Celsius: Heat from waste water

In large cities like Cologne, the supply of heat accounts for more than two thirds of the stationary energy consumption. In order to make this more sustainable, the consistent use of low CO2 heat sources is essential. This includes the residual heat stored in waste water. In Cologne and in four other European cities, the EU's "Celsius"project examines which processes for heat recovery from waste water lead to the best possible results. One of the three Cologne systems appears to be particularly efficient.

In comparison with the gas heating previously used, the use of heat from waste water leads to a reduction in CO2 emissions of 35 to 45 per cent. The waste water plants are usually equipped with drain heat exchangers. Here, the water is pumped through the space inside the double wall heat exchanger, that is heated by the waste water and the heat is then sent to a heating system circuit. Direct evaporator systems are even more efficient. Here, the heat is transported directly to the refrigerant via water heat pumps. Thus, the interim medium between the channel and the water pump can be omitted, whereby heat losses are reduced.

Engine for progress:

  • the largest direct evaporator plant in Germany
  • increase in efficiency of 15 per cent
  • research on more efficient heat utilisation from waste water
  • international cooperation promotes exchange
  • a blueprint and quick check list support urban planning

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Photo: RheinEnergie AG

In the Nippes District of Cologne, three schools are supplied with eco-friendly heat by means of heat recovery from a nearby wastewater plant and a heat pump station.

All Good Things Come in Threes

At the Cologne site, three plants have been installed at three schools in the four year period. Each plant is combined with a natural gas condensing boiler to cover peak load. Two of the systems are equipped with classic drain heat exchangers, the third system follows the principle of the direct evaporator. Since the waste water in this system is pumped directly to the cellar of the school and therefore does not require an intermediate medium, the efficiency is increased by up to 15 per cent. The direct evaporator plant installed in Cologne-Nippes with an output of 400 kW is by far the largest of its kind in Germany and the only one in NRW, providing heat for 4,000 school pupils. Research into the efficient use of waste water in metropolitan areas contributes to providing a climate-friendly and reliable heat supply in large cities and ensures the international exchange of experience.

Photo: RheinEnergie AG

""Love Your City" is not just a slogan for Cologne, but rather real proof of identity. In this sense, RheinEnergie AG’s declared objective is to also test unconventional, new ways of ensuring an energy-efficient and environmentally-friendly energy supply for Cologne."

Dipl.-Ing. Heinz Menda, Head of Commercial and Industrial Customers Engineering and Technical Project Leader for "Celsius"

Partners and sponsors

  • RheinEnergie AG
  • Stadt Köln
  • Fachhochschule Köln
  • Stadtentwässerungsbetriebe Köln
  • EU-Förderung