A heat pump system, wherein the flowing speed of the heating circuit liquid is adjusted in the condenser to regulate the temperature of the heating circuit liquid. The system also includes a sub-cooling heat exchanger for sub-cooling the refrigerant after the condenser to the ground heat collection circuit liquid. Domestic hot water is produced in two phases: in the first phase water is pre-heated with the heat absorbed from the refrigerant in the condenser. A super-heat exchanger is provided for heating the domestic hot water to its final high temperature in the second phase. The super-heat exchanger includes a flowing tube which is used to control the position of the condensing point of the refrigerant vapor and to remove the excessive super-heat to a heat accumulator when domestic hot water is not used.
