Innovative passive heat-storage walls improve thermal performance and energy efficiency in Chinese solar greenhouses for non-arable lands

摘要

Chinese solar greenhouses rely entirely on solar energy to provide a suitable growing environment for crops. Moreover, they offer a remarkable opportunity for boosting 'Gobi agriculture' and promoting the economy and ecology of non-arable lands. Further, enhancing the thermal performance of the north wall has been considered an efficient way of improving the greenhouse's thermal environment and thereby increasing agricultural productivity. To improve the solar energy efficiency and boost 'Gobi agriculture', five passive heat-storage north walls were designed for non-arable lands by using non-soil and locally available inexpensive materials. These included a flange-layered wall (FL), a concrete-layered wall (CL), a gravel-layered wall (GL), an aerocrete brick-layered wall (AL) and a concrete hollow block-layered wall (HL). A mathematical model of the thermal environment of a solar greenhouse in non-arable lands was established, and a comparative study was conducted to evaluate the designed walls' effectiveness over conventional walls. Their thermal performances were quantitatively assessed using both theoretical and simulation methods. Moreover, the impacts of these walls on the greenhouse's thermal environment were investigated using an unsteady-state simulation analysis. The results verified the larger contributions of FL, CL, and GL toward promoting the thermal environment of solar greenhouses. FL, CL, and GL enhanced the heat storage/release performance by 5.0%, 38.0%, and 37.3% and the energy efficiency by 9.2, 12.9, and 13.5 percentage points, respectively, resulting in average increases in the nocturnal interior temperature of 0.7, 2.5, and 2.5 degrees C, respectively.