What is a heat pump

Looking to find out what is a heat pump and how does it work? Find out how a ground source heat pump works from the UK’s number one manufacturer of ground source heat pumps.

What is a heat pump?

Not to be confused with geothermal heating or air source heat pumps, a ground source heat pump works by extracting solar energy stored in the ground or water sources and converting this to a higher temperature for use in a building's heating distribution system.

Wondering how efficient is a heat pump? A ground source heat pump produces up to three times more energy than it consumes. So for every 1kWh of energy your heat pump uses to power itself, you will get typically 3kWh of energy to heat your property.

1kW of electricity = 3kW of heat

This means heating costs are effectively reduced by two thirds. This is known and the coefficient of performance (COP).

Due to the high efficiency of a heat pump, CO2 emissions are significantly lower than traditional fossil fuelled systems (up to 43% lower than gas).

How does a heat pump work?

This three minute video by Kensa Heat Pumps explains what a heat pump is and how a ground source heat pump works.

For a more detailed technical explanation an extended version is available here, with commentary from Kensa's Technical Director, and co-founder, Guy Cashmore.

Heat pump process

  • A cold water anti-freeze mix is pumped through the ground within a series of energy absorbing pipes, known as ground arrays. As heat naturally flows from warmer to cooler places, the anti-freeze mix circulating around 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 which 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, which makes 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, if required, 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 commence the cycle all over again.
Watch the video

What is a heat pump? Ground source heat pump process diagram

Improving heat pump efficiency

In order to improve heat pump efficiency it is worth considering that the lower the flow temperature required in your heating distribution system, the less work your ground source heat pump will need to make. This will therefore make it even more efficient, and possibly even reduce the size and of pump required and lower how much a heat pump costs.

To achieve as low flow temperatures as possible, insulation is the first place to look.

better insulation = lower flow temperature = less work & more efficient heat pump

I think ground source heat pumps are the future of energy generation and everyone should embrace this technology.

Alistair Mackintosh, Selfbuilder