Thermodynamic performance analysis of low-GWP refrigerants in high-temperature heat pumps

• Thermodynamic comparison of low-GWP refrigerants for HTHPs. • Performance analyzed at 40 °C and 80 °C lifts, with condenser temperatures of 100–150 °C. • R718 achieved the highest COP (6.9 at 40 °C) and second-law efficiency (55% at 80 °C). • R718′s COP improves with higher condenser temperatures, unlike other refrigerants. • R1234ze(Z) and R123 are suitable for compact systems with moderate efficiency requirements. • R600 and R245fa are suitable for low-cost systems with standard compressors. • R718 is optimal for high-efficiency industrial heating with advanced compressors. High-temperature heat pumps (HTHPs) are a promising solution for reducing carbon emissions in industrial heating by upgrading low-grade waste heat to temperatures above 100 °C. A key challenge in designing efficient and practical HTHP systems is choosing the right refrigerant. This study presents a comprehensive thermodynamic analysis of seven low-global-warming-potential (GWP) refrigerants R718 (water), R600, R123, R1234ze(Z), R1233zd(E), R1224yd(Z), and R245fa for high-temperature heat pump (HTHP) applications. The refrigerants were evaluated under temperature lifts of 40 °C and 80 °C and condenser temperatures between 100 °C and 150 °C. Key performance metrics including coefficient of performance (COP), volumetric heating capacity (VHC), compressor pressure ratio (PR), discharge temperature, volumetric flow rate, power consumption, and second-law efficiency were analyzed to identify optimal working fluids. Results show that R718 achieved the highest COP, up to 6.9 at 40 °C lift and 3.0 at 80 °C lift, along with the highest second-law efficiency, reaching 55% at 80 °C lift, due to its superior thermodynamic properties. However, R718 also exhibited the lowest VHC (1900 kJ/m 3 at 40 °C lift) and the highest discharge temperatures (>520 °C at 80 °C lift), requiring larger compressors and advanced materials. Conversely, R1234ze(Z) and R600 demonstrated higher VHC (>7000 kJ/m 3 at 40 °C lift) and moderate discharge temperatures (<180 °C), enabling more compact and cost-effective designs but at a reduced COP (5.5 at 40 °C lift). This study highlights that R718 has clear advantages in HTHP applications. In industrial heat recovery, an R718-based HTHP can provide the required high output temperatures while achieving better overall performance. These findings provide practical guidance for engineers and designers working on next-generation heat pumps for industrial heating applications.