Drilling method can significantly determine the thermal performance of the borehole.
It is well known that site geology, the groundwater, its presence and movement, determine borehole performance and the transfer of ground heat into the collector loop. Less well known is that...
Drillers can use increased drilling speed, use drilling fluid forced pumping, get more borehole metres per day, reduce spoil removal costs (returns to the surface), reduce grout usage and, Offer cheaper quotations
Fast, forced drilling compacts the drilling shavings into the borehole walls, rather than expelling them to the surface, thus forming a sheath around the column of grout. This impervious layer obstructs the transfer of heat from the surrounding strata into the borehole. Particularly in geology condusive to plastic forming, commonly clay, mudstone and chalk (South England)
The downside is significant. Unless the borehole array designer has allowed for this effect by allowing for more borehole meterage, the boreholes will not provide the heat transfer predicted by the site geology.
Large industrial drilling projects, for array dimensions based upon TRT values from a well drilled pilot borehole, but then done for the cheapest quotes, can generate problems with relatively poor borehole array performance.
This is not theory. Thermal Response Testing measures and quantifies this. It can be reliably shown that the effect of forced drilling can reduce thermal borehole performance by up to 50%
A borehole quote 15% cheaper, results in boreholes 30%-50% less productive than drilled using best practice. This will damage the efficiency of the GSHP installation (reducing the COP), in the worst case lead to medium term deterioration and failure of the GSHP system performance.
Boreholes drilled by Synergy compared to others have been frequently TRT tested and consisitently demonstrated to fully utilise the thermal potential of the site geology