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Modeling the microclimate of a greenhouse located in Baghdad under its weather conditions to calculate the heating and cooling loads by computer simulation. Solar collectors with a V-corrugated absorber plate and an auxiliary heat source were used as a heating system. A rotary silica gel desiccant dehumidifier, a sensible heat exchanger, and an evaporative cooler were added to the collectors to form an open-cycle solar assisted desiccant cooling system. A dynamic model was adopted to predict the inside air and the soil surface temperatures of the greenhouse. These temperatures are used to predict the greenhouse heating and cooling loads through an energy balance method which takes into account the soil heat gain. This is not included in conventional methods. The results showed satisfactory agreement with published papers. Also, the results of heating and cooling loads obtained revealed good agreement with those obtained from conventional methods when the soil heat gain is included. Two identical collectors in series of total area of 5.4m2 were employed as a heating system which provides an outlet air temperature of 30 o C at air mass flux of 0.06 kg/s.m2 at midday in January. While, a 65 oC outlet air temperature was achieved for the same mass flux at midday in August. The desiccant cooling system was operated in five operating modes; the ventilation mode and four recirculation modes with 20%, 50%, 70%,and 90% recirculation. The simulation results showed that a regeneration temperature of 60-70 o C is satisfactory for a cool supply air temperature of about 19.5 o C. Also, it was noted that 20-30 % recirculation of return air would result in suitable indoor greenhouse conditions for most periods of system operation. In addition, the coefficient of performance COP of the system was high compared with the conventional vapor compression systems.

Solar energy has an enormous contributions in numerous sectors. Among these sectors, agricultural greenhouses still receiving more interests to reduce the energy consumption which in turn mitigates the reliance of greenhouses to conventional energy sources and minimizes greenhouse gas emission (GHG). A greenhouse is an enclosed structure made of wood or metal frames covered with transparent materials such as glass, plastic, and fiberglass that allow solar radiation to enter the greenhouse. The primary objective of a greenhouse is to provide a shelter for plants against the harsh weather conditions such as strong winds and heavy rain. Further benefits of a greenhouse are to produce agricultural products out of season for both commercial sales and research purposes and attain better quality and quantity of plants as well. To maintain the microclimate of a greenhouse at an appropriate level which is more favorable for various crop growth, systems such as heaters, coolers, fans, thermostats, and other equipment must be used. However, in cold climates or arears with prolonged cloud cover, a greenhouse can be heated conventionally by burning fossil fuels and using electric heaters or by utilizing solar heaters that convert solar energy into thermal energy. In this study, MATLAB software was used to predict the heating load of a greenhouse using an energy balance method that takes into account the heat gain from soil. This is not considered in conventional methods. The results of heating load obtained revealed good agreement with those obtained from conventional methods when the soil heat gain is included. Two identical collectors in series of total area of 5.4m2 were employed as a heating system. This arrangement provides an air outlet temperature of 30oC with an air mass flux of 0.06 kg/s.m2 at midday in January. In addition, a rock- bed thermal storage system was adopted to store the excess heat which can provide about 58.5% of the total heat demand, while the remaining amount can be supplied by an auxillary heating system.