Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pumps and refrigerators. A heat pump is a machine or device that moves heat from one location (the source) at a lower temperature to another location (the sink or heat sink) at a higher temperature using . When a heat pump is used for heating, it employs the same basic refrigeration-type cycle. A heat pump is subject to the same limitations from the second law of thermodynamics as any other heat engine and therefore a maximum efficiency can be calculated from the Carnot cycle. Heat Pumps are usually characterized by a coefficient of performance which is the number of units of energy delivered to the hot .
By lowering pressure, a medium can be evaporated at low temperatures while an increase of pressure will lead to a high boiling point. If so, there is now net work into the system and net heat out of the system. Refrigerators and Heat Pumps.
There will be a quantity of heat $ Q_2$ rejected at the higher temperature and a quantity of heat $ Q_1$ absorbed at the lower . It does so by the following process: Liquid refrigerant absorbs heat in the evaporator from the outdoor air, turning into a gas.