Section II- Measuring Energy
a.) Energy Values
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British Thermal Unit (BTU) is the amount of energy required to raise the
temperature of one pound of water one degree Fahrenheit. The content of
different energy sources can be measured in Btu.
o Examples:
 Sunlight- 200 Btu (per hour per square foot)
 Wood- 8,000-10,000 Btu (per pound)
 Natural Gas- 950- 1,150 Btu (per cubic foot)
Power: Energy per unit in time. Power can refer to any type of energy.
Therm: (100,000 Btu) heat energy sources such as natural gas and steam
may be sold in therms
MMbtu: 1,000,000 Btu
Decatherm: 10 therms, or 1 MMBtu
Kilowatt (kW): A measure of electrical power equal to 1,000 watts. It’s also
equal to 3,412 Btu/hr.
Kilowatt-hour (kWh): The quantity of energy delivered when power flows at
a rate of one kilowatt for one hour. It’s equal to 3,412 Btu.
Horsepower: A measure of mechanical work per unit time, sometimes
expressed as brake horsepower (bhp). It is used to describe the rate of
work output by devices such as motors, engines, and turbines, or the rate
of work input required by devices such as pumps and fans. One
horsepower is equal to 2,545 Btu/hr.
Boiler Horsepower (BHP): The rate of boiler heat output may sometimes
be given in boiler horsepower. This is left over from the days when many
boilers were used to provide steam for steam engines which were then
used to produce mechanical horsepower. A boiler horsepower may be
designated as BHP and should not be confused with brake horsepower
which is designated as bhp. If you see BHP or bhp on a boiler, it’s boiler
horsepower. A boiler horsepower is equal to 33,480 Btu/hr.
Cooling Ton: The rate of cooling required to produce one ton of ice in a
24-hour period. It is equal to 12,000 Btu/hr. The capacity of most air
conditioning systems are expressed in tons.
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b.) Conversion Factors
One of the most fundamental and useful energy management skills is the ability
to express values of energy and power in different forms. The word “express” is
used here in the same sense as translating in language. Each of the above
definitions contain a conversion factor. The following examples illustrate how
these conversion factors are used:
Cancelling Out Units: Units cancel out the same as fractions. For example…
3,412 Btu x 1 kWh = 3,412 Btu
kWh
Day
Day
and
3,412 Btu
30 days
1 therm
1.024 therm
Day
x month x 100,000 Btu = month
Useful Conversions:
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Energy (Btu conversions):
o 1 kWh= 3,412 Btu
o 1 therm= 100,000 Btu
o 1 cubic foot gas= 1,020 Btu
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Power (Btu/hr):
o MBH= 1,000 Btu/hr
o 1 ton= 12,000 Btu/hr
o 1 hp= 2,545 Btu/hr
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Power (Boiler)
o 1 hp= 33.4 MBH
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