High-temperature heat pump design promises greater water-heating efficiency

High-temperature heat pumps (HTHPs) extract and reuse heat from a source, reducing energy costs and carbon emissions. They are increasingly appearing in households and a range of commercial and industrial applications. While the design of these systems, which include refrigerants and compressors, have improved in recent years, the majority are still “single-stage” systems, limited by original heat source conditions and vulnerable to strained compressor pressure ratio in colder temperatures.

Yan et al. introduced an auto-cascade heat pump design with large temperature lift potential —the ability to achieve high temperature differences — and a low Global Warming Potential refrigerant that is more efficient and effective than existing HTHPs.

“We made a smart design tweak,” said author Gang Yan. “Cold water first goes through a ‘cascade heat exchanger’ to warm up to a middle temperature before moving to the condenser to reach a final hot temperature. It’s like boiling water — first you warm it with a small flame, then crank up the heat to boil it. Smaller temperature jumps mean less wasted energy.”

The researchers used a thermodynamic analysis model to compare their design with other auto-cascade heat pumps, and found its efficiency is about 50% greater on average, meaning it makes more heat with the same amount of electricity it heats water much faster, with heating capacity increased by around 50%; and it uses 38.7% less refrigerant on average. Plus, it wastes much less energy because its design shrinks the temperature difference between the refrigerant and water, cutting energy waste in the condenser by more than half.

“This is a game changer for the industry because it not only solves practical problems but also points out an optimization direction,” Yan said.

Source: “Performance assessment of a novel auto-cascade heat pump using low GWP refrigerant for obtaining high-temperature water,” by Gang Yan, Yuqing Yang, and Yinlong Li, International Journal of Fluid Engineering (2025). The article can be accessed at https://doi.org/10.1063/5.0238307 .