Waste heat
Waste heat is the by-product heat of machines and technical processes for which no useful application is found.
A fraction of input energy is always converted to heat by friction between machine parts and other processes such as liquid friction (see: viscosity).
Mechanical drives can be designed to run smoothly, with little loss of energy to heat. Machines for conversion of energy contained in fuels to mechanical work or electric energy produce large amounts of waste heat (see: Second law of thermodynamics).
This waste heat can be re-used if a cogeneration system is used. It is hard to use waste heat because it is difficult to transport the heat to another place, and it is difficult to store the heat for use at another time. In electrification of waste heat, organic matter can be used as a working medium to produce electricity on much lower temperatures compared to the water steam cycle.
Waste Heat Media
Thermal oxidizers can use a regenerative process for waste heat from industrial systems.
Air conditioning units extract heat from a dwelling interior with coolant, and transfer it to the dwelling exterior as waste. They emit additional heat in their use of electricity to power the devices that pass heat to and from the coolant.
A coal-fired power station. These transform chemical energy into 36%–48% electricity and the remaining 52%–64% to waste heat.
Cooling towers evaporating water at Ratcliffe-on-Soar Power Station, United Kingdom
Anthropogenic heat output based on world energy consumption data.
