A Study on the Performance Comparison of a Mobile Heat Pump Based on the Mixing Ratio of R744 and R290 Refrigerant Mixture

This study aimed to analyze the heating and cooling capacity and refrigerant charge variation according to the mixing ratio of R744 and R290 in a mobile heat pump system. Results showed that as the mass fraction of R290 increased, both heating and cooling capacity, as well as the coefficient of performance (COP), improved. In particular, performance differences were observed depending on the outdoor temperature. The maximum difference was 55.5% in cooling mode and 54.5% in heating mode. When applying an R-404A compressor for the present model, the COP did not exhibit a linear increase within the R290 mass fraction range of 0.4 to 0.6. Additionally, the refrigerant charge decreased linearly with an increasing R290 mass fraction, attributed to the differences in density and void fraction between R744 and R290. The maximum reduction for refrigerant charge was 52.0% in cooling mode and 56% in heating mode. This study confirms that the compressor can significantly impact the overall performance of the heat pump system, indicating that compressor selection is a critical factor in the design process of a mobile heat pump system utilizing an R290 and R744 mixture.