A small cul-de-sac in Shropshire consisting of 16 bungalows has had Ground Source Heat Pumps installed throughout. The brief called for the bungalows to have 2 bore holes a piece in a quiet cul-de-sac in Shropshire. There had to be minimal disruption to the residents.
Multiple installations were needed to be run from single drill chambers. This involved a complex drill plan incorporating 32 bores needed to be designed, making sure not to hit any existing utility lines In order to save space on the small estate, one drill chamber serves two properties simultaneously.
The main challenge with this project for the contractors, Eco Friendly Installations, was the positioning of the bores. A complex drill plan of 32 bores was designed, due to the boundary restrictions it was imperative that the bores were placed in the right areas and at the right angles to ensure enough metres were in the ground. The specialist contractors design and install ground source heat pumps by drilling radial bore (GRD) holes up to 50 m in length at a casing diameter off 110 mm and a rod diameter of 92 mm.
Typically they drill 3 bore holes giving 150 m of underground pipe work, this can increase or decrease depending on the property. Gareth Davies, Production Manager at Eco Friendly Installations said "We have drilled in many challenging locations and ground conditions over the past few years, our toughest challenge was this housing association project drilling 19 homes each having 2 bore holes and a community center for Shropshire Housing under there "Affordable warmth Scheme".
"It was challenging due to the ground conditions and the geographical location. It was on an ancient glacial river bed, which meant that, as we were drilling, the ground was so unstable it kept collapsing so we had to case the entire bore - something we don"t often do as its slower and its more expensive to back fill with Heidleburg thermal grout."
This project started in February and was completed in July requiring 3 drillers, 2 heat pump installers, 1 electrician and 3 grounds men. The logistics were more demanding than normal. Access was difficult so the contractors had to use back roads and farm tracks, this was possible by good communications and traffic management. So far, the outputs (Ground Return Temp) have been as expected but is calculated on a yearly basis "Every job we take on is individually planned and designed as no project is the same, once we are drilling, we inspect drill samples every meter to determine that what is below our feet, so the system will work as efficiently as designed. If there is a change in the geology, we may have to adjust our drill plan to drill more or less meters”.
The drilling work is done with a Tracto Technik Geodrill 4R drill rig supplied by TT-UK, a machine recognized for its compact dimensions and power. This is mounted to a central drill chamber (depth = 1.2 metres, diameter = 1.0 metre). The drilling chamber is prepositioned and remains in the ground providing a clean environment for maintenance needs. The rotary ring connects the drill rig to the drill chamber so that the system can be rotated 360°. The angle of inclination is also adjustable, with a range between 35 to 65 degrees. Number, layout and position of the heat pipes are planned in advance.
To make sure that the heat pipes work properly, a pressure test is conducted. While the grout hoses are removed heat conductive thermal grouts secure the heat pipes from bottom to top in the borehole. This also prevents their thermal "short-circuits". A skilled and well trained drilling team is able to install heat pipes up to a length of 100 m per day depending on ground conditions.