When installing vertical closed system are there additional requirements the
contractor must adhere to regarding the boreholes and grouting. Typically it takes 1-3 holes per dwelling to
provide the geothermal energy required and the depths of boreholes are dependent on the geology of the
locality. Typically, the boreholes are spaced several meters apart, but this distance also varies depending on
the geological conditions of the site. Once the boreholes are drilled and the geothermal loops are placed in
the hole, the hole must be injected with grout, thus surrounding the loops.
The grout enhances the conduction of heat into the fluid within the
loops. In years gone by, the main purpose of grout was to
protect the ground water from surface run-off above, interaquifer flow, or antifreeze leakage. At this time
there was little consideration given to the grout’s thermal properties. In fact, standard grout used in the
water well industry acts like an insulating blanket around the pipes in the bore hole, requiring the
installation of more bores. Standard grout can have as little as one-half to one-quarter of the ability of
the surrounding soil to transfer heat.
Newer grout mixtures improve the ability of the grout to exchange heat with the
surrounding ground. Thermally enhanced grout, developed for use in geothermal systems, can double or nearly
triple the ability to exchange heat with the ground by controlling the sand particle size used in the grout
formulation. The thermally enhanced bentonite grouts that have been developed have thermal conductivities of
0.85 to 1.4 BTU/ hr ft °F, while retaining low hydraulic conductivity (<10-7 cm/sec), (based on technical
data from manufacturers). To boost the thermal conductivity of grouts, manufacturers mix silica sand and
bentonite, and at times other materials such as cement and superplasticizer. Additionally, the grout protects
the loops from elements and adds stability to the borehole. Generally drilling and installation of vertical
loops takes about two days.