Effectiveness of phase change materials and their properties on the performance of geothermal and foundation-based energy systems: A review

Abstract

As buildings contribute notably to emissions of greenhouse gases, it is important to move towards building heating and cooling systems with good sustainability attributes and efficiencies, such as ground-source heat pumps (GSHPs). In this review, an integrated picture of the effect of utilizing phase change material (PCMs) having various physical properties on the performance of GSHPs and foundation-based geothermal systems is presented. Two major questions are addressed in this paper: how effective is a PCM for enhancing the performance of both conventional GSHP systems and foundation-based geothermal energy systems? The results show that PCMs can be effective at enhancing performance for conventional GSHP and foundation-based geothermal energy systems by, on average, 17% and 36%, respectively. However, the degree of PCM effectiveness depends on some parameters such as its physical characteristics (thermal conductivity, latent heat, phase change temperature) and design considerations (ground loop configuration, depth, etc.) among other factors. The results also show that, in general, the greater the PCM thermal conductivity, the higher the effectiveness of the PCM. Furthermore, by adding composites such as expanded graphite to the PCM, the thermal conductivity of a PCM increases more than 250% which can potentially improve the performance of geothermal systems. More research is warranted to maximize the system performance improvements by enhancing the PCM.