Lonny Grafman, Environmental Resources Engineering

Basic Units

Exercise

• In 30 minutes, as a group, bring back a photo or video of:

Energy Unit Definitions

Unit Definition

Joule (J)Work done by the force of 1 Newton acting over a

distance of 1 meter (J = Nm = kgm2/s2)

calorieEnergy required to raise the temperature of 1 gram

of water by 1°C

kcal (Calorie) 1,000 calories

Kilowatt-hour (kWh)

Energy delivered when 1 kilowatt of power is delivered for a period of 1 hour

British Thermal Unit

(BTU)

Energy required to raise the temperature of 1 pound (lb) of water by 1°F

Therm 105 BTUs

Quad 1015 BTUs

http://fti.neep.wisc.edu/neep602/FALL97/LEC3/IMAGES/Table1Definitions.gif

Unit Definition

bblEnergy contained in a barrel of oil

(42 gallons)

m3 gasEnergy contained in a cubic meter of natural gas

at standard temperature and pressure (1 atmosphere & 273 K)

ft3 gasEnergy contained in a cubic foot of natural gas

at standard temperature and pressure (1 atmosphere & 273 K)

terawatt-year (TWy)

Energy delivered when 1 terawatt (1012 Watts) of power is delivered for a period of 1 year

Energy Unit Definitions (a few more…)

http://fti.neep.wisc.edu/neep602/FALL97/LEC3/IMAGES/Table1Definitions.gif

A BTU?

Energy Conversion Factors (a few examples)

1st Unit 2nd Unit

1 BTU =1055 Joules (J),252 calories

1 x

1 Joule = 9.478x10-4 BTU A baseball 2ft above ground

1 calorie = 4.187 Joules (J) ~ 1 gram of water by one degree Celsius

1 kWh = 3.6 megajoules (MJ) ~ 12 cents

1 bbl = 6.1 gigajoules (GJ)

1 Mtoe = 41.9 petajoules (PJ)

1 m3 gas = 37.3 megajoules (MJ)

A cliff bar?

= 252 Calories = 252 kilocalories = 1000 BTUs (1 BTU = 252 cal) = 1000

Watts the deal?

http://www.appropedia.org/Power_and_energy_basics

Some Models are Simple (e.g. estimate of gasoline used when driving)

driven miles

gallon x

trip

driven miles rip)(gallons/t on trip used gas

Source: Koomey, 2001

Using models: Let’s say that you are planning to drive 1,000 miles in a car that typically gets 25 mpg. How much should you plan to spend on gas on the trip?

driven miles

gallons x

trip

driven miles x

gallon

price gas ($/trip)money gas

Some Models are Simple (e.g. estimate of gasoline used when driving)

Source: Koomey, 2001

Refining the model: what if the 1,000 mile trip consists of 90% highway driving and 10% city driving, and your car actually gets 30 mpg highway and 22 mpg city? How much should you plan to spend now and how does this differ from the previous result?

mileshighway

gallonsx

trip

miles totalhwy x%

driven milescity

gallons x

trip

miles totalcity x%

x gallon

price gas

trip

($)money gas

Back-of-the-Envelope Estimates(a very powerful tool)

1) How many gallons gasoline are used on average by light duty vehicles (passenger cars, trucks, and SUVs) in the USA each day?

• Unit conversions: – Mundane, but critically important for energy analysis– Practice makes perfect (but don’t spend all your time

memorizing conversion factors)

• Simple mathematical models and “back of the envelope” calculations– Most energy problems have a quantitative dimension (though

numbers are rarely the whole story)

Orders of Magnitude (prefixes)pico- x 10-12 p

nano- x 10-9 n

micro- x 10-6

milli- x 10-3 m

-- x 100

kilo- x 103 k

mega- x 106 M

giga- x 109 G

tera- x 1012 T

peta- x 1015 P

exa- x 1018 E

See http://www.appropedia.org/Powers_of_10 for more.

Energy Unit Definitions

Unit Definition

Joule (J)Work done by the force of 1 Newton acting over

a distance of 1 meter (J = Nm = kgm2/s2)

ergWork done by the force of 1 dyne acting over a

distance of 1 cm (10-7 Joules)

calorieEnergy required to raise the temperature of 1

gram of water by 1°C

kcal (Calorie) 1,000 calories

Kilowatt-hour (kWh)

Energy delivered when 1 kilowatt of power is delivered for a period of 1 hour

British Thermal Unit (BTU)

Energy required to raise the temperature of 1 pound (lb) of water by 1°F

Therm 105 BTUs

Quad 1015 BTUs

http://fti.neep.wisc.edu/neep602/FALL97/LEC3/IMAGES/Table1Definitions.gif

a Joule is the

• work done to produce one watt continuously for one second• kinetic energy of a 2 kg mass moving at 1 m/s. (given by E = ½mv²)• potential energy of a 1 kg mass 1 m high in a gravitational field of 1

m/s². Earth's gravity is 9.81 m/s² at sea level, so 1 kg at 1 m has a potential energy of 9.81 joules.

• energy required to lift a small apple one meter straight up.• amount of heat energy that a quiet person generates every

hundredth of a second.• energy required to heat one gram of dry, cool air by 1 degree Celsius.