102 residential units in a total of 11 buildings have been heated in sewage water in Bavarian Straubing since October 2010. Two heat pumps from OCHSNER Wärmepumpen GmbH remove the energy from the sewage from the sewer and thus feed two low-temperature local heating networks, which supply these 102 residential units with heating energy and hot water.
The sewage is removed from the main collector by means of a removal structure and fed to the two wastewater heat exchangers via a pressure line. When the water is removed, the waste water is sieved in order to separate the solids. The two heat exchangers of Huber SE are specifically designed for energy generation from waste water. They have an automatic cleaning device which removes the resulting deposits on the heat exchanger tubes at periodic intervals so that the transmission power (in this case 100 kW) is maintained.
After the energy is extracted, the wastewater flows back to the main collector in a newly constructed sewage collector.
Overall the plant achieves an annual utilization rate of approx. 4.0. This means that a quarter of the energy from electricity is supplied, three quarters of the heating energy comes from the wastewater, so that the already used primary energy is reused for the warming up of the water. The current required for the heat pump drive is also obtained in the sewage treatment plant, it is produced from sewage gas generated in the sewers. Thus, this type of heating system saves about 80% to 90% of primary energy and carbon dioxide emissions compared to a conventional plant.
Through the thermal renovation of the 11 buildings, the specific heat requirement could be reduced accordingly. The heating system can thus also be operated at low flow temperatures, as a result of which the efficiency of the heat pumps is correspondingly increased.