The design, installation, and testing of an innovative geothermal heat exchanger, tailored for tunnels excavated by Tunnel Boring Machines, will be presented. The prototype was developed by the joint efforts of BBT SE, involved in the construction of a new railway base tunnel system connecting Italy and Austria, and the University of Bologna, engaged in applied research over various aspects of the BBT system. The geothermal heat exchanger consists in a modular horizontal closed-loop system located in the exploratory tunnel of the BBT system, specifically in the space dedicated to collect the drained water at the lining invert. Due to the type of the heat exchange process, working with the drainage water, and for its compact design and simple installation procedure, the prototype was called “Smart Flowing”. Modules were built outside and later moved inside the tunnel, and eventually placed and assembled concurrently to the advancement of the Tunnel Boring Machine. Specific tests were performed to prove the reliability and the efficiency of the system, by simulating the work of a heat pump conditioning system in both heating and cooling modes. Finally, a preliminary assessment of the economic and environmental potential of this innovative prototype was carried out. First results showed the performance of the system for both heat dissipation and extraction. The drainage water flow guarantees a continuous recovery to the natural state, thus improving efficiency compared to classic geothermal heat exchangers. Economic savings and reduction of pollutants and greenhouse gases, as compared to burning fossil fuels, can reach up to 70%
