Researchers at EPFL have precisely quantified convection heat transfer in rail tunnels. Using the new model, they estimated how much energy Lausanne could save by fitting the future M3 metro line with a geothermal heat-recovery system, in what would be a world first.
Heat transfer happens in various ways in rail tunnels. For instance, when trains brake or accelerate, they produce heat that warms the surrounding air. That hot air mixes with other air in the tunnel and with heat radiating from the ground.
Until now, engineers have been unable to accurately calculate the amount of heat that tunnel air contains. Researchers at EPFL’s Soil Mechanics Laboratory (LMS) have overcome that problem by precisely estimating the convection heat transfer coefficient. Their findings have been published in Applied Thermal Engineering.
This breakthrough paves the way for innovative applications involving so-called energy tunnels that can supply energy to built environments. The team also tested its model on Lausanne’s future M3 metro line which, once complete, will carry passengers between the city’s train station and the Blécherette district to the north.
Enough heat for 1,500 apartments
“Our research shows that fitting the heat-recovery system along 50–60% of the planned route – or 60,000 square meters of tunnel surface area – would cover the heating needs of 1,500 standard 80m2 apartments, or as many as 4,000 Minergie-certified energy-efficient units,” explains Margaux Peltier, a scientific assistant at the LMS, whose Master’s research forms the basis of the article. The system also allows heat to be stored so it can be supplied to homes when needed. “Switching from gas-fired heating would cut the city’s CO2 emissions by two million tons per year,” adds Peltier. Her calculation does not include the savings gleaned from metro stations or at the planned rolling-stock depot in the north of the city, which could also benefit from the system.
As the temperature naturally stabilizes in underground tunnels, excess heat or cold is evacuated to the surface. The resulting warm airflow can often be felt at metro tunnel entrances. The idea behind the innovation is to harness this surplus warmth in addition to heat naturally present in the ground.
The system works in a similar way to a refrigerator, with plastic pipes containing heat-transfer fluid, or simply water, placed at regular intervals inside the concrete tunnel walls and connected to a heat pump. In winter, cold water will be pumped into the pipes, emerging hot at the surface. The opposite will happen in summer. According to the researchers, the system would be cheap and energy-efficient to install and would have a lifespan of between 50 and 100 years, with only the heat pumps having to be replaced every 25 years.
Heating and air-conditioning
Once equipped, heat from the tunnel would cover up to 80% of the heating needs of local apartments throughout winter, with the shortfall preferably coming from other renewable sources. But what makes geothermal systems like these unique is that they work in summer too. “The tunnel would act like a highly reliable, year-round heating and air-conditioning system,” says Peltier, adding that it would make a real difference to keeping Lausanne’s homes cool during hot weather. The system could even chill the ice rink set to be built in the city’s new Métamorphose eco-district.
“This article underscores the fact that energy-tunnel technology is mature and could be deployed at district-wide scale,” explains LMS head Lyesse Laloui. “It remains to be seen whether Swiss companies are now prepared to take the lead. Globally, we’ve only seen systems like these used on test sections so far.” The researchers have presented their findings to Lausanne’s utility agency (SIL), local public transport operator (TL), the Canton of Vaud, the prime contractor working on the new metro line, and the City of Lausanne.
Learn more: Engineering heat out of metro tunnels
The Latest on: Geothermal heat-recovery system
via Google News
The Latest on: Geothermal heat-recovery system
- Notre Dame to cease burning coal a year ahead of scheduleon October 14, 2019 at 12:50 pm
The renewable projects include the university’s hydroelectric plant on the east bank of the St. Joseph River, a new thermal energy East Plant, three solar arrays and a new south campus geothermal ...
- Geothermal energy – a heating source for France utilising geoexchange, deep geothermal and heat recoveryon October 7, 2019 at 6:50 am
e.g. through geo-exchange system, deep geothermal heating in Paris and a planned project in Bordeaux, and through heat recovery of the subway/ metro in Rennes. A recent article in L’Usine Nouvelle in ...
- Warmed Tunnel Air Provides Heating/Cooling Energyon July 3, 2019 at 4:01 am
Researchers at EPFL have calculated the benefits of a geothermal heat recovery system, using fluid-filled plastic pipes, for train tunnels. (Image source: LMS / 2019 EPFL) Turning waste energy into ...
- Turning train tunnels into giant "fridges" could heat thousands of homeson June 26, 2019 at 12:30 am
Now, researchers at EPFL have crunched the numbers on heat transfer in the air of train tunnels, and outlined a geothermal heat recovery system that could potentially supply heating and cooling to ...
- PwrCor Collaborates with SMU Geothermal Laboratories to Pursue an Unexploited Geothermal Applicationon June 12, 2019 at 5:50 am
Geothermal production facilities typically return ... and has successfully executed more than $200 Million in revenue, 150 Advanced Heat Recovery power generation systems sold, totaling over 150 MW’s ...
- New East Plant builds on commitment to sustainabilityon January 24, 2018 at 11:55 am
With a capacity of 1,350 tons, the East Plant’s five geothermal heat recovery chillers will provide both heating and cooling. The chilled water they produce will be a source for the campus ...
- New geothermal system will heat and cool historic St. Patrick’s Cathedralon March 14, 2017 at 2:49 pm
Those wells distribute heat to a Dedicated Heat Recovery Chiller, which then sends it out to the 76,000 square feet of cathedral for heating or cooling. Unlike most geothermal systems, St. Patrick’s ...
- Geothermal: Digging Deep for Efficient Energyon October 24, 2016 at 5:00 pm
heat recovery from ventilation exhaust air and aluminum sheathing. While the 15-story, 215,000-square-foot office building stands today, the geothermal system was decommissioned in 1992. The building ...
- Geothermal System Nears Fourth Decade of Performanceon February 8, 2015 at 4:00 pm
I saw a lot of potential for heat recovery and transfer with a geothermal system,” McDermott said. “At the end of the day, it’s actually a very simple concept.” Whether he takes credit for his ...
- Green Heat Recovery System Eliminates Heating Bills At Commerce Township Wastewater Treatment Planton September 2, 2014 at 5:00 pm
A new heat recovery system developed by Giffels Webster is expected ... and reduces its reliance on commercial energy providers. In 2013, the Commerce Township wastewater treatment plant received the ...
via Bing News