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at DOE for providing oversight and guidance throughout the project. The authors would like to thank Reid Hart at PNNL for providing a detailed technical review of cost estimates and the analysis results and Bing Liu, Manager of the Building Energy Codes Program at PNNL, for insightful comments on the contents of the report.

A thermal analysis of a GCHP system is performed to investigate the effect of adding micro-encapsulated PCM into the borehole grout to improve the thermal performance of GCHP systems. The apparent heat capacity method is used in the numerical model, simulated in COMSOL. The PCM’s thermal properties were varied to study the effect of each property, such as PCM melting temperature, transition temperature range, PCM thermal conductivity, and the amount of PCM within the grout. Even though the low thermal conductivity of PCM compared to ordinary grout adversely affects the GCHP system performance, a potential reduction (∼2%) in borehole length is achieved. The best melting temperature is that which results in a complete melting of PCM around the peak load, instead of around the average load. The melting temperature must be chosen properly for each GCHP scenario, otherwise the benefit from using PCM may not be achieved. There is an insignificant change in the heat pump consumption because EFT is more favorable in PCM cases around the melting temperature, but less favorable after melting completely.