In order to answer the central questions regarding performance and practicability of absorber systems in tunnels as well as regarding the aptitude of the applied planning tools, a pilot project entailing horizontal absorbers is planned. The energetic modelling which the test is based upon is verified by means of measurement results. With the test set-up, the real extraction performance is measured and the environmental conditions are monitored by way of measurement techniques. Besides the influence that geothermal factors have on heat output (e.g. thermal resistance of the backfill material and the absorber pipes, insulation by waterproofing etc.), constructional details (e.g. fixation of the absorber pipes upon the waterproofing membrane) shall be examined, as well.
The experimental layout envisages the establishment of three test areas at a mutual distance of at least 4 m, which shall be observed over a one-year period. Test areas 1 and 2 are going to be equipped with double-shell lining and a waterproofing membrane, while the absorber pipes will be placed in front of this membrane in one case and behind it in the other. The test areas 1 and 2 correspond to the lining of a new tunnel and are efficient for various purposes (heating and cooling). Test area 3 will be adopted to the results of test area 1 and 2 and
be assigned to the layout of existing tunnels (refurbishment, maintenance).
Based on the measurement results, the simulation techniques are gauged and the relevant parameters and characteristics (e.g. resistance coefficient) are defined so that solid planning criteria are available for future use. Furthermore, indications for constructional realisation and operational integration of the absorber systems are given.
