Design of heat pump system for a railway train’s cabin applications utilizing R744 and R290

Abstract Among greenhouse gases, R-134a, commonly used in train HVAC systems, has a high global warming potential (GWP) of 1430. Korea is required to reduce R-134a usage by 80% by 2045, necessitating the development of eco-friendly alternatives. In this study, a heat pump system using the eco-friendly refrigerants R744 (CO₂) and R290 (propane) was designed, and the finned tube heat exchangers for trains were developed by using the EVAP-COND program. Commercial compressors were selected too. The R744 system was designed with a gas cooler outlet temperature of 35 ℃ and an evaporation temperature of 5 ℃ under transcritical operation, while the R290 system was designed with a condenser outlet temperature of 45 ℃ and an evaporation temperature of 0 ℃. The superheat values were set to 5 ℃ for R744 and 20 ℃ for R290. Performance comparison showed that the cooling COP of R744 was up to 18.9% higher than that of R290, while the COP of R290 was 3.8% lower than that of R-134a due to differences in compressor power consumption.