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The British thermal unit (BTU or Btu) is a traditional unit of work equal to about 1055 joules. It is the amount of work needed to raise the temperature of one pound of water by one degree Fahrenheit (Physical analogue: one four-inch wooden kitchen match consumed completely generates approximately 1 BTU). In science, the joule, the SI unit of energy, has largely replaced the BTU. The BTU/h is most often used as a measure of power in the power, steam generation, heating, and air conditioning industries, and also as a measure of agricultural energy production (BTU/kg). It is still used in metric English-speaking countries (such as Canada). In North America, the heat value (energy content) of fuels is expressed in BTUs. The special notation MMBtu or mmBtu is often used to represent one million BTU. == Definitions == A BTU is the amount of heat required to raise the temperature of 1 avoirdupois pound of liquid water by 1 degree Fahrenheit at a constant pressure of one atmosphere. As with the calorie, several definitions of the BTU exist, because the temperature response of water to heat energy is non-linear. This means that the change in temperature of a water mass caused by adding a certain amount of heat to it will be a function of the water's initial temperature. Definitions of the BTU based on different water temperatures can therefore vary by up to 0.5%. A BTU can be approximated as the heat produced by burning a single wooden kitchen match〔Energy and the Environment. Ristinen, Robert A. c. 2006, pg 13〕 or as the amount of energy it takes to lift a one-pound weight .〔Energy and the Environment. Ristinen, Robert A. c. 2006, pg 14〕 The unit MBtu or mBtu was defined as one thousand BTU, presumably from the Roman numeral system where "M" or "m" stands for one thousand (1,000). This notation is easily confused with the SI mega- (M) prefix, which denotes multiplication by a factor of one million (×106), or with the SI milli- (m) prefix, which denotes division by a factor of one thousand (×10−3). To avoid confusion, many companies and engineers use the notation "MMBtu" or "mmBtu" to represent one million BTU (although, confusingly, MM in Roman numerals would traditionally represent 2,000) and in many contexts this form of notation is deprecated and discouraged in favour of the more modern SI prefixes. Alternatively, the term therm may be used to represent 100,000 (or 105) BTU, and quad for 1015 BTU. Some companies also use BtuE6 in order to reduce confusion between 103 BTU and 106 BTU. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「British thermal unit」の詳細全文を読む スポンサード リンク
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