Some Basic Concepts of Energy
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Transcript of Some Basic Concepts of Energy
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Kenneth M. Klemow, Ph.D.Wilkes University
Prepared for BIO/EES 105
Energy in our World
II. Concepts relating to heat
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Property of all systems Based on kinetic energy of molecules
◦ Heat is TOTAL energy of all molecules in a system Typically measured in Calories or BTUs
◦ Temperature is AVERAGE energy of all molecules in a system Typically measured in degrees
Property of all systems Based on kinetic energy of molecules
◦ Heat is TOTAL energy of all molecules in a system Typically measured in Calories or BTUs
◦ Temperature is AVERAGE energy of all molecules in a system Typically measured in degrees
Fahrenheit Celsius Kelvin
Water freezes 32 0 273
Water boils 212 100 373
Human body 98.6 37 310
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Within a system◦ Increase in heat causes increase in temperature◦ Governed by equation
Within a system◦ Increase in heat causes increase in temperature◦ Governed by equation
http://www.thekitchn.com/thursday-giveaway-instantread-56533
Q = mc(T)Where:Q – heat (cal., BTU)M – massC – specific heatT – change in temp.
Q = mc(T)Where:Q – heat (cal., BTU)M – massC – specific heatT – change in temp.
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Between systems◦ Not related◦ One system can have higher heat yet lower
temperature
Between systems◦ Not related◦ One system can have higher heat yet lower
temperature
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Heat can move from one system to another◦ Only when there is a temperature difference◦ Move from higher temperature to lower
temperature object.
Heat can move from one system to another◦ Only when there is a temperature difference◦ Move from higher temperature to lower
temperature object.
http://www.ces.fau.edu/nasa/
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http://www.grc.nasa.gov/WWW/Wright/airplane/heat.html
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Measure of change in temperature as a result of heat absorbed.◦ Metric system: # joules needed to raise 1 kg of
material by 1 oC.◦ English system: # BTUs needed to raise 1 lb of
material by 1oF.
Measure of change in temperature as a result of heat absorbed.◦ Metric system: # joules needed to raise 1 kg of
material by 1 oC.◦ English system: # BTUs needed to raise 1 lb of
material by 1oF.
http://addheat.wordpress.com/2011/03/24/
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Vaporizationliquid <-> gas
For water: 540 kcal / kg
Vaporizationliquid <-> gas
For water: 540 kcal / kg
Fusionsolid <-> liquid
For water: 80 kcal / kg
Fusionsolid <-> liquid
For water: 80 kcal / kg
http://blogs.yis.ac.jp/19miyoshiay/ http://ww.abc6.com/story/
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Heat absorbed or released depending on direction
Important in heat balance at earth’s surface, regulating temperatures of organisms
Heat absorbed or released depending on direction
Important in heat balance at earth’s surface, regulating temperatures of organisms
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Energy of molecules directly transferred to adjoining molecules◦ Causes them to gain heat
Energy of molecules directly transferred to adjoining molecules◦ Causes them to gain heat
http://www.physicstutorials.org/
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High inmetalsHigh inmetals
Intermediate in brick
Intermediate in brick
Low in styrofoam
Low in styrofoam
These make good insulatorsThese make
good insulators
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Occurs in liquids and gases Warm liquid / gas becomes less dense and
rises through medium◦ Creates eddy currents◦ Carries much energy
Occurs in liquids and gases Warm liquid / gas becomes less dense and
rises through medium◦ Creates eddy currents◦ Carries much energy
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Involves electromagnetic waves Produced by charged particles Travel at speed of light Wave components include:
◦ Amplitude◦ Frequency◦ Wavelength
Electric and magnetic waves are perpendicular to field of travel
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Velocity (m/s) = wavelength (m) x frequency (#/second)
As wavelength increases, frequency decreases
Velocity (m/s) = wavelength (m) x frequency (#/second)
As wavelength increases, frequency decreases
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More energyMore energy
Less energyLess energy
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When radiation strikes a body, it causes that body to start radiating, itself.◦ Will the wavelengths of that energy likely to be
longer or shorter than the energy striking it?◦ When sunlight hits the earth, will the re-radiated
energy be more likely to be in the form of: Ultraviolet, Visible, Infrared energy
◦ When light strikes a chlorophyll solution, some of the energy is reradiated as visible light. What is the most likely color for that light? Blue, Green, or Red
When radiation strikes a body, it causes that body to start radiating, itself.◦ Will the wavelengths of that energy likely to be
longer or shorter than the energy striking it?◦ When sunlight hits the earth, will the re-radiated
energy be more likely to be in the form of: Ultraviolet, Visible, Infrared energy
◦ When light strikes a chlorophyll solution, some of the energy is reradiated as visible light. What is the most likely color for that light? Blue, Green, or Red
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Conduction, convection and radiation all occur in windless environment.◦ Convection sets up eddies of moving air
Adding wind can rapidly remove energy by mass transfer.
