square feet of grate
surface required. The above basis of computation will be found
convenient in determining the size heater to be used for a baptistry
pool, when the volume to be heated, the time and the temperature
to be attained are known.

Heating Water. 81

By installing a storage tank of good size a small heater may
be made to do as good service as a much larger one with a small
tank. That is, with a large tank, holding several times the proba-
ble maximum hourly volume required, a sudden draft in excess
of the ability of the heater to make good immediately is not ac-
companied by a lowering of temperature at the faucets, as would
be the case with a small tank. The assumption is sometimes
made that, unless stated to the contrary, heaters rated to supply
tanks of certain capacities are capable of heating a volume of
water equal to the tank capacity in one hour. As just stated, it
is better that the tank capacity should be several times the average
hourly consumption.

Taking the ratings of a prominent manufacturer:

Heater with 12-inch grate is rated to supply a 200-gaIlon tank.
Heater with 15-inch grate is rated to supply a 325-gallon tank.
Heater with 18-inch grate is rated to supply a 485-gallon tank.

Averaging these gives i square foot of grate to 266 gallons
tank capacity. Even with a rapid rate of combustion, say 5
pounds per square foot per hour, a square foot of grate would heat
only about 48 gallons per hour 100 degrees, showing the tank
capacity stated in these ratings to be over five times the hourly
heating capacity of the heaters.

Suppose the water is heated from a street main at a tempera-
ture of 60 degrees to only 120 degrees; then I square foot of
grate with a 5-pound rate of combustion would heat 80 gallons
per hour, or only about one-third the rated tank capacity per
square foot stated in the manufacturer's ratings. On the basis
of 80 gallons per hour heated from 60 to 120 degrees per square
foot of grate, a 32O-gallon boiler, contents to be used once an
hour, should have a heater with at least 4 square feet of grate
surface, equivalent to a grate 27 inches in diameter. This would
be uncommonly large for a tank of the size stated, showing that
with the ordinary proportions of grate to tank capacity it must
not be expected that the contents of the tank will be heated in
less than several hours.

WATER BACKS AND GAS HEATERS.

Water backs in ranges ordinarily have 2 to 2^2 square inches
of heating surface per gallon capacity in the hot water boilers

Principles of Heating.

with which they are connected. The ordinary temperature of
water from city mains would be 50 degrees or more, running up
to 70 degrees or so in summer. While 160 degrees is a common
temperature for the hot water supply in large buildings having a
separate heater, the temperature of a domestic supply is generally

Q -Jjjg^

Fig. 32. — Gas Heater Connected with Range Boiler.

much lower, say not over 130 degrees as a rule, though in some
cases much higher — even above boiling temperature at atmos-
pheric pressure. Now, under the most favorable conditions the
hot water supply must be heated from 70 to 130 degrees, equal
to 60 degrees rise.

Take, for example, a 4<D-gallon boiler connected with a water
back of 100 square inches area. To heat 40 gallons per hour 60
degrees would take 40 X 8 1-3 X 60 = 20,000 heat units, which

Heating Water. 83

with a water back area of about 2-3 square foot would mean over
30,000 heat units per square foot per hour transmitted to the
water. Such a rating would be altogether too high with the pro-
portions of water back and tank capacity just stated.

Similar surfaces in furnaces with combination heaters are sel-
dom rated to carry over 75 square feet of direct radiating surface
for each square foot of heating surface exposed to the fire; this
is equivalent to only 75 X 150 ('150 being the heat units given
off per square foot of radiating surface per hour) =11,250 heat
units. This is only a little more than the heat given off per square
foot by steam coils in contact with water. The low rating is due
to the chilling effect of the coil or water back on the fire in con-
tact with it.

For ordinary working conditions the writer believes a rating
of 10,000 heat units per square foot per hour for water backs to
be a fair one, but with a brisk fire, as on ironing days, the water
back will probably take up as much as 15,000 heat units per
square foot per hour.

It is pretty difficult to determine in advance in any household
the approximate volume of hot water that must be supplied.
Families of the same size differ greatly in the amount of water
they are in the habit of using. A water back to meet maximum
use would be altogether too large for ordinary use. The best way
to meet excessive occasional demands is to use a gas heater, con-
nected as shown in Fig. 32, in addition to the water back.

Tests of ordinary gas heaters used in connection with hot
water boilers are stated to have shown efficiencies of 52 to 74 per
cent., when burning gas having a heating power of 540 heat units
per cubic foot.

COILS FOR HEATING WATER.

Coils for heating the domestic water supply are frequently
placed in hot water or steam heaters. On the basis of 15,000
heat units per square foot per hour ; to heat 40 gallons per hour,
for example, from, say, 60 to 130 degrees, or through 70 degrees,
40 X 8 1-3 X 70 = 23,310 heat units would be necessary, re-
quiring about il/2 square feet of heating surface, equal to 4l/2
lineal feet of i-inch pipe or 3.5 feet of i ^4 -inch pipe.

If the coil is suspended in the combustion chamber above the
fire a much lower rating must be assumed. It is well to arrange

84 Principles of Heating.

the coil so that the fire may be brought in contact with it when
desired by carrying a deep bed of coal on the grate. The heating
capacity of a coil placed above the fire varies greatly with the
condition of the fire on top ; a bright fire giving good results and
one black on top heating the water but little. As a rule it is a
rather unsatisfactory way to heat a water supply unless the fire is
run very regularly. A good sized tank should be used to avoid
overheating.

An independent hot water stove or tank heater is generally to
be preferred. A rating as high as 15,000 heat units should hardly
be used, except when the fire is sure to receive careful attention.
A rating of 10,000 to 12,000 heat units would represent more
closely what could be expected in ordinary practice.

CHAPTER VII.
CAPACITIES OF PIPES FOR HOT WATER HEATING.

THE FLOW OF WATER IN PIPES.

The force causing circulation in a hot water heating system,
due to the difference in temperature of the water in the supply
and return pipes, is very slight and amounts to only i grain, or
1-7000 pound per square inch per degree difference in tempera-

Fig. 33.— Head of Water Causing Flow.

ture per foot of hight. In ordinary two-pipe up-feed systems the.
hight is to be considered as that between the middle of the boiler
and that of the topmost radiator. Suppose the supply and return
risers to be 25 feet high with 20 degrees difference in temperature,
then the excess of weight in the return over that in the supply
line will be 25 X 20 — 500 grains = 1-14 pound for each square

86 Principles of Heating.

inch cross sectional area. Since I pound pressure is equivalent
to about 2.3 feet, 1-14 pound is equal to a head of, approximate-
ly, 0.165 feet, or about 2 inches.

Put in another way, let H in the accompanying sketch repre-
sent the hight of a column of water at 170 degrees and h the
hight of a column of equivalent weight at 150 degrees. Let
H = 25 feet, then

_ 25 X 60.801 (weight of i cubic foot at 170 degrees)
61.204 (weight of i cubic foot at 150 degrees)
= 24.835 feet. Then, H — h, the hight representing the head or
unbalanced force causing circulation of the water, is 0.165 foot,
or about 2 inches, as above.

Were it not for friction the velocity corresponding to this
head would be about 195 feet per minute, since the velocity in
feet per second, neglecting friction, is approximately eight times
the square root of the head, expressed in feet. Friction, however,
plays a very important part in the laws governing the flow of
water in pipes, and the actual velocity is only a fraction of the
theoretical velocity, computed as above. The resistance to the
flow is proportional fo the length of the pipe to the square of the
velocity, and decreases as the diameter increases. That is, the
resistance varies inversely as the diameters.

VOLUME OF WATER TO SUPPLY RADIATORS.

The volume of water that must pass through a radiator of a
given size to maintain a certain output of heat may be determined
as follows: Take, for example, a direct radiator of 100 square
feet, in which the water is cooled 15 degrees and which gives
off 150 heat units per square foot per hour. The heat given off
equals 100 X 150, or 15,000 heat units per hour. Since the water
is cooled 15 degrees, each pound gives up 15 heat units; therefore,
looo pounds must be cooled in an hour. Suppose the water
enters at 170 degrees. Table XVIII, herewith, shows that water at
this temperature weighs 60.801 pounds per cubic foot. Therefore,
looo -r- 60.801, or 16.41 cubic feet, must pass through a 100 square
foot radiator to give up the heat units stated. This number of
cubic feet multiplied by 7^2 gives the number of gallons required
—viz., 123.1.

Capacities of Pipes for Hot Water Heating. 87

TABLE XVIII.

VOLUME AND WEIGHT OF DISTILLED WATER.

" Weisbach."

Tempera- Weight of Tempera- Weight of

ture in a cubic foot ture in a cubic foot

degrees F. in pounds, degrees F. in pounds.

32 62.417 170 60.801

39.1 62.425 180 60.587

40 62.423 100 60.366

50 02.409 200 60.136

60 62.367 210 59.894

70 62.302 212 59.707

80 62.218 220 59.641

00 62,119 230 59.372

100 62 240 59.096

110 61.867 250 58.812

120 61.720 260 58.517

130 61.556 270 58.214

140 61 .388 280 57.903

150 61.204 290 57.585

160 61.007 300 57.259

THE VELOCITY IN HOT WATER HEATING PIPES.

To compute the velocity in pipes, suppose, for example, a
2-inch pipe supplies 200 square feet of surface, the water to drop
20 degrees in passing through the radiator. This amount of
surface will give off about 200 X 150 heat units = 30,000 heat
units per hour. Suppose the water enters at 170 degrees, weigh-
ing 60.801 pounds per cubic foot. Each pound gives up 20 heat
units; then, 30,000 -f- (60.801 X 20) 24.6 cubic feet must pass
through the radiator per hour, equal to about 0.41 cubic foot per
minute. A 2-inch pipe has an area of 0.0233 square foot, there-
fore the velocity must be about 17.6 feet per minute, or 0.293
foot per second.

The velocities in the pipes of hot water heating systems are
very low, as they must be, for the water to circulate with the small
head, due to the difference in temperature between the water in
the flow and return pipes.

RADIATING SURFACE SUPPLIED BY PIPES OF DIFFERENT SIZES.

If the volume of water passing through pipes of different sizes
is known, the radiating surface they will supply may be readily
computed. With the same drop in temperature in radiators, the
force causing circulation will be alike in all. With pipes of equal
length the resistance will vary as the square of the velocity, and

38 Principles of Heating.

v2
inversely as for the diameter expressed, as™

Now, if we assume, for example, that a 2-inch pipe will supply
200 square feet of direct radiation — which in practice it will

v* v2

readily do — and compute the value of— f then make— r- the same

a a

for pipes of other sizes, a table may be prepared showing the
radiating surface that may be supplied by pipes of different diame-
ters when working under the same conditions with respect to the
head causing the flow and the resistance to the circulation. This
has been done, and the results are stated in the following table:

TABLE XIX.

THE CAPACITY Or MAINS 100 FEET LONG EXPRESSED IN THE NUMBER OF SQUARE
FEET OF DIRECT HOT WATER RADIATING SURFACE THEY WILL SUPPLY WITH
THE OPEN TANK SYSTEM, WHEN THE RADIATORS ARE PLACED IN ROOMS ATI
70 DEGREES F.

Capacity in

Actual

Nominal

square feet

inside

Actual

Capacity

diameter

of direct

diam-

inside

Area in

in gallons

of pipes.

radiating

eter in

diameter

square

per foot

Inches.

surface.

inches.

in feet.

inches.

feet.

length.

1.38

0.125

1.49

0.0104

0.0777

Ifc

107

1.61

0.134

2.04

0.0141

0.1058

200

2.07

0.172

3.35

0.0233

0.1743

314

2.47

0.206

4.78

0.0332

0.2483

540

3.07

0.256

7.39

0.0513

0.3835

780

3.55

0.296

9.89

0.0687

0.5136

1,060

4.03

0.333

12.73

0.0884

0.6613

4%-

1,410

4.50

0.375

15.94

0.1108

0.829

1,860

5.04

0.417

19.99

0.1388

1.038

2,960

6.06

0.500

28.89

0.2006

1.500

4,280

7.02

0.5S3

38.74

0.2690

2.012

5,850

7.98

0.666

50.04

0.3474

2.599

NOTE. — The above ratings in the second column are based on buildings hav-
ing not more than three floors above the basement. With higher buildings the
capacities would be increased.

It is of some interest to compare with Table XIX the pipe
capacities that have been . presented in various publications and
trade catalogues. Table XX gives such a comparison, and
shows a wide variation in the computed capacities stated by
various engineers:

Capacities of Pipes for Hot Water Heating. 89

TABLE XX.

THE CAPACITY OF HOT WATER HEATING MAINS EXPRESSED IN THE NUMBER OF
SQUARE FEET OF DIRECT RADIATING SURFACES SUPPLIED.

Diameter
of pipe.

Inches.

....

IV*

140

100

111

100

130

200

202

156

176

184

200

250

325

359

256

275

260

350

400

450

561

381

400

405

550

540

700

807

531

540

576

850

740

900

1,099

706

710

784 1

200

890

1,200

1,436

41/3

906

890

990

1,100

1,500

1,817

1,131

1,100

1,240

1,600

2,000

2,244

1,525

1,600

1,920

....

3,000

3,228

2,150

2,760

. . .

• «. . •

4,200

4,396

2,750

....

3,570

....

5,600

5,744

3,625

....

. . .

...»

....

7,268

4,525

....

6,050

....

8,976

Authorities.

A — J. L. Bixley ; B — J. H. Kinealy : C — J. L. Mott Iron Works ; D — C. L.
Hubbard ; E — R. C. Carpenter ; F — Model Heating Company ; G — Nason Mfg.
Company.

PIPE SIZES FOR INDIRECT HEATING.

Since indirect radiators are placed at a much lower level, with
reference to the heater, than are direct radiators, the head corre-
sponding to the difference in temperature between the supply and
the return pipes is much less than is the case with the latter, and
scarcely exceeds 1-20 foot. Since cold air comes in contact with
the radiators, the loss of heat per square foot is much greater
than from direct radiators. These two causes make it necessary
to provide much larger pipes to supply a given amount of surface
than in the case of direct radiators.

For supplying indirect radiators, C. L. Hubbard recommends
using i % -inch pipes for 30 square feet, i^-inch for 31 to 50, 2-
inch for 51 to 100, 2^2-inch for 101 to 200, 3-inch for 201 to 300,
3j^-inch for 301 to 400, and 4-inch for 401 to 600. Baldwin
recommends allowing a 2-inch pipe to 100 square feet of indirect
radiation. This rule gives much larger pipes than customary.
Certain hot water fitters use i^-inch pipes to 60 square feet. 1^2-
inch for 61 to 120, and 2-inch for 121 to 240 square feet. With
pipes carrying so much radiating surface as the latter, the drop in
temperature of the water in passing through the radiators must

go Principles of Heating.

be greater than when larger pipes are used. The objection to
small pipes, with consequent increased drop in temperature to
overcome resistance, is that the mean temperature of the radiator
is lowered, and the heat given off per square foot is diminished.
What is saved in piping must be made up in radiation.

The writer considers it unwise to supply more than 200 square
feet of indirect radiation with a 2-inch pipe, and prefers rating a
2-inch pipe to supply 150 square feet of indirect surface. Taking
the latter as a basis, pipes of other sizes would supply the surface
stated in Table XXI when working against the same resist-
ance, which varies as the square of the velocity and inversely as
the diameter.

TABLE XXL'

THE CAPACITIES OF PIPES EXPRESSED IN THE NUMBER OF SQUARE FEET
OF INDIRECT HOT WATER RADIATING SURFACE THEY WILL SUPPLY WITH THE
OPEN TANK SYSTEM.

Indirect

Diameter

radiating

Diameter

radiating

of pipes.

surface.

of pipes.

surface.

Inches.

Square feet.

Inches.

Square feet.

IVi

790

iy9

414. .

1,060

150

1,400

2~y>

935

2 220

405

3 200

3V4. .

. . 585

8 .

. .4,400

SIZES OF RISERS.

The capacities of risers recommended by different writers are
as follows :

TABLE XXII.

COMPVRISON OF RATINGS FOR HOT WATER RISERS.

(Hight of floors approximately 10 feet each.)
Sizes

of pipes. , First-floor risers. N f Second-floor risers. s

in inches. Square feet direct radiation. Square feet direct radiation.

% 27 ... 50 ... 35 ... 52

1 39 48 30 89 45 62 55 92

114 64 75 60 140 73 97 90 144

1% 95 108 100 202 110 140 140 209

2 156 191 200 359 179 250 275 370

01/2 256 300 350 561 294 390 475 577

3 381 430 550 807 438 ... ... 835

3Vi 531 590 850 1,099 610 ... ... 1,132

4 706 770 ... 1,436 812 1,478

4y2 906 970 ... 1,817 1,042 1,871

5 1 ,131 1,200 . . . 2,244 1,301 2,309

6 . ..1,525 1,700 ... 3,228 1,753 3,341

!•%

110

149

118

140

165

214

126

194

250

375

380

206

318

390

. . .

595

338

473

. . .

856

503

sya

659

1,166

701

876

1,520

932

41/a

1,124

1,927

1,196

1,402

2,376

1,493

1,891

3,424

2,013

Capacities of Pipes for Hot Water Heating. 91

TABLE XXII— Continued.

, Third-floor risers. N , Fourth-floor risers. x

Square feet direct radiation. Square feet direct radiation.

75 98
125 153
185 222
425 393
613
888

. . . 1,202
1,571
1,988

. . . 2,454
. . . 3,552

The figures stated in the first, second, third and fourth columns, giving ca-
pacities, are by Bixley, Kinealy, Hubbard and Nason, respectively. It will be
noted that here, as in the case of mains, the capacities given by the Nason Com-
pany are much in excess of others. The figures given by Prof. Kinealy are based
on water at high temperature and may be increased 25 per cent, for water at
160 degrees in the radiator.

The following table has been compiled by the writer, using as
a basis a i^-inch pipe rated to supply 100 square feet of direct
radiation on the first floor, 140 square feet on the second, 175
square feet on the third and 200 square feet on the fourth. The
capacities of other pipes are based on a flow that represents the
same resistance to be overcome as in the i^-inch pipes, as above
rated; that is, the capacities of pipes larger than i^-inch are
based on a higher velocity and smaller pipes on a correspondingly
lower velocity, since the resistance varies directly as the square of
the velocity and inversely as the diameter.

TABLE XXIII.

THE CAPACITIES OF RISERS EXPRESSED IN THE NUMBER OF SQUARE FEET
OF DIRECT HOT WATER RADIATING SURFACE THEY WILL SUPPLY ON DIFFER-
ENT FLOORS. FLOOR HIGHTS APPROXIMATELY 10 FEET. OPEN TANK SYSTEM.

RADIATORS IN ROOMS AT 70 DEGREES F.

Diameter

of riser. , — Square feet of direct radiating surface supplied. — x

in inches. First floor. Second floor. Third floor. Fourth floor.

1 33 46 57 64

1*4 71 3 04 124 142

iya 100 140 175 200

2 187 262 325 375

2ya 292 410 492 580

3 500 755 875 1,000

RADIATOR CONNECTIONS.

Direct hot water radiators are commonly tapped i inch up to
40 square feet, 1*4 inches for 41 to 72 square feet, and 1^2 inches
for ordinary sizes larger than 72 square feet.

92 Principles of Heating.

ELBOWS AND BENDS.

The resistance interposed by elbows to the passage of water is
a subject on which there appears to be little available data of
value. Fortunately, it is unnecessary, in ordinary heating work,
to compute the loss of heat due to this resistance. The writer, in
a series of articles on the flow of steam, gives a table showing
the lengths of straight pipe that would present the same resistance
as a standard elbow. The values there given will be found con-
. venient for use in case it is desired to allow for the resistance of
elbows in an extensive system of hot water heating.

In the smaller sizes of fittings, say from \]/2 to 4 inches, the
radius of the center line of the elbow is roughly 1^4 x the diameter
of pipe for standard elbows; 1^4 x the diameter of pipe for the
long turn patterns and 2j4 x the diameter of pipe for extra long
turn elbows. The relative resistance, or loss of head, computed
from Weisbach's formula is, for these three patterns, as follows :
Standard, 100 ; long turn, 83 ; extra long turn, 77. While these
figures may be considered merely approximate, they serve to show
in a general way the great advantage of long turn elbows over
those of standard patterns for hot water work.

Ordinary wrought iron or steel pipe bends have a radius of
axis equal to, at least, 5 x the diameter of pipe. With such bends,
Trautwine states, the flow will not be materially diminished. In
first-class hot water heating plants long turn elbows are used, and
the ends of the pipes are reamed inside to reduce, as far as possi-
ble, the resistance to the flow of water and to permit the least
difference possible between the temperature in the supply and
return pipes.

EXPANSION TANKS.

Hot water expands about 4 per cent, of its volume at 40
degrees when heated to 200 degrees. Taking these as the ex-
tremes of temperature between the water when the system is first
filled and when operating in coldest weather, and assuming that
the expansion tank should have a capacity equal to twice this
increase in volume, the tank should be made 8 per cent., or about
one-twelfth, of the total volume of radiator and piping. Sup-
pose the piping is equivalent to one-third the direct radiating stir-

Capacities of Pipes for Hot Water Heating. 93

face and the volume of water in the system to amount to il/2
pints per square foot of radiating surface, including mains, then,
for example, a lo-gallon expansion tank would be adapted to a
system holding 120 gallons, which, on the basis of i^ pints per
square foot of radiation, mains included, would be 640 square
feet. And, since mains are reckoned at one-third the actual sur-
face in radiation, the latter would amount to three-fourths of
640 square feet equal 480 square feet, or, say, in round numbers,
500 square feet. On the same basis the capacity of other tanks
would be in proportion, as follows :

TABLE XXIV.
CAPACITY OF EXPANSION TANKS.

Capacity in square feet of

Capacity actual surface in hot water

of tank radiator to which tank i»

in gallons, adapted.

5 250

10 500

15 750

20 1,000

30 1,500

40 2,000

50 2,500

60 3,000

It will be noted that the capacities in the above table are
equivalent to I gallon in expansion tank to each 50 square feet
of surface in radiators; a convenient rule. While tanks may be
made smaller, the saving would be slight, and they would require
more frequent attention, unless fitted with an automatic water
line regulator.

It is beyond the scope of this work to discuss methods of pip-
ing; yet the writer feels constrained to warn fitters against the
danger in placing a valve in the expansion pipe, which is some-
times done, and also to see to it that the expansion pipe and tank
are located where there will be no danger from freezing.

CHAPTER VIII,

THE FLOW OF STEAM IN PIPES AND THE CAPACITIES

OF PIPES FOR STEAM HEATING SYSTEMS

AND FOR STEAM BOILERS.

The following chapter is intended not as an exhaustive dis-
cussion of the various methods of proportioning piping systems,
nor of the formulas on which the flow of steam is based, but to
provide, by tables, a ready means of solving problems relating to
pipe sizes. The formulas on which the tables are based make due
allowance for the diminished resistance due to an increase in the
size of pipes.

The cruder, yet common, method of allowing, for large and
small pipes alike, a certain number of thousandths of a square
inch in cross sectional area to each square foot of radiating sur-
face makes the larger pipes much greater in area in proportion to
the surface supplied than the smaller ones.

A COMPARISON OF FORMULAS.

D'Arcy's modified formula, stated in Kent's " Mechanical En-
gineer's Pocketbook," gives the weight of steam that will flow per
minute through pipes of various sizes as

where w = the density or weight per cubic foot of steam at pres-
sure pi', (pi — p2) = drop in pressure, or the difference between
initial and terminal pressure ; d = diameter of pipe in inches ; L
= length of pipe in feet ; c = coefficient, as follows :

Diameter of pipe in inches. 1 2.3 4 5 6 7 8 9

Value of c ............... 45.3 52.7 56.1 57.8 58.4 59.5 60.1 60.7 61.2

Diameter of pipe in inches. 10 11 12 14 16 18 20 22 24

Value of c ............... 61.8 62 62.1 62.3 62.6 62.7 62.9 63.2 68-2

Babcock's formula, given in " Steam," is

:. r ; -

The Floiv of Steam in Pipes. 95

This may be reduced to a form similar to D'Arcy's formula, but
with different coefficients.

Table XXV has been computed from these formulas in order
to compare the results for pipes of different sizes. This table is
based on the actual inside diameter of standard wrought iron
pipes of nominal sizes stated up to 12 inches, inclusive. Sizes
of 14 inches and larger are nominal outside diameters of O. D.
pipe, the inside diameter of each being ^4-inch less than the
outside.

TABLE XXV.

SHOWING THE WEIGHT OF STEAM IN POUNDS THAT WILL PLOW PER MINUTE
THROUGH STRAIGHT PIPES 300 FEET IN LENGTH; NO ALLOWANCE BEING MADE
FOR RESISTANCE AT THE ENTRANCE TO THE PIPE.

Initial pressure, 5 pounds by gauge, less a drop in pressure in a length of 100
feet, 1 pound.

Formula, , Nominal diameter of pipe in inches. ^

1 Hi 1% 2 2% 3 3M, 4 4V2 5 6 7
. , — Weight of steam, in pounds, flowing through pipe per minute. — ^

D'Arcy's .1.14 2.38 3.7 G.7 11.6 20.8 30.3 41.4 56 73 118 174

Babcock's ....1.05 2.31 3.6 7.3 11.9 21.9 32.7 46.5 63 86 141 208

Formula. r Nominal diameter of pipe in inches. ^

8 9 10 12 14 16 18 20 22 24

, — Weight of steam, in pounds, flowing through pipe per minute.-^

D'Arcy's 246 327 438 694 910 1,266 1,735 2,285 2,945 3,660

Babcock's 293 394 533 853 1,140 1,590 2,210 2,910 3,760 4,730

APPLICATION OF FACTORS TO TABLE XXV.

Both formulas show the weight of steam delivered to be pro-
portional : ( i ) To the square root of the density or the square
root of the weight per cubic foot; (2) to the square root of the
d-rop in pressure; (3) to the square root of the fifth power of the
diameter of the pipe, and (4) to be inversely proportional to the
square root of the length of the pipe.

For any other pressure than 5 pounds, on which Table XXV is
based, mu'tiply the figures there stated by the square root of the
density at the given pressure, divided by the square root of the
density at 5 pounds pressure. This gives the following factors
for different pressures :

TABLE XXVI.

FACTORS TO BE APPLIED TO TABLE XXV FOB OTHER GAUGE PRESSURES THAN

5 POUNDS.

Gauge pressure in pounds 1 2 5 10 15 20 30 40

Multiplier 0.90 0.93 1.00 1.11 1.21 1.31 1.47 1.61

Gauge pressure in pounds 50 60 70 80 90 100 110 120

Multiplier .« 1.74 1.86 1.97 2.07 2.18 2.26 2.37 2.46

g6 Principles of Heating.

This table shows, for example, that with 50 pounds pressure
1.74 times as much steam by weight will flow through a given
pipe as with 5 pounds pressure; the drop in pressure being the
same in each case.

For a drop in pressure other than I pound, on which Table
XXV is based, multiply the figures in that table by the square
root of the given drop corresponding to these factors.

TABLE XXVII.
FACTORS APPLYING TO TABLE XXV FOR OTHER DROPS IN PRESSURE THAN 1 POUND.

Drop in pressure in pounds (pl— pa) y» ^ % % 1 2 3

Multiplier 0.354 0.500 0.709 0.865 1.00 1.41 1.73

TABLE XXVIII.

FACTORS FOR OTHER LENGTHS THAN 100 FEET. TOTAL DROP IN PRESSURE ASSUMED
TO BE 1 POUND, WHATEVER THE LENGTH OF THE PIPE THE CAPACITY OF
WHICH IS BEING COMPUTED. FACTORS OR MULTIPLIERS TO BE. USED IN CON-
NECTION WITH TABLE XXV.

