Enhancing the Thermal Performance of Air‑Conditioning Systems Using Phase Change Materials: A Comprehensive Review

Abstract

With the use of conventional vapor-compression heating, ventilation, and air conditioning (HVAC) systems, the air-conditioning system electrically consumes most of the electricity for the building, particularly due to peak electrical demand and greenhouse gas emissions associated with air-conditioning systems. This review describes how using thermo-responsive phase change materials (PCM) can help to enhance the thermal performance of air-conditioning (AC), as well as reduce energy consumption. The types of PCM characterised include: organic, inorganic, and composite/eutectic materials; the importance of the characteristics (phase change temperature, heat of fusion, thermal conductivity, cycling stability, and HVAC compatibility) of PCM to any HVAC application is discussed with a particular emphasis on the methods of improving heat transfer and controlling leakages through the use of nano-enhanced and encapsulated composites. Additionally, this paper covers the three strategies of integrating PCM within an AC system, PCM-enhanced heat exchangers; PCM-based thermal energy storage (TES) devices; and PCM-embedded building materials. The results from experimental, field, and numerical studies indicate that PCM integration in AC systems can substantially reduce indoor temperature fluctuations (up to 46%), reduce heating/cooling loads (up to 31%), improves the coefficient of performance (COP) for air-conditioning by 7-88%, shift as much as 89% of the cooling load to off-peak times and produce annual cooling-energy savings of 7-32% - depending on the specific climate and/or configuration types and controls. The thermophysical enhancement techniques (nanoparticle additives, porous supports/metal foams, encapsulation) have been summarized in this review along with significant reductions in CO₂ emissions e.g. in operational terms due to life cycle studies of these techniques but the payback times are dependent on weather and costs. This paper has evaluated the major technical barriers (long term stability, supercooling, phase separation, flammability and corrosion), manufacturing & scalability issues and integration with existing infrastructure along with the various economic and market barriers. Finally, we have identified emerging opportunities for the PCM ‑enhanced cooling systems, such as solid to solid PCMs, bio-based PCMs, multi-functional nano-composites, advanced control or optimisation (including AI-based) and coupling with renewable energy systems, and highlighted a number of research gaps that must be closed for the large scale and cost-effective deployment of PCM-enhanced cooling to be realized