Long Term Influence of Multiple Heat Extraction Boreholes. Program 3-D FRACTure and comparison with a g-function calculated with the SBM program

Brenni, Renzo and Kohl, Thomas and Pahud, Daniel (2001) Long Term Influence of Multiple Heat Extraction Boreholes. Program 3-D FRACTure and comparison with a g-function calculated with the SBM program. Project Report. UNSPECIFIED.

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Abstract

For typical borehole heat exchangers (length of about 100m), the long term influence of neighbouring borehole heat exchangers normally appears after several years of operation, and approaches asymptotically a stationary state. Depending on the number of boreholes involved, it may take from several tens up to several hundred of years before the magnitude of the influ-ence stabilises. In these conditions it is difficult to collect measurements of thermally interact-ing borehole heat exchangers. However there is a need to be able to answer the question of the long term influence of neighbouring borehole heat exchangers, as this situation is supposed to occur more often in the future, as the number of ground coupled heat pump systems (GCHP system) steadily increases with time. This topic needs also to be studied if themes such as “neighbour rights” or sustainability related to GCHP system are discussed. This report is focused on the first phase of the project, whose objective is to check the g-function calculation with a more detailed programme. Three boreholes on a equilateral trian-gle is the borehole configuration chosen for the comparison between the two programs FRACTure and SBM. SBM is used in the g-function mode, in order to test the concept of g-function against the more detailed program FRACTure. The agreement between the results obtained with the two programs indicate that for typical boreholes of 100 meters deep the g-function analysis provides fast and sufficiently accurate results.

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