Length of pipe in feet 50 100 150 200 250 300 350 400 450
Multiplier 1.41 1.00 0.816 0.710 0.632 0.578 0.535 0.500 0.471

Length of pipe in feet... 500 550 600 650 700 750 800 850
Multiplier 0.447 0.427 0.407 0.392 0.379 0.365 0.353 0.343

Length of pipe in feet... 900 950 1,000 1,200 1,400 1,600 1,800 2,000
Multiplier 0.333 0.325 0.316 0.288 0.268 0.250 0.236 0.224

To illustrate the use of Tables XXV, XXVI, XXVII and
XXVIII, suppose it is desired to compute the flow of steam at 50
pounds gauge pressure through a 3-inch pipe 400 feet long, the
drop in pressure to be 2 pounds. Table XXV gives, with
D'Arcy's formula, 20.8 pounds as the weight of steam passing in
one minute through a pipe 100 feet long, with i pound drop in
pressure. Applying the factors in Tables XXVI, XXVIII and
XXVII, respectively, corresponding to the above conditions, we
have 20.8 X i-74 X 0.5 X 1.41 = 25.43 pounds as the weight of
steam flowing through the pipe per minute.

RESISTANCES TO THE FLOW OF STEAM.

In computing the flow of steam from Table XXV, the resistance
at the entrance to the pipe at elbows and globe valves should be
allowed for by adding to the actual length of the pipe a length
that would produce the same resistance to the flow as that at these

The Flow of Steam in Pipes. 97

points. The resistance at the entrance is commonly expressed in
connection with Babcock's formula by the equation

_ 114 diameters l( „

= i + (3.6 TT) '

where R equals a length of straight pipe expressed in diameters
that would interpose the same resistance as that at the entrance
and d equals diameter of pipe in inches.

Very little has been published giving the results of tests bear-
ing on this subject. Treatises on hydraulics, in discussing the
flow of water in pipes, which follows the same general laws as the
flow of steam, give tables and data showing the length of pipe
equivalent in resistance to that at entrance to be approximately
one-third of that given by formula " c." The use of formula " c "
in computing pipe sizes for steam heating systems gives sizes
much in excess of those found necessary in practice. The author,
therefore, favors the use of

114 diameters „ , „

*=**•!+ (3.6 -rf) a'

The values corresponding to the latter formula, reduced to
feet, are as follows :

TABLE XXIX

THE RESISTANCE AT THE ENTRANCE OF PIPES EXPRESSED IN THE NUMBER OF FEET
OF STRAIGHT PIPE THAT WOULD PRODUCE THE SAME RESISTANCE AS THAT AT
THE ENTRANCE.

*Nominal Resistance *Nominal Resistance

diameter based on diameter based on

of pipes Formula of pipes Formula

in inches. " d.' — Feet. in inches. " d." — Feet.

1 0.8 7 14.7

1% 1.2 8 17.5

1V2 1.6 9 20.4

2 2.4 10 23.4

2y2 3.1 12 29.4

3 4.5 14 35.3

3Va 5.1 16 41.3

4 6.7 18 47.3

4% 7.9 20 53.6

5 9.3 22 60.0

6 12.1 24.. ..66.0

* Nominal diameter of 14-inch pipes and larger is the outside diameter.

The resistance at a globe valve of given size is commonly al-
lowed for by adding to the actual length of pipe a length three
times that stated in Table XXIX,, and for a standard elbow a
length twice that stated in the table. These values are, however,

98 Principles of Heating.

to be considered as only approximately true, although they are
near enough for practical use. The longer the pipe the less will be
the error in the computed flow due to any uncertainty or error
in the allowance made for the three resistances at entrance, elbows
and globe valves.

The use of long turn elbows and straightway gate valves
practically eliminates two of these resistance losses, and the other
is considerably reduced by reaming the pipes at the ends, as is
common in hot water work.

The following example will illustrate the use of Table XXV,
the multipliers in Tables XXVI, XXVII, and XXVIII, and allow-
ance in Table XXIX.

How many pounds of steam will flow per minute through a
45/2 -inch pipe 800 feet long, with four elbows and one globe
valve? Initial gauge pressure, 10 pounds. Drop in pressure, 2
pounds.

Feet.

Actual length of pipe 800

Allowance for loss at entrance (Table XX approximately) 8

Allowance for two elbows 32

Allowance for one globe valve 24

Total equivalent length of straight pipe, making due allowances as above. 864

A length of 850 feet is the one most nearly corresponding
to this length in Table XXVIII. The factor for this length is
0.343; for 10 pounds pressure the factor in Table XXVI is i.n ;
for 2 pounds drop in pressure the factor in Table XXVII is
1.41. The flow of steam in pounds by D'Arcy's formula, stated in
Table XXV, to which these factors apply, is for a 4^2 -inch pipe
56 pounds. For a length of 800 feet, with conditions as stated,
the computed flow would be 56 X 0.343 X i.n X 1.41 = 3ai
pounds per minute.

EFFECT OF CONDENSATION.

No account has been taken in the foregoing of the effect of
condensation on the flow of steam. It is assumed that pipes will
be covered, which will reduce this effect to about one-third of
what it would be if they were bare. The condensation, while it
cuts down the volume of steam, at the same time causes a greater
drop in pressure. This, in turn, increases the velocity, tending to

The Flow of Steam in Pipes. 99

offset the loss by condensation. A further discussion of this sub-
ject may be found in Kent's " Mechanical Engineers' Pocket
Book."

STEAM FLOW WITH MORE THAN 40 PER CENT. DROP IN PRESSURE.

It is to be borne in mind, in making computations of the flow
of steam, that steam of 25 pounds gauge pressure or more, dis-
charged from a pipe against atmospheric pressure or against a
pressure less than three-fifths the initial pressure, has a nearly
constant velocity of 900 feet per second, in round numbers, the
weight discharged increasing with the pressure and being propor-
tional to the density or weight per cubic foot. The approximate
weight of steam that will flow per hour through a pipe under the
conditions just stated is equal to 50 X (absolute pressure of
steam) X (area of pipe in square inches).

This constant velocity applies only to very short pipes.

RELATIVE CAPACITIES OF PIPES.

The relative capacities of pipes under the same conditions are
shown in Table XXV, D'Arcy's values being the safer to use.
This table will be found convenient in determining the size of pipe
necessary to supply a number of smaller ones.

Example: What size pipe is required to supply one 2^, two
3 and one 4 inch pipes ?

The capacities in Table XXV are, in the order stated, i x n.6,
2 x 20.8, i X4I.4; total, 94.6. A 6-inch pipe with a capacity of
118 should be used, since a 5-inch pipe has a capacity of only 73.

It will be noted that the capacity of pipes increases much more
rapidly than their area — e. g., the relative capacities of 8 and 4
inch pipes in Table XXV are 246 and 41.4, or in the ratio of 6 to
i, whereas their areas are in the ratio of about 4 to i.

Table XXX, which has been computed from Table XXV, gives
the proper size of mains to supply branches of the sizes stated in
the upper and side lines.

100

Principles of Heating.

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o * '[

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10 to to M

co to to to i

if ff a

CC 03 CO CO

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I I + I I

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ll'l

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rfk.WWtOtOMMMCr

The Flow of Steam iti Piper.

1C*

TABLE XXXI.

THE AMOUNT OF ORDINARY CAST IRON RADIATING SURFACE THAT MAT BE SUPPLIED
BY PIPES OF DIFFERENT SIZES, 100 FEET LONG, WITH 5 POUNDS INITIAL GAUGE
PRESSURE AND THE DROP IN PRESSURE STATED IN THE COLUMN AT THE LEFT.
FOR OTHER PRESSURES AND FOR LENGTHS IN EXCESS OF 100 FEET, USE FACTORS
IN TABLES XXVI AND XXVIII. RESISTANCE AT ENTRANCE, ELBOWS AND GLOBE
VALVES MAY BE ALLOWED FOR AS STATED IN TABLE XXIX, BUT THIS IS GENER-
ALLY UNNECESSARY FOR ORDINARY WORK, A SLIGHT EXCESS IN THE DROP IN
PRESSURE OVER THAT ASSUMED COMPENSATING FOR THE RETARDING EFFECT OF
THE ENTRANCE. ELBOWS AND VALVES.

Diameter of pipes,
Inches ........ 1

Drop in
pressure.
Line. Pounds.

1% 2 2% 3 3Ms

Square feet of radiating surface.-

% 226 472 732- 1,325 2,300 4,120 6,000 8 210 11,100

i£ 185 386 600 1,087 1,881 3,370 4,930 6,730 9,100

D ....

^4 130 273 423 767 1,330 2,385 3,475 4,750 6,210

y8 92 193 299 543 940 1,680 2,460 3,360 4,530

. . . 1/ia 65 136 212 384 665 1,192 1 740 2 380 3 210

G..

. . VM 46 96 150 . 272 470 845 1,230 1,680 2,270

Diameter of pipes,

inches

Drop in
pressure.

i-me.
A

trounus.
... 1

16,710 27,000 39,800 56,
L4,450 23,350 34,400 48, 1
11,810 19,100 28,200 39,
8,355 13,500 19,900 28,
5,900 9,530 14,060 19,
4,180 6,750 9,950 14,
2,960 4,780 7,050 10,

14 16 18

C5nnfirr> ffr>f rv

300 75,000
(50 64,800
800 53,000
150 37,400
900 26,400
100 18,700
000 13,300

, 20

C radiating su
524,000
453,000
371,000
262,000
185,000
131,000
93,000

100,000
86,500
70,800
50,000
35,400
25,000
17,700

159,000
137,500
112,500
74,500
56,200
39,800
28,200

%. 3

i/19

.... Vs2

Diameter
inches .

Line.
A

of pipe,

Drop in
pressure,
Pounds.
. . . . 1

214,000

186,000
151,000
107,000
75,100
53,300
37.900

290,000 398,000
250,000 343,000
206,000 282,000
145,000 198,000
102,500 140,000
72,600 99,000
51,300 70,500

675,000
583,000
478,000
338,000
238,000
169,000

845,000
730,000
598,000
425,000
298,000
212,000

.... %

. . . %

.... }4

. . Via

G. .

. . Vaa

NOTE. — Sizes 14 inches and larger are outside diameters. For sizes of returns
see note under Table XXXIV.

t02 -Principles of Heating.

SIZES OF STEAM HEATING MAINS.

For steam heating work it is generally more convenient to
deal with heat units and the amount of direct rediating surface
that pipes of different sizes will supply, than with the weight of
steam they will carry. A conservative basis is to allow 250 heat
units per hour per square foot of ordinary cast iron direct radiat-
ing surface, with steam at low pressure, say 3-5 pounds.

A pound of steam at 5 pounds pressure has a latent heat of
954.6 units — that is, it will give up 954.6 heat units when con-
densed to water at the steam temperature in the radiator.

Table XXXI has been deduced from the flow of steam com-
puted from D'Arcy's formula, as stated in Table XXV, on the
basis of 250 heat units per square foot of radiation and 954.6' heat
units given off per pound of steam, which is equivalent to 0.262
pounds of steam condensed per hour per square foot of direct
radiating surface.

Table XXXI shows a marked difference in the amount of ra-
diating surface that may be applied with different assumed drops
in pressure.

Mains may be proportioned as follows:

For systems trapped to an open receiver with the heating sur-
face located well above same, a drop of *4 to l/2 pound may be
allowed.

For gravity return systems, where the radiators are located
some distance, say 5 feet or more, above the water line in the
boiler, 1-16 to l/% pound drop may be assumed in proportioning
the piping. Where the radiators are but little above the water line,
as in indirect systems, use 1-32 pound dfop.

When exhaust steam is used and it is desired that the minimum
back pressure be carried on the system, an assumed drop of 1-32
to 1-16 pound may be used, preferably 1-32 pound drop.

The size of vertical pipes or overhead feed risers of single pipe
systems may be based on line G, Table XXXI. This will give sizes
corresponding to those based on 2 pounds pressure with a little
greater drop than 1-32 pound, and will be found ample for exhaust
steam heating.

The Flow of Steam in Pipes.

103

In high buildings, with the single pipe overhead feed system,
the risers must be very liberally proportioned on the lower stories,
since they must carry not only steam to the radiators below, but
the condensation from the radiators above.

It should be noted that pipe sizes based on the recommenda-
tions just made will be large enough to supply steam at, say, 2 or
3 pounds pressure to the radiating surface stated, but with a
slightly greater drop in pressure.

Pipe sizes given in Table XXXI to supply a given radiating sur-
face with^ steam at 5 pounds pressure will be very nearly correct

Branch

THE MBTAL WORKER

Fig. 34.

Fig. 35.

for higher pressures within the ordinary limits of steam heating,
say up to 15 pounds. This is true, since the total heat supplied
by the steam at higher pressures, taking into account its increased
weight and decreased latent heat just about keeps pace with the
increased radiation of heat.

104 Principles of Heating.

Direct steam radiators are commonly tapped as shown in the
following table:

TABLE XXXII.

DIRECT RADIATOR TAPPING.
ONE-PIPE SYSTEMS.

Up to 24 square feet inclusive 1 inch

24- 60 " 1 14 "

60-100 «* * 1 % "

Over 100 " 2 "

TWO-PIPE WORK

Up to 48 square feet inclusive 1 x % inch

48-96 1 % x 1

Over 96 , l%xl^4 "

SIZES OF RISERS ONE-PIPE SYSTEM.

The risers of one-pipe up feed steam heating systems must be
made large enough to supply the radiators and also permit the
condensation to return by the same route. It is, therefore, well
to limit the velocity to, say, 15 feet per second. On this basis,
with steam of 2 pounds pressure, pipes will supply ordinary cast
iron direct radiators as follows :

TABLE XXXIII.
CAPACITY OF UP FEED RISERS, ONE-PIPE SYSTEM.

Size of Approximate Size of Approximate

riser, one-pipe sys- radiating surface riser, one-pipe sys- • radiating surface

tern. — Velocity steam, supplied. — Steam, tern. — Velocity steam, supplied. — Steam,

15 feet per second. 2 pounds pressure. 15 feet per second. 2 pounds pressure.

Inches. Feet. Inches. Feet.

1 *50 2V2 300
1% *90 3 460
1% 130 3% 620

2 210 4 800

* It is advisable to make the upper end of riser the full size of standard radi-
ator connections — viz., 1 inch up to 24 feet and 1*4 inches for 25 to 60 feet.

Down feed risers may be safely rated to carry at least 25 per
cent, more surface than stated in the table. Care should be taken
to proportion the risers liberally near the lower end to provide
for the removal of condensation.

Branch connections with radiators should be the same size as
regular tapping, except when radiators are located more than 4 or

The Flow of Steam in Pipes. 105

5 feet from risers. In this event the connections should be in-
creased one size to lessen the velocity and permit the condensation
to easily flow back against the current of steam.

It is better to drip the riser as indicated in Fig. 34 than as
shown in Fig. 35. With the latter the condensation is apt to be
swept up along the heel of the elbow, causing a click, or water
hammer. The arrangement shown in Fig. 34 forms a separator
and the condensation trickles away quietly through the relief or
return pipe.

SIZES OF RISERS — TWO-PIPE SYSTEM.

With the two-pipe up feed system risers may be considerably
smaller for a given radiating surface than in the one-pipe system,
since the condensation from the radiators is conducted away
through separate returns.

Safe allowances are given in the following table:

TABLE XXXIV.

CAPACITIES OF UP FEED RISERS, TWO-PIPE SYSTEM.

Approximate Approximate

Size of riser. radiating surface Size of riser radiating surface

for two-pipe, up supplied. — Steam at for two-pipe up supplied. — Steam at

feed steam heating. 2 pounds pressure. feed steam heating. 2 pounds pressure.

Inches. Feet. Inches. Feet.

1 *70 2% 570
1*4 *130 3 . 1,020
1% *190 3^ 1,490

2 330 4 2,000

* It is advisable, at the upper ends of long risers, to make the riser the full
size of standard radiator connections — viz., 1 inch up to 48 feet ; 1% inches for
49 to 96 feet, and 1% inches for 97 and up to 190 feet.

For down feed risers it is safe to allow 25 per cent, more sur-
face than 'stated in the above table.

In high buildings, say over five or six stories, allow 10 per
cent, less surface than that stated to allow for the increased length
of and condensation in risers. Returns .are commonly made one
size smaller than the supply up to 2.y2 inches ; above that the re-
turns may be two sizes smaller, and for larger pipes, where the
return has ample fall, it may be made one-half the diameter of the
supply pipe, or even smaller.

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io8 Principles of Heating.

COMPARISON OF DIFFERENT METHODS OF DETERMINING THE SIZE
OF STEAM MAINS TO SUPPLY RADIATING SURFACES.

In addition to the foregoing it seems wise to reprint here an
article by Earnest T. Child that appeared under the above head-
ing in The Metal Worker of Aug. 19, 1899.

The primary method of figuring the sizes required is to ascer-
tain the volume of steam which will be condensed by the radiating
surface. This being known, the size of pipe may be computed
by assuming a velocity of flow, which will cause a loss of pressure
not exceeding 12 inches water head per 100 feet of pipe ; say, a
velocity of 50 feet per second, which will give an approximate
frictional resistance of 8 inches of water per 100 feet.

For instance, to supply 1000 square feet of radiating surface
at 5 pounds gauge pressure:

Temperature of steam = 227 degrees F.
Temperature of air in room, 7° degrees F.

Difference, air and steam, 157 degrees F.

British thermal units radiated per square foot of surface as
per experiments by Wm. J. Baldwin, J. H. Mills, and others aver-
age 275. This gives 275,000 British thermal units per hour. As
each pound of steam at this pressure is capable of yielding 954
British thermal units, it will require 288 pounds of steam per
hour. One cubic foot of steam at 5 pounds weighs 0.05 1 1 pounds,
so 288 pounds equal 5636 cubic feet per hour, or 1.56 cubic feet
per second, which, flowing at the rate of 50 feet per second, will
require an area of 0.0312 square foot, or 4.59 square inches. This
would require a pipe 2.4 inches in diameter, and as the next higher
commercial size is 2^ inches in diameter, this would be the size
required.

This is a roundabout way, however, and various formulas
have been evolved for figuring the pipe sizes.

Robert Briggs in his " Steam Heating " uses a formula which
has been extensively followed either directly or in a modified
form, in which d — diameter of pipe; Q= 9.2 cubic feet of steam

The Floiv of Steam in Pipes. 109

per 100 square feet radiating surface ; / = length of main in feet ;
and h — head of steam to produce the flow. From this

0-5374V -xv-/
h

Frederic Tudor used a modified form of the same, in which
C = volume of steam per minute = 9.2 X total radiating sur-
face -r- 100 ; L = length of main in yards ; and H — head in
inches of water lost [loss in] pressure; d = diameter of pipe.
From which

d= V -^-jj^ *• "

These two formulas, when figured on a basis of 6 inches lost
[loss in] pressure in a loo-foot run, agree very closely.

A rule given by Wm. J. Baldwin in his " Steam Heating for
Buildings," and also published by Geo. H. Babcock, states that
diameter of main in inches should equal one-tenth of the square
root of the total radiating surface, mains included. This rule,
when compared with the two previous ones, provides for a much
more ample pipe, and on systems of over 4000 square feet it
would be safe to use on mains as long as 600 feet, though it does
not primarily take in the element of distance at all. Even for
smaller systems k gives a relatively large diameter, and for 10,000
square feet of surface it gives a diameter fully 35 per cent, larger
than the best accepted practice, which means an area which is
nearly doubled.

A. R. Wolff, in his " Addendum to Steam Heating " by Briggs,
gives the following : " For determining the cross section area of
pipes (in square inches) for steam mains and returns, it will be
ample to allow a constant of 0.375 square inch in coils and radia-
tors, 0.375 square inch when exhaust steam is used, 0.19 square
inch when live steam is used and 0.09 square inch for the return
for each 100 square feet of heating surface. If the cross sectional
areas thus obtained are each multiplied by one and three-elevenths,
and the square root extracted from each product, the respective
figures will represent the proper diameters in inches of the several
steam pipes referred to. The steam mains should never be less

no Principles of Heating.

than i y2 inches in diameter, nor the returns less than 94 inch in
diameter."

This rule does not take into account the relative decrease in
friction in pipes of larger diameters, and while in systems under
2500 square feet it follows the Briggs and Tudor formulas very
closely, on larger areas it goes up more rapidly on account of the
fact that the area of the main is directly proportional to the area
of the radiating surface. This formula is safe to use for mains
under 200 feet in length, but if this be exceeded the area should
be proportionally increased.

Prof. R. C. Carpenter, in his " Treatise on Heating and Ven- .
tilating Buildings/' uses Briggs' formula, with the exception that
for a f rictional resistance of 6 inches water column he uses the
value of 318.6 for h instead of 477.8, which gives a 50 per cent,
larger area of main ; but as this table is figured for a single pipe
system, 50 per cent, larger areas will, of course, be necessary.
In figuring for a separate return he uses the Briggs formula with-
out change. His rule for bends and obstructions is as follows:
" Right angle ells add 40 diameters ; globe valve, 60 diameters ;
entrance tee, 60 diameters. For other resistances and steam pres-
sures multiply the diameters by the following factors :

Water level above boiler 2 inches. 12 inches. 18 inches.

Multiply by 1.25 0.88 0.80

Steam pressure above atmosphere 0 pound. 3 pounds. 30 pounds.

Multiply by 1.03 .1.02 0.97

For indirect heating with separate return use the result as ob-
tained."

The result of the above formula when plotted gives diameters
about */2 inch larger than A. R. Wolff's rule up to 5000 square
feet, and at about 7600 square feet the lines cross (see chart).
On the other hand, when the " double pipe system " line is plotted,
it follows the Wolff and Tudor curves quite closely up to 4000
square feet, and at 7000 ^square feet it drops below them all. '

The results of all the above formulas have been plotted on a
chart presented herewith, and it will be seen that for practical work
as well as handiness in figuring and ease in remembering a simple
formula, A. R. Wolff's rule of 0.375 square inch per 100 square
feet of surface is best adapted to ordinary conditions of low pres-
sure heating.

The Flow of Steam in Pipes.

A line for sizes of returns has also been plotted, based on o.i
square inch for each 100 square feet of surface. This gives an
area about n per cent, larger than that used by Mr. Wolff; but

DIAMETER OF STEAM MAfM

CO W^ W O5

it will be noticed that the results are very nearly in line with the
best practice.

Various rules for pipe sizes may be found, all of which vary
in a greater or less degree, and seem to have been arrived at in a

ii2 Principles of Heating.

more or less roundabout way, or by some rule of thumb. To
illustrate the range covered by these rules a comparative table is
given herewith, which may prove interesting :

TABLE XXXVII.

DIAMETER OF PIPE AND NUMBER OF SQUARE FEET SUPPLIED.

Name. 1-incb. 1^4-ineh. 1^-inch. 2-inch. 2%-inch. 3-inch. SV^-inch.

Billings .. 225 450 700 1,200 1,500

Tudor 40 80 160 320 640 1,280

Nason 125 200 500 1,000 1,500 2,500

Willett 40 70 110 220 360 560 810

Wolff 60 120 200 480 880 1,500

Billings, in his " Ventilating and Heating," states that the only
objection to having steam mains large is increased first cost, but
this is a poor argument for an engineer to set forth, as it is his
business to design a system which will give the best and most eco-
nomical results at a moderate first cost. He also overlooks the
fact that larger pipes cause a greater loss by radiation.

The sizes used by Frederic Tudor are for connections to radia-
tors only, the mains being determined by the formula previously
stated. This is a simple rule, and has been proven very satisfac-
tory. He allows 40 square feet radiation for each i-inch pipe,
and doubles the figure for each successive size up to 3 inches.

The sizes given by J. R. Willett are very large indeed compared
with other authorities, and are not to be recommended.

The sizes used by the Nason Mfg. Company and A. R. Wolff,
as given on pages 540 and 541 of Kent's Handbook, are almost
identical. Of these five cases the rule used by Tudor appeals to
the writer [E. T. Child] as being the simplest and most practical,
in that it is easily applied and not easily forgotten; and while it
gives sizes which are ample to fulfill the requirements it does not
overdo the matter. Of course single radiators seldom aggregate
more than 300 square feet on direct work, and it will be noted that
up to this size there is very little variation in the sizes used by all.

The formulas given in the foregoing relate entirely to direct
radiation. It has been found that indirect stacks condense from 50
to loo per cent, more steam than direct, depending upon the ve-
locity of the air passing over them, other conditions being the
same. R. C. Carpenter states in his " Heating and Ventilating
Buildings " :

The Flow of Steam in Pipes. 113

" The indirect heating surfaces require about twice as much
heat as the same quantity of direct radiating surface, and hence,
for same resistance in the pipe, the area should be twice that re-
quired in direct heating. It will usually be sufficiently accurate to
use a pipe the diameter of which is 1.4 times greater than that for
direct heating." But he makes a statement earlier in the book that
for indirect heating with separate return an area 50 per cent, larger
than that used for direct heating will be sufficient. To cover all
contingencies, however, it will be safe to figure an area twice as
large as for direct, and the same rule, of course, applies to the
return.

Indirect heaters, when used in connection with a fan, condense
even more steam than when operated under natural draft, on
account of the greater velocity bringing more air into contact with
the radiating surface in a given time. The quantity of steam
which will be condensed in them under these conditions is, how-
ever, a decidedly variable quantity. Suppose, for instance, that
the air entering the heater is at o degrees F., then the condensation
will be 36 per cent, greater than it would if air were returned
from the building at 60 degrees F. ; velocity being constant and
steam pressure 5 pounds gauge. If the velocity of air passing
through the heater changes from 750 to 1500 feet per minute
there will be a further increase of at least 30 per cent. ; making a
total variation of about 77 per cent, in the amount of steam con-
densed. J. H. Mills states that 1000 cubic feet of air passing over
each square foot of surface will cause it to condense from 900 to .
1300 British thermal units.

LOW PRESSURE HEATING MAINS.

The following extracts from an article by C. E., which ap-
peared in The Metal Worker of June 25, 1904, are reprinted here
as adding something to the general fund of information on this
subject:

" Gradually a set of rules for accurately determining the size of
steam mains is being evolved. One of the earliest of these, and
one of the most extensively used, states that a square inch of free
cross sectional area in a steam pipe will supply 100 square feet of
radiating surface. This rule is qualified by its originator in many
different ways, so much so that he is reputed to have said that if

H4 Principles of Heating.

a pipe proved too small to double its size. This rule totally ne-
glects the varying amount of frictional*resistance between large
and small pipes. It is rather absurd, of course, to assume that the
carrying capacity of an 8-inch pipe can be computed by the same
rule as a 1*4 -inch pipe."

There are numerous other rules which have appeared in the
more recent scientific books, all of which are helpful in their way,
but none of which is in very general use among engineers, owing
to the fact that they cannot be applied to pipes of all sizes.

Probably one of the safest rules in calculating the size of a
steam heating main is that in common use among engine builders
— that is, basing the size of the pipe to give an arbitrary velocity
of steam flowing through. In high pressure work the safe veloci-
ties are well known; but in low pressure work this is not so, as
there are only a few offices in which this method of calculating
sizes has been experimentally reduced to a comparatively exact
science and in which the safe velocities for various sizes of pipes
used for different purposes are definitely known.

The basis, of course, for any such rule must be the amount of
steam condensed by a direct radiator of the usual type working
under normal conditions with the outside temparature at zero.
After an exhaustive series of experiments it has been determined
that this will amount to approximately 0.3 pound of steam con-
densed per hour per square foot of radiating surface. This
amount, 0.3 pound, is based on using steam at zero pressure ; but.
as the ordinary steam heating plant is designed to operate at I
to 10 pounds pressure, the difference in the amount of condensa-
tion at pressures within that range, although considerable, would
not be enough to overload liberally designed piping.

Given the square feet of heating surface, the cubic feet of I
pound of steam and the safe velocity, it is an easy matter to deter-
mine the size of the piping. The only difficult part is to determine
what is the safe velocity for a given condition. No set of calcula-
tions, no matter how elaborate, will give this; nor can one fall
back on the experience of the steam fitter, as he hasn't the slightest
idea how fast the steam is going.

