Cool Roofs to Cool the World(Global Use, Potential and Policies)

.

Jayant SathayeSenior Scientist

Lawrence Berkeley National Laboratory

University of California

Berkeley

jasathaye@LBL.gov

With inputs from

Drs. Art Rosenfeld and Surabi Menon, LBNL, and Prof. Vishal Garg, IIIT

IGBC – Green Building Congress

21 October, 2011 22

BirdBird’’s eye view of urban land uses 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, CA

is about

• 20% roofs• 30% vegetation

• 40% pavement

2

3

Reflective roofs stay cooler in the sun

0.0 0.2 0.4 0.6 0.8 1.0

Te

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°C

)

Galvanized Steel

IR-Refl. Black

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Solar Absorptance = 1 – Solar Reflectance

Solar Reflectance1.0 0.8 0.6 0.4 0.2 0.0

50

40

30

20

10

0

4

White roofs, cool-colored roofs save money

flat, white

pitched, white

pitched, cool & colored

OLD NEW

AC savings ≈ 15%

AC savings ≈ 10%

AC savings ≈ 5%

Chicago Heat Wave 1995, 739 Deaths

The most lethal floor was the top floor of a

building with a black roof

5

European Heat Wave 2003, 30,000 Deaths

Moscow-Centered Heat Wave 2010,~10,000 Deaths

6

White roofs around the world

88

…in Santorini, Greece

8

99

Walmart store in northern California

910

10

Congratulations to Univ. of California, Davis

10

1111

White roofs are popular in Tucson, AZ

1112

12

Washington, DC (Federal) has problems

12

• Use of broken china

mosaic and lime wash in

traditional Indian roofs

• Traditional Knowledge

• Increasing awareness

• Development of codes and

other voluntary programs

Ahmedabad Mumbai

New Delhi Bangalore

1414

…in Hyderabad, India

14

Cooling our planet

1616

Solar-reflective surfaces cool the globe

via “negative radiative forcing”

Source: Intergovernmental

Panel on Climate Change (IPCC)16

1717

GLOBAL COOLING: making 100 m2 (1000 ft2) of gray

roofing white offsets the emission of 10 t of CO2

18

How much CO2 equivalent is offset if we whiten all

eligible urban flat roofs world-wide? (i/ii)

• Answer: 24 Gigatonnes (Gt)

– 2/3 of a year’s worldwide emission

– Gigatonne = billion metric tons

• If implemented over 20 years (the life of a roof or a program) this is ≈ 1.2 Gt/year.

19

How much CO2 equivalent is offset if we whiten

all eligible urban flat roofs world-wide? (ii/ii)

• Offset is equivalent to taking 300 million cars off the road for 20 years.

– There are about 600 million passenger cars world wide, and they each emit ≈ 4 t CO2/year.

In terms of avoided power plants

Full white roof potential can offset the

emissions from 500 medium-sized coal

fired power plants or 1,000 medium-

sized gas fired power plants.

That is just the albedo effect – if the building

is air conditioned, it will avoid comparable

real CO2 back at the power plant.

20

In terms of avoided power plants

Full white roof potential can offset the

emissions from 500 medium-sized coal

fired power plants or 1,000 medium-

sized gas fired power plants.

That is just the albedo effect – if the building

is air conditioned, it will avoid comparable

real CO2 back at the power plant.

21

22

Two almost identical buildings – West Bldg and East Bldg

West Bldg East Bldg

Roof shifted from concrete to white (Reflectivity: 0.70-0.30 = 0.40)

Annual savings kWh/m2 13 14

Percentage Savings 10% 19%

24

Cool colored roofs available today

cool clay tile

R ≥0.40

Courtesy

MCA Clay Tile

cool metal

R ≥0.30

Courtesy

BASF Industrial

Coatings

Courtesy

American

Rooftile

Coatings

+0.37 +0.29+0.15+0.23+0.26 +0.29

cool concrete tile

R ≥0.40

standard concrete tile

(same color)

solar reflectance gain =

cool fiberglass asphalt shingle

R ≥0.25Courtesy

Elk Corporation

25 26

Progress in energy efficiency standards

• In 2005, California’s “Title 24” energy efficiency

standards prescribed white surfaces for low-sloped

roofs on commercial buildings. Several hot states are

following.

