Heating a greenhouse using a solar air collector assisted by thermal storage: a simulation study

Abstract

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 30^oC 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.