What is a borehole? 

A borehole is a hole drilled in the earth around 20cm wide. They are used to hold vertical ground collectors which circulate thermal energy from the earth to a ground source heat pump to use it for heating or cooling a building. The depth of a borehole and the amount required will depend on the building and its heat requirement. On average most boreholes are around 100 metres deep and it will take around a day to drill to this depth.

In house drilling team

We have 3 bespoke drilling rigs and as part of our Partner Installer Network you can benefit from competitive prices and greater capacity enabling you to complete your projects quicker.

We can drill closed loop boreholes of depths up to 180m, with single or double loop installations.  We then install PE100 pipe, either 32mm to 40mm diameter. All loops are flow and pressure tested before being sealed with a geothermal grout. This ensures the correct thermal properties of the loop in the borehole, and avoids ground contamination of local water sources.

The grout we use is a Thermal Bentonite Grout combined as required with Silica Sands depending on the specification and geological requirements of the ground. This is mixed using our specialised grout mixer and pumped into the borehole to seal the complete borehole from bottom to ground level.

We can also drill open loop boreholes with sizes and depths being drilled to suit the geothermal requirements of the project.

Typical drilling methods we can use include air, air/mist, water and drilling muds. We can also offer simultaneous drilling & casing methods for poor ground conditions with the final borehole finished to a maximum of 150m. Borehole sizes vary from 115mm upwards. This is complemented with our ancillary equipment as required for the complete installation of the works.

Vertical Borehole Drilling - What to expect

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Vertical borehole drilling is the process of drilling boreholes or water wells in order to extract heat energy from the earth. Boreholes are mainly used as part of a system for a ground source heat pump which is sustainable low carbon heating and hot water solution.

Drilling boreholes is quite a process and if you're considering a ground source heat pump it's important for you to be aware of the associated works and disruption it can cause. You can see a video of one of our drilling rigs in action here.

Preparation

Before drilling any boreholes it is recommended that you check to see if planning consent is required from your local planning authority. In the majority of cases planning consent will already exist under the permitted development provision of the Town and Country planning act but local restrictions may apply if, for example, the site is in a Conservation Area, Site of Special Scientific Interest (SSSI) or a National Park.

The start of drilling

When the drilling team arrive they will be in one or two crew vehicles with the drilling rig on a transporter together with a large compressor and various smaller items of equipment including a trailer, fuel bowser and grouting machine, these all require space.The drilling rig runs on rubber tracks but weighs 8 tons so it will create some marks and ruts on soft surfaces such as grass – especially in wet conditions. The compressor is the size of a 4 x 4m and weighs 3.5 tons. All need to be parked as close to the drilling rig as possible.

During drilling

As the drill works into the ground it passes through the soil and soft materials at the top into the rock below, to stop the borehole sides from collapsing, we insert metal casing into the hole down as far as required, as we don’t know the depth of rock until we start drilling and the amount of soft materials at the top so we allow 15m (50ft) of metal casing as standard in our price, generally this is enough to cover the cost of casing, if metal casing is still required below this depth it will be added as an additional charge as detailed on your estimate or proposal.

Water

Experience shows that we will almost always hit water whilst drilling, 100m is a long way down! The amount of water involved can be considerable and as the water includes soil and spoil from the borehole it must be treated as foul rather than clean water. Ideally we try to channel or discharge the water to an area of ground where it can safely soak away, we do have pumps and we will make every effort to control the water, however where this is not possible we will try to divert the flow to a foul drain (sewer) or in extreme cases arrange for it to be contained and transported from site. Where additional permissions or costs are incurred for water disposal these will be charged as extra to our original estimate or proposal. Discharge to a foul sewer requires a discharge licence from the environment agency, not normally a problem as long as we take steps to reduce the solids in the discharge before we put it down the sewer.

Spoil and Sand

In addition to water, the drilling will produce a mix of broken rock and soil from the borehole – generally about 1.5 tonnes of waste per 100m of depth. Unless otherwise stated, disposal of this spoil is the responsibility of the customer. In practice there will be more excess material when the trenching is completed and the hole prepared for the manifold chamber, any excess can be removed at the end of the project by the groundworks contractor or stored on site.

When drilling is completed, geothermal loops / probes are inserted down the boreholes. In order to ensure they absorb as much energy from the ground as possible, the spaces around the loops are then filled by pumping a mixture of sand and bentonite (grout) down the borehole to fill any air gaps between the probes and the borehole.

The sand required for the filling is delivered in 1 tonne bags and any sand left over after grouting the boreholes is left on site for the customer to either dispose of or any surplus sand can be used to bed the pipes connecting the boreholes to the manifold and heat pump as well as protect the pipes from damage by sharp rocks etc after backfill.

After Drilling

Once the boreholes are completed, the geothermal loops inserted and the boreholes grouted, the pipework will be left protruding above ground level. This is just a temporary measure. Your ground worker will need to excavate a 1 - 1.2m deep by 1m wide hole around each borehole for us to cut off the outer metal casing below ground and fusion weld our pipes to the geothermal loops.  These pipes will be laid in trenches provided by your ground worker to the manifold position, once we have welded and tested the pipework, the trenches can be backfilled leaving no evidence of the boreholes above ground.

The manifold connects all the pipes from the boreholes to one point and then onwards to the heat pump, via the header pipework. The manifold as standard has a plastic manhole cover, we recommend the manifold is situated in a soft landscape area where it can be disguised with pots of flowers, shrubs or under garden furniture etc.

Unless otherwise agreed, your ground worker is responsible for all digging, backfill and backfill materials, we will lay the pipes in suitable trenches lined with sand if required for protection. We will supply a drawing and specification of the trench work requirements.  We need two access points to the plant room, 500mm apart and sweeping bends to enable us to get the header pipework into the plant room. Your builder is responsible for providing the access points and for the remedial works afterwards. 

If you have any questions please don’t hesitate to contact us.