Geohydrological and geophysical investigation
Depth-temperature profiles
Measuring temperatures in or around a heatexchanger borehole can reveal information on the specific conductivity of strata. This can be actual thermal conductivity or a groundwater effect. In combination with borehole records or geophysical profiling of a borehole an estimate of the contribution or groundwater effects can be made.
Groundwater effects
The presence, quality and movement of groundwater can have a significant effect on the long term thermal behaviour of a BHE installation.
Dry boreholes, allthough rare, do occur and ensuring long term conductivity between the loop, the borehole filling and the parent material is essential for the operating temperatures and efficiency of the installation.
Most boreholes are to well below the groundwater table or intercept strata that are water bearing (aquifers). Especially where aquifers are a groundwater resource or where strata with different groundwater quality (potable, salt, contaminated) are crossed within the borehole, environmental consideration dictates design.
Groundwater movement whether vertical (seepage, artesian) or lateral (Darcian, fracture flow) can have a very significant effect on long term operational BHE temperatures and therefore on the design and robustness of the BHE.
Especially for larger BHE systems where strata with groundwater movement are anticipated, such aquifers with a groundwater gradient or tidal influence, it is worthwhile to conduct at GRT (Geothermal Response Test) that will quantify flow and to make an inventory of available data from local observation wells.