Study on heat-transfer mechanism of wallboards containing active phase change material and parameter optimization with ventilation

This study evaluated the thermal performance of a new ventilated Trombe wall integrated with phase change materials (PCMs-VTW) in a building in hot summer and cold winter region of China. The Trombe wall was constituted of double PCM wallboards, consisting: an exterior PCM wallboard with a high absorptivity/reflective coating and an interior PCM wallboard fitted with active hot/chilled water pipes. A numerical model using a heat-source transitioning method was developed to characterize the heat transfer mechanism of both PCM wallboards. The concept of energy storage and release efficiency (ESRE) has been defined and calculated to illustrate the potential of the new system for energy saving during both cooling and heating periods. Our findings show that the overheating and super-cooling problems could be mitigated by the use of either a high-reflective or high-absorptive coating on the exterior PCM wallboard depending on local climate, such as solar air temperature and radiation, achieving a 10% enhancement in ESRE in summer and 13% in winter. The optimum melting temperatures of exterior and interior PCM were 26 K and 22 K respectively in terms of ESRE enhancement, under which maximum values of ESRE: 16.8%/18.9% for exterior/interior PCM in summer and 23%/18.2% for exterior/interior PCM in winter, were achieved. Optimum thicknesses for exterior and interior PCM were 8 mm and 28 mm, resulting in 20.2% average ESRE for exterior PCM and 20.25% for interior PCM.