Impact of Compressor Drive System Efficiency on Air Source Heat Pump Performance for Heating Hot Water

A standard Polish household with a central heating system powered by a solid fuel furnace was chosen as a case study. The modular Air Source Heat Pump (ASHP) was used to heat the hot water outside the heating season. In this article comparative studies of the impact of the compressor drive system used on the energy efficiency of the heat pump have been carried out in operating conditions. The ASHP heating capacity and coefficient of performance (COP) were determined for the outside air temperature in the range from 7 to 22 degrees C by heating the water in the tank to a temperature above 50 degrees C. For the case of a fixed speed compressor, average heating capacity in the range 2.7-3.1 kW and COP values in the range 3.2-4.6 depending on the evaporator supply air temperature were obtained. Similarly, for the inverter compressor, the average heating capacity in the range of 2.7-5.1 kW was obtained for the frequency in the range of 30-90 Hz and COP in the range 4.2-5.7, respectively. On cool days, the average heating capacity of the heat pump decreases by 12%. For the simultaneous operation of two compressors with comparable heating capacity, lower COP values were obtained by 20%.