The temperature of the ground at around 2.0 m depth is relatively stable at approximately 10-14ºC. Whilst the temperature above ground can fluctuate at say close to zero during some harsh winters to mid 20’s °c during summer this stable below ground source can be used in conjunction with other systems to either heat or cool as required.
The use of the ground as a thermal storage device depends on correct interaction of the following energy handling processes:
- The thermal behavior of the earth’s geology at and near its surface
- The ground heat exchange process and selection of a suitable exchanger
- The device linking the ground heat exchanger to the building.
It is vital to know in detail the building’s energy load profile. Although there are many installations of varying types world wide, this technology is limited in some situations.
There are two basic types of closed loop systems, horizontal laid pipework and vertical pre-fabricated bored tube pipework. The former is installed in a similar fashion to an underfloor heating system with continuous loops of pipework buried around 1.8-2.0 metres below ground.
The latter is installed by drilling several cores to a depth of between 30-100 metres using specialist equipment and backfilling ‘grout’.
In reality the horizontal type system is more suited to a new build where plenty of open ground is available to bury pipework.
The vertical type system is suited to sites where space is limited, however the drilling is a specialist exercise and therefore costly.
This type of system would also require to have a conventional oil or gas fired system as backup.