background

Buried loops of pipes extract heat from the ground to provide indoor space heating, and pre-heating for domestic hot water. Modern ground source heat pumps have better control systems than ever before, which ensure more effective heating, cooling and heat recovery, and so offer an attractive option both financially and environmentally.

There are three major components to a ground source heat pump system:

• The ground loop - closed circuit pipework filled with a mixture of water and antifreeze is buried, either in a horizontal trench or in boreholes. The liquid is pumped around the pipework absorbing heat from the ground as it goes. Spiral, coil or 'slinkys' can be utilised to save on space and reduce trench lengths required.
• The heat pump - which has three main parts: evaporator - absorbs heat using liquid in ground loop, compressor - circulates refrigerant round heat pump and compresses gaseous refrigerant to required temperature for the heat distribution circuit, condenser - provides heat to a hot water tank to feed distribution system
• Heat distribution system - usually underfloor heating pipework, radiators for space heating, or pre-heating of stored water in a cylinder for hot water supply.

As groundwater below the depth of 2.5m maintains a relatively constant temperature (around 10°C) all year round, the heat pump will have to work less hard and consume less power. Therefore the same heating effect as an air source heat pump can be met more efficiently by a ground source heat pump. Unfortunately, the need to create trenches or boreholes to run the pipes means a greater installation cost. Allowing for seasonal variation the average yearly CoP is between 3.0 and 4.0. If the system is powered by grid electricity, running costs can be reduced by using the Economy 7 tariff.

benefits

• No on site emissions
• No flammable oil, LPG or gas
• No unsightly pipelines, flues or chimneys and no expensive fuel tanks
• No regular servicing or annual safety checks - very low maintenance costs
• Heat derived from the ground surrounding your property is free from future price rises - offering greater energy security
• Design life in excess of 40 years
• Reverse-cycle heat pumps can deliver both heating and cooling
• Predominantly used for space heating, but can also heat hot water by utilising immersion heaters installed in high efficiency indirect water cylinders (best done utilising night time off peak rates)
• The initial higher capital cost of a ground source heat pump compared to a gas or oil boiler is offset by the lower energy and running costs

potential savings

Savings vary depending on the type of fuel being replaced. If replacing an oil, electric, coal or LPG system the ground source heat pump system will pay for itself quickly. More efficient systems like gas will take longer to recoup the initial cost of installation.

According the The Energy Saving Trust the prospective financial and carbon savings from installing a ground source heat pump are as follows:

All savings are approximate and are based on a grounds source heat pump system providing around 50% of domestic hot water and 100% of space heating requirements in a detached property.

installation requirements

• Space is required indoors and outdoors – externally, for the ground loops laid in either horizontal trenches or in boreholes; internally, for the heat pump unit, sizes vary but are comparable to a similar capacity gas or oil boiler
• The ground surrounding the property needs to be suitable for digging a trench or drilling boreholes
• A number of heat pumps are available which can run on a standard UK single-phase 22/240v supply, but for units larger than 10kW, a three-phase supply will be required
• High levels of insulation are crucial to ensure the system works efficiently

how much space is required?

Externally - Collector pipes in boreholes require much less open ground than trenching for the same size of heat pump; however, boreholes are more expensive than trenches. In both cases nothing is left visible above the ground. A heating-only installation for a 4-bed, new build detached house would require two 300mm wide trenches, 40 to 50 metres long and 1.8 metres deep. Trenches can be curved if required to suit conditions and laid in any direction so long as they are maintained at least 5 metres away from each other.

Internally - It is advantageous if the heat pump can be installed as close as possible to the collector pipework, so an external wall is ideal (although not essential).

suitable heating systems

Deciding on the most suitable heating system for your home must be a careful consideration. Ground source heat pumps can combine with radiators, but larger models than would be required with a standard system would, as the circulation temperature will be around 35-45°C, rather than 60-70°C of a conventional boiler systems. This can be remedied with the use of back up electric heater coils, but this will increase running costs and CO2 emissions.

Underfloor heating is the distribution system of choice, as, when combined with a heat pump, it creates a well-distributed background heating effect which is better suited to the heat pump’s lower operational temperatures.

The type of heat distribution system needs to be considered carefully.

cost

Price on application. Please call us for a quote.

A typical 8 - 12kW system costs from £6,000 - £10,000 installed (not including the price of distribution system). This can vary with property, system size and location. Boreholes for vertical ground loop systems are considerably more expensive to install than horizontal ground loops.

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