| Autor: |
Liebel, H. T., Huber, K., Frengstad, B. S., Ramstad, R. Kalskin, Brattli, B. |
| Předmět: |
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| Zdroj: |
Proceedings of the Renewable Energy Conference; Jun2010, p145-154, 10p |
| Abstrakt: |
Borehole heat exchanger (closed-loop) systems coupled to a ground-source heat pump are applied for space heating and cooling using the ground as energy source or storage medium. For accurate dimensioning of a ground-source heat installation, knowledge of the thermal conductivity of the subsurface is vital. Thermal response tests (TRT) are widely used to measure the in situ thermal conductivity in a well. Alternatively, the thermal conductivity in a borehole is approximated from rock core samples based on lab measurements. Rock core data and thermal conductivity maps are financially more attractive for planning purposes than expensive TRTs. The value of both approaches was statistically tested using data from the geologically diverse Oslo region (Norway). Effective thermal conductivity data measured via TRTs show a clear trend towards higher thermal conductivity values in comparison to lab measured thermal conductivity values from rock cores (in 82 % of cases). The deviation from the rock core samples, however, varies strongly as several geological layers may be represented in one single well. Furthermore, the thermal conductivity of the rock core samples varies strongly within individual geological units. The comparison of both techniques of thermal conductivity measurement shows that the in situ thermal conductivity at a location cannot be predicted from rock core data of a geological unit. The results of this study indicate that the dimensioning of a large ground-source heat project cannot be based on rock core measurements or thermal conductivity maps only, without analysing the in situ thermo-, hydro- and geological conditions in fractured rocks. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Supplemental Index |
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