The best sources of information available indicate that the fol-
lowing velocities are safe. They are based on extensive experi-

The Flow of Steam in Pipes. 115

ments and observations among old buildings in which the piping
is very small : A velocity of 80 feet per second is perfectly safe in
mains 2 to 3^ inches, inclusive. On mains of these sizes the fric-
tional resistance is rather high, so that the velocity used is low.
Still, even at that, a 3-inch main will supply 1800 square feet of
direct radiation. According to the old rule of a square inch of
area to 100 square feet of surface, the same pipe would supply only
about 750 square feet — rather a wide variation between two rules ;
yet the former has been demonstrated time and again to be per-
fectly true.

For i^4 and i^rinch mains the safe velocity is hardly more
than 50 feet per second; but, as a matter of practice, these sizes
are rarely used with any but an arbitrary amount of radiation,
depending on local conditions. At 50 feet velocity a ij^-inch pipe
will supply 300 square feet of radiation. A velocity of 90 feet is
low enough for 4 to 6 inch pipe, inclusive. On this basis a 5-inch
main will supply 5700 square feet. This is probably considerably
more than current practice among steam fitters allows. On pipes
larger than 6 inches a velocity ranging from 95 to 100 feet per
second is considered good practice. An 8-inch pipe at 100 feet
velocity, will carry about 15,000 square feet of direct radiation,
and a 1 2-inch pipe about 35,000 square feet.

It is presumed, of course, in giving the above figures that the
pipes are insulated with a fair make of covering and that they are
reasonably dripped.

An elaborate system of drips is not essential, but the impor-
tance of a reasonable dripping cannot be overestimated. A main
cannot be expected to carry its maximum amount of surface if in
addition it must carry the condensation from a long system of
mains. Furthermore, it is necessary that the drips be made in a
way that will avoid any churning of water in the fittings at the
drips. There is nothing so fatal to the capacity of a main as the
churning and splashing caused by badly made drips and by wrong
pitch.

For continuous circuit main work, so largely used nowadays,
especially in the smaller class of buildings, it is necessary to provide
carrying capacity in the mains for the entire amount of condensa-
tion as well as the steam, although it may be urged that as the

n6 Principles of Heating.

amount of water increases the amount of steam decreases. Still it
is usual to make large allowance for the water in this class of
work, using a velocity of about 60 feet for the smaller size mains
and 70 feet for the larger sizes. On this basis a 5-inch continuous
circuit main will supply about 4000 square feet of radiation.

The proper proportioning of the risers in a heating plant is
probably the most difficult part. It is of course fatal to the entire
apparatus to get them too small ; and, at the same time, structural
conditions usually, and the wishes of the architect or owner, neces-
sitate making them as small. as possible. A low velocity must be
used on account of the reverse flow of water ; much more serious
in one-pipe work than in two-pipe. A velocity of 40 feet per
second is perfectly safe on one-pipe risers and 50 feet for two-pipe
risers. On this basis a 2l/2 -inch one-pipe riser will supply 600
square feet of radiation and 2^2 -inch two-pipe riser about 750
square feet. These figures may seem excessive, but they are con-
stantly in use and give excellent results. [These are greatly in excess
of the capacities given in Author's Tables XXXIII and XXXIV.]

No set velocities for radiator connections can be given, as these
are determined arbitrarily by good practice, it being necessary to
make allowance for many other things besides the amount of
steam a connection will normally carry. The sizes are well known
and will not be repeated here.

It is essential, in designing any steam heating apparatus, to
provide for the very heavy demand for steam when the plant is
put in operation in the morning. The effect of this, of course, is
to increase the velocities, which effect is most troublesome in the
risers and radiator connections. The velocities as given above are
sufficiently low to provide for this, so that no further allowance
need be made. It will be noticed that the risers will be far largei
than the mains in proportion to the amount of steam they carry.
Radiator connections in good practice are made larger than any
possible demand for steam would necessitate.

SIZES OF MAIN STEAM PIPE CONNECTIONS WITH BOILERS.

Suppose a boiler is supplying steam to an engine cutting off at,
say, one-third of the stroke — that is, admitting steam about one-
third of the time? Assuming a maximum velocity in the supply

The Flow of Steam in Pipes. 117

pipe of 6000 feet per minute, if steam is passing through the same
only one-third of the time, the average velocity will be 2000 feet
per minute. Basing the size of main steam connections with boil-
ers on this velocity gives the following size pipes when the steam
pressure is 80 pounds. The pipe sizes for higher pressures would,
of course, be smaller if computed in the same manner, but it is
advisable to use as large pipes as those stated in the table, which
conform pretty closely with present boiler practice:

TABLE XXXVIII.

SIZE OF MAIN STEAM PIPES FOR BOILERS OF HORSE-POWER STATED. STEAM

PRESSURE ASSUMED TO BE 80 POUNDS BY GAUGE ; AVERAGE VELOCITY IN PIPE,
2000 FEET PER MINUTE.

Size of pipe

Boiler Pipe area. corresponding,

horse-power. Square feet. Inches.

50 0.057 3

62^ 0.071 3V2

75 0.085 4

100 0.114 4^

125 0.142 5

150 0.171 6

200 0.228 7

250 0.285 8

300 0.342 8

NOTE. — Four and one-half inch pipes and valves being an odd size, it is advis-
able to use 5-inch instead. When globe valves are used in boiler connections, it is
well to make the pipes one size larger than when straightway gate valves are
used, to compensate for the increased resistance.

SIZES OF STEAM AND EXHAUST PIPES FOR ENGINES.

The steam ports and supply pipes to engines are commonly
proportioned on a basis of a maximum velocity flow of 6000
feet per minute. A simple automatic or throttling engine running
on, say, 80 pounds steam pressure and taking 30 pounds of steam
per horse-power per hour would require about 137 cubic feet of
steam at the pressure stated for each horse-power per hour. The
admission of steam is cut off anywhere from one-quarter to three-
quarter stroke; seldom over one-half stroke, unless the engine is
very much overloaded. If we assume a cut-off of four-tenths of
the stroke as a fair basis on which to compute the horse-power for
pipes of different sizes we have under these conditions the capaci-
ties stated in the following table.

Principles of Heating.

TABLE XXXIX.

SIZES OF SUPPLY PIPES FOR STEAM ENGINES.

Nominal diameter Engine horse-

o.f pipe in inches. power supplied.

2 24

2% 35

3 54

3% 72

4 92

4% 117

5 145

6 210

7 283

8 364

Engines exhaust during- almost the entire stroke — say 95 per
cent, as a fair average. On this basis, assuming i pound back
pressure, 30 pounds steam per horse-power per hour and a maxi-
mum velocity through the exhaust pipe of 5000 feet per minute,
the appropriate horse-power for exhaust pipes of given sizes has
been computed and is stated in the following table: [4000 feet
velocity is not an uncommon velocity to assume.]

TABLE XL.

SIZES OF EXHAUST PIPES FOR STEAM ENGINES.

Nominal diam-
eter of «xhaust
pipe in inches.
2%

Engine
horse-power.
20

115

153

200

10..

. 312

A comparison of Tables XXXIX and XL shows the size
exhaust pipe for a given horse-power to be one size larger than
the steam pipe, which accords very well with the general prac-
tice of engine builders. Some engine builders make their steam
and exhaust connections abnormally large to provide for cases
where the pipe lines are long. The foregoing tables give permis-
sible sizes that may be used in proportioning the piping in office
and other buildings having individual or isolated mechanical
plants.

The Flow of Steam in Pipes. 119

EFFECT OF BACK PRESSURE ON SIMPLE AUTOMATIC ENGINES.

With a simple automatic engine carrying a back pressure of 5
pounds the loss in power due to back pressure will be as follows :
Take, for example, a high speed engine commonly used to drive
a direct connected dynamo. With 90 pounds initial gauge pres-
sure, equal to about 105 pounds absolute pressure, and steam
cut off at one-quarter stroke, the average pressure per square
inch on the pushing side of the piston throughout the stroke will
be about 63 pounds.

From this must be deducted the atmospheric pressure, equal to
15 pounds per square inch, or say 16 pounds, to allow for the re-
sistance of the exhaust pipe and elbows. The mean effective pres-
sure, equal to the average pressure on the pushing side of the
piston minus that on the exhausting side is 63 — 16 = 47 pounds.
Now with 5 pounds back pressure, or a total of 20 pounds above
a vacuum, the steam pressure on the pushing side remaining the
same, the mean effective pressure will be 63 — 20 = 43 pounds.
The horse-power will be in proportion to the mean effective pres-
sures computed above; that is, with 5 pounds back pressure the
engine will have only 43-47^5 or 91^ per cent, of the horse-
power it has when exhausting freely to the atmosphere. In other
words the loss in power due to the back pressure would be nearly
9 per cent.

EFFECT OF BACK PRESSURE ON COMPOUND ENGINES.

The effect of back pressure is a more serious matter in the case
of compound engines than with simple ones, since it acts on the
relatively large area of the low pressure piston. To show to what
extent the engine horse-power is reduced by a 5-pound back pres-
sure on a compound engine, take for example an engine with a
1 6-inch high pressure cylinder, a 24-inch low pressure cylinder and
a i6-inch stroke. A 5-pound back pressure exerted over the large
area of the low pressure piston would with a piston speed of 600
feet per minute amount to 452 (square inches) X 5 (pounds) X
600 (feet) -r- 33,000 (foot pounds per horse-power) =41 horse-
power. Such an engine with 125 pounds gauge pressure when run
non-condensing is rated to develop about 225 horse-power, hence
an increase in the back pressure of 5 pounds decreases the effective
output of the engine about one-fifth or 20 per cent.

120 Principles of Heating.

COUNTERACTING BACK PRESSURE BY INCREASED BOILER PRESSURE.

With a back pressure exhaust heating system either larger
engines must be used to secure a given horse-power or a higher
boiler pressure must be carried. If the latter is done considerably
more than the 5 pounds back pressure commonly allowed on the
engine must be added to the boiler pressure, since the back pres-
sure is maintained throughout the stroke of the engine, but the
boiler pressure is cut off at one-quarter, one-third, or some other
point of the stroke, as the case may be. To counteract 5 pounds
added to the back pressure of an engine cutting off at one-quarter
stroke about 8 pounds must be added to the boiler pressure. A
few pounds added in this way is not a serious matter so far as fuel
consumption is concerned, since the total heat necessary to make
steam increases very slowly with an increase in pressure and not
at all in proportion to the pressure increase. With ordinary tubular
boilers, however, the allowable pressure that may be carried is cut
down from time to time by the insurance companies, so that if 10
pounds more pressure must be carried, for example, to overcome a
certain back pressure than would otherwise be necessary, the boiler
must be condemned so much the sooner.

STEAM HEATING IN CONNECTION WITH CONDENSING ENGINES.

In the case of plants having condensing engines, either simple
or compound, the question arises whether it is better economy to
run the engines noncondensing part of the time and heat with the
exhaust .steam, or to always run them condensing and heat with
live steam. Which is the better policy depends chiefly on the
amount of steam required for heating in comparison with'the total
exhaust from the engines. If the amount is very small manifestly
it would be better to run condensing and secure the marked sav-
ing in steam and supply the heating system with live steam
through a reducing valve. When there are several engines it is
well to have the exhaust pipes connect with a header with*cut-out
valves between the engines, one end of the header connecting with
the condenser and the other with the line leading to the heating
system. Then one, two or more engines may be run condensing
and the others exhaust to the heating system.

As to the economy: Suppose a compound condensing engine
will develop an indicated horse-power with the consumption of

The Flow of Steam in Pipes. 121

1 6 pounds of steam per horse-power per hour, and will require 23
pounds of steam to develop a horse-power when running non-
condensing, a difference of 7 pounds. Under the conditions stated
a 300 horse-power engine would consume when running noncon-
densing 300 x 23 = 6900 pounds per hour. If the engine were
run condensing it would consume 300 x 16 = 4800 pounds. In
the case assumed whenever more than 6900 — 4800 = 2100
pounds of steam per hour are required by the heating system it
will be cheaper to run noncondensing.

Suppose for example that 3600 pounds of steam are necessary
to supply the heating system for one hour. If the engine is run
condensing 4800 pounds of exhaust steam will be condensed and
3600 pounds of live steam must be supplied, a total of 8400 pounds
in one hour, whereas if the engine were run noncondensing 6900
pounds of exhaust steam would be secured, of which 3600 would
be used for heating, the rest escaping through the exhaust head,
except that utilized in heating the feed-water.

With the steam consumption assumed, whenever more than 7
pounds of steam may be utilized in the heating system to each
horse-power developed by the engine it would be better economy
to run noncondensing. When less than 7 pounds is needed the
engine should be run condensing. For example, suppose steam i«
required by the heating system at the rate of 4 pounds to each
horse-power developed by the engine, one horse-power condensing
will take 16 pounds of steam, which, plus the 4 pounds of live
steam supplied to the heating system, amount to 20 pounds per
engine horse-power, whereas if the engine were run noncondens-
ing 23 pounds would be consumed. Against this method of heat-
ing must be charged the larger size engine required to produce a
given horse-power when running noncondensing.

In the case of a Corliss simple noncondensing engine taking,
say, 26 pounds of steam per horse-power per hour and 21 pounds
when condensing, it will be found cheaper to run noncondensing
whenever the heating demands more than 5 pounds of steam to
each horse-power developed by the engine ; in other words, when-
ever the steam for heating exceeds more than about one-fourth
that for power it will be better economy to run noncondensing,
and when less than that amount to run condensing.

CHAPTER IX.
MODIFIED SYSTEMS OF STEAM HEATING.

Under the above heading will be described the essential fea-
tures of vacuum, vapor and fractional valve systems of steam
heating. These methods have to a great extent taken the place
of the old-fashioned plain one-pipe and two-pipe systems with air
valves.

While differing in details these modified systems may be
divided in general classes which will be described to an extent
that will make clear their essential features ; readers in search
of more specific information are referred to manufacturers'
catalogs.

TWO-PIPE VACUUM SYSTEMS.

In the Webster system, the best known two-pipe method of
vacuum heating, the steam supply to the radiators is controlled
by a hand valve as in the ordinary two-pipe system. At the
return end of each radiator is placed an automatic water and air
relief valve which permits the escape of air and water and pre-
vents the escape of steam. Since air is heavier than saturated
steam, in the ratio of i to ^ at atmospheric pressure, the location
of this valve at the lower end of the radiator opposite the steam
inlet is stated to be the most effective one possible. Air valves
are not required with this system. Typical radiator connections
are shown in Fig. 36. It is essential that each unit of radiation
and each drip point in supply lines (unless a special system of
drips be provided) be equipped with one of these automatic return
valves, otherwise any unit or drip point without one would permit
steam to pass into the returns and destroy the vacuum which it is
the function of the pump to maintain. By means of this suction a
continuous removal of condensation and air from the heating
system is secured.

The water and air drawn from the system is discharged by the
vacuum pump to an air-separating chamber. When a closed

122

Modified Systems of Steam Heating.

123

feed-water heater is used the vacuum pump discharges to an
open receiver from which the water is pumped through the
heater to the boiler.

The vacuum pump exerts a suction on the return ranging as
a rule from 4 to 12 inches mercury column, according to the
length and size of the pipes. With this system high-pressure
returns should not as a rule be connected with the returns leading
to the vacuum pump, since the high temperature of the conden-
sation causes a portion of the water to vaporize in the returns

AUTOMATIC

WATER AND

AIR RELIEF

VALVE

Fig. 36. — Typical Radiator Connections.

and interferes with the maintenance of the vacuum. The exhaust
from the pump is utilized in the heating system.

In buildings heated by this system it is possible to supply an
amount of steam less than that required to completely fill the
system at atmospheric pressure, hence a saving may be made by
heating at night or during mild weather with steam at a pressure
below that of the atmosphere.

It is often necessary to locate some radiating surface at a
point lower than the main return. With the vacuum system the
condensation may be raised several feet above the level of the
radiator to be drained, by reason of the suction in the returns.

The back pressure and pressure reducing valves need not be
set to produce initial pressure in the heating mains in excess of
that required to supply the most remote unit of radiation with
steam at atmospheric pressure.

In the case of high pressure plants, two reducing valves, set

124 Principles of Heating.

tandem, are sometimes installed, the first to reduce from boiler
pressure down to 15 or 20 pounds or thereabouts, the latter to
reduce to atmospheric pressure or to a few ounces above the
pressure of the atmosphere.

Among the advantages claimed for two-pipe vacuum systems
are:

1. Absence of back pressure on motive engines when exhaust
steam is utilized.

2. A perfect drainage of supply pipe systems preliminary to
an equally perfect drainage of radiating surface without the loss
of steam.

3. A continuous automatic drainage of condensation and the
prevention of any accumulations of water.

4. A positive and consequently effective steam circulation.

5. Perfect control of circulation with power to vary it at will.

6. Removal of air and gases from heating surfaces and feed
water.

7. Power to independently modulate temperature in any part
of the heating surface.

8. The return of condensation from points somewhat below
the line of drip or drainage mains when necessary.

9. Smaller pipes may be used than with the ordinary low pres-
sure two-pipe system.

It is pointed out by the manufacturers that the positive
removal of air from the radiators is alone a great advantage, since
automatic air valves seldom properly perform the function for
which they were designed, and unless air lines lead from them to
some suitable point of discharge the ill-smelling air from the
radiators is discharged into occupied rooms.

Water hammer, due to ignorance or carelessness in operating
radiator valves, is entirely overcome by the use of the
two-pipe vacuum system. The supply valve is the only
one that requires^ any attention, the return being auto-
matic. The supply of steam may be throttled down at will.

The steam pressure in the radiators is not reduced by the
vacuum maintained on the return, but depends solely on the
amount of steam admitted to the radiators. Indirectly the vac-
uum on the return affects the steam pressure, since no pressure

Modified Systems of Steam Heating.

125

126 Principles of Heating.

whatever above the atmosphere is required in the radiators for
the purpose of forcing the water of condensation through them
and the air out of them. In the case of old plants having insuffi-
cient radiation for the most severe weather, when using the very
low pressures common with vacuum systems it is often better pol-
icy to carry a few pounds back pressure on the engines furnish-
ing the exhaust steam during such weather than to overhaul the
entire heating system.

This system secures the ready circulation of steam through-
out buildings widely separated, and that, too, with only a slight
back pressure on the engines. With the usual methods of steam
heating it is necessary to carry a back pressure, even during mild
weather, when the full efficiency of the radiating surfaces is not
required, and when but few of the radiators of an extensive sys
tern may be needed. Under certain conditions it would be cheaper
to supply live steam at reduced pressure than to carry back pres-
sure on the engines in order to supply a small amount of radiating
surface.

Since with this system no pressure is necessary in the radi-
ators to force out the air and water, it follows that a drop in pres-
sure of only a few ounces from the initial pressure will be suffi-
cient to cause the necessary flow of steam through the pipes.

These may be made smaller than is customary with the ordi-
nary two-pipe low pressure system, and the returns may be decid-
edly cut down in size owing to the action of the vacuum pump
creating a rapid flow in them. See pipe sizes, pages 1 06 and 107.
The supply pipes may be made one or two sizes smaller with the
vacuum system, and the returns two to three sizes smaller than
would be used with the ordinary low pressure system.

THE AIR-LINE VACUUM SYSTEM.

This system, commonly known as the "Paul," secures the
removal of air from radiators through air valves of the expansible
plug type connected with air lines leading to a steam ejector. See
Fig. 38. It may be applied either to one-pipe or two-pipe systems
(see Figs. 39 and 40), the water returning in the same manner as
in ordinary low pressure steam heating plants. This system
handles the air alone, whereas the system just described removes
both the air and condensation from radiators.

Modified Systems of Steam Heating.

127

That air is the most serious hindrance to the proper opera-
tion of a steam heating plant is a well-known fact. To attempt
to get rid of it by forcing it through ordinary automatic air valves
by steam pressure is a rather slow process, especially in the case
of large coils or radiators. With a common low pressure system
the air remains in the radiators until forced out by the steam.
With the vacuum system the air may be removed from the radia-

Fig. 38. — Front Elevation of Exhausting Apparatus.

tors by starting the ejector before steam is turned on the system.
The radiators then become quickly filled with, and remain full of,
steam, since the air is automatically removed as rapidly as it
accumulates.

ABSENCE OF BACK PRESSURE.

One of the chief advantages of this system over ordinary low
pressure heating is the removal of back pressure from the engines
and pumps. By exhausting the air from the radiators by means

128

Principles of Heating.

of the steam ejector they become practically condensers, the en-
gines exhausting into them. In manufacturing plants where the

Jft

;X- AIR VACVE

-x" MT

Q ^

(

& it

TO EJECTOR^

Fig. 39. — Connection for One-Pipe System.

AIR VALVt

Fig. 40. — Connections for Two-Pipe System.

power requirements may be in excess of those for heating the
importance of the elimination of back pressure is apparent.

Modified Systems of Steam Heating. 129

STEAM TO OPERATE THE EJECTOR.

As to the amount of live steam required to operate the ejector :
To compute the volume of steam escaping from an orifice to
the atmosphere, allow about 900 feet velocity per second and mul-
tiply by the area of the opening expressed in the decimal part of
a square foot. As to the amount of steam required to operate
the ejector, A. B. Franklin, in a paper on exhaust steam heating,
read before the Master Steam and Hot Water Fitters' Associa-
tion of the United States, June 7, 1893, states that in ten hours'
run, with a fan system of heating having heaters containing an
aggregate of 24,150 linear feet of i*4~mcn pipe, supplied by a
6-inch main, the ejector discharging to a condenser used 300
pounds of steam in that length of time. A test made at the Ohio
State University showed the total weight of water returned from
the radiators to be 8,160 pounds and the steam used by the ex-
hauster or ejector to be 432 pounds.

Claims for this system are:

1. A positive and uniform circulation of steam without pres-
sure above that of the atmosphere.

2. Utilizing the heat of steam at low temperatures, thereby
gaining great economy.

3. Warming without impairing the quality of the air in the
rooms.

4. The independent and automatic removal of the air and
water of condensation from the heating apparatus.

5. A sealed system ; no leakage, no smell or dripping from air
.valves.

6. All heating surface held in the best condition to operate
promptly when desired, and all parts of the surface rendered
uniformly efficient when steam is turned on.

7. Exhaust steam utilized without back pressure at engine
or pumps.

8. The water of condensation returned quickly and econom-
ically at highest temperatures.

9. Less steam used, less coal burned, to heat a given space.

130 Principles of Heating.

HEATING WITH RADIATORS AT A RELATIVELY LOW TEMPERATURE.

Professor Kinealy, reporting on some tests to show the effect
of the relatively low temperatures secured by the use of a vacuum
system, makes the following statement : " The radiator at high
temperature probably kept the air at the top of the room, when
the temperature about 5 feet from the floor was 70 degrees, at
a much higher temperature than it was kept when the temperature
in the radiator was low. The higher the temperature of the air
at the ceiling of the room the greater will be the average tem-
perature of the air in contact with the cooling windows and walls
of the building, and therefore for a given outside temperature
the greater will be the difference between the average temperature
of the air inside and that of the air outside, and hence the greater
will be the amount of heat transmitted through the cooling walls
and windows per hour. As the occupants of heated rooms live
in the air which is within 6 feet of the floor, that system of heat-
ing must undoubtedly be the best and the most economical which
will maintain the desired temperature of the room nearly uniform
from the floor to 5 feet above it, with a low temperature in the
upper part of the room, and this is, I think, done by radiators sup-
plied with steam at low temperatures." (See "Heating with
Steam at or Below Atmospheric Pressure," by J. H. Kinealy, in
The Metal Worker, Plumber and Steam Fitter, July 29, 1899).

THE POSITIVE DIFFERENTIAL SYSTEM OF STEAM CIRCULATION.

In this system a controlling valve is placed at the foot of
return risers as indicated in Fig. 41. These valves are designed
to maintain any desired difference in pressure between the supply
and return risers. By maintaining this constant pressure differ-
ence it is claimed that a special type of swing check valve may
be used at the return end of each radiator. A small opening is
provided for the removal of air when this valve is closed. When
open, both air and water pass through it.

Fig. 41 illustrates the application of this system to coils. The
main supply riser is drained through a siphon loop to the return.
It is claimed, since all return risers may be kept in the same con-

Modified Systems of Steam Heating. 131

dition by means of the controlling valve that all air and con-
densation is drawn away from the radiating surfaces to the
vacuum pump.

Fig. 41. — Application of the Positive Differential System to Radiating Coils.
FRACTIONAL VALVE SYSTEMS OF STEAM HEATING.

These systems of low pressure steam heating provide for the
control of the heat emitted by radiators by regulating the admis-
sion of steam to them. A control valve is connected with the
inlet of each radiator. These valves are capable of adjustment
to admit enough steam to fill one-quarter, one-half, three-quarters
or a fractional part of the radiator, a dial being provided to indi-
cate the degree of opening.

At the return end of each radiator is placed a combined air
valve and expansion or float trap. This valve is designed to
allow water and air to escape from the radiator, but to prevent
the escape of steam. Valves of the thermostatic type are oper-

132

Principles of Heatimj.

ated by a liquid sealed in a suitable chamber. When steam comes
in contact with it the liquid is vaporized and creates a pressure
sufficient to force the valve disk or spindle against the seat.
When the liquid cools, the valve opens and permits water and
air to pass to the return pipe.

Fig. 42 shows a radiator equipped with supply and return
valves as described. With this system radiators of the hot water
type are preferable to those of the ordinary steam pattern, as the
control valve may be more conveniently located and because the

Fig. 42. — Radiator Equipped with Fractional Supply Valve and Automatic Return

Valve.

circulation in the radiator is said to be somewhat better than with
steam radiators.

When a control valve is partially closed the steam is condensed
in the upper portion of the radiator, the lower portion is cold and
becomes filled with air that backs up through the return valve or
trap, the return risers being open to the atmosphere and free from
pressure.

When the water of condensation is returned to a low pressure
boiler it must be permitted to back up the returns above the water
line in the boiler sufficiently to overcome the boiler pressure acting
on the return where it connects with the boiler. The lowest radia-
tors and drip points must therefore be well above the water line
of the boiler. Since I pound pressure is equal to about 2.3 feet
of water head, the maximum pressure that may be carried with-
out flooding the radiators is limited by the available head, unless

Modified Systems of Steam Heating. 133

special apparatus be provided. The use of a return tank and auto-
matically controlled pump is recommended for large jobs. When
the condensation is returned to a tank, as in large buildings, the
tank must be vented to the atmosphere.

The piping of a fractional valve system is practically the same
as a regular two-pipe system except that the returns must be open
to the atmosphere. The main returns are run wet or dry, as best
suits the conditions.

Advantages claimed for these systems are:

1. Positive circulation, due to absence of pressure at the re-
turn end of the radiators.

2. Quietness of operation.

3. Control of each unit of radiation independent of others.

4. Absence of separate air valves and lines, these being com-
bined with the return carrying the water of condensation.

5. Convenience in operation, there being but one valve to
manipulate.

6. Saving- in fuel, due to absence of overheating in rooms, the
heating being more easily controlled than with ordinary steam
heating systems.

7. The quick heating of radiators, due to the rapid expulsion
of air, there being no steam pressure in the returns to be over-
come.

8. The drop in pressure between the supply and return lines
being greater than in the ordinary two-pipe system, somewhat
smaller pipes may be used if necessary.

GRAVITY RETURN VACUUM SYSTEMS.

In one of these vacuum systems air valves of the expansible
plug type are attached to the radiators, and air lines are joined
and led to the mercury seal shown in Fig. 44, and at A in Fig. 43,
which shows a typical lay out of a one-pipe system. This method
of piping is considered preferable, not only because of the greater
convenience of having but one valve on each radiator, but because
the fewer the valves the less the leakage through stuffing boxes,
causing the loss of vacuum.

