Cool Roofs Cool Your Buildings, Your Cities, and OUR PLANET

Heat Island Group, Lawrence Berkeley National Laboratory11

Arthur H. RosenfeldFormer Commissioner,

California Energy CommissionGuest Faculty Scientist,

Lawrence Berkeley National Lab

[email protected] Phone: 510-527-1060

Cell Phone: 916-205-3965Cell Phone: 916-205-3965

This talk available on CoolWhitePlanet.org

Cool Roofs Cool Your Buildings, Cool Roofs Cool Your Buildings, Your Cities, and OUR PLANETYour Cities, and OUR PLANET

Washington DC, May 2010

Ronnen Levinson, Ph.D.Acting Leader, Heat Island GroupLawrence Berkeley National Lab

[email protected]. 510-486-7494

http://CoolColors.LBL.gov


I. Urban heat islands and cool roofsI. Urban heat islands and cool roofs


Summer in the citySummer in the city

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summer urban heat island


Bird’s eye view of urban land useBird’s eye view of urban land use

Tree Cover 13%

Sidewalk 5%

Barren Land 8%

Misc. 6%

Road 22%

Parking Area 12%

Grass 15%

Roof 19%

Area by Land-Cover Category Above the Canopy

~ 1 km2

The surface of Sacramento, CAis about

• 20% roofs• 30% vegetation• 40% pavement

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Reflective roofs stay cooler in the sunReflective roofs stay cooler in the sun

50

40

30

20

10

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0.0 0.2 0.4 0.6 0.8 1.0

Tem

pera

ture

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(°C)

Galvanized Steel

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Solar Absorptance


White roofs, cool-colored roofsWhite roofs, cool-colored roofs

flat, white

pitched, white

pitched, cool & colored

OLD NEW

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AC savings ~ 10%

AC savings ~ 15%

AC savings ~ 5%

AC savings ~ 10%


Potential U.S. white-roof benefits Potential U.S. white-roof benefits

• Retrofitting 80% of U.S. air-conditioned commercial buildings (2.1B m2) would annually save– $735M– 6.2 Mt CO2 (=1.2M cars)

– 9.9 kt NOx (=0.6M cars)

– 26 kt SO2

– 126 kg Hgthrough energy conservation

• Product lifetime energy savings has present value of

$11B

New York Times, 30 July 2009

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II. Cool roofs of tomorrowII. Cool roofs of tomorrow


Advanced cool-colored asphalt shinglesAdvanced cool-colored asphalt shingles

Prototype cool asphalt shingles• use new coating process• offers wide color palette• reflect up to 35% of sunlight• can save up to 60% more energy

today’s cool asphalt shinglesreflect ~ 25% of sunlight

CourtesyElk Corporation

Solar reflectance ≥ 25%


Advanced white roof coatings, membranesAdvanced white roof coatings, membranes

• White roof coatings, membranes soil rapidly, lose solar reflectance (SR)

– initial SR ~ 0.80– aged SR ~ 0.55

• How to keep white roofs clean and reflective?

– reduce leaching of plasticizers

– decrease surface roughness & stickiness

– photocatalyticself-cleaning

– photoinduced hydrophilicity

White metal roof stays clean,saving 70% more energy than

soiled white coating.

both roofs exposedfor 9 years in Florida


III. White roofs around the worldIII. White roofs around the world


White is “cool” in BermudaWhite is “cool” in Bermuda

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……in Santorini, Greecein Santorini, Greece

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……in Hyderabad, Indiain Hyderabad, India

…and widelyin the state of Gujarat, India.

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Walmart store in Chico, CAWalmart store in Chico, CA

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Congratulations to UC DavisCongratulations to UC Davis

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White roofs are popular in Tucson, AZWhite roofs are popular in Tucson, AZ

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……and in and in Punta Gorda, FLPunta Gorda, FL

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Washington, DC (Federal) has problemsWashington, DC (Federal) has problems

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PentagonPentagon


IV. Cooling our planetIV. Cooling our planet


Solar-reflective surfaces cool the globeSolar-reflective surfaces cool the globevia “negative radiative forcing”via “negative radiative forcing”

Source: Intergovernmental Panel on Climate Change (IPCC)

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White roofs cool your buildings and citiesWhite roofs cool your buildings and citiesand (this is NEW)… our planet!and (this is NEW)… our planet!


