Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat. Energy conversion efficiency is not defined uniquely, it depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle. In physics and engineering, energy conversion is any process of converting energy from one form to another. ... Electric power is the amount of work done by an electric current in a unit time. ... Mechanical work is a force applied through a distance, defined mathematically as the line integral of a scalar product of force and displacement vectors. ... In physics, heat, symbolized by Q, is defined as energy in transit. ... Waste heat is the by-product heat of machines and technical processes for which no useful application is found. ... A thermodynamic cycle is a series of thermodynamic processes which returns a system to its initial state. ...

Even though the definition includes the notion of usefulness, efficiency is considered a technical or physical term. Goal or mission oriented terms include effectiveness and efficacy. Efficiency is the capability of acting or producing effectively with a minimum amount or quantity of waste, expense, or unnecessary effort. ... By the mid 20th century humans had achieved a level of technological mastery sufficient to leave the surface of the planet for the first time and explore space. ... Physics (from the Greek, (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and understanding of the fundamental laws which govern matter, energy, space and time. ... Effectiveness means the capability of, or success in, achieving a given goal. ... In general, efficacy is the ability to produce an effect, usually a specifically desired effect. ...

Generally, energy conversion efficiency is a dimensionless number between 0 and 1.0, or 0 to 100%. Efficiencies may not exceed 100%, e.g., for a perpetual motion machine. However, other effectiveness measures that can exceed 1.0 are used for heat pumps and other devices that move heat rather than convert it. In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... This article or section should include material from Parallel Path See also Perpetuum mobile as a musical term Perpetual motion machines (the Latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which would produce useful energy in a way science cannot explain (yet). ... The thermal efficiency of a heat engine is the efficiency in which the chemical energy of a fuel is turned into useful work, though it is also used as a synonym for thermodynamic efficiency. ... A heat pump is a machine, which moves heat from a low temperature reservoir to a higher temperature reservoir under supply of work. ...

Related, more specific terms include:

• Electrical efficiency, useful power output per electrical power consumed
• Mechanical efficiency, where one form of mechanical energy (e.g. potential energy of water) is converted to mechanical energy (work).
• Thermal efficiency or Fuel efficiency, useful heat and/or work output per input energy such as the fuel consumed
• 'Total efficiency', e.g., for cogeneration, useful electric power and heat output per fuel energy consumed. Same as the thermal efficiency.

The efficiency of an entity (a device, component, or system) in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a fractional expression). ... In physics, mechanical efficiency is the effectiveness of a machine and is defined as Efficiency is often indicated by a percentage, the efficiency of an ideal machine is 100%. Due to the fact that energy cannot emerge from nothing and the Second law of thermodynamics which states that the quality... Look up work in Wiktionary, the free dictionary. ... The thermal efficiency of a heat engine is the efficiency in which the chemical energy of a fuel is turned into useful work, though it is also used as a synonym for thermodynamic efficiency. ... Fuel efficiency sometimes means the same as thermal efficiency or fuel economy. ... In physics, heat, symbolized by Q, is defined as energy in transit. ... Look up work in Wiktionary, the free dictionary. ... Fuel is any material that is capable of releasing energy when its chemical or physical structure is changed or converted. ... Cogeneration (also combined heat and power or CHP) is the use of a power station to simultaneously generate both heat and electricity. ... Electric power is the amount of work done by an electric current in a unit time. ... The thermal efficiency of a heat engine is the efficiency in which the chemical energy of a fuel is turned into useful work, though it is also used as a synonym for thermodynamic efficiency. ...

Fuel heating values and efficiency

In Europe the usable energy content of fuel is typically calculated using the lower heating value (LHV) of that fuel, i.e. the heat obtained by fuel combustion (oxidation), measured so that the water vapor produced remains gaseous, and is not condensed to liquid water. Using the LHV, a condensing boiler can achieve a "heating efficiency" in excess of 100% which violates the first law of thermodynamics. This is because the apparatus recovers part of the heat of vaporization, which is not included in the definition of the lower heating value of fuel. In the U.S. and elsewhere, the higher heating value (HHV) is used, which includes the latent heat for condensing the water vapor, and thus the thermodynamic maximum of 100% efficiency cannot be exceeded with HHV's use. The lower heating value (also known as net calorific value) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25°C) and returning the temperature of the combustion products to 150°C. The lower heating value assumes the latent heat of... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... Water vapor or water vapour, also aqueous vapour, is the gas phase of water. ... Water vapor condensing over a cup of hot tea Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. ... A condensing boiler is a kind of hydronic boiler which achieves enhanced efficiency by incorporating an additional heat exchanger. ... The first law of thermodynamics, a generalized expression of the law of the conservation of energy, states: // Description Essentially, the First Law of Thermodynamics declares that energy is conserved for a closed system, with heat and work being the forms of energy transfer. ... The heat of vaporization is a physical property of substances. ... The Higher Heating Value (HHV) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25°C) once it is combusted and the reactants have returned to a temperature of 25°C. The Higher Heating Value takes into account the latent heat of...