630.4 C212 P 1816 1987 OOAg c.3 commercial i growers Agriculture Canada Publication 1816 g AgncuUure § Q C3 £ otTA*A OHTWIO £, Solar greenhouses for commercial growers GJ. Monk Director Western Bio Tech Engineering Ltd. West Vancouver, B.C. D.H. Thomas Coordinator Greenhouse Horticulture Technology Malaspina College Nanaimo, B.C. J.M. Molnar Director Agassiz Research Station Agriculture Canada Agassiz, B.C. LM. Staley Professor Bio Resource Engineering University of British Columbia, B.C. Research described in this publication was conducted at Saanichton Research and Plant Quarantine Station Requests for further information should be addressed to the Director Research Station Agriculture Canada P.O. Box 1000 Agassiz, B.C. V0M1A0 Prepared for Agriculture Canada under the terms of Supply and Services Canada Con- tract No. 08SB.01843 1 ER04. Specific mention of a product type, brand name, or company does not constitute endorsement by the Government of Canada or by Agriculture Canada. Research Branch Agriculture Canada Publication 1816 1987 © Minister of Supply and Services Canada 1987 Available in Canada through Associated Bookstores and other booksellers or by mail from Canadian Government Publishing Centre Supply and Services Canada Ottawa, Canada K1A0S9 Catalogue No. A15-1816/1987E Canada: $6.75 ISBN 0-660-12643-5 Other Countries: $8.00 Price subject to change without notice Canadian Cataloguing in Publication Data Solar greenhouses for commercial growers (Publication ;1816E) Issued also in French under title: Serres solaires commerciales. Bibliography: p. 1 . Solar greenhouses - Design and construction. 2. Greenhouses -Heating and ventilation. I. Monk, G.J. (Gordon J.) II. Series: Publication (Canada. Agriculture Canada). English ;1816E. SB416.S6 1987 690\892 C87-099203-1 Contents Introduction 5 Climatic Considerations 6 Sunshine 6 Temperature 7 Snowfall 8 Wind 8 Site Selection 9 Topography 9 Water table 9 Greenhouse orientation 10 Earth Thermal Storage Solar Heating System 11 Description 11 Applications 12 Design guidelines 18 Pipe material selection 18 Pipe length, spacing, depth, and slope 19 Air circulation rate and fan sizing 20 Plenums and ductwork 21 Below-grade perimeter insulation 21 Installation costs 21 Annual operating costs and returns 22 Economic analysis 22 Shed-type Solar Heating System 23 Description 23 Applications 26 Design guidelines 28 Installation costs 29 Annual operating costs and returns 29 Economic analysis 29 Water Storage Heating Systems 30 Environmental Control for Solar Greenhouses 32 Conclusions 33 Acknowledgments 34 References 35 Appendixes 37 Introduction The North American greenhouse industry is relucant to adopt solar heating as a measure for reducing energy costs. The technology is viewed as being too expensive, complex, and unreliable. However, solar greenhouse research sponsored by Agriculture Canada has produced promising results. Successful solar greenhouse studies have been done at the Agriculture Canada Research and Plant Quarantine Station in Saanichton, B.C., located 48° 37' latitude north, 25 km north of Victoria. The experimental green- houses receive approximately 2100 hours of bright sunshine on an annual basis. This is slightly above the average of 2035 hours for 38 different locations throughout the southern part of Canada. Three different solar greenhouses have been constructed at the research station. The first greenhouse is a 10.8 m * 19.2 m glass-covered conventional even-span gable greenhouse. It has an earth thermal storage (ETS) heating system and is equipped with thermal screens. The second greenhouse is a 6.4 m x 18.3 m shed-type structure. It is one half of a conventional prefabri- cated glass-on-galvanized steel greenhouse with the north roof eliminated and the north wall insulated. This greenhouse is equipped with an internal solar collector and a rock storage heating system as well as thermal screens. The third greenhouse is a prefabricated polyethylene quonset house, measuring 8.84 m * 15.24 m. This greenhouse is heated exclusively by an ETS solar heating system. This publication is intended to supply commercial growers with some basic information on solar heating. It examines some of the different methods of storing excess solar energy and provides guidelines on the design, cost effectiveness, and reliability of solar greenhouses that are either new structures or retrofitted conventional ones. The guidelines are based solely on findings obtained from the experiments conducted at Saanichton, B.C. The information will help the grower to decide whether or not to seriously consider installing solar systems. However, an agricultural engineer should be consulted before a final decision is made to proceed. Climatic Considerations For obvious reasons, climate is of special importance to the proper function of a solar greenhouse. The four weather elements to be considered are sunshine, temperature, snowfall, and wind. Some of the weather records of representative weather stations across Canada are provided in Appendix A. Mean values of daily global solar radiation and hours of bright sunshine are listed in Tables 1 and 2, respective- ly. Temperature data are presented in Table 3 and snowfall records are given in Table 4. Finally, Table 5 provides information concerning mean wind speed and prevailing direction (Canada Atmospheric Environment Service \9&2a,b,c,d,e). For bright sunshine and windspeed, there are a few instances where data are unavailable for the station listed. In those cases, data from the nearest reporting station (not identified) have been supplied. For locations not listed, the grower is directed to contact the nearest Environment Canada Weather Office to obtain representative weather data. Most commercial operators purchase prefabricated greenhouses with structurally engineered frames consisting of galvanized steel and aluminum. However, if any readers wish to plan and build their own greenhouses, they are advised that extreme weather records should not be used, otherwise the structure, heating systems, and so forth will be overdesigned. The green- house must be designed in accordance with the National Building Code of Canada. Before beginning construction, readers should consult additional literature concerning greenhouse design standard guidelines (American Society of Heating, Refrigerating and Air-Conditioning Engineers 1981; National Greenhouse Manufacturers Association 1981; Flowers Canada Inc. 1983). Given the wide variety of climatic conditions, greenhouse structures, crop requirements, and so forth encountered in Canada, it is difficult to make recommendations concerning the suitability of a particular location for solar greenhouses. The solar designs tested at Saanichton have not been evaluated in other regions of the country. However, the following preliminary guide- lines are offered with respect to climate. Sunshine The availability of solar energy is influenced by season, time of day, atmospheric conditions, and surface orientation and placement (Jackson 1983). Normally, temperature conditions and sunshine data must be consid- ered when determining the potential for solar heating (see following section for discussion). However, the successful operation of a solar greenhouse is highly dependent upon the mean daily amounts of global solar radiation and number of hours with bright sunshine. If the solar radiation levels received at a location are below average for Canada, solar heating is probably not feasible. The critical months to consider are March through October; during the winter period of November through February virtually all the solar radiation trapped inside a greenhouse is required for daytime heating demands (Blom etal. 1982; Jackson 1983). The results of experiments at Saanichton have been used to establish minimum levels of sunshine necessary for solar heating. If the sum of the values of mean daily global radiation for each month in the March-October period exceeds 125 MJ/m2, the location may be suitable for solar green- houses (Table 1). In the absence of global radiation data, the total number of hours with bright sunshine in the same period should be studied. Solar heating may be feasible if the total exceeds 1500 hours (Table 2). Temperature After available sunshine has been considered, temperature becomes the most critical climatic factor influencing the operation of solar greenhouses. In cold climates, low winter temperatures increase the rate of heat loss from the greenhouse interior as well as from the underground thermal storages. During sunny days, excess solar energy does not become available for storage if cold outside temperatures produce excessive heat losses. If the ground surrounding the thermal storages is also very cold, heat losses from the storages make it difficult to maintain adequate reserve heat levels. It is important to note that even if the thermal storages are much warmer than the surrounding ground, the stored heat becomes useless if the storage tempera- ture is below the interior nighttime set point. The procedure for calculating heat losses and net daytime solar heat gains is well established (National Research Council of Canada 1981/?; Blom et al. 1982; Darby 1982; Kadulski et al. (date unknown); Roberts et al. 1985). Table 3 provides the annual heating degree-days for different Canadian locations. One degree-day is equivalent to a daily mean temperature one degree below 18° C for a duration of 24 hours. As the number increases, proportionally greater amounts of heat are required to maintain the green- house environment at 18° C. If the available solar radiation is sufficient in comparison to the heating load during the growing season between March and October, solar heating may be economical for greenhouses. To quantify the relationship between solar radiation and heat load, the ratio of the sums of the values of mean daily global radiation to number of degree-days for each month in the growing season must be examined. If this ratio exceeds 0.08, solar heating may be feasible for that particular location. For example, this ratio for Edmonton, Alta., one of the sunniest locations in Canada, is 131. 