Objects often covered by boundary layer of still air◦ Conduction and convection predominate
Increasing wind speed causes boundary layer to become thinner.◦ Transfer of energy greater when wind increases
Conduction, convection and radiation all occur in windless environment.◦ Convection sets up eddies of moving air
Adding wind can rapidly remove energy by mass transfer.
Objects often covered by boundary layer of still air◦ Conduction and convection predominate
Increasing wind speed causes boundary layer to become thinner.◦ Transfer of energy greater when wind increases
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Indoor environments often more comfortable than outdoor.◦ Stay dry◦ Regulate light◦ Regulate temperature
People prefer temperatures between 65-75oF◦ When T<65, we heat◦ When T>75, we cool
Indoor environments often more comfortable than outdoor.◦ Stay dry◦ Regulate light◦ Regulate temperature
People prefer temperatures between 65-75oF◦ When T<65, we heat◦ When T>75, we cool
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When cold we add heat via radiators, fireplaces, space heaters
Heat generators warm the air via radiant energy
If air carried away, need to warm the new air.◦ Energy needed = 0.018 BTU / ft3 / oF
When cold we add heat via radiators, fireplaces, space heaters
Heat generators warm the air via radiant energy
If air carried away, need to warm the new air.◦ Energy needed = 0.018 BTU / ft3 / oF
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Imagine you come upon a small, uninhabited, single-roomed cabin in the winter◦ Height = 10’◦ Width = 20’◦ Length = 20’
It’s 15oF outside, you want to heat it to 65oF. How many BTUs will it take?
Imagine you come upon a small, uninhabited, single-roomed cabin in the winter◦ Height = 10’◦ Width = 20’◦ Length = 20’
It’s 15oF outside, you want to heat it to 65oF. How many BTUs will it take?
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If energy costs $30.00 / million BTUs, how much will initially heating the cabin cost?
If energy costs $30.00 / million BTUs, how much will initially heating the cabin cost?
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Heat losses due to conduction through the walls.
Heat losses due to infiltration of cold air.
Heat losses due to conduction through the walls.
Heat losses due to infiltration of cold air.
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Building has four walls, a ceiling, and a floor◦ Heat will be lost through each◦ Go back to formula Q/t = (k x A x T)
k = thermal conductivity of wall / floor / ceiling = thickness
For building material, we don’t consider thermal conductivity, per se.
Instead we express as thermal resistance (R value), where R = /k.◦ Units = ft2-hr-oF/Btu
Building has four walls, a ceiling, and a floor◦ Heat will be lost through each◦ Go back to formula Q/t = (k x A x T)
k = thermal conductivity of wall / floor / ceiling = thickness
For building material, we don’t consider thermal conductivity, per se.
Instead we express as thermal resistance (R value), where R = /k.◦ Units = ft2-hr-oF/Btu
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Material Thickness R value
Plywood 0.5” 0.62
Fiberglass insulation
3.5” 10.9
Hardwood floor
0.75” 0.68
Asphalt shingle
---- 0.21
Wood siding 0.5 0.81
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Remember R = /k◦ So 1/R = k/
Remember Q/t = (k x A x T)◦ So Q/t = k/ (A x T)◦ And then 1/R (A x T)◦ And then Q = 1/R (A x T x t)
Remember R = /k◦ So 1/R = k/
Remember Q/t = (k x A x T)◦ So Q/t = k/ (A x T)◦ And then 1/R (A x T)◦ And then Q = 1/R (A x T x t)
Q = 1/R (A x T x t)
http://www.kfiam640.com/
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How much energy (in BTU) is lost through a wall measuring 20’ x 10’ in an hour.
Assume:◦ Wall covered by 0.5” plywood◦ It’s 65oF inside and 15oF outside
How much energy is lost over the course of 24 hours?
How much energy (in BTU) is lost through a wall measuring 20’ x 10’ in an hour.
