A field study of the performance of a heat pump installed in a low energy house

• An efficiency field test of a heat pump was performed.
• The thermodynamic cycle of the heat pump was controlled by an electronic expansion valve.
• A high COP of the heat pump was obtained for underfloor space heating.

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.