Effect of temperature settings
on energy efficiency of a hair
dryer
Angela Taylor
Bellwood-Antis High School
Grade 11
Problem
• I wanted to find out if a hair dryer is more
energy efficient on the hot or cold
temperature setting.
How a Hair Dryer Works
http://www.petervaldivia.com/technology/el
ectricity/electrical-power.php
Power of Hair Dryers
– Wattage=power setting
• Hair dryers range from 600 to 2500 watts
• Mine is rated at 1875 watts
• Higher wattage uses energy faster
– Higher fan speed=more watts
– Higher heat setting=more watts
Evaporation
• Process in which atoms/molecules in liquid
state gain enough kinetic energy to
become a gas
http://www.tonywhiddon.org
Temperature vs. Speed
– Cold
setting=lower
wattage
– Less
energy=more
efficient
– Evaporation
happens
faster at
higher
temps-less
time needed
– Higher
temperature
=more
efficient
Hypothesis
• I think the hair dryer will be less energy
efficient on the cold setting because it will
take much longer to evaporate all the
water.
General Procedure
• Measure energy used to dry 15mL of
water in a Petri dish for 15 minutes on
both the hot and cold setting as well as
high and low fan speed
• Weigh dish before and after to find amount
evaporated
Procedure: Set up
Procedure: Set up
Experimental Design
• Experimental Variables:
– Different temperature settings
• Experimental Groups:
– Hot Temp/High Fan settings, Hot/Low
settings, Cold/High settings, Cold/Low
settings
• Control Group:
– Petri dish of water allowed to dry for 15
minutes without the hair dryer
Control Variables
•
•
•
•
•
Hair dryer at set length from water
15mL of water
Same hair dryer
15 minutes of drying time
Always inside (same location in the room)
Humidity and Evaporation
• More humidity=less evaporation
• Important because if the room I tested in is
too humid, the tests won’t accurately
reflect the amount of water that could be
evaporated in 15 minutes.
Procedure: Analyze Data
Trial Set 1
Amt.
Dish w/ water Weight after evaporated kWh
(g)
drying (g)
(g)
used
High/Hot
21.97
17.731
4.239
0.39
• Find the amount of evaporated water
Comparing Data using Ratio
Trial Set 1
Fan/Temp
High/Hot
Low/Hot
High/Cool
Low/Cool
Amt. evaporated
Energy use
(g)
kWh used (kWh/g)
4.239
3.163
2.978
2.509
0.39
0.20
0.06
0.03
0.092
0.063
0.020
0.012
Standardizing Data
High/Hot
Total
Energy to
Amt. evaporated
Energy use Dry
(g)
kWh used (kWh/g) (kWh)
4.239
0.39
0.092
1.380
• Set up a proportion to find out how much
energy is needed to completely dry the water
– Ex: High/Hot:
– 15g * 0.092kWh= 1.38 kWh for 15 g
1g
• You wouldn’t just dry 15 minutes worth of
water
Trial Set 1
Total kWh
needed- all
trials
High/Hot
Low/Hot
High/Cool
Low/Cool
High/Hot
Low/Hot
High/Cool
Low/Cool
High/Hot
Low/Hot
High/Cool
Low/Cool
Amt.
evaporated kWh
(g)
used
4.239
0.39
3.163
0.2
2.978
0.06
2.509
0.03
Trial Set 2
4.249
2.942
2.942
2.089
0.39
0.2
0.06
0.03
Trial Set 3
4.302
0.39
3.12
0.2
2.8
0.06
2.129
0.03
Energy
use
(kwh/g)
0.092
0.063
0.020
0.012
Total
kWh
needed
1.380
0.948
0.302
0.179
0.092
0.068
0.020
0.014
1.377
1.020
0.306
0.215
0.091
0.064
0.021
0.014
1.360
0.962
0.321
0.211
Averages Adjusted to Evaporate
all 15g of water
Setting
High/Hot
Low/Hot
High/Cool
Low/Cool
kWh
1.37 ± 0.01
0.98 ± 0.04
0.31 ± 0.01
0.20 ± 0.02
Average energy needed to
evaporate 15g
1.600
1.400
k 1.200
W
1.000
h
0.800
n
e 0.600
e
0.400
d
e 0.200
d
0.000
High/Hot
Low/Hot
High/Cool
Hair Dryer Settings
Low/Cool
Further Trials
• Petri dish is not realistic
• Tried hair.
