PCM-based Ceiling Panels for Passive Building Indoor Cooling: Experimental and Numerical Study

Abstract

To relieve the upsurge of the energy demand associated to building indoor cooling, passive cooling employing phase change materials (PCMs) has been proposed as a promising technique to stabilise indoor air temperature fluctuation and reduce building energy demand. PCMs can exchange a large amount of latent heat during the melting and solidification processes, which can be utilised in line with the discharging and charging processes of a cooling system. The use of encapsulated PCM ceiling panels in buildings has immense application potential for passive cooling, which has attracted investigations in recent years. The geometry selection of the PCM ceiling panel is vital as it determines the exposed surface area to the surrounding air and the natural convection, and therefore the heat transfer rate to/from the PCM, which generally suffers from low thermal conductivity. This study builds on the geometric optimisation of enclosed PCM capsules driven by natural convection, aiming to investigate the phase change behaviour and thermal performance of encapsulated PCM ceiling panels of different geometries. Here, the presented study focuses on the conjugate heat transfer phenomena through the surrounding air, panel shell, and PCM. A mixture of lauric, capric, and oleic acids was selected as PCM encapsulated in a thin-shell enclosure made of acrylonitrile butadiene styrene plastic, which forms the aesthetic panels attached to the ceiling. A computational fluid dynamics model was validated using full-scale experimental data and further employed to analyse the discharging process and design considerations of the PCM ceiling panels. The effects of various influencing factors were explored, such as panel volume, the initial temperature difference between PCMs and surrounding air, shell thickness, and geometrical features. The results indicate that the panel comprised of a pyramid array is more advantageous than the tetrahedral-based panel in terms of thermal performance. In addition, tweaking the geometric features of the panel will largely impact its thermal performance as the effective heat transfer area and natural convection conditions are varied. Finally, it was found that hanging the panel to the ceiling will effectively enhance the heat transfer compared to directly attaching it to the ceiling.

To build on the prior numerical investigations on the phase change behaviour and thermal performance of individual encapsulated PCM ceiling panel of different geometries, we aim to further investigate the thermal performance of multiple encapsulated PCM ceiling panels (i.e. PCM ceiling panels array) in an outdoor storage enclosure with negligible thermal mass. A mixture of lauric and capric acids was selected as PCMs encapsulated in self-designed thin-shell panels. Through additional simulations, the performance of PCM panels under realistic varying ambient temperature were investigated and compared to that under constant ambient temperature. Through a holistic experiment, the panel performance was evaluated with metrics of indoor-outdoor temperature difference and indoor temperature homogeneity, considering the effects of outdoor temperatures and solar irradiations. It was found that the PCM panels reduced the daily average indoor-outdoor temperature difference by 88.4% under similar daily weathers and generally reduced the indoor-outdoor temperature difference for the studied days. With PCM panels, the indoor temperature can sometimes be lower than the outdoor temperature, which is not possible without PCM. The vertical temperature gradient showed better homogeneity in the upper part, which was evidenced by both experiment and simulations. This study complements to the current research on PCM ceiling panels for building passive cooling. Show more