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Concept
Therm
Résumé
The therm (symbol, thm) is a non-SI unit of heat energy equal to 100,000 British thermal units (BTU), and approximately 105 megajoules, 29 kilowatt-hours, 25200 kilocalories and 25.2 thermies. One therm is the energy content of approximately of natural gas at standard temperature and pressure. However, the BTU is not standardised worldwide, with slightly different values in the EU, UK, and USA, meaning that the energy content of the therm also varies by territory.
Natural gas meters measure volume and not energy content, and given that the energy density varies with the mix of hydrocarbons in the natural gas, a 'therm factor' is used by natural gas companies to convert the volume of gas used to its heat equivalent, usually being expressed in units of 'therms per CCF' (CCF is an abbreviation for 100 cubic feet). Higher than average concentration of ethane, propane or butane will increase the therm factor and the inclusion of non-flammable impurities, such as carbon dioxide or nitrogen will reduce it. The Wobbe Index of a fuel gas is also sometimes used to quantify the amount of heat per unit volume burnt.
Therm (EC) ≡ 100000 BTUISO
= 105506000 joules
≈ 29.3072 kWh
The therm (EC) is often used by engineers in the US.
Therm (US) ≡ 100000 BTU59 °F
= 105480400 joules
≈ 29.3001111111111 kWh.
Therm (UK) ≡ 105505585.257348 joules
≡ 29.3071070159300 kWh
A decatherm or dekatherm (dth or Dth) is 10 therms, which is 1,000,000 British thermal units or 1.055 GJ. It is a combination of the prefix for 10 (deca, often with the US spelling "deka") and the energy unit therm. There is some ambiguity, as "decatherm" uses the prefix "d" to mean 10, where in metric the prefix "d" means "deci" or one-tenth, and the prefix "da" means "deca", or 10, though decatherm may use a capital "D". The energy content of natural gas measured at standard conditions is approximately equal to one dekatherm.
This unit of energy is used primarily to measure natural gas.
Source officielle
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