Numerical research on R32/R1234ze(E) air source heat pump under variable mass concentration

R32/R1234ze(E) mixtures are potentially low-GWP alternative refrigerants for air conditioning and heat pumps while the rare pure refrigerants can totally meet the requirements of new international protocols on environmental conservation, thermodynamic performance, and safety. The system performance under different concentrations is important for selection of working concentration for the new R32/R1234ze(E) refrigeration or heat pump. In this paper, the thermodynamic model of an ASHP with R32/R1234ze(E) mixtures is built and used to investigate the influence of the refrigerant composition on the performance of the system. The results show that when the mass fraction of R1234ze(E) changes from 0% to 100%, the heating capacity of the ASHP decreases by 67.2%, while the COP continuously increases by 70.3%, which means the changing tendency of system COP is quite different from previous research under fixed evaporating and condensing temperature. Adjusting the refrigerant concentration will be a good system modulation method for ASHPs with R32/R1234ze(E) to meet both the heating capacity and energy efficiency requirements. Furthermore, temperature matching degree is an important factor that affects the energy efficiency of ASHPs with non-azeotropes, which can guide the circuitry optimization of evaporator and condenser in ASHPs with non-azeotropes.