CMS UK

Rural, Business and Renewable Energy Consultants

Ground Source Heat Pumps

The principle behind a GSHP is the same as that employed in a refrigerator (which is actually and Air Source Heat pump) and relies on the second law of thermodynamics (heat travels from hot to cold).

• 20 year predicted system lifespan.
• Can save up to 70% on energy bills depending on replaced fuel.
• Grants are available under Low carbon Buildings Programme. Inflation proofed energy
• Fuel efficiency claimed up to 5:1 (energy out to energy in)
• Reduced CO2 emissions compared to fossil fueled systems.
• Potential to meet all space and DHW requirements.
• Can be programmed to heat domestic hot water DHW during the night.
• Can be reversed to give cooling in summer.

In the UK, the ground temperature is 10-12 deg C at about 3 feet deep and this does not vary much with depth. Cold brine or water + antifreeze is pumped round a 40mm PEM pipe buried in the soil. This heats to 10 -12 degrees C.

The heat is extracted in the 'refrigerator' part of the heat pump system, transferred to the buildings heating system and the (now colder) brine is pumped back round the earth to be recharged with heat. The longer the pipe length, the more heat can be picked up.

Ground work

The transfer pipes can be laid straight in a narrow trench system, 1-2 metre deep, either as single straight pipes, or looped or as panels. To save trench length pipes can be coiled as slinky coils in a shorter wider trench.

Alternatively pipes can be laid vertically in a 6-inch dia borehole system 25-150 metre deep. Loop length and number of trenches /boreholes depends on heat demand and thermal efficiency of the building.

The type of collection facility trench, or borehole (or combination) will depend on site space available and ground conditions.

Output

Approximately 15 watt per metre of horizontal pipe rising to 30-40 watt per metre of pipe laid vertically in a bore hole can be collected depending on the heat transfer properties of sand, rock or clay).

What is the tangible financial return?

For single residential systems, GSHP costs about £1000 / kw installed but the cost will vary depending on site conditions and delivery system.

Another factor to take into account is that GSHP because they work optimally delivering water at 30-50 degrees C are best hooked up to underfloor central heating systems, and because underfloor are slow recovery systems good insulation and control of ventilation are essential.

If you have any comments or queries on GSHP contact:

Renewables Energy Manager
CMS UK
Spring Farm Business Centre
Moss Lane
Minshull Vernon
Crewe
Cheshire CW1 4RJ
Tel: 01270 522645