Preparation and Performance Evaluation of Phase-Change Wallboards for Chinese Solar Greenhouses

Highlights A novel CaCl2·6H2O–MgCl2·6H2O (30%)–SrCl2·6H2O (1%) composite phase-change material (PCM) was developed. The composite PCM achieved a phase-change temperature of 20–21.1°C and a minimal supercooling degree of 0.3–0.4°C at ambient temperatures of 5–10°C. A method for determining optimal wallboard thickness was established, identifying 2–3 cm as the ideal range for solar greenhouses in Urumqi. A 2-cm thick wallboard demonstrated superior heat release, outperforming 3-cm, 4-cm, and 5-cm panels and brick walls by 14%, 89%, 34%, and 36%, respectively, on clear winter nights. ABSTRACT. In this study, a composite phase-change material (PCM) was developed through the modification of CaCl2·6H2O with MgCl2·6H2O and SrCl2·6H2O to mitigate low nighttime temperatures in Chinese solar greenhouses (CSGs) during winter. The optimal CaCl2·6H2O–MgCl2·6H2O (30%)–SrCl2·6H2O (1%) composite PCM exhibited a phase-transition temperature of 20–21.1°C and a minimal supercooling degree of 0.3–0.4°C at ambient temperatures of 5–10°C. The formulated PCM was incorporated into wallboards with varying thicknesses (2–5 cm). Laboratory experiments and field tests in a Urumqi CSG revealed that on a typical clear winter night, the 2-cm-thick phase-change wallboard released the most heat (2.79 MJ/m 2 ) and significantly outperformed thicker panels and conventional brick walls. Therefore, a wallboard thickness of 2 cm was identified as optimal for balancing heat storage and release efficiency under the tested conditions. These findings provide a practical strategy for improving the thermal environment in CSGs, particularly during winter nights. Keywords: Energy conversion, Greenhouses, Heat flow, Heat transfer, Solar heating.