A new office complex developed out of the famous Galeria Kaufhof department store in Berlin is giving new meaning to the phrase ‘waste not, want not’ via a 200-metre-long heat exchanger install in the sewer next to the Koppenstraße building.

The 600kW project, being orchestrated by utility E.On along with partner real estate firm Signa and Berliner Wasserbetriebe, will see the 50,000m2 office supplied with heat and cold water from the waste-waters flowing past in the 100-year-old cloaca.

“This way, we cover around 50% of the heating and cooling needs of the building in a sustainable way and save around 400 tons of CO2. This energy plant in the middle of Berlin is a prime example of the efficient use of local energy sources,” says Nikolaus Meyer, head of solution development at E.ON.

Reiner Müller, head of project development at Signa, added that the project, which will involve outfitting the existing architectural structure with state-of-the-art heating and cooling technology, was part of its wider ambition to “make a contribution to combating climate change and consistently plan our projects with regard to their environmental sustainability”.

According to figures supplied by the project partners, almost 1,220TWh is used in the heating sector in Germany, but only 15% is currently powered by renewable sources.

Energy generated from wastewater – which has a year-round constant temperature of up to 20°C but loses that energy to the surrounding soil – “could mathematically cover 14% of the heat demand in the building sector and be used equally for cooling”, said E.On

“Wastewater heat is a component of the energy transition of the Berlin heating sector. The innovative potential-atlas of the water companies shows that 586km of the sewer and wastewater pressure networks in Berlin are suitable for using this technology,” says Alexander Schitkowsky, project manager of Berliner Wasserbetriebe.

The sewer energy system is based around a stainless-steel heat exchanger that extract existing heat from passing wastewater, after which a large heat pump increases the temperature of the heat generated and channels in into the building. In the summer, the principle is reversed, and the channel can be used as an efficient source of cooling.