This paper deals with the experimental performance evaluation of a geothermal heat pump (GHP) intended to produce space heating (SH) and domestic hot water (DHW) simultaneously. The GHP uses R407C as refrigerant and its main components are a scroll compressor, a thermostatic expansion valve, a plate heat exchanger as evaporator and a condensing section composed of two plate heat exchangers connected in series, operating as a desuperheater and a condenser. In the condensing section, water is heated at two temperature levels for the SH and DHW systems. The experimental results realize the high influence of the water temperature at the condensing section inlet on the GHP behaviour. The COP and the heating capacity decrease 48.7% and 5.6% by increasing the water temperature at the condenser inlet from 20 to 50 degrees C, respectively. The percentage of water flow rate diverted to the desuperheater for DHW production depends on the water temperature and flow rate at the condensing section inlet. However, the heat transfer rate at the desuperheater remains nearly constant regardless of the water flow rate at the condensing section inlet and the water flow rate driven through the desuperheater. The experimental results also show that the water temperature inlet at the condensing section determines the proportion of the heat transfer rate delivered at the desuperheater for DHW production and at the condenser for SH. (C) 2012 Elsevier Ltd. All rights reserved.