Underground heat transfer: Utilizing subway systems to warm nearby apartments - Underground heat transmission: Utilizing subway systems for residential warmth
Unleashing Subway Heat's Hidden Potential: From A to B and Beyond
Subway trains glide through tunnels, whisking passengers from one destination to another, all while packing quite a punch - a punch of heat. Typically, this heat wafts away through vents. But researchers from the University of Stuttgart have unearthed a different use for it. Their trial ran in the Stuttgart city railway tunnel for line U6 at the Fasanenhof stop.
Christian Moormann, from the Institute of Geotechnology, spearheaded the project. His crew installed temperature sensors and plastic pipes within the tunnel walls — absorber systems akin to those employed in floor heating systems. The water inside these pipes absorbs ambient temperatures, and a heat pump elevates the water temperature further.
Paris already puts this concept into practice. Heat from a metro tunnel warms a building housing 20 apartments, covering about a third of its heating needs, on average. This revelation made headlines in the "Tagesspiegel."
Experts agree that the heat-harvesting approach could be fruitful in large urban areas. Sebastian Blömer, from the Institute for Energy and Environmental Research Heidelberg (Ifeu), points out, "The heat demand per unit area is astronomical." Finding heat sources for a climate-neutral heat supply is no small feat.
Roughly 10 degrees Celsius in subway stations
The subway tunnel's local waste heat plays a significant part in this scenario. This waste heat byproduct stems from technical machines or processes, such as ground heat and heat from train friction when they decelerate or accelerate. According to environmental researcher Bloomer, the temperature in the train tunnels usually holds steady at about 10 degrees Celsius, even in winter.
In 2023, ifue researchers and their partners from the Institute for Ecological Economy Research in Berlin calculated that the Berlin subway network generates around 460 gigawatt hours of waste heat annually. This equates to 4% of the city's overall district heating requirements. Bloomers team concluded that it was more waste heat than that generated by industrial or data center operations in Berlin.
Leveraging London's example
London provides a useful blueprint for harnessing waste heat from subway tunnels. At a disused station, waste heat from the subway tunnel fuels a local heat network since 2020, supplying around 1,300 households with heating and hot water.
Austria and Switzerland offer further examples of waste heat recovery from subway tunnels. The Stuttgart project from 2010 to 2015, alas, was discontinued, says Moormann. However, the project revealed that using waste heat was technically feasible and involved minimal effort.
Electricity costs, but it's friendly to the planet
The drawback? Operating costs are high, cites Bloomfield. Heat pumps require electricity, and its relatively expensive compared to natural gas. The long-term operational costs can soar.
From an environmental perspective, the technology has merit. It can utilize shallow geothermal energy, and the environmental impact is negligible.
Strategic placements for future tunnels
The heat can be sourced using large fans that draw in warm tunnel air and transfer heat to water via a heat exchanger. Locating substations closer to the heat source, like stations in metropolitan areas, can optimize energy distribution.
As subway systems expand, it's vital to consider extending these installations to new lines as well. "No more tunnels without integrated absorbers," says Moormann.
Potential benefits for Stuttgart's zoo
The technology demonstrates promise outside of mainline stations, too. For instance, the Rosenstein tunnel of the federal road 10 in Stuttgart was activated geothermally during construction, aiming to heat the future elephant facility in Stuttgart Zoo.
Moormann surmises, "we are far enough along that we can plan this as a standard solution and have reliability."
Enrichment Data:
Using subway train waste heat for district heating can prove both efficient and eco-friendly, particularly in large cities boasting extensive underground rail networks. This ingenious plan capitalizes on the heat created by subway trains, lighting, and HVAC systems, which would otherwise be squandered, supplying warmth to structures. Below, we evaluate this concept's potential in Germany.
Effectiveness and Affordability
- Waste Heat Recovery: Subway systems generate significant quantities of waste heat from trains' braking systems, lighting, and heating, ventilation, and air conditioning (HVAC) systems. This heat can be captured and put to good use, lessening reliance on non-renewable energy sources for district heating.
- Environmental Impact: Eliminating waste heat from urban infrastructure helps cities reduce carbon emissions and promote cleaner environments.
- Cost Efficiency: While initial investment costs might be substantial, the ongoing operational expenditures tend to be lower than traditional heating methods. By reducing emissions and promoting sustainability, districts can save money in the long term.
German Projects and Plans
Though specific major projects in Germany employing subway waste heat for district heating aren't extensively documented, there is growing interest in tapping waste heat from various urban sources.
- A Wider Focus: Germany has a strong focus on district heating, with over half of residential buildings relying on this warming method. The country's largest district heating network is in Berlin, underscoring the country's commitment to sustainable energy practices.
- Subway Heat Application: Although not extensively highlighted, the principle of using waste heat from urban infrastructure aligns with Germany's broader efforts to boost energy efficiency and minimize carbon emissions. Integrating subway waste heat into existing district heating systems is a viable possibility within this broader strategy.
- Regulatory Framework: Germany's legal framework supports combined heat and power plants (CHP) but lacks specific regulations for district heating. However, EU directives and national policies encourage sustainable energy practices, paving the way for innovative waste heat implementation.
To summarize, while only a few innovative projects in Germany focus on using subway waste heat for district heating, the concept aligns with wider efforts to boost energy efficiency and reduce emissions. As cities continue to seek novel ways to save money and reduce carbon footprints, integrating subway waste heat into district heating systems may become a compelling option in the future.
- The researchers found that the temperature in the subway tunnels typically stays around 10 degrees Celsius, even in winter, providing a consistent source of waste heat.
- As Moormann suggests, integrating absorber systems into new subway lines could significantly reduce the need for traditional heating methods, making the city's district heating requirements more reliant on waste heat.
- The waste heat from subway tunnels, as demonstrated in the Stuttgart project, can be used to heat structures outside of mainline stations, such as the future elephant facility in Stuttgart Zoo, showcasing the versatility of this eco-friendly heating solution.
