Status: 05.02.2023 3:33 p.m
Gas and oil have become expensive and bad for the climate. The EU only wants to classify wood as a sustainable fuel to a limited extent. An alternative with great potential: heat from waste water.
An excavation pit in northern Bavaria: new apartments are being built on the site of the former Lagarde barracks in Bamberg. Construction cranes stand between multi-storey new buildings, and pipes laid in pits are still open. What currently looks like a dirty construction site will later be an extremely clean energy supply.
In the future, heating and hot water for around 1,400 apartments are to be supplied largely with renewable energies. With heat that is obtained directly on site – including from the sewer.
Combine different systems
An ambitious project funded by the federal government. But also a big challenge, says Stefan Loskarn from Stadtwerke Bamberg: “Here in Lagarde, as in many other urban areas, we have very narrow and dense buildings. This means that there is less space for renewable energies.” Therefore, different systems would have to be combined with each other to cover the total demand.
One source that provides the heat here is the ground. Large areas of ground collectors are already under the new buildings, which absorb heat from the ground. There are also so-called geothermal probes, which absorb the temperature in deeper layers in a brine mixture. Depending on the season, this warms or cools apartments and commercial buildings with the help of heat pumps.
Use heat from the environment
From the point of view of Volker Stockinger, professor of mechanical engineering and supply engineering at the Technical University in Nuremberg, we should use more heat from the environment in the future: from the air, the ground and even from our waste water. There must be no high temperatures in the ground or in the waste water. The thermal energy is sufficient to be compressed with the help of modern heat pumps so that rooms can be heated and water can be heated for bathrooms, showers and kitchens.
This type of technology is now used as standard in modern single-family homes, but it is still new territory on a large scale, for example for blocks of flats with many apartments. According to Stockinger’s vision, even entire districts could be supplied with such renewable and almost free heat sources.
Up to 30 percent of the heating energy
In the construction project in Bamberg, there is another heating source: heat from waste water. It is still rarely used in Germany. Heated bath, shower and toilet water flows everywhere through our channels. So-called heat exchange mats have already been laid under the street in the underground sewage system. They absorb the heat from the waste water over a distance of 250 meters and feed it into the local heating network.
This should provide at least 50 percent of the thermal energy required for the apartments. Loskarn is surprised that more municipalities are not already using this potential: “The use of waste water heat has the potential to cover around 30 percent of the total energy requirement for living.”
Big potential
The project manager of the Bamberger Stadtwerke assumes that the potential of the technologies used in the Lagarde campus can be increased over the next few years and can also be used for existing buildings. Professor Stockinger’s research group at the Technical University of Nuremberg is evaluating exactly how well the interaction between waste water and ground heat works on the Lagarde site. According to Stockinger, this is important so that even more municipalities soon have the courage to completely rethink the energy use of building areas.