Cool Roofs Cool Cities Cool Planet Ronnen Levinson

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Summer in the city 2

Bird’s eye view of urban land use © 2010 Ronnen Levinson (RMLevinson@LBL. gov) The

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Heat island mitigation strategies 4

What makes a surface cool? reflected sunlight Rsol I net emitted thermal radiation E

Sunlight — more than meets the eye © 2010 Ronnen Levinson (RMLevinson@LBL. gov) AM

White, cool color, warm color white roof © 2010 Ronnen Levinson (RMLevinson@LBL. gov) cool

Types of cool roofs Old New © 2010 Ronnen Levinson (RMLevinson@LBL. gov) flat, white

Cool colored roofing cool concrete tile R ≥ 0. 40 Courtesy American Rooftile Coatings

Prototype shingles Solar reflectance >= 0. 25 © 2010 Ronnen Levinson (RMLevinson@LBL. gov) (for

Prototype concrete tiles Solar reflectance >= 0. 40 © 2010 Ronnen Levinson (RMLevinson@LBL. gov)

Vegetation • Plants cool air by evaporating water – sensible heat → latent heat

Cool pavement technology: cement concrete • • Study by Portland Cement Association shows that

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Cool pavement technology: asphalt concrete (? ) •

Potential benefits of white roofs on commercial buildings • DOE-2. 1 E building energy

Annual energy cost saving ($/m 2) © 2010 Ronnen Levinson (RMLevinson@LBL. gov) R-19 roof

Annual CO 2 emission reduction (kg/m 2) © 2010 Ronnen Levinson (RMLevinson@LBL. gov) R-19

Potential white-roof benefits to U. S. • Retrofitting 80% of U. S. airconditioned commercial

Global cooling © 2010 Ronnen Levinson (RMLevinson@LBL. gov) • “Global cooling” offers further CO

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Buildings, cities and planet (oh my!) 20

On the web • Cool Colors Project – Cool. Colors. LBL. gov • Heat

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Supplemental slides 22

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Electricity price ($/k. Wh) 23

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Natural gas price ($/therm) 24

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) CO 2 emission factor (kg/k. Wh) 25

Slides: 25

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Cool Roofs Cool Cities Cool Planet Ronnen Levinson, Ph. D. Acting Leader, Heat Island Group Environmental Energy Technologies Division Lawrence Berkeley National Lab © 2010 Ronnen Levinson (RMLevinson@LBL. gov) RMLevinson@LBL. gov; tel. 510 -486 -7494; http: //Cool. Colors. LBL. gov Presented to the China NDRC Delegation to Berkeley Lab 22 April 2010 1

What makes a surface cool? reflected sunlight Rsol I net emitted thermal radiation E σ (T 4 - Tsky 4) incident sunlight I convection opaque surface at temperature T © 2010 Ronnen Levinson (RMLevinson@LBL. gov) conduction • High solar reflectance (Rsol) lowers solar heat gain (0. 3 - 2. 5 µm) • High thermal emittance (E) enhances thermal radiative cooling (4 - 80 µm) high solar reflectance + high thermal emittance = low surface temperature 5

Sunlight — more than meets the eye © 2010 Ronnen Levinson (RMLevinson@LBL. gov) AM 1 GH = (clear sky) air mass 1 global horizontal Solar reflectance Rsol = 6 6. 6% ultraviolet reflectance Ruv + 44. 7% visible reflectance Rvis + 48. 7% near-infrared reflectance Rnir

Cool colored roofing cool concrete tile R ≥ 0. 40 Courtesy American Rooftile Coatings standard concrete tile (same color) solar reflectance gain = +0. 37 +0. 26 +0. 23 +0. 15 +0. 29 cool clay tile R ≥ 0. 40 cool metal R ≥ 0. 30 © 2010 Ronnen Levinson (RMLevinson@LBL. gov) Courtesy MCA Clay Tile Courtesy BASF Industrial Coatings cool fiberglass asphalt shingle R ≥ 0. 25 Courtesy Elk Corporation 9

Vegetation • Plants cool air by evaporating water – sensible heat → latent heat – most effective in arid climates • Plant matter remarkably solar reflective © 2010 Ronnen Levinson (RMLevinson@LBL. gov) – R ≈ 0. 3 for leaves – R ≈ 0. 4 – 0. 5 for wood – reflectance results from cellular structure 12 • Trees can shade buildings • Green roofs – – – high thermal mass moderate solar reflectance evaporative cooling rainwater control extensive (shallow soil) or intensive (deep soil)

Cool pavement technology: cement concrete • • Study by Portland Cement Association shows that cement concretes have solar reflectances of 0. 30 – 0. 65 LEED compliant (SRI ≥ 29) © 2010 Ronnen Levinson (RMLevinson@LBL. gov) Solar reflectances of 45 concrete mixes 13

© 2010 Ronnen Levinson (RMLevinson@LBL. gov) Cool pavement technology: asphalt concrete (? ) • Cool asphalt concrete still in its infancy • We seek to identify cool solutions for resurfacing asphalt concrete pavement 14

Potential benefits of white roofs on commercial buildings • DOE-2. 1 E building energy simulations • Two roof types – aged gray roof (solar reflectance=0. 20) – aged white roof (solar reflectance=0. 55) © 2010 Ronnen Levinson (RMLevinson@LBL. gov) • Four building prototypes – new office, old office – new retail, old retail 15 • • • 235 U. S. cities Local energy prices Local emission factors Local building stock Local population density Results: local, state, national – – cooling energy saving heating energy penalty energy cost saving reductions in emission of CO 2, NOx, SO 2, Hg

Potential white-roof benefits to U. S. • Retrofitting 80% of U. S. airconditioned commercial buildings (2. 1 B m 2) would annually save © 2010 Ronnen Levinson (RMLevinson@LBL. gov) – – – $735 M 6. 2 Mt CO 2 (=1. 2 M cars) 9. 9 kt NOx (=0. 6 M cars) 26 kt SO 2 126 kg Hg through energy conservation • Product lifetime energy savings has present value of $11 B 18 New York Times, 30 July 2009

Global cooling © 2010 Ronnen Levinson (RMLevinson@LBL. gov) • “Global cooling” offers further CO 2 reductions – negative radiative forcing: high Rsol lowers T, reducing both convection and thermal radiation into the atmosphere – 80% of reflected sunlight escapes into space – 100 m 2 (1000 ft 2) of white roof retrofit offsets 10 t of CO 2 emission (once) – retrofitting 80% of U. S. commercial buildings yields one-time offset of 200 Mt CO 2 (= 4 M cars x 10 years) 19

On the web • Cool Colors Project – Cool. Colors. LBL. gov • Heat Island Group – Heat. Island. LBL. gov • Cool Communities Project – Cool. Communities. LBL. gov • Cool California – Cool. California. org • EPA Heat Islands – epa. gov/hiri • Energy Star Cool Roofs – Energy. Star. gov • Roof Savings Calculator – Roof. Calc. com © 2010 Ronnen Levinson (RMLevinson@LBL. gov) • Cool Roof Rating Council – Cool. Roofs. org 21 Thank You!