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.