Comparative study on heat pump cycle using R32/R1234yf and R744/R32/R1234yf mixtures

The widely used refrigerants, such as R410A, have high global warming potentials (GWP). From a viewpoint of environment conservation, it is necessary to find a low GWP alternative refrigerant. In this situation, one of the hydro-fluoroolefins (HFOs) R1234yf having GWP of less than 1 attracts attentions as the prospective candidate alternative to R410A. In this study, COP is experimentally evaluated in heating and cooling modes for binary mixtures R32/R1234yf and ternary mixtures R744/R32/R1234yf. To increase the volumetric capacity, adding R744 to R32/R1234yf was attempted. Effects of the additive R744 is discussed from the experimental results. The test compositions of these mixtures are designated by GWP values of approximately 300 and 200. The COP of binary and ternary mixtures with GWP of 300 are comparable to or slightly higher than that of conventional refrigerant R410A. On the other hand, the binary with GWP of 200 show slightly lower COP than R410A. The ternary mixture of GWP 200 show always notably lower COP than that of R410A. The mixtures having larger volumetric capacity can decreased the pressure drop. The larger loss is encountered in expansion valve with the mixtures having larger temperature glide. The quantity of heat transfer losses in heat exchangers depends on the temperature change of heat source and heat sink.