energy
Warmth from the tunnel – how subways can heat apartments
U-railways can bring people from A to B. But you can do more: heat apartments. Some European cities do that. Is that also possible in Germany?
Every minute rush through the tunnels in the country – and with them a lot of warmth. Normally, this heat is lost through ventilation shafts. A few years ago, researchers from the University of Stuttgart examined that it can also be used. Test object: The Stuttgart Stadtbahn tunnel for the U6 line at the Fasanenhof stop.
Christian Moormann from the Institute of Geotechnic was responsible for the pilot project at the time. In the tunnel walls, they laid temperature sensors and plastic pipes. “These are absorber systems as we basically know them,” says Moormann. The water in these absorber lines absorbs the ambient temperature, a heat pump further increases the water temperature.
Paris metro heated 20 apartments
This is how it works in Paris. The heat from a metro tunnel lands in a house with 20 apartments using a heat pump. According to the state railway company Ratp and the housing company Paris Habitat, around a third of the heating requirement of the building are covered on average. The “Tagesspiegel” had already reported on this.
According to experts, what works in Paris also has potential in this country – especially in large cities: “The warning question is incredibly high in terms of area,” says Sebastian Blömer from the Institute for Energy and Environmental Research Heidelberg (IFEU). Finding heat sources for the possible climate -neutral heat supply is not easy.
At least ten degrees in subway stations
According to Blömer, local waste heat comes into play here – the warmth that arises in technical machines or in processes as a by -product. Together with the Institute for Ecological Economic Research in Berlin, he and his team calculated in 2023 how much waste heat is generated in the Berlin subway network.
Conclusion: In the entire subway network, around 460 gigawatt hours are waste heat per year – this corresponds to four percent of the city’s district heating requirement. According to the study, this is more waste heat than is created in the industry (340 gigawatt hours) or at data centers (120 gigawatt hours) in Berlin.
The reason for this is the geothermal energy, says the environmental researcher. As a result, the temperature in the rail tunnels does not fall below about ten degrees even in winter. Added to this is due to the friction when braking and accelerating the trains.
Moormann: “Technically feasible”
The heat can also be obtained via large fans, says Blömer. These can vacuum the warm tunnel air and transfer the heat to water via a heat exchanger. For example, it runs at a disused train station in London: According to the city, the waste heat from the subway tunnel has been fed into a local heating network since 2020. Around 1,300 households are thus supplied with heating air and hot water.
There are also examples in Austria and Switzerland. The Stuttgart pilot project between 2010 and 2015, on the other hand, was closed after the end, which was already agreed at the beginning, says Moormann. The measurements have confirmed that the use of the heat energy is technically feasible and associated with relatively little effort.
High electricity costs, but environmentally friendly
However, the operating costs of such technology are high, says Blömer. Because heat pumps need electricity, and it is currently relatively expensive compared to gas. “You don’t just have to take money into your hand, but if you operate these systems for many years or decades, then there is a lot of things together in electricity costs,” says the IFEU researcher.
From an ecological point of view, the technology has advantages, says Andreas Bertram from the Federal Environment Agency, because: The on -surface geothermal energy can be used in tunnels already built. The environmental effects with additional use of the tunnels as a source of heat should therefore be neglected.
Also a plus: train tunnels run in the inner city, says Moormann. So the energy is already where it is needed. In order for rail tunnels to act as a heat source in the future, the installation of absorber lines must be considered when building the tunnels. This is hardly possible afterwards. However, new rail tunnels are rarely built, says Bertram.
Tunnel heat for Stuttgart elephants
According to the researchers, the technology can also work in sewers or street tunnels. According to Moormann, this is already a reality in Stuttgart: the Rosenstein tunnel of federal road 10 was activated in the Geothermisch during construction. It is to heat the future elephant plant in the Stuttgart Zoo, which is to be built in the coming years.
Moormann considers the technology to be mature for local heat supply: “I would say that we are so far that we can plan it as a control solution and also have reliability,” says the head of the institute. It is important to think about the geothermal use from the start, for example with new street tunnels. “No tunnel anymore without integrated absorber,” he says.
dpa
Source: Stern
