Sources for first article summaryChoose one energy/climate related

article from either:

Sept. 2006 Scientific American or July 2008 Physics Today

http://www.libraries.iub.edu/index.php?pageId=92 (Swain library website)

Swain Hall West- 2nd Floor

Swain Hall Library http://www.libraries.iub.edu/index.php?pageId=92

Chapter 5 Home Energy Cons.

• Thermal Resistance:Q/t = kAT/L =: AT/R

R:= L/k• This is useful because it folds in both the

material property (k) and the thickness of the insulating layer (L), AND if you combine layers, then the thermal resistances (R) simply add, as shown on the next slide.

R-value for a typical wall

See table 5.2 in H&K for typical values of building materials

Some typical R valuesMaterial Thickness R (ft2.h.oF/Btu)

Hardwood 1” 0.81

Concrete block 8” 1.25

1-pane window 0.125” 0.88

2-pane window 0.5” air 1.72

Fiberglass 7” 21.8

Polyurethane 1” 6.3

Nylon carpet 1” 2.0

Wood siding 0.5” 0.81

Plywood 0.5” 0.627

Plasterboard 0.5” 0.45

Steel 1” 0.0032

Infiltration

Q/t = 0.018 Btu/ft3.Fo V K T

Here K is the number of “Air exchanges per hour”and V is the interior volume of the house/building.Note: some exchange of airis necessary (you need to breath!), and this is not readily apparent in this figure.

Chapter 5 Degree Days• Note that for conduction and convection the rate

of heat exchange is proportional to |Tout-Tin|, and so the total heat exchanged over a season will be proportional to the average temperature difference times the number of days experiencing that temperature difference.

• The # of “degree-days” is just a simple way to perform this average:

Q/t = AT/R and Q/t = 0.018 V K T• Multiply through by t, the product t,

averaged over a month or season, is the number of “degree days” (DT computed with respect to some reference temp for the home interior).

Degree-Days Heating/Cooling

http://www.ersys.com/usa/18/1836003/wtr_norm.htm

Indianapolis

Exam I Review• EXTRA OFFICE HOURS:

– Tuesday 11:00 to NOON AND 2:00 to 3:30– WED 2:00 to 3:45– THURS: 8:15 TO 9:00

• Covers Chapter 1 section A through Chapter 5 section E• 22 questions, 5 points each• About half involve no calculation, only about 5 or 6

involve calculations with more than 1 step.• Only 4-6 questions from each other chapter [slightly

fewer for chpt. 3 (short) and chpt. 5 (incomplete)].• Exam cover page is on ONCOURSE. Does NOT give

simple formulae that are really just definitions (e.g. Power=W/t; =(useful E transferred)/(total energy input))

• CLOSED BOOK, CLOSED NOTES• Calculators are allowed (but not cell phones!).

Key points so far

• Chapter 1– Working with numbers, units, uncertainties– Energy: definition, patterns of use, types, sources– Exponential growth: annual and continuous compounding,

doubling time, – Hubbert’s curve– Renewable/non-renewable energy resources– Energy conservation

• Chapter 2– Energy Conversions– Newton’s laws– Mechanical Energy: Kinetic, Potential– Work– Power– Electrical suppliers cost structure

Key points so far (cont.)

• Chapter 3– First law of Thermodynamics– Efficiency of energy conversions– Energy content of fuels and unit conversions– Lighting (as an example of new technology giving better

efficiency)• Chapter 4

– “Zeroth” law of Thermodynamics (the real meaning of temperature)

– Second Law of Thermodynamics– Heat Capacity and specific heats– Latent Heats (fusion and vaporization)– Heat transfer mechanisms: conduction, convection, radiation– Radiant transfer (higher T, more light, shorter wavelength).– Reversibility – Heat Engines and Carnot Efficiency

Key points so far (cont.)

• Chapter 5 (through section E).– Conduction as a source of inefficiency in

building climate control (R values)– Control of heat transfer as a way of improving

efficiency (convection, radiation, conduction).– Infiltration– Degree-day (concept thereof)

Example questions

1. (5 points) Provide names and brief descriptions for 4 different forms of energy and list with each one the physical quantity that is associated with it.

2. (5 points) A 150 W light bulb was accidentally left on in an attic for 14 full days. If the cost of electricity is $0.078/kWh, how much did this oversight cost the homeowner?

3. (5 points) Of the three forms of heat transfer we considered in class, which one does not require a physical link (i.e. one made up of atoms) between the hot and cold object? For this mechanism, how does the rate of energy transfer depend on the temperature of the hot object (for a fixed temperature of the cold object)?