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Ten Years at the Calif. Energy Commission & White Roofs to Cool your Building, your City and
(this is new !) Cool the World
UC Sustainability Committee UCOP, Oakland, Sept 29, 2011
Arthur H. Rosenfeld, Former Commissioner California Energy Commission.
Distinguished Scientist Emeritus Lawrence Berkeley National Lab.
[email protected] 510 495-2227
Presentation available at www.ArtRosenfeld.org
Filename UC Sustainability fm IEA Annex 53 LBNL fm Carnegie DC fm Russian Talk 6-5-11 + DR from EE Summit Sacto. Path DinnerTalk Life at CEC. ARPA-E
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Summer in the city
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summer urban heat island
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Bird’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, CA is about
• 20% roofs • 30% vegeta;on • 40% pavement
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Reflective roofs stay cooler in the sun
0.0 0.2 0.4 0.6 0.8 1.0
Tempe
rature Rise ( °C)
Galvanized Steel
IR-‐Refl. Black
Black Pa
int
Green Asph
alt S
hingle
Red Clay Tile
Lt. R
ed Paint
Lt. G
reen
Paint
Whi
te A
spha
lt Sh
ingl
e
Al R
oof
Coa
t.
Opt
ical
Whi
te
Whi
te P
aint
Whi
te C
emen
t Coa
t.
Solar Absorptance = 1 – Solar Reflectance
Solar Reflectance 1.0 0.8 0.6 0.4 0.2 0.0
50
40
30
20
10
0
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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%
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Chicago Heat Wave 1995, 739 Deaths The most lethal floor was the top floor of a building
with a black roof
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European Heat Wave 2003, 30,000 Deaths Moscow-Centered Heat Wave 2010,~10,000 Deaths
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White roofs around the world
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…in Santorini, Greece
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…in Hyderabad, India
…and widely in the state of Gujarat, India.
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Walmart store in northern California
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University of California 9 campuses viewed by
Google Earth
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University of CA at Berkeley
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University of CA at Davis
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University of CA at Irvine
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University of CA at Los Angeles
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University of CA at Merced
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University of CA at Riverside
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University of CA at San Diego
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University of CA at Santa Barbara
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UCSF Parnassus Campus
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Cooling our planet
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Solar-‐reflec=ve surfaces cool the globe via “nega=ve radia=ve forcing”
Source: Intergovernmental Panel on Climate Change (IPCC)
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GLOBAL COOLING: making 100 m2 (1000 I2) of gray roofing white offsets the emission of 10 t of CO2
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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.
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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.
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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. 27
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Global Cool Cities Alliance could unite many initiatives and trade associations
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A UC White Roof Information Exchange
• For facilities staff to exchange experience between campuses, with the Heat Island Group at LBNL, and with Global Cool Cities Alliance
• Sample topics for “flat” (low-slope) roofs: – Initial cost premium for choosing white? – Does white have a longer service life than dark? – Annual maintenance? – Annual A/C savings (as a fraction of cooling load of space under
roof)? – Complaints about glare? – Cost-effectiveness of cisterns to hold and use storm water?
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Cool UC Information Exchange
• Sample topics for pavements: – Why give repaved asphalt a superblack coating?
• Does anybody know how to overcome this practice? – Consideration of light-colored aggregate for “asphalt” roads?
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• If you have experience and/or ideas with cool roofs or pavements, please contact Benjamin Mandel with thoughts on these issues: • [email protected] • (516) 672-2680
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Resources on the web
• Art Rosenfeld’s website – ArtRosenfeld.org
• Cool Colors Project – CoolColors.LBL.gov
• Heat Island Group – HeatIsland.LBL.gov
• Cool Communi;es Project – CoolCommuni;es.LBL.gov
• Roof Savings Calculator – RoofCalc.com
• Global Cool Ci;es Alliance − GlobalCoolCi;es.org
• Cool Roof Ra;ng Council − CoolRoofs.org
• Cool California – CoolCalifornia.org
• EPA Heat Islands – epa.gov/hea;sland
• Energy Star Cool Roofs – EnergyStar.gov
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Sunlight — more than meets the eye
0.0
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)
Nor
mal
ized
Sol
ar Ir
radi
ance
near-infrared visibleUV
Solar 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
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White, cool color, warm color
white roof
cool red roof
gray roof 0.0
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)
Refle
ctan
ce
0.0
0.5
1.0
1.5
2.0
Irradiance (W m
-2 nm-1)
white membraneG:sol=0.82,uv=0.12,vis=0.90,nir=0.83
red tileG:sol=0.39,uv=0.07,vis=0.20,nir=0.60
400 nm line
700 nm line
Duro-Last membrane (dark gray[LBNL]/matte)G:sol=0.23,uv=0.09,vis=0.26,nir=0.22
(G) AM1GH Solar Irradiance, ASTMG173-03 (uv=7%,vis=45%,nir=49%)
nir visuv
sol=300-2500 nm; uv=300-400 nm; vis=400-700nm; nir=700-2500 nm
cool red (Rsol=0.39)
standard white (Rsol=0.82)
solar irradiance
dark gray (Rsol=0.23)
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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 ≥0.25 Courtesy
Elk Corporation
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Resources on the web
• Art Rosenfeld’s website – ArtRosenfeld.org
• Cool Colors Project – CoolColors.LBL.gov
• Heat Island Group – HeatIsland.LBL.gov
• Cool Communi;es Project – CoolCommuni;es.LBL.gov
• Roof Savings Calculator – RoofCalc.com
• Global Cool Ci;es Alliance − GlobalCoolCi;es.org
• Cool Roof Ra;ng Council − CoolRoofs.org
• Cool California – CoolCalifornia.org
• EPA Heat Islands – epa.gov/hea;sland
• Energy Star Cool Roofs – EnergyStar.gov