Since these buildings needed a new heating source, the solution took shape in the form of a CHP which supplies 314 kWe and 220 kWth, along with a high-temperature 865 kWth thermeco2 heat pump. The heat pump uses the 26°C sump water from the mining pit as a heat source.
The electric output of the CHP can supply 100% of the electricity for the heat pump and together they feed almost 1 MW of heat into the network. This solution was chosen as the CHP-heat pump system features a fuel utilization coefficient of 167%, compared to 90% for a boiler. Since the communal district heating network works at a temperature of 80 – 93°C, this scenario proved suitable for a CO2 heat pump which is designed to work at high, transcritical temperatures. However, since this heat pump requires a low return temperature, the district heat was adjusted to provide a return water temperature of max. 50°C, allowing the heat pump to achieve a COP of 3.
The system also contains two 12,6 m3 storage tanks which can be filled up in approximately 2 hours and can supply the heat in the district heating network for several hours. For peak loads, a gas boiler is used, kept from the previous system. Overall, the CHP-heat pump system reduced the fuel demand by 26%, and the CO2 emissions by 32%.