82 MJ/m2 of mean daily global radiation to 2425 degree- days. After division, this results in a value of 0.054. Consequently, Edmonton is not suitable for solar greenhouses because of its cold nights in the spring and fall. However, Toronto, Ont., has a ratio of 135.86 MJ/m2 to 1591 degree- days, which equals a value of 0.085. Therefore, a properly designed solar greenhouse may be economical there. If global daily radiation data are not available for the location in question, the ratio of hours of bright sunshine to number of degree- days should be evaluated. In this situation, solar heating should be seriously c< >nsidered if the ratio exceeds 0.8. For example, in Vancouver, B.C., the total number of hours of bright sunshine during March-October is 1669, whereas the number of degree- days is 1372. This results in a ratio of 1.22, indicating that a preliminary design evaluation should be done. Readers are cautioned that the second method is less accurate and not quite so conservative. Snowfall A greenhouse structure must be designed to withstand the weight of snow accumulation, in accordance with the National Building Code of Canada. The design snowload is calculated on the basis of a location's maximum 24-hour snowfall (Table 4). Readers may be contemplating using solar heat to extend the growing season in a structure that would otherwise be unheated. In such instances there will be no heat available for melting. Therefore, the roof must be built to withstand design accumulations or, alternatively, the roof must be pitched at a steep enough angle to ensure that snow will slide off and the sidewall height must then be sufficient to allow snow to clear the roof. The grower is directed to Flowers Canada Inc. (1983) and National Greenhouse Manufac- turers Association (1981) for a thorough discussion of this subject. Wind A greenhouse location with constant exposure to high wind speeds can result in increased heat loads of up to 25% annually. Greenhouses are not generally recommended in exposed locations where mean wind speeds in excess of 25 km/h are encountered during any of the winter months (Table 5). Exposure can be reduced and heat losses cut by 5% to 10% by erecting a windbreak. The windbreak must not shade the growing area, an especially critical point with solar greenhouses. For guidelines on the construction, costs, and benefits of windbreaks, see Roberts et al. (1985). 8 Site Selection Several factors must be considered when selecting a site for any commercial greenhouse operation. The location should be relatively flat, because a level grade must be established before construction begins. The site should provide good drainage and the space and orientation that may be required for future expansion. Distances to markets and the condition of interconnect- ing roads are also important considerations. Obviously it is essential that there be a considerable degree of exposure to the sun. When presented with the choice, it is desirable to have exposure to the early morning sun as opposed to the late afternoon or evening sun. Plants become photosynthet- ically active as soon as they receive their first light of the day. However, on long, hot days, some plants may slow photosynthesis in midafternoon due to high water loss from rapid transpiration and other stress- related factors. In low- lying, sheltered areas such as frost pockets the early morning sun is critical for reducing heat loads and burning off fog. When selecting a site for a solar greenhouse, special attention must be given to the topography, the water table, and the greenhouse orientation. Topography The site must be virtually free from obstructions that could otherwise block incoming solar radiation. If obstructions cannot be removed, the percentage of daily sunshine being lost must be determined, using the procedures and charts contained in Appendix B. If the percentage of blocked sunlight exceeds 15% during any of the months in the growing period of March-October, then the site is probably not suitable for solar heating. The solar heating systems discussed here are designed to use under- ground thermal storages installed to depths of about 1 m. The cost projections for the economic feasibility studies assume that a trencher, or backhoe, can be used to install piping or rock storages. These cost projections would rise dramatically if it became necessary to blast rock in order to install the solar systems and could seriously influence the economic potential of any project. Therefore, it is critical to ensure that no bedrock lies closer to the surface than 1 m below site grade. Large boulders are also likely to cause problems. A silty loam is the ideal material to contend with, but few problems should occur with any type of free and loose material. Water table Locating thermal storages underground also makes the water table an important site consideration. If groundwater can migrate transversely across a storage, the collected heat will be lost very quickly. This can be prevented by installing drainage around the entire greenhouse at a depth of 0.5 m below the thermal storage. It is recommended that the drain pipes be placed in drain rock or gravel. The rock material surrounding the pipes should extend from 30 cm below grade down to 10 cm beneath the pipes. If the heat storage system is installed against the north wall the water table can be as high as 1 m below grade. Greenhouse orientation The ETS solar greenhouse design is adaptable to any orientation. However, other designs, including the solar shed-type configuration, only function propely in an east-west alignment. Most greenhouse operations are located in the southern part of Canada (43°-50° northern latitude). In some areas, winter light levels can be a limiting factor. For single-span greenhouses an east-west orientation is generally preferred over a north-south orientation because this maximizes light levels in winter and reduces light levels in summer, thereby decreasing ventilation requirements. This advantage of an east-west alignment becomes more evident with increasing distance from the equator. Furthermore, if a grower decided to insulate the north wall in a single-span greenhouse, the reduction of heat losses would be much greater with an east-west orientation. In multispan, gutter-connected greenhouses, the light transmission advantage of an east-west alignment is more than offset by fixed areas of shading produced by the gutters. For this reason, multispan, gutter-connected greenhouses are almost always oriented north-south. This orientation allows gutter shadows to move from west to east across each bay during the day. 10 Earth Thermal Storage Solar Heating System Description An ETS solar heating system (Fig. 1) uses the soil beneath the floor as heat storage material. As the greenhouse air temperature rises above the set point, hot air that collects near the peak is drawn through a network of buried pipes below the floor, using a large electric fan. As heat is transferred to the pipes they increase in temperature and transfer the heat to the surrounding soil. The cooled and dehumidified air is then blown back into the green- house. Therefore, although the ETS system is collecting heat it is also functioning as a first-stage cooling system. The storage becomes fully charged when the temperature of the air exiting the pipes is equal to or greater than the temperature of the air entering the pipes. The solar fan should not be operated whenever the earth storage is at maximum tempera- ture, because then the electrical input energy is wasted. A second-stage cooling system must be provided for these occasions and for whenever the ETS system has insufficient cooling capacity to maintain the set point temperature. When the inside air temperature falls below the set point, heat can be released from the storage if the soil is at a higher temperature. Most of the heat is released into the greenhouse by circulating the inside air through the pipes again. The air absorbs the heat through the pipe sidewalls before it is returned to the greenhouse. A small portion of the stored heat is transferred by conduction to the interior through the greenhouse floor. Air intake (second stage of cooling) Polyethylene plastic Air intake (charging, first and second stages of cooling) Air intake (discharging, first stage of heating) Air outlet (charging, second stage of cooling) Eggfe Fig. 1. An ETS beating system design for gutter connected, et>en span gable greenhouses 11 The storage is discharged completely when the temperature of the air exiting the pipes is equal to or less than the air temperature inside the greenhouse. The solar fan should not be operated when the storage is empty because this wastes electrical power. If a minimum set point temperature must be maintained, a backup heating system is required. It should be sized for the winter design heat load, because no solar heat would be available under those conditions. The backup heating system can be used in conjunc tion with the ETS system whenever solar heat is available, but it is insufficient to maintain the set point temperature. The efficiency of the solar fan can be increased by enabling it to provide forced-air ventilation in the greenhouse as a second stage of cooling. If an air inlet with a motorized shutter is installed at the opposite end of the green- house from the fan, fresh air will be drawn through the greenhouse interior. The air will then enter the air intake, pass through the fan, and be forced back through the pipes. The ETS system will serve as a heat exchanger to remove heat from the ventilated air before it is discharged outside through a motor- ized outlet. The overall efficiency of the ETS system can also be increased by raising the air inlet temperature during charging. This can be accomplished by extending a single layer of clear polyethylene film along the peak, creating a horizontal zone of relatively undisturbed air. The plastic should extend longitudinally from the gable adjacent to the fan inlet to a point about 1 m from the opposite gable. This would leave a gap for air intake. The separation distance between the roof cover and the plastic should also be about 1 m. Readers are cautioned that this measure significantly reduces the effective- ness of the ridge ventilators, because the film blocks the free movement of air to the crop. If thermal screens are installed in the greenhouse, a single air inlet can be installed underneath. However, a second daytime air inlet should be installed above the screens if temperatures in the peak are at least 3°C higher than below the screens. Applications ETS systems do not depend on any type of solar collector to accumulate heat. The greenhouse itself serves as a solar collector, utilizing both direct beam and scattered diffuse solar radiation transmitted through every surface of the structure. Consequently, an ETS system can be installed in any green- house, regardless of orientation or structural configuration. A north-south alignment enhances summertime performance, since more light enters the structure. For even-span gable greenhouses, the ideal roof slope for maximum light transmission is about 10° lower than latitude. For example, if the greenhouse location is at a latitude of 49° , the ideal roof slope would be 39° . However, the high peak on such a greenhouse would require costly construc- tion and operating expenses. Most greenhouses constructed for commercial use have a roof slope of 26° or 32° (Mastalerz 1977). At a reasonable cost, this provides for snow slippage, a high level of light transmission, and prevents condensation drips. 