Overview
The 2020 objective of Switzerland for CO2 emissions is to decrease the emissions by 20% in comparison with 1990. In order to reach that goal, renewable energies must be improved or developed. Geothermal energy has a specific place among the available renewable energies, in the sense that it is independent on wind, weather conditions or solar radiations. It is always available.
The purpose of the research project is to demonstrate if the heat and/or cold production from Swiss tunnels is viable. In order to do so, the feasibility and economical aspects of different heat exchange systems, like anchors, heat exchangers integrated in the tunnel wall or pre-integrated in concrete pieces will be evaluated.
Investigations will be done for typical profiles of road tunnels. Urban road tunnels or local bypass can be suitable for heat production, as heat and cold consumers are located in the direct neighbourhood, above the tunnel or at the portal.
If a substantial energy potential of such structures can be demonstrated, it is suggested to include generally investigations in geothermal energy utilisation in projects for new or existing tunnels. In a next step, a test is planed and industrial partners will be asked for financial support.
The project has the following objectives - to:
- Investigate possible heat/cold exchangers for tunnels
- Determine the best possible heat exchanger system for different tunnels (section type, field temperature, tunnels situation), paying special attention to the Swiss tunnel conditions.
- Evaluate economic viability of heat from the ground thanks to urban tunnels.
- Test the logistic suitability of such systems and plan test installations for the determination of thermal efficiency of such systems.
- Identificate appropriate and interested industrial partners.
After a baseline study and the test of the prior art, a systematic analysis of absorber systems that can be used in urban tunnels will occur. These systems will be evaluated and assessed using a questionnaire. For the best systems of typical tunnel cross-sections a pilot plant are planned.
The research project is limited to inner-city tunnel (cleared roads tunnel) and tunnel of bypass routes. These tunnels are particularly suitable for the use of geothermal energy, because customers are available for the heat in the immediate vicinity portal or at a short distance above the tunnel. The typical streets tunnel, safety lug and other underground infrastructure tunnels cross sections are collated.
Choice of absorber elements
Based on the typical cross-sections different absorber elements are evaluated. This possible installation types and locations are investigated and listed in a first step.
Geothermal questions:
- If the system is thermally sustainably, that is, flows enough heat even after 10 years still to withdraw enough heat?
- What is the maximum energy yield and the requirements that they be limited (no effect on durability of the tunnel)?
- How affect seasonal variations the energy gain?
- How and how well the rock temperature at the absorber element is transferable?
- What properties must the customer structure in order to actually use the tunnel warmth as possible without losses?
Constructive questions:
- How has an absorber element look?
- Where can it be integrated into the tunnel?
- Where can the ports and utilities lines are housed?
- How can the maintenance and repair done?
Construction methodological questions:
- How should the installation and configuration take place so that there is no extension of time?
- How can the system be designed so that it is the construction conditions in tunneling justice?
- How can existing tunnels to be retrofitted?
- As the connecting cables and hydraulics are controlled and from where?
- How can the installation, maintenance and operation of the geothermal system take place as smoothly as possible for the very purpose of the tunnel?
Economic questions:
- Is the use of geothermal energy from tunneling politically desired and will they support?
- Can a financial security are
Funding
Results
This research represents a theoretical basis for a pilot plant (planning of the practice test is in this project included), and the subsequent use in practice.
Urban tunnels are as yet hardly equipped as geothermal heat exchanger; the development is still in its infancy. This is certainly the fact that the planning of such systems at an early stage. To date, planning offices have hardly used this potential. Geothermal planners learn usually too late of tunnel projects, which could be interesting for energy production. In this project, an early co-operation was funded through the collaboration of tunnel designers and geothermal experts.