In Berlin, the first buildings are using the energy from the sewage in sewers for heating. It is a small answer to the big question of how houses should be warm in a climate-neutral way in the future.
When the employees of the online retailer Zalando populate their new headquarters in Berlin in the fall and winter, an unusual technology will heat the offices: the energy company Eon and the real estate developer Signa have now put a system into operation, which is the former Kaufhof building near the Ostbahnhof to supply a large part with heat from the sewer system.
The cooperation with Berliner Wasserbetriebe is intended to provide a small answer to the big question of the future: How will houses be kept warm in the future without burning natural gas or oil on a large scale? After all, buildings are responsible for around a sixth of all CO₂ emissions in Germany. So much remains to be done there if the federal government wants to become climate neutral by 2045. “For us this is a lighthouse project,” says Eon manager Nikolaus Meyer. “Wastewater heat is one of the most important future-oriented energy sources that can be used in a big city.”
In the specific case, the partners were lucky: the former department store is near an old clinker canal that collects rainwater and sewage from the settlement over a diameter of two meters and transports it away. Such water can have a temperature of up to 20 degrees – energy that has so far been released into the ground without being used. Instead, Eon and Signa built a heat exchanger underground. The 200 meter long stainless steel system guides cold water through the warmer channel during the heating season without the liquids mixing. In this way, the wastewater gives off a small part of the energy. An electricity-driven heat pump finally raises the temperature to the level that the heating systems in the renovated building need.
The solution in Berlin is far from being completely climate-friendly
However, it must be stated that the system is not yet completely climate-friendly in this case: Firstly, the heat pump does not draw its electricity from a solar system, but from a small, gas-powered block power plant. Second, the building also has a gas boiler for safety, so that the employees do not freeze even on particularly cold days.
According to information from Berliner Wasserbetriebe, only sewer systems that can stably transport at least 15 liters of water per second are suitable for heat exchangers. Corresponding potential is seen along a good 580 kilometers of canals in the capital. “We now have a dozen such wastewater heating projects in Berlin,” says project manager Alexander Schitkowsky. Eon assumes that nationwide up to 14 percent of the heat required could be obtained from wastewater.
The so-called heating transition definitely needs other solutions: for example, district heating networks that use energy from industrial processes or geothermal energy. As a large operator of regional networks, Eon also hopes that it will at least partially succeed in making existing gas pipelines “green”. This would of course require gas from renewable instead of fossil sources – or hydrogen, which would have to be obtained with a lot of green electricity. From the point of view of the Essen-based company, it doesn’t hurt to put a somewhat strange heat pump application in the shop window.