12 The type of material covering the structure is not critical because the inside surfaces absorb either beam or diffuse light and subsequently transmit heat back into the greenhouse air. Glass transmits more light than other materials but offers little resistance to heat loss. Double polyethylene films do not transmit as much light, but their resistance to heat transfer is much higher. Since heat losses through the covering are lower, a greater portion of the accumulated excess heat is available for storage. Ideally, the covering should provide both high light transmittance and high resistance to heat loss. Some double layer acrylic materials offer both advantages but at a very high cost. Double-polyethylene quonset greenhouses are currently the most inexpensive and simplest greenhouses to construct. The galvanized steel arches are supported by concrete friction footings and the end walls are usually framed with 2 * 4s to support a sliding door. Growers who are just starting their commercial greenhouse operations often initially build quonset greenhouses because of their low capital and heating costs. ETS systems are compatible with this type of structure, especially if they are made as inexpensively as possible (Fig. 2). The ductwork above the ground can be eliminated by extending the pipes up out of the ground and turning the ends in toward the greenhouse so that the exhaust air is blown over the crop. In moderate climates, an ETS system in a double-polyethylene quonset greenhouse can maintain a frost- free environment unless temperatures fall below -10° C Such a greenhouse can be an inexpensive shelter for overwinter ing young nursery stock. The ETS system can also extend the growing season in an unheated tunnel. When backup heating systems are installed, the ETS system can provide cost effective energy savings. Air intake Side ventilators Fan with simple air outlet Fig. 2. An ETS beating system for an onset type greenhouses. 13 Obviously, it is more simple and less expensive to install an ETS system in the ground before the greenhouse is erected. However, an ETS system can be easily retrofitted into any greenhouse that does not have a concrete floor. If crops are being grown directly in the soil, an ETS system will not only conserve energy but will function as a root zone heating system. As a result, plant development may accelerate and crop yield may increase (Figs. 3 and 4). • Z ' Fig. 3- Five-week-old cauliflower, cabbage, and broccoli crops in an ETS solar quonset house. Note that rows almost touch one another. Fig. 4. Five-week old cauliflower, cabbage, and broccoli crops in an unheated quonset house. Note slower plant development. 14 After the ETS system is installed, the floor can be covered with gravel, wood chips, or porous concrete. Porous concrete (Fig. 5) is a mixture of cement and gravel without the addition of sand. Water flows readily through the void spaces around the stones. It is important to allow excess irrigation water to flow into the soil around the pipes to prevent the soil from drying out. If the soil is allowed to dehydrate, its thermal conductivity and heat storage capacity decreases substantially (National Research Council of Canada 1977). Furthermore, the soil may shrink, causing it to separate its contact with the pipes. This would drastically reduce heat transfer rates between the pipes and the soil. Soil shrinkage could also crack and damage the concrete floor. For second-stage cooling in glass gable greenhouses, natural ventilation is preferable to forced ventilation, because exhaust fans are costly to operate. In greenhouse sections with sidewall and ridge ventilators (Fig. 6), the sidewall ventilator should be opened first to prevent the escape of accumu- lated excess heat in the peak. This warm air is then drawn into the buried pipes, allowing cooler air to rise and take its place. The ridge ventilators should only be opened when the inside air temperature increases well above the set point or if the thermal storage is fully charged. 15 'JSSKoi f US ■« ii i *! mailing! nsE^Jiiu jiik' Fig. 6. An ei vn -span gable greenhouse with the sidewall ventilator opened first, followed by the leeward ridge ventilator. w^ Fig. 7. A fan jet and perforated convection tubesystem withheatkit. The duct conveying warm air from the solar storage is on the left. The propane unit heater is at the right. In polyethylene houses, forced ventilation is often used in the absence of either sidewall or ridge ventilators. Fans with perforated polyethylene convection tubes are popular (Fig. 7). Sometimes a heat kit is installed behind the fan. This allows warm air that is being blown out of the thermal storage and/or unit heater to be distributed down the perforated tube. If the perforations in the tube are pointed upward, the hot air blows across the greenhouse roof rather than directly onto the crop. Some plants, including tomatoes, do not transpire properly if hot air is blown onto their leaves. Also, air movement against the roof diminishes water condensation drops. 16 Fig. 8. A polyethylene sidewall ventilator rolled up on shaft. Fig. 9. An inflated polyethylene sidewall ventilator dosed with a tight seal. Reduced condensation decreases condensation heat losses and the threat of disease spreading. It also increases light transmittance through the cover during the day. Double polyethylene greenhouses can be cooled with natural ventila tion by installing roll-up sidewall ventilators (Figs. 8 and 9). If the ventilators are inflated with a small centrifugal fan, they will form a tight seal when closed and reduce heat loss across the plastic layers. The shaft that winds the ventilator up and down can be motorized. This eliminates manual labor and provides automatic control, but the cost is prohibitive relative to the cost of the structure. 17 Design guidelines The design guidelines that follow are based upon experimental results from the work at Saanichton and recommendations included in other re- search publications. To assist readers, examples are given of how some of the guidelines would apply in a greenhouse about 930 m2 in size. It is assumed that the greenhouse has a length of 48 m and a width of 19. 2 m. The dimensions are based on the column spacings of a Venlo-style gable glass- house. Pipe material selection ETS studies in Japan concluded that the total surface area of the buried pipes should at least equal the surface area of the greenhouse floor (Sasaki and Itagi 1979). The surface area of the pipes is determined by their diameter and spacing. These factors also influence the amount of air that can be conveyed by the pipes. After taking all parameters into consideration, the Japanese researchers concluded that a pipe diameter of 10 cm is ideal. The ETS pipes are not subjected to much pressure either from the air or from the surrounding soil. Since the pipe walls do not have to be very strong, inexpensive drainage pipe or sewer pipe is adequate. The cheapest material available is non-perforated, corrugated, drainage tubing. However, the corru- gations greatly increase the friction between the moving air and the pipe wall. In their comprehensive design guide for underground heat storage, Lawand et al. (1985) report that corrugated pipe has 3-2 times the pressure loss of smooth 10 cm ID (internal diameter) pipe. This means that about three times as much fan power is required to move an equivalent amount of air through corrugated pipe. One might think that corrugated pipes are capable of transferring more heat to the surrounding soil than smooth pipes because of their greater surface area. However, Sibley and Raghavan (1984) measured the heat transfer coefficients of a variety of corrugated drainage tubes and found that their heat transfer coefficients were similar in magnitude but somewhat less than those found in smooth pipes. Calculations show that corrugated and smooth pipes transfer similar amounts of heat overall for a given airflow. One of the cheapest smooth pipe materials available is ASTM 2729 plastic drain pipe; it costs about $1.15 (1986 funds) per metre more than corrugated drainage tubing. A 930-m2 greenhouse requires about 3170 m of ETS pipe, allowing for some extra waste material. If corrugated tubing is selected, the capital cost saving is approximately $3650. The additional electricity required for the fans to overcome the increased friction costs about $245 annually. As a result, the smooth pipes should pay for themselves over a 15-year period and will provide operating cost savings over the remaining 15 years of the system's life. However, the difficulty of transporting rigid pipes and the additional labor required to install them in the ground must also be taken into account. Once these factors have been considered, it would seem that 10 cm ID non-perforated, corrugated, drainage tubing is the superior material for the ETS system. Since common perforated tubing fills with water, preventing airflow, non- perforated tubing should be used for the ETS application. 