Assessment of a two-stage compression heat pump cycle using mixture R290/R744 for water heater applications.

In this study, the mixture R290/R744 were chosen as promising alternative refrigerants in a two-stage compressor heat pump cycle and their performance potentials were evaluated by using the developed mathematical model. As the additive amount of R744 in the refrigerant mixture increases from 5% to 15%, the progressive rise in volumetric heating capacity is presented, but the heating COP tends to decrease while the system pressure rises. When the mass concentration of R744 varies from 5% to 15%, the volumetric heating capacity increases by 412.72 KJ m-3 and the heating COP reduces by 0.79 on average under the evaporator outlet temperature varies from -30 to 20 °C. Considering the potential in reducing the irreversibility of heat exchangers, however, the zeotropic refrigerant R290/R744 can yield very attractive advantage in heat pump water heater applications due to its larger gliding temperature features.