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Energy from the sewer – that only sounds strange at first glance. Under the "House of Statistics" at Berlin's Alexanderplatz, work is currently underway on a future heat supply. Over a length of 350 metres, Berliner Stadtwerke is laying so-called heat exchange surfaces directly in the sewer. Every time wastewater from households or industry rushes over the stainless steel plates, it can be used for several purposes at once.
Mathias Kersten, Berliner Stadtwerke:
"So, these silver plates are so-called heat exchanger modules. The wastewater flows over it and the water flows in the modules, which we then distribute in the neighborhood. And due to a temperature difference, it can absorb heat from the wastewater or also release it in summer when it cools down."
For example, the energy from the wastewater is to supply an area of around 110,000 square meters with the help of large-scale heat pumps. According to engineer Kersten, the use of wastewater is a real alternative to the better-known energy sources.
Mathias Kersten, Berliner Stadtwerke:
"So there are a wide variety of sources that can be used in the heat pump process. Most people are probably familiar with air as a heat source. Then there is near-surface geothermal energy. Then you could also use sea water or river water. Or, for example, how we are now using wastewater heat here in the project.«
In principle, a heat pump works just like a refrigerator, according to the expert. One medium is cooled, which in the case of the refrigerator is the air in the interior, and another medium is heated, which is then the air in the outdoor space.
Mathias Kersten, Berliner Stadtwerke:
"In our process, the medium that is cooled is indirectly the wastewater, and what is heated is the heating water, which then ultimately runs through the radiators in the building and heats the rooms."
So far, the energy from households, industry and the ground has been lost unused in the sewer system – wasted potential, says engineer Kersten.
The project is scheduled for completion in April 2024. Until then, construction will continue on Berlin's Otto-Braun-Straße to supply heat through wastewater.