18 Pipe length, spacing, depth, and slope Lawand et al. (1985) recommend pipe lengths between 10 m and 20 m for maximum efficiencies in ETS applications. Accordingly, in greenhouses more than 20 m long, the configuration of the fan, plenums, and pipes should be similar to the one depicted in Fig. 10. If the greenhouse is longer than 40 m, two sets of ETS systems should be installed end-to-end. The fans can either draw air from the pipes (negative pressure, Fig. 10) or blow air into the pipes (positive pressure, Fig. 1). In the first instance, air enters intake ducts above the end plenums and is exhausted through outlets above the fan mounted on the central plenum (Fig. 10). Alternatively, air enters an intake above the fan on the central plenum and is exhausted through outlets above the end plenums (not illustrated). The location of the fan on the central plenum is not critical, nor is the location of the inlet or outlet ducts. Shading can be reduced by locating ductwork in the corners of the house or at the sidewalls. However, an even air distribution is important for maximum efficiency; therefore, the number of ducts and their location should be selected to balance the air distribution. In Venlo-style greenhouses, the air intake height need only be as high as the gutters. In all ETS systems, the exhaust air should be blown across the top of the crop. Perforated convection tubes are ideal for distribution of the exhaust air. In our example of the 48-m-long greenhouse we can assume that the plenum chambers would occupy approximately 2 m of the overall length. Since the pipe length should not exceed 20 m, it would be necessary to install two ETS systems end-to-end. This would result in individual pipe lengths of 11.5 m, which falls within the specified design criterion. Air intake (charging) Air intake (discharging) Fan location with air outlets (charging and discharging) Central plenum Fig. 10. An ETS beating system for conventional greenhouses more than 20 m long. 19 Lawand et al. (1985) determined that the minimum pipe spacing should be at least 40 to 60 cm centre to centre. Based on the ETS performance at Saanichton, the authors recommend a lateral pipe spacing of 55 cm. This takes into account the pipe surface area requirement, as stipulated by Sasaki and Itagi ( 1979). It also provides for an adequate number of pipes to convey the required airflow rate, while maintaining an acceptable cost for the pipe material. Although our example greenhouse is 19.2 m wide, a clearance space must be left between columns and adjacent pipes of about 30 cm centre-to- centre. This allows clearance for the concrete friction footings that support the columns. Let us assume that besides the exterior columns, there are two rows of internal truss support columns. This will reduce the effective ETS field width by 1.8 m, leaving 17.4 m of available space. A 55-cm lateral pipe spacing will allow 33 rows of pipes to be installed if the outside rows are squeezed in slightly. The total number of pipes in this ETS system will equal 33 rows * 2 layers * 4 pipe lengths, resulting in a total of 264 pipes. The pipes should be installed at depths of 40 and 80 cm, floor grade to centres. These depths meet the minimum spacing requirements and result in an effective and adequate storage depth of about 1 m. At the same time, trenching and installation costs are minimized. When the greenhouse air is hot and very humid and the storage tem- perature is sufficiently lower, water may condense out of the air into the ETS pipes. To facilitate drainage of the condensate, the pipes should be installed at a 0.5% slope downward in the direction of airflow. The condensate then flows into the soil at the bottom of the plenum chamber where it drains away to the perimeter drainage system. If only one plenum chamber is installed, as shown in Fig. 2, the direction of the airflow and the pipe slope must be toward the plenum; otherwise, the condensate will not drain from the pipes, preventing dehumidification from occurring. Air circulation rate and fan sizing As the total air circulation rate increases, the heat transfer rate in the pipes increases, as does the amount of energy available for storage. It follows that the capacity and responsiveness of the ETS system will improve as a result. However, the power required to move air increases exponentially by a power of three as the airflow rates increase. With increased airflow rates, a point is reached where the overall system efficiency starts to decline. If excessive input energy is required to operate the solar system, the net energy savings become too low for economic returns. The optimum air velocity in the pipes is about 2 m/s, according to Lawand et al. (1985). Despite this, they report that velocities of 5 m/s, or more, are acceptable in ETS systems with short pipe lengths (5 to 10 m) or fewer fittings, such as elbows or transition sections, which cause large dynamic losses. A velocity of 2 m/s corresponds to an airflow rate of 0.016 m3/s per pipe at a pressure loss of 35 Pa, given a length of 15 m. Research at Saanichton indicates that the ETS system performance is most efficient when the air circulation rate moves the total volume of air in the greenhouse through the pipes once every 9 min. 20 If the Venlo-type greenhouse in our study has a gutter height of 3 m, then the volume is approximately 3130 m3. The total airflow rate should therefore be 5.80 m3/s, which is equivalent to 0.022 m3/s in each of the 264 pipes. The pipe air velocity is 2.7 m/s. This may initially appear to be excessively high but the pipe lengths are near the lower end of the recom- mended range. A calculation of the pressure drop will determine if the design is adequate. Using methods outlined in the ASHRAE handbook, Fundamentals (American Society of Heating, Refrigerating and Air- Conditioning 1981), and data taken from Carson et al. (1980), a pressure loss of 50 Pa is calculated. Depending on the design of the inlets, outlets, and transitions from the pipes to the plenums, as well as the number of elbows, the total pressure loss may be anywhere from 100 to 150 Pa. Our design example requires two fans, each capable of moving 2.9 m3/s against the total pressure loss. These fans require a motor size of about 1.87 kW. The studies at Saanichton have shown that a 930- m2 greenhouse requiring 37 kW of solar fan input energy is economical to operate (see Annual operating costs and returns, p. 22). For an actual ETS system design, the system pressure losses would have to be carefully determined according to the methods recommended by ASHRAE. Plenums and ductwork The plenum chambers can be built with pressure-treated plywood and 2" x 4"s (5 x 10 cm), and these should extend across the full width of the greenhouse. The covers should be sealed well to eliminate air leakage. It is not advisable to cover the bottom of the plenum, otherwise condensate from the pipes cannot drain away. The ductwork is usually constructed of plywood and 10-cm cant strip, and should be painted white to reflect light onto the crop. An ETS system requires a smooth, aerodynamical ly efficient network of plenums and ducts. The details of the configuration, the intersections of the components, and their dimensions should be checked by an expert. The operation of an ETS system cannot be economical if the airflow pressure losses are unacceptably high. Below-grade perimeter insulation Since stored heat does not migrate very far below the lower pipes, there is no need to install insulation below the storage. However, heat moves laterally from the storage to colder external soil. Heat loss to the outside ground can be controlled by installing perimeter insulation to a depth of 1.2 m. This will also provide frost protection for the column footings. The material should have an insulation value of at least Rsj = 0.9 m2°C/W (R = 5 ft2h°F/BTU) but it can be cost effective up to Rsi = 2.6 m2°C/W (R = 15 ft2h ° F/BTU) (Towning and Turkewitsch 1981). The cost of excavation is included if the insulation is installed in either the perimeter drain trench or the outside pipe trenches. Installation costs The total capital costs to install an ETS system similar to that depicted in Fig. 10 in a 930-m2, even-span gable house are about $11.40/m2 (1985 funds). 21 Labor costs to install the pipes, fans, and electrical connections are also included. It is assumed that growers will supply their own labor to build the ducts. Annual operating costs and returns The experimental ETS system at Saanichton has reduced the heating requirements of a commercially sized gable glasshouse by 25.1% annually, compared to an identical control structure. However, electrical energy consumption has been 33-696 higher due to the power requirements of the solar fan. This translates to a total energy savings of 22.196, given that the ratio of heat energy to electrical energy requirements in the control house is 19.25:1. Agriculture Canada made all the experimental data concerning capital and operating costs available to Arcus Consulting Limited, independent specialists in agricultural economics. They summarized the annual costs and returns, using estimates of annual maintenance costs as supplied by the researchers at Saanichton. The cost of propane was assumed to be 10.2275/L, and the overall efficiency of the conventional hot water boiler heating system was calculated at 75%. The electricity costs selected were $0.06l9/kWh for the first 550 kWh consumed per month and $0.0431/kWh for any additional monthly consumption. Economic analysis Arcus Consulting Limited (1985) determined the net present value and benefit-cost ratios for the ETS system. The benefit-cost ratios were 1.8, 1.4, and 1.1 for interest rates of 5, 10, and 15%. The internal rate of return was estimated to be 18% per annum. The results showed that the ETS system has potential economic viability at all three rates of interest, assuming that the performance measured is the same as that measured at Saanichton. The technology will likely be most profitable at low interest rates. The analysis was repeated, assuming that No. 2 fuel oil was the fossil fuel being used at a cost of 10.2690/L In this analysis, the overall efficiency of the conventional heating system was calculated at 65%. With oil, the benefit-cost ratios are 35, 2.7, and 2.2 for each of the three rates of interest, respectively. The internal rate of return is then 55% per annum. Arcus Consulting Limited also studied the economics of installing an ETS heating system in an unheated double-polyethylene quonset with vegetable crops grown directly in the soil. It was concluded that the system is not economic under any conditions if the benefits are based on increased vegetable production due to the effect of elevated night temperatures, an extended growing season, and root zone heating. An economic analysis of ETS systems in heated double-polyethylene quonsets based on energy savings alone is not available. 