Exploring the potential of independent PCM-based free cooling in climate-dominant building structures

Abstract

Passive cooling (or free cooling) technology employing phase change materials (PCMs) is a promising strategy to stabilise indoor air temperature fluctuation and reduce the energy costs for buildings. The PCM ceiling panels have substantial potential for the application of passive cooling, however its ability of temperature conditioning in climate-dominant building structures has never been explored. This paper builds on the prior geometric optimisations of individual encapsulated PCM ceiling panel, aiming to further investigate the thermal performance of multiple encapsulated PCM ceiling panels (i.e. PCM ceiling panel array) in an outdoor storage enclosure with negligible thermal mass, where the impact of climate is dominant. The selected PCMs comprised of a mixture of lauric and capric acids and they were encapsulated in thin-shell panels attached to the ceiling. Through additional simulations, the performance of PCM panels under varying ambient temperature were investigated and compared to that under a constant ambient temperature. Through a holistic experiment during the transitional period between summer and autumn, the panel performance was evaluated with metrics of indoor-outdoor temperature difference and indoor temperature homogeneity, considering the effect of outdoor temperature. An 88.4% reduction in the daily average indoor-outdoor temperature difference was noticed after installing PCM panels by comparing to the case without PCM under a similar weather condition. Notably, the PCM panels allowed indoor temperatures to fall below outdoor temperatures, contrary to cases without PCM. The study also revealed a vertical temperature gradient due to cooler air sinking from the PCM panels, with better temperature homogeneity in warmer-air regions. These research findings complement to the current research unknowns on PCM ceiling panels for building passive cooling.