Assume:◦ Wall covered by 0.5” plywood◦ It’s 65oF inside and 15oF outside
How much energy is lost over the course of 24 hours?
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How much energy (in BTU) is lost from the entire house by conduction in an hour?◦ Hint 1: Calculate loss through the four walls◦ Hint 2: Calculate loss through the ceiling◦ Hint 3: Calculate loss through the floor◦ Hint 4: Add together
Then calculate loss from the house in a 24 hour day.
How much energy (in BTU) is lost from the entire house by conduction in an hour?◦ Hint 1: Calculate loss through the four walls◦ Hint 2: Calculate loss through the ceiling◦ Hint 3: Calculate loss through the floor◦ Hint 4: Add together
Then calculate loss from the house in a 24 hour day.
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What is daily cost to heat house if energy = $30.00 / million BTUs?
What would be the monthly cost?
What is daily cost to heat house if energy = $30.00 / million BTUs?
What would be the monthly cost?
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Go back to case of wall. How much heat was lost in an hour when wall was 0.5” plywood?
Now suppose that your wall was composed of 3.5” of fiberglass insulation.◦ Hint 1: Find R value for 3.5” of fiberglass◦ Hint 2: Recalculate based on that value.◦ Express the difference here____________
If wall was 0.5” plywood AND 3.5” insulation, add the two R values together.◦ Then recalculate
Go back to case of wall. How much heat was lost in an hour when wall was 0.5” plywood?
Now suppose that your wall was composed of 3.5” of fiberglass insulation.◦ Hint 1: Find R value for 3.5” of fiberglass◦ Hint 2: Recalculate based on that value.◦ Express the difference here____________
If wall was 0.5” plywood AND 3.5” insulation, add the two R values together.◦ Then recalculate
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What would be hourly loss if all four walls were covered by 3.5” insulation?
What would be hourly loss if ceiling was covered by asphalt shingle above plywood?
What would be hourly loss if floor covered by 0.75” hardwood floor?
Next calculate over course of a day Next calculate over course of a month
What would be hourly loss if all four walls were covered by 3.5” insulation?
What would be hourly loss if ceiling was covered by asphalt shingle above plywood?
What would be hourly loss if floor covered by 0.75” hardwood floor?
Next calculate over course of a day Next calculate over course of a month
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Premise◦ Houses leak warm air, and allow
cold air to enter◦ That air needs to be warmed up.◦ Formula for calculating this:
Premise◦ Houses leak warm air, and allow
cold air to enter◦ That air needs to be warmed up.◦ Formula for calculating this:
Qinfil = 0.018 x V x KT x t
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What would be energy loss in an hour, if all of the air is exchanged over the course of an hour?
How much energy would be lost over the course of 24 hours?
How much energy would be lost if the house leaked air at 1/10 the rate?
What would be energy loss in an hour, if all of the air is exchanged over the course of an hour?
How much energy would be lost over the course of 24 hours?
How much energy would be lost if the house leaked air at 1/10 the rate?
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Basis for home energy audit! Basis for home energy audit!
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Renewable vs nonrenewable Traditional vs new energy Commercialized vs non-commercialized Centralized vs distributed generation On-grid vs off-grid
Renewable vs nonrenewable Traditional vs new energy Commercialized vs non-commercialized Centralized vs distributed generation On-grid vs off-grid
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Primary energy is the energy as it is available in the natural environment, i.e. the primary source of energy.
Secondary energy is the energy ready for transport or transmission.
Final energy is the energy which the consumer buys or receives.
Useful energy is the energy which is an input in an end-use application.
Primary energy is the energy as it is available in the natural environment, i.e. the primary source of energy.
Secondary energy is the energy ready for transport or transmission.
Final energy is the energy which the consumer buys or receives.
Useful energy is the energy which is an input in an end-use application.
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energy technology examples
Primary coal, wood, hydro, dung, oil
Conversion power plant, kiln, refinery, digester
Secondary refined oil, electricity, biogas
Transport/transmission
trucks, pipes, wires
Final diesel oil, charcoal, electricity, biogas
Conversion motors, heaters, stoves
Useful shaft power, heat
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CO2H2O C6H12O6
Carbon reduction
Energy
Energy
Carbon oxidation
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Energy Stored
Energy consumed
Energy Respired
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Energy lost at each step
(usually 90%)
Energy lost at each step
(usually 90%)