Exam I results P120/2007Histogram

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30 40 50 60 70 80 90 100 115

Bin

Freq

uenc

y

Frequency

Avg: 85.9 = 74.6%

Infiltration

Q = 0.018 Btu/ft3.hr.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.

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

Hardwood 1” 0.81Concrete block 8” 1.251-pane window 0.125” 0.882-pane window 0.5” air 1.72Fiberglass 7” 21.8Polyurethane 1” 6.3Nylon carpet 1” 2.0Wood siding 0.5” 0.81Plywood 0.5” 0.627Plasterboard 0.5” 0.45Steel 1” 0.0032

Degree-Days Heating/Cooling

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

Indianapolis

Price of Natural Gas(dollars/MBtu wholesale I believe)

http://futures.tradingcharts.com/chart/NG/W

“Low-e” (emissivity) coatings on windows

Conducting oxide

Double metal layer Single metal layer

Phys. Today Nov. 2000

Heat Pumps

Coefficient of Performance

• As the outside temperature goes down, the performance of a heat pump also goes down. You can, however, design the system to exchange heat with the earth instead of the air (geothermal systems sold locally)!

http://eosweb.larc.nasa.gov/EDDOCS/images/Erb/components2.gif

Spectrum of Solar radaition at the Earth’s surface

H&K fig 6.2

Components of solar Energy on Earth

H&K fig 6.7

Insolation (Btu/ft2.day)Horizontal surf.surf. at = latitudeMean monthly T (oF)

H&K Appendix D

Fundamental components(any solar energy system)

• Solar collector• Storage system of some sort (to account

for night and cloudy days).• Energy transfer fluid (which could be air,

as in some systems we have seen, antifreeze, or even electrons)

• Auxilliary/backup system (typically)

Fundamental components(any solar energy system)

• Solar collector• Storage system of some sort (to account for

night and cloudy days).• Energy transfer fluid (which could be air, as in

some systems we have seen, antifreeze, or even electrons)

• Auxilliary/backup system (typically)

• Q: Does solar energy go to zero on cloudy days?

H&K fig 6.8, 6.9 & 6.32Clear Day Insolation as a function of collector angle

Why does the angle make a difference?

Typical Passive Domestic solar heating systems

H&K 6.26 “Trombe” WallH&K 6.24

Typical Active Domestic solar heating system

E.G. Domestic hot-water system

Typical collector design(fig 6.18)

Can we understand the design criteria for each of these components?

What happens if you run such a collector too hot?

Focusing collectors(parabolic)

National Solar (thermal) test Facility (Sandia New Mexico)

http://www.sandia.gov/Renewable_Energy/solarthermal/nsttf.html

5 MW of thermal power for (with 222 “heliostats”)$21M (1978 $’s)