With this system special care must be exercised in packing
radiator valves to prevent air leaking into the system and destroy-

134

Principles of Heating.

ing the vacuum. It is claimed, however, that since the valves are
used much less frequently than with low pressure systems, as

Fig. 43. — Trane One-Pipe Vacuum System.

tne temperature of the house is approximately controlled by vary-
ing the vacuum on the system, the stuffing boxes receive less
-wear, and if well packed give little trouble from leakage.

This system is so arranged that with a steam pressure of a

Modified Systems of Steam Heating. 135

pound or two, the air in the radiators will be forced through the
mercury and out of the system. The air valves prevent the escape
of steam from the radiators. When the steam pressure is allowed
to fall air is prevented from entering, the system by the mercury
column which rises in the pipe. The vacuum has no effect on the
water line in the boiler, as the pressure on supply and return lines
is the same. Of course, it will be necessary from time to time,
even in mild weather, to get up sufficient pressure to expel the
air from the system, as no job of piping can be made perfectly
tight. Every precaution must be taken, however, to make the
system as tight as possible, and all lines should be thoroughly
tested with at least 30 pounds pressure, which should be carried
for 24 hours without serious loss.

With this system it is recommended that gauge cocks be
omitted from the water column, as they are sometimes the source
of air leakage when the system is running under vacuum. The
gauge glasses should be thoroughly packed ; the stuffing boxes on
radiator valves must be tightly packed. The same care must be
taken to prevent pockets in the piping as with a regular low
pressure system. The patentees recommend that the air pipe and
fittings be made of galvanized iron to avoid trouble from stoppage
by scale, etc.

Damper regulators of special design are used in connection
with mercury seal systems, or thermostatic control may be ap-
plied, operating the boiler drafts from the thermostat located at a
point that will represent as nearly as possible the average tem-
perature of the house.

ADVANTAGES CLAIMED FOR THE MERCURY SEAL VACUUM SYSTEM.

The principal advantages claimed for this system of steam
heating over ordinary ones are :

i. That it is as well adapted to mild weather as cold, whereas
with a steam heating system a temperature of 212 degrees must
be attained to secure any effect from the radiators.

2. That considerable saving in fuel may be effected in mild
weather, due to the circulation of steam below atmospheric pres-
sure, thus avoiding overheating, so common with low pressure

136 Principles of Heating.

steam heating. In many sections in the northern part of this
country the average outside temperature during the heating sea-
son is 35 to 40 degrees above zero.

Steam heating systems based on 70 degrees in zero weather
are difficult to control with an outside temperature of, say, 40
degrees, when the loss of heat from a building is only about three-
sevenths that in zero weather. The difference in temperature
between the steam or vapor and the air in the room need be, under
the stated conditions, only three-sevenths as much as in zero
weather.

3. The mercury seal vacuum system when applied to a steam
heating apparatus secures a wide range in the temperature at
which the radiators may be kept to provide for different weather
conditions.

The lack of this range of temperature in the ordinary low
pressure steam system is the greatest drawback to its successful
use in house heating. It is said to be practicable to maintain tem-
peratures varying all the way from 170 to 230 degrees or more,
which would permit the system to meet practically any outside
weather conditions.

The following table shows the temperatures corresponding to
different pressures :

TABLE XLI.

SHOWING STEAM PRESSURE AND VACUUM AND CORRESPONDING TEMPERATURE.

In. of mercury. Temperature. Gauge pressure. Temperature.

Vacuum gauge. Fahr. Lb. per sq. In. Fahr.

28 101 .4 0.304 213.0

26 125.6 1.3 216.3

24 147.9 2.3 219.4

22 152.3 3.3 222.4

20 161.5 4.3 225.2

18 169.4 5.3 227.9

16 176.0 6.3 230.5

14 182.1 7.3 233.0

12 187.5 8.3 235.4

10 192.4 9.3 237.8

5 203.1 10.3 240.0

0 212.1

The pressures are not given in even pounds. The 1.3 pound
gauge pressure corresponds to 16 pounds absolute pressure, and
so on.

Modified Systems of Steam Heating. 137

COMPARISON WITH HOT WATER HEATING.

Advantages claimed for this system over hot water heating
are:

1. Saving in cost of installation, as the pipes may be made
smaller and smaller radiators may be used, owing to the higher
temperatures carried in cold weather.

2. The ability to increase or decrease the temperature in the
radiators more quickly, owing to the much smaller volume of
water in the system.

3. The absence of danger of damage from leaks.

On the other hand, in weather, say, from 50 to 60 degrees,
when it is only necessary to take the chill off a house, a hot water
system is especially well adapted to fulfill the requirements, and
the temperature of the water may be kept as low as desired,
whereas with the mercury seal vacuum system 170 degrees F. is
about as low a temperature as can be maintained, and then not
for any length of time, owing to imperceptible air leaks, which
destroy the vacuum.

The advantage of quick heating in the vacuum system is, in a
measure, offset by the advantage possessed by hot water for stor-
ing the heat during the night. With the mercury seal system
all radiators are kept at the same temperature. The steam
supply may not be throttled without fear of water backing up
in the radiators and causing noise. In hot water heating
systems the temperature of each radiator may be controlled at
will by throttling down the supply, thus giving individual
control of the temperature of each room.

SUGGESTIONS TO FITTERS FOR INSTALLING GRAVITY VACUUM

SYSTEMS.

The same care must be exercised in draining and dripping the
piping that would be necessary if it were intended 'to erect the
apparatus without the use of the vacuum system. Extra precau-
tion should be taken, however, to have all joints tight, and to have
all fittings free from sand holes.

Care should be taken that all valves used are carefully packed
so as to avoid the leakage of air into the system while the vacuum

138

Principles of Heating.

is being maintained. The manufacturers' packing in the valves
should not be depended on but should be removed and carefully
replaced with lamp wick dipped in oil and plumbago, being sure
that sufficient wick is used to make the valve tight around the
stem. All check valves used should be swing checks, with as-
bestos or Jenkins' seats. Care should be taken to see that
is no leak of air into the system through the safety
valve, water glass, gauge cocks or other trim-
mings.

The air pipe should not be less than y^ mcn be-
tween the air valve and the first fitting, where it
should increase to y2 inch pipe. The first fitting
below the air valve should therefore be a *4 x YZ
inch elbow in every case. No air riser should be
less than y2 inch, and where the air riser extends
above the second floor or is connected to more than
two air valves should not be less than ^4 mcn- The
horizontal air main should be run on the basement
ceiling, and need not be larger than i inch except
in cases of extreme length, where it should be 1^4
inches.

In making up the air lines, it is recommended
that galvanized fittings be used and that the joints
on the air lines be made up of asphaltum and
the fittings painted all over on the outside with
asphaltum in order to close up any sandholes. Care
must be taken to have the air piping tight. Care
must also be taken to give the air piping a good
pitch of not less than i inch to 10 feet toward the
boiler. The air piping must contain no pockets or
traps of any kind. The connections of the air pip-
ing to the air valves should be made with ground
joint brass unions.

Fig. 44. — Mercury
Seal.

VACUUM AIR VALVE SYSTEMS.

Several patterns of vacuum air valves have been put on the
market designed to permit the escape of air from radiators and
to prevent its reentering them when the steam pressure falls.
With a system perfectly tight at all valves, fittings, etc., and with

Modified Systems of Steam Heating. 139

all vacuum air valves in working order a steam plant may be run
as a vacuum system. It can derive the advantage of a great range
in the temperature of the radiators by simply raising the steam
pressure sufficiently to drive out all the air, for then when the
pressure falls below that of the atmosphere the radiators will re-
main filled with steam at a minus pressure and at a temperature
below the boiling point, viz., 212 degrees F.

Mr. George D. Hoffman writes of one of these systems as
follows :

" The difficulty heretofore existing of being able positively and
automatically to prevent the air from going back into the system
when the steam pressure is reduced below that of atmosphere, is
overcome by the use of the automatic air and vacuum valve and
the air line system of vacuum heating.

" The valve is intended to be a vacuum system in itself. With
an apparatus that is practically air-tight in all its joints and con-
•nections, simply screw on the valves in place of the ordinary air
valves and you have installed a complete system of vacuum steam
heating. The use of these valves does not necessitate air lines
or any mechanical appliance for exhausting the air. Pressure
exhausts the air from the system through the valve, and then
when pressure goes off the valve automatically closes, preventing
the ingress of air into the apparatus through the valve. The valve
is especially designed for use in connection with residence work,
stores and small apartments where the number of radiators in
connection with any one plant is limited."

It is not wise to attempt to provide a vacuum system in large
buildings by simply attaching vacuum air valves to the radiators,
because of the great number of valve stuffing boxes, fittings, etc.,
at which an inleakage of air is liable to occur and destroy the
vacuum, necessitating the raising of steam pressure at frequent
intervals to force the air out of the system.

THE VAPOR SYSTEM OF HEATING.

The vapor system is a modified two-pipe system of steam
heating, arranged with devices to prevent more than a few ounces
pressure accumulating in the boiler or radiators. Each
radiator is equipped with a special supply valve, designed

140

Principles of Heating.

to admit a volume of vapor or low pressure steam sufficient to
supply a portion or all of the radiating surface. At the return
end of each radiator is placed a small combined water seal and
air vent (see Fig. 46), designed to permit the escape of air and

Fig. 45. — Vapor System Supply Valve.

Fig. 46. — Union Elbow for Return End of Radiator.

the water condensed in the radiator. Fig. 47 shows a radiator
equipped with the supply valve and the combined water seal and
air vent. Radiators of the hot water type are invariably used in
connection with this system.

The returns from the radiators, this being a two-pipe system,
are combined in the basement and lead to a receiver (see Fig. 48)
connected with the boiler. The main return is sealed at the end, as

Modified Systems of Steam Heating.

141

illustrated in Fig. 49, to prevent the escape of vapor to the cellar.
From the chamber C the air combined with some vapor from

Fig. 47. — Radiator Connected on Vapor System.

the system escapes through the air line to the condensing radi-
ators suspended from the basement ceiling as shown in Fig. 48.
The vapor is condensed in these radiators and flows back by grav-
ity to the boiler, the air escaping to the smoke flue. The latter is
preferable to any other point of escape since the heat in the flue
causes a slight pull on the air line accelerating the removal of
the air from the system.

The receiver is open at the top, and there is no check valve
between it and the boiler.. It, therefore, acts as a perfect safety
valve to prevent any excess of pressure in the boiler. Should
the boiler pressure increase, the water would be driven out into
the receiver. The float therein would be raised and the drafts

142

Principles of Heating.

closed. Should the pressure continue to increase from any cause
the float in the receiver would rise until the lever of the relief
valve is raised, permitting the escape of steam and reducing

/CONDENSING RADIATOR

AIR VENT TO CHIMNEY _

RECEIVES OPEN AT TOP

PIPE TO STEAM SPACE
IN. BOILER

iCOPPER FLOAT
CONNECTED BY CHAIN
WTH DAMPERS

J0UN fiETUJU* JO .BOI^EB

Fig. 48. — Connections at Boiler, Showing Condensing Coil.

the pressure. A glass water gauge is attached to the receiver, and
a scale indicates the boiler pressure in ounces. No other pressure
gauge is necessary.

The maximum pressure never exceeds 13 ounces, and therefore
the size of the radiators must be based on relatively low tempera-
tures, and an amount of surface within 10 or 15 per cent, of that

Modified Systems of Steam Heating.

143

required with hot water heating is commonly provided to warm
the rooms properly in the coldest weather. With this system one
cannot overcome the effect of a shortage in radiating surface by
increasing the pressure and temperature as in low pressure steam
heating, since the water would be backed out of the boiler through
the main return connected with the receiver.

The water line of the boiler should be at least 4 feet below
the basement ceiling to give sufficient pitch to the pipes and to
provide ample hight to cause the water to flow back into the
boiler. A common arrangement of piping is shown in Fig. 50.
The returns must be run overhead in the basement, that is, they
must be " dry." These pipes are preferably left uncovered in
order to promote the condensation of any vapor escaping to
them from the radiators.

The vapor system may be used in connection with exhaust
steam plants supplemented by live steam and with central heating
plants, as shown in Fig. 51. When the condensation is not re-
turned to the boilers the pump and receiver are omitted, and the
condensation is discharged to the sewer through a cooling coil.
Central station heating companies commonly require the cooling

OPEN AT TOP

AIR LINE

NDENSER

SECTION
THROUGH RECEIVER

Fig. 49. — Seal at End of Main Return.

coil on low pressure systems to contain one-fifth to one-sixth of
the entire direct radiating surface in the building.

In moderate weather the regulator is set to close the draft on
i to 2 ounces, in severe weather 4 to 6 ounces.

144

Principles of Heating.

Modified Systems of Steam Heating

146 Principles of Heating.

ADVANTAGES CLAIMED FOR THE VAPOR SYSTEM.

1. The control of the heat given off by each radiator inde-
pendently by means of the quintuple valve shown in Fig. 45, which
may be set to admit any desired amount of steam. This is of great
value when there is but one radiator in a room, for with ordinary
steam heating one has practically no control of the room tempera-
ture under these conditions.

2. Freedom from any danger of over-pressure on the boiler.
The safety valve of an ordinary system may stick or the water
in the expansion pipe of a hot water system may become frozen.

3. Economy in fuel because of the easy control of temperature
afforded, thus avoiding overheating.

4. Much smaller pipes may be used than with low pressure
steam or hot water heating. With the vapor system the supply
connections practically never exceed ^/\ inch in size, and the
returns ^ inch for direct radiators.

5. Air valves are not required, the air being removed through
the small vent in the special fitting attached to the return end of
each radiator.

6. Quick heating ability. A vapor may be very quickly
secured sufficient to fill the radiators without forcing the fire.

THE ATMOSPHERIC SYSTEM OF STEAM HEATING.

This system is based on the principle of supplying steam at
practically atmospheric pressure in the form of vapor as the
source of heat.

The supply of steam is delivered to the top of the radiator,
which must be of the hot water type, with top and bottom con-
nections.

Under normal conditions, the radiator is filled with air at
atmospheric pressure, and the steam on entering forces this air
out, through the return piping along with the condensation into
the basement, where the return lines are open to the atmosphere.
The supply of steam to the radiator is regulated by means of a
specially constructed valve, which will admit the desired quantity

Modified Systems of Steam Heating.

147

148

Principles of Heating.

of steam to the radiator. When the steam is admitted, it spreads
in a thin layer along the top of the radiator, and as it changes to
water, runs down the walls of the radiator, heating them and
becoming cooled.

This system as applied to individual plants is illustrated in
Fig. 52.

Fig. 53. — Damper Regulator.

When the boiler pressure rises above that desired (five to
eight ounces) the water is forced from the boiler into the
stand-pipe, which raises the float, causing the draft door to
close and the check draft in the smoke pipe to open. (See Fig.
54.) If this does not check the fire sufficiently the float will
continue to rise, causing check valve at H to close, preventing
standpipe overflowing. In addition to the above is the safety
valve on the boiler.

Modified Systems of Steam Heating.

149

No valve is used at the return end of radiators.

No air valves are required.

Since a portion of the radiator acts as hot water radiation,
about 25 per cent, more radiation must be used than would be
required with steam radiation.

In this system " the control of steam supply to the radiator is
accomplished by means of a specially constructed valve, and is
the only appliance which is made particularly for the system.

VALVE.

CHECK. VALVE.

BASEMENT

Co*

L DOOR.

DRAFT

ASH

SUPPLY to STAND PIPE.

STA.NO PIPE.

FLOAT.

DKAFT Doo*

PULLEYS

CHECK

STOP

CHECK

CHECK Vkuvt Roo

BOIUM

Fig. 54. — Damper Regulator Atmospheric System.

" This valve is made only in 24-inch size. The opening in the
valve seat is proportional to the size of the radiator which the
valve is to serve, and the amount of surface in the radiator must
always be specified when ordering valves. For instance, a valve
constructed for a 40- foot radiator cannot be used properly on any
other size, and if put on an 80- foot radiator, would only admit
steam enough in maximum open position to heat half the
radiator.

" Steam is admitted to the radiator by opening the valve, turn-
ing to the left in the usual manner.

" It is desirable at periods of maximum demand to heat the

1S° Principles of Heating.

upper four-fifths of the radiator; this will have to be determined
by experiment, as no two radiators of the same size are set under
the same conditions. The valve opens full in four turns, one
complete turn will open it one-quarter, two turns one-half, and

CHAPTER X.
HOT WATER HEATING BY FORCED CIRCULATION.

In this chapter extracts from several articles relating to large
installations are given which bring out a number of interesting
features.

One of the arugments frequently advanced in favor of hot
water heating in connection with condensing plants is that the
condensing water from the surface condenser may be circulated
through the heating coils and is sufficiently hot to keep up the
temperature in the buildings in mild weather. Of course the out-
side temperature at which it is necessary to change from con-
denser water to the heating of same by live steam depends on the
proportioning of the radiation. During cold weather the surface
condenser is operated entirely with cold water and the water for
the heating system is passed through a live steam heater.

A velocity of flow of 400 feet per minute is about the maxi-
mum commonly used.

CENTRAL HOT WATER HEATING PLANTS.*

" The equipment and operation of the system is, in brief, as fol-
lows : The steam boilers, engines, and dynamos are such as may
be used in the ordinary electric light station. Heaters of the
tubular type, through which the water passes from the pumps to
the mains, receive the exhaust steam from the engines, heating the
water to any desired temperature. When more exhaust is being
produced than is required to heat the water, the excess is deliv-
ered to a water-storage tank to be used later when the electrical
output is small. The circulating system consists of two wrought-
iron pipes, laid side by side in the ground, carefully protected by
insulation (See Fig. 55), one pipe for the outflow of hot water

* Extracts from paper by H. T. Yaryan, A. S. M. E., Cincinnati meeting, 1900.

151

152

Principles of Heating.

impelled by the pumps, the other for the return water from the
coils in the various houses heated, going back to the suction end
of the pumps, to be forced again through the heaters, where the
loss in temperature is restored. The heaters used are surface
condensers.

The houses are equipped with radiation sufficient to heat them
to a temperature of 70 degrees F. when the outside temperature
is freezing, with water entering at 160 degrees. By raising or
lowering the temperature of the water one degree for each degree
of variation in the outside temperature, it is stated that a con-
stant temperature may be maintained in the houses in all kinds of

Fig. 55. — Arrangement of Insulation.

weather. The extreme limits of the water temperature is 130
degrees in moderate weather and 212 degrees in the coldest. The
water reaches the extreme end of the lines, three-quarters of a
mile from the station, in the coldest weather, with a loss of 12
degrees F., which would be an average of 6 degrees to all of the
houses. As the water returns to the station with a drop of 35
degrees, this would indicate about 17 per cent, loss in the ground,
which the author thought was about correct. A pressure of 60
pounds is maintained on the feed line during cold weather and
40 pounds during moderate weather. The service pipes to the
various houses are i-inch pipe, and the return line is throttled
with a disk inside the building, the size of opening depending on
the quantity of radiation, but averaging y% inch.*'

As to the corrosion of mains, the author had this to say:

Hot Water Heating by Forced Circulation.

" 10,000 feet of pipe were relaid last summer, after being in use
five years. The wrought-iron pipe showed no signs whatever of
corrosion, but steel pipe was perceptibly affected. The pipe
showed the formation of nodules on the inside, varying in num-
ber from a dozen to 100 in a length of pipe, and in size from a
grain of corn to a hazel nut. When the nodules were removed,
a soft under layer of carbon remained, and with the finger nail
this could be removed, developing a perfectly round pit from ^
to 3/16 inch deep; but in no instance had the pit perforated the
pipe. As a matter of curiosity, some steel pipe which had been
in use two years was examined, and found to be in exactly the
same condition as that of five years' use. The action seems to be
electrolytic, some particle of impurity forming the nucleus for
decomposition of the steel. If any inference can be drawn from
the facts stated, it is that the impurity has lost its power to cause
electrolysis after being surrounded by a sufficient amount of
graphite.''

HOT WATER HEATING BY FORCED CIRCULATION.*

"A type of heating system that is gaining in favor as its advan-
tages are becoming better known is hot water heating by forced
circulation. By this is meant a system of hot water heating in
which a circulation is induced by means of a pump placed in the
circuit of the mains, the water being heated by either exhaust or
live steam, or both. The advantages claimed for this system are
economy in steam consumption, ease of control, the maintenance
of a constant temperature in the building irrespective of the out-
side temperature, and the ability to run the mains anywhere re-
gardless of grades, thereby permitting the location of the power
house at a desirable location. This is often impossible with a
steam system unless pumps or other devices are installed to return
the condensation if it is desired to save it, or unless expensive
tunnels are built.

The disadvantages of this system are that it is necessary to
have an independent steam system if steam is required for other

* Extract from an article on " The Choice of Heating Equipment for Manufac-
turing Plants," by G. W. Stanton, in The Engineering Magazine.

154 Principles of Heating.

purposes (but as before stated, in ray mind this is a wise pro-
vision and one that conduces to economy in operation) ; that it
requires a greater amount of heating surface than a steam system,
and a consequent greater first cost ; that it requires greater engi-
neering ability or knowledge in design (this fact may be dis-
puted, but I know from personal experience that a great deal of
the prejudice against this system has been caused by the knowl-
edge of the unsuccessful operation of poorly designed hot water
systems) ; and that it demands more careful and better installa-
tion than the usual type of steam system, to prevent leaks and
consequent damage.

It also uses power for the operation of the circulating pumps,
but in this it is on a par with vacuum systems and (except in
small installations) smaller in its demands than hot-blast systems.

Owing to the circulation being forced, the pipe sizes can be
very much smaller than in any type of steam system ; where the
mains are long this is a distinct advantage. The radiation re-
quired is usually 12 per cent, in excess of that required for
vacuum steam systems, and 20 per cent, above that of gravity low-
pressure steam systems.

One of the great advantages of this system — and one that
deserves consideration — is the ability to control the temperature
in the buildings at the power house, besides the individual control
of the radiators or coils. That this means much will be con-
ceded when one considers the great variation in temperatures to
which residents in the climate of eastern North America are sub-
jected to. In New York City, for example, the temperature
during the heating season ranges from zero to 50 degrees and
even higher. As sufficient radiation must be installed to heat the
rooms to 70 degrees in zero weather, and as the average temper-
ature for the heating season in New York City is approximately
35 degrees, therefore with a steam system 100 per cent, more
capacity must be provided for heating than is normally required.
Of course, if proper attention could be given to a steam system
and the radiation were shut off when the temperature gets above
70 degrees, this excess use would not occur; but unfortunately
this close attention is rarely given where there are a great number
of radiators or coils, and besides it is so much easier to open a

Hot Water Heating by Forced Circulation.

155

window and let the surplus heat escape, and this is what is usually
done.

In the better class of buildings, thermostatic valves are in-
stalled on the heat sources, and these regulate the temperature of
the rooms by regulating the supply of steam to the radiators ; but
as such devices are an expense to install and expensive and
troublesome to maintain, their installation has been confined gen-
erally to the better classes of schools, office buildings, hotels and
public buildings, and where first cost is not the only con-
sideration.

It may be asserted that it is possible to obtain a degree of regu-
lation with steam by varying the pressure ; but the best results
obtainable by such a method depend on the use of high pressure
steam direct from the boiler, and even then it is not advisable to
use a greater pressure than 30 pounds in cast-iron radiators. This
would give an increase in the temperature of the steam from 212
degrees to 274 degrees, and if exhaust steam is used, would in-
volve the increase of the back pressure on the engines, which is
certainly inadvisable unless the engine be small or the engine load
light.

The hot water system is especially applicable to the heating of
many widely separated buildings supplied from a central power
plant, and where ventilation is required the fans are driven by
motors. If hot water is required for lavatory, domestic, or other
purposes, that would have to be furnished by a central hot water
lavatory system, the water for this system and also for the heating
system being heated by the exhaust steam from the power units
and all apparatus centralized in the power house.

This mode of heating has been installed to operate in connec-
tion with condensing engines and turbines, the vacuum on the
engines or turbines being reduced or increased to correspond to
the outdoor temperatures. For instance:

Temperature outdoors.

10
20
30
40
50

Degrees.

Vacuum in inches at engine.

10
16
20
24
26

156 Principles of Heating.

From the reports of the U. S. Weather Bureau* the following
table was compiled, giving the number of hours of different
degrees of temperature during a ten-hour working day and on
Sundays and holidays during an entire heating season of 200 days.

Outdoor
temperature,
degrees.

Hours of heating,
working
days.

Hours of heating,
nights, Sundays
and holidays.

0-10

10-20

220

20-30

320

675

30-40

465

1,124

40-50

400

920

50-60

260

270

Total hours
per

TABLE XLII.

68
315
995
1,589
1,320
530

1,545 3,272 4,817

The time of heating per working day is based on ten hours per
day during which exhaust steam is available ; during the re-
mainder of the time live steam would have to be used.

Where it is possible to operate the engines condensing, such a
combination is certainly most attractive and offers great possi-
bilities in saving of coal through the reduction of steam consump-
tion of the engines during the day, in the saving of live steam,
when exhaust steam is not available, by using only just enough
live steam to maintain the actual temperature required."

EVANS-ALMIRALL HOT WATER HEATING SYSTEM. f

"In this system, water is set in motion through a series of pipes
by means of a centrifugal or other pump and from the pump is
carried through an exhaust steam heater and if desired through
an economizer, and possibly in addition through a live steam
heater. Any combination of heating devices may be used as the
circumstances of any case require.

From the heating devices the water is circulated through mains
to the various radiators and from these is brought back in a
single return to the pump.

Any form of closed feed-water heater or condenser may be

* These temperatures and hours are taken from the report of the U. S. Weather
Bureau at Scranton, Pa., and are representative of a large section of the United States,
t Extracts from article in The Engineer, January 1, 1906.

Hot Water Heating by Forced Circulation.

used, the steam being sent through the tubes and the water cir-
culated around the outside of the tubes in the usual construction.
The heater may be inserted in the exhaust line of either a con-
densing or non-condensing plant and the condensed steam may be
returned to the boiler or allowed to go to waste as is most
economical.

By the series arrangement of exhaust heater, economizer and
live steam heater, it is possible to heat the water to any desired
degree of temperature, and by regulating the amount of live steam
used, there is no waste, as just sufficient live steam can be used to
produce the desired temperature. Exhaust and live steam are
never mixed, as the two heaters are entirely separate, so that live
steam can always be returned to the boiler without the use of any
purifying apparatus.

In the construction of the pipe system, since the flow is forced
by means of a circulating pump, the grade of the overflow and
return mains is a matter of no importance and can be made to suit
the convenience of the system.

Double- or single-pipe systems may be used, according to cir-
cumstances. In the double-pipe system, mains and returns are
carried to each radiator and circulation is effected from one sys-
tem to the other. In the single system, the water is passed
through one pipe which forms a loop from the pump to the dis-
trict to be heated and back again to the pump, connections being
made to various buildings or radiators by shunts to and from the
single pipe.

In underground construction, full-weight wrought-iron pipe
is used with screwed cast-iron fittings for service connections.
These fittings are provided with valves and enclosed in brick
boxes, so that they can be easily gotten at and new connections
can be made without disturbing the mains. Slip expansion joints
are provided to take care of the go and come in the pipe, and
these are also encased in brick boxes, anchors being provided by
means of wrought-iron bands and masonry so that the pipe is
forced to take up its expansion at the joints provided.

For covering the underground mains, Wykoff wood stave is
used.

The radiators are of the regular hot water type connected on

158 Principles of Heating.

the single-pipe system. The connections are from opposite ends
of the radiator with a down-feed riser, the radiator valve being
placed in the return connection.

In the system described it is stated that the entire system has
about 30,000 square feet of radiation and requires 12 horse-power
at the circulating pump. The temperature of the circulating
water is varied to suit conditions between 100 and 185 degrees and
at the same time no change in the back pressure on the engine is
ever produced. By the utilization of heat from the flue gases, a
considerable economy is effected. The piping is arranged so that
each particle of water travels the same distance from the time it
leaves the pipe till it returns, thus avoiding short-circuiting."

