Investigation of the R744 Heat Pump System for an Electric Vehicle to Cool Down the Battery Subsystem

The heat pump system employing R744 has several benefits for mobile air conditioning, since it has a minimal influence on global warming and the system's components can be compact. In addition, it can increase the range of an electric car in cold weather because the R744 heat pump shows superior heating capacity that can covers heating demands of cabin and battery. However, there is a concern that it has inferior cooling performance than the systems with other refrigerants. This study numerically analyzes the R744 heat pump system when it operates to cool down the battery subsystem of an electric vehicle in cooling mode. The system had six major components: an evaporator, an internal heat exchanger, a compressor, a gas cooler, an expansion valve, and a chiller for battery cooling. A simulation model for the system is developed by MATLAB, including physical models of each component. At three different ambient temperatures of 25, 35, and 45 degrees C, numerical calculations were conducted with varied thermal loads for battery cooling. The research explored the impact of battery cooling on system performance and heat capacity. As the battery cooling load increased, the coefficient of performance (COP) increased due to the difference in the overall heat transfer coefficient. The COP increased about 0.2 and the temperature of air to the cabin increased to 26.2 degrees C, when the battery cooling load risen from 0 kW to 3 kW, at the ambient temperature of 45 degrees C.