Task: Drilling

We are now near the end of the second week on site at Ashfield Court. The drilling is in full swing and there are now three boreholes drilled with the fourth expected to be completed by the end of the day. Two of the holes are 151m deep and the other two are 142m deep. Each hole will provide heat to a pair of flats – one on the ground floor and one on the first floor.

As commonly occurs when drilling boreholes, the first hole took the longest. Kensa always carry out a detailed desktop geological study of the site to inform the borehole design and also to inform the drillers of the expected ground conditions. However, it is only when you actually start drilling that you know the exact ground conditions you are facing. While drilling the first hole, it became clear that the first 50 metres or so were relatively unstable. These first 50 metres are primarily made up of sands, gravels and clays and the hole was collapsing after drilling, thus preventing the pipework from being installed in the borehole. The drillers are therefore installing temporary casing for the first 50 metres to prevent the hole collapsing, a common practice in such ground conditions.

After 50 metres the geology is chalk, which is relatively easy to drill through, with three metres being drilled roughly every minute!

Once the hole is drilled to depth, the pipework is installed in the borehole. Once installed, the casing is removed.

There are three pipes sticking out the end of each finished hole. Two of them are the pipes that will actually be filled with water and glycol to transfer heat from the ground to the flats. The third is used to grout the holes from the bottom up. The drillers use a specialist bentonite mixture which ensures good contact between the pipes and the surrounding earth. This means there is good heat transfer from the ground to the flats.

Despite the temporary loss of their car parking spaces and the increased activity on site, all the residents remain happy and excited about the project. In fact, one tenant commented:

The borehole drillers are the most professional contractors we’ve ever had on site. They work hard all day and are doing a great job!

The drilling of all twelve holes is still on schedule to be completed within the next two weeks.

Next week’s key project stage: Headering & trenching.

This will take the borehole pipework to the boundary of the flats in preparation for the plumbers attending site to take the pipework into each flat.

Keep following our blog to stay up to date with this brilliant first project between Kensa Heat Pumps and Hanover Housing Association.


Project in brief:

  • 22 flats – 21 are 1 bedroom and 1 is a 2 bedroom flat;
  • Built in 1977;
  • Heated by electric night storage heaters which have reached the end of their useful life and need replacing;
  • Residents aged 55 +;
  • A Kensa Shoebox ground source heat pump (6kW) to be installed inside each flat;
  • New 150 litre unvented hot water cylinders in each flat;
  • New radiators in each flat;
  • New heating controls in each flat, which will be much easier for the residents to use;
  • A ground source heat pump for the site office;
  • 12 boreholes will be drilled with depths up to 154 metres to form a communal ‘micro district ground source heat pump system’.

Read more about the background to this first project between Hanover Housing Association and Kensa Heat Pumps here.

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