Sustainable energy from the depths: Optimization strategies for hydrothermal tunnel water systems

In principle, a distinction can be made in tunnel geothermal energy in closed and open hydrothermal systems. Closed systems use absorbers operating in a closed circuit for heat exchange, while open systems use the energy inherent in the drainage water directly. Closed systems are constantly evolving, whereas the performance of open hydro-thermal systems is dictated by the amount of discharge and the temperature. In this context methods have been investigated to optimize power output. On the one hand by separating cold tunnel water inflows, and on the other hand by installing absorbers in combination with open systems. Using sample data, it was shown that such measures can increase the thermal output by up to 0.5 MW. Although the system effectiveness decreases slightly over time, a significant increase in output was observed in the long term compared to systems without absorbers. The results show that the thermal performance of open hydrothermal tunnel systems can be increased at a later stage. This allows existing tunnels to be used for sustainable applications, thus contributing to a more environmentally friendly energy industry.