Research On North Wall Thermal-release Controling Based On Tempetature Modelling In Solar Greenhouse

Chinese solar greenhouse is one unique greenhouse type in china. It possesses the structure of north wall and soil to preserve heat during daytime and release heat at night. So the indoor temperature can be preserved on the higher level than outdoor. Although many experts research on the optimal of heat storage and heat preservation capability of north wall, the lowest indoor temperature during winter is still not high enough for plant growth. Heat-hold cover (HHC) can be used to delay heat releasing of north wall and in that way the heat released in the first half of the night can be moved to latter half of the night. And the lowest indoor temperature can be promoted. The effect of heat-hold cover was also analyzed by modeling. The conclusions were as follows:Tests used two types of HHC which were called as TypeⅠand TypeⅡas Type in Beijing showed that: when the north wall was covered by HHC at night the heat releasing of north wall in test greenhouse (TG) was reduced 38%~40% compared to control greenhouse (CG), after the HHC was rolled up the heat releasing of north wall in TG was 68.3% higher than CG at most, the lowest temperatures were promoted 0.4℃in cloudy day and 1.03℃in sunny day. The HHC should be used in sunny days according to the test results.Comparing the measured data of environment factors in greenhouse with the simulated values, IA of indoor air temperature in CG was 0. 92, IA of indoor air temperature in TG was 0.79, IA of north wall surface temperature in TG was 0.58, IA of air layer temperature in TG was 0.79, IA of soil surface temperature in TG was 0.94。It was shown that model could simulate the temperature change generally.The effect of HHC using was calculated by model. Some results were found: the lowest indoor temperature can be promoted with the increasing of convention parameters of HHC, the promotion is minor by changing of air layer's thickness, the lowest indoor temperature can be increased by the delaying the HHC rolling time and the highest promotion value can be 2.45℃if north wall is covered by HHC.