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Boreholes vs Trenches

There are two ways to lay ground collector pipe in order to collect heat from the ground:

Horizontally

The pipe is laid down in trenches at least 1.2 m deep. This can either be in slit trenches as single pipes or in open trenches which are 1m wide, allowing the pipe to run down one side and loop back to run down the other side. These trenches may run from anywhere between 50m to 200m depending on the space available.

Vertically

Here the pipe is fed vertically into a borehole. Boreholes are created by a large rotary drilling rigs which bore down into the ground vertically. They typically have diameters of 6 inches and can reach depths of up to 120 m depending on the heat requirements of the property and lithology present.

If you are interested in how we calculate how much borehole or trenching is required please refer to our 'sizing ground loops for ground source heat pumps' guide.

Which method you choose is ultimately dictated by the space that is available. Where there is significant space (at least half an acre, which is more than most people would think!) trenches is the favourable option as it is much cheaper than boreholes, keeping the cost of the installation down. Where space is premium or restricted, boreholes are required.

Here are some other pros and cons to each method to consider

Boreholes

  • Necessitates a small portion of ground area
  • Less pipework is required
  • Systems on boreholes can reach very high efficiency
  • Ground which it is exchanging heat with has relative constant parameters, therefore even in winter efficiencies remain high
  • More likely to benefit from ground water influence

Con - More significant initial investment

Trenches

  • Lower installation costs
  • Less specialist equipment meaning customers are often able to dig their own trenches
  • Smaller environmental impact

Con - more variable performance due to seasonal exposure and presence of water saturation fluctuations

Some benefits common to both system

  • Post-install both systems will be unnoticeable and can be planted over, covered or tarmacked.
  • The ground loop is MDPE, expected to last up to 100 years.
  • Subsidised by the government
, Cotswold Energy Group

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