High-glide refrigerant blends in high-temperature heat pumps: Part 1 – Coefficient of performance

Abstract

Climate change necessitates the reduction of primary energy consumption. Industrial heat pumps can contribute by replacing oil and gas fired boilers in various applications. To cater the application, heat pumps must often impose temperature differences of 25 K or more to the heat source and heat sink, causing great irreversibility if evaporation and condensation occur at constant temperatures. Many theoretical studies suggest that high-glide refrigerant mixtures designed to match the temperature differences have a superior COP for such applications. In contrast to the numerous theoretical studies, systematic experimental studies are missing. This study tests high-glide mixtures at varying compositions at constant operating conditions. COP improvements of 16 % are shown comparing the best mixture against the best pure fluid. The improvement was established despite a significant degradation in the heat transfer coefficient, which could presumably be alleviated with larger heat exchangers. Additional parametric studies are conducted on the temperature differences of heat sink and source as well as the temperature level. The results show that mixtures not only outperform pure fluids at certain operating conditions but can maintain a higher COP across varying operating conditions. The binary and ternary mixtures in this study have glides between 10 and 40 K and consist of R1336mzz(Z), R1233zd(E), R1224yd(Z), R1234yf and R32.