In locations where horizontal ground loops cannot be considered, usually because of a lack of horizontal ground space, or the only available space is below concrete - a car park or parking space for example, vertical bore holes can be used but access for a drilling rig must be available and cost will be a major consideration because they are expensive! However, grants are usually available for captor insertion which can reduce these costs significantly.
Vertical bore holes are usually 20 cms in diameter and are spaced about 5 metres apart. The depth of a bore hole is calculated by taking account of ground composition and the size of the heat pump. In most cases depths of between 12 to 15 metres for each kilowatt of pump output is sufficient, so for a 12 kilowatt heat pump in a location where the ground is made up of hard rock 150 metres of bore hole would be sufficient. In normal circumstances the drilling contractor would achieve this depth by driling three 50 metre holes.