Experimental Investigation of Using Phase Change Materials in Heating System of a Solar Greenhouse

The use of solar greenhouses has increased manifold over the last two decades and this is the main reason for thermal systems development in greenhouses. Most of the energy sources are not reliable because of the environmental problems and continuous climb in energy prices, thus using renewable and pure energies such as solar energy in the thermal systems is very important. In this paper, the use of phase change materials in the heating system of a model solar greenhouse in Dezful is analyzed and discussed experimentally. A model greenhouse with a ground area of 3 m2 has been coupled with a heating system that consists of two flat collectors and a water store that contained 18 kg paraffin wax (latent heat 190 kJ/kg and melting point 55ºC) as phase change material. Temperature variations of soil, greenhouse, and ambient were evaluated to indicate the thermal performance of this energy storage system. Results of this study indicated that the maximum average temperature of a store during energy storage is 67ºC . Over the night in the heat dissipation cycle, the rate of heat transfer and the temperature difference between inlet and outlet of the store is higher in earlier hours in comparison with later hours due to the high-temperature difference between store and greenhouse. The minimum night time temperature of greenhouse rose by 3ºC and nighttime greenhouse average temperature increased by 4ºC. Furthermore, a 6-8ºC increased in temperatures of soil in different depth was achieved.