"The water is heated by exhaust steam from the engines,*
which passes through tubular heaters of a construction similar to
that used in the ordinary closed feed-water heater. They are so
connected to the exhaust piping that steam may be passed through
them singly or in series for moderate heating, or in multiple for
colder weather. Their construction and piping arrangements are
such that they may also be used for heating when the engines are
operated condensing, in which case the exhaust passes through
them before entering the condenser. The vacuum is then varied
in the condensing system to suit the outside temperature, the cir-
culating water in the heating system being maintained at a tem-
perature within ten degrees of that of the steam at the existing
vacuum.

The hot water is passed through the heating coils and radiators
in the buildings by the turbine-driven centrifugal pumps. One of
these units is operated continuously when heating is required.
The pumps are operated at a comparatively high pressure for this
service, inasmuch as the volume of flow is large and the distances
covered are comparatively great. The systems of heating coils
in the various buildings are connected in multiple or parallel.

The hot water may be passed through either heater singly,
through both in series, or through both in multiple. An auxiliary
live steam heater is provided for use in heating the circulation
to higher temperatures in case the exhaust steam is not sufficient

* Extract from an article in The Engineering Record, April 22, 1905.

Hot Water Heating by Forced Circulation.

in quantity or is unavailable ; this heater may be by-passed or cut
into the circulating line by handling three valves. An air trap is
set at the point where the line leaves the power house for freeing
the system of entrained air."

VOLUME OF WATER REQUIRED FOR HOT WATER HEATING SERVICE.*

"Each square foot of hot water radiation in the city zvill
require approximately one gallon of water per hour. It is very
certain that some plants are designed to supply less than this
amount, but in such cases it requires a higher temperature of the
circulating water and allows little chance for future expansion of
the plant. A drop of 20 degrees, i.e., 20 B.T.U. heat loss per
pound of water passing through the radiator, is probably a maxi-
mum and indicates the minimum amount of water that should be
circulated. In practice, this heat loss would probably be nearer
15 B.T.U. per pound, and consequently, would necessitate the use
of somewhat more than one gallon of water per square foot of
heating surface per hour. All things considered, the above itali-
cised statement will satisfy every condition. Having the total
number of square feet of radiation in the district, the total
amount of water circulated through the mains per hour can be
obtained, after which the size of the pumps in the power plant
may be estimated. . . .

The district is first chosen and the layout of the conduit sys-
tem is made. This is done independently of the sizes of the pipes.
When this layout is finally completed, the pipe sizes are roughly
calculated for all the important points in the system. .

In some cases, when close estimating is not required, it is
satisfactory to assume a velocity of the water and find the diam-
eter without considering the friction loss. In many cases, how-
ever, this would soon prove a positive loss to the company. With
a low velocity, the pipe would be large, the first cost would be
large, and the operating cost would be low. On the other hand,
if the velocity were high, the pipe would be small, the first cost
would be small, and the operating cost and depreciation would be
large. . . .

* Extract from " Handbook for Heating and Ventilating Engineers," by Prof.
J. D. Hoffman.

160 Principles of Heating.

It is found in plants that are in first-class operation that the
velocities range from 5 to 7 feet per second."

HOT WATER HEATING BY FORCED CIRCULATION.*

Hot Water vs. Steam for Mill Heating.

"Because of the exceptionally high specific heat of water, as
well as its relatively high specific gravity, it possesses special value
as a medium for the storage, as well as for the carriage of heat.
Also, because its rate of flow through heaters, either radiators or
circulation coils, can be closely regulated by a single valve, a water
system furnishes better means than a steam system for temper-
ature regulation. A system having 10,000 square feet of radiat-
ing surface will contain from seven to eight tons of water, and
a change of 30 degrees in the temperature of that water involves
the transfer of nearly 500,000 thermal units, or an hour's loss of
heat through 36,000 square feet of 1 8-inch brick wall in zero
weather. Water is thus to a heating system what a large fly-
wheel is to an engine. It stores up the surplus when a surplus
exists, and it carries over and yields that surplus when the supply
at the source drops or fails. By adding a storage tank of 250
cubic feet capacity for each 10,000 square feet of heating surface
used, the storage value of the water in the system may be doubled.

The cost of installing a hot water system must exceed thatvDf
an equivalent steam system, for the reason that radiating surfaces
must be larger and because power must be used for mechanically
circulating water. The power necessitates engines and pumps
and some small outlay for steam, the steam, however, not being
lost, as it may be turned to account in heating the water it circu-
lates. The engine and pump work also ultimately resolves itself
into heat, so that nothing is lost. The mechanical circulation of
water makes a rapid flow and use of small pipes practicable in
mains and branches. It eliminates the necessity of providing and
carefully maintaining such carefully made grades in pipe runs as
are essential to water flow in gravity work. Water may be sent

* Extracts from paper on " Warming and Ventilating of Mills," by Prof. S. H.
.Woodbridge, N. E. Cotton Mfg. Association, April 25, 1900.

Hot Water Heating by Forced Circulation. 161

in any and every course under the action of a centrifugal or
screw pump. In a paper prepared for the purpose of promoting
economy in methods and practice the plunger or piston direct
acting pump can be mentioned only to hold it up to condemnation.

The advantages of water over steam for heating work are in
a measure offset by the fact that power is essential to the circu-
lation of water, whereas steam, even at low pressure,, is auto-
mobile. For night or shut-down heating work beyond the ca-
pacity of the system's storage, a use of water necessitates the use
of power, though in small amount, approximating a range of from
500 to 1,500 foot-pounds per cubic foot of water circulated.

In the summing up for water as against steam it may be said :
First, that by its use the engine exhaust may be condensed and
the water heated without back pressure effects, the heater playing
to some extent, at times, the part of a condenser. Second, that
when required, as in extreme weather, the water so heated may be
further heated by live steam surfaces, either in the same or in
another steam heater or by a furnace heater. Third, that the
water within pipes and the storage tanks conserves heat by storing
it. Fourth, that the temperature of the entire body of water is
made perfectly controllable, either by hand or by automatic means.
Fifth, that room temperatures are made easily controllable by
regulating, by means of a single valve, the water flow through the
heaters within any room or apartment. Sixth, because of its heat
storage capacity, water can maintain mill temperatures after shut-
down as steam can not. If equal volumes of water and of steam
at 212 degrees be cooled to 32 degrees, the water yields 257 times
the heat yielded by steam. Seventh, that the heating action of
water is more steady, or less fluctuating than that of steam and
that by as much as the temperature of the water surface is lower
than that of steam, the quality of water heat is better than that
of steam. Water heating by forced circulation is cheaper than
steam only as waste may be conserved and made usable. In the
initial cost and maintenance of the plant the water is slightly the
more expensive of the two. A water plant is wholly unsuited
to large mill work in which heating is required when power is not
available."

162 Principles of Heating.

HOT WATER HEATING IN THE SOUTH STATION, BOSTON.*

"Hot water was chosen for the circulating medium only after
a thorough study of the possibilities and limitations in the use of
both steam and hot water. This made it evident that a hot water
circulating system in the form of a loop with return mains in
transverse subway not only overcame all physical difficulties en-
countered in the problem of distribution, but under the rather
unusual conditions which surrounded the heating plant, was
superior in every respect. The rapid circulation secured by the
use of pumps made all points in the system equally accessible and
easy to heat. The amount of water necessary to supply the heat
required could be conveyed in a flow main no larger than 8 inches
in diameter, and without difficulty due to unavoidable pockets at
certain points, notably at the main suburban exit.

Owing to the storage value of the large body of water con-
tained in the system, the surplus of waste steam at periods of
heavy load could be absorbed, within limits, for use when there
might be a deficiency of exhaust at times to reduction of load, and
be utilized to a greater extent than possible by other methods.
Furthermore, while all heating apparatus must be adequate for
the severest weather conditions, the hot water system possessed
the considerable advantage of being capable of operating at low-
ered temperatures corresponding to mild or moderate weather,
thus preventing waste and discomfort from overheating and un-
due radiation and leakage losses.

The water is circulated by one of two 8-inch centrifugal
pumps, each driven at a speed of about 375 revolutions per minute
by an 8^2 by 8 Westinghouse standard engine. The water
reaches the pump suctions through the 8-inch return main, by
way of transverse subway, and is delivered to the supply side of
the system after becoming heated to a suitable temperature in a
central heating plant located near the circulating pumps in the
power house. This consists of three specially designed heaters,
two being for exhaust and a third and smaller one for the use
of live steam whenever there may be an insufficient supply of

* Extract from paper by Walter C. Kerr, A. S. M. E., Dec., 1899.

Hot Water Heating by Forced Circulation.

exhaust. Two exhaust heaters were used largely because of the
inexpediency of installing a single heater of large dimensions,
and partly on account of the advantage of having the principal
part of the heating plant in duplicate. There was also advantage
in regulation, by subdivision. The exhaust steam heaters are
capable of condensing 24,000 pounds, and the live-steam heater
approximately 18,000 pounds steam per hour, live steam being
admitted to the heater only to supply deficiency, the quantity
being regulated by an automatic thermostat valve.

The heated water passes from the central heating plant into
the flow main and to the exterior circuit, which forms a loop over
five-eighths o>f a mile in length. This entire system, in which there
is necessarily a large amount of expansion and contraction, con-
tains no expansion joints, the design of the piping and the free
use of long radius pipe bends permitting the strains due to expan-
sion to be taken up without imposing undue stress on fiber or
joint. All turns in the flow and return mains were made by
these bends, no elbows being used, thus materially reducing the
circulating head, which would otherwise have been excessive ex-
cept where larger and more expensive mains were provided. The
engineering problem involved in the proper design, support, and
anchoring of these hot water mains was not the least interesting
of the several somewhat unusual features of the work. In this
connection, it is interesting to note that the actual circulating
head proved to be within 2 per cent, of the estimated amount."

HOT WATER HEATING FOR MILLS.*

"In order to obtain satisfactory results with the hot water or
forced circulating system, the speed of the water through the
circulating pipes must be high to prevent any too sluggish move-
ment in the shunts or isolated coils that offer a little more fric-
tional resistance than the direct lines. The temperature should
also not be allowed to fall very much during its passage through
the entire system to secure uniform efficiency throughout. In
ordinarily cool weather it should be sent out as warm as 200
degrees F., and returned at not less than 150 degrees F.

" Extract from a paper by A. G. Hosmer, presented before the National Associa-
tion of Cotton Manufacturers, in 1908.

164 Principles of Heating.

In some plants this system has been installed with a view of
utilizing the heat of the exhaust steam from condensing engines
on its way to the condenser, by placing a heater between and run-
ning the engines with a vacuum more or less reduced. If, as has
been mentioned, the temperature of the outgoing water should
be about 200 degrees F. and that entering the heater 150 degrees
F., 'it is evident that to enable it to absorb any heat from the
exhaust, the vacuum would have to be adjusted to make the tem-
perature of said exhaust somewhat above 150 degrees, or at least
160 degrees F. ; this corresponds to a vacuum of about 20 inches,
or 5 pounds, absolute pressure. At a temperature of 180 degrees
F. we have only 12 inches, and at 200 degrees F., 6 inches, or a
little less than one-fourth of the usual efficiency of the condenser.
The choice is offered then to run either a low vacuum and sacri-
fice a portion of the benefit derived from the condenser, or to add
live steam in a secondary heater to make up for what the low-
pressure steam cannot do.

For efficient results with this method of heating the water
while passing through the exhaust chamber, the size of engines
and capacity or requirements of the circulating system should be
so proportioned that the passing water will absorb the entire
amount of available heat in the exhaust steam. To illustrate, sup-
pose the engines are running with a vacuum of 12 inches to give
the exhaust a temperature of about 180 degrees F. ; our circu-
lating water enters the heater at 150 degrees F., thus we have
30 degrees F. available. If the quantity of water exposed in the
heater is sufficient to absorb all the heat passing in the exhaust
(that is, heat above 150 degrees F.), all is well, but as the tem-
perature of this heating medium is governed wholly by the con-
dition of the vacuum, regardless of the quantity of exhaust going
by, any excess will pass through without giving up its available
heat, and the impaired vacuum will have to be made up by steam
from the boilers, for a part of which there will be no return. In
other words, enough extra heat in form of boiler steam will have
to be added to raise the mean effective pressure to the point it
would be with regular conditions in condenser, and as a return
only what heat has been absorbed by the circulating water will be
received.

Hot Water Heating by Forced Circulation. I^^

Every 2.04 inches taken from the vacuum decreases the mean
effective pressure I pound. It will be remembered that the
back pressure or vacuum, as the condition on the discharge side
of an engine may be called, applies to the entire length of stroke
the same as mean effective pressure. It is therefore evident that
the raising or lowering of this pressure, even a few pounds, on
a large engine cylinder means quite a serious difference in the
important work done by the condenser and the power output of
the engine.

If the quantity of exhaust steam is insufficient at times, care
must be taken to avoid lowering the vacuum too much, as it will
spoil regulation, and complicate things generally, especially with
compound engines. The line between waste and economy in this
proposition is so finely drawn that to use the minimum temper-
ature of the exhaust with also the minimum amount of direct
steam and realize the best conditions, the adjustments should be
wached very closely.

In installations where the engines and condenser systems are
not considered and direct steam used entirely, the heaters are
usually placed in the boiler house enough above the water line of
boilers to insure a gravity return for the condensation. Pro-
vision must, of course, be made for operating the circulating
pump at night and during holidays and Sundays. In nearly all
equipments of this kind a supplementary heater or section of one
of the heaters is used for the exhaust from the pump engine or
turbine.

The most severe duty on the system comes when the plant is
shut down, particularly early mornings. At such times the water
must be used at the maximum temperature, and as the exhaust
from engine is not over 210 degrees F., unless back pressure is
made use of, the steam will pass by the water coils, transferring
little or no heat to them. In places where condensing water is
available it is sometimes better to install a small condenser for
the pump engine and to do away with the inefficient exhaust
heater.

The circulating system is sometimes connected with the econo-
mizers to use the waste heat passing to chimney during non-
running hours. While the theory of this is excellent, in practice

1 66 Principles of Heating.

it is hardly ever desirable, for the reason that the economizers
during working hours are handling water quite hot and at a high
pressure, and if cooler water at a much lower pressure is intro-
duced it contracts the joints and produces a change in conditions
which usually develops more or less serious leaks and perhaps
the loss of a gasket when the high pressure is again admitted.
The repairing of economizer joints is not a pleasant task, to say
nothing of the trouble and expense of having the machine out of
commission when needed.

This system cannot be hurried to any extent, and it is conse-
quently advisable to avoid letting a building cool down very much
during cold weather by running the circulation continually. In
this respect a direct-heating system using steam has a material
advantage, as it is seldom needed until a few hours before starting
time and rarely through the entire day.

In case of accidents to the machinery driving the pump a bad
feature presents itself, as it is necessary to use steam in the circu-
lating pipes instead of water. This is almost sure to cause trouble
'f the pockets or drops in the lines are not properly drained, as
the entrapped condensation will cause hammering with innumer-
able leaks and frequently split some large fitting. Particular at-
tention should be always given to installations of this kind to
arrange the pipes with the same pitch and draining facilities that
would be required if high-pressure steam was used."

STEAM VS. HOT WATER FOR CENTRAL HEATING SYSTEMS.
(The Author.)

While a number of features incident to the system of hot
water heating by forced circulation favor its adoption in certain
cases, there are features in connection with steam heating systems,
especially the vacuum system, which commend themselves and
which are peculiarly valuable in the overhauling of old plants and
the substitution of a better system. As a rule old buildings are
provided with steam radiators, viz., those having the loops nipple-
connected at the bottom only. Radiators of this type are not
adapted to hot water heating. On the other hand hot water type

Hot Water Heating by Forced Circulation. ^y

radiators, viz., those with loops connected both top and bottom,
are well adapted to steam heating.

With this system the steam, either live or exhaust, is delivered
directly to the radiators, there condensed and the water of con-
densation discharged directly to the sewer through cooling coils
in the basement or returned to the power house to be again evap-
orated in the boilers. Where no back-pressure is permissible or
where the runs are long and trenching must be shallow, the two-
pipe vacuum system may be used. With this system the con-
densation may be lifted if necessary.

Practically no pressure is carried in the radiators, whereas
with the hot water system a heavy pressure is not uncommon.

Repairs are easily made to a steam heating system.

Although the supply lines may be made smaller in forced hot
water systems than in steam systems, the returns in connection
with the latter, especially with vacuum systems, may be made very
much smaller than the returns from a hot water system. The
mains, both supply and return, must be of the same size where
they leave and enter the power house in hot water systems.

A single hand control valve is the only one necessary on each
radiator with either the hot water or vacuum steam systems.

The automatic return valve in the latter takes the place of the
air valve commonly used on radiators heated by hot water; the
automatic return valve mentioned serves both as an air valve and
a condensation remover.

It is in the power house that the simplicity of the steam system
is apparent, as here the pressure reducing valve takes the place
of the exhaust and live steam heaters used with the hot water
system, and a steam-driven vacuum pump, with relatively small
pipe connections, takes the place of the centrifugal pump driven
by an engine or motor.

A quicker change in heating effect can be secured with steam
than with hot water. Steam may be shut off for hours at a time
during sunny days when the outside temperature runs up and in
mills and plants not operated Sundays the heat may be shut off
a greater number of hours than in the case of hot water owing
to the longer time required to reheat the building after a shutting
off of heat than in the case of steam.

1 68 Principles of Heating.

With the vacuum system a partial heating of radiators may
be secured in mild weather, each occupant having control of his
room temperature. With hot water the temperature at which the
water is delivered from the heaters in the power house is regu-
lated by hand according to the weather, based on a chart giving
water temperatures necessary to meet given weather conditions.

By this method it is necessary to send the water out at a tem-
perature high enough to heat the most remote points and the
most exposed rooms. Since the water loses temperature con-
stantly from the time it leaves the power house, in the case of
very long runs the buildings near the power house are likely to
be overheated unless this effect is compensated for by allotting
radiators more liberally at remote points.

With vacuum *steam heating the radiator temperatures are the
same in all buildings regardless of the distance from the power
house.

In the case of old buildings heated by independent hot water
heaters, if for any reason it is desired to continue to use water
as a heating medium, tubular heaters may be placed in the base-
ment and supplied by steam, thus heating the water.

As to using eduction water from condensers for hot water
heating, since the temperature of this water is, say, 100 to no
degrees or thereabouts, and must come back to the power house
20 degrees or so cooler, in order that the system shall be at all
efficient it is evident that the low temperature of the radiators
under these conditions limits the use of this method to mild
weather conditions, unless the radiating surface be made inordi-
nately large in proportion to the space heated. As the weather
becomes colder heating by condenser water must be abandoned
and the water be heated by live steam, assuming that the plant
continues to run condensing, otherwise, if run non-condensing,
the exhaust steam may be utilized.

In hot water systems where the heating is not continuous,
there is a considerable loss due to the cooling of the large volume
of water in pipes, radiators and heaters when heat is no longer
wanted. ^

Danger of damage from freezing is of course much greater
in hot water systems than with steam. The first cost of a steam
heating system is as a rule considerably less than for hot water.

CHAPTER XI.

CENTRAL STEAM HEATING PLANTS AND MILL
HEATING.

. . This chapter is devoted to the gist of a number of reports
and articles on central steam heating plants. The reader is
referred to the last article in the preceding chapter, which article
relates to this chapter as well.

CENTRAL STEAM HEATING PLANTS.*

What to do with his exhaust steam is a question for the man-
ager to decide. Which is best : to install condensers and thereby
increase the efficiency of the engines 20 per cent, or more, and the
capacity as well, or to sell this by-product as it is, in the form of
heat? If the rates obtainable are fair, that is, if the heat can be
sold nearly on a live steam basis, the plant should receive from the
latter course at least three-quarters of the original value of the
steam ; while a condensing outfit would save but one-quarter to
one-third of its value. If water for condensing is not available
the argument for district heating is strengthened. Very many
plants have short and sharp winter peak loads; and it would
seem that under such conditions, their managers might be war-
ranted in installing some inexpensive, simple, non-condensing
engines, the exhaust from which would be well utilized for heat-
ing purposes, or it might even prove to be best, under proper
conditions of load and fuel costs, to install condensing apparatus
which would be run during the summer, but which in the heating
season would be cut out, the exhaust steam then being utilized on
the heating system. The use of the exhaust steam for heating
will necessitate the carrying of some back pressure on the engines,
thereby reducing both capacity and efficiency, a point not to be
lost sight of.

* Extracts from Report of Committee on District Heating, National Electric Light
Association, Denver, 1905.

169

170 Principles of Heating.

Before making the investment, the manager desires to know
what income he may expect and how many square feet of radia-
tion his exhaust steam will care for. Knowing the pounds of
water per horse-power per hour consumed by his engines, and
referring to his load curve of the previous winter, he can readily
figure the minimum amount of exhaust steam that can be counted
on for any single hour, and this should be the basis of his figures.
Now come certain deductions : feed-water heaters and station
leakage will probably take 15 per cent., while losses in mains and
services may be as much more, though on the latter point we can
cite one plant where the losses are less than 3 per cent.

The returns that we get from steam heating plants indicate
that it is safe to figure for ordinary conditions about .20 pound of
water per hour per square foot of radiation (varying from .05
to .50). As all the consumers are not using the steam at the same
time, particularly if on a meter basis, the load factor should be no
more neglected than in the lighting business. Naturally, with the
heating business it is higher; and if we use the figure of 85 per
cent, we shall probably be on the safe side.

Together with the above must be figured the interest charges
on the total underground installation and that portion of the cen-
tral station plant which is used for heating purposes; and lastly,
depreciation — an item that is often neglected but which should
nevertheless be estimated. From the best evidence at hand the
last item seems to be about 5 per cent, per annum on the total cost
of the investment.

It is a well-recognized fact that a district heating system has
often enabled a company to secure contracts for light and power
which it would not otherwise have obtained. These then produce
an increase in load, which in turn supplies more exhaust steam
to sell for heat.

Though it is generally considered good practice to limit the
heating business to that which can be taken care of by the exhaust
steam, in many cases live steam has to be supplied at certain times
in order to give good service. Where this condition exists and the
demand on the live steam increases, it soon becomes necessary to
set aside or to install a boiler solely for this purpose. Then comes
the turning point of the plant. The chances are that it is selling

Central Steam Heating Plants and Mill Heating Iji

live steam on an exhaust steam basis, and it soon becomes evident,
if the question is investigated, that there is no profit in the busi-
ness. This condition of affairs has occurred repeatedly and in
many cases has both cut down the net earnings of the company
and given the heating business a bad name.

The lower the load factor of the plant, the less the induce-
ment to undertake the heating business. In general, a railway
plant is better adapted to care for district heating with its exhaust
than is a simple lighting plant. As railway plants are generally
located on the outskirts or in the country, the heating business
may be considered as belonging more especially to lighting com-
panies, and must usually be cared for by them.

While it is true that the demand for heat comes at about the
same time of the year as does the demand for light, yet it is also
true that it may not come at the same time of the day that the
plant is producing its maximum amount of exhaust steam; in
other words, the lighting peak and the heating peak may not be
coincident, and, in fact, there is no reason why they should be.

So long as the demand does not exceed the supply of exhaust
steam, but follows it closely, and the rates are kept up, the plant
is in a fair way to make money, but any plant that undertakes to
sell live steam on an exhaust steam basic is doomed to failure. . . .

Following is a summary of the information collected ; it is
divided into three groups ; data are from metered customers :

TABLE XLIII.

KECORD Or STEAM REQUIREMENTS IN CENTRAL HEATING.

Class of
Service.
Residences ..
Residences . .
Residences ..
Stores . .

Conden
of

Av.
. . 3.83
. . 2.49
. . 1.69
. . 4 48

sation per sq. ft.
radiation
per day.
Max. Min.
5.20 1.79
2.49 2.49
3.22 0.54
10.1 1.01
4.03 1.18
3.77 0.64
3.4 1.8
7.94 2.13
3.70 1.73
1.83 1.19
3.62 0.89
3.8 1.8

Condensation per 1,000 Ratio
cu. ft. of space heated cu. ft. space Av.
per day. to sq. ft. Temp.
Av. Max. Min. radiation. F.
51.3 75.2 27.4 76 34°
34.6 34.6 34.6 72 44°

29.0
17.1

50.2
37.0

11.4
9.2

115
181

34°
44°

40.5°
34°
44°
43.5°

40.5°

Stores

. 2 61

Stores
Stores .

.. 1.94
2 32

20.0
51.5
25.1
26.0

29.0

28.5
78.0
32.2
30.4

49.7

13.6
24.9
19.7
19.8

14.9

136
81
120
60

111

Offices

5 02

Offices

2 92

Offices

1 56

Offices

2 27

Offices .

. 2.97

NOTE. — While there is a large variation between maximum and minimum, it was
found when making the tabulation that most of the figures ran very close to the
averages given above.

172 Principles of Heating.

CENTRAL POWER AND HEATING PLANT FOR GOVERNMENT
BUILDINGS.*

This report deals with the problem of a central station for
thirteen existing and projected government buildings on the Mall
and in the vicinity of the White House. The report states : An
examination of the several items of unavoidable costs, as also
those of possible profit, in the erection and operation of a central
plant, led Professor Woodbridge to decide that in order to secure
the largest profit, the ^station should furnish the largest service.

The economies possible under any scheme for installing and
operating either a power or a heating central station plant, and
the retention of the other in the buildings, would be so seri-
ously narrowed as to make the grounds for advocating such
a plant far less tenable than are those found to exist in sup-
port of a central plant which ohall unite the two divisions of the
work. Any such partial treatment of the problem would result,
in Professor Woodbridge's opinion, in a costly increase of steam
generating plants, including emergency reserves, however the
division might be made ; in large increased cost in generators and
other equipment, if these are segregated, and in an unreduced
pay roll under any divided arrangement. The losses which neces-
sarily would be entailed are those due to failure to secure from
one division of the service the economic advantages it would con-
tribute to the other, and also those due to the absence of the
effective organization and vigilant surveillance which are far more
easily obtainable in an aggregated than in a segregated plant.
Little, if any, usable space would be gained within buildings; the
nuisance of dirt and smoke and heat would be but little abated ;
and the high cost of smokeless coal would make against economy,
whatever the division, and the waste attending low efficiency in
engine work would be continued and increased by an extension
of the system, and the heat of engine-exhaust steam' would be
but partially utilized, or wholly lost, if the segregation were on
the side of power. . . .

* Extracts as reprinted in the Engineering Record, Feb. 11, 1905, from a report
by Professor S. H. Woodbridge, dated Jan. 7, 1905, transmitted to Congress through
Bernard R. Green, Superintendent Library Buildings and Grounds.

Central Steam Heating Plants and Mill Heating

The required maximum power and heating capacities of a cen-
tral station were computed from data furnished from records and
logs obtained from the superintendents, custodians, or engineers
of those buldings by means of season aggregates, and the daily
average.

The power of the proposed combined plant for the above
group of buildings is made less than that of the total equipment
for segregated plants in the same buildings ; first, because of the
higher steaming efficiency practically obtainable in the boilers of
a highly organized and skillfully operated power plant ; and sec-
ond, for the reason that the isolated plants must each be given a
generous factor of safety for performing occasional exception-
ally heavy duty as well as providing against breakdown and other
emergencies. The serving of the executive group of buildings
from one common plant would remove the necessity of furnishing
a surplus of power and equipment equal to performing such
duties or to meeting such emergencies in all of the buildings at one
and the same time. Because of that fact, a substantial reduction
in the steam generating plant of a central station may be safely
made, Professor Woodbridge states. In place of the present 73
boilers in twenty or more isolated stations, aggregating some
4,500 horse-power, a central station equipment, which shall in-
clude boilers for the three additional and large buildings, may not
contain more than ten boilers of 400 horse-power each, all in one
boiler room. On an emergency, high efficiency boilers having a
nominal capacity of 4,000 horse-power could be 'easily forced to
a 6,000 horse-power steam output. . . .

