The residential area Köln-Stammheim is located in the north of Cologne. The local housing association GAG Immobilien AG owns 1700 apartments and 100 houses there. From 2005 to 2007 GAG modernized 633 apartments and 87 houses. The required heat for this buildings is about 10 GWh p.a.. Located a kilometer away from the residential area is one of the largest sewage treatment plants in Germany, Großklärwerk Stammheim.
In 2010 the municipal water company (Stadtentwässerungsbetriebe StEB), GAG Immobilien AG and RheinEnergie AG started a joint project to use the digister gas and supply the residential area in Stammheim with heat. For this purpose, StEB invested about 11.5 million € in an existing CHP to improve the electrical efficiency and the use of the heat. RheinEnergie AG built a peak- and backup-boiler to compensate for seasonal variations in the digester gas and a one kilometer connecting pipe from the sewage plant to the residential area. For allocation to the houses RheinEnergie bought and refurbished the existing, five-kilometer pipeline network in Stammheim. All in all RheinEnergie invested 4.7 million €. On average, the required heat is supplied about 80 % from sewage gas. The rest is generated by natural gas. The new, innovative concept lead to a saving of 4,100 tonnes of CO2 per year and a cost reduction for the residents by 17 %.