Hair
Hair Trials
Trial 1-Hair
Mass w/ Mass after
water (g) drying (g)
High/Hot
164.29
89.08
Low/Hot
125.51
87.35
High/Cool 134.80
114.90
Low/Cool 141.22
132.35
Amt. Evap (g) kWh used
75.20
0.41
38.16
0.20
18.78
0.07
8.88
0.03
kWh/g
0.0055
0.0052
0.0037
0.0034
Total kWh
needed
0.501
0.267
0.232
0.243
kWh/g
0.0081
0.0037
0.0011
0.0014
Total kWh
needed
0.480
0.308
0.092
0.111
Trial 2-Hair
Mass w/
water (g)
High/Hot
139.90
Low/Hot
161.33
High/Cool
152.24
Low/Cool
146.12
Mass after
drying (g)
89.29
104.69
98.78
125.10
Amt. Evap (g) kWh used
50.61
0.41
56.63
0.21
53.47
0.06
21.02
0.03
Averages Adjusted to Evaporate
all water
0.600
0.500
k
W
h
0.400
0.300
n
e
e
d
e
d
0.200
0.100
0.000
High/Hot
Low/Hot
High/Cool
Hair Dryer Setting
Low/Cool
Conclusion
• In a Petri dish, the low/cool settings are
the most energy efficient.
• On real hair, high/hot was least efficient,
but the other three weren’t statistically
different
• I reject my hypothesis that cold would be
the least efficient
Improvements
• Hair had a high standard deviation
– Hard to standardize/weigh
• Shorten distance
– Not realistic
Sources
• http://atoc.colorado.edu/~englishj/Humidity.htm
1-31-11
• http://tlc.howstuffworks.com/style/hair-dryer.htm
1-2-11
• http://www.petervaldivia.com/technology/electrici
ty/electrical-power.php 2-1-11
• http://www.sciencedaily.com/articles/e/evaporati
on.htm 12-28-10
• http://www.ehow.com/how-does_4564927_blowdryer-work.html 1-2-11
• http://www.webchem.net/notes/how_far/kinetics/
maxwell_boltzmann.htm 12-28-10
Standard Deviation

(Xav-Xi)2
N-1
•  = Sum
• Xav = Average
• Xi = Trial
•N
=
# of Trials
Materials
•
•
•
•
•
•
•
•
•
Hair Dryer
Ring stand
Petri dish
Graduated cylinder
Pitcher
Force meter
Hair sample
Physics books
Kill-a-watt meter
Data
• Petri Dish
• Hot air
• High setting
– 1: hair dryer wasn’t steady or lined up; water
spilled
– 2: hair dryer wasn’t lined up; water spilled
• Decided to measure masking tape square to align
dryer with dish
– 3: With masking tape square; water did not
spill; evaporated 1.7g, used .12kwh in 5
minutes
Evaporative Cooling
• As evaporation occurs, temp of liquid
decreases
– As faster-moving molecules escape,
remaining molecules have lower kinetic
energy
• This is why sweat cools the human body
• Explains why the water in my experiment
was cooler, even after having hot air blown
on it for 15 minutes.
Hair Data Analysis
Trial 1-Hair
High/Hot
Low/Hot
High/Cool
Low/Cool
Amt. Evap (g)
75.20
38.16
18.78
8.88
kWh used
0.41
0.2
0.07
0.03
kWh/g
0.0055
0.0052
0.0037
0.0034
Total kWh
needed
0.501
0.267
0.232
0.243
kWh/g
0.0081
0.0037
0.0011
0.0014
Total kWh
needed
0.480
0.308
0.092
0.111
Trial 2-Hair
Amt. Evap (g)
High/Hot
50.61
Low/Hot
56.63
High/Cool
53.47
Low/Cool
21.02
kWh used
0.41
0.21
0.06
0.03
Averages Adjusted to evaporate
all water
Setting
High/Hot
Low/Hot
High/Cool
Low/Cool
kWh
0.490 ± 0.014
0.287 ± 0.029
0.162 ± 0.099
0.177 ± 0.093