Cold and warm at 11 degrees Celsius
Tunnel thermics from Vienna underground tunnels
What miners have always known and energy engineers are now exploiting in Vienna is the constant temperature that occurs in tunnels. The difference in air temperature in tunnels and at the ground level is used for heating in winter and cooling in summer by means of heat exchangers. For the first time in Viennese tunnel construction, tunnel components with integrated energy diaphragm walls and energy base slabs have been installed below ground. The new underground tunnel of the U2 line now provides the tunnel itself as well as neighbouring residential buildings with environmentally friendly heating and cooling.
Inside a mountain there is the same climate at a constant temperature of approx. 11 degrees Celsius throughout the year. In winter it is warmer in the tunnel and in summer it is cooler than at ground level. Wiener Linien, the Vienna Public Transport Authority, make use of this fact to equip their underground tunnels with a tunnel thermics system. Heat exchangers, which are called geothermal energy absorbers, enable the difference in temperature to be used for cooling in summer and heating in winter.
In tunnel construction, the installation of geothermal energy absorbers is frequently problematic because the heat exchange probes need to be fitted into the tunnel wall
in difficult conditions. In Vienna, a newly developed system was employed. The probes were placed in the diaphragm walls and base slabs before the concrete and transport heat out of the ground -- as well as back into the ground. A challenge encountered with this system is the necessity to quickly install the concrete elements in difficult construction conditions without damaging the sensitive components. In Vienna, bored piles normally used for stabilisation were enhanced and installed for use as energy piles on an experimental basis. A sloping rock face in the Viennese "Lainzer Tunnel" was studded with a number of energy piles, injected deep into the earth rather like needles.
In the construction of the new U2 line extension, Wiener Linien have for the first time implemented geothermal energy exploitation on a large scale and installed heat exchangers in the tunnel wall. Four new stations on the U2 line have been provided with heat exchanger absorber equipment. They heat the underground stations in winter and air-condition them in summer.
In 2008, the "ESYS - energy system for tunnel thermics" project was awarded the Austrian national prize for transport, "Focus 2008: efficiency for climate protection", by the Federal Ministry of Transport, Innovation and Technology. The pilot system within the Austrian Federal Railways' (ÖBB) tunnel connecting the Westbahn and Südbahn, western and southern railway trunk lines, and the Donauländebahn, the Danube bank railway, (Lainzer Tunnel) has been heating the Hadersdorf secondary sport school in the 14th district of Vienna since 2004. The low CO2 emission generation of heat and cold in underground tunnels not only improves the ecological balance of Wiener Linien, but has at the same time given rise to a new business sector. Tunnel thermics helps to protect the environment and save energy.
Facts & Figures
- Saving of approx. 51mt CO2 for a system serving 10 detached houses
- Saving of (direct + upstream) CO2 emissions of 340kg per metre of traffic tunnel
- TU Wien, Institut für Geotechnik (Vienna University of Technology, Institute of Geotechnical Engineering)
- TU Wien, Institut für Verkehrswissenschaften (Vienna University of Technology, Institute of Transportation)
- Geotechnik-Adam ZT
- Atlas Copco MAI GmbH
DI Rainer Müller
Tel. +43 1 4000 84267
Fax +43 1 4000 7997