Study On Performance Of Heat Preservation Of The Greenhouse In Which Phase Change Materials Was Hanged On Inner Surface Of Back Wall

In the most part of northern china, the temperature in the greenhouse at night is often lower than it is required by crops growing. Therefore, extra heat should be provided to raise it for the greenhouse normal production. The traditional heating methods using coal are polluted and consume precious energy. Nowadays, the energy became less and the environment is increasingly seriously contaminated, so these methods should be instead by some clean and effective ways to heat the greenhouse.Our country's solar energy resource is extremely rich, especially in the northwest part of it. The amount of heat which was accumulated by many greenhouses far exceeds its need at night. According to this, we use the phase change material in greenhouse, which can move excess energy accumulated by the greenhouse in the daytime to the night to protect the plant in the daytime from the high temperature and ease the shortage of heat in the greenhouse in night.The text use CaCl₂·6H₂O as phase change material in the greenhouse. Commercial CaCl2 was used for CaCl₂·6H₂O preparation in large quantity. Then a new greenhouse was made by hanging the CaCl₂·6H₂O on the inner surface of wall of a greenhouse which was made of bricks. We studied the performance of heat preservation of the new greenhouse and a built phase change material greenhouse with its wall material mixed with the phase change material. Finally, we compared the performance of heat-stored of two kinds of phase change material greenhouses.Results showed that CaCl₂·6H₂O is a good material in greenhouses. Through analyzing the total amount of heat in the greenhouse during 19:00-7:30 before and after the installation, we found that convection heat of all the inner surface of the greenhouse with the air is almost equal with the heat reduction of the air before installation, while exceeded the heat reduction of the air after the installation. The difference value, which was released by the CaCl₂·6H₂O, was 4944.58kJ.Analysis on performance of heat preservation of built phase change material greenhouse which wall material is mixed with phase change material showed that this kind of greenhouse has a good heat-stored ability. The indoor temperature of it is 0.9℃higher at night on average than the ordinary greenhouse on sunny days, while 0.3℃higher on cloudy days. The temperature of inner surface of wall of the greenhouse is 1.6℃higher at night on average than the ordinary greenhouse on sunny days, while 0.6℃higher on cloudy days.Through contrasting the performance of heat-stored of two kinds of phase change material (PCMs) greenhouse, we found that the built PCMs greenhouse is better than the new PCMs greenhouse. The temperature of built greenhouse is 0.2℃higher at night on average than the new greenhouse on sunny days, while 0.3℃higher on cloudy days. The temperature of inner surface of wall of built greenhouse is 1.1℃higher at night on average than the new greenhouse on sunny days, while 0.5℃higher on cloudy days.The paper provides reference for the application of phase change material in greenhouse.