The construction of vertical geothermal boreholes is a common practice for the operation of geothermal systems. Drilling is an ideal solution in the case of small available installation sites.

A ground source heat pump borehole represents a closed loop system comprising a set of polyethylene pipes inserted vertically into the ground and circulating water to and from the geothermal heat pump. In most cases, the depth of drilling ranges from 80 to 100 meters.

The space between the pipes and the wall of the ground source heat pump is filled with a special grout mixture that usually contains a combination of bentonite, sand and clean water, which is fed into the drilling from the bottom up. Bentonite is preferable to other waterproofing materials, as it is waterproof and a good conductor of heat. Therefore, while retaining a significant amount of moisture, it rarely dries, which ensures proper heat transfer from the ground to the pipe and vice versa. At the same time, due to its low permeability properties, the liquid bentonite mortar provides a self-sealing barrier to groundwater intrusion.

The geothermal wells are 5-6 m and 6-7 m apart from the nearest building. Their depth depends on the characteristics of the property (size, insulation, heating capacity) that require heating. A house that needs about 10 kW of heating capacity, will probably need three wells 80-100 m deep.

In the areas where there is underground water supply, wells are pumped and water is returned. The return well is used to return water to the ground, as this returns heat to the heat pump exchanger. The pumping and return wells must be spaced far enough apart to avoid mixing the feed water and the return water. The return borehole must be at least the same size as the feed borehole to properly handle the water flow. If the feed water is mixed with the return water, then the feed water temperature may increase or decrease, depending on the season. This can seriously affect the performance of the heat pump. For the above reasons the drillings are usually at least 30-35 meters apart.

Construction of Geothermal Drilling

The smaller the system, the higher the cost per kW of output. For all types of ground heat pumps that use boreholes as the main heat source collector, installation costs are the most important part of the total cost.

This means that, for a complex of ten houses located on the same plot, the cost of the system per house will be about 20% lower than for a single house.