Bremen’s data centre requires cooling for servers around the year. Cooling units require so much electricity that the energy consumption is the biggest cost factor in the operation of a data centre. In Bremen Geo-En has realised a concept which manages to function without using cooling units and consequently reduces operating costs. Besides the hot spell, the ambient air is used as a cooling source and a heat exchanger (ventilators) is also operated. In the transitional periods, the heat exchanger is operated adiabatically and generates temperatures below the ambient temperature. In the hot spell, when cooling units usually consume the highest amount of power, Geo-Engroundwater circulation wells provide cost-effective geothermal cooling. They pump groundwater to the surface, direct it to a heat exchanger and then direct it again a few meters over the extraction point in the aquifer. The heat exchanger obtains heat from the cooling circuit of the data centre and delivers it to the groundwater. This so-called passive cooling is done through minimal power consumption and without a cooling unit. During cold nights and besides the hot summer days, the heat exchanger is also used to restore cold energy back into the ground and to regenerate geothermal energy. This way the groundwater circulation well acts as a cold reservoir which keeps loading cold energy and can be utilised to the fullest.