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Challenge / Goal

The main objective of this project in Cologne is to recover heat from sewage water and use it in decentralised local heating networks by supplying heat and domestic hot water (DHW) to local school buildings.


The Cologne case consists of three different operation sites; Wahn, Mülheim and Nippes. In all sites, sewage source heat pumps recover heat from sewage water. The main components of the system are: heat exchangers, water-to-water heat pumps, gas boilers and heat buffer tanks. One innovative part of the project is the heat exchanger, which is installed inside the sewage pipe. This indirect heat extraction technique is used in two of the sites (Wahn and Mülheim). In the third site, a direct heat extraction technique is used. This means, part of the sewage water is bypassed and pumped directly to the evaporator of the heat pumps.


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Time period

Planning time: 2 to 5 years


City of Köln (Coordination of Climate Protection)IVL Swedish Environmental Research Institute

Service providers

Rheinenergie AGStebUHRIG Straßen und Tiefbau GmbHTH-Köln

    Main benefits

  • Recycling waste

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