Concept, design, and testing of an innovative geothermal heat exchanger installed at the Brenner Base Tunnel

This master’s thesis was enabled thanks to the cooperation between BBT-SE, the project company appointed to design and build the Brenner Base Tunnel, and the University of Bologna. The thesis discusses the design and installation of an innovate geoexchanger that exploits geothermal energy through drainage water. Although the Brenner Base Tunnel has been the object of extensive research related to the geothermal resource, its indirect exploitation has never been investigated before by in-field tests on the Italian side of the BBT. For this purpose, the Smart Flowing prototype was proposed: it consists in a horizontal closed-loop system located into the central drain system formed by the invert elements of the lining. The major challenges faced during the prototype’s implementation were connected to the exploratory tunnel's specific geometry and the strict workflow of the Tunnel Boring Machine advance. In fact, the Smart Flowing layout was designed to adapt itself to the elements of the underground infrastructure and an efficient installation sequence was set up to avoid hindrances to the excavation activities. The prototype was subjected to field investigations together with a water circulation test, which provided the basis for the system’s boundary conditions. The modelling was addressed through an analytic formulation that aimed at quantifying the exploitable power in heating and cooling modes. Furthermore, a parametric analysis was developed to predict the heat output possible results based on the boundary conditions change. A testing and monitoring system was defined to simulate the Smart Flowing’s operation and evaluate the heat exchange performance. The positioning of the system was studied to find a suitable location that could comply with the exploratory tunnel's space requirements. Finally, the total costs of the materials and workforce needed to manufacture and install the prototype were compared to the costs of standard geothermal heat exchangers.