GLOBAL COOLINGGLOBAL COOLING: making 100 m: making 100 m2 2 (1000 ft(1000 ft22) of gray ) of gray roofing white offsets the roofing white offsets the emissionemission of 10 t of CO of 10 t of CO22


Study(available at

CoolWhitePlanet.org)

Method Cloudcover esti-

mation

CO2 offset(atmos-pheric) per 100

m2

CO2 offset(emitted)per 100

m2

World-wide potential

CO2 offset (emitted) from cool

roofs

CO2 offset compared to

Akbari et al. 2009

1 Akbari et al. 2009 (LBNL) calculation ~ 50% 5.5 t 10 t 24 Gt 100%

2 Menon et al. 2010 (LBNL)GCM + land use model

(summer only) GCM 7 t 13 t 30 Gt 130%

3

Oleson et al. 2010 (NCAR)[CO2 values from private communication between

Oleson & Menon]

GCM + urban canyon model GCM 7 t 13 t 30 Gt 130%

4 VanCuren et al. 2010 (CARB) measured solar radiation

not needed 3 t 5 t Addresses CA only;

coastal CA is foggy. 50%

3 papers and 1 memo estimate tonnes of CO3 papers and 1 memo estimate tonnes of CO22 offset by 100 moffset by 100 m22 (1000 ft (1000 ft22) of white roofing ) of white roofing

It is assumed that of 1 tonne of CO2 emitted only 0.55 tonnes remain in the atmosphere after one year,so the atmospheric and emitted columns are just in the ratio of 0.55/1.


How much COHow much CO22 equivalent is offset if we equivalent is offset if we whiten all eligible urban flat roofs world-wide?whiten all eligible urban flat roofs world-wide?

• Answer: 15 gigatonnes (Gt)– one third of a year’s worldwide emission– gigatonne = billion metric tons

• If implemented over 15 years (the life of a roof or a program) this is ~ 1 Gt/year.

• 1 Gt/year is equivalent to offsetting the emissions of 250 million cars for 15 years. – There are about 600 million passenger cars world wide,

and they each emit ~ 4 t CO2/year.


V. What to do nowV. What to do now


StrategiesStrategies


Building standardsBuilding standards

For planning purposes, follow the lead of the California Public Utilities Commission and internalize externalities. Currently it’s only $10/tonne CO2, but it’s a start.

Thus, California already plans to incorporate externalities when optimizing building standards.

Externalities justify cool roofs on non-air conditioned buildings.

Apply externalities also to cool pavements, vehicle roofs, even train roofs.


100 Cool Cities would 100 Cool Cities would coordinatecoordinatemany initiatives and trade associationsmany initiatives and trade associations


100 Cool Cities initiative100 Cool Cities initiative

DOE should offer:• U.S. technical support to promote local study

teams in China, India, etc.• Cash incentives to first 10 cities• Funding for Cool Cities staff in U.S.


AgreementsAgreements

Well before the July Ministerial Conference, DOE and State Department should convince5 - 10 charter countries to sponsor an agreement to promote Cool Roofs.

Interested countries already include Brazil, China, India, and Australia.


Resources on the webResources on the web

• Cool White Planet– CoolWhitePlanet.org

• Cool Colors Project– CoolColors.LBL.gov

• Heat Island Group– HeatIsland.LBL.gov

• Cool Communities Project– CoolCommunities.LBL.gov

• Roof Savings Calculator– RoofCalc.com

• Cool Roof Rating Council− CoolRoofs.org

• Cool California– CoolCalifornia.org

• EPA Heat Islands– epa.gov/hiri

• Energy Star Cool Roofs– EnergyStar.gov

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Cool Roofs Cool Your Buildings, Your Cities, and OUR PLANET

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