The British thermal unit ( Btu or BTU ) is a traditional heat unit; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. This is part of the customary unit of the United States. The counter in the metric system is the calorie, which is defined as the amount of heat required to raise the temperature of one gram of water to one degree Celsius. Heat is now known to be equivalent to energy, whose SI unit is joule; one BTU around 1055 joules. While hot units are often replaced by energy units in scientific work, they are still important in many areas. For example, in the United States the price of natural gas is quoted in dollars per million BTU.
Video British thermal unit
Definition
A BTU was originally defined as the amount of heat required to raise the temperature of 1 pound avoirdupois liquid water by 1 degree Fahrenheit at a constant pressure of one atmosphere. There are several different definitions of BTU that are now known to be slightly different. This reflects the fact that the temperature change of the water mass due to the addition of a certain amount of heat (calculated in units of energy, usually joules) is slightly dependent on the initial temperature of the water. As can be seen in the table below, the definition of BTU based on different water temperatures varies up to 0.5%. In the table, thermochemical values ââand the steam table (TI), now defined in terms of exact values ââin joules, have been rounded into four decimal places.
Prefix
The kBtu unit is used in building energy usage tracking and heating system sizes. The Energy Use Index (EUI) represents kBtu per square foot of the conditioned floor area. "k" means 1,000.
The MBtu and MMBtu units are used in natural gas and other industries for each indicating 1,000 and 1,000,000 BTUs. There is ambiguity in the metric system that uses the prefix "M" to denote a million (1,000,000), and "MBtu" is also used to denote one million BTUs. Due to this ambiguity, some authors have discontinued the use of MBtu.
Energy analysts accustomed to the "k" metric for 1,000 are more likely to use MBtu to represent a million, especially in documents where M represents one million units of energy or other costs, such as MW, MWh and $.
The therm unit is used to represent 100,000 (or 10 5 ) Ã, BTU. Decatherm is 10 therms or one MBtu. The quad unit is usually used to represent one BTUs quadrillion (10 15 ).
Maps British thermal unit
Conversions
One Btu about:
- 1,054 to 1,060 kJ (kilojoules)
- 0,2931 W? h (watt hour)
- 252 to 253 calories (calories, or "few calories")
- 0.25 kcal (kilocalories, "large calories", or "food calories")
- 25.031 to 25.160Ã, ft? pdl (foot-poundal)
- 778 to 782Ã, ft? lbf (foot-pound-style)
- 5.40395 (lbf/in 2 )? ft 3
A Btu can be estimated as heat generated by burning a wooden kitchen game or as the amount of energy required to lift a pound (0.45 kg) by weight 778 feet (237 m).
For natural gas
- In natural gas prices, Canadian definition is 1 MMBtu? 1 000 000 Btu? 1.054615 GJ.
- The energy content (high or low heat value) of natural gas volume varies with natural gas composition, which means there is no universal conversion factor for Btu to volume amount. 1 standard cubic feet of average natural gas yield? 1030 Btu (between 1010 Btu and 1070 Btu, depending on quality, when burned)
- As a rough approximation, 1000Ã, ft 3 natural gas yield? 1 MMBtu? 1 GJ
- For natural gas price conversion 1000 m 3 ? 36,906 MMBtu and 1 MMBtu? 27,096 m 3
As power units
When used as a power unit for heating and cooling systems, Btu per hour (Btu/h) is the correct unit, although this is often abbreviated to "Btu" only. MBH - thousands of hours per hour - also common.
- 1 watt is about 3,41214 Btu/hr
- 1000Ã, Btu/h is about 293.071,070,159,3Ã, W
- 1 horsepower is about 2544 Btu/hr, or Btu/s
Related units
- 1 cooling tonne , a common unit in North America's cooling and air cooling app, is 12,000 Btu/h (3.52 kW). This is the heat transfer rate required to freeze 1 ton of short (907 kg) of water into ice within 24 hours.
- In the US, the R-value describing thermal insulation performance is usually quoted in ft 2 ? Ã, à ° F? hr/Btu. For one square foot of insulation, one BTU per hour of heat flows across the insulator for each level of temperature difference on it.
- 1 therm is defined in the United States and EU as 100,000 Btu - but the US uses Btu 59Ã, à ° F while UE uses Btu IT . The term is used in the price of natural gas in the UK.
- 1 quad (short quadrillionÃ, Btu) is 10 15 Ã, Btu, about 1 exajoule ( 1.055 ÃÆ' - 10 18 Ã, J ). Thighs are used in the United States to represent large annual economic energy consumption: for example, the US economy uses 99.75 thighs in 2005. 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 3.412 Btu).
The Btu is often used to express the conversion efficiency of heat into electrical energy in a power plant. The numbers cited in terms of quantity of heat in Btu are required to produce 1 kW? H electrical energy. A typical coal-fired power plant works on 10 500 Btu/kW? H, efficiency 32-33%.
Centigrade heat unit (CHU) is the amount of heat required to raise the temperature of one pound of water to one degree Celsius. This equals 1.8 BTU or 1899 joules. This unit is sometimes used in England as an alternative to BTU but is now obsolete.
See also
- Unit conversion
- Latent heat
- Metrics
- Cooling targets
References
External links
- "The Units of Measurement Regulations 1995". www.legislation.gov.uk . HMSO. 1995-07-13 . Retrieved 2018-02-23 .
- "Natural Gas: A Primer". www.nrcan.gc.ca . Natural Resources Canada. 2015-11-27 . Retrieved 2018-02-23 . Ã,
Source of the article : Wikipedia