CO2 Heat Pump in High-Temperature District Heating Plant

In 2019, an oil-fired boiler was replaced by a ground-source CO2 heat pump system in a military facility in Norway. The facility was heated by a district heating plant with forward temperatures up to 80 degrees C, and return temperatures varying from 35 degrees C to 55 degrees C. These relatively high return temperatures result in low COP for the CO2 heat pump. Nevertheless, CO2 was chosen as refrigerant for the heat pump because the high forward temperature was a serious obstacle for the alternative HFO1234ze heat pump system. The CO2 heat pump system was competitive with regard to energy savings as well as profitability compared with the alternative HFO heat pump. The CO2 heat pump system has performed well, and the energy savings have been greater than expected. One of the reasons for that is due to the implemented measures in the district heating network in order to reduce the district heating water return temperatures.