Endothermic and exothermic phenomena
General principles - the theory of refrigerating machines

To transfer heat from a low-temperature medium to a higher-temperature medium, you need to :

• an endothermic phenomenon, taking place at the temperature T _F of the cold source to extract heat from the cold external environment;

• a thermodynamic process, to raise the thermal level of this heat from T _F to T _C ;

• an exothermic phenomenon, taking place at the temperature T _C of the hot well to reject heat to the hot external environment.

These phenomena may occur simultaneously in the various parts of the system, which thus produces cold or, more generally, continuously...