The subway tunnels are full of trains, electricity and people crammed into little space like sardines and launched at high speed. In theory, all the heat produced by these elements can be a large source of energy.
Today, researchers from the Lausanne Polytechnic University (EPDFL) have estimated the amount of heat that passes through the metro tunnels and have designed a geothermal heat recovery system that could provide energy to heat (or cool) thousands of nearby homes.
The underground air that passes through the tunnels of the subways has many origins. It comes up from the ground. It comes out of accelerating and braking trains. It is given off by electronic devices such as lights and signals. It also comes from the heat of the bodies of the many passengers. This is a lot of potential energy.
Calculating the average amount of heat in these areas is rather difficult, but researchers from the Lausanne Polytechnic have developed a model that derives a precise energy coefficient. The formula can be used to create systems that collect this energy and bring it to the surface for residential use.
The concept behind this technology is similar to that of a giant fridge. Plastic pipes are integrated into the walls of the tunnels and filled with a thermally conductive fluid (even if water would be enough). By pumping liquid at room temperature and taking out the heated liquid from the underground activity, the game is done.
The team declares that the system for obtaining energy from subways is efficient and economical to install, with a duration of over a century. Obviously, heat pumps would be the most delicate part of the system, and should be replaced approximately every 25 years.
Practical examples: the Lausanne Metro
To better understand the project to obtain energy from the metro, the EPDFL team showed the data applied to the metro in the city where it is based, Lausanne in Switzerland.
"By setting up the energy recovery system in 60% of the underground network or 60 square kilometers of tunnel surface, we could meet the needs of 1500 apartments of 80 square meters. In case of energy efficient apartments up to 4000 homes. Inserting this system would cut CO2 emissions of over two million tons per year ".
It is not the first attempt to derive energy from the meter. A few years ago Transport for London also tested a regenerative braking for the London Tube trains which would return energy to the electricity grid.
In short, energy only needs to be captured. It is everywhere around us. And under.
The research was published in the journal Applied Thermal Engineering.