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
- Promising Power Plant Plots Province’s Futureon October 1, 2020 at 11:41 am
It plans to double its generation from renewables, adding wind, solar, and geothermal capacity ... for the gas turbine generator, heat recovery system generator, and building mechanical ...
- Warmed Tunnel Air Provides Heating/Cooling Energyon September 29, 2020 at 5:00 pm
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 ...
- Zero Energy Buildings: When Do They Pay Off in a Hot and Humid Climate?on September 28, 2020 at 5:00 pm
Geothermal systems are often classified with renewable energy sources ... and hot water plant serving individual room fan-coil units. Adding air-to-air heat recovery by enthalpy to this design ...
- Geothermal system helps home achieve net-zero energy usageon September 21, 2020 at 5:00 pm
With the WaterFurnace geothermal system, the home is designed for heating ... According to Wahl, the house also features a graywater heat recovery system in which the heat from waste water (graywater) ...
- More than 300 contractors attend ClimateMaster’s GeoFarm Field Training, a geothermal system design and installation experienceon September 15, 2020 at 5:00 pm
Early in the design process it was apparent a geothermal system offered numerous advantages to the net zero objective by tying in with other clean energy technologies such as water heat recovery, ...
- Thermosensitive crystallization–boosted liquid thermocells for low-grade heat harvestingon September 12, 2020 at 8:29 am
A vast amount of low-grade heat (below 373 K) is distributed in industrial processes (waste heat), environment (solar-thermal and geothermal energy), and the ... 6 /K 4 Fe(CN) 6 system. (B) ...
- Heat Pump Water Heater Market worth $2.1 billion by 2026 - Exclusive Report by MarketsandMarkets™on September 10, 2020 at 4:41 am
10, 2020 /PRNewswire/ -- According to the new market research report "Heat Pump Water Heater Market by type (Air Source, Geothermal), Storage (Up to 500 L, 500–1000 L, Above 1000 L), Capacity ...
- How engineers help developers meet green building objectiveson September 3, 2020 at 5:01 pm
On the Building Team: GET Solutions (geothermal engineer), R ... Achieving that target meant integrating a water-to-water heat pump system, heat recovery, VAV air-handling units, daylight harvesting, ...
- SK 9 set for early 2018 clincker productionon August 21, 2020 at 5:00 pm
PPC senior projects manager Dipeen Dama explained that the SK 9 unit would incorporate the latest technologies and energy efficient systems ... increases the heat recovery of the kiln.
- Photovoltaic Power Teamon August 17, 2020 at 1:38 am
A large number of photovoltaic (PV) systems have been installed under the Feed-In Tariff ... New concept solar cell: “Heat recovery solar cell” Conventional solar cells discard more than half of solar ...
via Bing News