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Researchers develop train tunnel fridge system to heat homes



As anyone who’s sweltered through a London Underground commute on a summer’s day is well aware, subway tunnels create a lot of heat.

(Image via EPFL)

This has also been noted by researchers from Swiss University: École polytechnique fédérale de Lausanne (EPFL), who claim that underground rail systems can be used to potentially supply heating and cooling to thousands of homes.

The team have developed a model that allows them to precisely calculate the convection heat transfer coefficient of tunnel environments - taking into account the heat generating from trains braking and accelerating, electronics, body warmth from passengers and other atmospheric factors.

They say that this formula could be used to develop a geothermal heat recovery system, that would operate like a similar way to a fridge. 

It involves building plastic pipes into the tunnel walls, which are then filled with a cold fluid that will absorb heat from the tunnel as it’s pumped through. The now hot fluid will then emerge at the surface, where the pipes can be connected to homes to provide heat. 

The system would also work in reverse during the summer - with homes transferring heat to the fluid which then disperses it into the ground. 

The team applied their proposed model to a currently in-development metro line in the city of Lausanne, to demonstrate the potential benefits.

"Our research shows that fitting the heat-recovery system along 50 to 60 percent of the planned route – or 60,000 sq m (645,000 sq ft) of tunnel surface area – would cover the heating needs of 1,500 standard 80 m2 (860 sq ft) apartments, or as many as 4,000 Minergie-certified energy-efficient units," says Margaux Peltier, lead researcher on the study. 

"Switching from gas-fired heating would cut the city's CO2 emissions by two million tons per year."

The team claim that the system would be relatively cheap and energy-efficient to install, and would have an expected lifespan of up to a century - though they anticipate the heat pumps would need replacing every 25 years.

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Researchers develop train tunnel fridge system to heat homes - Time to read 2 min
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