Preliminary Study On Phase Change Material Wall Of Heat Preservation In Sinking Solar Greenhouses

With the development of solar greenhouse, the problem of wintervegetable supply in the north china has been solved, it have a good effect on peoplelife, but it also has some problems such as: ventilation cooling difficulties in summer,energy consumption too much in winter, and the too much energy consumption inwinter has become a restrict to the further development of solar greenhouse. With thedevelopment of global industrialization, extreme weather frequently, low temperaturein winter also appear constantly in our country. In order to provide an appropriateclimate environment for the plant growth, at the same time meet the requirements ofenergy-saving, environmental protection, low carbon, people have focus on the heatpreservation in solar greenhouse. Phase change materials (PCM) because of its owncharacteristics which in the process of phase transition to absorb or release latent heatand the temperature of itself has a small variations, in recent years, PCM has beenwidely studied and applied to the facility agriculture.This experiment materials were made of CaCl2-centered hydration inorganic andPCM embedded in solar greenhouse back wall, eventually form phase changewallboard, observed the inside temperature, outdoor temperature and the temperatureof different measuring points in the back wall, and discusses the variation oftemperature regular in typical weather between composite phase change materials(CPCM) greenhouse and common greenhouse (CK). Thus, we could providetheoretical basis to the heat preservation and low energy-consumption, also for itspopularization and application in solar greenhouse.This experiment took the sinking greenhouse in XinZheng as example, adoptexperimental tesr and theoretical analysis as a combination of methods, the concreteresults were as follows:1. In typical weather condition, PCM have obvious characteristic of absorbing orreleasing large amount of latent heat, the effect of CPCM greenhouse is betterthan CK; CPCM greenhouse can provide better and more stable environment forcrop growth: the temperature of night and the day average indoor temperatureboth higher than common greenhouse, at the same condition of hest source, CPCM greenhouse indoor temperature heating rate is lower than CK in thedaytime, CPCM greenhouse indoor temperature cooling rate also lower than CKin the night; the average temperature difference inside and outside of CPCMgreenhouse is higher than CK throughout day; the temperature of inner surface ofback wall and average temperature throughout the day of CPCM greenhouse arehigher than CK at night (18:00-6:00), temperature heating rate of inner surface ofback wall （1.25℃/h）significantly slow and lower than common greenhouse(1.90℃/h) within11:30-13:30.2. The temperature of back wall in two greenhouses shows the same change trend inwinter and early spring, the heat preservation performance of back wall in CPCMgreenhouse is more apparent: with the depth of back wall increase (from outsideto inside), the temperature of back wall has increased both in two greenhouses, thevariation trend of temperature is more and more intensely; as temperature outsiderise, the temperature of the wall rise obviously in two greenhouses; the processwhich absorbing or releasing latent heat mainly in28cm,37cm two depth, thevariation trend of temperature in their depth of CPCM greenhouse is less than CK.3. The temperature variation of back wall in different measuring points of CPCMgreenhouse showed the following characteristics:The surface of back wall in different horizontal position of CPCM greenhouse:before Jie Shan, the temperature of central location temperature is higher than theedge, the temperature of laying of PCM area is higher than CK; after Jie Shan, thetemperature heating rate of the area without laying of PCM is higher than the layingarea, in the same area, the area more closer to central, the temperature heating ratemore higher; the temperature cooling rate of laying of PCM area is lower than CK, thearea which laying of PCM as the main heat source to release heat to around at night,especially the area of the central.The surface of back wall in different vertical position of CPCM greenhouse:before Jie Shan, the temperature of central location temperature is higher than theupper central position, the temperature of laying of PCM area is higher than CK, afterJie Shan, the temperature heating rate of the central location is higher than the uppercentral position, in the area without laying of PCM, the area more closer to central,the temperature heating rate more higher; the area which laying of PCM as the mainheat source to release heat to around at night, especially the area of the central.The surface of back wall in different depth measuring points of CPCM greenhouse: the temperature of all the depth are relatively stable at night (22:00-8:00).With depth increase, the variation of temperature is obviously at daytime. The backwall of CPCM greenhouse mainly though the inner surface of back wall (47cm) forabsorption of heat, though the area which laying of PCM for heat storage, mainlythrough the inner of PCM (42cm) that release to the conservatory.