Cool Roofing…Cutting Through the Glare
May 12 & 13, 2005Atlanta, Georgia
Sponsored by
– Roof Consultants Institute Foundation (RCIF)
– Oak Ridge National Laboratories (ORNL)
– National Research Council of Canada (NRC)
Attended by
– Over 200 construction and design professionals
– Industry media & trade associations
Presented by
– 30 researchers from universities, government, industry
Cool Roofing…Cutting Through the Glare
Environmental Issues
Economic Issues
Cool Roofing…Cutting Through the Glare
Key Symposium Topics
Highly reflective roofs can reduce urban temperatures in the summer….
Reducing ozone formation
Reducing energy costs
Reducing fossil fuel demand
Cool Roofing…Cutting Through the Glare
Cool Roofs & the Environment
….. but the cooling effect of highly reflective roofs may be overstated
– Wind effects not always considered
– Degradation due to roof aging not fully addressed
– Alternative approaches not always considered
Cool Roofing…Cutting Through the Glare
Cool Roofs & the Environment
Cool Roofing…Cutting Through the Glare
Cool Roofs & Wind Effects
The Effects of Wind on Roof Surface Air Temperature
31
29
27
25
23
Air
Tem
per
atu
re (
oC
)
Roof Reflectivity (%)
0 10% 20% 30% 40% 50% 60% 70% 80%
Summertime Daily Average and Maximum Air Temperatures for Roof System Reflectivity Simulations Conducted for City of Chicago
Source: Dupuis , R. & Graham, M. (2005) “Study on Roof System Reflectivity and Near-Surface Air Temperatures in Chicago, IL.”Paper presented at “Cool Roofing … Cutting Through the Glare”, Atlanta Georgia.
No WindWith Wind Effect Added
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
6 12 18 24 30 36 42
Cool Roofing…Cutting Through the Glare
Cool Roofs & Surface Aging
50% to 60% Reflectivityafter 3 Years
Ref
lect
ivit
y (%
)
Exposure (Months)
Roof Reflectance After Field ExposureOak Ridge Laboratories Envelope Systems Research Apparatus (ESRA)
Source: Miller, W.A., M. Cheng, S. Pfiffer and N. Byers. (2002). The Field Performance of High-Reflectance Single-Ply Membranes Exposed to Three Years of Weathering in Various U. S. Climates. Oak Ridge, TN: Oak Ridge National Laboratory.
75% + Initial Reflectivity
Declines to…
Test Membrane A
Test Membrane B
• Ballasted Roofs
• Increased Roof Insulation
Cool Roofing…Cutting Through the Glare
Cool Roof Alternatives
Cool Roof Alternatives:
Ballasted Roofs
White Roof with
70% Reflectance
Black Roof with
5% Reflectance
Ballasted Roof with
10 lb. Stone
Ballasted Roof with
17 lb. Stone
Ballasted Roof with
Concrete Pavers
Which Roof Saves The Most Energy?
Cool Roof Alternatives:
Ballasted RoofsRoof Membrane Surface Temperature:Clear Summer Day In East Tennessee
(Oak Ridge National Laboratories)
Exposed White TPO Membrane
Exposed Black EPDM Membrane
Ballasted EPDM Under 10 lb. Stone
Ballasted EPDM Under Concrete Pavers
Source: Gillenwater, D., Petrie, T., Miller W., & Desjarlais, A. (2005) “Are Ballasted Roof Systems Cool?”Paper presented at “Cool Roofing … Cutting Through the Glare”, Atlanta Georgia.
Note: Area Under Curve Indicates Total Heat Absorbed
180ºF136ºF122ºF
120ºF
Cool Roof Alternatives:
Ballasted Roofs
Source: Gillenwater, D., Petrie, T., Miller W., & Desjarlais, A. (2005) “Are Ballasted Roof Systems Cool?”Paper presented at “Cool Roofing … Cutting Through the Glare”, Atlanta Georgia.
Roofing Alternative:
Roofs with Light Stone Ballast(10 lb. / sq. ft.)
Roofs with Heavy Stone Ballast(17-20 lb. / sq. ft.)
Roofs with Concrete Pavers
Overall Energy Savings:
Equivalent to an aged reflective roof (50% reflectivity)
Equivalent to a new reflective roof (70% reflectivity)
Equivalent to any reflective roof (Up to 100% reflectivity)
Cool Roof Alternatives:
Increased Roof Insulation
White Roof with
55% Reflectance
Black Roof with
5% Reflectance
R-20 InsulationR-? Insulation
v.
What is the R-Value for a Non-Reflective Roof to Provide Equivalent Energy Savings to a Reflective Roof with R-20 Insulation?
Source: Hoff, J. L. (2005). “The Economics of Cool Roofing: A Local and Regional Approach.”Paper presented at “Cool Roofing … Cutting Through the Glare”, Atlanta Georgia.
Cool Roof Alternatives:
Increased Roof Insulation
Source: Hoff, J. L. (2005). “The Economics of Cool Roofing: A Local and Regional Approach.”Paper presented at “Cool Roofing … Cutting Through the Glare”, Atlanta Georgia.