The usual and required emergency equipment for the aggre-
gated plant should have reference to excessive loads of short
duration, or to temporary disablement of apparatus which may
be quickly restored to service. These occasions must be provided
for by reserve or emergency equipment, if the performance of
the plant is to satisfy a reasonable demand. In the matter of
light and power, that equipment may be either in boilers, engines,
and generators, to create and furnish emergency power or de-
mand, or else, with a more equal work of boilers and engines in
the storing of electrical energy unused during the long periods of
light load, and made available for use in the shorter " peak "

174 Principles of Heating.

periods of high loads or at times of accident or other emergency.
The cost of emergency or accident equipment by the reservoir
method is approximately the same as that for the generating
method of equal capacity, and the cost of maintenance is some-
what greater in the former than in the latter. The economic gain
in operating costs by storage methods is chiefly on the side of
reduced fuel consumption. Roughly the capacity of a plant for
generating emergency or " peak " power on demand must, in this
instance, be approximately 40 per cent, in excess of that of a
plant capable of the same work by a stored electrical supply. The
usual practice of continuously maintaining full steam pressure in
all power boilers, even in summer time, in order to be prepared
for a suddenly darkened sky or other emergency, is so productive
of fuel waste and of service expense as to warrant the installation
and use of a storage plant which shall reduce by 40 per cent, the
capacity of the generating equipment, lessen the summer coal
consumption, and curtail the expenses of labor service by making
night attendants for boilers and engines unnecessary during the
summer months. To the advantages named must be added the
further important function of the storage battery already noticed,
viz., that of evening the work of boilers and of fires and of reduc-
ing and removing the causes which tend to produce smoke.

The hourly maximum heat required for warming and venti-
lating the executive group of buildings during the periods of ex-
treme weather is considerably reduced, Professor Woodbridge
points out, by the massiveness and the high specific heat of
which the buildings are constructed. Such material in such mass
in itself stores large heat quantities, which it partially yields to
contained air whenever the temperature of that air falls even a
little below the temperature of the material. Such storing and
yielding of heat in buildings of monumental character make un-
necessary that provision in the power of the heating system which
is requisite in lightly constructed buildings for maintaining an
even internal temperature during short and sharp depressions of
outside temperature. . . » -

Weather temperature changes take place with such relatively
gradual movement and with such premonitory warnings, that fires
can easily be built, forced, banked, or drawn to meet requirements,

Central Steam Heating Plants and Mill Heating

as cannot be done on either the electric side in lighting, to meet the
quick darkening of the sky or winter daily calls, morning and
afternoon, for light ; or in office fan work with the dying out of
summer breezes, or the quick rise of oppressive humidity or the
shifting of heating sunshine from one already heated side of the
building to heat the other ; or, on the power side, to meet the peak
elevator work, as four times a day thousands crowd the elevator
service. . ,l ' .- '.;

Low pressure live steam for heat transmission is economically
disadvantageous on account of the larger costs of piping material,
of trenches, and of insulation, and because of the large loss of
heat in exhaust steam, which, under such conditions, would prob-
ably be thrown to waste. High pressure steam service is superior
to low only on the score of lower first cost of pipe installation, and
a somewhat lower rate of heat loss, the small pipe surface more
than offsetting its greater per-unit-of-service rate of heat loss.

The heat quantities lost by steam piping when properly pro-
tected from ground and atmospheric moisture, and when thor-
oughly insulated with the best non-conducting material, is shown
in the table for pipes of equal length and for the 'various sizes
indicated, and when supplied with steam at the initial pressure,
the steam dropping to atmospheric pressure at the delivery ends.
The heat losses are expressed in thermal units per hour, and are
probably the lowest economically obtainable by the best practic-
able protection and insulation, as hereinafter described. The
length of pipe is one-fourth mile ; the steam quantity passing into
pipes for transmission is 150 pounds per minute, a pressure drop-
ping from the initial given to atmospheric at the delivery ends.

TABLE XLIV.

HEAT LOSSES IN ONE-FOURTH MILE OP PROTECTED STEAM PIPE.

Size.
4-inch pipe

Initial
pressure, Ibs.
to square in.
45 00

Heat losses
per Hr.
B. T. U.
81 600

5-inch pipe

25 00

94 200

6-inch pipe

10 80

101 900

7-inch pipe

6 00

113 300

8-inch pipe

3 70

126 000

9-inch pipe

1 50

138 100

10-inch pipe. .

1.00 •

152.500

176 Principles of Heating.

The table makes evident the economic advantage of high
pressure over low in the single matter of relative heat wastes from
small and large pipes and is in itself an argument against the use
of low steam pressures in large distributing pipes.

The cost of maintenance of high pressure pipe lines would,
however, prove larger than that for low pressure pipes, because
of expansion strains, and also on account of the higher temper-
atures and humidities of trench spaces, which would tend to a
deleterious condensation of moisture on and to a rusting of the
cooler return piping, both of which processes would be more
active than if pressure and temperatures were low. . . .

Water may be driven through pipes at any advantageous speed
by centrifugal pumps and at a negligible cost, since all the heat
of the steam used in driving of pumps to impel water motion may
be given to the water moved, and the energy of water motion
itself is finally transformed into heat within the water. Further-
more, the heat yielded or conveyed by a cubic foot of water when
its temperature is dropped through 30 degrees F. is largely in
excess of that yielded or conveyed by a cubic foot of steam, even
at very high pressure.

Water pipes have one distinctive and important advantage
over steam pipes, since the pressures to which the water pipes are
subjected are nearly constant, and for the larger pipes those pres-
sures are relatively low. Strains are therefore light and but
slightly variable.

In the matter of durability, under favorable conditions water
piping may outlast steam piping. If the system is reasonably tight
and the same body of water is continuously used the free oxygen
in the water supply having been once expelled or exhausted, in-
ternal corrosion is arrested, and the piping will then last indefi-
nitely. The temperature of supply and return mains are so nearly
the same that condensation on the external surface of the cooler
pipe is retarded, if not prevented, and external corrosion due to
that cause is correspondingly prevented and a long life of the
piping is equally insured. Furthermore, the temperature of the
pipe line is low and the heat loss is proportionately reduced. The
necessity of doubling the pipe surface, by running both supply and
return pipes of the same size, brings up the total loss for the same

Central Steam Heating Plants and Mill Heating jyy

heat transmission to nearly that of high pressure steam piping
and of its condensation return piping.

The accompanying table gives the heat losses in thermal units
per hour from single water pipes of the sizes given, one-fourth
mile long, and containing water at a temperature of 150 degrees,
and when the pipes are in parallel, and insulated and protected
against moisture in the very best manner practicable, the mean
temperature of earth about the trench being 50 degrees F.

TABLE XLV.

HEAT LOSSES IN ONE-FOURTH MILE OF HOT WATER PIPE.

Water Heat Losses

Pipe sizes. Temperature. B. T. U., prr hr.

4-inch 150° 48,100

5-inch 150° 57,200

7-inch 150° 65,800

8-inch 150° 71,400

9-inch 150° 83,300

10-inch 150° 93,000

The use of water makes continuity in gradient lines unneces-
sary, avoids the use of trench traps, and reduces the number of
expansion joints required, so favoring minimum costs in con-
struction, in waste, and in maintenance. Furthermore, some of
the largest buildings are at present equipped with hot water heat-
ing systems, making the cost of change to adapt them to a central
plant relativeiy small. For these reasons of major and minor
economies the preference is therefore given to water as the most
appropriate vehicle for heat conveyance.

The pressures required to distribute water through a pipe sys-
tem one-fourth mile in length and in sufficient quantity when
cooled 30 degrees to convey per minute the heat equivalent to 150
pounds of steam at atmospheric pressure and condensed to 212
degrees, are shown in the following table :

TABLE XLVI.

PRESSURE REQUIRED TO DISTRIBUTE WATER THROUGH ONE-FORTH MILE OF PIPE.

Water v

Pressure

Pipe Volume,

sizes. Steam.* gal

4-inch 45.0 606

5-inch 25.0 606

6-inch 10.8 606

7-inch 6.0 606

8-inch 3.7 606

9-inch 1.5 606

10-inch 1.0 606

* Initial pressure per square inch.

178 Principles of Heating.

The two essentials to an economical transmission of heat
through long pipe-line distances are: First, such rapidity of
travel of the thermal vehicle through the channels that time for
leakage of heat from each unit of volume or of weight of that
vehicle shall be short: second, such insulation of the pipe sur-
faces that the rate of heat leakage from each unit of pipe surface
shall be small. Swift flow and small leakage are both favored by
a use of the smallest pipes practicable. Such pipes have already
been noted as possessing other economic advantages.

Defectiveness of insulating material and in methods of its
application are responsible for the excessive losses which attend
much of present heat distribution from central stations. In scores
of cases on record the mean of such loss reaches from 15 per cent,
at the lowest to 33 per cent, at the highest of the total heat passing
into interred pipe systems. These high losses are partly due,
however, to the large number of branch connections made with
buildings along the entire lines of pipe lines, and also to a prob-
ably inferior manner in insulating and protecting such branches
against heat loss.

For the purpose of reducing the first cost of installation and
also the after cost of heat loss from pipes, the pipe plan is pro-
portioned for a working pressure difference between the feed and
discharge sides of the centrifugal pump of 200 feet hydraulic
head, or 100 feet propulsion and 100 feet suction. Such a drop of
pressure on the suction side of the pump is made practicable be-
cause of the hydrostatic head of 122 feet to which the circulating
system would be subjected, due to the height of the fourth floor
of the State, War and Navy Buildings. Such static pressure
would utilize the suction effect of the pump, and with pump work-
ing on the cooler side of the heater, would prevent any liability of
a vapor break in the water.

It is further advised that the water be circulated in such man-
ner that in the coldest weather it shall lose not more than 30
degrees in temperature in complete circuit, and the ratio of the
length of time the water may be retained in the buildings to that
it shall be in traversing the pipes shall be made as large as prac-
ticable.

Central Steam Heating Plants and Mill Heating

DATA ON CENTRAL STATION HEATING.*

A valuable lot of information concerning the proportions and
operation of central station heating is contained in Bulletin 373
of the United States Geological Survey. The pamphlet is a dis-
cussion of smokeless combustion in boiler plants, written by D. T.
Randall and H. W. Weeks, but the last ten or fifteen pages are
devoted to central station heating on account of its relation to
smoke abatement in substituting a central heating station for
numerous individual heating plants. . . .

The plants range in size from 300 to 16,000 horse-power,
though only 25 per cent, are of 600 horse-power or less. Sixteen
of the plants have mechanical stokers. The price of coal ranges
from $4.60 per short ton in Montana to 90 cents in Illinois, the
average cost from all plants being $2.05 per short ton. Both
direct and indirect radiation are used, but by far the greater pro-
portion is direct. The greatest distance to which heat is sent
from the station varies considerably, but a reasonable distance
seems to be about 4,000 to 5,000 feet.

Payment for the use of steam is made in two ways: (i) At
a flat rate, based on square feet of radiating surface installed or
on 1,000 cubic feet of contents heated, or (2) at a meter rate,
based on 1,000 pounds of condensed steam. The price paid per
square foot of radiating surface averages 33^ cents and varied
from 22*/2 cents to 65 cents. The plants selling on a basis of
1,000 cubic feet of contents charge an average of $4.46, the price
varying from $2 to $6. On the basis of 1,000 pounds of
condensed steam the payments average 50^2 cents, ranging from
40 cents to 66 cents. One plant that sold heat on this basis of
40 cents intimated that such a rate was not profitable.

The hot water plants sold heat only on a basis of square feet
of radiating surface installed, the average rate being 1^/2 cents,
and the range from i2l/2 cents to 25 cents per square foot. Two
plants, one selling at 12^2 cents and the other at 15^2 cents,
claimed that their prices were too low for successful operation.

A comparison of the prices charged by central stations, as

* Extract from an article published in The Metal Worker, Sept. 4, 1909.

1 80 Principles of Heating.

compared with the cost of fuel only for a house heating
boiler, as published in bulletin 366, shows that in many cases
the cost of producing heat on the premises equals the price
charged by the central station. When heat is purchased the
customer avoids the annoyance of having to supervise the opera-
tion of the heating plant, as well as the dust resulting from the
delivery of fuel and the removal of ashes. Some allowance should
also be made for the space that would be occupied by the heater
and for the expense necessary to install and keep a boiler in repair.

The following suggestions have been made by the managers of
the plants and are worthy of consideration:

Heat from a central plant should be, as largely as possible, a
secondary product.

Heating mains should be concentrated and should not extend
too far from the station.

Direct radiation should be installed.

Mains should be of sufficient size to avoid the necessity of
high pressure at the station.

Heat should be under automatic control.

The flat rate is not- a successful basis for payment; the ser-
vice should be metered.

The costs for coal are for short tons. Many of the plants sup-
plied have very little indirect radiation, and many of them none
at all.

EXHAUST STEAM FOR HEATING PURPOSES.*

Amount of Heat in the Exhaust Steam.

" The number of British thermal units exhausted in the steam
in any case is equal to the total heat in the steam at the admission
to the engine, minus the heat radiated from the cylinder of the
engine and also minus the amount of heat absorbed in the actual
work done in the steam engine cylinder. Professor Hoffman
investigated four different cases.

Case i comprehended a boiler pressure of 100 pounds gauge ;
pressure at the cylinder 97 pounds gauge; quality of steam at

* Notes based on a paper by Professor J. D. Hoffman, read before the National
District Heating Association, Toledo. — Metal Worker, June 4, 1910.

Central Steam Heating Plants and Mill Heating I^I

cylinder 98 per cent. ; steam consumption 34 pounds per indicated
horse-power per hour; I per cent, loss in radiation from the
cylinder, and exhaust pressure 2 pounds gauge. The total heat
in the steam is of course found by multiplying the latent heat at
the boiler pressure by the quality of the steam; that is, taking
into account such moisture as may be in entrainment in the steam
and adding to this product the heat of the liquid ; that is, the num-
ber of heat units required to raise the water from some standard,
like 32 degrees to the boiling point. In Case i, multiplying the
total heat of the steam by 34 gives the total supply of heat avail-
able to the engine of 39,793 B. T. U. Taking into account that
i per cent, of the heat is radiated from the engine cylinder, leaves
39,395 B. T. U. available for useful work. One horse-power
mechanical work maintained one hour is equivalent to 2,545
B. T. U., so that the amount of heat given into the exhaust per
horse-power per hour is 36,850 B. T. U. As compared with the
total amount of heat in steam at 2 pounds' pressure the heat given
to the exhaust from the steam engine is only 94 per cent, of the
amount of heat in the saturated steam at 2 pounds' gauge.

For the second case he assumed an engine receiving steam at
125 pounds' gauge boiler pressure, with the steam at 122 pounds
at the engine. The steam consumption was taken at 22 pounds per
indicated horse-power per hour ; in other respects the data were
the same. In this case the total amount of heat delivered to the
engine with 2 per cent, reduction for radiation losses amounts to
25,321 B. T. U., so that subtracting 2,545 B. T. U. the equivalent
of the mechanical work of i horse-power leaves 22,776 B. T. U.
given up to the exhaust. This is but 90 per cent, of the amount
of heat which is available in the saturated steam at 2 pounds'
gauge.

For the third case he assumed the conditions the same as in
Case i, with the exception that the steam was superheated to 150
degrees of superheat. This increased the amount of heat supplied
to the engine by the fact that for every one of the 34 pounds re-
quired per horse-power per hour, the 150 degrees superheat repre-
sent very nearly 75 B. T. U. per pound. The total figures out at
42,411 B. T. U. and with a subtraction for the equivalent of I
horse-power leaves 39,867 B. T. U. available in the exhaust steam.

Principles of Heating.

This figures out as 102 per cent, of the amount of heat available
in the saturated steam at 2 pounds' gauge.

From Cases i and 2 it would appear that the greatest amount
of heat that can be expected from engine exhausts, for use
in heating systems, at or near the pressure of the atmosphere,
is 90 to 94 per cent, of that of saturated steam at the same pres-
sure. The percentage will, in most cases, drop much below this
value. All things considered, exhaust steam having 80 per cent,
of the vaue of saturated steam at the same pressure is probably
the safest rating when calculating the amount of radiation to be
supplied by the engines. In many cases no doubt this could be
exceeded, but it is always best to take a safe value."

EXPLANATION OF HIGH VALUE OF EXHAUST STEAM.

" In plants where the exhaust steam is used for heating pur-
poses and where the amount supplied by direct-acting steam
pumps is large compared with that supplied by the power units,
it is possible to have the quality of the exhaust steam fairly high.
This condition is sometimes met with in practice, and may be the
explanation of the statement sometimes heard, that exhaust steam
gives better service for heating purposes than saturated steam at
the same pressure. It should be understood that saturated steam
at any stated pressure always has the same number of British
thermal units in it no matter whether it is taken directly from the
boiler or from the engine exhaust. A pound of the mixture of
steam and entrained water, taken from engine exhausts, should
not be considered as a pound of steam. If we are speaking of a
pound of exhaust steam without the entrained water as com-
pared with a pound of saturated steam at the same pressure, they
are the same, but a pound of engine exhaust of mixture is a dif-
ferent thing. In cases where engine and pump exhausts are
mixed, the available heat per pound of steam will be somewhere
between 800 and 1,000 B. T. U. As suggested above, however,
a safe value for general work is the lower figure."

Central Steam Heating Plants and Mill Heating

EXHAUST STEAM HEATING.*

The steam engine of today has reached a degree of perfection
beyond which it seems improbable that any material advance in
efficiency will be made. . . . Under the best conditions possible,
a maximum of only 20 per cent, of the heat delivered to the
engine in the form of steam is transformed from thermal to
mechanical energy, and under commercial conditions of variable
load the efficiency seldom exceeds 10 per cent. . . .

The advisability of using exhaust steam as a heating agent has
long been recognized, yet there are many who have the false im-
pression that the steam that has passed through the engine pos-
sesses but little heat compared with what it had when it entered
the cylinder. But steam manufactured at high pressures and
reduced to a heating pressure is, in fact, drier, and thus more
effective than if sent out at heating pressure. Steam exhausted
from the engine answers this condition and is thus in the line of
economical duty. This misapprehension should be entirely cleared
away by reference to the eminently satisfactory results as ob-
tained by the companies using exhaust steam for heating pur-
poses, of which there are more than one hundred. . . .

The conditions of operation that are necessary, in order that
exhaust steam may be utilized in a heating system, vary through
wide limits, depending upon the local conditions, class of engines
operated, maximum and minimum demand for heat, and the
maximum and minimum output of the plant in electrical or power
load during the heating and non-heating season. .

Competent engineers assert that during the hours when the
electric plant is idle and the fires are banked, it costs, approxi-
mately, 10 per cent, of what the fuel and labor expense would be
to run at full working capacity, which, of course, brings no return,
but by the addition of a steam heating plant continuous work is
given to boilers and men, and a profit secured in place of this
loss. . . .

* Extract from American District Steam Company's 1905 Catalog, on District
Steam Heating.

Principles of Heating.

HEATING VERSUS C6NDENSING.

By present methods employed by the American District Steam
Company, the connections at the engines are so arranged that only
a needed number of engines will be operated non-condensing
when heat is required and furnish their exhaust for heating pur-
poses ; while the balance of them can be operated condensing. . . .

To illustrate the increased value of utilizing the heat in the
exhaust steam from the engines instead of condensing it, without
going into technical arguments, we instance that companies that
are operating non-condensing when heat is needed receive an in-
come from the sale of exhaust steam for commercial heating pur-
poses, during the heating season of from seven to eight months,
exceeding in amount the cost of fuel at the station for the entire
season required to manufacture light, heat and power, plus in-
terest on the cost of the steam heating plant. No advocate of
condensing can even hope to approximate such a result.

Electric companies operated by water power find it a great
advantage to construct a direct steam heating plant to operate
in conjunction with their electrical business, not only on account
of the- revenue and profit derived from the steam heating enter-
prise, but the advantage gained in doing away with competition
of isolated plants that are forced to construct a heating plant and,
naturally, furnish their own light and power as well. . . .

We now use nothing but full-weight strictly wrought-iron line
pipe. The increased cost over merchant standard and steam pipe
is more than compensated for by greater durability. As to steel
pipe, the irregular distribution of carbon, even though in amount
less than i/io of I per cent, used in its manufacture, positively
precludes its use at any price.

In some cases it is desirable to return the water of condensa-
tion to the station for re-evaporation on account of its purity and
also on account of its action in preventing the formation of scale
in the boilers, or because of the high cost of water for steam-
making purposes. . . . Steel pipe cannot be used for this purpose
on account of the pitting and corrosive action which is immedi-
ately set up by the water of condensation, thus rendering the life
of the steel- pipe extremely short. . . .

Central Steam Heating Plants and Mill Heating

As an alternative to the use of wood water pipe for returning
condensation, this company is also prepared to install, where
desired, a cast-iron return main, properly insulated, in which case
pipe is used having threaded ends and with special threaded cast-
iron couplings similar in a general way to those used for wrought-
iron pipe. With this type of construction, however, expansion
and anchorage devices are required.

SOME OF THE FACTORS THAT AFFECT THE COST OF GENERATING AND
DISTRIBUTING STEAM FOR HEATING.*

The comparative heat value of fuels, taking into consideration
relative furnace efficiency, is approximately as follows :
2,000 Ibs. coal containing 10,000 B. T. U.=
3.23 bbls. crude oil or 135.66 gals.=
20,000 cubic feet natural gas.
2,000 Ibs. coal containing 11,000 B. T. U.=
3.55 bbls. crude oil or 149.1 gals.=
22,000 cubic feet natural gas.
2,000 Ibs. coal containing 12,000 B. T. U.=
3.87 bbls. crude oil or 162.5 gals.=
24,000 cubic feet natural gas.
2,000 Ibs. coal containing 13,000 B. T. U.=
4.19 bbls. crude oil or 176.0 gals.=
26,000 cubic feet natural gas.
2,000 Ibs. coal containing 14,000 B. T. U.=
4.52 bbls. crude oil or 189.8 gals.=
28,000 cubic feet natural gas.
2,000 Ibs. coal containing 15,000 B. T. U.=
4.84 bbls. crude oil or 203.28 gals.=
30,000 cubic feet natural gas.

Clean boilers are also imperative in steam plants. The influ-
ence of scale on boiler tubes varies largely with reference to its
thickness, ranging in decrease in heat conductivity from 3 per
cent, to 19 per cent, when from .02 to .085 thick, but not in pro-
portion to thickness, but being very greatly affected by its char-

* Extracts from a paper by Charles R. Bishop, read before the National District
Heating Association, held at Toledo, Ohio, June 1 to 3, 1910.

Principles of Heating.

acter, such as hard, soft, dense or porous. Water, containing
from 15 to 20 grains of calcium carbonate, magnesium carbonate
and magnesium chloride per United States gallon is fair; when
less, is either good or very good ; 8 grains or less being consid-
ered very good; over 30 grains is very bad. Where the feed
water is bad something should be done to either neutralize or
eliminate the impurities, through mechanical or thermal means ;
using boiler compounds or puifying systems — tube cleaners and
frequent blow-off of boiler, or by feed-water heaters.

With a good quality of fuel and water and a generating plant
containing economical boilers of proper size, selected with refer-
ence at least to load conditions, attention should be given to an
economical means of utilizing the greatest percentage of heat
units contained in the fuel to be burned, and it is generally con-
sidered good practice to equip plants of 1,000 or more horse-
power with mechanical stokers, adapted to the kind of fuel
burned. Such an installation not only increases efficiency, but de-
creases the firing cost per ton. In hand-fired plants one fireman
can attend to the coal, water and ashes for 200 horse-power, while
with good automatic stokers, overhead bunkers and down-pour
spouts, he can easily attend to 2,000 horse-power or even 3,000
horse-power. The first cost of mechanical stokers is not the only
feature for consideration, and those not adapted to the service,
poorly designed or constructed, should be avoided on account of
liability of shut-downs and large repair bills. A good type of
stoker, properly set, is inexpensive to maintain and exceedingly
reliable. . . ..

It cannot be denied that marked fuel economy will result from
proper feed-water heating. This is accomplished in various ways
— principally exhaust steam heaters, flue gas heaters, and live
steam heaters. As local conditions largely enter into the factors
which must determine the installation of these types of apparatus,
no general rule can be given, but it can be stated that the fuel
savings can range from less than i per cent, to over 20 per cent.,
against which must be charged interest, maintenance and depre-
ciation upon the cost of heaters, and economizers, and extra cost
of stack or forced draft apparatus, with allowances for reduction
in boiler heating surfaces thus made possible.

Central Steam Heating Plants and Mill Heating jgy

After a consideration of the factors which largely enter into
the generation of steam, next comes the question of its utilization.

If the plant in mind is a combination electric generating and
steam heating plant, it will first be assumed that it intends to have
or does have a market sufficient to utilize the full amount of ex-
haust steam at such times as it is developing the greatest electrical
load, and that its steam demand will at least equal the exhaust
during that portion of the heating season between November ist
and April ist. In such cases the question of engine efficiency is not
as serious as engine capacity, up to the point of approximately 65
per cent, of engine capacity, although this figure varies with dif-
ferent companies due to the proportion of summer to winter
maximum electric load. Some companies desiring to install a
sufficient amount of high efficiency engines or turbines to permit
of summer operation under economic generating costs, other com-
panies believing the installation of exhaust turbines for summer
operation as advisable. The proper installation is a matter quite
easy to work out, but depends very largely upon the size of the
plant and its power and load factors.

It is a fact that engines act in a sense as reducing valves be-
tween the boilers and the heating system, but while performing
such functions, produce mechanical energy without appreciably,
at least, lessening heat energy; therefore, were there a heat
demand in excess of the amount of steam exhausted by high effi-
ciency engine, the deficiency in steam would have to be made up
direct from the boilers, and thus the quantity of steam generated
in the boilers would not be less than if it had all passed through
the engines in the manufacture of a given quantity of engine
horse-power or its equivalent in kilowatt hours. By this state-
ment I do not, however, mean to convey the idea that it is advis-
able to install or continue to operate engines of very low
efficiency. . . .

After being exhausted from the engines, the steam enters a
main delivery pipe, having at one point a fitting through which
the steam is taken to feed-water heaters and through a balanced
back pressure valve to the air, such discharge connection being
necessary to relieve the engine from any unnecessary back pres-
sure at such times as the quantity of exhaust exceeds the heating

i88

Principles of Heating.

'5,
>>
H

Central Steam Heating Plants and Mill Heating

demand. A direct connection from the boilers is made to the
exhaust main for the purpose of supplying the system with the
necessary amount of live steam at such times as there exists a
heating demand in excess of the exhaust steam supplied. In the
large steam connections an automatic pressure reducing valve is
placed and in the exhaust steam main, before leaving the station,
there is located an oil and water separator, having an automatic
trap discharge.

Where the station contains several engines, an additional ex-
haust main should be installed, so that any engine can be run con-
densing or exhausting to the atmosphere, while other engines are
exhausting into the heating mains. . . . (See Fig. 56.)

Transmission losses are increased or decreased by the follow-
ing factors :

Efficiency of insulation.

Outside water coming into contact with the distributing mains.

Air in motion coming into contact with the distributing mains.

Actual leakage of steam, through imperfect conditions of the
mains, and of expansion joints, or due to drip traps blowing.

Frequent inspection of the distributing mains should be made,
and if there is found any indication of leakage, or electrolytic
action, immediate steps should be taken to overcome the condi-
tion. If outside water is in contact with the steam mains, the
insulation, etc., should at once be protected, and even more im-
portant, the source of the trouble should be checked, otherwise a
recurrence is to be expected, and while the trouble remains the
deterioration of the supply system is made rapid.

Street traps should be kept in perfect working condition and
they should be inspected at least as often as every seven or ten
days.

