Simulation on the Performance of Carbon Dioxide and HFC-125 Heat Pumpsfor Medium-and High-Temperature Heating

In order to compare the performance of the carbon dioxide and HFC-125 heat pumps for medium-and high-temperature heating, both heat pump cycles were optimized using a simulation method. To fairly compare the performance of the cycles by using different working fluids, each cycle was optimized from the viewpoint of heating COP by two design parameters. The first is the gas cooler exit temperature and the other is the ratio of the overall heat conductance of the gas cooler to the combined overall heat conductance of the gas cooler and the evaporator. The inlet and outlet temperatures of secondary fluid of the gas cooler were fixed at 40/90°C and 40/150°C.The results shows that the HFC-125 heat pump has 6% higher heating COP than carbon dioxide heat pump when the heat sink exit temperature is fixed at 90oC, while the latter outperforms the former when the heat sink exit temperature is fixed at 150oC under the simulation conditions considered in the present study. Keywords—Carbon Dioxide, HFC-125, Transcritical, Heat Pump