Heat generation from infrastructure projects and integration in decentralized low-temperature heating and cooling networks for plus-energy districts

The use of geothermal energy from civil engineering structures and tunnels ("tunnel geothermics") offers the possibility of using it for environmentally friendly heating and cooling in local areas (Adam et al., 2005). Due to its proximity to the city of Innsbruck, the Brenner Base Tunnel offers the optimal conditions to determine the effectiveness and application limits of tunnel thermal energy, to simulate its distribution in the city and thus to explore its technical and economic feasibility. In view of demographic change and the increasing demand for energy and heat, forwardlooking heat supply technologies such as geothermal energy are key functions. Especially in alpine areas, large railway tunnels structures are currently being built. Due to the large superpositions of these tunnels and the resulting prevailing temperatures, it is possible to extract the energy provided by the mountains at a temperature level above 20°C, which is higher than that of conventional geothermal plants, and to use it for heat supply. Depending on superposition and the associated temperature, it is often necessary to cool the tunnel drainage water with special equipment before it can be discharged into the corresponding receiving watercourses (Moormann et al. 2016). As this seems grotesque in times of climate change and the ever increasing demand for heat, this heat should be used and distributed in a sensible way. Since these large-scale infrastructure projects serve to improve the traffic and transit situation in the country, it is important to find opportunities and synergies between traffic engineering, tunnel construction and geothermal use. Up to now there are only potential assessments of geothermal use in shallow tunnels and on a small scale, therefore the Brenner Base Tunnel serves as a great opportunity to analyze and evaluate the longest railway tunnel in the world, which represents a major innovation in the field of climate-friendly energy supply. In order to enable an integrative system analysis, the integration of the heat into a possible plus-energy quarter of the city of Innsbruck is also being investigated. This is strongly dependent on the prevailing network and consumer structure as well as the distance between the consumers and the tunnel portal. In order to determine the highest possible efficiency of distribution, a wide variety of scenarios, based on the latest technologies and the existing energy infrastructure, must be calculated and evaluated. The overall objective of this exploration can therefore be defined as the integrative consideration of the geothermal potential of the Brenner Base Tunnel and the subsequent distribution of the heat produced from it to the end consumer. The aim is to evaluate how much heat (energy) is contained in such infrastructure and whether it is worth extracting and distributing it. By using this energy, provided by these already built buildings, its value increases many times over and thus contributes to a futureoriented, climate-friendly and CO2-free energy policy.