Experimental comparison of HFO-1234ze(E) and R-515B to replace HFC-134a in heat pump water heaters and moderately high temperature heat pumps

•This article is the first to test the new non-flammable mixture R-515B.•R-515B is experimentally compared to HFO-1234ze(E) and HFC-134a.•Different heat pump applications have been covered through 65 steady-state tests.•The analysis considers operational, energetic, and environmental parameters.•The operating range of heat pumps has been extended with R-515B and HFO-1234ze(E). Heat pumps are gaining interest to replace fossil fuel burners with the increase of the share of renewable sources in the electricity generation mix. Moreover, low global warming potential (GWP) alternatives offer a more environmentally friendly option as refrigerants. HFO-1234ze(E) and its non-flammable mixture R-515B are experimentally investigated for the first time to replace HFC-134a in heat pump water heaters (HPWH) and moderately high temperature heat pumps (MHTHP). Tests are performed in a test rig equipped with a variable frequency compressor at evaporating temperatures of 7.5, 15 and 22.5 °C and condensing temperatures from 55 to 85 °C (65 experimental tests). HFC-134a outperforms both alternatives in heating capacity (approx. 26% higher) due to the higher mass flow rate and heating effect. However, this effect is compensated by, on average, 25% lower compressor power consumption. Therefore, the coefficient of performance (COP) is comparable or slightly higher (up to 5%) for HFO-1234ze(E) and R-515B. Considering the positive results in COP and the reduced GWP, both options decrease HFC-134a MHTHP equivalent carbon emissions down to 28%. Besides, given the 20 K lower discharge temperature reached by the alternatives, the compressor operating map can be significantly extended. Finally, it is demonstrated that R-515B is a suitable non-flammable alternative to HFO-1234ze(E) that keep energetic and environmental benefits while offers a safer system operation.