One Mixture to Rule Them All: Enhancing Efficiency and Standardization of Industrial High-Temperature Heat Pumps

Abstract

High-temperature heat pumps are preferred for decarbonizing many industrial processes, but are still being adopted slowly. Major barriers to adoption are low efficiency, leading to high operational cost, and the need for custom-made designs, increasing investment cost. In this work, refrigerant mixtures are exploited to overcome these barriers for high-temperature heat pump adoption. Mixtures have been known to improve heat pump efficiency if their nonisothermal phase change is matched to heat source and sink temperature changes. Beyond that, we improve standardization by using mixture composition as an additional degree of freedom to tailor a standard heat pump designed for a specific refrigerant pair to various applications. By model-band screening of 703 refrigerant pairs across 81 combinations of heat source and sink temperature changes, we identify a maximum COP advantage of 26% for a refrigerant mixture when the maximum heat source and sink temperature changes of 40 K occur. Several mixtures are identified yielding near-optimal efficiencies across all 81 heat source and sink temperature changes. The best all-rounder mixture, diethyl ether/cyclopropane, retains, on average, 97% efficiency of the individually optimal mixtures. These findings support the development of more efficient and less costly high-temperature heat pumps, a crucial step in the heat transition.