Underground rail networks and heat transfer
When discussing Underground rail networks and heat transfer, one immediately thinks of the re-use of heat generated in underground tunnels and transferred to the heating systems of neighbouring buildings: a procedure focused on sustainability, with the capability of reducing electricity consumption as well as harmful emissions.
This process has already been exploited in countries such as Switzerland, France, Russia and Austria and is now starting in Italy, thanks to the Enertun project. Turin is the first Italian city to embrace this technology and the experimental project involves the development of a geothermal Underground system, connecting the tunnels on Line 1 (stations between Porta Nuova and Lingotto).
In order to put this idea into practice, engineers Alice Di Donna and Marco Barla carried out the thermal activation of the tunnel linings in order to make use of the thermal inertia below ground. The aim was to transform the reinforced concrete into an exchanger, containing tubes of heat transfer fluid, able to remove or inject heat for distribution to surrounding buildings via pumps.
Considering that on average, every ten metres of Underground network produces 14.4 degrees Celsius of heat, the tunnel lining consists of seven prefabricated hedging stones for each ring. During the winter heat transfer takes place between the two surfaces, generating heat for nearby homes. During summer however, the process is inverted, because the temperature below ground is lower than that at the surface.
According to recent estimates, it appears that the project will reach a capacity of 53 W/m2 in winter and 74 W/m2 in summer. These are the ideal quantities to meet a thermal requirement of approximately 2822 kw for heating and 3756 kW for cooling. Of course, one cannot compare this to the performance of traditional heat exchangers, but the results are satisfactory nonetheless.
As for costs, the experts emphasise that that the equipment implemented is very cost-effective: its cost is in fact equivalent to less than 1% of the cost of the entire structure. It remains to be seen if the example of Turin will be followed by other Italian cities.
Bringing together the Underground rail network and heat transfer is certainly an idea capable of drastically reducing harmful emissions. The hope is that with the passing of time, more and more projects of this kind may come to fruition in Italy, but also in the rest of the world.
Translated by Joanne Beckwith
