Thermodynamic analysis of novel eco-friendly binary refrigerants in high-temperature heat pumps for industrial heating recovery

High-temperature heat pumps (HTHPs) offer a promising route to replace traditional industrial boilers that rely on fossil fuels due to their potential for recovering and upgrading low-grade waste heat. Their viability for replacing conventional industrial boilers depends on performance at large temperature lifts and high supply temperatures. The development and deployment of HTHPs are constrained by the availability of eco-friendly, high-performance refrigerants. Based on detailed thermodynamic modeling, this study investigates zeotropic binary refrigerant mixtures containing cyclobutane (critical temperature 186.9 °C, normal boiling point 12.5 °C) as the base fluid with R601, cyclopentane, hexane, isohexane and cyclohexane. The mixtures are evaluated in an intermediate vapor injection heat pump cycle integrated with an economizer and internal heat exchanger (IHX). The analysis emphasizes temperature-matching behavior and the effects of key operating parameters on cycle performance. The results show that at a heat source inlet temperature of 40 °C and a heat sink outlet temperature of 170 °C, pure cyclobutane attains a COP of 1.49. Zeotropic mixtures improve performance, with cyclobutane/cyclopentane (0.5/0.5) reaching a COP of 2.06, a 38.26% increase over pure cyclobutane. Optimizing temperature matching substantially reduces irreversible losses during heat transfer for zeotropic mixtures. Adjusting the intermediate pressure yields up to a 5.60% additional performance gain. This work fills the research gap in cyclobutane-based mixtures, and offers a useful reference for the development of ultra-high temperature lift heat pump refrigerants.