Therm
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rm copyvio from http://www.gordonengland.co.uk/conversion/sidef.htm
The '''therm''' (symbol '''thm''') is a non-[[SI]] [[Units of energy|unit]] of [[heat]] [[energy]] equal to 100,000 [[British thermal unit]]s (BTU). It is approximately the energy equivalent of burning 100 [[cubic foot|cubic feet]] (often referred to as 1 [[hcf]]) of [[natural gas]].
A '''therm factor''' is used by gas companies to convert the volume of gas used to its heat equivalent, and thus calculate the actual energy use. The '''therm factor''' is usually in the units therms/Ccf. It will vary with the mix of hydrocarbons in the [[natural gas]]. [[Natural gas]] with a higher than average concentration of [[ethane]], [[propane]] or [[butane]] will have a higher '''therm factor'''. Impurities, such as [[carbon dioxide]] or [[nitrogen]] lower the '''therm factor'''.
The volume of the gas is calculated as if it was measured at [[standard temperature and pressure]] (STP). The heat content of [[natural gas]] is solely dependent on the composition of the gas, and is independent of temperature and pressure.
The therm is equal to about 25 200 (large) calories or about 29.3 kilowatt hours of electrical energy. One therm can also be provided by about 96.7 cubic feet of natural gas. The therm has sometimes been confused with the thermie (see below). The names of both units come from the Greek word for heat, therme.
thermie (th)
a metric unit of heat energy, part of the meter-tonne-second system sometimes used by European engineers. The thermie is equal to the amount of energy required to raise the temperature of 1 tonne of water by 1°C. The thermie is equivalent to 1000 (large) calories , 4.1868 megajoules or 3968.3 Btu.
==Definitions==
*Therm (EC) ≡ 100,000 [[BTU|BTU<sub>IT</sub>]]<ref>[http://europa.eu.int/eur-lex/lex/LexUriServ/LexUriServ.do?uri=CELEX:11972BN01/10/PT1A16:EN:HTML Official Journal L 073, P. 0114] [[27 March]] [[1972]]</ref>
::= 105,506,000 [[joule]]s
::≈ 29.3072222 [[kilowatt-hour|kWh]]
::The therm (EC) is often used by engineers in the US.
*Therm (US) ≡ 100,000 [[BTU|BTU<sub>59°F</sub>]]<ref>[http://uscode.house.gov/download/pls/15C6.txt 15 USC Chapter 6]</ref>
::= 105,480,400 joules
::≈ 29.3001111 kWh.
*Therm (UK) = 105,505,585.257 348 joules<ref>[http://www.opsi.gov.uk/si/si1995/Uksi_19951804_en_2.htm The Units of Measurement Regulations 1995]</ref>
::≈ 29.30710701583 kWh
Ten therms are a decatherm. Common abbreviations are as follow:<ref> [http://financial.washingtonpost.com/wpost/Quote.asp?Symbol=STR&Mode=EDGARDISPLAY&ReleaseDate=2004-06-30 washingtonpost.com]</ref>
{| border="1"
|Dth||decatherm
|-
|MDth||thousand decatherms
|-
|MMDth||million decatherms
|}
==Usage==
United Kingdom regulations were amended to replace therms with joules with effect from 1999; despite this, natural gas is now usually retailed in kilowatt-hours, although the wholesale UK gas market trades in therms, with a typical forward transaction being for 25,000 therms/day (30.528 MW). In the United States, however, natural gas is commonly billed in therms.
==References==
{{reflist}}
[[Category:Units of energy]]
{{industry-stub}}
[[de:Therm (Einheit)]]