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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 &deg, C by heating the water in the tank to a temperature above 50 &deg, C. For the case of a fixed speed compressor, average heating capacity in the range 2.7&minus, 3.1 kW and COP values in the range 3.2&minus, 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&minus, 5.1 kW was obtained for the frequency in the range of 30&ndash, 90 Hz and COP in the range 4.2&minus, 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%.

The paper presents selected technical and economic aspects related to the use of air heat pumps for the preparation of domestic hot water DHW. The research shows that heating the water in the 130 dm3 storage tank with the A21/W30-50 profile lasted an average of 130 minutes, and the heat pump consumed about 2.2 kWh of energy per one heating cycle. Heating water in a 130 dm3 storage tank from 25°C to 40°C lasted an average of 60 minutes, while heating water for another 5°C took 30 minutes. The operation of the heat pump in the higher temperature of the water in the storage tank is less effective, making the heating of water in the tank above 50°C is ineffective.

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.

The experimental studies of the thermal performance of a ground source heat pump (GSHP) described in this paper were conducted in a single-family house. These studies were aimed at performing a field test for the heating capacity of a heat pump. The studies were conducted for 3 cases of variable demand for heat: when space heating was used on the ground floor (75 m2); when space heating was used on the ground and first floors (140 m2) and with the additional heating of domestic hot water mode on (hot water tank 250 L). During the measurement cycle the evaporation temperature of the R407C refrigerant was maintained at a constant level using an electronic expansion valve. Series of measurements were conducted for the evaporation temperature ranging from −5 °C to 2.5 °C. The COP increases along with the evaporation temperature of the R407C refrigerant, yet in the case of the heat pump the maximum COP value was obtained for the evaporation temperature about −2.5 °C. The obtained results were considerably influenced by the temperature of glycol in the secondary circuit of the low temperature source. The heating performance of the heat pump within the investigated period ranged from 8.4 kW to 9.2 kW. While heating domestic hot water, the system could heat the water in the storage tank to a temperature of 45 °C. The control system of the heat pump should enable keeping the condensation temperature as low as possible thus maintain a high COP value. The heating capacity can be adjusted to match the heat demand for space heating by controlling the duration of compressor operation.