Effect of heat capacity modulation of heat pump to meet variable hot water demand

This paper analyzes the results of experimental studies of an Air Source Heat Pump (ASHP) for Domestic Hot Water (DHW). The tests were carried out by using a commercial heat pump in real conditions in Poland. The modular heat pump with ON/OFF compressor was additionally expanded with a variable speed rotary compressor. Two 130 dm3 water tanks were connected to the condenser output of the heat pump. The COP and heating capacity of the ASHP were investigated under different compressor speeds, water flow rates and different hot water temperatures in the condenser and different outside air temperatures in the evaporator. The DHW was heated in a storage tank whose temperature was changing from room temperature to a temperature above 50 °C. The ASHP subsystem was analyzed for the DHW heating in a typical family of four (130 dm3 at 50 °C, about 6 kWh per day). The test results show that the heating capacity has an approximately linear and proportional relationship with the speed of the compressor. A proportional increase in input power demand was also observed with an increase in compressor speed and refrigerant condensing temperature.