Mock-up experimental study on the performance of a combined cooling-domestic hot water-ground source heat pump system

A ground source heat pump (GSHP) delivers heat from a condenser to the ground when it operates with cooling mode. However, the ground temperature increases when the GSHP system operates for a long time. The increased ground temperature can deteriorate the GSHP’s coefficient of performance (COP). To maintain the balance between the ground temperature and COP, the condensation heat from the cooling GSHP can be used for other heating systems before it is transferred to the ground. This study proposes a combined GSHP system connecting a three RT cooling GSHP with a 1.5 RT domestic hot water (DHW) heat pump, and the performance of the system was evaluated through mock-up experiments. In the combined GSHP system, the condensation heat of the cooling system was used as the heat source of the DHW system. Therefore, the ground temperature could be reduced, and the performances of both the GSHP cooler and DHW heater pump could be enhanced. Mock-up experiments for performance evaluation were conducted with cooling-only, DHW-only, and cooling-DHW operational modes. The results showed that cooling-DHW operation slowed down the change in heat source temperature. In comparison with those of the cooling-only and DWH-only heat pumps, the COPs of the cooling heat pump and DHW heat pump of the combined system were increased by 12.93% and 15.47%, respectively. Moreover, the total COP of the cooling-DHW combined GSHP system increased by 4.4% and 29.55% in comparison with those of the cooling-only GSHP and DHW-only GSHP systems, respectively.

A combined GSHP system was proposed by connecting a GSHP for space cooling with a heat pump for DHW to mitigate the ground temperature changes due to the long-term operation of the GSHP system. The combined system reuses the condensation heat generated by the cooling heat pump as the heat source of the DHW heat pump for ensuring the system performance and building energy saving. Therefore, this system is suitable for buildings with large energy use and heavy hot water demand, especially in summer, such as hospital and hotel buildings.