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# Units of Measurement for Secondary Energy Sources

Whatever its source, secondary energy (or energy carriers) can be quantified by a number of units that are widely used for electricity and heat. Electrical power (measured in watts) equals voltage (measured in volts) times current (measured in amps). © AFP

## Measuring Heat

• The (J) is an SI unit. It is the universal unit for quantifying energy, whether in the form of work (the movement of a mass propelled by a force) or . The joule is a very small unit unsuitable for measuring large amounts of energy. This is why its multiples are more frequently used, such as the gigajoule (GJ), where 41.855GJ = 1 toe.
• The calorie (cal), sometimes used to measure a quantity of heat, is a non-SI unit. A calorie is the quantity of heat required to raise the temperature of one gram of water by one degree Celsius under normal atmospheric conditions of 1013.25 hPa from a standard initial temperature of 15°C. The thermie (th) — a multiple of the calorie, equal to 1 million calories — is sometimes used by heating engineers in Europe.
• The British Thermal Unit (BTU) is used in the United Kingdom. It corresponds to the quantity of heat required to raise the temperature of a pound of water by 1 degree Fahrenheit (°F). This is equivalent to heating 450 grams of water under normal atmospheric pressure of 1013.25 hPa from a standard initial temperature of 58.1°F, or 14.5°C.

## The Watt, Used to Measure Electricity

• The (W) is used to measure electrical , or the electrical energy produced per unit of time. One watt is equivalent to one joule per second. The kilowatt-hour (kWh) is used to express the power consumption of a household or an item of equipment. This unit is equivalent to electrical power of 1 watt used for one hour, or 3.6 MJ. Annual consumption, excluding heating, for a family of four people is about 7,000 kilowatt-hours.