Research On Hygrothermal Performance Of Assembled Soil Sandwich Composite Wall In Chinese Solar Greenhouse

Solar greenhouse is a unique type of greenhouse in China.It can absorb solar energy through the back wall to achieve heat storage and release,maintain the temperature in the greenhouse to meet the growth of fruit and vegetable crops,and effectively solve the problem of winter fruit and vegetable supply in northern China.In order to solve the problems of large thickness,easy collapse and low land use efficiency of traditional soil wall,an assembled soil sandwich composite wall is developed.Prefabricated ordinary reinforced concrete slabs and light energy-saving thermal insulation slabs are used on both sides of the wall,respectively.The thickness of soil sandwich layer can be flexibly adjusted according to the different needs of different crops for temperature.The interior and exterior wall panels shall be backfilled with soil and connected with FRP bars or columns.The exterior insulation panels can effectively prevent heat transfer.In order to deeply and systematically research the heat and moisture transfer and thermal storage and release performance of the assembled soil sandwich composite wall in the solar greenhouse,and to reveal the lag effect of the response of the filled earth in the wall to the temperature change,the author have carried out some research work on the wall temperature,relative humidity,thermal storage and release through the indoor model test,theoretical derivation and numerical analysis.The main achievements are as follows:(1)The hygrothermal performance of the assembled soil sandwich composite wall in the solar greenhouse is provedBased on comprehensive consideration of the indoor and outdoor thermal and relative humidity environment in winter and the technical parameters of the self-developed controllable thermal and humidity coupling test-bed,it is found through the research of the diurnal cycle test and the external steady-state test: the coupling effect of heat and moisture in the assembled soil sandwich composite wall of solar greenhouse is not obvious,the temperature in the wall can rise and fall rapidly with the heat storage and release,and the relative humidity is high and stable;the layered heterogeneous composite wall is not sensitive to the change of outdoor relative humidity,which is conducive to the construction of solar greenhouse thermal environment;the relative humidity of the filled earth in the wall is kept at about 99%,which makes the wall have stable and efficient heat storage and heat release capacity,and the filled earth is the main heat storage body of the wall,accounting for 75.81% of the heat storage ratio;the heat storage ratio of the outer light energy-saving insulation board is 2.27%,which mainly plays the role of heat preservation and insulation,and basically realizes the one-way heat transfer between the wall and the indoor environment;the 280 mm thick wall near the indoor side has a rapid response to the indoor temperature change,and the response of the temperature field inside the wall to the external temperature change has a lag effect in time and space.The smaller the temperature difference between the two sides of the wall,the more obvious the effect.(2)The theoretical calculation and numerical analysis method of the heat storage and release of the soil sandwich composite wall are modified and establishedBased on the experimental data,the discrete difference method is adopted for the wall based on the advanced heat transfer theory,and the theoretical calculation method of the heat storage and release of the assembled soil sandwich composite wall in the solar greenhouse is modified and established,which is used for the quantitative analysis of the heat storage and release of the wall under various cases involved in the hygrothermal performance test and numerical expansion analysis;based on ANSYS and APDL parametric language,the numerical model of assembled soil sandwich composite wall is modified and established by adopting the modification of 2-D 4-node thermal analysis unit PLANE 55,and the reliability of the numerical analysis results is verified by the measured data,which provides a simple method for carrying out the thermal storage and release performance analysis of walls with different external insulation methods and different thickness of sandwich soil layer.(3)The influence of external heat preservation method and soil sandwich layer on the hygrothermal performance of the wall is provedThe comparison and analysis of the hygrothermal performance and the heat storage and release capacity of the wall with different external insulation methods show that the increase of EPS board on the outdoor side can reduce the lag effect of the response of the temperature field in the wall to the external temperature change,shorten the heat release time and improve the heat release efficiency;when 50 and 100 mm EPS board are added outside the wall,the heat storage capacity of the wall is increased by 19.63% and 24.95% respectively,and the indoor heat release capacity is increased by 25.74% and 41.72% respectively,and the hourly average heat release capacity is increased by 1.59 and 3.08 times respectively;EPS board also improves the resistance of the wall to the external temperature and humidity environment,effectively preventing the heat exchange between the wall and the external environment.The research on the influence of the thickness of the soil sandwich layer on the heat storage and release performance of the wall shows that: the heat storage and release capacity of the soil sandwich layer to the wall is obviously improved.When the wall with the same thickness of EPS board is adopted at the outdoor side,the total heat storage and the heat released to the indoor increase with the increase of the thickness of the soil sandwich layer.By comparing the effect of external insulation and soil sandwich layer on the heat storage and release performance of the wall,the effective methods to improve the heat storage and release performance of the wall are obtained: when the wall thickness is thinner,adding EPS board outside the wall chamber is more effective;when there is no EPS board or EPS board is thinner outside the wall,increasing the thickness of the sandwich soil layer inside the wall is more effective.In conclusion,the design concept of the assembled soil sandwich composite wall is advanced.The outer wall is thermal insulation layer and the inner wall is heat storage and release layer.Compared with the traditional earth wall,it has superior heat storage and release performance,less land occupation,and can be quickly assembled,reused and returned to the field,which is suitable for popularization and application in cold winter areas in China.