Performance testing and analysis of flexible composite walls in assembled solar greenhouse

In order to solve the issue of limited heat storage capacity of assembled solar greenhouse wall, an assembled flexible composite wall incorporating heat storage, insulation, and waterproof functionalities was developed by integrating a heat storage layer within the wall structure. Initially, after evaluating the performance of various materials, premium surface and insulation materials were meticulously chosen and combined to create a flexible insulation wall. Subsequently, according to the different types and amounts of thermal storage materials on the surface of flexible insulation wall, six experimental treatments were designed in this study: The surface of A1, A2 and A3 wall were treated with the same amount of phase change hydrogel(PCH), water and sand thermal storage materials, respectively; The surface of A4, A5 and A6 wall were 5, 4 and 3 kg/m² PCH thermal storage materials, respectively. Finally, the wall performance was tested in four model greenhouses and the flexible insulation wall without thermal storage layer was taken as the control (CK) to analyze the thermal storage and insulation performance of the treatment wall by collecting related indexes such as indoor temperature, wall temperature and heat flux.The analysis of individual wall components revealed that the surface materials of aluminized woven cloth and black coated felt had excellent tensile and impermeable properties with the breaking force of 1.06, 0.56 kN and breaking elongation of 30.99 %, 65.91 %, respectively. In the insulation materials, the thermal resistance of recycled cotton, space cotton, and air column were 0.30, 0.50 and 0.76 (m²·℃)/W, respectively, which had the advantages of efficient insulation effect and low usage cost. When all treatments were tested in model greenhouses, the test results of A1, A2 and A3 showed that the heat storage effect of latent heat storage material of PCH was better than water and sand. This indicated that the A1 wall had the best heat storage and insulation performance and the maximum heat absorption and release per unit area were 0.91 and 0.73 MJ/m², respectively; Under typical sunny and cloudy conditions, the average indoor temperature of the A1 at night was 2.74 and 1.20 ℃ higher than CK and the average wall temperature at night was 7.33 and 2.34 ℃ higher than CK, respectively. The test results of A4, A5 and A6 showed that with the increase of the amount of PCH thermal storage material, the thermal storage and insulation effect of the wall gradually increased. This indicated that the A4 wall had the best thermal storage and insulation performance, and the maximum heat absorption and release per unit area were 1.48 and 1.13 MJ/m², respectively; Under typical sunny and cloudy conditions, the average indoor temperature of the A4 wall at night was 3.08 and 1.87 ℃ higher than CK and the average wall temperature at night was 7.16 and 3.02 ℃ higher than CK. The above analysis shows that the notable enhancement in heat storage and insulation efficiencies is achieved by incorporating a phase change heat storage layer within the flexible insulation wall.This study can provide theoretical basis for the design and material selection of flexible composite wall of assembled solar greenhouse in the future.