An Experimental Comparison of the Performances of a Small Water-to-Water Heat Pump Working with R1234ze(E) and Its Mixture R515B

The study presents the results of an experimental investigation aimed at evaluating the performance of a water-to-water heat pump utilising R1234ze(E) and R515B in a drop-in application. Several operating conditions are tested, varying the mass flow rates and temperatures of the secondary fluids that pass through the heat exchangers while maintaining the compressor shaft rotational frequency and the vapour superheating at the evaporator outlet constant. Overall, when compared to R1234ze(E), the utilisation of R515B results in capacity and COP variations within −6.81% to +2.46% and −2.41% to +6.29%, respectively. Regarding the performance of the compressor, R515B exhibits comparable volumetric and overall efficiency, while a slightly lower refrigerant temperature at the compressor discharge is found, with differences ranging from −3.1 °C to −0.5 °C. Overall, R515B appears to be more suitable than R1234ze(E) for applications in the high-temperature range.