Thermal utilization of subway waste heat

Do you travel on the subway from time to time? Then you have probably been confronted with warm, stuffy air on the platforms and in the corridors. In the tunnels where subway trains run, there are constant temperature changes. A lot of heat is generated, especially during acceleration and braking phases. This is normally conducted outside via ventilation ducts and dissipates unused.

Scientists at L’Ecole Polytechnique Fédérale de Lausanne (EPFL) have come up with the idea of using the heat from subway tunnels to heat homes. To do this, plastic pipes have to be laid at regular intervals in the concrete walls of the tunnels. Heat pumps then ensure that a heat transfer fluid flows through these pipes, which absorbs the heat and then transports it into the buildings. On the newly planned M3 metro line in Lausanne, the researchers have calculated that it would be sufficient to equip 50 to 60 percent of the tunnel walls with such a heat exchanger system in order to supply around 1,500 apartments with an average size of 80 square meters with heat.

In addition, the city of Lausanne could avoid two million tons of CO₂ per year compared to gas heating systems. If it all works like this and the economics are right, the concept should have enormous potential, as there are many metro lines around the world.