(Drilling engineer from drilling company)
Following the initial site survey I was able to contact the British Geological Survey and obtain the geological data for the site. This data allowed the exact depth and number of bore holes to be calculated, ensuring long term reliability of the heat pump.
With the information we got from the survey and the site data we acquired from the first visit, I calculated the required depth for the ground loop collector. In this case, two 90 metre deep boreholes were needed to provide enough energy for the heat pump.
After we set up the drilling equipment, a safety fence was erected to protect neighbours and passer-bys from potential harm caused from inadvertently entering the work area.
During the drilling I continuously checked the wash out from the borehole to ensure that the soil in the ground conformed to the material which was used as basis for the calculations. Unexpected conditions in the ground could result in the fact that the energy taken from the ground would be lower than anticipated and the heat pump would not operate as efficiently as intended. The system used for drilling recycles the wash and separates the soil removed during the drilling process. The soil is collected in a suitable container for easy removal at the end of the project.
After the drilling was completed, my team and I lowered the ground loop collector into the borehole. Due to the risk that the pipes forming the ground loop collector were damaged during the transport or installation, I pressurised the system to check for leaks.
Once the pipework had been inserted into the hole, it was re-filled with a special concrete mixture. This mixture has a high thermal conductivity and will help the ground loop collector take energy from the ground.
What we learnt: During the drilling process different, unexpected things can happen. The Geological Survey gives a basic understanding of the ground conditions. It is essential to monitor the ground material during the entire drilling process to ensure it matches, or betters, that expected from the survey. Drilling heads can block or get damaged by stones and boreholes can collapse. Experienced drillers know their equipment and how to handle the problems they encounter. As the unexpected can and does often happen, two days per borehole should be planned.
