There are two ways to lay ground collector pipe in order to collect heat from the ground:
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.
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
Con - More significant initial investment
Con - more variable performance due to seasonal exposure and presence of water saturation fluctuations
Some benefits common to both system