Influence of nocturnal thermal insulation on thermal performance improvement of solar air collector with phase-change material

Solar air collectors (SAC) are widely used for the wintery heating, but they have a mismatch shortcoming between supply and demand periods of heat quantity. Integrating phase change material (PCM) into solar air collectors was usually employed to overcome this mismatch, but it was proved that the heat loss through the glass covers reduced utilization efficiency largely in the actual application. According to this, the study employed PCM and nocturnal thermal insulation (NTI) to overcome the mismatch between supply and demand time and improve the nocturnal thermal insulation performance, respectively. Three air collectors (traditional SAC, collector in-tegrated with phase change material (SAC-PCM), collector integrated with both phase change material and nocturnal thermal insulation (SAC-PCM-NTI)) were built to analyze the influence. Experimental results showed PCM could change the heat output time by the latent storage, but the low thermal insulation of the glass plate caused the much heat loss and reduced the thermal efficiency obviously. Employing NTI was highly efficient for collectors which PCM by reducing the heat loss, while it could increase the average temperature of indoor air by 2.49 degrees C. Employing PCM could reduce the heat collecting efficiency by 13%-21% due to the much heat loss during the heat storage and release processes, while using NTI could increase heat collecting efficiency from 24.46% to 32.63%.