Simulation study on performance of a dual-source hybrid heat pump unit with alternative refrigerants

•A novel double-source hybrid heat pump unit is proposed.•The mathematical models of the unit with alternative refrigerants are established.•The unit characteristic of R134a is compared with those of R32, R290 and R600a. To solve the problems of single heat source heat pump systems in severe cold regions, a dual-source hybrid heat pump unit (DSHHPU) is proposed. The mathematical models of the DSHHPU when charging R134a or its alternative refrigerants R32, R290 and R600a were established respectively, and the performance was simulated and analysed. The results showed that the four refrigerants have different performance characteristics in different aspects. In heat pipe mode, the heating capacity and evaporating pressure of R32 are 36.94% and 59.94% higher than those of R134a. The heating capacity and evaporating pressure of R290 are 5.73% and 22.99% lower than those of R134a. The heating capacity and evaporating pressure of R600a are 43.29% and 68.08% lower than those of R134a. In vapour compression heating mode, the discharge temperature of R32, R290 and R600a are 184.88, 72.98 and 66.44% of that of R134a. The coefficient of performance (COP) of R32, R290 and R600a are 72.65, 111.59 and 117.94% of that of R134a. Finally, the effects of radiation intensity and ambient temperature on key performance parameters of the different refrigerants were analysed. The research results provide a reference for research on refrigerant replacements for multi-heat source composite heat pump systems.