With floor heating and cooling ceilings, the modern multi-family house in Berlin-Mitte offers residents maximum comfort. The geothermal energy system supplies energy to the system in a climate-friendly and cost-effective manner. Passive cooling is used for cooling: Water circulates through the cooling ceilings and absorbs the heat of the building. A heat exchanger transfers this heat to the cold brine which flows through the borehole heat exchangers and the heat is transferred to the ground. Thus, cooling is done without cooling machines and only circulationpumpispowered. In winter the heat pump uses the heat which has been transferred to the in the summer. As the cooling requirement in summer is lower than the heating requirement in winter, the solarabsorbers also collect heat from the roof and transfer it to the borehole heat exchangers. In extreme frost periods, the heat pump and CHP are supported by a condensing gas boiler. Thus, the geothermal energy system can work in a small space and still be utilised optimally.