The Value of Reflective Wall Coatings

1
The Value of Reflective Wall Coatings

• André Desjarlais
• Oak Ridge National Laboratory
• 17 February 2011

2
Presentation summary

• Is energy efficiency in buildings and walls
  important? Some statistics
• What research is going on to measure energy
  benefits of Cool walls?
• What are the energy savings of this technology?

3
Energy is the defining challenge of our time
Global energy consumptionwill increase 50 by
2030

• The major driver for
• Climate change
• National security
• Economic competitiveness
• Quality of life
• Incremental changes to existing technologies
  cannot meet this challenge
• Transformational advancesin energy
  technologiesare needed
• Critically dependent on the best science and
  technology

3 Managed by UT-Battellefor the Department of
Energy
4
North American countries can improve their
efficiency
Norway
Sweden
United States
Canada
Italy
Japan
Czech Republic
Russia
Chile
China
Source Energy Information Administration and
United Nations Statistics Division
5
Improvements in energy efficiency of the economy
have been essential to the stabilization of U.S.
energy consumption . .
Estimated energy savings
Non-hydro renewables
Quadrillion Btu
Nuclear
Natural gas
Hydro
Petroleum
Wood
Coal
Source Energy Information Administration, U.S.
Bureau of Economic Analysis
6
Buildings energy use is large and growing
40 of U.S. Primary Energy Consumption (39 of
U.S. Carbon Emissions)
Industry 377 MMTC (25)
Buildings 658 MMTC (43)
Source 2007 Buildings Energy Data Book. Tables
1.1.3, 1.2.3, 1.3.3
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The building envelope is the key!!
8
Quiz
With Comfort and Energy Efficiency in mind, which
car do you select to drive during the summer?
9
Proof of concept
10
Solar energy spectrum
11
Critical properties
Reflectance (rsolar) Emittance (eIR)
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rsolar and eIR are both very important!
Total Solar Irradiation
Convection
Net Infrared Radiation
hair(tair-ts)
rsolar It Reflected
It
eIRDR
with DRs(Ts4-Tsurr4 )
(asolarIt Absorbed)
Net Heat Flux into Building
13
Camouflage invisible to night vision
Near Infrared Film
Conventional Film
14
Conventional vs. infrared pigments
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Higher reflectance without sacrificing color
choice
Regal White
Rawhide
Slate Blue
Standard SR .67 Cool SR .72
Standard SR .47 Cool SR .56
Standard SR .21 Cool SR .33
Slate Bronze
Brick Red
Charcoal Gray
Hartford Green
Standard SR .08 Cool SR .26
Standard SR .14 Cool SR .28
Standard SR .11 Cool SR .28
Standard SR .25 Cool SR .30
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Solar energy spectrum
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Overview scope of work

• Compare thermal performance of walls with cool
  (high infrared reflectance) and standard colors

18
ORNL test site

• IR coating on right stud space and upper half of
  middle Non-IR coating on rest except for strip
  of uncoated primer at bottom

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ORNL test site

• Data acquisition continuous for three years
• Check consistency of data with program to
  estimate wall properties from temperature and
  heat flux measurements. 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 test site Non vs IR -- summer day
Non Outside
Wall Solar
Non Inside
Non Heat Flux
IR Outside
IR Heat Flux
IR Inside
Air
Heat Flux,
2
Solar/100
1
Temper- ature (F)
Btu/(hft²)
0

• Air temp warmer but wall solar lower vs 4/16/05
• Behavior of Non and IR again same at night
• Peak temps again consistent with coatings over
  primer

-1
130
110
-2
90
70
50
30
24
0
4
8
12
16
20
Hours into July 25, 2005
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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 68F winter 76F
  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

Texcote coatings with different solar reflectance
Fiberglass batt (R-11)
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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Model generalizations

• Building America Performance Analysis Resources
  at http//www.eere.energy.gov/buildings/building_a
  merica/pa_resources.html gives energy use
  profiles for three occupants (3 BR home). Choose
  to heat and cool with air-to-air heat pump (76F
  cooling 68F heating no setup or setback)
• Choose seven different climates to show response
  of typical house to cooling and mixed climates of
  interest

4500
CDD65 (F-day)
4000
HDD65 (F-day)
3500
Average Daily Solar (Btu/ft²)
3000
2500
2000

• Cities arranged by decreasing cooling degree
  days

1500
1000
500
0
Miami
Phoenix
Las Vegas
Richmond
Knoxville
Bakersfield
Sacramento
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Model generalizations

• IR reflective coating on conventional walls saves
  cooling energy. Savings are 4 to 9 compared to
  non-IR reflecting walls

6000
Annual Electricity for Cooling (kWh)
Walls Wood Studs R-11 Batts
4.2
Non Walls
5000
5.0
IR Walls
4000
Savings for IR Walls
5.3
3000
6.2
2000
7.6
7.1
9.0
1000
0
Miami
Phoenix
Knoxville
Las Vegas
Richmond
Bakersfield
Sacramento
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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
Annual Electricity for Cooling (kWh)
Walls 8 in. CMU R-5 Foam
6.4
6.9
Non Walls
5000
IR Walls
4000
Savings for IR Walls
6.7
3000
8.6
2000
11.0
10.4
13.0
1000
0
Miami
Phoenix
Knoxville
Las Vegas
Richmond
Bakersfield
Sacramento
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Project summary

• Full year of ORNL 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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The Value of Reflective Wall Coatings

• Questions or comments?