22 Shed-Type Solar Heating System Description The shed-type solar greenhouse (Fig. 11) is designed for northern latitudes above 52°, where the sun is closer to the horizon and winters are extremely cold. The east-west oriented structure is formed from one half of a conventional galvanized steel and aluminum gable frame with an insulated vertical north wall. Since the resulting configuration is costly to build, has a narrow width, and shades the area to the north, its application is limited. It can only be installed during the initial construction of a greenhouse. There- fore, it is not described here in as much detail as the ETS system. The shed-type profile has a greater ratio of glazed surface area to floor area than a conventional gable structure. Consequently, it transmits 30-45% more light to the interior on a unit floor area basis, depending upon the month (Lau et al. 1984). An insulated north wall will reduce heat loads by 15% compared to an uninsulated gable glasshouse of equal area. Black collector curtains Hot air withdrawal Insulated north wall Arrows indicate airflow during charging procedure. Fig. 11. A beating system design for detached shed- type greenhouses. 23 Solar collecting panels made of reinforced polyethylene covered in flat black latex paint to increase absorptivity hang in front of the insulated wall. They are suspended from a scroll attached to a hot air collecting duct in the peak and are designed to be rolled up and down, according to the demand for heat and the height of the crop. The inside surface of the north wall insulation is painted with white high-gloss interior latex paint. This paint protects polystyrene insulation, whereas other paints may corrode the insulation material. When the collecting panels are rolled up, the white surface is designed to reflect light onto the crop and also to reflect excess radiation out of the greenhouse (Fig. 12). The reflective paint also increases the efficiency of the solar-collecting panels when they are rolled down, because light passing around the panels is reflected back onto the inside collector surface. Fig. 12. An insulated north wall in a shed type greenhouse. The solar collecting panels, which are suspended from a scroll, are retracted to reflect light. 24 The vertical slope of the collecting panels results in maximum efficien- cies in spring and fall because the sun's rays strike the collecting panels at a lower angle. The panels heat the air surrounding both sides, causing the air to rise passively toward the peak. A large electric centrifugal fan draws the heated air into the duct and transfers it to rock storages beneath the greenhouse floor (Fig. 13). The air is then forced through void spaces between the rocks, which absorb the heat. The cooled and dehumidified air is subsequently returned to the green- house interior. If the temperature of the air exiting the storages reaches the inlet air temperature, the storages are fully charged. The solar fan should not be operated in the charging position again until some heat has been recover- ed from the storages. The stored heat should be released at night by reversing the airflow direction, using motorized dampers in the ductwork surrounding the fan (Fig. 14). Rock storages develop longitudinal temperature stratifications during charging. In contrast to earth thermal storages, the regions near the point where the hot air enters become warmer than the opposite ends. Airflow reversal during discharge allows the circulated air to pass through the warmest rocks before reentering the greenhouse. This ensures that the recovered heat is available at the maximum possible temperature. If the discharged air temperature falls below the interior temperature, the solar fan should be shut off until more heat is collected. Fig. 13. An insulated north wall and solar fan. 25 Fig. 14. Motorized dampers for airflow reversal. Applications The shed-type solar heating system is only compatible with an east-west alignment. The covering material must not diffuse the transmitted light, because the collecting panels only function effectively with direct-beam radiation. The only practical glazing is therefore single- layer glass. Experiments at Saanichton have shown that the shed's collecting panels are capable of collecting far more heat than can be contained in rock storages beneath the shed's floor. On a commercial scale the system is only economi- cally feasible if it is gutter-connected to a second east-west-oriented, even- span gable glasshouse to the south containing additional rock storages beneath its floor (Fig. 15). By adding the gutter-connected structure, the cost of the insulated north wall, collector, and solar fan will apply to three times as much greenhouse floor area. 26 Air pressures in rock storages must be fairly high in order to force circulation through the void spaces. To ensure a tight seal, the rock storages should be covered with polyethylene before the floor material is placed on top. The polyethylene also prevents excess irrigation water from entering the rock storages. A 10-cm layer of fine gravel or coarse sand is sufficient to hold the polyethylene in place. Alternatively, a solid concrete floor can be laid down. Natural ventilation by means of a ridge ventilator does not work in a solar-heated shed. For one thing, a ridge ventilator cannot provide sufficient cooling capacity because some outside air is drawn into the peak collecting duct. Also, the resulting downdrafts interfere with the passive movement of hot air that rises from the collector. The best method of ventilation is to install a fan jet convection system above the crop, with shutters at each end to allow outside air to flow across the greenhouse. The warm air recovered from the rock storages can be ducted into a heat kit whenever solar heating is required. Another method is to install exhaust fans with shutters. Although exhaust fans with shutters do not distribute the solar heat, they are desirable if evaporative cooling pads are required to maintain acceptable maximum daytime temperatures. In addition, a solar fan will have adequate power to distribute the discharged solar- heated air down a perforated convection tube if the air-handling system has been properly designed, thereby eliminating the requirement for a fan jet. Hot air withdrawal Black collector curtains Insulated north wall East plenum Air duct hot air supply (charging) Central plenum Solar fan West plenum Fig. 15. A beating system design for gutter connected, shed type greenhouses 27 Design guidelines The airflow dynamics in rock storages are very complex and depend upon numerous critical factors, including the air circulation rate, the indivi- dual rock size range, the void space ratio, and the dimensions of the storages. Consequently, it is impossible to offer design guidelines such as those discussed for the ETS system. Readers who wish to gain an understanding of the airflow principles involved are referred to publications by the National Research Council of Canada (1979, 1980, and 1981a). The air circulation rate is determined by the characteristics of the solar radiation available at the site and the dimensions of the shed and its collector. A monthly analysis of the anticipated solar collector performance should be performed according to the principles outlined by the National Research Council of Canada (1977). The duct design and fan sizing are determined, using the guidelines published in ASHRAE handbook, Fundamentals (American Society of Heating, Refrigerating and Air-Conditioning 1981). The ductwork can be built with the same materials that are used for the ETS system (plywood and 10-cm cant strip), and should also be painted white to reflect sunlight. The plenum chambers in the experimental house at Saanichton are made with concrete block. Because the outer walls of the plenum chambers at the ends of the storages must be airtight, the blocks are laid on end in conventional fashion. The walls of the central plenum and the inside walls of the plenums at the ends of the storages must contain large holes to allow air to pass through and be strong enough to resist the lateral load imposed by the rock beds. To facilitate these requirements, the blocks are laid sideways and their inner surfaces are covered with two layers of 13-mm steel mesh to prevent rock from falling through (Fig. 16). Fig. 16. A concrete block plenum construction. 28 The top, bottom, and sides of the rock storages and the north wall should be insulated with a material that has an insulation value of at least Rsj = 0.9 m2°C/W (R = 5 ft2h°F/BTU). Extruded polystyrene foam is ideal for this purpose. The rock storage should also be sealed with a vapor barrier of 0.15 mm (6-mil) polyethylene film. The outside surface of the north wall can be covered with an inexpensive material that is easy to install, such as fiberglass. Installation costs Typical installation costs for a 945-m2 solar shed gutter connected to an even-span gable glasshouse are about $35.00/m2 (1985 funds). The solar shed is assumed to be one half of a standard 12.8 m * 54.9 m gable house. Dimensions of the gutter-connected house are 10.8 * 54.9 m. Annual operating costs and returns During tests done at Saanichton, a solar shed used 47% less heat energy and 73-1% more electricity than a gable house, for an overall energy savings of 40.3%. Agriculture Canada supplied Arcus Consulting Limited with cost and energy saving data for the experiments. The company determined the annual costs, using similar methodology to that which was applied to the ETS system. Economic analysis The benefit-cost ratios for the 945-m2 solar shed gutter connected unit with natural gas heating are 1.3, 1.0, and 0.7 at interest rates of 5, 10, and 15%, respectively. The internal rate of return for this technology is 9% per annum. The results show that with this fossil fuel the solar shed system may only be economically feasible at an interest rate of 5%. The technology has a higher net present value, a higher benefit-cost ratio, and an internal rate of return when No. 2 fuel oil is used for heating. With this method of heating, the system was economic at all three rates of interest studied. Benefit-cost ratios observed were 2.5, 1.8, and 1.4, respective- ly, and the internal rate of return increased to 25% per annum. Despite the fact that the solar shed is capable of delivering significantly higher energy savings than the ETS system, its higher capital costs result in much lower economic potential. For many reasons, the ETS system is better suited for commercial application. 