Kenneth M. Klemow, Ph.D.Wilkes University

Prepared for BIO/EES 105

Energy in our World

II. Concepts relating to heat

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

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.

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

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/

http://www.grc.nasa.gov/WWW/Wright/airplane/heat.html

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/

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/

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

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/

High inmetalsHigh inmetals

Intermediate in brick

Intermediate in brick

Low in styrofoam

Low in styrofoam

These make good insulatorsThese make

good insulators

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

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

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

More energyMore energy

Less energyLess energy

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

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

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

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

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?

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?

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.

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

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

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/

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?

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.

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?

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

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

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

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?

Basis for home energy audit! Basis for home energy audit!

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

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.

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

CO2H2O C6H12O6

Carbon reduction

Energy

Energy

Carbon oxidation

Energy Stored

Energy consumed

Energy Respired

Energy lost at each step

(usually 90%)

Energy lost at each step

(usually 90%)