18 May 2017
With the continued expansion in the implementation of heat pump systems in buildings there is a strong need to better characterize their energy performance at different operating conditions. However, for the case of fixed-capacity water-to-water heat pumps, existing rating methods to determine systems performance at part load have not been assessed for their validity to represent efficiency at real operating conditions. An improved method is proposed in the present study for the characterization of the part load performance of fixed-capacity heat pumps based on reduced experimentation. The methodology is based on the performance of one experiment at stand-by and another at intermediate part load conditions, combined with the use of a partial load factor theoretical equation, in order to determine the degradation coefficients for start-up and stand-by efficiency losses. The method is compared with current methodologies in technical standards and is shown to improve the predictions of part load performance over previous techniques. A black-box empirical model for the heat pump under study is developed and validated with experimental data, demonstrating the potential of using computationally simple methods to model the transient behavior of fixed-capacity heat pump systems, including all energy parasitic losses.