Ground Source Heat Pumps – Their Cost, Their Installation and Their Efficiency
Heating accounts for a significant portion of a household’s energy demand and a ground source heat pump system can provide a cost-effective and sustainable way to warm a home. The pump uses a small amount of electricity to transfer naturally occurring heat from the adjacent ground into the house. As the temperature just a couple of metres below the surface remains more or less constant at 11°C to 12°C, it is possible to design a very efficient heat transfer system.
How does it work?
A sealed loop of fluid-filled pipe is buried in the garden or driveway. The length required depends on the size of the home and the amount of heat required. An average system for a family dwelling will typically require pipework up to 100m long. Vertically drilled boreholes and deeper pipes can be used in more confined spaces. Once installed, the ground is restored to its original condition and the system becomes invisible.
The ground source heat pump circulates water and antifreeze around this loop. The fluid absorbs heat from the ground before it passes through a heat exchanger. Energy is then transferred to the heating and hot water circuits of the home. The cooled fluid flows back into the ground loop in a continuous process for as long as the heating is required. Some systems can also be designed to meet cooling needs in summer.
While there are some minor residual energy and carbon costs, hooking the pump up to a home renewable technology such as a solar panel can increase its sustainability credentials even further.
What properties are suitable?
Ground source heat pump systems are not suited to every type of property. In general, they work most efficiently in well insulated homes with a relatively even and low heat demand. They produce heat at a lower temperature than more conventional central heating so a larger area is required for heat distribution. Underfloor heating is the ideal partner, though large heat pump system radiators are available. The system also requires sufficient outside space for installation. While minimal on-going maintenance is required, there can be considerable disruption during installation, and the system tends to be more attractive for new-build or as part of a wider home improvement project.
A typical domestic ground source pump is the size of a large upright fridge freezer. To save indoor space they can be installed in an outbuilding or basement. They just need to be as close as possible to the end of the ground loop pipe. With a typical noise level of a little over 40dB at one metre away, they are as quiet as a fridge. That’s considerably quieter than a typical gas or oil central heating boiler.
What do they cost and how much will I save?
Costs and savings will be dependant on the size of the pump, the length and depth of loop installation, the energy efficiency of the property, the sort of heating system that is being replaced and whether any additional work is required on the wider home heating system. A typical domestic installation costs £12,000 to £15,000, with annual running costs of £600 to £700. At current prices, the payback from a ground source heat pumps is unlikely to represent an attractive alternative to an established mains gas central heating system. However, installers claim energy savings of nearly £1,500 annually for a typical four-bedroom house when compared with standard electric heating, or around £600 when compared to oil-fired central heating. That represents a saving of nearly 5,000kg of CO2 emissions each year. Government Renewable Heat Incentive grants are currently available for installation.
Their installation will also greatly improve your energy efficiency score on your EPC.
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