In Berlin, the first buildings use energy from wastewater in sewers for heating. It’s a small answer to the big question of how climate-neutral homes should be warm in the future.
When employees of online retailer Zalando populate their new headquarters in Berlin in the fall and winter, unusual technology will heat the offices: energy company Eon and property developer Signa have now commissioned a system, which is the old Kaufhof Building near the Ostbahnhof to provide much of the heat from the sewage system.
The cooperation with Berliner Wasserbetriebe aims to provide a small answer to the big question of the future: how will houses be warm in the future without burning natural gas or oil on a large scale? After all, buildings are responsible for around one sixth of all CO₂ emissions in Germany. So much remains to be done there if the federal government is to become climate neutral by 2045. “For us, this is a flagship project,” says Eon director Nikolaus Meyer. “Wastewater heat is one of the most important future energy sources that can be used in a large city. “
In this specific case, the partners were lucky: the old department store is located near an old clinker channel which collects rainwater and wastewater from the city over a diameter of two meters and evacuates them. Such water can have a temperature of up to 20 degrees – energy that has so far been released into the soil without being used. Instead, Eon and Signa built an underground heat exchanger. The 200-meter-long stainless steel system guides cold water through the warmer runner during the heating season without the liquids mixing. In this way, the wastewater releases a small part of the energy. Finally, an electric heat pump raises the temperature to the level that the heating systems of the renovated building need.
The solution in Berlin is far from being totally green
However, it must be said that the system is not yet fully climate-friendly in this case: Firstly, the heat pump does not get its electricity from a solar system, but from a small block power plant running on gas. . Secondly, the building also has a gas boiler for safety, so that employees do not freeze even on particularly cold days.
According to information from Berliner Wasserbetriebe, only sewage systems capable of stably transporting at least 15 liters of water per second are suitable for heat exchangers. A corresponding potential is visible along 580 kilometers of canals in the capital. “We now have a dozen wastewater heating projects in Berlin,” explains project manager Alexander Schitkowsky. It is assumed that nationally up to 14% of the required heat could be obtained from wastewater.
The so-called heating transition certainly 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 to be at least partially successful in making existing pipelines “green”. This would of course require gas from renewable sources instead of fossil sources – or hydrogen, which would have to be obtained with a lot of green electricity. From the perspective of the Essen-based group, it doesn’t hurt to put a little weird heat pump app in the store window.