Drop-in experiments and exergy assessment of HFC-32/HFO-1234yf/R744 mixture with GWP below 150 for domestic heat pumps

Research trends in the heat pump systems can mainly be categorized into the developments of the cycle and the working fluids. Regional and global watchdogs regulate the fate of working fluids in the name of environmental issues, especially global warming. Examples include the Montreal Protocol, the Kyoto protocol, and lately, the European “F Gas” Directive (No. 542/2006). The urgent and pressing call is next-generation refrigerants that are benign to the environment without compromising the performance. Pure substances are known to be limited, while refrigerant mixtures have been gaining significant attention due to their flexibility in tuning flammability, stability, and low GWP values. In this work, we investigated a ternary mixture of HFC-32/HFO-1234yf/R744 (22/72/6mass%) with the targeted GWP less than 150. Three operation modes (cooling for summer, Cooling, low-temperature heating, Heating#1, and high-temperature heating, Heating#2 for winter) were investigated experimentally. Optimal refrigerant charge amounts for all operation modes followed by the system performance were evaluated from part-load to full-load operations. The system is further scrutinized using the 2^nd Law of Thermodynamics by tracking exergy destructions in major components. Among the selected operation modes, Heating#1 provides the highest system COPs for all loads due to the lower lift and smaller temperature difference between the inlet and outlet of the coolant to the condenser. The cycle exergetic efficiencies were 31.7%, 37.8%, and 43.3% for Cooling, Heating#1, and Heating#2 modes, respectively. The results presented in this work will be useful in the refrigerant design (ternary mixtures) and the system development for low-GWP refrigerant applications.