Low-GWP refrigerants in heat pumps: An experimental investigation of the influence of an internal heat exchanger

In heat pumps, the use of refrigerants with a low global warming potential (GWP) gains importance due to increasingly strict regulations regarding their ecological impact. In this regard, hydrocarbons (HCs), hydrofluoroolefins (HFOs), and their mixtures are the most promising options due to their thermodynamic properties. Besides the impact of the refrigerant, the cycle configuration (e.g., basic cycle and internal heat exchanger cycle) strongly influences the efficiency of the heat pump. While the potential of low-GWP refrigerants in internal heat exchanger (IHX) cycle configurations is widely investigated in numerical studies, there is a lack of experimental validation. Therefore, this work experimentally evaluates four HCs (R290, R600a, R436A, R1270) and the HFO R1234yf in comparison to R134a in a brine-water heat pump test bench. The test bench design allows to switch between the basic and IHX cycle, thus, enabling the simultaneous impact evaluation of the cycle configuration and the refrigerant on the performance. In the experiments, R1270 shows the highest efficiency for all operating points followed by R290 in the basic cycle. The IHX cycle improves the efficiency for all refrigerants in comparison to the basic cycle. The zeotropic mixture R436A achieves the highest efficiency improvements of up to 27.5% compared to the basic cycle, whereas the efficiency of the single-component refrigerants increases by 10% on average. Despite the significantly higher improvements of R436A due to the IHX, R1270 still leads to the highest coefficient of performance (COP) of up to 6.6 (B12/W35) in the IHX cycle configuration.