29 Water Storage Heating Systems The heat storage capacity of water is 2.8 times greater than that of rock and is similar to that of wet soil. However, solar systems that use water as a heat-transfer fluid are costly, restricting their use in commercial greenhouse applications. The large collectors must be situated outside the greenhouse, which presents problems in gutter connected ranges. These systems are also often plagued with leaky fittings. In several research projects external solar collectors were used with hot water storage in insulated tanks. It was found that the collector area to greenhouse floor area ratio must be 1 : 1 to provide significant energy savings. The high capital investment required to install such a system and the high cost of the land occupied by the solar collectors are not offset by the savings achieved. The resulting pay back period is 15-20 years. Solar ponds are open bodies of water that simultaneously collect and store solar energy by absorbing the sun's rays. They can be installed inside a greenhouse, but the floor area they occupy cannot be used to grow crops. The hindrances that internal solar ponds create also make plant transporta- tion difficult. Barrels or other containers can be filled with water and stacked against an insulated north wall, where they are exposed to the sun's radiation (Fig. 17). They absorb heat during the daytime. At night the accumulated heat is passively radiated back into the greenhouse interior. Although this simple application of solar heating only provides a significant energy savings in small greenhouses, the low cost can make this technique cost effective. 30 Fig. 17. Water barrels that are used as beat storage in a small greenhouse. 31 Environmental Control for Solar Greenhouses To ensure optimum efficiency of solar heating systems, the environmental control equipment must be responsive to changing heat balances inside the greenhouse. Set point temperatures must be maintained, regardless of the heating method used for the greenhouse. Greenhouses that are heated by a combination of two different heating systems require advanced environmental control devices in order to function effectively. Solar systems operate most efficiently when ventilation and cooling equipment and the first and second stages of heating are initiated at the correct temperature. The sequence of these functions must be defined properly. To better understand possible sequences, various steps are described for a typical ETS greenhouse. The temperature set points are assumed to be 18 °C during daytime and 21 °C at nighttime. The first stage of cooling is initiated when the interior air temperature rises above the set point. At approximately 23 ° C the solar fan starts operating, resulting in the withdrawal of hot air into the pipe network. Interior tempera- tures stabilize when climatic conditions permit. The second stage of cooling is initiated when increased solar radiation causes the interior air temperature to rise farther. At approximatley 25 °C the side ventilator opens, then the ridge ventilator opens. In the case of gutter connection, the exhaust fans are switched on sequentially. More advanced controls stop the charging if the inlet air temperature falls below the soil temperature. This situation sometimes occurs after several days of bright sunshine, during which the storages reach maximum temperature. Opera- tion of the solar fan for heating must be locked out if the storages are empty until more heat is collected. The solar fan does not operate at the set point temperatures, and will only withdraw heat from the storages if the interior air temperature drops below the set point by more than 1.5°C. If the temperature falls another 1.5°, the conventional heating system turns on. 32 Conclusions In certain areas of Canada where climatic factors are favorable, an earth thermal storage solar greenhouse may be economically feasible, based on experimental results obtained at the Agriculture Canada research station in Saanichton, B.C. The technology is suitable for any new greenhouse regard- less of structure, covering, or orientation. It can easily be retrofitted into existing greenhouses provided they do not have concrete floors. A grower who is considering using this technology is advised to carefully consider the topics discussed in this brochure before proceeding. An agricultural engineer should approve a solar- heating design, because it is critical for efficient operation. 33 Acknowledgments The authors thank the following contributors to this publication: Dr. Ed van Zinderen Bakker, Agriculture Canada Saanichton Research and Plant Quarantine Station, Sidney, B.C., for conducting experiments to determine the effects of solar heating on plant growth and maintaining the computerized control-data acquisition system; Chris Dyble, B.C. Hydro and Power Authority, for arranging to lend the researchers several electricity meters belonging to the public utility; Henk Grasmeyer, Frank Jonkman & Sons Ltd., for valuable advice on greenhouse designs; Peggy Watson, Agriculture Canada Saanichton Research and Plant Quarantine Station, Sidney, B.C., for assistance in obtaining research material; Norman Dressier and the Atmospheric Environment Service Office, Victoria International Airport, Sidney, B.C., for supplying climatic data; Bob Duncan, Victoria, B.C., for permission to photograph his facilities; and George Lechleiter, Greenwood Indoor Plants Ltd., Surrey, B.C., for providing a grower's viewpoint through many helpful suggestions and constructive criticisms. 34 References Arcus Consulting Limited. 1985. An economic evaluation of three new greenhouse technologies. Prepared for Agriculture Canada, Regional Development Branch, Vancouver, B.C. American Society of Heating, Refrigerating and Air-Conditioning Engineers. 1981. ASHRAE Handb. Fundamentals. New York, NY. Blom, T.; Ingratta, E; Hughes, J. 1982. Energy conservation in Ontario greenhouses. Ont. Minist. Agric. Food Publ. 65. 24 pp. Canada. Atmospheric Environment Service. 1982a Canadian climate normals. Vol. 1. Radiation. Canada. Atmospheric Environment Service. 1982b. Canadian climate normals. Vol. 7. Bright sunshine. Canada. Atmospheric Environment Service. 1982 c. Canadian climate normals. Vol. 4. Degree days. Canada. Atmospheric Environment Service. 1982 d. Canadian climate normals. Vol. 3. Precipitation. Canada. Atmospheric Environment Service. 1982 e. Canadian climate normals. Vol. 5. Wind. Carson, W.M.; Watts, K.C.; Desir, F. 1980. Design data for air flow in plastic corrugated drainage pipes. Trans. ASAE (Am. Soc. Agric. Eng.) 23(2): 409-413. Darby, D. 1982. Greenhouse heating requirements: Calculating heat loss. Alberta Agriculture, Print Media Branch. Agri-fax. (Agdex 731T). Flowers Canada Inc. 1983- A design standard guideline for Canadian greenhouses. Guelph, Ont. 32 pp. Jackson, H.A. 1983- Solar energy in Canadian agriculture. Agric. Can. Eng. Stat. Res. Inst. Contrib. I 569. 90 pp. Kadulski, R. ; Lyster, E.; Lyster, T. Solplan 3- The Drawing Room Graphics Services Ltd., Vancouver, B.C. 60 pp. Lau, A.K.; Staley, L.M.; Monk, G.J.; Molnar, J.M. 1984. Solar radiation transmission in greenhouses. Trans. ASAE (Am. Soc. Agric. Eng.) Pap. 84-4535. Lawand, T.A.; Coffin, W; Alward, R. ; Chagnon, R. 1985. Design guide for underground heat storage. Agriculture Canada Research Station, Saint Jean sur Richelieu, Quebec. Tech. Bull. 21. MastalerzJ.W 1977. The greenhouse environment. New York, NY: John Wiley & Sons. 35 Molnar, J. M.; Monk, G.; Staley, LM. 1983. Greenhouse energy conservation studies at the Saanichton Research and Plant Quarantine Station. Presented to the 1983 Ornamentals North West Seminars, Oregon. Monk, G.J.; Staley, L.M.; Molnar, J.M.; Thomas, D. 1983- Design, construction and performance of two earth thermal storage solar greenhouses. Can. Soc. Agric. Eng. Pap. 83-405. National Greenhouse Manufacturers Association. 1981. Standards: Design loads in greenhouse structures: Ventilating and cooling greenhouses: Greenhouse heat loss. Saint Paul, MN. 51 pp. National Research Council of Canada. 1977. Solar energy program: In ground heat storage. Sol. Energy Proj. Rep. STOR 5. 33 pp. National Research Council of Canada. 1979. A heat storage subsystem for solar energy: Final report — phase 2. Sol. Energy Proj. Rep. STOR-6. 85 pp. National Research Council of Canada. 1980. Rock bed thermal energy storage. Sol. Energy Proj. Rep. STOR-8. 57 pp. National Research Council of Canada. 1981a A guide to rock bed storage units. Sol. Energy Proj. Rep. STOR 10. 53 pp. National Research Council of Canada. 1981 b. The solarium workbook. Sol. Tech. Ser. 2. 112 pp. Roberts, WJ.; Bartok, J.W.; Fabian, E.E.; Simpkins, J. 1985. Energy conservation for commercial greenhouses. Northeast Regional Agricultural Engineering Service. NRAES-3. 40 pp. Sasaki, K.; Itagi, T 1979- Studies on solar greenhouses heated by means of an earth-storage heat-exchange system. 1. Effects of atmospheric and thermal conditions in a greenhouse on growth and yield of tomatoes. Canada, Dep. Secretary of State, Translation Bureau. Translation 235467. (Translated from Bull. Kanagawa Hortic. Exp. Stn, 26 October 1979.) Sibley, K.J.; Raghavan, G.S.Y. 1984. Heat transfer coefficients for air flow in plastic corrugated drainage tubes. Can. Agric. Eng. 26(2): 177-180. Staley, L.M.; Molnar, J.M.; Monk, G.J. 1981. Design, construction and operating experience with two commercial solar heated greenhouses. Can. Soc. Agr. Eng. Pap. 81-232. 25 pp. Staley, L.M.; Monk, G.J.; Thomas, D.; Lau, A.; Molnar, J.M. 1983- Earth thermal heat exchange systems for solar greenhouses. Trans. ASAE (Am. Soc. Agric. Eng.) Pap. 83-4525. 