Opportunities and challenges of PCM-to-air heat exchangers (PAHXs) for building free cooling applications—A comprehensive review

Abstract

With high energy consumption trend in buildings, the adoption of thermal energy storage systems toward reducing cooling load has been increased in recent years. Subsequently, utilizing the concept of latent heat thermal energy storage (LHTES) through phase change materials (PCMs) have been widely discussed in the literature. This paper is a comprehensive review of the utilization of PCM-to-Air Heat Exchangers (PAHXs) for building free cooling applications. The potential and limitations of using PAHXs in free cooling applications are discussed in detail, focusing on hot desert climate. Significant system influencing factors such as inlet temperature, phase change temperature, and airflow rates are analyzed and their impact on the thermal performance of PAHXs free cooling applications are addressed. Previous studies claimed that continuously maintaining outlet air temperature (of PAHX) within the preferred indoor thermal comfort is a system limitation, especially in extreme climates with exceptionally high cooling demand. However, they have assured the increased cooling potential by adopting multi-PCM approach and integration with other passive technologies in free cooling systems to increase system storage abilities and satisfy workability under high inlet temperatures. For magnifying the free cooling system's cooling abilities in hot desert climate, this paper recommends considering the potential of nighttime sky radiation during the PCM charging process. The discussions made in the paper will be helpful in understanding the influencing parameters of PAHXs system for free cooling application, especially in hot desert climate.