Coupled operations and decoupled performance: Field testing and operational assessment of a ground source heat pump integrating energy piles and boreholes

Ground source heat pump (GSHP) systems with energy piles (EPs) and borehole heat exchangers (BHEs) provide a potential pathway for building decarbonization. However, how these components share thermal loads and how factors affect the system energy efficiency remain unclear. This study evaluated a full-scale GSHP system consisting of 20 EPs and 6 BHEs installed in cohesive soil during winter and summer operation. The seasonal thermal responses, load-sharing behaviors, system energy efficiency, and parameter sensitivities were quantified. An operational evaluation was conducted. The seasonal load-sharing patterns differed between winter and summer. During the initial winter heating stage, EPs dominated heat extraction (load-sharing index>0.6) because of their structural thermal mass. Deep BHEs dominated early summer heat rejection because they were less affected by surface temperature variations. Furthermore, the pile and ground temperature changes indicated a thermal hysteresis effect caused by the thermal inertia of cohesive soil. Statistical analysis revealed that the ground-side pump frequency showed the highest contribution to energy efficiency variations, and indoor parameters determined thermal comfort. The proposed operational strategy achieved a coefficient of performance (COP) of 3.68 and an energy efficiency ratio (EER) of 3.91 while maintaining a small indoor temperature deviation of ≤0.34 °C.