The Use of Phase Change Materials in Ground Source Heat Pump Applications: Research Review and Future Opportunities

This paper provides a critical review of the existing technical literature on various methods for integrating phase change materials (PCMs) into ground source heat pump (GSHP) systems. It identifies the main barriers and challenges associated with the proposed methods, as well as proposes viable ways to overcome them. The methods for integrating PCMs into GSHPs are grouped into five categories: (1) PCM incorporated into GHE backfill or grout; (2) PCM used in thermal storage tanks coupled to GSHP systems; (3) PCM incorporated into heat-transfer fluid as microencapsulated or related PCM slurries; (4) PCM incorporated into energy geo-structures; and (5) PCM incorporated into building envelopes. The outcomes of this critical review highlight that utilising PCMs in backfill materials around ground heat exchangers (GHEs) enhances thermal performance, regulates soil temperature, and reduces the need for large ground space, though challenges such as low thermal conductivity and potential leakage remain. PCM storage tanks offer energy efficiency benefits, but their cost-effectiveness and long-term performance have yet to be addressed. The use of PCM fluids in GSHP applications is still limited, facing issues such as tube clogging and viscosity-related pressure drops. Integrating PCMs into energy geo-structures shows potential for improved heat transfer efficiency and reduced thermal stress. Incorporating PCMs into building envelopes can boost GSHP system performance, but this requires a thorough evaluation of the long-term performance, material durability, and environmental impacts. Addressing these challenges is essential for effective utilisation of PCMs in GSHPs and validating their benefits in enhancing the performance of GSHP systems.