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 does the heat from a heat pump reach the house?
- The ground loop in the system contains a carrier fluid which absorbs the heat in your ground. It's pumped around to the pump unit in your house, which transfers the heat from the carrier fluid to your water and concentrates it at the same time, meaning that it is hot enough to be used in your heating and as hot water.
- 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.
- Where should I put my heat pump unit?
- Usual locations include your utility room, basement or even out in the garage.
- Can a ground source heat pump be installed in an old building?
- You can install ground source heat pumps in old buildings, and there are lots of examples of this being done. The design phase is very important as there are lots of issues to overcome in older buildings, especially if it is listed.
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