Heat pumps

The principle of a heat pump is that it is able to produce more than 1 kWtherm of usable heat from 1 kWh of electricity. All electric heaters other than heat pumps just produce exactly 1 kWtherm of heat from 1 kWh of electricity, effectively 100% efficient. The amount of ‘additional’ heat that a heat pump creates is called the Coefficient of Performance (CoP). So a heat pump with a CoP of 3 can make 3kWtherm of heat from every 1kWh of electricity. This varies in all heat pumps and this variation is a factor of:

• Different companies’ technology
• Ambient temperatures (in the air or soil)
• Required temperatures inside the home
• The requirement to heat hot water as well as space heating

The most important of these factors is the temperature difference between where the heat pump collects the heat (i.e. outside) and the temperature of whatever you are heating (i.e. the water circulating in your radiators). The greater this temperature, the lower the CoP.

This is important to know, because for instance if you have small radiators, you need to keep them hotter to provide enough heat to keep your house warm, and this means the CoP is low so the heat pump will use more electricity.

For a heat pump to be economical to run, the system must be designed to operate at as low an operating temperature as possible, and that means radiators as large as possible, or ideally under-floor heating (UFH).

It also means that air source is less efficient when it is colder outside.

Generally Air Source Heat Pumps (ASHP) run at around 2-2.5 CoP in the UK, but a Ground Source (GSHP) are more efficient at around 3-3.2 CoP. This is because ground temperatures are steadier and also higher than air especially when needed most in colder weather.

GSHP are much more expensive to install as it requires either laying out a lot of pipes in a garden space or drilling down a deep borehole.

Heat pumps are not a direct replacement for your existing heating system. The need for larger radiators or UFH as well as reducing demand for energy via fabric improvements generally means that systems will cost into the tens of thousands. The big advantage is that it removes the demand for gas / oil / coal and puts it onto the electrical supply and this is ultimately easier to decarbonise through the grid.

Air source vs Ground source

A ground source heat pump will be slightly cheaper to run, because on the coldest winter days, the ground source heat pump will be able to access slightly warmer ambient heat from below ground than the air source heat pump from above ground. However, the ground source heat pump will cost approx. twice as much or more to install, so overall the air source heat pump will be a more economical solution for most people.

You can find more information about heat pumps here:

https://energysavingtrust.org.uk/advice/air-source-heat-pumps/

https://energysavingtrust.org.uk/advice/ground-source-heat-pumps/

The UK Government is encouraging the installation of heat pumps via grant support. For more information visit: https://www.gov.uk/apply-boiler-upgrade-scheme