ground collectors

Borehole Drilling

Boreholes are a good option for heat pumps, particularly when space is limited. We have access to some very compact drilling equipment so access is rarely a problem.

Our very experienced team consider the heat loss of the property and geology of the ground to specify the meters of boreholes required. If there is any doubt of ground type, we undertake a thermogeological survey to confirm the right specification for your project, so you can be confident that the proposed heat pump is the right one for your home.

Depending on the ground type boreholes often extract between 35 – 50 Watts per meter making this a very efficient and an ultimately cost-effective option.

The Cornish Expertise

Our boreholes are drilled by very experienced local drillers who know Cornwall and the ground beneath very well. Once the borehole is drilled, polyurethane pipe is lowered into it with a U-bend at the bottom.  When the pipe is in place the borehole can be back filled with Bentonite which can improve the thermal conductivity. In some cases, the soil extracted from a borehole may have very good thermal conductivity and can be reused instead of Bentonite, this decision would need to be carefully considered.

The Drilling Process

Step 1: Design
It is crucial at the design stage to:

• Ensure correct spacing between boreholes
• Determine the run hours of the heat pump or otherwise known FLEQ hours
• Ensure active collectors – if the pipework is too close at any point, the collectors become inactive and therefore redundant.
• Ensure a good depth borehole to manifold
• Consider waterproof insulation from the manifold back to the plant roots

Step 2: Borehole drilling, installation of collector/pipework and back-filling

Step 3: Trench work to the subterranean manifold chamber

Step 4: Fusion welding and installation of pipework

Step 5: Trench work from the manifold to the plant room

Step 6: Pipework from the manifold to the plant room

Step 7: Fill pipework with water and anti-freeze solution

Horizontal Ground Arrays aka Trenches

A horizontal ground array is an alternative worth considering if you have some land.  As specialist drilling equipment is not required, a horizontal ground array often costs less than a borehole.

You do need for much more space for trenches because the extraction rate is a lot less. It’s around 20 Watts Per Metre for trenches where as boreholes are 40-50.

Things to note when considering trenches as your preferred collector:

• Width and depth of trench – for health and safety reasons the majority of trenches are kept to 1-1.5m to prevent collapsing during works.
• Position of subterranean manifold – The wrong positioning can cause constant after install problems with trapped air.
• Length of pipework run
• Pipe protection by sand once in place to prevent stones from the back-fill damaging the pipework.
• Disposal of soil from trench work.

The Digging Process

Step 1:Trench work in a series of straight trenches linked to subterranean manifold.
Step 2: Pipework/collectors to manifold, fusion welding and back-filling.
Step 3: Trench work from the manifold to the plant room.
Step 4: Flow and return pipework from the manifold to the plant room.