What is a heat pump?A heat pump is a machine or device that transfers thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. While compressor-driven air conditioners and freezers are technically heat pumps, the class includes many other types of devices, and the term "heat pump" usually implies one of the less-common devices in the class that are not dedicated to refrigeration-only.
During the operation of a heat pump, some of the thermal energy must be transformed to another type of energy before reappearing as thermal energy in the heat sink. The heat pump uses mechanical work, or some source of thermodynamic work (such as much higher-temperature heat source dissipating heat to lower temperatures) to accomplish the desired transfer of thermal energy from source to sink.
In the classical thermodynamic sense, a heat pump does not actually move heat, which by definition cannot flow from cold to hot temperatures. However, since the effect of the device in moving thermal energy is the same as if heat were flowing (albeit in the incorrect direction with regard to temperature difference), the "heat pump" is named by analogy