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In the United States, U-value is expressed as British thermal units (Btu) per hour-square feet-degrees Fahrenheit: Btu/(h⋅ft 2 ⋅°F) Within this article, U-values are expressed in SI unless otherwise noted. To convert from SI to US customary values, divide by 5.678. [1]
Architects and engineers call the resulting values either the U-Value or the R-Value of a construction assembly like a wall. Each type of value (R or U) are related as the inverse of each other such that R-Value = 1/U-Value and both are more fully understood through the concept of an overall heat transfer coefficient described in lower section ...
Last, multiply the original expression of the physical value by the fraction, called a conversion factor, to obtain the same physical value expressed in terms of a different unit. Note: since valid conversion factors are dimensionless and have a numerical value of one, multiplying any physical quantity by such a conversion factor (which is 1 ...
The SI units are defined by declaring that seven defining constants [1]: 125–129 have certain exact numerical values when expressed in terms of their SI units. The realisation of the definition of a unit is the procedure by which the definition may be used to establish the value and associated uncertainty of a quantity of the same kind as the ...
The SI (metric) unit of R-value is kelvin square-metre per watt (K⋅m 2 /W or, equally, °C⋅m 2 /W), whereas the I-P (inch-pound) unit is degree Fahrenheit square-foot hour per British thermal unit (°F⋅ft 2 ⋅h/BTU). [13] For R-values there is no difference between U.S. and Imperial units, so the same I-P unit is used in both.
Traditional Burmese units of measurement are used in Burma, with partial transition to the metric system. U.S. units are used in limited contexts in Canada due to the large volume of trade with the U.S. There is also considerable use of imperial weights and measures, despite de jure Canadian conversion to metric.
James Clerk Maxwell played a major role in developing the concept of a coherent CGS system and in extending the metric system to include electrical units. Each variant of the metric system has a degree of coherence—the derived units are directly related to the base units without the need for intermediate conversion factors. [18]
The British imperial units and U.S. customary units for both energy and work include the foot-pound force (1.3558 J), the British thermal unit (BTU) which has various values in the region of 1055 J, the horsepower-hour (2.6845 MJ), and the gasoline gallon equivalent (about 120 MJ). Log-base-10 of the ratios between various measures of energy