How Ground Source Heat Pumps Work
Heat from the ground is absorbed at low temperatures into a fluid inside a loop of pipe (a ground loop) buried underground. The fluid then passes through a compressor that raises it to a higher temperature, that can then heat water for the heating and hot water circuits of the house or business premises.
The cooled ground-loop fluid passes back into the ground where it absorbs further energy from the ground in a continuous process as long as heating is required.
If there is enough space, the collector loop can be laid horizontally in a trench about a metre or so below ground. Where there isn’t room to do this, you can drill vertical boreholes to extract heat from much further down, typically between 90m and 160m deep.
The space you need for a horizontal loop, and the depth you need for a borehole, will depend on many factors. We will provide advice on system design and layout following a site visit.
How the process works
- A cold water anti-freeze mix is pumped through the ground within a series of energy-absorbing pipes. These pipes are called a ground array. As heat naturally flows from warmer to cooler places, the anti-freeze mix circulating the array is constantly warmed by the ground’s low-grade heat.
- Having increased in temperature, the anti-freeze mixture is fed into a heat exchanger called the evaporator.
- Within the secondary sealed side of the evaporator heat exchanger is a refrigerant that acts as a heat transfer fluid. When the water anti-freeze mixture enters the evaporator, the energy absorbed from the ground is transferred into the refrigerant which begins to boil and turn into a gas.
- The refrigerant never physically mixes with the water anti-freeze mixture. They are separated like sandwich layers by the plates of the heat exchanger which permit the heat transfer.
- This gas is then fed into a compressor. The pressure of the refrigerant gas is increased in the compressor, causing the gas temperature rise.
- The hot refrigerant gas then flows into a second heat exchanger, called the condenser, which features an identical set of heat transfer plates.
- The condenser delivers water hot enough to serve the space heating system and the property’s hot water needs. Having transferred its heat, the refrigerant gas reverts to a liquid.
- This liquid is then passed through an expansion valve at the end of the cycle to reduce its pressure and temperature, ready to start the cycle again.
- Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, the air, or water is constantly being renewed naturally.
Caplor Energy specifically partners with the UK’s leading manufacturer of Ground Source Heat Pumps, Kensa.
Is a ground source heat pump right for me?
There are a few things to consider when deciding whether a ground source heat pump is right for you.
You don’t necessarily need a large space, but you will need land near your home suitable for digging trenches or drilling boreholes.
The ground will need to be suitable for digging and accessible to machinery from a road entrance. The area will need to avoid trees, as roots will cause problems when digging trenches. The length of ground loop and trenches depend on the size of your home and the amount of heat you need.
If space is limited, it may be possible to drill vertical boreholes to gather heat. This is usually more expensive than digging trenches and usually needs a specialist ground (thermogeological) survey.
Larger houses may require more than one borehole. Borehole depth depends on the heat demand of a property and the underlying geology but is likely to be around 75-200 metres deep.
Inside the house
You will need space inside your home for the indoor heat pump unit, which contains key components. The inside unit often contains the hot water cylinder and is roughly the size of an American style fridge.
Most homes in the UK use radiators or underfloor heating to circulate hot water, which is known as a ‘wet system’. Ground source heat pumps need a wet system.
If you don’t currently have a wet system, you will have to decide whether you’d like to install one. This is a great opportunity to make sure the wet system is optimised for a heat pump, resulting in lower running costs.
You can find more information about the most effective wet system for your heat pump here.
Don’t want or can’t have a wet heating system? Click here for air-to-air heat pumps.
The cost of a ground source heat pump installation varies, influenced by:
- Access to the ground and whether you choose trenches or a borehole to lay the ground loop.
- The brand, model and size of heat pump chosen.
- The size of the property and how much heat it needs.
- Whether it’s a newbuild or an existing property.
- Whether you’re opting to make any improvements to your radiators to improve the efficiency of the heat pump, or if you are installing radiators or underfloor heating for the first time.
Typical costs are around £24,000 if your ground loop is buried in trenches, and could be around £49,000 if you need to dig a borehole.
Running costs will depend on how your heat pump is designed and how it is operated. Savings on your energy bill will also depend on the system you are replacing.
You can see potential annual savings of installing a standard ground source heat pump, including any recommended radiator upgrades, in an average sized, four-bedroom detached home, below.
England, Scotland and Wales
Potential annual savings of installing a heat pump in a average, four bedroom detached home, with radiator upgrades as required.
Figures are based on fuel prices as of April 2022. Negative fuel savings indicate a fuel bill increase. The saving you can expect will depend on the size of your home, any heating system upgrade and fuel type being replaced. You can expect the saving to range between old and new, depending on the age of your current heating system.
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