| Chinese Solar Greenhouse (CSG), as a typical type of agricultural protected facilities, is playing an important role in the development of agriculture in China recently. Most of them, however, provide a relatively suitable environment for the plants to live through the severe cold winter during the productive process practically, especially at the cold regions such as the northern areas. Some of them even consume amount of energies to improve the lowest temperature of indoor environment, which could increase the cost to maintain the production and operation management. A series of further studies on the phase change materials (PCM) in recent years explored a novel method to enhance the ability of passively energy-saved CSG. It may largely decrease the energy consumption, improve the indoor thermal environment, and even optimize the north wall structure of CSG if the energy storage technique of PCM could be applied appropriately and practically in CSG, which would be a remarkable improvement in this study field. The main contents of this research are as follows:(1) The author made the ternary fatty acids available for CSG and also did the determination of material properties. The results showed that:in the composite PCM, the phase change temperature was 21.82℃, the latent heats was 121.5J/g. The mass fraction of the expanded graphite (EG) in the composite PCM was 8%, with the maximum absorbing capacity. The PCM was successfully absorbed in the micro holes of theEG under the surface tension and the function of capillary tubes, which could not be leaked out when melt. The accelerated cooling and heating recycle, method used by 1000 times in PCM, the result showed that the melting point and latent heats were decreased by 0.22℃ and 2.3%, respectively, the range ability could almost be ignored, which showed a good heat stability. The heat conductivity coefficient of the composite PCM is 1.79W/(m·K),6.5 times higher than the pure PCM which made of fatty acids.(2) By combining composite phase change material and magnesium wallboard, a kind of phase change heat storage wallboard was designed, and the application effect of the wallboard was analyzed. The environmental data was analyzed and compared by selecting air temperature under typical weather condition, soil temperature below 20cm, wall temperature and wall heat flux. Results indicated that on sunny days, daily highest air temperature of the greenhouse with phase change heat storage wallboard was 0.9℃ lower than the contrasting greenhouse,3.4℃ lower at peak. The lowest air temperature at night was 2.3℃ higher than the contrasting group,2.9℃ higher at peak. Soil temperature below 20cm was 0.8～1.1℃ higher than the contrasting. Accumulation of heat absorption of daily phase change heat storage wallboard was 6.18 MJ/m2,2.05 MJ/m2 higher than the contrast. Accumulation of heat absorption of phase change heat storage wallboard at night was 2.24MJ/m2,1.01 MJ/m2 higher than the contrasting. On cloudy days, daily average air temperature of the greenhouse with phase change heat storage wallboard was 1.1～1.7℃ higher than the contrast. Soil temperature below 20cm was 0.9～1℃ higher than the contrast. Accumulation of heat absorption of daily phase change heat storage wallboard was 0.79 MJ/m2,0.14 MJ/m2 higher than the contrast. Accumulation of heat absorption of phase change heat storage wallboard at night was 0.53 MJ/m2,0.3 MJ/m2 higher than the contrasting greenhouse.The application of phase change heat storage wallboard significantly improve the greenhouse heat, reduce excessive temperature in the greenhouse during the day, and enhance the indoor minimum night temperature contributes to the indoor heat "peak shaving" regulation. The study is to further improve thermal environment of greenhouse and reduce energy consumption in greenhouses, which provides some reference values. |
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