**Introduction**: first, we define some *basic units* to measure general
properties of any energy carrier or source
(like fuel and electricity). Then come a few more *specific units*
for specific energy sources, like nuclear energy and oil.
The *International System of Units
(SI)* is used whenever appropriate, e.g. joule == Ws for energy.
Ultimately, the SI units are based on
three core ones - meter (length), kilogram (mass), and second (time).

**List of energy units:**

*Calorie ("cal", cal-15th_degree)*== amount of thermic energy required to heat 1 gram of air-free water from 14.5 to 15.5 degrees C at a constant atmospheric pressure of 1 bar.

Nowadays, 1 cal-intl =~=*4.1868 joule*(SI unit).

NB: cal means implicitly "kilo"cal, when applied to food and fysiology.*Btu ("British Thermal Unit")*== amount of thermic energy required to heat one pound (BP =~= 0.454 kg) of air-free water from 39 to 40 degrees F (Fahrenheit) at a constant atmospheric pressure of 1 bar.

Digression: We would expect that one Btu becomes: 454 * 5 / 9 cal = 252.2222 cal, vs. the actual value of 251.9967 cal, or less than 0.1 % off.

Nowadays, 1 Btu-intl =~=*1055.06*joule (SI unit).*Therm-UK*(pronounced "thm") ==*100 000 Btu*(aggregated unit).*Cubic Foot*("CF") == amount of thermic energy released by burning such a volume (not mass!) of average natural gas =~=*1020 Btu*.*Cento Cubic Feet*("CCF" or "100 CF") =~=*102 000 Btu*.*Therm-US*==*heat energy released by burning one CCF of nat'l gas*=~=*102 000 Btu*,

i.e. 2 % more than a Therm-UK.- In SU-units then, a
*Therm-UK*=~= 100*1000 * 1055 joule ==

105.5 mill. joule (=Ws) == (105 500 K W) / (3600) h ==*29.31 kWh*; or inversely:

1 kWh = 3 600 000 J / (1055.06 J/Btu) = 3412 Btu.

1 kWh = 3 600 000 J / (4.1868 J/cal) = 852 000 cal = 852 kcal.

1 cal =~= 0.00396831 Btu; 1 Btu =~= 252 cal.

1 joule = 0.252 cal; 1 joule = 0.00094281 Btu (or 1 kJ = 0.94281 Btu).E = m * c**2 => 30 tWh/kg.

Electron Volt = ca. 10**(-19) joule.

- Volume of a
*CF*== (0.3048m)**3 == 0.02832 m3 == 28.32 liter. - Volume of a
*CCF*== 100 that of the CF == 2832 liter. - The average mass (i.e. "weight") of a corresponding CCF energy carrier,
here natural gas, is calculated from its constituents, typically:

75 % methane (w/ specific weight 0.717 kg/m3),

15 % ethane (1.28),

5 % propane/butane etc. (ca. 1.5),

5 % other gases such as CO2, H2O, sulfor etc. (ca. 1.3).

We shall assume an*average specific weight of 0.8 kg/m3*, cf. air weighing 1.3 kg/m3. - The volume of a
*therm-US or CCF*== 2832 liter, and weighing 2.832 m3 * (0.8 kg/m3) == 2.0xx kg. - Energy per volume or weight:
Burning an average CCF gives a thermic energy of 29.31 kWh,

i.e. 10.8?? kWh/m3 or 13.5 kWh/kg. *25 000 therm/day*is an effect unit much used in UK = 30 538 KW.

reidar.conradi@idi.ntnu.no Last modified: Fri Aug 5 16:07:45 MEST 2011