Heat pumps allow to transfer heat from a low-temperature source (for example, lake or river water at 5 °C) to a high-temperature sink (for example, water at 60 °C). This sink can then be used to heat buildings, water, infrastructure or industrial processes.
Heat pumps perform the heat transfer through compression and expansion cycles. For this, they require an external source of energy - often electricity. The coefficient of performance (COP) of a heat pumps is measured by the ratio between the produced heat and the required energy. Heat pumps are more efficient if either the heat source is warmer or the heat sink is colder.
Throughout the world, heat pumps represent only a small fraction of the total heat production. In Switzerland in 2008, the primary heat source was roughly distributed as follows: 58 % ambient air, 39 % ground (geothermy) and 3 % waterbodies (lakes, river and groundwater) (Zogg, 2009).