Study On The Heat Transfer Charateristics Of Sunken Solar Greenhouse Soil Wall Of

In recent years, sunken soil wall sunlight greenhouses have rapidlyspread in northern China, but till now, its structural parameters are unreasonablebecause of Hack of systematic research, the suitable wall thickness is one typicalproblem.Since January2010to June2011, This paper measured the two greenhouseindoor and outdoor temperature, terrestrial solar radiation, wind speed and direction,indoor and outdoor wall surface temperature, heat flux, and other environmentalfactors in Zhengzhou, that structure parameters are same but wall thicknesses aredifferent, at the same time carried on an actual test to the hot work parameters of thesoil wall.The test greenhouse soil wall thermal parameters are: coefficient of thermalconductivity is1.32W m-1℃-1, thermal resistance is0.758(m2K)/W, the heatstorage coefficient is14.3W m-2℃-1, these number show that the soil wall has agood stockpile and release heat energy performance, and greatly influences on thegreenhouse thermal environment especially nighttime temperatures. But the indoortemperature in the soil wall greenhouse is vulnerable to outdoor How-temperaturebecause the thermal conductivity of the soil wall is higher wall and the thermal inertiaindex is Hower. So the pure soil wall must be constructed a certain thickness, itsinsulation capacity will be sufficient.There is a shaded area along the south edge in sunken greenhouse. The area sizeis decided by the facores like the sunken depth and the position of the sun; affected bythe shadow, the temperature in the area is lower than others, so the area is called low-temperature-region. Its temperature and area have a diurnal and seasonal variation.Compared with the non-sunken greenhouse in the same season and at the same time,the area of the low-temperature-region in the sunken greenhouse decreasedsignificantly and the temperature increased. In sunken greenhouse, the heat fluxconducting from indoor subsidence ground to outdoor soil reduced greatly, the southedge soil temperature and air temperature increased. Another reason is that the southsunken wall constantly released heat to the room. The heat flux is much smaller thannorther wall. In winter, the depth that40cm horizontal direction away from the southsunken wall, is the heat exchange equilibrium point of the south sunken wall andoutdoor soil;North wall is an important source of heat in the greenhouse at night. In thedaytime, the soil wall absorbs the sun radiation, but in the nighttime it releases theheat flux to the room, impacts on the indoor night temperature especially beforemidnight. There are temperature differences along the wall in the thickness direction,the length direction and height direction. In the thickness direction, from the innersurface to the outer surface, the temperature decreasing; surface temperature day range is greater than inside, and the more depths in the wall, the more relaxation thetemperature changes; in the center of the thickness, there is a thermal stability layer,its thickness and position change with the wall thickness and the season. It can reflectthe level of the wall heat preservation performance that the thermal stable layer exit ornot and its thickness.In the vertical direction, from bottom to top, the temperaturedecreasing; In the length direction of the wall, not only the temperature difference butalso the temperature gradient is small, so the thermal conductivity of the soil backwall is two-dimensional unsteady state heat conduction;Carried out a detailed analysis of the heat conduction characteristics of the wall,and modeled the wall two-dimensional unsteady heat transfer model. The numericalcalculation and simulation by the software Fluent using finite difference method onthe model showed the wall temperature field at different times and in differentweather conditions. Compared the experimental data, the simulation date was higher,but their curve fitted well. Combined with the values of model numerical calculations,the construction costs, land utilization and other factors, the paper concludes that4mis the suitable thickness of sunken sunlight greenhouse soil wall in Zhengzhou area.