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Cool Pavements for Cool Communities August 1, 2013. Heat Island Group Lawrence Berkeley National Laboratory http://HeatIsland.LBL.gov. Global Cool Cities Alliance http://GlobalCoolCities.org http://CoolRoofToolkit.org. Outline. Hot cities Cool science Benefits of reflective pavements

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Cool Pavements for Cool Communities August 1, 2013


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    1. Cool Pavements for Cool CommunitiesAugust 1, 2013 Heat Island Group Lawrence Berkeley National Laboratory http://HeatIsland.LBL.gov Global Cool Cities Alliance http://GlobalCoolCities.org http://CoolRoofToolkit.org

    2. Outline Hot cities Cool science Benefits of reflective pavements Cool pavement options Cool ideas for existing hot pavements Things to consider

    3. Cities can be HOT NASA infrared Sacramento (1998) Image: NASA/Marshall Space Flight Center

    4. Summer afternoons in the city Source: LBNL – Heat Island Group

    5. One reason cities are hot is that they have many dark surfaces Other 9% Roofs 22% Pavements 34% Vegetation 35% Average urban fabric above tree canopy in Chicago, IL, Houston, TX, Sacramento, CA, and Salt Lake City, UT A square kilometer in Sacramento, CA Sources: Akbari and Rose (2008), LBNL Heat Island Group

    6. About 1/3 of urban surfaces are paved Of that third, about 45% are streets (usually asphalt concrete) 15% are sidewalks (usually cement concrete) 40% is exposed parking (usually asphalt concrete) Source: Akbari and Rose (2008)

    7. And we all know that pavements can get HOT Visible image Rio Verde, Arizona Infrared image Pavement is > 30°F hotter than vegetation Image: Larry Scofield - APCA

    8. Cool science

    9. Hot city surfaces warm the air Sunlight does not directly heat the air Opaque surfaces (e.g., pavements & roofs) absorb part of the sunlight & reflect part

    10. How do you measure reflective pavements? solar reflectance scale perfect absorber perfect reflector High solar reflectance usually results in cooler pavement Solar reflectance (SR) = fraction of sunlight reflected = reflected sunlight ÷ incident sunlight

    11. High solar reflectance low pavement temperatures Increase pavement SR by 0.1 to decrease temperature ~ 7°F Source: LBNL Heat Island Group

    12. Example from the LBNL Cool Pavement Showcase SR 0.06 SR 0.32 SR 0.46 58.8°C (138°F) 46.2°C (115°F) 41.4°C (107°F) • Measurements performed in Berkeley, 26 June 2012 • Ambient air temperature at 2:45 pm PDT 22.5°C (72.5°F) • No wind or clouds

    13. Benefits of reflective pavements

    14. Longer pavement life HOT WARM Source: Pomerantz, Akbari, Harvey (2000)

    15. Enhanced visibility and safety • Reflected illumination is roughly proportional to solar reflectance • Nighttime illumination Source: Pomerantz et al (2003)

    16. Energy savings Source: Stark, R.A. (1986) 39 light fixtures 27 light fixtures = Dark pavement Light pavement • Reduced energy for street lighting • Enhanced illumination or fewer fixtures • Also reduces indoor air conditioning demand

    17. Improved outdoor comfort Flisvos Park in Athens, Greece (Santamouris et al. 2012) • Improved outdoor comfort • An urban park in Athens, Greece installed 4500 m2 of cool pavements • Reduced peak air temperatures by 2°C (Santamouris et al. 2012)

    18. Preserved water quality Brook Trout Source: US EPA • EPA’s Clean Water Act addresses heat pollution – temperature is “pollutant of concern” • Ultra urban streams warm by 8°F one hour after summer squalls • A change of 5°F over 5 hours can induce stress in most desirable species of fish Photo: Eric Engbretson

    19. Other benefits • Reduced heat related stress • Improved air quality • Increases in temperature lead to increases in smog • Canceled emissions of CO2 • 44 billion tons of emissions would be “canceled” if hot cities converted to cool roofs and pavements • About 1.5 years' worth of current CO2 emissions

    20. Can result in monetary savings! • Example - LBNL study of Los Angeles Basin • Rosenfeld et al. (1998) considered only energy and air pollution savings • Cooler pavements (SR = 0.25) • Reduce peak air temperature by 5.4oF (3oC) -> • Reduces peak power demand by 1.6 GW • Reduces smog exceedance by 12% • Annual savings from cool pavements ≈ $91 million (1998)

    21. Cool pavement options

    22. Pavement materials span a range of solar reflectance Source: Rowland “Concrete for Cool Communities”

    23. Cooler asphalt concrete pavements * Depends on availability of suitable aggregate.Don’t want to ship heavy rocks over long distances. Cool: Use light-colored aggregate* Aggregate shows as asphalt binder rubs off Initial SR ≈ 0.05 (increases over time) Coolest: Use reflective coatings, slurries, overlays on top of asphalt Initial SR ≈ 0.25-0.55

    24. Cooler cement concrete pavements Source: Concrete Technology Laboratory Source: Slag Cement Association Cool: Gray-cement concrete with light colored fine aggregate Initial SR ≈ 0.30-0.40 Coolest: Slag concrete, in which slag replaces about 50% of gray cement Initial SR ≈ 0.40 – 0.60