Aon Hijazi, Charaka Beragama Jathunge, Aggrey Mwesigye
As the global transition toward net-zero greenhouse gas emissions accelerates, decarbonizing space heating in cold climates remains a critical challenge. Ground source heat pumps (GSHPs) coupled with thermo-active foundation piles offer an efficient and low-emission alternative to conventional heating systems by integrating ground heat exchange within structural foundation elements. However, their application in heating-dominated regions is constrained by long-term thermal performance considerations, as well as by structural and geotechnical requirements that are not addressed through thermal design alone. The objective of this study is to numerically evaluate the thermal and operational performance of a partially loaded thermo-active foundation pile system coupled with a GSHP under a cold-climate load profile representative of Calgary, Canada. Two per-pile design capacities of 0.4 ton and 0.5 ton are examined under three operating conditions corresponding to 60 percent, 70 percent, and 100 percent of the normalized per-pile peak heating load. In the partially loaded cases, the remaining load fraction is supplied by an auxiliary electric resistance heater. Transient threedimensional simulations are conducted over a five-year equivalent period to assess ground temperature evolution, pile inlet and outlet fluid temperatures, and system coefficients of performance (COP). The results show that all configurations exhibit near steady ground temperature behaviour over the considered period, with small year-to-year variations consistent with heating-dominated operation. Relative to unshaved operation, partial-load configurations show smaller long-term ground temperature shifts and slightly higher minimum entering water temperatures during peak winter conditions. System reliability, defined in this study as thermal operability based on the duration of sub-threshold entering water temperature, improves modestly for the 0.4- ton configurations under partial-load operation. Heating COP values decrease slightly over time for all cases, while cooling performance remains mostly unaffected by load-shaving.