Refrigerant charge optimization of a dual sorurce heat pump using the ground and water source

The objective of this paper is to optimize the refrigerant charge amount of a dual source heat pump (DSHP) system using the ground and water as heat sinks. The system has two refrigerant flow paths in the condenser composed of two condensing plate heat exchangers (PHEX) in the cooling mode, which are a bypass flow path and a non-bypass flow path. The DSHP was tested by varying the refrigerant charge amount from 1800 g to 3000 g in 300 g increments with the bypass flow path and non-bypass flow path in a single source heat pump (SSHP) mode, while maintaining entering water temperature (EWT) for the evaporator and condenser at 12°C and 25°C, respectively. In the DSHP operation mode, the optimum charge test was conducted at 12°C and 35°C of the EWT for the evaporator and the condenser, respectively. The optimum charge amounts of the bypass flow path and the non-bypass flow path were 2400g and 2100g in the SSHP mode, respectively. The optimum charge amount for the DSHP mode (1800 g) was relatively lower than that for the SSHP mode. The optimum charge amount of the DSHP system should be determined in the non-bypass flow path of the SSHP mode.