17 pp. Towning, D.J.; Turkewitsch, A. 1981? Pages 1-217 in Energy efficient greenhouse design and operation. Bradford, Ont.: Frank Jonkman and Sons Ltd. 36 Appendixes Appendix A The following weather stations correspond to the numbers in Tables 1-5: No. Station Province 1 Agassiz British Columbia 2 Kamloops British Columbia 3 Kimberley British Columbia 4 Prince George British Columbia 5 Summerland British Columbia 6 Vancouver British Columbia 7 Victoria British Columbia 8 Brooks Alberta 9 Calgary Alberta 10 Edmonton Alberta 11 Grand Prairie Alberta 12 Lethbridge Alberta 13 Medicine Hat Alberta 14 Estevan Saskatchewan 15 Moose Jaw Saskatchewan 16 Regina Saskatchewan 17 Rosetown Saskatchewan 18 Saskatoon Saskatchewan 19 Swift Current Saskatchewan 20 Yorkton Saskatchewan 21 Cypress River Manitoba 22 Morden Manitoba 23 Portage La Prairie Manitoba 24 Rivers Manitoba 25 Winnipeg Manitoba 26 Brockville Ontario 27 London Ontario 28 North Bay Ontario 29 Ottawa Ontario 30 Peterborough Ontario 31 Sudbury Ontario 32 Toronto Ontario 33 Windsor Ontario 34 Drummondville Quebec 35 Montreal Quebec 36 Quebec Quebec 37 Sherbrooke Quebec 38 Tadoussac Quebec 39 Trois Rivieres Quebec 40 Gander Newfoundland 41 St. John's Newfoundland 42 Stephenville Newfoundland 43 Fredericton New Brunswick 44 Moncton New Brunswick 45 Saint John New Brunswick 46 Charlottetown Prince Edward Island 47 Halifax Nova Scotia 48 Sydney Nova Scotia 37 Table 1. Mean values of daily global solar radiation (MJ/m2) on a horizontal surface Weather Stn Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. 4 2.73 5.30 10.09 15.79 18.15 21.42 20.81 17.04 11.12 6.14 3.07 1.78 5 3.44 6.48 11.54 16.66 20.82 22.64 23.68 19.55 14.47 8.45 3.82 2.50 6 2.94 5.53 10.03 15.09 20.15 21.78 22.95 18.62 13.22 7.38 3.59 2.28 10 3.65 7.09 12.43 17.53 20.21 21.87 21.89 18.09 12.11 7.69 3.95 2.59 19 5.05 8.72 14.05 17.86 21.58 23.14 24.35 20.13 14.36 9.45 5.27 3.83 25 5.25 9.05 14.06 17.74 20.90 22.74 22.99 19.00 13.32 8.15 4.64 3.82 29 5.74 9.44 13.61 16.75 19.88 21.37 21.28 18.11 13.36 8.58 4.72 4.33 32 6.09 9.33 12.92 17.33 19.96 21.74 21.94 18.74 14.09 9.14 4.79 4.33 35 5.30 8.80 12.51 15.87 19.07 20.25 20.96 17.23 13.45 8.04 4.61 3.92 41 4.14 7.08 10.42 13.60 16.54 19.60 19.94 15.72 12.02 6.82 4.11 3.03 43 5.48 8.92 12.35 15.32 17.94 19.91 19.61 17.32 13.20 8.50 5.05 4.12 46 5.32 8.97 12.61 15.88 18.57 20.92 20.10 17.71 12.93 7.90 4.94 3.79 47 5.11 8.14 12.09 14.54 17.38 20.00 19.11 17.94 13.98 8.96 5.32 3.85 38 Table 2. Average monthly and total annual duration of bright sunshine in hours Weather Stn Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual 1 42 68 102 135 177 174 246 210 157 105 58 35 1818 2 54 93 150 187 245 244 208 275 194 121 63 43 1977 3 31 109 183 181 276 242 346 307 182 146 89 32 2124 4 54 89 139 187 255 256 279 245 158 104 60 39 1865 5 49 83 148 198 250 261 320 277 206 140 63 40 2040 6 55 93 129 180 253 243 305 255 188 116 70 44 1931 7 70 98 150 198 277 176 338 287 209 139 81 60 2183 8 88 116 158 206 270 287 341 304 201 173 111 76 2334 9 99 121 156 196 237 240 317 278 188 166 116 94 2208 10 91 113 176 223 272 265 306 269 185 161 105 80 2237 11 83 116 154 204 245 254 281 246 163 151 93 66 2056 12 95 123 167 198 263 284 345 299 213 175 116 90 2370 13 91 118 149 199 256 261 342 292 188 165 105 86 2170 14 121 135 185 210 289 303 356 310 212 188 120 103 2536 15 105 125 166 218 279 285 344 297 202 173 110 85 2394 16 98 117 156 210 271 253 337 293 194 169 96 83 2277 17 99 117 163 208 279 283 334 290 179 157 95 77 2281 18 99 129 192 225 279 280 342 294 207 175 98 84 2403 19 92 114 156 208 177 281 342 297 194 168 110 85 2328 20 108 129 165 223 281 288 329 285 184 157 90 87 2328 21 115 136 158 202 253 260 313 272 186 158 96 94 2241 22 115 136 158 201 252 260 312 272 185 157 96 93 2241 23 121 144 176 220 266 276 316 283 185 152 91 93 2321 24 116 141 174 210 261 270 339 294 193 170 93 94 2359 25 112 139 170 209 246 259 331 276 183 158 81 86 2230 26 104 115 171 206 258 264 302 264 189 152 81 81 2186 27 69 96 128 170 233 243 274 253 177 153 73 61 1930 28 97 130 158 188 231 246 267 226 158 115 59 70 1945 29 96 115 150 175 231 245 277 243 171 138 76 78 1995 30 73 101 133 165 228 236 270 224 168 132 73 40 1843 31 100 131 152 207 247 246 288 251 150 122 77 84 2060 32 87 110 145 179 221 256 281 256 197 153 82 77 2045 33 83 104 123 169 201 221 239 216 121 84 47 58 1687 34 92 112 149 173 224 237 260 233 176 133 75 73 1936 35 93 109 156 171 220 241 264 238 180 140 70 77 1959 36 81 99 139 163 198 196 223 208 167 126 63 65 1708 37 83 107 136 167 227 245 266 231 167 131 72 65 1900 38 94 109 155 179 199 211 225 215 165 123 78 78 1832 39 97 113 161 180 228 230 241 226 174 134 78 80 1941 40 73 85 102 116 155 169 202 180 145 112 62 60 1461 41 64 76 89 116 158 188 213 184 145 111 62 52 1458 42 44 71 105 131 186 189 206 186 133 92 54 32 1432 43 103 118 141 160 201 203 234 218 166 140 85 91 1860 44 103 120 135 168 212 226 247 223 166 141 87 90 1918 45 99 118 143 160 202 199 218 204 163 138 87 88 1819 46 83 105 137 156 199 215 244 220 180 133 72 59 1803 47 93 118 140 165 206 203 226 216 182 154 95 84 1885 48 81 106 126 161 204 222 251 225 168 139 74 67 1824 39 Table 3. Degree-days below 18.0°C Weather Stn Jan. Feb Mar. Apr. May Jun. Jul Aug. Sep. Oct. Nov Dec Total 1 524 382 368 255 159 83 2 748 545 450 268 128 41 3 860 642 584 380 236 122 4 931 681 613 411 268 156 5 664 505 443 278 144 52 6 479 379 378 277 180 91 7 463 374 382 288 197 113 8 988 776 701 402 211 92 9 923 713 681 441 265 141 10 1068 829 764 443 245 123 11 1108 851 781 459 248 131 12 876 661 622 392 219 95 13 949 726 645 371 183 71 14 1062 849 740 418 211 71 15 1046 832 730 415 208 68 16 1113 894 800 440 221 84 17 1139 880 806 451 222 91 18 1155 920 825 441 217 88 19 1012 800 733 434 235 101 20 1178 947 854 475 241 91 21 1137 927 806 434 215 76 22 1094 883 766 428 202 57 23 1126 919 787 444 220 66 24 1155 933 832 457 239 83 25 1154 948 811 439 219 69 26 820 716 591 341 163 38 27 763 681 585 349 183 51 28 960 827 721 445 235 88 29 896 777 650 374 174 44 30 851 747 645 366 195 66 31 982 863 745 458 238 84 32 766 680 588 355 187 51 33 709 616 520 299 135 27 34 891 783 655 380 176 48 35 874 762 636 368 165 40 36 932 815 698 442 227 72 37 921 800 690 437 235 95 38 908 794 694 475 292 114 39 933 811 677 408 196 59 40 749 699 666 512 366 192 41 666 621 610 479 364 196 42 711 683 645 485 343 183 43 842 745 633 419 229 79 44 809 727 648 450 266 103 45 798 721 635 443 278 128 46 778 719 654 471 295 117 47 743 680 609 440 274 106 48 703 674 634 481 328 152 37 36 88 221 362 464 2983 11 19 102 296 493 645 3751 47 64 193 391 617 770 4910 98 127 247 410 625 803 5376 13 19 94 279 467 593 3556 39 41 114 248 362 438 3030 64 66 124 251 360 427 3115 31 54 187 361 628 847 5283 68 98 223 386 620 800 5365 79 108 246 414 705 962 5990 78 108 245 430 719 973 6135 32 52 167 327 563 735 4745 19 36 155 329 587 793 4868 18 39 174 359 648 902 5496 20 39 175 360 648 890 5434 29 50 196 398 693 955 5876 38 62 206 409 702 971 5982 32 60 208 407 711 995 6062 37 60 196 381 652 873 5509 35 65 217 410 716 1009 6242 21 46 186 382 677 963 5875 13 28 156 339 643 943 5560 18 40 175 357 663 967 5787 24 45 196 389 704 1012 6075 21 43 178 369 676 991 5923 6 19 100 262 448 720 4229 13 22 101 267 448 665 4132 36 61 182 360 568 858 5348 10 27 127 306 504 797 4691 20 36 140 314 475 733 4593 30 56 181 361 576 874 5451 12 20 102 272 440 666 4143 2 6 61 218 409 615 3622 9 31 134 313 487 791 4701 8 23 116 289 481 771 4537 23 48 169 352 546 838 5165 44 73 183 356 529 805 5173 53 81 204 376 549 806 5350 16 41 150 329 529 837 4993 72 91 200 371 486 674 5083 79 77 175 322 425 587 4606 72 70 182 338 453 640 4811 20 37 153 326 497 758 4739 28 44 156 323 481 726 4763 48 55 162 321 470 705 4768 28 37 139 306 456 683 4688 29 32 131 292 437 646 4424 45 45 140 297 425 612 4540 40 Table 4. Greatest snowfall in 24 hours (cm) Weather Stn Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Year 1 45.7 45.7 30.5 15.2 5.1 0.0 0.0 0.0 0.0 5.1 35.6 33.0 45.7 2 33.8 10.7 16.8 2.8 T 0.0 T 0.0 T 2.8 30.2 23.9 33.8 3 32.3 23.6 17.8 18.5 6.6 T T 0.0 3.3 10.2 38.1 31.0 38.1 4 29.2 22.9 19.8 21.8 9.4 0.5 T T 9.1 22.1 26.9 29.0 29.0 5 19.1 30.5 33.5 5.1 0.0 0.0 0.0 0.0 0.0 12.7 19.8 45.7 45.7 6 29.7 18.3 25.9 3.6 T 0.0 0.0 0.0 0.0 0.3 22.1 31.2 31.2 7 29.2 22.4 21.3 5.1 T 0.0 0.0 0.0 T T 16.0 34.8 34.8 8* 16.5 17.5 18.0 17.3 15.5 0.0 0.0 0.0 7.6 20.3 18.8 35.1 35.1 9 25.4 27.7 24.1 45.7 48.3 24.9 0.3 6.1 22.9 29.7 35.6 21.8 48.3 10* 20.3 19.1 21.1 22.6 12.8 T 0.0 0.0 7.6 31.5 15.7 16.8 31.5 11 21.8 21.3 22.1 15.7 17.5 T 0.0 19.3 12.7 36.3 21.3 23.4 36.3 12 18.8 24.4 33.5 52.6 32.5 10.9 T 3.8 55.1 35.8 37.8 21.6 55.1 13 26.4 27.9 33.8 25.4 14.0 1.5 0.0 0.0 26.2 21.6 26.7 22.9 33.8 14 15.5 24.9 15.7 35.1 16.8 T T 0.0 11.7 29.0 18.0 18.8 35.1 15 16.8 20.8 16.3 24.1 11.2 T 0.0 0.0 27.2 18.3 14.5 13.2 27.2 16 14.0 19.1 25.4 23.2 19.8 7.6 T 0.0 21.6 21.3 23.9 14.2 25.4 17 25.4 15.2 15.2 25.4 19.1 T 0.0 0.0 10.2 27.9 20.3 22.9 27.9 18 15.5 30.0 26.9 19.1 18.5 T T 0.0 7.1 28.4 19.1 16.3 30.0 19 13.7 22.1 33.5 22.9 20.1 5.1 0.0 0.0 12.7 17.8 22.9 18.3 33.5 20 24.9 43.2 21.8 23.6 9.1 T 0.0 0.0 13.2 26.4 24.1 19.1 43.2 21 21.0 40.6 30.5 38.1 13.0 0.0 0.0 0.0 2.5 25.4 28.2 25.4 40.6 22 35.6 25.4 45.7 25.4 22.9 T 0.0 0.0 7.6 15.2 40.9 38.1 45.7 23 22.4 18.8 25.4 53.8 11.7 0.0 0.0 0.0 12.2 21.8 18.8 16.5 53.8 24 17.8 65.0 18.5 20.1 13.2 T 0.0 0.0 3.3 40.6 19.3 25.4 65.0 25 19.1 23.6 35.6 21.3 21.1 0.3 0.0 0.0 1.8 24.6 27.7 21.6 35.6 26 51.8 47.5 45.0 30.5 7.1 0.0 0.0 0.0 2.5 29.0 40.6 31.8 51.8 27 32.5 30.0 27.4 21.8 5.8 0.0 0.0 0.0 T 15.7 40.6 57.0 57.0 28 26.0 26.2 26.7 27.7 10.2 0.0 0.0 0.0 2.0 11.4 27.9 20.3 27.9 29 38.6 39.6 40.6 26.7 15.0 T 0.0 T 1.5 15.5 25.4 30.4 40.6 30 66.0 40.6 55.9 23.4 15.2 0.0 0.0 0.0 2.5 15.2 27.9 30.5 66.0 31 37.0 37.8 34.0 33.5 9.9 T 0.0 0.0 1.8 17.0 21.8 27.2 37.8 32 36.8 39.9 32.3 26.7 2.3 T 0.0 0.0 T 7.4 33.5 28.2 39.9 33 23.9 36.8 22.4 14.2 0.5 T 0.0 0.0 T 2.4 34.8 32.3 36.8 34 71.1 38.1 38.1 27.9 15.2 0.0 0.0 0.0 0.8 29.2 50.8 36.3 71.1 35 32.8 39.4 43.2 25.7 21.8 0.0 0.0 0.0 6.1 14.2 30.5 37.8 43.2 36 32.3 29.2 43.9 33.0 7.1 0.3 0.0 0.0 T 17.3 30.5 35.6 43.9 37* 40.3 31.2 33.0 27.7 16.3 T 0.0 0.0 T 24.4 37.8 34.8 40.3 38 45.7 55.9 61.0 30.5 10.2 T 0.0 0.0 T 25.4 45.7 45.7 61.0 39 38.1 40.6 41.9 43.7 12.7 0.0 0.0 0.0 0.0 10.2 41.1 48.3 48.3 40 35.2 47.8 41.4 37.8 16.5 21.8 T T 5.1 20.8 43.8 45.7 47.8 41 38.4 54.9 45.7 31.6 25.4 13.5 T 0.0 0.3 19.8 25.3 49.3 54.9 42 56.1 41.7 33.0 21.1 14.0 2.5 0.0 0.0 0.3 12.7 16.5 35.3 56.1 43 36.1 40.6 34.8 26.4 15.2 0.0 0.0 0.0 T 11.4 35.1 78.0 78.0 44 40.6 76.2 40.6 45.7 21.6 1.3 0.0 0.0 T 22.4 31.0 38.1 76.2 45 42.4 34.8 40.1 26.2 10.2 0.0 T 0.0 0.0 19.8 21.3 58.2 58.2 46 47.2 47.5 33.5 38.1 13.2 T 0.0 0.0 T 21.6 30.5 32.0 47.5 47* 43.7 47.2 24.6 28.4 26.9 T 0.0 0.0 T 38.6 20.3 47.5 47.5 48 44.5 45.2 37.3 