Why not use the heat that is already being generated to help reduce costs? It's a surprise more of this is not done around the world, but of course, they already do in Norway and Sweden. The Guardian:
Warmth generated by sweaty passengers as they commute on the Paris Mètro may be used to heat a block of low-income flats located near the Pompidou Centre in the city centre. This could slash the building's energy bill and carbon footprint by a third, according to the property's owner.
The temperature in nearby Rambuteau Mètro station stays at a toasty 14-20C degrees all year round thanks to the heat generated by passengers, trains and other machinery. Paris Habitat-OPH, the owners of the building, plan to use the underground heat to warm up water as it courses through pipes. It will then be pumped to the surface into an underfloor heating system in the block of flats.
"It's a huge source of free, zero-carbon heat so it couldn't make more sense," said Dr Patrick James, a researcher at the University of Southampton's School of Civil Engineering and the Environment. "I guess the only problem will be if there's a train strike in the winter, in which case they'll need a back-up source of heat."
