High temperature heat pumps for industrial heating processes using water as refrigerant

Abstract

High-temperature heat pumps (HTHPs) provide a promising approach to reducing CO₂ emissions in industrial heating applications. However, developing large-scale, high-temperature-output, and large temperature-lift heat pumps that utilize low-GWP refrigerants remains a challenge. Natural working fluids, particularly water, show potential due to their exceptional thermodynamic properties and environmental friendliness. Our findings indicate that by employing water as a refrigerant, high-temperature heat pumps can achieve a significant temperature lift of up to 100 °C while maintaining a satisfactory coefficient of performance (COP). Additionally, these systems demonstrate high flexibility, enabling them to operate as closed-cycles, hybrid closed and open cycles, or hybrid vapor compression and absorption systems. Furthermore, we identify feasible matching strategies for industrial high-temperature heat pumps, focusing on working fluids, components, and cycle structures, with variables such as compressor type, heating temperature, and capacity. Through this research, we highlight the unique performance advantages of water across a 100 °C temperature range and propose detailed design sketches centered on water, capable of achieving large temperature lifts and high-temperature outputs. These include compression cycles, absorption cycles, and mechanical vapor compression cycles, with particular attention to closed and open cycle combinations. Moreover, we emphasize the research gap in current industrial heat pump technologies, providing a forward-looking technological perspective on heat pumps as a key component in further industrial decarbonization.