Geothermal hydronic pavement heating and cooling systems using tunnel geothermal energy

• First novel use of tunnel drainage water to operate a hydronic pavement. • First successful implementation of a direct passive concept for hydronic pavements. • Innovative method for passive heating without employing heat pumps. • The system melts snow in the winter and cools the surface in the summer. • Developed an autonomous control system using weather forecast for operation. The utilization of geothermal energy from tunnel drainage water presents a promising approach for sustainable heating solutions, particularly in the context of keeping roads and pavements clear of ice and snow. Tunnel structures, due to their large surface contact with both tunnel air and the surrounding soil, fundamentally possess significant thermal potential. This potential arises from the natural geothermal heat flux present in the earth as well as the heat generated within the tunnel by vehicular activities such as exhaust and braking energy. The two primary methods of utilising this thermal energy are the hydro-geothermal (open) system and absorber-heat pump (closed) system. A particularly interesting application of this geothermal potential is the direct passive geothermal surface heating through a Geothermal Hydronic Pavement system (HAP). This system utilises the tunnel water as the heat transfer medium without the need for heat pumps. The tunnel water flows through bifilarly arranged tubes installed beneath road surfaces. This system not only ensures ice and snow-free road surfaces during winter but can also prevent plastic deformations, such as rutting, during summer. A large-scale pilot project, termed the “Technical facility Füssen,” was implemented at the north portal of the “Grenztunnel Füssen”, a border tunnel connecting Germany with Austria. This project involved the development of nine test surfaces, each with different configurations of pipe materials, depths, and spacings. The results from this pilot project, combined with extensive numerical studies, underscore the viability and efficiency of using tunnel drainage water for passive geothermal heating of road surfaces.