A brine* circulates in a collector loop and absorbs heat energy from the bedrock, ground, air or water.
In a heat exchanger (evaporator) the tepid brine in the collector loop meets refrigerant** circulating in the refrigerant loop. The refrigerant heats up and converts into gas.
The pressure of the refrigerant is raised in the compressor, which also raises the temperature to a useable level.
Via a condenser, the refrigerant releases the heat to the heating system for the house, and in connection with this the refrigerant is cooled.
The refrigerant circulates further. The pressure is lowered in an expansion valve. It reduces the temperature, the refrigerant returns to liquid form. The process restarts when the refrigerant once again meets the brine.
* Brine is a mixture that cannot freeze, for example water together with alcohol or glycol.
** These days environmentally friendly refrigerants such as carbon dioxide and hydro carbons are used. Freon was previously used.
Heat pumps are based on the principle that when a gas is compressed it heats up, while gas that expands becomes colder.