• In 2008, California prescribed “cool colored” surfaces

for steep residential roofs in its 5 hottest climate

zones.

• Other U.S. states & all countries with hot summers

should follow.

27

US -- Recent cool roof progress (2005 – 2011)

• 2005

– California Title 24 – “Flat roofs shall be white” (15 out of 16 climate

zones). Walmart adopts white roofs for ALL stores.

– EPA ENERGY STAR lists Cool Roof Materials

• 2010

– June 1st, 2010 – Memo from U.S. Energy Secretary Steven Chu

calls for all DOE Buildings to have white roofs, if cost-effective

– June 16th, 2010 – Marine Corp follows suit, Pentagon following slowly

– June 19th, 2010 – RetroFIT Philly announces winner of “coolest block”

contest to white-coat black roofs of row houses.

• 2011

– 100 Cool Cities launched – see www.WhiteRoofsAlliance.org

– Spring 2011 – US launched, at G20 Energy Ministers meeting, a

voluntary Cool Roofs & Pavements initiative and offered technical

assistance to developing countries who join early. Joined so far: India,

Japan, Mexico, US.

To come 2012…

• Model codes will be modified to prescribe “flat roofs shall

be white”

– ASHRAE for commercial buildings

– EECC for residential buildings

• But states and cities have to adopt model codes

28

India Technology Scope

� Cool Roof technology would be

effective in almost 90% of the Indian

region.

� It has wide scope of being an

effective energy savings solution for

both new and retrofit buildings.

India Policy and Code Bodies

�ECBC-2007 - Bureau of Energy Efficiency

(BEE)

�LEED India- Indian Green Building Council

(IGBC)

�GRIHA - The Energy and Research

Institute (TERI/ MNRE)

Indian Green Building Council - IGBC

• Use roofing materials with a solar reflectance index (SRI) equal to or

greater than the values in the table below for a minimum of 75% of the

roof surface. Roofing materials having a lower SRI value than those

listed below may be used if the weighted rooftop SRI average meets

the following criteria: Credit - Heat Island effect: Roof

Area of Roof Meeting Minimum SRI SRI of Installed Roof

—————————— x —————— ≥

75%

Total Roof Area Required SRI

Roof Type Slope SRI

Low-sloped roof ≤ 2:12 (15%) 78

Steep-sloped roof > 2:12 (15%) 29

Refers to Cool Roof Rating Council for product information. Default value in IGBC

32

Global Cool Cities Alliance could unite

many initiatives and trade associations

33

Resources on the web

• Art Rosenfeld’s website

– ArtRosenfeld.org

• Cool Colors Project

– CoolColors.LBL.gov

• Heat Island Group

– HeatIsland.LBL.gov

• Cool Communities Project

– CoolCommunities.LBL.gov

• Roof Savings Calculator

– RoofCalc.com

• Global Cool Cities Alliance

− GlobalCoolCitiesAlliance.org

• Cool Roof Rating Council

− CoolRoofs.org

• Cool California

– CoolCalifornia.org

• EPA Heat Islands

– epa.gov/heatisland

• Cool Roof Calculator

– Coolroof.cbs.iiit.ac.in

February 2011

34

Other Slides

February 2011

353535

PentagonPentagonRostov on Don, white roofs

Baku, dark roofs

39

Sunlight — more than meets the eye

0.0

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1.0

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

No

rma

lize

d S

ola

r Ir

rad

ian

ce

near-infrared visibleUV

Solar Irradiance DistributionSolar Irradiance DistributionSolar Irradiance DistributionSolar Irradiance Distribution

■ ■ ■ ■ 6.6% ultraviolet (300 - 400 nm)

■ 44.7% visible (400 - 700 nm)

■ 48.7% near-infrared (700 - 2500 nm)

Air Mass 1 Global Horizontal (AM1GH) Solar Irradiance

40

White, cool color, warm color

white roof

cool red roof

gray roof0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

Re

fle

cta

nce

0.0

0.5

1.0

1.5

2.0

Irrad

ian

ce

(W m

-2 nm

-1)

nir visuv

cool red (Rsol=0.39)

standard white (Rsol=0.82)

solar irradiance

dark gray (Rsol=0.23)

4141

Summer in the citySummer in the city

41

summer urban heat island