Pure Refrigerants vs. Zeotropic Mixtures in Heat Pumps: Do zeotropic mixtures exceed the efficiency of R-290?

The refrigerant has a significant influence on the operating characteristics (efficiency, heating capacity, operating envelope) of a Heat Pump. Due to political regulations (e.g., European F-Gas Regulation), the hydrocarbon R-290 (propane) is currently state of the art for new Heat Pumps within the building sector. In addition, many research studies deal with zeotropic mixtures based on low-GWP refrigerants to further improve the operating characteristics of heat pumps by utilizing the temperature glide of the mixtures. However, most investigations are simulation-based and their experimental validation is missing, yet.

Thus, we present the experimental results of low-GWP refrigerants (pure fluids and mixtures) in a brine-water Heat Pump testbench and compare the results to R-290. The experimental investigation is part of the BMWK-funded project “LOGIN” (03EN4011). Within the experimental investigation, two cycle configurations, the basic cycle configuration and the internal heat exchanger (ihx) cycle configuration are included to fully utilize the temperature glide of zeotropic mixtures. All refrigerants are investigated in both cycle configurations and in operating points based on EN 14825. In the basic cycle configuration, the hydrocarbon R-1270 (propene) shows the highest efficiency and heating capacity and exceeds the values of R-290. However, all investigated zeotropic mixtures decrease the heat pump efficiency in comparison to R-290 since the temperature glide cannot be utilized in the basic cycle configuration. When using the ihx cycle configuration, the efficiency of all refrigerants increases. The highest improvements due to the ihx are found for the zeotropic mixtures. Due to the high improvements when adding an ihx, the zeotropic mixture R-477A exceeds the cycle efficiency of R-290, indicating the improvement potential of zeotropic mixtures.