Experimental investigation of temperature gradient in a greenhouse bed soil containing phase change material

Most of energy sources have some disadvantages such as environmental problems and being expensive, so using solar energy for greenhouse heating in cold seasons is a very important issue. Solar energy is a periodic source, so using of energy storage systems is inevitable. In this paper, phase change materials was used in heating system of a solar greenhouse built in Dezful and its influence on temperature gradient of bed soil is experimentally investigated. A model greenhouse with a ground area of 3 m2 was coupled with a heating system consisting of a water tank contained 18 kg paraffin wax (latent heat 190 kj/kg and melting point 55ºC) as phase change material. During the daytime, temperature of the paraffin wax reaches to melting point, with energy of solar radiation absorbed by tow collectors, and daily available energy stored as thermal energy (sensible heat and latent heat). This stored energy is released during the night to heat bed soil of greenhouse. Temperature gradient of soil were evaluated to figure out thermal performance of this energy storage system. Results of this study indicates that about 10 ºC increase in minimum nighttime temperature and average temperature of soil in different depths was achieved.