horizontal installation method

method 1 - horizontal installation of ground loop into trenches

Burying pipe in the ground in horizontal trenches is the most common and cheap method of extracting heat from the ground. 

Description

Trench length is carefully calculated to match the heat load of the building.  Pipe is filled with a mix of water, antifreeze and inhibitor and then sealed.  IHS normally recommends a maximum trench length of 50 metres but no shorter than 25 metres into which 100 metres of pipe is installed.  Each 100 metre length of ground loop (pipe) normally runs 50 metres out, then 50 metres back. A typical trench is dug to a depth of 1.2 metres.  The pipes are brought together at a collector manifold which can be sited underground in an inspection chamber near or beside the heat pump itself. 

See diagram below for a typical trench system. 

Trenches can run in any direction or uphill or downhill.  They should be a minimum of 1 metre apart.  The standard width of a trench is 600-900mm.  The maximum length of each ground loop (pipe) is 100 metres.  Each ground loop must be equal in length and a minimum of 600mm apart to ensure equal flow to all manifolds and pipes.

Less space?

In a confined space, an option is to dig a double trench to a length of 25 metres, lay pipe at a depth of 1.8 metres, backfill with soil and lay another layer of pipe at 1.2 metres.

Typical options

In general, pipe instlalation options are as follows:

• Single:  Trench is dug 1 metre wide, 50 metres long and 1.2 metres deep.  There should be a gap of 1 metre between each trench.  100 metres of pipe is installed into each trench.  So for example, 700 metres of pipe would require 7 trenches; this would need a width of 13 metres (assuming trench length is 50 metres).

• Double Trench (50 metre length):  Trench is dug 1 metre wide, 50 metres long but 1.8 metres deep.  A first layer of 100 metre pipe is installed.  The trench is then back-filled and a second layer of pipe is laid at a depth of 1.2 metres. Again, there should be a gap of 1 metre between each trench.  Using the above example of 700 metres of pipe, 4 trenches would be required (3 double, 1 single) and an overall width of 7 metres would be needed (again assuming trench length of 50 metres).

• Short of space?  Double Trench (25 metre length):  As above, except the length of trench is 25 metres.  100 metres of pipe is installed in each trench.  Using the example of 700 metre pipe requirement, 7 trenches would be required in a total width of 13 metres. 

IHS supply a proposed ground loop layout with each heating system that we design.  Frequently in a new build situation, the trenches are dug and pipe installed when the building's foundations are being dug.

IHS do not recommend the use of slinkies (coils of pipe) which is often offered as an option where space is limited.  They are less efficient than lengths of pipe - a good spread of pipe will give the best return and allow surrounding ground time to recover.  Slinkies don't offer the ground nearly enough recovery time.

Every 100 metres of ground loop will yield approximately 1.5kW of energy.

Trees and plants can be planted over the trenched area; growth will not be affected.

Vertical Installation

Vertical Installation (Open Well)