Portland
Boston
New York
Pittsburgh
BaltimoreCleveland
Detroit
Indianapolis
Chicago
Milwaukee
Minneapolis
Richmond
CharlotteNashville
Atlanta
St. Louis
Little Rock
Jacksonville
Miami
TampaNew Orleans
Houston
Ft. Worth
Phoenix
Boulder
Cheyenne
Boise
Reno
Portland
Seattle
SLC
Las Vegas
Los Angeles
Albuquerque
Louisville
Birmingham
Kansas City
San Francisco
R-21
R-19R-20
R-23
R-26R-30R-33
R-Value For A Non-Reflective Roof To Provide Equivalent Energy Savings to a Reflective Roof with R-20 Insulation
Scale: What does it mean to the individual building owner?
Location: What does it mean to a building owner in a particular location?
Cool Roofing…Cutting Through the Glare
Economic Issues
The Economics of Cool Roofing
Scale EffectsPotential net annual energy savings from reflective roofs
for an entire city
Source: Lawrence Berkeley National Laboratory Heat Island Group
Chicago:$10 Million
Dallas:$20 Million
Miami:$20 Million
Los Angeles:$35 Million
New York:$16 Million
Source: DOE Cool Roof Calculator
Potential net annual energy savings for a typical 20,000 square foot building
Chicago
$20
Dallas
$520
Los Angeles
$300
New York
$360
Miami
$760
The Economics of Cool Roofing
Scale Effects
Source: DOE Cool Roof Calculator
Potential net annual energy savings per square foot of roof
Chicago
$0.001
Dallas
$0.026
Los Angeles
$0.015
New York
$0.018
Miami
$0.38
The Economics of Cool Roofing
Scale Effects
The Economics of Cool Roofing
Regional Differences
Climate Metric
Heating Degree Days
Cooling Degree Days
Solar Load(BTU/ Sq. Ft. / Day)
U.S. Low*
141 (Miami)
69 (San Francisco)
1061 (Seattle)
U.S. High*
7521(Milwaukee)
4127 (Miami)
1839 (Phoenix)
Variance
5234%
5881%
73%
* For Standard Metropolitan Statistical Areas
Source: DOE Cool Roof Calculator
Everyone is aware that there are significant climate differences across the United States…
Energy Source
Electricity($ / KWH)
Natural Gas($ / Therm)
U.S. Low*
$0.0558(Louisville)
$0.0724(Salt Lake City)
U.S. High*
$0.1236(New York City)
$1.2500(Atlanta)
Variance
122%
73%
* For Standard Metropolitan Statistical Areas
Source: Energy Information Administration, June, 2004
…but differences in energy costs are just as important
The Economics of Cool Roofing
Regional Differences
The Economics of Cool Roofing
Building Comparison
55% Reflectance
80% Emittance
Elec. Cooling (COP = 2.0)
Gas Heat (70% Efficiency)
5% Reflectance
80% Emittance
Elec. Cooling (COP = 2.0)
Gas Heat (70% Efficiency)
R-20 Insulation R-20 Insulation
20,000 Sq. Ft. 20,000 Sq. Ft.
v.
Portland
Boston
New York
Pittsburgh
BaltimoreCleveland
Detroit
Indianapolis
Chicago
Milwaukee
Minneapolis
Richmond
CharlotteNashville
Atlanta
St. Louis
Little Rock
Jacksonville
Miami
TampaNew Orleans
Houston
Ft. Worth
Phoenix
Boulder
Cheyenne
Boise
Reno
Portland
Seattle
SLC
Las Vegas
Los Angeles
AlbuquerqueOk. City
Louisville
Birmingham
Kansas City
San Francisco
$0$100$200
$300$400$500
$0$100$200
$300$400$500
Annual Heating / Cooling Cost Savings:
Reflective Roof versus Non-Reflective Roof
(-$50)
(-$100)
(-$50)
(Dollars per 20,000 Sq. Ft. Roof Area / R-20 Insulation)
Source: Hoff, J. L. (2005). “The Economics of Cool Roofing: A Local and Regional Approach.”Paper presented at “Cool Roofing … Cutting Through the Glare”, Atlanta Georgia.
Cool roofs offer tangible benefits for individuals and the community:
• Energy savings
• Reduced urban heat island effect
Cool Roofing…Cutting Through the Glare
Recommendations(For Dallas / Ft. Worth)
Cool Roofing…Cutting Through the Glare
Recommendations(For Dallas / Ft. Worth)
… but there are several cool roofing alternatives to consider:
• Reflective membranes
• Reflective coatings
• Ballasted membranes
Cool Roofing…Cutting Through the Glare
Recommendations(For Dallas / Ft. Worth)
… and several important issues must be recognized:
• The total energy payback is fairly small• Less than $0.03 per sq. ft. annually
• May be inadequate to justify a significant cost up-charge
• Reflective membranes will age• Assume 50% to 55% as a reasonable long-term value
• Energy payback may be inadequate to justify cleaning & maintenance
• Roof insulation will lose less long-term energy value