cool roofing… cutting through the glare

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


Environmental Issues

Economic Issues


Key Symposium Topics

Highly reflective roofs can reduce urban temperatures in the summer….

Reducing ozone formation

Reducing energy costs

Reducing fossil fuel demand


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 Roofs & the Environment


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 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 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?


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


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)


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.


Increased Roof Insulation


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?


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


Scale Effects


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


Scale Effects


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


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


Regional Differences


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)


Cool roofs offer tangible benefits for individuals and the community:

• Energy savings

• Reduced urban heat island effect


Recommendations(For Dallas / Ft. Worth)



… but there are several cool roofing alternatives to consider:

• Reflective membranes

• Reflective coatings

• Ballasted membranes



… 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

cool roofing… cutting through the glare

Documents

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ballasted roof systems

stoneballasted roof

reflectanceblack roof

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environmentcool roofingcutting

consideredcool roofingcutting