Energy Savings for Stucco
Walls Coated with Cool
Colors
Tom Petrie, Jerry Atchley, Phil Childs, and
André Desjarlais
Oak Ridge National Laboratory
Building Envelopes Group
6 December 2007
Pop Quiz
With Comfort and Energy Efficiency in mind,
which car do you select to drive in Clearwater
Beach during the summer?
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Solar Energy Spectrum
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Camouflage Invisible to Night Vision
Conventional Film
Near Infrared Film
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Conventional vs. Infrared Pigments
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Overview: Scope of Work
• Compare thermal performance of walls with
cool (high infrared reflectance) and
standard colors
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Overview: Scope of Work
• Phoenix site: Stucco-coated with various
constructions facing east, south, southeast
and southwest already covered with gray
color. Install instrumentation and recoat test
areas.
• Jacksonville site: Wood siding facing south
already covered with aqua color. Install
instrumentation and recoat test areas.
• Oak Ridge site: Bare stucco-coated test area
facing south. Add instrumentation; prime and
coat test areas.
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Oak Ridge Site
• Stucco test section on south wall of Envelope
Systems Research Apparatus (ESRA)
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Oak Ridge Site
• Cool color on right stud space and upper half of
middle; Non-IR on rest except for strip of
uncoated primer at bottom
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ORNL Site
• Data starting 7/30/04 with coating on 8/3/04.
Data acquisition through August 2005
• Check consistency of data with program to
estimate wall properties from temperature
and heat flux measurements (PROPOR). Data
very consistent from month to month
• Behavior of solar radiation control on vertical
walls more complicated than low-slope roofs.
Difficult to generalize simply
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ORNL Site: Non vs IR -- Spring Day
Non Outside
Non Inside
IR Outside
IR Inside
Air
Wall Solar
Non Heat Flux
IR Heat Flux
2 Heat Flux,
Solar/100
1
[Btu/(h·ft²)]
0
Temperature
(°F)
130
-1
110
-2
90
• Heat fluxes
•
70
50
30
0
4
8
12
16
Hours into April 16, 2005
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20
24
•
delayed four
hours relative to
outside temp
Peak temps
consistent with
coatings over
primer
Non and IR
behave identically
at night
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Model for Wall Behavior
• Seek a model that can be generalized to give
results for whole buildings
• Have done extensive validation of a model in
DOE 2.2 for a 1100 ft² ranch house
Conventional Wood-Framed Construction
• Heat/cool with
•
heat pump: 68°F
winter; 76°F
summer; size
heat pump for
climate
Occupy with 3
people + Building
America energy
use profiles
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Model for Wall Behavior
• To validate model, generate climatic data from
ORNL weather station records for year of test
• Use properties of wall materials along with
construction details for test section
Fiberglass batt (R-11)
Coatings with different
solar reflectance
Measured temperatures
Gypsum wallboard
Stucco (1 in.)
Measured heat flux
Non-vented air space
Extra gypsum layer
(only for validation)
Oriented strand board
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Solar Reflectance of Coatings
• Test Site
Primer
IR
Non IR
8/4/04 9/27/04 5/18/05 8/3/05
0.71
0.49
0.24
0.67
0.50
0.24
0.72
0.49
0.24
0.66
0.49
0.24
Use averages
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Model of South Wall vs Measurement:
Temperatures at Outside – Spring Day
Measure (solar reflectance):
IR surface (0.49)
Non surface (0.24)
Air
Outside Temperature (°F)
130
DOE 2.2 with ground reflectance =
x
o
0.24
0.08
x
o
0.24
0.08
120
• Surface
110
100
90
•
80
70
•
60
50
40
0
2
4
6
8
10 12 14 16 18 20 22 24
Hours into 4/16/2005
measurements and
DOE 2.2 predictions
equal air temperature
at night
DOE 2.2 peak
predictions above
peak measurements
Ground reflectance
of 8% (dark soil,
asphalt) better than
24% (dry grass) for
spring day
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Model Generalizations
• Building America Performance Analysis Resources at
http://www.eere.energy.gov/buildings/building_america/pa_resources.html
gives energy use profiles for three occupants (3 BR
home). Choose to heat and cool with air-to-air heat
pump (76°F cooling; 68°F heating; no setup or setback)
• Choose seven different climates to show response of
typical house to cooling and mixed climates of interest
4500
4000
3500
3000
2500
2000
1500
1000
500
CDD65 (°F-day)
HDD65 (°F-day)
Average Daily Solar (Btu/ft²)
• Cities arranged by
decreasing cooling
degree days
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OAK RIDGE NATIONAL LABORATORY
U. S. DEPARTMENT OF ENERGY
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Model Generalizations
• IR reflective coating on conventional walls saves
cooling energy. Savings are 4% to 9% compared to nonIR reflecting walls
6000
5000
Walls: Wood Studs + R-11 Batts
4.2
Annual Electricity
for Cooling (kWh)
Non Walls
IR Walls
5.0
4000
3000
• Absolute savings
% Savings
for IR Walls
5.3
vary from +240
(Phoenix) to +110
(Richmond)
6.2
2000
7.1
7.6
9.0
1000
0
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OAK RIDGE NATIONAL LABORATORY
U. S. DEPARTMENT OF ENERGY
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Model Generalizations
• IR reflective coating on CMU walls shows larger savings
of cooling energy. Savings are 6% to 13% compared to
cooling energy with non-IR reflecting walls
6000
6.4
5000
Walls: 8 in. CMU + R-5 Foam
6.9
4000
Annual Electricity
for Cooling (kWh)
Non Walls
IR Walls
3000
• Absolute savings
% Savings
for IR Walls
6.7
vary from +360
(Phoenix) to +160
(Richmond)
8.6
2000
10.4
11.0
13.0
1000
0
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OAK RIDGE NATIONAL LABORATORY
U. S. DEPARTMENT OF ENERGY
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Project Summary
• Full year of field data validated DOE 2.2 model
• Complexity of real wall applications (different
orientations, shading and construction) makes
generalization very difficult
• DOE 2.2 whole building annual energy
estimates for ranch house show that IR
reflecting pigments save 4% to 13% of cooling
energy
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U. S. DEPARTMENT OF ENERGY
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Energy Savings for Stucco
Walls Coated with Cool
Colors
Questions or comments?