A heat pump is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.
While air conditioners and freezers are familiar examples of heat pumps, the term "heat pump" is more general and applies to many HVAC (heating, ventilating, and air conditioning) devices used for space heating or space cooling. When a heat pump is used for heating, it employs the same basic refrigeration-type cycle used by an air conditioner or a refrigerator, but in the opposite direction - releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground.[58] In heating mode, heat pumps are three to four times more efficient in their use of electric power than simple electrical resistance heaters.
In the context of renewable energy, heat pumps are able to use electricity from renewable sources to provide heating and cooling of structures in a cost and energy effective way, displacing non renewable sources.[citation needed] It has been concluded that heat pumps are the single technology that could reduce the greenhouse gas emissions of households better than every other technology that is available on the market. With a market share of 30 % heat pumps could reduce global CO2 emissions by 8 % annually.[59] Using ground source heat pumps could reduce around 60% of the primary energy demand and 90% of CO2 emissions in Europe in 2050 and make handling high shares of renewable energy easier.[60] Using surplus renewable energy in heat pumps is regarded as the most effective household means to reduce to reduce global warming and fossil fuel depletion.[61]
Commercialization