British thermal unit

The British thermal unit (BTU or Btu) is a unit of energy used in the power, steam generation, heating and air conditioning industries. Although it is still used 'unofficially' in metric English-speaking countries (such as Canada, the United Kingdom, and sometimes in New Zealand), its use has declined or has been replaced in other parts of the world. In scientific contexts the BTU has largely been replaced by the SI unit of energy, the joule (J), though it may be used as a measure of agricultural energy production (BTU/kg).

In North America, the term "BTU" is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills, and air conditioners. When used as a unit of power, BTU 'per hour' (BTU/h, that is, BTU divided by hour) is understood, though this is often confusingly abbreviated to just "BTU".

The unit MBTU was defined as one thousand BTU presumably from the Roman numeral system where "M" stands for one thousand (1,000). This is easily confused with the SI mega (M) prefix, which adds a factor of one million (1,000,000). To avoid confusion many companies and engineers use MMBTU to represent one million BTU. Alternatively a "therm" is used representing 100,000 or 105 BTU, and a "quad" as 1015 BTU.

Definitions

A BTU is defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree from 60° to 61°Fahrenheit at a constant pressure of one atmosphere. As is the case with the calorie, several different definitions of the BTU exist, which are based on different water temperatures and therefore vary by up to 0.5%:

Conversions

One BTU is approximately:

* 1 054 – 1 060 J (joules)
* 2.931 ×10-4 kWh (kilowatt hours)
* 252 – 253 cal (calories, or "little calories")
* 0.25 kcal (kilocalories, "large calories", or "food calories")
* 25 031 – 25 160 ft·pdl (foot-poundal)
* 778 – 782 ft·lbf (foot-pounds-force)

Other conversions:

* In natural gas, by convention 1 MMBtu (1 million BTU, sometimes written "mmBTU") = 1.054615 GJ. Conversely, 1 gigajoule is equivalent to 26.8 m3 of natural gas at defined temperature and pressure. So, 1 MMBtu = 28.263682 m3 of natural gas at defined temperature and pressure.
* 1 standard cubic foot of natural gas yields ≈ 1030 BTU (between 1010 BTU and 1070 BTU, depending on quality, when burned)

Associated units

The BTU per hour (BTU/h) is the unit of power most commonly associated with the BTU. The term is sometimes shortened to BTU hour (BTU.h) but both have the same meaning.

* 1 watt is approximately 3.413 BTU/h
* 1000 BTU/h is approximately 293 W
* 1 horsepower is approximately 2,544 BTU/h
* 1 "ton of cooling", a common unit in North American refrigeration and air conditioning applications, is 12,000 BTU/h. It is the amount of power needed to melt one short ton of ice in 24 hours, and is approximately 3.51 kW.
* 1 "therm" is defined in the United States and European Union as 100,000 BTU—but the U.S. uses the BTU59 °F whilst the EU uses the BTUIT.
* 1 "quad (energy)" (short for quadrillion BTU) is defined as 1015 BTU, which is about one exajoule (1.055 × 1018 J). Quads are used in the United States for representing the annual energy consumption of large economies: for example, the U.S. economy used 99.75 quads/year in 2005. [http://wilcoxen.cp.maxwell.syr.edu/pages/804.html] . One quad/year is about 33.43 gigawatts.

The BTU should not be confused with the Board of Trade Unit (B.O.T.U.), which is a much larger quantity of energy (1 kW·h, or about 3412 BTU).

See also

* Conversion of units
* Latent heat
* Metrication

External links

* [http://www.opsi.gov.uk/si/si1995/Uksi_19951804_en_2.htm The Units of Measurement Regulations 1995]
* [http://www2.nrcan.gc.ca/es/erb/CMFiles/Natural_Gas_Facts209JLL-06032006-3651.pdf Natural Gas: A Primer]


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • British Thermal Unit — Pour les articles homonymes, voir BTU. Le British Thermal Unit (abrégé en Btu ou BTU) est une unité d énergie anglo saxonne qui est définie par la quantité de chaleur nécessaire pour élever la température d une livre anglaise d eau d un degré °F… …   Wikipédia en Français

  • British thermal unit — n. a unit of heat equal to about 252 calories; quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit: abbrev. Btu …   English World dictionary

  • British thermal unit —   [ brɪtɪʃ θəːməl juːnɪt], Einheitenzeichen BTU, auch B. Theodor U. oder B. th. und, in Großbritannien verwendete Einheit der Wärmeenergie: diejenige Wärmemenge, die erforderlich ist, um ein Pound Wasser bei der Temperatur 39,2 ºF und bei einem… …   Universal-Lexikon

  • British thermal unit — n the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at a specified temperature (as 39°F) abbr. Btu * * * (BTU) the amount of heat necessary to raise the temperature of one pound of water one degree …   Medical dictionary

  • British thermal unit — (B.T.U., BTU, Btu) The amount of heat required to raise a pound of water one degree Fahrenheit …   Black's law dictionary

  • British thermal unit — (B.T.U., BTU, Btu) The amount of heat required to raise a pound of water one degree Fahrenheit …   Black's law dictionary

  • British thermal unit — Pour les articles homonymes, voir BTU. Unité d énergie, BTU Le British Thermal Unit (abrégé en Btu ou BTU) est une unité d énergie anglo saxonne qui est définie par la quantité de chaleur nécessaire pour élever la température d une livre anglaise …   Wikipédia en Français

  • British thermal unit — Einheit Norm Angloamerikanisches Maßsystem Einheitenname British thermal unit Einheitenzeichen BTU Dimensionsname Energie Dimensionssymbol …   Deutsch Wikipedia

  • British thermal unit — Equivalent E*quiv a*lent ([ e]*kw[i^]v [.a]*lent), n. 1. Something equivalent; that which is equal in value, worth, weight, or force; as, to offer an equivalent for damage done. [1913 Webster] He owned that, if the Test Act were repealed, the… …   The Collaborative International Dictionary of English

  • British thermal unit — (Btu or BTU or BThU)    a unit of heat energy defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In America the British thermal unit is sometimes called the heat unit. In defining the… …   Dictionary of units of measurement

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”