22 Dec 2017
by ReUseHeat Project

Sewage water demonstrators in Cologne, Germany

Three demonstrators in Cologne in the areas Mülheim, Nippes and Wahn, aim to utilize heat recovery from waste water. Heat is used to warm schools in a decentralized local heating network. More than 84 % of the EU population is connected to a sewage network and it is assumed, that 5 % of the total heat demand in cities and towns could be covered with heat recovered from sewage systems.


The three demonstrators are a part of the EU-funded CELSIUS-project, a platform of networking and knowledge-sharing regarding barriers to district heating and cooling solutions. All sites utilize sewage pipelines as source for heat recovery through heat pumps. The overall system at the three demonstrators is composed of heat exchangers, water-to-water heat pumps, additional gas boilers for peak-loads and heat buffer tanks to increase heat production flexibility. At the two sites Mülheim and Wahn, the heat exchanger is installed inside the sewage pipe, making the heat exchange technique unique. At Nippes, the heat extraction is directly with sewage water, meaning that a part of the sewage water is withdrawn from the pipeline and pumped directly into the evaporator of the heat pumps.

The CELSIUS project found, that sewage temperatures of at least 12°C are necessary to ensure economic feasibility. If low district heating supply temperatures are sufficient, high COP-factors can be obtained. There is accordingly a need of a relatively high heat demand above 150 kW to pay off the investment costs, and the sewage solution is most applicable in new construction or major refurbishment of buildings with a substantial heat demand. Further, there should be a short distance between the sewerage piping system and the building and the sewage pipeline should have an adequate size and flow.

In general, the CELSIUS demonstrators have showed, that the technical dimensioning must be optimal if the sewage heat recovery is to be economically durable. Further, the heat customer must be convinced, that a sustainable solution is better than the alternative, which in Europe often is natural gas boilers.


Facts about this case

Annual thermal energy provided: 1109 MWh (Wahn) and 762 MWh (Mülheim)
Heat source: Excess heat from sewage water (at least 12 °C)
Energy efficiency: 116 % in Wahn and 128 % in Mülheim
Annual greenhouse gas savings: 214 tonCO2e in Wahn and 150 tonCO2e in Mülheim
Period: From 2012 to 2016
Support: FP7-supported CELSIUS-project
Link to web page: http://celsiuscity.eu/
Contact information: CELSIUS project: Rhein Energie, Fachhochschule Köln, D’Appolonia




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