| Title | How Renewable Are Borehole Heat Exchanger Systems? |
|---|---|
| Authors | Walter J. Eugster & Ladislaus Rybach |
| Year | 1999 |
| Conference | European Geothermal Conference |
| Keywords | Shallow geothermal resources, long term performance, sustainability, numerical modelling |
| Abstract | Extensive measurement campaigns have been performed at a commercially delivered BHE/HP installation in Elgg near Zurich. Object of the campaigns is a single, coaxial, 105 m long BHE, in use since its installation in a single family house. The BHE supplies a peak thermal power of about 70 W per m length. The measurement results were used to calibrate a 2D numerical code. Ground temperatures over the frst five years of measurement were fitted to within one or two tenths of a degree Celsius. Additionally the formation temperature was predicted for several further years using assumed load profiles.The immediate surroundings of the BHE cools down in the first years and does not fully recover during the system lifetime. The long-term performance stabilizes afterwards, albeit at a somewhat lower but constant level. Thus sustainable production can be achieved on the long term. Heat extraction over decades causes heat depletiodtemperature decrease in a certain volume of the ground. After termination of BHE operation thermal recovery beings. Different simulation runs have been performed with different operation durations. The results show that the duration of ground thermal recovery for the analyzed simple case (single BHE) roughly equals the duration of heat extracting operation (e.g. for 30 years of BHE operation: ground recovery in about 30 years). |