Seite - 187 - in Clean Water Using Solar and Wind - Outside the Power Grid

Conversion of units 187 In 1948 it was decided that, since heat is a form of energy, the SI unit for heat should be the same as for all other forms of energy, the joule. One cal is defined to be 4.1860 J (exactly) with no reference to heating of water. (The “calorie” used in nutrition is really a kilocalorie.) The relationship between the kWh and the Btu depends upon which “Btu” is used. 1 megajoule (MJ) = 106 J = 0.278 kWh = 947.8 Btu; 1  kWh = 3412 Btu 1,000 Btu = 0.293 kWh; 100,000 Btu = 1 therm The unit “quad” is often used in the U.S.: 1 quad = 1 quadrillion (1015) Btu = 1.05506 * 1012 megajoule (MJ) = 1.055 EJ (note that quadrillion in Europe = 1024) A2.4 VOLUME, AREA AND LENGTH Some common metric length units: 1 micron = 1 micrometre = 10−6 m 1 angstrom (Å) = 10−10 m (named after the Swedish physicist A.  J.  Ångström, 1814–1874) 10 Å = 1 nm = 10−9 m Metric area units: 1 hectare = 1002 m2 1 km2 = 10002 m2 Non-metric units: 1 US gallon = 3.78 litres; 1 UK gallon = 4.546 litres = 1.2 US liquid gallons 1 American barrel = a liquid measure of oil, usually crude oil = 42 US gallons = 159 litres Barrel of oil equivalent refers to the energy equal to a barrel of crude oil, = 5.8*106 Btu or 6119 MJ Acre-foot (the volume of one acre (4,047 m2 or 43,560 ft2) with the  depth of 1 foot (0.305 m)) is often used, particularly in the Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user