How do heat pumps work?
They take the ambient heat from the ground, typically, and concentrate this for use in your home.
This heat can be used to heat your home directly or heat water to feed into your central heating or hot water system. This reduces the amount of fuel you need to burn for heating, saving you money. The government are supplementing the cost of installation for ground source heat pumps with the RHPP scheme, offering one-off grants of £1,250.
Technical information made simple
You will need enough outside space to bury a loop of pipe called a ‘ground loop’ which collects the heat from the earth, although they can be buried in vertical boreholes if space is really tight.
- A mixture of water and antifreeze circulates around the ground loop – which is buried in the garden. This absorbs the heat from the ground.
- Then the heated ground loop fluid is pumped through a heat exchanger passing the heat to the refrigerant.
- The refrigerant is compressed and the heat concentrated into a higher temperature in a compressor. This makes it hot enough to heat water for either heating or hot water.
- The ground loop fluid, now cooled, passes back into the ground where it captures more heat and repeats the whole process.
The size of your home, and your requirement for heat will determine the length of the ground loop – longer loops can draw more heat from the ground, but need more space to be buried in.
There are other types of heat pump and they work on a very similar principle, but tend to draw heat from different sources:
- Air Source Heat Pumps: They draw heat from the outside air and are popular as they are cheaper and easier to install, particularly if you live in a city with limited outside space.
- Water source heat pumps: This is very similar to a ground source system except that the ground loop is immersed in water, such as a lake or river.
- MVHR (Mechanical Ventilation and Heat Recovery): This is effectively exhaust-air-source; these recover the heat from air leaving your home via vents. This is most effective in more air-tight homes.
- How long should the ground loop be?
- That depends on the energy requirements of your house, the space that you have available and the type of ground you have. The larger the home that is to be heated, more energy that is required thus more loop needed in the ground. When planning and designing your system your installer will design your system so that it meets your needs.Typical systems are 6 to 12kW, and you'll usually need 10m of coiled pipe per kW for installation in horizontal trenches - you'll need less piping if you're installing it in a vertical borehole. If ground space is restricted, a vertical borehole (or several) is a good choice - these are now comparable in cost to installing the loops in horizontal trenches.
- Can a ground source heat pump be used with underfloor heating?
- Underfloor heating is a great choice for use with a ground source heat pump, but large radiators or a mix of both can be used for distributing heat around your home. Heat pumps produce a lower temperature heat than conventional boilers, therefore they are far more effective if used with a larger surface heating distribution system such as underfloor heating or large radiators. A good rule of thumb is that if used with heat pumps, the radiators should be around 30% larger compared to the size of radiator that would be used with a conventional boiler.
- Will a ground source heat pump provide enough hot water for heating and baths/showers?
- Yes, with the correct design and equipment, a ground source heat pump can meet all your domestic hot water requirements throughout the year. If you do not have enough space in your garden for a system large enough to meets your needs you can top up the heat the heat pump produces with the help of a more conventional system. Your installer will be able to confirm whether the size of system you can accommodate will meet your needs.
- Can a ground source heat pump be used to cool my house?
- Yes, in some ground source heat pump systems this can be achieved as either passive or active cooling.
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