Thermal Environment Testing And Simulation Of Chinese Solar Greenhouse With Brick-polystyrene Board Compound Wall

The back wall of the solar greenhouse has thermal preservation and storage functions, isan important part of greenhouse maintenance structure, suitable materials and structure ofwall can ensure plants growth normally in the greenhouse. Solar greenhouses with brick-polystyrene board compound wall are widely used for plants cultivation through the winter innorth areas, has important significance for stable, rich fruit and vegetable market, and canincrease farmers’ income. But some places designed unreasonable thermal preservation andstorage layers, walls were too thick or too thin in the process of building brick-polystyreneboard compound walls, and leaded to an insufficient thermal environment in solargreenhouses in winter, crop failure happened. It’s necessary to continue researching thethermal preservation and storage performance of brick-polystyrene board compound walls.This study based on a normal greenhouse with wall of brick clamping polystyreneboard as the comparative greenhouse, analysize the thermal preservation and storageperformance of the compound wall greenhouse with polystyrene board to the outer(hereinafterreferred to as polystyrene board outer greenhouse) in the winter of2013. The results showedthat, the inner surface average temperature of polystyrene board outer greenhouse is2.4°Chigher than the comparative greenhouse during the day,2.7°C higher at night; absorption heatflux is2.2MJ/m2bigger than the comparative one during the day, the release of heat flux is2.3MJ/m2bigger at night; the average air temperature is2.7°C higher than the comparativeone during the day and1.3°C higher at night; the relative humidity decrease5.6%on the basisof comparative greenhouse, and average soil temperature is2.5°C higher than the comparativeone. The conclusion is that the thermal preservation and storage performance of compoundwall with polystyrene board to the outer is significantly better than the comparative wall, airtemperature has improved in the day and night, and air temperature rising is beneficial to soilheat absorption and release during the day and night, Finally, under the interaction of wall,indoor air and soil, the thermal environment of polystyrene board outer greenhouse hasimproved significantly based on contrast. To continue to optimize the heat preservation and storage performance of back wall ofthe polystyrene board outer greenhouse, reveal the relationship between thickness ofbrick-polystyrene board compound wall and indoor temperature, this paper established aphysical model based on the polystyrene board outer greenhouse, using computational fluiddynamics (CFD) technique to simulate the greenhouse temperature changing during the nightand build a verification test. Results show that the greenhouse temperature distribution ofeach part is consistent with other researcher’s results, and simulated results of walltemperature and indoor temperature are consilient with measured values. Based on thesimulation of polystyrene board outer greenhouse, loaded same outdoor boundary conditionsto greenhouses with9kinds of different thickness brick-polystyrene board compound walls,analyzed the influence of greenhouse thermal environment when wall thickness changing.The simulation results show that the "490mm thick brick wall+300mm thickpolystyrene board" composite wall’ heat preservation is optimal,"240mm thick brick wall+100mm thick polystyrene board" composite wall is worst, the two greenhouses’ airtemperature is difference between3.6°C;"370mm thick brick wall+200mm thickpolystyrene board" composite wall has the most significant effect to improve the thermalenvironment of greenhouse, can ascend air temperature2.3°C based on "240mm thick brickwall+100mm thick polystyrene board" composite wall greenhouse, only lower1.3°C than"490mm thick brick wall+300mm thick polystyrene board" composite wall greenhouse.Thus it can be seen, when the brick wall or polystyrene board thickness increases to a certainsize, continue to increase the thickness has limited effect to the greenhouse temperature rising,CFD simulation can predict the different thermal environment of greenhouses with differentwalls thickness, provide the scientific basis when choosing appropriate wall in different areasor under different climate conditions.