Every time energy is converted, various types of losses occur, depending on the degree of efficiency . The sum of all energy lost in a period of time related to the period of time is called power loss . In most processes, this power is generated almost exclusively as heat. Ultimately, useful energy such as the sound energy of a loudspeaker or the flight performance of an aircraft is converted into heat. In the opposite direction, heat can only be partially converted into another form of energy, and only if and as long as there is a temperature difference (Second Law of Thermodynamics , Carnot Process ). Therefore, in many contexts, heat is synonymous with lost energy.
Frictional losses in mechanical systems, thermal losses in combustion engines , winding and iron losses in electric motors or losses in electronic components cause the machine, the device or individual components to heat up. This heating can go so far that machine parts such as cylinder heads or winding insulation are destroyed. Therefore, the heat loss must be dissipated by cooling .