WHAT IS ENERGY?
Energy is a substance (or property) which can be converted into work. The two laws which energy follows are:
- Energy cannot be created or destroyed (1st Law)
- When converting heat into work the conversion cannot be complete (2nd Law)
ENERGY AND POWER
Power = Energy/Time
- Power is Energy per unit time.
- Energy is related to power as gallons are related to gallons per minute.
ENERGY AND POWER TERMS
- British Thermal Unit (Btu) - A Btu is the amount of energy required to raise the temperature of one pound of water 1 degree Fahrenheit.
- therm –100,000 Btu, heat energy sources such as natural gas and steam may be sold in therms
- Kilowatt (kW) – a measure of power equal to 1,000 watts, it is also equal to 3,412 Btu/hr
- Kilowatt-hour (kWh) - A kilowatt-hour is the quantity of energy delivered when power flows at the rate of one kilowatt for one hour. It is equal to 3,412 Btu.
- Cooling Ton - A cooling ton is 12,000 Btu/hr. It is the rate of cooling required to produce one ton of ice in a 24 hour period. The capacity of most air conditioning systems are expressed in tons.
SOURCES OF ENERGY
- The Sun
- Fossil Fuels
- Renewable Fuels
- Wind, Solar, Hydropower, Biomass
- Nuclear Reactions
- Nuclear Decay
- Nuclear Fission
- Nuclear Fusion (someday?)
HOW MUCH ENERGY IS IN?....
| Energy Source |
Energy Content (Btu) |
Units |
| Sunlight |
200 Btu |
per hour per square foot |
| Wind |
75 Btu |
per hour per square foot of wind turbine swept area in 22 mile per hour wind. |
| Biomass |
7,000 Btu |
per pound (value is for switchgrass) |
Wood |
8,000 to 10,000 Btu |
per pound |
| Coal (Anthracite) |
14,000 to 15,000 Btu |
per pound |
| Coal (Bituminous) |
10,500 to 14,000 Btu |
per pound |
| Oil (#2 Fuel) |
137,000-141,800 Btu |
per gallon |
| Natural Gas |
950 to 1,150 Btu |
per cubic foot |
| Gasoline |
109,000 -125,000 Btu |
per gallon |
| Kerosene |
130,000 to 140,000 Btu |
per gallon |
| Nuclear Fuel (Uranium) |
35,000,000,000 Btu |
per pound Uranium-235 |
ENERGY BENCHMARKING
- Use your energy bills to estimate:
- $/sf per year (quick and dirty use with caution, it depends on your utility's rates)
- around $1/sf = good
- $1 to $2/sf = fair to slightly poor (typical about $1.89/sf)
- $2 to $3/sf = probably room for improvement
- $3/sf and above = not good (unless there is a process)
- kBtu/sf per year –more accurate than dollar metric –can use ENERGY STAR TargetFinder
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