Normal transmission losses are practically constant in well-
insulated and properly installed mains, and are approximately
uniform per square foot of mains and fillings and should never
exceed .045 pound per hour per square foot. The percentage of
loss to output depends upon load factor, and should not exceed
15 per cent, at times of minimum demand during the heating sea-
son, nor exceed 1^2 per cent, in periods of maximum demand,
with an average of not to exceed 4 per cent, during the heating

Principles of Heating.

season. Meters to measure these losses should be in use in all
steam plants, and if the losses exceed the amount stated, the
cause should at once be determined and overcome. . . .

The real cost of steam delivered to the consumer must neces-
sarily include:

Total generating cost, made up of fuel, water, firing and other
station costs.

Transmission losses.

Unaccounted for steam.

Overhead expenses.

Depreciation and amortization.

HEATING SYSTEMS FOR MILLS.*

In the use of direct radiation operated with exhaust steam
from non-condensing engines, by placing a light back pressure on
the engines to force the exhaust through the pipes at the proper
velocity, it should be borne in mind that the adding of one pound
of back pressure to an engine cannot be made up by adding one
pound to the initial pressure. . . .1

Adding back pressure to an engine, especially if it is large and
well loaded, should be avoided if possible. From the foregoing
it would seem that the entire heat from exhaust steam cannot
usually be utilized without running more or less back pressure on
the engines. In some instances the circulation of the exhaust is
assisted by applying a vacuum at the discharge end of the system,
thus doing away with the objectionable back pressure on the
engines. This is a decided advantage if the engines are large, but
it necessitates the complication of piping, with the cost and run-
ning expense of some more or less elaborate system for the main-
tenance of the vacuum. As a rule, the method of heating by ex-
haust steam leaves a great deal to be desired and is not advisable
unless it is necessary to use non-condensing engines.

Taking low pressure steam from the receiver of a compound
engine is a common practice in some mills. If the quantity of
steam taken is fairly constant and the engine is designed with that

* Extracts from a paper by A. G. Hosmer, presented before the National Associa-
tion of Cotton Manufacturers in 1908.

Central Steam Heating Plants and Mill Heating

object in view, the results are quite satisfactory, although this
idea is usually more popular with the designing than with the
operating engineer.

It is well to remember when designing any supply of heat for
the purpose of warming buildings of a manufacturing plant that
exhaust or receiver steam is available only during running hours,
and that the heating system's highest duty is usually required
when the engines are shut down ; consequently, it is more impor-
tant to have an efficient service during non-running hours than at
times when machinery friction and other causes contribute to the
warmth of the workrooms. . . .

A direct system designed for the use of live or boiler steam
alone, which is reduced in pressure and sent to the heating pipes,
if piping is large and well installed with separate traps for each
considerable unit of circulation will be found to be one of the
most economical and satisfactory methods of heating. It can be
forced or moderated within reasonable limits by raising or lower-
ing the pressure at the reducing valve and, with everything right,
will give return for practically all the heat expended.

The benefit of returning the condensation to the boilers is
quite often not realized in many plants fitted for so doing, for the
reason that a pump designed and used for handling very hot water
is one of the most difficult appliances to keep in repair with which
the mechanic has to deal. Consequently, the general tendency is
to neglect this important feature, and as the heating can be done
without it, that is, by running the water to waste, the pump is
allowed to stand idle for a great part of the time. This should not
be permitted, as the expense of keeping the pump in first-class
order is a small item, compared with the loss of the heated con-
densation.

THE USE OF STEAM FROM THE RECEIVER OF COMPOUND ENGINES
FOR HEATING PURPOSES.*

It has been common practice for many years to use the by-
products such as exhaust steam and warm water from the steam

* Extract from paper by Chas. T. Main on " Central Stations vs. Isolated Plants
for Textile Mills," presented at a joint meeting of Local Chapters of A. I. M. E. and
A. S. M. E., Boston, Feb. 16, 1910.

JQ2 Principles of Heating.

plant for manufacturing purposes and heating buildings, etc. It
has been also very common practice to take steam out of the
receiver, between the cylinders of a compound engine for these
purposes. In many mills all of the exhaust of simple non-
condensing engines is used for manufacturing purposes.

The saving from using the exhaust of a non-condensing
engine, which would otherwise go to waste is large, because there
is no additional steam required for the engine, unless the back
pressure is increased. Any use of the steam is nearly all clear
profit and if all of it is used the only part left to charge to power
is the difference in B. T. U. due the difference in pressure and
the condensation in the engine cylinder and jackets.

There seems to be no good reason why in time the practice of
bleeding turbine should not become as common as bleeding engine
receivers.

RECEIVER STEAM.

Table XLVII shows the amount of coal chargeable to power
when certain percentages of the steam entering the high pressure
cylinder are taken out of the cylinder. This table takes into con-
sideration the effects on the economy of the engine of not passing
all of the steam into the low pressure cylinder, cylinder condensa-
tion, etc.

The percentages in the first column are the percentages of the
steam passing the high pressure cylinder which is taken out of the
receiver for manufacturing purposes. The second column is the
total coal burned and the third is the coal chargeable to power
after deducting the coal chargeable to manufacturing.

TABLE XLVII.

EFFECT OF EXHAUST STEAM UTILIZATION ON COMPOUND ENGINE ECONOMY.

Per cent of exhaust steam Pounds of coal per one ^^0°™°'^ hou?

used for heating pur- horse-power per hour. after deducting for ex

poses. All coal charged to power. haust steam usjd.

0 1.75 1.75

25 2.06 1.50

50 2.38 1.25

75 2.69 1.00

100 3.00 0.75

If the mill did not obtain its power from steam, so that it
could use the low pressure steam of the plant for manufacturing

Central Steam Heating Plants and Mill Heating jg^

it would have to maintain a boiler plant of sufficient size to pro-
duce an amount of steam equivalent to that bled out of the
receiver. The amount of B. T. U. its equivalent in coal charge-
able to power is represented by the amount of work done by the
engine and the losses due to the presence of the engine. The cost
of generating the rest of the steam is chargeable to the manufac-
turing processes.

HIGH PRESSURE STEAM HEATING.*

In some factory plants, conditions are such that the most
economical system to install — both as to first cost and operation
— is high pressure steam — that is, a system using steam at 20 to
50 pounds pressure. This condition occurs only where the power
load greatly exceeds the heating load and the engines are run
condensing, and where calculations show that it would not pay
to place a back pressure on the engines and increase the steam
consumption; or that it would not be more economical to run
with a high vacuum and use live steam in the heating system,
varying the pressure by means of the pressure reducing valve to
suit the outside temperature. If proper attention is given to such
a heating system and the piping is designed to operate with the
lowest pressure to be used, satisfactory regulation can be ob-
tained; for steam at 60 pounds pressure has a temperature of
307 degrees and at 20 pounds the temperature is 259 degrees,
leaving a considerable range between these extremes. With such
a system it is advisable to use coil surface only, as the steam
pressure would be too high for the ordinary type of cast-iron
radiators.

RELATIVE ECONOMY OF HIGH AND LOW PRESSURE HEATING.

In a paper on " Cost of Heating Storehouses/' by H. O.
Lacount, presented at the Indianapolis meeting of the A. S. M. E.,
1907, it is stated that tests showed that with about 10 pounds
steam pressure in the heating system night and day, the average

* Extract from an article on " The Choice of Heating Equipment for Manufactur-
ing Plants," by G. W. Stanton, Engineering Magazine.

Principles of Heating.

temperature throughout the storehouse was substantially the same
as when the steam was in the pipes during the daytime only —
that is, from 6 A. M. to 6 p. MV but at 60 pounds pressure.

The steam consumption per 24 hours was about 35 per cent,
greater with 60 pounds steam pressure during the days than with
10 pounds continuously.

CHAPTER XII.

'-' - •' /•

THE STEAM LOOP.

•

This interesting method commonly employed for returning
live steam drips to the boilers in power plants and also used in
low-pressure plants is here described by extracts from two papers
or articles, accompanied by illustrations.

THE STEAM LOOP.

This device is well described in a paper by Walter C. Kerr,
Journal of the Franklin Institute, February, 1891, from which the
following extracts are taken :

" Steam loop," a name which, though almost meaningless,
seems very consistent with its simplicity. The name has the
further merit of not portraying any of its functions or peculiari-
ties, and hence cannot be an embarrassing restraint, as is so fre-
quently the case with names attached to mechanical apparatus.

That so simple an application of Nature's laws as is involved
in the steam loop should not have been turned to useful effect
earlier is, at first thought, strange, but as one looks deeper into
the subject, the reasons become more apparent. While no engi-
neer is unfamiliar with the phenomena on which it depends, it
has been interesting to note that even those best informed in
practical steam engineering or theoretical research in thermo-
dynamic science, seldom understand its action on first acquaint-
ance, though they soon recognize in it a new combination of
functions.

Its mission is the simple and useful one of returning water of
condensation to steam boilers. Its chief characteristics are that
its action is continuous, rapid and positive, and that it is a closed
system operating under widely varying conditions, without valves
or adjustments. Its construction is simply that of ordinary
piping.

195

Principles of Heating.

The principles on which its action depends are as follows :

Differences of pressure may be balanced by a water column.

Vapors or liquids tend to flow to the points of lowest pressure.

Rate of flow depends on difference of pressure and mass.

Decrease of static pressure in a steam pipe or chamber is pro-
portional to rate of condensation.

In a steam current water will be carried or swept along rapidly
by friction.

To these simple statements there will probably be no dissent.
We have all used them in many ways, and some of them have dis-

Fig. 57.

agreeably used us in a manner quite unwelcome. But it remained
for the steam loop to collect a few of these erratic agents and
from them create a useful system, combining the certainty of flow
due to difference of pressure, with the quiet uniformity with
which steam condenses, and with the force we see uselessly ex-
pended in the hammering of our steam heating apparatus.

It will be evident that the steam loop, therefore, contains no
mysterious factors, even though, like the steam injector, it has
been called a paradox.

Fig. 57 shows a steam pipe passing from the boiler to a sep-
arator near the engine, which separates the water of condensa-
tion and entrainment from the steam. The drip from the sep-
arator is below the boiler, and evidently were a pipe run from
this drip outlet directly to the boiler we would not expect the

The Steam Loop.

water to return uphill. Moreover, the pressure in the boiler is
(say), 100 pounds, while in the separator it is only ninety-five
pounds, due to the decrease in pressure in the steam pipe by rea-
son of which the steam flows to the engine. Thus the water must
not only flow up hill to the boiler, but also must overcome the
difference in pressure. The device to return it must perform
work, and in so doing heat must be lost. The loop, therefore,
may be considered as a peculiar motor doing work, the heat ex-
pended being radiation from the upper or horizontal portion.

We are now prepared to examine its mechanical operation,
which is best done with the model in action. The form of sepa-
rator is immaterial, there being many kinds, differing more or
less in construction and efficiency. The one in model is simply
an elbow turned down into the body of the device throwing the
steam against a perforated plate, above which the dry steam is
removed by a pipe leading to engine, while the water collects
below.

From the separator drain leads the pipe called the " riser,"
which at a suitable hight empties into the " horizontal." This
leads to the " drop-leg " connecting to the boiler anywhere under
the water line. The riser, horizontal and drop-leg form the loop,
and usually consist of pipes varying in size from 1/4. inch to 2
inches, and are wholly free from valves, the loop being simply
an open pipe giving free communication from separator to boiler.
(For convenience, stop and check valves are inserted, but they
take no part in the loop's action.) Suppose steam is passing,
engine running and separator collecting water. The pressure of
95 pounds at the separator extends (with even further reduction)
back through the loop, but in the drop-leg meets a column of
water (indicated by the heavy broken line), which has risen from
the boiler, where the pressure is 100 pounds, to a hight of about
10 feet. That is to the hydrostatic head equivalent to the 5
pounds difference in pressure. Thus the system is placed in
equilibrium.

Now, the steam in the horizontal condenses slightly, lowering
the pressure to 94 pounds, and the column in the drop-leg rises
2 feet to balance it, but meanwhile the riser contains a column of

Principles of Heating.

mixed vapor, spray and water, which also tends to rise to supply
the horizontal as its steam condenses, and being lighter than the
solid water of the drop-leg, it rises much faster. If the contents
of the riser have a specific gravity of only one-tenth of that of the
water in the drop-leg, the rise will be ten times as rapid, and when
the drop-leg column rises I foot, the riser column will lift 10 feet.
By this process the riser will empty its contents into the hori-
zontal, whence there is a free run to the drop-leg and thence into
the boiler. In brief, the above may be summed into the statement
that a decrease of pressure in the horizontal produces similar
effects on contents of riser and drop-leg, but in degree inversely
proportional to their densities. When the condensation in hori-
zontal is maintained at a constant rate sufficient to give the neces-
sary difference in pressure, the drop-leg column reaches a hight
corresponding to this constant difference, and rises no further.
Thus, the loop is in full action, and will maintain circulation so
long as steam is on the system, and the differences of pressure
and quantities of water are within the range for which the loop is
constructed. ...

Generally speaking, the limits within which the steam loop is
applicable are very wide, for the principle applies quite as well
to great as to small differences of pressure. Similarly, an enor-
mous quantity of water may be handled quite as easily as a small
amount. The action will continue reliably through long pipes,
overhead or underground. Water may be lifted from levels far
below the boilers. The use to which the steam may be applied
after the loop and separator have dried it, of course has no effect
upon the loop system. Wherever steam is so used that it con-
denses rapidly, as in dryers, steam heating systems, jacket steam
kettles, etc., the loop can be applied to the return of this water of
condensation the same as from an ordinary separator, and that,
too, against any difference of pressure.

The above statements are made to illustrate how thoroughly
and completely the loop can be applied to a wide range of condi-
tions, but when we come down to the practical application, and
say how far is it expedient to apply it, the field contracts some-
what.

The loop's application is limited most often by the head room

The Steam Loop.

for its erection. If the pressure in a separator, dryer, or return
from a steam heating system be 10 pounds below the boiler and
a loop about 30 feet high is necessary to make the return, it is
evident that a difference of 50 pounds in pressure requires a loop
about 150 feet high, and the riser, drop-leg and large portion of
the horizontal being well covered with non-conductor, such a loop
would operate efficiently, but generally speaking, a line of small
pipe of that hight would seldom be convenient, inasmuch as it
would require some peculiar structure to hold it, or possibly
might need to be erected on the side of a smokestack. In high
city buildings such a loop may be practicable where convenient
air shafts allow easy support, but in ordinary manufacturing
plants it would seldom be constructed.

While speaking of difference of pressure, attention should be
called to the fact that the absolute pressure is of no importance,
as a loop will work quite as well under low pressure as high.
Its construction and operation recognize only the difference of
pressure. A special case occurs, however, where the difference of
pressure is very large compared with the lowest pressure in a
system. For instance, if a boiler carries 25 pounds of steam and
at the end of a series of heating or drying coils the pressure is
i pound, then with a loop about 100 feet high it would be evident
that if the condensation in the horizontal were so performed as to
even produce a perfect vacuum, the water column in drop-leg
would stand about 80 feet high, but it is doubtful whether the
pressure of I pound at foot of riser plus the 14,7 pounds due to
vacuum would be sufficient to force the contents of riser up 100
feet and into the horizontal. It certainly would not be sufficient
if there were a considerable quantity of water to be handled, thus
causing a high specific gravity of riser contents. Such case, how-
ever, is so seldom met in practical loop application, that it
scarcely need be considered a limiting condition.

Roughly speaking, differences of 10 to 15 pounds are the
largest experienced in good practice, and the loop can generally
be conveniently erected to operate against such differences, and
where excessive discrepancies in pressure are observed, it is
usually very desirable to make such changes as will diminish dif-
ferences, they being usually due to faulty piping. While, there-

200

Principles of Heating.

fore, excessive difference of pressure is practically a limiting con-
dition to steam loop practice, it is not found to be an annoying
interference. . . .

Throughout this discourse the description has been confined
almost wholly to the application of the loop to the one case where
moisture is to be removed before steam passes to an engine or
pump. It is thought best to keep this one case clearly in mind,
for the loop thoroughly understood on this basis may be easily
conceived to serve similar purpose in any other connection.
Where live steam is used for drying purposes, the loop may be

Fig. 58.

attached directly to the return, as shown in Fig. 58, thus maintain-
ing a powerful circulation through the heating coils and ridding
the system from the condensation which is the natural product of
the heating or drying process. In this service, however, the loop
has opened up a new feature, that of drying the steam before it
enters such heaters, and it is found to yield very beneficial results,
by keeping up temperatures and pressures. Similarly, steam ket-
tles, jackets of steam jacketed cylinders, and even steam heating
apparatus can be handled with ease and efficiency. Much appa-
ratus of this nature, however, is throttled down to a degree that
seriously interferes with loop application, and in ordinary steam

The Steam Loop.

201

Directions for Starting the Holly System

Open return valves "A'A "at Boilers (under steam)

Open regulating valve "B" (slightly)

Open valve "E"in Riser Line

Open all valves in Drip Lines to Receiver

Open Starting valve "C "untiisteam blows thro',

The •system is then in operation.—

When plant is not under steam open valves C-D.

Discharge _„.•'
Chamber

Drip lines N° 1,2, 3,4.
Riser line » 5
Return • 6
Vent r 7

Fig. 59.

2O2 Principles of Heating.

heating the opportunity is exceptionally good for large air leak-
age, which would be deleterious. It is, therefore, not easy to con-
cisely state to just what purposes the loop may be practically
applied, but it is safe to say that it is desirable on any live steam
pipe or any high pressure or unthrottled dryer, heater or jacket.
Fig. 59 shows a modern arrangement of the Holly return sys-
tem as applied to the draining of high pressure steam mains and
branches,

THE STEAM LOOP.*

In a heating apparatus it is always best that the condensation
be returned by gravity alone, and this can usually be effected
without difficulty. However, conditions are occasionally met with
that tax the ingenuity of the engineer, and render it necessary to
employ mechanical means, but as the water can always be re-
turned by one means or another, it may be said that, at the present
time, no plant that permits the condensation to be wasted can be
termed complete or successful.

It is perhaps true that in no branch of steam engineering has
more ingenuity been displayed than is involved in the production
of appliances for returning condensation from radiation and other
condensing mediums located below the water line in a boiler.

An ordinary duplex pump in combination with a receiving
tank, pump, governor and automatic return trap are all good illus-
trations of this statement.

We also have a more recent device which is perhaps not so
well known, but it is simple, and when properly installed, suc-
cessful. This appliance is the steam loop, the foundation patents
of which are owned by Westinghouse, Church, Kerr & Co. In
the operation of the steam loop, the well-known vacuum principle
is employed. There are many modifications of this device, some
of which are simply to avoid patent infringements, but, in all of
the modifications, the same general principle is maintained.

The steam loop is constructed of iron pipe, and has no mov-
able or working parts, other than what may be found on any ordi-
nary arrangement of piping for conveying steam to an engine or
system of radiators. It consists of three principal parts arranged

* These extracts are from a paper by James Mackay, published several years ago
(date uncertain), in Domestic Engineering.

The Steam Loop.

203

something like an ordinary syphon, the long leg being termed the
main riser, the short leg the drop return, and the horizontal, con-
necting the two legs together, is termed the condenser. A refer-

Fig. 60.

ence to the accompanying diagram, Fig. 60, will convey an idea as
to the operation of this device. The main riser and drop return
are of i^-inch or I ^2-inch pipe; the horizontal condenser of 2l/2
or 3-inch pipe, connected with the main riser by an eccentric
reducer with the eccentric at the top, and with the drop return

Principles of Heating.

by a similar reducer with the eccentric at the bottom. A compres-
sion air valve or pet cock is placed at each end of the loop at A
and B in the diagram ; a gate and check valve at C upon the return
just before it enters the boiler.

To put in operation, turn on steam at D and close valve C.
Open A until steam appears, then close it and open B. When
steam appears, close B and open C. In a short time sufficient
condensation will accumulate at A to choke off the passage of
steam to the horizontal condenser. The steam already there will
condense and produce a vacuum ; then the water which has accu-
mulated at C will flow into the vacuum, over the top of the main
riser, thence back to the boiler by gravity. When once started
the loop will continue in operation until stopped by some derange-
ment of the system or through the absence of steam. The pipe
at the bottom of the main riser, which acts as a receiver for the
condensation, should be one or two sizes larger than the pipe in
the main riser. The water line will be higher in the drop return
than in the boiler, due to the difference in pressure in the boiler
and the drop return. In the latter the pressure will vary from
i to 3 pounds less than in the boiler, and the water will stand 27
inches higher in the drop return for every pound difference in
pressure. For instance, if the difference in pressure is 2 pounds,
the water line in the drop return will be 54 inches higher than in
the boiler. It is necessary to ascertain the pressure on the return
and locate the top of the drop return at 10 inches above the water
line therein.

The power of the steam loop depends upon the completeness
of the vacuum formed in the horizontal condenser, and the longer
the condenser the greater will be the capacity for producing a
vacuum, although longer than is necessary for the work in hand
is simply waste.

The loop will work under all steam pressures, but is not as
reliable at low as at high pressure, say from 20 to 50 pounds.
Still, good results are being obtained upon low pressure steam
heating apparatus at pressures below 5 pounds.

CHAPTER XIII.

NON-CONDUCTING COVERINGS. MISCELLANEOUS
TABLES AND FURNACE TESTS.

TESTS OF STEAM PIPE AND BOILER COVERINGS BY C. L. NORTON, OF

THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY, FOR THE

MUTUAL BOILER INSURANCE CO., 1898.

TABLE (XLVIII.

DATA OF PIPE AND BOILER COVERING TESTS.

L4 1.4

Name and Maker.

Nonpareil Cork Standard — Nonpareil Cork Co

Nonpareil Cork Octagonal — Nonpareil Cork Co

Manville High Pressure — Manville Covering Co. ...

Magnesia — Keasby & Mattison Co

Imperial Asbestos — H. F. Watson

" W. B."— H. F. Watson

Asbestos Air Cell — Asbestos Paper Co

Manville Infusorial Earth — Manville Covering Co. . .

Manville Low Pressure — Manville Covering Co

Manville Magnesia Asbestos — Manville Covering Co. .

Magnabestos — Keasby & Mattison Co

Moulded Sectional — H. F. Watson

Asbestos Fire Board — Asbestos Paper Co

Calcite — Philip Carey Co

Bare Pipe

TABLE XLIX.

PARTIAL COMPONENTS OF DIFFERENT COVERING MATERIAL.

-Percentage Composition-

Name.

K. & M. Magnesia

Manville H. P. Lining

Watson Moulded

Carey Calcite

Manville Magnesia Asbestos.

Mg.C03
Carbonate of Magnesia.

80 to 90
less than 5
20 to 25
less than 5
10 to 15

Ca.SO4
Sulphate of Calcium.

65 to 75

50 to 60

none

205

206 Principles of Heating.

TABLE L.

THE SAVING, IN DOLLARS, DUE TO THE USE OF VARIOUS COVERS.

Loss per Saving Saving per

Name. sq. ft. B. T. U. B. T. U. year per

at 200 Ibs. per sq. ft. 100 sq. ft.

Nonpareil Cork Standard 2.20 11.64 $37.80

Nonpareil Cork Octagonal 2.38 11.46 37.20

Manville Sectional High Pressure... 2.38 11.46 37.20

Magnesia 2.45 11.39 36.90

Imperial Asbestos 2.49 11.35 36.80

"W. B." 2.62 11.22 36.40

Asbestos Air Cell 2.77 11.07 36.00

Manville Infusorial Earth 2.80 11.04 35.85

Manville Low Pressure 2.87 10.97 35.65

Manville Magnesia Asbestos 2.88 10.96 35.60

Magnabestos 2.91 10.93 35.50

Moulded Sectional 3.00 10.84 35.20

Asbestos Fire Board 3.33 10.51 34.20

Calcite 3.61 10.23 33.24

Bare Pipe 13.84

Generally speaking, a cover saves heat enough to pay for itself
in a little less than a year at 310 ten-hour days, and in about four
months at 365 twenty-four-hour days.

It is evident that the decision as to the choice of cover must
come from other considerations, as well as from the conductivity.

The question of the ability of a pipe cover to withstand the
action of heat for a prolonged period without being destroyed or
rendered less efficient is of vital importance.

TABLE LI.

LOSS OF HEAT AT 200 POUNDS FROM BARE PIPE.

Condition of Specimen. B' T' &%££."•' "'

New pipe 11.96

Fair condition 13.84

Rusty and black 14.20

Cleaned with caustic potash inside and out 13.85

Painted dull white ' 14.30

Painted glossy white . . 12.02

Cleaned with potash again 13.84

Coated with cylinder oil 13.90

Painted dull black 14.40

Painted glossy black 12.10

Non-Conducting Coverings, Etc. 207

STEAM PIPE COVERING AND ITS RELATION TO STATION ECONOMY.

By H. G. STOTT.*

An attempt was made to determine the law governing the
effect of increasing the thickness of the insulating material, and
for all the 85 per cent, magnesia coverings the efficiency varied
directly as the square root of the thickness, but the other materials
tested did not follow this simple law closely, each one involving
a different constant. . . .

To determine^ which covering is the most economical for fol-
lowing quantities must be considered.

1. Investment in covering.

2. Cost of coal required to supply lost heat.

3. Five per cent, interest on capital invested in boilers and
stokers rendered idle through having to supply lost heat.

4. Guaranteed life of covering.

5. Thickness of covering.

From an inspection of the first three quantities it is apparent
that the covering which shows a minimum total cost of the three
at the end of a specified time is the best covering to adopt, for the
loss in heat at the end of ten years may readily cost over three
times as much as the first cost of covering. . . . While pipe cover-
ing is a relatively small portion of the many problems confronting
engineers, yet its scientific solution will yield rich results out of
all proportion to the time required to solve it.

There seems to be no reason for the former practice of putting
on different thicknesses of covering on different sized pipes, ex-
cepting the mechanical difficulty of applying a very heavy cover-
ing to a small pipe. This difficulty can be overcome by putting
the covering on in two separate layers, and this plan should be
used on all sizes in order that the joints may be broken, as poor
joints may reduce the efficiency of the best covering 6 per cent,
or more.

* Extracts from paper read before Twenty-third Convention Association of Edison
Illuminating Companies.

208

Principles of Heating.

£ « •9'*«-!l>W<0,Ht,,0

> ** s 2 t fi *** ft <•$ l» trf dJ o

^jaj OW«rHNrHNN(NrHSw

0 « « 0 f

0 1 8 2 : : : • • g * • « •

K3> S • :•«'•>

. . * 00 OJ CO <» 0 l> 00

0 * I oSSS^1"*^ • * t -"»

« s, • • • ( -

- £ a

l«f 8 S : S : 2 S : : : : :

^ flj O

,ts

.g « t- ^

.§|1 12:::::2::2:

rH Pi

•

0 OS"

H « 00 g 0 rH . . . . . ^ g, . . .

Si :

H o . ca TJI eo ^

1— '

1 Hill I * * - : : i i * : **

&, - - ^.

s
I

S S'i.«2 ^"? iHNCO

h Slgo^gSg :::;;». co oo

o
o

*-!"

S^rf-fl" • w 0 0 <0 0
1 1 1 § 8 1 § S : : S : S s : : : :

.2 3

1 ^^^ a

S,"

•g .^ - • «

•59

S|S|8§1 l--^:::S:::r

,_: a . OQ rH ... ....

2 S
5 5

S - W ft

. §06 ^ °> NO*

^is 1 * : : : " : : S 5 S s

StfM. « oo 9 s s § 5 S
2||§| I ? * s * s S : ::/3-: ;

o ft •••':::::::::

N. — The cond
am condensed

2 S

iri'-'-S*'^.

S «

< «4

i i . 1* 1 • :u: 1 1 •* • 1 1 •• i

55 o

3 j.

