Heat and moisture transfer and heat storage and release performance of assembled soil sandwich wall in 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 vegetable crops, and effectively solve the problem of winter fruit and vegetable supply in northern cold region of China. In order to solve the problems of excessive thickness, easy collapse and low land-use efficiency of traditional soil wall, an assembled heterogeneous composite soil sandwich wall was developed. Prefabricated ordinary reinforced concrete slabs and light energy-saving thermal insulation slabs were used on both sides of the wall, respectively. The thickness of the soil sandwich layer could be flexibly adjusted according to the different needs of different crops for temperature. The interior and exterior wall panels are backfilled with soil and tied with reinforcements. The exterior insulation panels can effectively prevent heat transfer. In order to deeply and systematically study the heat and moisture transfer and heat storage and release performance of assembled soil sandwich wall in solar greenhouse, and reveal the hysteretic effect of filling on the response of temperature change, indoor model tests were carried out. The test wall is 1.2 m long and 0.6 m high with a total thickness of 600 mm. CF autoclaved ceramic powder aerated concrete slab with excellent heat preservation and insulation characteristics is used outdoors with a thickness of 100 mm. The filling material in the wall is taken locally, and the cultivated land with good heat storage and heat release performance is tamped, with a thickness of 440 mm. The indoor side is made of ordinary reinforced concrete slab with a thickness of 60 mm, which is effectively supported and retained. While supporting the wall, it has high thermal conductivity and fast heat transfer. Considering the actual indoor and outdoor hygrothermal environment of solar greenhouse and the technical parameters of the self-developed controllable coupled heat and moisture test bench, two test groups were designed under seven cases. The temperature and relative humidity changes of the indoor and outdoor walls were accurately controlled by the test bench, and the temperature and humidity sensors embedded in the wall were used in advance. The data acquisition system is used to measure and analyze the steady-state distribution and transient change of temperature and relative humidity in the wall. The thermal storage and release performance of the wall is calculated and analyzed quantitatively through theoretical formula deduction. On the basis of experimental research, the numerical analysis method of thermal performance of the layered heterogeneous composite wall is revised and established. The results show that the heat and moisture transfer of the composite wall with layered heterogeneous structure is coupled but not significant; the filling in the wall keeps high humidity (more than 90%) all the time, which is conducive to the heat storage and release of the wall, and is the main heat storage and release body of the wall; the thermal insulation efficiency of the outer wall panel is remarkable, and the change of the outdoor environment affects the thermal insulation and storage performance of the wall. The heat release in the wall has a lag effect in time and space, the longest lasting time is 6 days and 6.5 hours, but the heat release in the fast exothermic period (within 4 days and 8 hours) accounts for 85.64% to 91.21% of the total heat release, and the 280 mm thick wall on the indoor side responds quickly to the change of indoor temperature. The numerical analysis method can provide reference for the design and construction of similar walls with different thickness, and has guiding significance for production. The new wall design concept is advanced. The outer wall is thermal insulation layer and the inner wall is heat storage and release layer. It has excellent heat storage and release performance, and it can be quickly assembled, reused and returned to the field in situ. It is suitable for wide application in China. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.