29.2 24.9 1.0 0.0 0.0 T 15.7 21.6 58.7 58.7 *Records with less than 25 years 41 Table 5. Mean wind speed (km/h) and prevailing direction Weather Stn Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov Dec. Annual 1 14.0 9.4 7.8 6.9 6.1 4.9 4.9 4.5 5.5 6.0 9.5 12.8 7.7 NE N N S S S S S S S N N S 2 11.8 11.5 13.4 13.2 12.3 11.8 10.5 10.0 10.2 12.1 13.1 13.9 12.0 E E E W W W W W E E E E E 3 8.5 9.0 10.0 12.1 11.0 11.1 10.5 9.9 9.3 10.4 9.4 8.6 10.0 S S s S S S S S S S S S S 4 11.4 11.9 11.9 11.7 10.8 9.9 8.7 8.3 9.2 12.5 12.2 12.1 10.9 S S S S S S S S S S S S S 5 5.9 4.8 6.0 6.8 6.3 7.0 5.8 5.4 4.8 4.3 4.4 4.8 5.5 N N N S S S N N N N N S N 6 12.2 12.4 13.5 13.3 11.8 11.5 11.4 10.6 10.6 11.2 12.2 13.0 12.0 E E E E E E E E E E E E E 7 12.5 12.1 12.5 12.1 11.1 10.5 9.5 9.2 9.1 10.0 11.4 12.7 11.1 W W W W W SE SE SE W w W W W 8 13.2 12.6 13.4 16.0 14.9 13.9 12.3 12.1 12.5 14.1 13.6 13.6 13.5 NW NW NW NW NW NW NW NW NW SW S SW NW 9 16.2 15.8 16.4 18.1 18.2 17.0 14.9 14.4 15.8 16.3 15.4 16.1 16.2 W S S NNW NNW NNW NNW NNW NNW W W W W 10 13.4 13.4 13.4 15.2 15.7 13.6 11.6 11.3 13.0 13.6 12.9 13.1 13.4 S S S S SE W W W S S S S S 11 11.5 12.3 12.8 14.5 16.8 16.2 14.1 13.6 13.7 14.4 12.0 11.3 13.6 NW NW NW W W W W W W W W NW W 12 21.2 21.2 21.0 21.3 20.4 20.0 16.9 16.8 18.4 22.5 22.4 23.1 20.4 W W W W W W W W W W W W W 13 15.3 15.2 16.2 18.1 17.3 16.1 14.4 14.5 15.7 17.3 16.7 16.8 16.1 SW SW SW SW SW SW SW SW SW SW SW SW SW 14 21.5 21.0 20.5 20.8 20.8 19.1 17.8 17.9 19.7 20.4 20.5 21.0 20.1 NW NW NW E E W NW E NW NW NW SW NW 15 21.6 21.2 21.2 21.3 21.4 19.8 17.5 17.4 20.3 20.9 21.0 21.8 20.5 WNW WNW WNW SE SE W W W W WNW WNW WNW WNW 16 21.8 21.6 22.0 22.6 22.1 19.9 17.7 18.1 20.4 20.5 20.9 21.7 20.8 SE SE SE SE SE SE SE SE SE SE SE SE SE 17 14.9 15.5 15.2 16.8 16.9 15.8 14.0 14.1 15.0 16.3 14.8 15.2 15.4 W SE SE SE SE NW NW SE NW NW SE W SE 18 16.8 16.4 17.5 19.0 19.4 18.2 16.7 16.5 18.1 18.0 16.9 16.8 17.5 WNW SW SE SE SE WNW W WNW WNW S WNW WNW WNW 19 25.1 24.4 23.4 23.3 22.9 21.7 19.4 19.6 22.1 23.6 23.7 25.1 22.9 W W W W W W W W W W W W W 20 17.3 16.7 17.5 18.3 19.2 17.8 16.0 15.6 17.8 18.6 18.0 17.3 17.5 NW NW NW S S S W S S S NW NW NW 21 18.2 17.6 18.1 19.0 19.4 17.9 15.6 15.4 17.6 19.0 17.9 17.3 17.8 NW NW NW NE NW NW NW NW NW NW NW NW NW 22 13.5 12.6 13.6 13.5 14.0 13.2 11.0 10.5 12.1 13.0 13.7 13.8 12.9 NW NW NW NW NW NW NW NW NW NW NW NW NW 23 17.9 16.8 17.7 18.7 18.3 16.0 14.4 14.4 16.4 18.0 17.8 17.2 17.0 NNW NNW NNW N N N W N N W W W NNW 24 18.7 17.5 18.5 21.3 21.8 19.3 17.0 17.1 19.1 19.9 19.4 18.4 19.0 NW NW NW NW E E NW E NW NW NW NW NW 42 Table 5. Mean wind speed (km/h) and prevailing direction (concluded) Weather Stn Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual 25 18.6 18.1 19.3 20.9 20.2 18.1 16.0 16.4 18.5 19.6 19.4 18.6 18.6 S S S S S S S S S S S S S 26 14.0 13.4 13.4 14.1 14.2 14.3 13.6 13.7 15.4 17.0 16.2 12.9 14.4 W NW NW NW NW SW NW NW SW NW NW W NW 27 19.7 18.4 18.9 18.4 15.9 13.5 11.8 11.5 12.9 14.7 17.6 18.4 16.0 W W E E E S SSW W E W WSW WSW W 28 15.1 15.4 16.3 16.4 15.1 13.8 12.9 12.5 13.4 14.3 15.6 14.8 14.6 N N N N SW SW SW SW SW SW W E SW 29 16.2 16.2 16.7 16.8 14.8 13.2 11.8 11.5 12.8 14.1 15.2 15.5 14.6 WNW WNW E E SW SW SW SW W E E WNW WNW 30 12.8 11.8 13.5 13.8 11.2 10.0 8.7 7.9 8.9 10.3 11.6 11.6 11.0 W WNW WNW WNW WNW WNW W W W W W WSW W 31 21.0 21.8 21.4 21.7 21.1 20.1 18.8 17.9 19.1 20.4 21.5 21.0 20.5 N N N N N SW SW SW S S S N N 32 18.4 17.6 17.6 17.3 14.9 13.4 12.5 12.3 13.0 14.1 16.6 17.0 15.4 WSW N N N N N N N N W W W N 33 20.0 19.9 20.6 19.7 17.2 14.8 12.9 12.5 13.7 15.7 18.4 18.9 17.0 WSW SW WNW SSW SSW SSW SW SW SSW SSW SSW SW SSW 34 11.5 12.0 12.4 11.8 10.6 9.2 8.2 7.9 8.5 9.9 10.3 10.6 10.2 W W W W W W W W W W W W W 35 18.3 17.9 17.9 16.9 15.3 14.5 13.1 12.2 13.1 14.8 16.6 16.8 15.6 WSW WSW WSW W SW SW SW SW SW W W W WSW 36 18.9 18.9 18.0 16.6 16.5 14.5 12.8 12.9 13.4 15.0 16.2 17.7 16.0 WSW WSW ENE ENE ENE WSW WSW WSW WSW WSW WSW WSW WSW 37 11.5 12.0 12.4 11.8 10.6 9.2 8.2 7.9 8.5 9.9 10.3 10.6 10.7 W W W W W W W W W W W W W 38 15.7 15.8 16.1 14.7 13.5 13.1 12.5 12.0 12.3 14.4 14.6 15.0 14.1 S S S N N S S S S S S S S 39 10.1 10.6 11.9 12.1 11.1 9.7 9.0 8.5 8.6 10.0 11.0 11.2 10.3 SW NE NE NE NE SW SW SW NE NE NE NE NE 40 24.4 23.9 23.4 21.6 19.7 18.7 17.3 17.2 18.9 20.6 21.8 22.8 20.9 W W W NNW W SW SW WSW W WSW W W W 41 27.5 27.5 26.9 24.4 22.9 22.2 21.4 21.2 22.1 23.8 25.2 26.8 24.3 W W W WSW WSW WSW WSW WSW WSW WSW W W WSW 42 19.3 18.3 16.9 15.5 13.9 11.9 11.1 12.7 13.9 14.8 16.9 18.5 15.3 W W ENE WSW WSW WSW WSW WSW WSW W W W W 43 14.6 14.8 16.0 14.8 14.7 13.6 12.3 11.6 12.0 13.0 13.4 14.3 13.8 WNW WNW WNW WNW SSW SSW SSW SSW SSW SSW WNW WNW WNW 44 20.3 19.8 20.5 19.0 18.1 16.9 15.2 15.2 16.2 17.7 18.7 19.9 18.1 W WSW WSW WSW WSW SW WSW WSW WSW WSW WSW WSW WSW 45 20.6 20.2 21.0 19.1 18.3 17.3 15.5 15.0 16.4 18.3 19.8 20.5 18.5 NW NW NW N SSW SSW S S SSW SSW NW NW S 46 22.1 20.8 21.7 19.9 18.9 18.0 16.1 16.0 17.2 19.1 20.4 21.5 19.3 W W W N WSW WSW WSW WSW WSW W W W W 47 20.2 19.7 20.7 19.2 18.5 17.3 15.9 15.4 15.7 17.2 18.5 19.8 18.2 WNW WNW N N S S SSW S SSW SSW N NW SSW 48 24.4 23.8 24.1 22.2 21.1 20.0 18.6 18.4 19.3 21.3 22.9 23.8 21.7 W W N N SSW SW SSW SW SW SW W W SW 43 Appendix B Sun path charts An appropriate sun path chart corresponding to a site's latitude can help a grower determine the amount of solar radiation reaching an existing greenhouse or a proposed greenhouse location. Sun path charts for latitudes of 43°, 49°, 53°, and 60° have been provided (Figs. 20, 21, 22, and 23, respectively). Trees, buildings, mountains, and so forth that could interfere with the incoming solar radiation should be drawn into the appropriate chart after their angular heights and azimuth bearings (horizontal angles from true south) have been established. A protractor can be used with a string and a weight (Fig. 18) to measure the angular altitude of obstructions around a greenhouse. A compass will indicate the horizontal angle from true south. The magnetic south pole must not be used; otherwise the readings on the charts will be incorrect. By drawing obstructions onto the chart, using their respective angular heights and azimuth bearings, the percentage of the radiation blocked by the obstructions can be read, using the figures in the shaded squares. Compass Fig. 18. Aprotractor, used to measure the angular altitude oj obstructions around a greenhouse. 44 Example: A tree located at 43° west of due south (horizontal axis) with an altitude (height) of 28° (vertical axis) blocks the direct solar radiation reaching the greenhouse as follows (refer to Fig. 19): - approximately 9% in December; - approximately 12% in January and November ( including shading of exterior branches); - approximately 9% in February and October; - almost 0% during the period March-September. Since less than 15% of the incoming light in October is blocked out and virtually no shading occurs during the remaining months of the March- October growing season, this site would be suitable for solar heating. 45 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 EAST SOUTH WEST Fig. 19- Sun path chart 49° north. Hourly fraction of daily total sunshine. 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 EAST SOUTH WEST Fig. 20. Sun path chart 49° north. Hourly fraction of daily total sunshine. The sun path chart records in two dimensions the annual movement of the sun across the sky for a specific latitude. The base line represents a flat horizon. The bottom arch is in the path of the sun at the winter solstice (21 December), the top arch is the summer solstice (21 June). Radial lines indicate the time of day (standard time). Time numbers are centered on each square. The number in each square indicates the fraction of solar energy (under ideal conditions) that occurs during a 1 hour portion, between 30 min., before and after the time indicated, on the 21st day of the month. The example plotted shows that on 21 March/ 21 September, 12% of the daily total solar energy falling on a vertical surf ace occurs (under ideal conditions) between 1:30 I'M and 2:30 i>m., local solar time. In this graph it is averaged, and assumed constant over a month. Local solar time is close to local standard time. 46 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 EAST SOUTH WEST AZIMUTH Fig. 21. Sim path chart 43° north. Hourly fraction of daily total sunshine. 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 EAST SOUTH WEST Fig. 22. Sun path chart 53° north. Hourly fraction of daily total sunshine. 47 AA TWotj 1 Ik* .14 .11 14 }£ 9i & 1" k^K^ tf xi )8/ .% * .11 / 1 K.O^ \ ,1 2 .12 J •^' 4 7 .09 .13 14 .15 .14 JSL. Nf \! ^ 02/1 .0 4 ] i .0 e \ Lo9_^ f .01 s.o: .02 16 .1 3 .16 K J 02 / / .04 fl» i .04 ' s ^ A f / \ V * 1 1 .19 BTr .19 JUw1 .w <] "*\ \i ?\ u i A / ^ >s U Jv M t 55 50 45 40 v I 35 t 5 30* 25 20 15 10 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 EAST SOUTH WEST AZIMUTH Fig. 23- Sun path chart 60° north. Hourly fraction of daily total sunshine. 48 CONVERSION FACTORS FOR METRIC SYSTEM Approximate Imperial units conversion factor Results in: LINEAR inch x25 millimetre (mm) foot x30 centimetre (cm) yard x0.9 metre (m) mile x 1.6 kilometre (km) AREA square inch x6.5 square centimetre (cm2) square foot x0.09 square metre (m2) acre x0.40 hectare (ha) VOLUME cubic inch x 16 cubic centimetre (cm3) cubic foot x28 cubic decimetre (dm3) cubic yard x0.8 cubic metre (m3) fluid ounce x28 millilitre (mL) pint x0.57 litre (L) quart x 1.1 litre (L) gallon x4.5 litre (L) WEIGHT ounce x28 gram (g) pound x0.45 kilogram (kg) short ton (2000 lb) x0.9 tonne (t) TEMPERATURE degrees Fahrenheit (°F-32)x0.5€ or (°F-32) x 5/9 degrees Celsius (°C) PRESSURE pounds per square inch x 6.9 kilopascal (kPa) POWER horsepower x 746 watt (W) x0.75 kilowatt (kW) SPEED feet per second x 0.30 metres per second (m/s) miles per hour x 1.6 kilometres per hour (km/h) AGRICULTURE gallons per acre x 11.23 litres per hectare (L/ha) quarts per acre x2.8 litres per hectare (L/ha) pints per acre x 1.4 litres per hectare (L/ha) fluid ounces per acre x70 millilitres per hectare (mL/ha) tons per acre x2.24 tonnes per hectare (t/ha) pounds per acre x 1.12 kilograms per hectare (kg/ha) ounces per acre x70 grams per hectare (g/ha) plants per acre x2.47 plants per hectare (plants/ha) !i.!r\?A,FY ' BIBLIOTHEQUE AGRICULTURE CANADA OTTAWA K 1A 0C5 3 T073 0005305b 0 DATE DUE DATE DE RETOUR AVR 1 1 1988 NLR 178 i