1 ! ! : i s ! * i i 1 1 1

H ~

sll.liilllil!l

N on-Conducting Coverings, Etc. 209

ECONOMIC VALUES OF STEAM PIPE COVERINGS.*

The economic value of non-conducting covering for steam
pipes has long been recognized. Especially in cases where the
heat radiated from the pipes cannot be utilized, the loss, in a very
short time, will more than equal the cost of a good covering.
According to Carpenter, the heat losses per square foot of surface
for small uncovered pipes is from 375 to 400 B. T. U. per hour.
This would mean an annual loss of 30 cents per square foot of
such surface, 75 to 80 per cent, of which could be saved by the
use of covering. This fact makes the decision to use some kind
of pipe covering an easy one, but when the selection of covering
is to be decided one immediately encounters much contradictory
data.

Reports of tests of pipe coverings are furnished by all dealers,
and, strange to say, they always show that the particular brand
advertised is superior to all others. This leads up to a brief
description of the different classes of covering.

It is generally admitted that loose wool, hair, cotton or feathers
are the best non-conductors ; but as these materials are all com-
bustible, their use is practically out of the question, except possi-
bly in the case of hair. The materials which are most used at the
present time are magnesia, rock wool, mineral wool, fire felt, hair
felt, fossil meal, asbestos sponge, nonpareil cork and asbestos
paper and air cell. According to Geo. M. Brill (A. S. M. E., Vol.
XVI), the composition of various substances is shown by the
following table :

TABLE LIII.

COMPOSITION OF COVERINGS (BEILL).

Moisture at 100° C
Organic matter

Mag-
nesia.

, . 1.23
7 64

Rock
wool.

0.00
0 00

Mineral
wool.

0.00
0 00

Fire
felt.

0.16
11 00

Hair
felt.

5.55

90 85

Fossil
meal.

1.78
10 02

Silica .

4 05

43 48

48 62

38 18

0 11

85 43

Iron and aluminum ox ills.
Lime (CaO)

. 3.74
22 95

11.95
22 96

9.20
24 10

9.56
0 10

0.28
2 33

1.78
0 32

Magnesia (MgO) ,

, . 19.58

18.24

17.26

37 55

0 21

0 13

Carbonic acid (Co 2)

. 38 00

0 00

3 75

0 00

Sulphurous acid (So 2 ) . . . .

. 1.57

4.67

1.75

3.60

0.00

Extract from article in the Metal Worker, August 13, 1904.

2io Principles of Heating.

It must, of course, be appreciated that the composition must
vary, depending upon very many causes, but these results show
the probable composition of the different coverings. It is not
advisable to use hair felt alone for pipe covering on account of
the tendency to char and break away from the pipe. This, how-
ever, may be overcome by the use of asbestos paper next the pipe,
and on the outside. A very good and comparatively inexpensive
covering is made up of several layers of corrugated asbestos paper
forming dead air cells to prevent the radiation of heat.

A great deal of data relative to the efficiency of various forms
of covering has been published, and the attempt has been made to
show comparatively the results of the experiments which have
been made by different engineers.

The results given by nine different authorities have been com-
piled and are given in the accompanying table. This table has
been plotted assuming the condensation of an uncovered pipe to
be 100 per cent., the various figures given opposite the different
materials used for covering showing the percentage of steam
which is condensed in the covered pipes. For instance, in the case
of magnesia, the average condensation is 20.8 "per cent, as much
when the pipe is covered with magnesia as it is when a bare pipe
is used.; in other words, the saving by the use of magnesia cov-
ering averages 79.2 per cent.

The results show quite wide variations, but from the whole a
much better average may be taken than can be obtained by study-
ing one or two tests independently. An average saving of from
70 to 85 per cent, is shown by the use of covering.

The proper care of covering has a great deal to do with its
effectiveness. If from any cause it becomes loose or discon-
nected, its efficiency is materially affected. It should be thor-
oughly inspected and repaired every year, the slight cost for this
attention being more than covered by the saving effected by
greater efficiency. A relatively poor covering properly applied
may be made to give better results than a better one which is put
on in a slipshod manner.

Non-Conducting Coverings, Etc.

211

TABLE LIV.

MINIMUM TEMPERATURE RECORDED IN VARIOUS PARTS OP THE UNITED STATES.

ALA.— Montgomery
A-n-rr7 ) Prescott ..

1896.
15

.— 4

1887.
13
8

1888
18
—12

1889
21
— 8

1890.
21
3

1891
23

1892
20

1893
17

1894.
13

i
1895. j

jowest
n ten
rears.

—12
11
— 2
31
19
—20

14
0
-28
-32
-18
—15
— 7
—27
—18
—10
16
— 7
1
—15
—12
—27
—41
4
—12
-42
1
-26
—22
—28
—44
—11
— 4
-10
—11
—15
— 3
—12
—11
—17
— 2
— 3
— 9
-7
12
—30
-32
— 6
11
-17
-6
-32
— 2
-30
—11
-42
—29

AKi/. -J Tucson

11
20
33
26
— 7
3
30
18

16
10
35
26
—17
0
29
13

11
31
28
— 2
— 3
24
8

18
1
32
26
— 8
— 5
14
4

— *2

34
28
—15
— 7
14
0

ARK Little Rock

10
. 36
34

0
33
28
—18
— 5
22
9
6

7
31
19
—20
— 4
28'
13
—28

17
32
31
— 7
— 3
30
14
2

16
34
29
— 8
4
27
17
— 9

t Los Angeles

V/A"' I Sacramento

COLO.— Denver
CONN,— New Haven
FLA Jacksonville ..

—11
— 2
31

GA. — Atlanta

.— 7

IDAH0 1 1daho Falls...

-22
—10
— 5

—26
—11
4
23
0
12
— 5
— 3
-10
—25
16
« 2

-22
18
—26

-j

— 1

1
— 5
8
— 5
—11
-12
20
10
2
— 1
25
-30
-32
10
19

~*10
-19
24
— 5
0
—20
—29

—22
—16
—15

-16

— 7

—10
29
— 4
1
— 9
- 10
-19
-26
20
— 2
-42
5
—16
8
—19
—41
- 9
— 4
—10
5
— 6
1
-12
— 2
—17
8
0
— 3
— 4
20
—26
-22
3
26
4
— 6
-27
28
—19
-11
—26
-4

—28
— 9

— 7

—27
-15
— 5
21
— 7
7
—15
—11
-17
—25
15
—11
—26
2
—22
— 7
—11
-33

*5
— 1

0
—11
1

— 4
— 8
— 7
18
4
— 4
— 7
14
—28

—'2
16
— 1
7
-31
21
— 2
— 4
—1ft
—17

-32
—15
—14

-is

—14
-10
16
— 6
1
—11
— 8
—16
—26
4
—12
—17
1
-20
— 4
—14
-39

— io

—11
—12
— 3
— 8
— 8
— 3
25
— 3
— 6
— 7
12
,—27

—'6
11
0
— 8
—17
27

-1

—24

—20;

ILL — Chicago . ~.

.—14
.—11
1

—15

—12

—17
— 5
21
— 5
7
—15
— 3
-21
-36
10
-10
-40
8
—22

—18
— 6
— 7
—27
—18
8
29
— 6
9
- 12
— 7
—27
-41
18
—12
-41
16
—25
—10
—28
—87
—11
2

—11
— 1

7
—13
-8
6
32
— 1
3
— 8
— 8
-21
—25
24
0
—15
13
—10
— 7
—14
-34
— 9
2

— 5
4

6
—18
— 6
13
30
0
12

+ 8
—12
—22
24
*
—29
19
—14
-22
—23
—35
— 6
10

— 4
6

— 8
— 8

-io

— 0
7
30
+ 2
16
— 4
2
—12
—25
22
4
—24

_ll

-8'
— 33

— 7
14

— *6
— 5
9
5
10
—11
23
12
9

IND.— Indianapolis. . . .
IND T Fort Sill .

IOWA— Des Moines
KAN —Dodge City

.—20
—18

KY.— Louisville
LA — New Orleans

.— 5

MASS — Boston

.— 2
. 3

MD — Baltimore

ME — Portland

.— 5

MICH. >8£°&*-'

MINN St Paul ... .

.—12
—15
.—36

MISS Vicksburg

j>IO — St. Louis

.—10

MONT.-Helena
N. C.— Charlotte
NEB.— Omaha
,TT7,,T i Carson City.

—15
11

.-18

NEV- 1 Winnemucca ..
N. D. — Bismarck
N. H.— Manchester. . .
TST T j Atlantic City...
w< J'|New Brunswick..

9
.--36

'. *5

— 8
—44
— 4
— 2

N. MEX.-Santa Fe ...
»T -\T t Albany

— 8

—10

— 8
-15
6
— 5

— 2
—10
2
2

— 1
— 5
2

N- Y-lNew?6rk....."'
OHIO — Columbus

—11

OKLA — Oklahoma City.

svn-ri 1 Baker City. . .

—14
10

ORE -1 Portland7 i..
T> A j Philadelphia
FA> 1 Pittsburgh
R. I.— Narragansett Pier.

17
. 0
.— 9

9
8

— 2
2
1

23
2
— 1

S. C.— Charleston
c TV i Pierre

. 22

29
—11
—19
17
25
0
16
—17
21
—10

-£

—-•7

&* 1 Yankton

—24

-29
- 2
17
9
6
—21
2
—11

-29
-13

—28
2
11
-17
11
-24
— 2
-30
12
-42
-27

—18
12
28
5
7
-32
20
-10
4
—23
—16

—22
16
21
— 6
19
-22
7
-23
4
-23
2

TENN. -Nashville.
TEX.— San Antonio . . .
UTAH— Salt Lake City..
VA.— Lynchburg
VT.-Northfield

— 2
. 26
. 5
. 4

•CTTAOTT ) Olympia. ..

. 23

WASH- Spokane..::.:..
W. VA.-Parkersburg.

.,14
.—25

WYO.— Cheyenne, , . ,

-19

212

Principles of Heating.

TABLE LV.

WIND VELOCITY.

Weisbach defines winds as follows:

Scarcely appreciable wind 90 feet per minute equals 1.02 miles per hour

Very feeble wind 180 feet per minute equals 2.04 miles per hour

Feeble wind 360 feet per minute equals 4.1 miles per hour

Brisk wind 1080 feet per minute equals 12.3 miles per hour

Very brisk wind 1800 feet per minute equals 20.4 miles per hour

High wind 2700 feet per minute equals 30.7 miles per hour

Very high wind 3600 feet per minute equals 40.1 miles per hour

Violent wind 4200-5400 feet per minute equals 47.8-61.4 miles per hour

Hurricane 6000 feet per minute equals 68.1 miles per hour

The United States Weather Bureau defines a gale as a wind blowing 40 miles per hour.

CHIMNEY FLUES.

For small heating plants the following table, reprinted from
Furnace Heating, by the same author as this treatise, may be
found useful.

TABLE LVI.

THE APPROXIMATE GRATE SURFACE OR FIRE POT AREA FOR CHIMNEYS OF VARIOUS

SIZES AND HIGHTS, BASED ON A RATE OF COMBUSTION OF FIVE POUNDS OF

HARD COAL PER SQUARE FOOT OF GRATE SURFACE PER HOUR.

Diameter of

chimney.

Inches.

50 " 60 ' 70

< Approximate grate surface. Square feet. >

Square or rec-
tangular

Flue.

8x 8

8x 12
12 x 12
12 x 16
16 x 16
16x20
20x20
20 x 24
24x24

TABLE LVII.

AREA OF FIRE POT IN SQUARE FEET.

Diameter. Area.

Inches. Square feet.

18 =1.76

19 =1.97

20 =2.18

21 =2.40

22 =2.64

23 =2.88

24 =3.13

25 . . . = 3.40

26.'! =3.68

27,., =3.98

Diameter.
Inches.
28

Area.
Square feet.
— 427

29;:: :::::•*::'"

— 4 59

— 4 90

31...

— 5.25

— 6 68

33...

— 5.93

34...

— 6.80

— 6 67

36...

..=7.08

N on-Conducting Coverings, Etc. 213

The above table was deduced from formula and table in Bab-
cock & Wilcox's book entitled " Steam." On the basis of 8,000
B. T. U. utilized per pound of coal burned and 250 B. T. U. per
square foot of direct steam radiation and 150 B. T. U. per square
foot of hot water radiation, the number of square feet grate sur-
face stated in table may readily be converted to direct radiating
surface, to which it is adapted by multiplying the square feet
grate surface (average firepot area) by 5 x 8,000 and dividing
by 250 or 150 for steam or water, respectively.

Mains and branches are to be allowed for as radiating surface.
This is expressed as follows :

Grate area x 5 x 8000 „ . ,. , .

= Capacity of chimney expressed

250 for steam or 150 for water

in square feet of radiating surface.

TESTS ON THE RATE OF COMBUSTION IN FURNACES AND THE
VELOCITY OF AIR IN THE PIPES.

The following tests were made on the heating apparatus in a
frame house 29 by 35 feet, with parlor, dining room and reception
room on the first floor, and four bedrooms and a bathroom on
the second floor, heated during one winter season by a brick lined
wrought iron furnace with a 22-inch fire pot, and during the fol-
lowing season by a cast iron furnace with a tapering fire pot hav-
ing an average diameter of about 23 inches.

The brick lined furnace was tested during a 20 days' run in
midwinter. The average outside temperature during this period,
based on readings taken night and morning, was 26.3 degrees;
total weight of coal burned, 2,328 pounds ; rate of combustion per
square foot of grate per hour, 1.84 pounds. A cold day run was
made a little later in the season, the thermometer ranging from 7
degrees below zero to 8 degrees above. During the 24 hours test
coal was fed six times, the total weight amounting to 258 pounds,
making the average rate of combustion 4.07 pounds per square
foot of grate per hour.

The cast iron furnace was tested during a 32 days' trial, the
average outside temperature based on three readings per day,
being 27^ degrees. The total weight of coal burned was 4,350
pounds ; the average per square foot of grate per hour being 1.97

214 Principles of Heating.

pounds. During this test a record of room temperatures was
kept, the average being fully 70 degrees.

A COLD DAY TEST.

During this test a particularly severe day occurred, the tem-
perature falling to 12 below zero. The coal burned during these
24 hours amounted to 300 pounds, giving an average rate of 4.35
pounds per square foot of grate per hour. Coal was fed seven
times. The fire pot was red hot while the thermometer remained
below zero. The weight of ashes and unconsumed fuel passing
through the grate was 10 per cent, of the weight of Lehigh egg
coal supplied. The house in which these furnaces were installed
was of ordinary frame construction, shingled on building paper
and plastered inside. The total cubic contents of rooms connected
with the furnace was 11,674 cubic feet. The total combined ex-
posed wall and glass surface was 1,683 square feet.

It is to be noted that both furnaces used were inside the aver-
age rating given by reputable manufacturers to furnaces of their
size — namely, about 14,000 cubic feet. If based on the exposure
such furnaces are expected to carry approximately 1,700 square
feet of combined wall and glass surface when the latter does not
exceed, say, one-sixth the total exposure. The exposure in this
case is practically the same as the above figure. The house had
storm windows on the north and west sides, yet an average rate
of combustion of nearly 5 pounds per square foot of grate per
hour was found necessary to keep the rooms comfortable in se-
vere weather. This high rate requires pretty frequent attention
and should be considered a maximum.

DATA ON SIZE OF ROOMS, PIPES, AND THE FLOW OF AIR.

The dimensions and other data of the several rooms are as
follows :

N on-Conducting Coverings, Etc.

215

TABLE LVIII.

ANEMOMETER TESTS. FURNACE HEATING.

Rooms.

First floor. Dime

Dining room 13

Parlor 14% x 15 x 8U?

Hall 14 xl8

Second floor.

Bedroom 9 x 12

Bedroom 10x19

Bedroom 10 x 12

Bedroom 13 x 13

Bath 6x 7%x

11,674

Anemometer tests were made with the following results :
Temper-
ature at Velocity Hori-
Room. register. in pipe.
First floor. Deg. F. Feet.

Approximate

Diam.

contents.

Sides

Size of

-Feet.

Cubic feet.

exposed.

pipe.

2,000

10x14

8U>

1,850

10x14

2,140

10x14

864

8x12

1,520

8x12

960

8x12

1,350

9x12

390

7x10

Dining room ......... 116 418

Parlor .............. 114 429

Hall ............... 146 465

Second floor.

Bedroom ............ 100 252

Bedroom ............ 104 320

Bedroom ............ 104 510

Bedroom ............ 127 570

Bath , . . 103 286

Size pipe, zontal run.
Inches. Feet.
10 8

Hi 2

10 4

f — Elbows.— N
90° 45°

1 1

The above tests were made with cold air box wide open and
with little or no wind. The outside temperature was 5 degrees.
The register temperatures were lower than would have been nec-
essary to keep the rooms comfortable had it not been that they
had been warmed to a temperature considerably in excess of 7°
degrees, and furnace drafts were checked to reduce the heat.

Other tests were made, closing all registers on the first floor,
giving velocities of over 500 feet in the rooms on the second floor
most remote from the furnace. Tests were made in 34 degree
weather, showing a velocity of only about 280 feet in rooms on
the first floor. Anemometer readings taken in the cold air box
showed a velocity of over 300 feet and a volume of 900 to 980
cubic feet per minute, corresponding to an air change in the rooms
heated once in about 13 minutes.

216 Principles of Heating.

OTHER TESTS.

Tests made in another house with outside temperature 24 de-
grees showed velocities in pipes leading to the first floor ranging
from 306 to 334 feet, the temperature at the registers ranging
from 104 to 109 degrees. Pipes leading to the second floor
showed velocities in excess of 450 feet per minute with slightly
lower register temperatures than on the first floor. The furnace
in this case had a 22 inch fire pot. The total volume of air sup-
plied to the house per minute was 850 cubic feet.

Still another test, made in a different house, gave these re-
sults for rooms located on the second and third floors, the test
being made in cold winter weather. It will be noted that the reg-
ister temperatures in this case are much higher than in the pre-
vious tests:

TABLE LLX.

FLUE VELOCITIES. FURNACE HEATING.

Temperature of Velocity Hori-

entering air. in pipe. Size pipe. zontal run.

Room. Deg. F. Feet. Inches. Feet. Elbows.

Parlor 138 250 6x10 oval. 9 3

Library 120 210 6 x 7% oval. 4 2

Dining room 140 275 7 diameter. 15 2

Hall 151 450 6x8 oval. 7 2

Bath 108 280 6 diameter. 8 2

Bedroom 152 500 4% x 7% oval. 4 3

Rear bedroom 140 540 5x7 oval. 12 3

These tests give only a general idea of what velocities may be
expected under ordinary working conditions. From the above
and other data the writer has adopted these velocities in making
furnace heating computations.

Approximate velocity in pipes leading to first floor, 280 feet
per minute; to second floor, 400 feet per minute; to third floor,
500 feet per minute.

During the test made in weather 12 degrees below zero the
temperature of the air delivered by the furnace was 113 to 115
degrees. When the outside temperature rose to 6 or 8 below
zero 122 degrees were indicated by the thermometer placed at
register nearest the furnace. The maximum increase in tempera-
ture noted was 130 degrees. The wind was blowing strongly into

N 'on-C Conducting Coverings, Etc. 217

a wide open cold air box. Had this been partially closed the max-
imum temperature would doubtless have exceeded 140 degrees,
which is commonly used as a basis for computations in work of
this kind.

ADVANTAGES OF AIR SUPPLY AT RELATIVELY LOW TEMPERATURES.

There are advantages in supplying air at, say, 120 degrees in
zero weather. There is less tendency for the air to remain at the
ceiling than when admitted at a higher temperature, thus pro-
moting a better circulation in the room and a nearer approach to a
uniform temperature throughout. On the other hand, the lower
the temperature of the air supply the greater must be the volume
to supply the number of heat units necessary to make good the
loss through exposed walls and glass, consequently the more fre-
quent the air change and the greater the fuel consumption.

TABLE LX.

SPACE OCCUPIED BY ANTHRACITE (HARD) COAL PER LONG TON (2240 POUNDS).

Prepared by the author from figures obtained from the Philadelphia and Beading
Coal and Iron Company.

Lump 40.6 cu. ft.

Broken 39.4

Egg 38.8

Stove 38.5

Nut 38.4

Pea... .. 42.1

INDEX.

PAGE

Absolute temperature 67

Air conditioning 66

Air cooling 61 , 63, 66

Air, expansion of 67

Air, heating of 62

Air leakage 45

Air-line vacuum system 126

Air, saturated, table of 65

Air, specific heat of 61

Air supply per pupil 36

Air supply, temperatures of 217

Air, temperature of with indirect heating 36

Air, weight of per cubic foot 62

American District Steam Co., exhaust steam heating 183

Aspirating coils 37

Atmospheric system of steam heating 146

Back pressure, absence of 127

Back pressure, counteracting by increasing boiler pressure 120

Back pressure, effect of 119

Baldwin rule 109

Bishop, Some of the factors that affect the cost of generating and

distributing steam for heating 185

Body, heat from 8

Boilers, computing size of 22

Boiler connections 117

Boilers, efficiency of 8

Boiler horse-power, definition of 8

Boiler horse-power required for heating 53

Briggs formula ? 109

Brill, Pipe covering tests. . 209

British thermal unit 7

219

220 Index.

PAGE

Carpenters rule 112

Central heating and power plant for government buildings. Wood-
bridge 172

Central heating plants, hot water 151

Central heating plants, steam requirements 171

Central station heating, U. S. Geological Survey 179

Central steam heating plants 169, 185

Central steam heating plants, Hoffman 180

Chimney flues 212

Circuit system, steam, capacities of mains 106

Coal, heating power of . . . » 8

Coke, heating power of 8

Coil heaters 14

Coil heaters for water 83

Coils, heating power of 27

Combination heaters 1 1

Combination heaters, types of 15

Combustion, rate of 1 1, 22

Combustion, rate of in furnaces 213

Compound engines, steam from 191

Concrete, transmission of heat through 58

Condensation, effect of, in flow of steam in pipes 98

Condensing engines 1 20

Coverings 205

D'Arcy's formula t . . . . 94

District heating, report by National Electric Light Association 169

District heating, steam, American District Steam Co 183

Elbows, resistance of 92, 97

Electric heating 20

Electrical heat units and equivalents 8, 21

Ejector for Paul system, steam used by 129

Energy, conservation of 60

Engines, condensing, heating from, with hot water system 155

Engines, condensing, used with steam heating 120

Engine exhaust pipes, sizes of 117

Engine supply pipes 118

Equivalent glass surface 36

Evans-Almiral hot water heating system 156

Evaporation 64

Exhaust pipe sizes .* 1 18

Exhaust steam for heating purposes 180

Exhaust steam heating, American District Steam Co 183

Exhaust steam, high value of, Hoffman 182

Index. 221

Expansion of air 67

Expansion tanks . . . 92

Factory heating 160, 163

Factory heating, Hosmer 190

Fire pot areas 212

Flow of steam in pipes 94

Flue areas for indirect radiation 32

Flue velocities, furnace heating 215, 216

Flues, velocity of air in 69

Flue velocities, table of 42, 71

Fractional valve systems of steam heating , 131

Fuels, heating power of , 8

Fuel per season 23

Furnaces, ratio heating to grate surface n

Furnace tests 213

Gas heaters 81

Gas, heating power of 8, 16

Gas vs. coal 16

Grate surface, computation of 10

Heat absorbed per square foot of heating surface 1 1

Heat and energy 60

Heat, loss of through walls, glass, etc 43

Heat losses from buildings, relative .'. 56

Heat losses from pipes 29, 30, 189

Heat losses from underground piping -175, 177

Heat transmission through walls, glass, etc 43

Heat unit, definition of „ 7

Heat units utilized per pound of coal _. 9, 10, 16

Heaters combined with fans 34, 54

Heating equivalents 61

Heating power of radiators and coils 26

Heating vs. condensing 184

Hoffman's description of air valve system 139

Hoffman, J. D., Exhaust steam for heating purposes 180

Hoffman, J. D., Hot water heating, forced circulation 159

Horse-power, heat equivalent of 60

Hosmer, Heating systems for mills >. 190

Hosmer, Mill heating by hot water 163

Hot blast heaters 34, 54

Hot water combination heaters 1 1

Hot water generators 73

Hot water heating by forced circulation. . . . 151, 153, 156, 159, 160, 162

222 Index.

PAGE

Hot water heating mains, table of capacities 89

Hot water heating, pressure required to distribute 177

Hot water heating, volume of water required 159

Hot water vs. steam for central heating plants — the Author 166

House heating boilers, fuel consumption of 21

Humidity 64, 66, 67

Humidity, cost of increasing 67

Indirect heating, pipe sizes 89

Kerr, Heating of South Station, Boston 162

Kerr, The steam loop 195

Kinealy's tests on low temperature heating 130

Lacount, Article on low pressure vs. high pressure steam heating. . . 193

Latent heat of vaporization 61

Liquids, heating of 74

Mackay, The steam loop • 202

Main, the use of steam from the receiver of compound engines for

heating purposes 191

Mechanical equivalent of heat 60

Mercury seal vacuum systems 135

Mercury seal vacuum systems, advantages claimed over hot- water

heating 137

Mill heating 160, 163, 190

Mill's rule 113

Modified systems of steam heating 123

National Electric Light Association report on district heating 171

Non-conducting coverings 205

Norton on heat transmission through concrete 58

Norton, Covering tests 205

Paul system 126

Pipes, capacities of, for hot water heating 85, 87, 88

Pipe covering 208, 209

Pipe coverings 205

Pipe Covering tests, by various engineers 208

Pipes, heat losses from 29, 30

Pipe sizes for indirect heating 89

Pipes, steam, capacities of 94, 101

Pipes, steam, equation of 100

Positive differential system of steam heating X3o

Index. 223

PAGE

Radiation, computation of by charts 46

Radiation, indirect, computation of 31

Radiators, heating power of 26, 27, 28, 29

Radiation, indirect heating power of 31

Radiators, steam, tappings 104

Radiator tappings, hot water 91

Receiver steam for heating ^ 191

Refrigeration 63

Reheating, allowance for 46

Resistance at entrance of pipes 97

Risers, capacities of, for hot water 90

Risers, steam capacities 104, 105

Scale, effect of in boilers 185

South Station, Boston, heating of 162

Specific heat 61

Stanton, Article by, on hot water heating by forced circulation 1 53

Stanton, High pressure steam heating 193

Steam, charges for 179

Steam flow in pipes with over 40 per cent drop in pressure 99

Steam, flow of, in pipes 94

Steam heating by high pressure 193

Steam heating by low pressure, advantages of 193

Steam heating mains, sizes of 101, 102

Steam heating ^with condensing engines 121

Steam loop . ' 195, 202

Steam mains, capacities of, by C. E 113

Steam mains from boilers 117

Steam mains, methods of determining sizes of (E. T. Child) 108

Steam temperatures corresponding to different pressures 136

Steam vs. hot water for central heating plants — the Author 166

Stott, Steam pipe covering and its relation to station economy 207

Swimming pools, heating of 75

Tank heaters 79, 84

Temperature, absolute 67

Temperatures, minimum recorded in the U. S 211

Tempering coils 35

Tudor formula 109

United States Geological Survey, report on central station heating. . 179

Vacuum air valve systems 138

Vacuum, pressures, and corresponding temperatures, table of 136

Vacuum systems, gravity, suggestions for installing 137

224 Index.

Vacuum system, pipe sizes 106

Vacuum systems, two-pipe 122

Vacuum system, two-pipe, advantages of 124

Vacuum systems, with gravity return 133, 134

Vacuum varied to suit weather conditions 155

Valves, resistances of 97

Vapqr system of heating 139

Vapor system, advantages claimed 146

Velocities of steam in pipes 115, 117

Water backs Si

Water, flow of, in pipes 85

Water, heating of 72

Water heating by coils 83

Water, table of weight of 87

Water, velocity of in pipes 87

Weather bureau records 156, 211

Webster vacuum system .122

Wind velocities 212

Woodbridge, Central power and heating plant for government

buildings 172

Woodbridge, Hot water vs. steam heating for mills 160

Wolff rule 109

Yaryan, Article by, on hot water heating 151

UNIVERSITY OF CALIFORNIA LIBRARY
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