SIMULATION ON THE PERFORMANCE OF CARBON DIOXIDE AND HYDROCARBON HEAT PUMPS FOR MODERATE TO HIGH TEMPERATURE HEATING

In order to compare the performance of the carbon dioxide, propane and isobutane heat pumps for moderate to high temperature heating, the three 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 (or condenser) 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 (or condenser) were fixed at 40/90°C and 40/150°C. The heat source inlet temperature was fixed at 10°C. The flow rates of both the heat source and the heat sink were also fixed. The results shows that the hydrocarbon heat pumps have 11–17% higher heating COP than carbon dioxide heat pump under the simulation conditions considered in the present study. However, for a high temperature heating, even though the isobutane heat pump shows the best performance, the carbon dioxide heat pump looks promising due to hydrocarbon heat pumps' high compression ratio.