Stadtwerke Münster, the municipal utility of the German city, has started exploratory drilling for near-surface geothermal energy on Kötterstraße in the Handorf district, ThinkGeoEnergy reported on 4 November. The borehole is planned to reach about 300 metres and will tell the utility what temperatures and soil layers it can count on before it lays out a future "cold" district heating network there.
How the earlier networks work
Münster has done this before. In the new Kirschgarten development the utility drilled 39 boreholes to 250 metres across three probe fields. Heat comes out of the ground at a low temperature, and brine-to-water heat pumps lift it to heating temperature before it reaches the homes. On hot days the same ground loop gives passive cooling. A similar system was built earlier in Albachten-Ost.
The city is also looking deeper. A completed seismic survey has mapped the subsurface to 6,000 metres, and early plans aim to drill to between 900 and 1,500 metres by 2028. The Geological Survey of North Rhine-Westphalia plans its own research borehole in Münster under the state's geothermal master plan.
Low temperatures, more heat exchangers
A cold network turns the usual district heating picture around. The pipes carry water close to ground temperature, and every building lifts it with its own heat pump. That means many small heat-transfer points instead of one large plant: the ground probes, the brine circuit, the heat pump and the separation to the building's heating water, often through a plate heat exchanger where the brine must stay out of the building system.
With such small temperature differences, fouling and air in the circuit cost more than they would in a hot network. Filters, venting and access for cleaning belong in the design from the first day.
Sources: ThinkGeoEnergy
