Development of PCM-to-air heat exchanger for integration in building envelope–modeling and validation

Abstract

Earlier applications of phase change material (PCM)-to-air heat exchangers (PAHXs) reported the insufficient cooling charging energy needed for complete solidification of the PCM in free cooling systems. Also, the prediction of PAHX performance under low airflow regimes is a system limitation for free cooling applications. Besides, the implementation of the long wave thermal radiation cooling concept has not gained much attention in the free cooling design of PAHX units. This paper reports the development of PAHX system for building envelope applications that promotes the thermal radiation loss to the sky during night-time to maximize the cooling potential. A 2D numerical model has been developed considering the PCM thermal behavior, short and long wave radiation, and convection phenomena. New thermal boundaries of long-wave radiation have been proposed between system elements and the sky temperature. In addition, the model considered various forms of convective heat transfer phenomena. The apparent heat capacity method was used to simulate the thermal storage process. Experimentally obtained data and inter-model comparison were used to validate the proposed model. Two full-scale prototypes of the developed PAHX system were designed and tested under real conditions using two different types of PCMs. A parametric analysis was conducted to investigate the system thermal behavior under various air velocity profiles in the air channel and various inlet air temperature conditions. The results indicate that the building envelope integrated PAHX can use the sky radiation as a cooling source.