All heat pumps except exhaust air heat pumps can provide cooling in the summer. Ground source systems can provide cooling even when the heat pump is not running by heat exchanging the heat transfer liquid from the ground (preferably boreholes) with the heating distribution system (typically underfloor heating). This is called “passive cooling”. Both ground source and air source systems can provide “active cooling” which involves running the heat pump. This type of cooling can be distributed either through the underfloor pipes or through fan coil units.

• Passive cooling with ground source Passive cooling means that the heat transfer fluid in the ground collector is heat-exchanged against the heat transfer fluid in the heating distribution system without running the heat pump compressor. This works best with boreholes. With horizontal loops, the cooling power can decrease towards the end of the summer as the ground warms up. The cooling is usually distributed through underfloor pipes, but can also be distributed by ceiling panels.


• Active cooling with ground source Active cooling means that the heat pump compressor is working to cool down a heat transfer liquid which is stored in a cold buffer tank, kept at a temperature around 7°C. The cooling is usually distributed by fan coil units or ceiling panels.


• Active cooling with air source The compressor in the heat pump is running in reverse, cooling down a heat transfer liquid. The cooling can be distributed though underfloor heating pipes and ceiling panels without using a buffer tank. If the cooling is distributed by fan coil units, a buffer tank is required. When an air source heat pump is set up to do cooling for dwellings, it is not a permitted development and planning is usually required.