Performance optimization of a hybrid ground source heat pump with the parallel configuration of a ground heat exchanger and a supplemental heat rejecter in the cooling mode

A hybrid ground source heat pump (HGSHP) combining a ground flow loop and a supplemental heat rejecter loop in parallel is proposed to overcome the degradation of the ground thermal condition. The objective of this study is to optimize the performance of the HGSHP with the parallel configuration by varying the amount of refrigerant charge, the secondary fluid flow rate of the ground loop, and the secondary fluid flow rate of the supplemental loop. The coefficient of performance (COP) of the HGSHP with the parallel configuration was 21% higher than that of the conventional ground source heat pump (GSHP), and the heat rejection rate of the ground flow loop was 42% lower than that of the GSHP at the entering fluid temperature (EFT) of 40 °C in the ground heat exchanger and the EFT of 28 °C in the supplemental heat exchanger.