Heat pumps are devices that transfer heat from a ‘low temperature’ source to a higher temperature sink. A heat pump uses some form of energy (usually electrical) to accomplish the desired transfer of thermal energy.
The most commonly used heat pumps are of the air-water type, which use the thermal energy of outside air, extract its heat, enhance it and, ultimately, transfer it to heat the water in the heating circuit. Head pumps can achieve a COP (Coefficient of Performance) as high as 5; this means that for every 5 units of thermal energy produced they consume 1 unit of electrical energy. Air-water heat pumps are mainly used for heating and water heating purposes. In Greece, when combined with a more modern heating system (floor heating, fan coils) the same devices can also be used for cooling purposes. Technological advances currently allow heat pump use even in regions with very low temperatures.