The Montreal Protocol banned R134a, previously used in automotive heat pump systems. R1234yf is currently being investigated as an alternative refrigerant for its potential application in automotive heat pump systems to replace R134a. However, R1234yf will also be subject to PFAS (per- and polyfluoroalkyl substances) regulations. It necessitates converting heat pump systems using R1234yf to utilize natural refrigerants. This study analyzed the interchangeability of R744 and R290 as alternative refrigerants in numerical heat pump model designed for R1234yf. When applying these natural refrigerants in the conventional system, R744 cannot be interchangeable as it shows a lower Reduced speed than the lowest value of reduced speed of the compressor. R290 can be interchangeable as its reduced mass flow rate, reduced speed, and pressure ratio have a value that includes the range of the compressor. When applying R290, heating & cooling capacity at each mode increases by 22.8% while COP decreases by 16.8%. When applying R290, the refrigerant at the condenser outlet cannot be subcooled. Even when changing the heat exchanger specification, R290 still cannot be subcooled at the exit of the condenser. However, when the refrigerant charge is increased by 0.6kg, R290 is completely condensed at the condenser exit in both cooling and heating modes. At 0.6kg, the heating & cooling capacities in each mode increase by up to 9%, while the COP increases by up to 12%. In conclusion, R290 can be interchangeable with minimal system redesign by adjusting the charge. • A study for substituting R1234yf is needed by PFAS regulations. • Interchangeability of R744 and R290 was studied in EV heat pump designed for R1234yf. • R744 cannot be used in R1234yf EV heat pump, while R290 can be used. • Methods for obtaining subcooling in EV heat pumps were conducted with R290. • Changing the charge makes the system subcooled at the inlet of the expansion valve.
Song et al. (Sun,) studied this question.