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A. Oberhauser, R. Markiewicz, D. Adam:
"Development of geothermal absorber elements for tunneling applications";
Vortrag: Geotechnika - 2006 - Geotechnics, Strbské Pleso, Slovenská Republika; 20.09.2006 - 22.09.2006; in: "Geotechnika 2006 - Constructions, Technologies, Materials and Monitoring", (2006), ISBN: 80-248-1124-3.

The usage of foundation piles for geothermal heating and cooling of buildings is already well-known in the field of geotechnical engineering. The application of geothermal energy systems to railway infrastructure, however, is a relatively new method to enclose renewable energy sources. Railway infrastructure e.g. tunnels consist of a large concrete surface, which are in direct contact to the surrounding soil or rock material. By implementing absorber elements into the concrete, thermal energy can be extracted from or conducted into the surrounding medium. The heat can be used for nearby buildings or factories. In summertime it is possible to cool these buildings with the same system. Surface heat is transferred to the ground and the building is climatized. By these means, large tunnelling projects could be used as geothermal "plants" to produce thermal energy for nearby villages or residential areas.

The implementation of absorber elements into geotextiles for tunnelling led to the invention of the "Energy Textile®". Synergy effects can be used by extracting thermal energy from an element, which is anyway necessary for the construction. A pilot plant for the Energy Textile already exists in a railway tunnel in Vienna.

A research project at the department of railway engineering, transport economics and ropeways in cooperation with the department of soil mechanics and geotechnical engineering and the Atlas Copco MAI deals with the development of structural elements for tunnelling and rock engineering, which can also be used as heat absorbers. Therefore numerical calculations are necessary, in order to examine the proper geometry for an optimal performance of the system. The transferred energy was simulated in 2D as well as in 3D by the means of the software tool FEMLAB® (COMSOL, 2004). This happened by multiphysics coupling of the flow of the absorber medium with the heat transfer by convection and conduction.
Furthermore a FEMLAB- subsytem was included into a Simulink® model. The connection of both programs allows the simulation of the whole plant during the year and to monitor the energy performance. The calculation of cost reduction by the usage of geothermal heat is an important contribution for a "geothermal design tool" for plant development. By considering the specific boundary conditions for every customer, the optimal layout for the system can be designed. Therefore it is possible to calculate amortization periods for the plant and to find an optimal solution for both operator and customer.