Drop-in analysis of R450A and R513A as low-GWP alternatives to R134a in a water-to-water heat pump

This paper discusses the results of an experimental analysis of the use of R450A and R513A as drop-in alternatives to R134a in a water-to-water heat pump. The heat pump is tested setting the rotational frequency of the compressor shaft, the vapour superheating at the evaporator outlet and the mass flow rates and temperatures of the secondary fluids at the heat exchangers outlets to the desired conditions. Compared to R134a, the use of R450A leads to a capacity reduction, that lays in the range 6.59% to 15.02%, and to a COP variation, that is within the range - 2.48% to +2.99%, whereas with R513A the variations of the heating capacity and COP lay in the range - 8.78% to +3.16% and - 7.48% to +2.22% respectively. The increase in the rotational frequency of the compressor shaft to bring the heating capacity back to the R134a values is discussed too. The required increase is in the range 10% to 16% with R450A and 2% to 8% with R513A, but a COP reduction in the range 0.14% to 5.22% with the former refrigerant and 2.34% to 6.48% with the latter consequently arises.