# Watts hr BTU eer

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```					http://physics.colorado.edu/phys3070
Judah Levine
JILA S-460
303 492-7785 (2-7785)
M,F 11-Noon, W 1-3 pm
also by appointment

Judah Levine, 3070L14 1
Refrigerator Energy Flow

Refrigerator transfers heat
TH
From the inside to the room.
Room warms up by QH
Refrigerator cools off by QL
QH            QH=QL+W > QL
W
QL

QL BTU / hr
eer =   =
TL             W   Watts

Judah Levine, 3070L14 2
Energy Efficiency Ratio
QL BTU / hr
eer =   =
W   Watts

Suppose eer=13 (a high-efficiency value).

Typical room air conditioner removes
12,000 BTU/hr (“1 ton” unit)

Input power= 12,000/13= 923 Watts

Energy used in 1 day= 923Watts×24hours= 22.2kWh
\$2.22/day @ \$0.10/kwh

Is this a lot or a little?

Judah Levine, 3070L14 3
Clicker question ..

A: This is a lot
B: Get a life, this is a little

Judah Levine, 3070L14 4
Energy Efficiency Ratio
QL
eer (ratio) =
W
BTU / hr
eer ( store) =
Watts
Suppose eer(store)=13

How much energy (in joules) does it take to move 10 joules of energy
from the cooler region to the warmer region?

A:   1.31 joules
B:   2.62 joules
C:   10.2 joules
D:   13.3 joules
Judah Levine, 3070L14 5
Energy Efficiency Ratio
BTU / hr
eer ( store) = 13
Watts

BTU / hr        1watt
eer ≈ 13          ×                = 3.81
Watts     3.41BTU / hr
QL
energy ratio =     = 3.81
W
QL 10 joules
W=      =            = 2.62 joules
eer      3.81

Judah Levine, 3070L14 6
Heat Pump Energy Flow
QH = W + QL > W                 Room warms up
QH               TH       by QH
COP =    >1
W
QH
W

QL

Extract energy QL
TL        from the great
outdoors

Judah Levine, 3070L14 7
Refrigerator
Evaporates at cold temp             Easy to liquefy

Cool (inside)                 Warm (outside)
Gas flow

Gas
Compressor
QL     Gas to liquid                        QH
Liquid      Expansion
valve

Liquid flow

Judah Levine, 3070L14 8
Refrigerants
F
Fluorine/Chlorine replace
Cl    C         Cl       hydrogen in methane
structure

F

Freon 12

Judah Levine, 3070L14 9
Refrigerants
F
H             F

Cl      C       Cl           F    C             C     F

F             H
F
Freon 12                         HFC-134

CF2Cl2                           CHF2 – CHF2

Chlorine primarily responsible for ozone depletion

Judah Levine, 3070L14 10
Electric power generation

Co
o il C       O3                il B
C

N            S

O2
O1
3-phase
“Delta”                   Coil A

Judah Levine, 3070L14 11
3-phase Delta transmission

Judah Levine, 3070L14 12
Electrical circuit parameters
joules
Volts = v =
charge
charge
current = amps = i =
second
joule charge   joule
Volts × amps = vi =       ×       =       = watts
charge second second
energy loss = i 2 r
r in ohms

Energy transfer/work requires motion of charges

Judah Levine, 3070L14 13
Transmission efficiency
power delivered = v × i
transmission loss = i 2 r
p = 1200 watts
v = 120volts
1200
i=       = 10amps
120
r = 1 ohm
loss = 10 2 ×1 = 100 watts
output 1200
efficiency =       =     = 92%
input 1300

Judah Levine, 3070L14 14
Transmission efficiency
power delivered = v × i
transmission loss = i 2 r
p = 1200 watts
v = 240volts
r = 1 ohm
efficiency =
A: 88%
B: 92%
C: 96%
D: 98%
E: 100%

Judah Levine, 3070L14 15
Transmission efficiency
power delivered = v × i
transmission loss = i 2 r
p = 1200 watts
v = 240volts
1200
i=       = 5amps
240
r = 1 ohm
loss = 52 ×1 = 25watts
output 1200
efficiency =       =     = 98%
input 1225
Judah Levine, 3070L14 16
High Voltage transmission

Judah Levine, 3070L14 17
Step-down transformer

Step up and
Step down
possible only with
alternating current
systems

Judah Levine, 3070L14 18
Alternating vs. Direct current

Extra credit study:

“War of the currents”

Thomas Edison
vs.
Nikola Tesla and George Westinghouse

1 paragraph min, 1 page max by Wednesday, 8 March, 9 am

Judah Levine, 3070L14 19
Light as a wave
Wavelength= distance between wave crests
1 micron=10-6 m
1 nano-meter=1nm=10-9 m

X-rays, gamma rays, …
< 400 nm ultra-violet

400 nm blue
500 nm green
670 nm red

> 700 nm near infrared
>1000 nm = 1micron= far infrared
cm – km: microwaves, TV, FM, AM …

Judah Levine, 3070L14 20
A Black Body

Absorbs all radiation that falls on it

Kinetic energy of atoms radiates
electromagnetic energy

What is spectrum of the radiation?

Judah Levine, 3070L14 21

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