Cool roofs and pavements to cool the world: An integrated mitigation/adaptation strategy for cities

Transcription

1 Cool roofs and pavements to cool the world: An integrated mitigation/adaptation strategy for cities Hashem Akbari Heat Island Group Concordia University, Montreal, Canada Tel: x3201 E_mail: Resilient Cities 2011: 2nd World Congress on Cities and Adaptation to Climate Change 5 June 2011

2 Aerial images of cities: Mostly roofs and pavements 2

3 Temperature rise of various materials in sunlight Galvanized Steel IR-Refl. Black Temperature Rise ( C) Optical White White Paint Lt. Red Paint Lt. Green Paint Red Clay Tile White Asphalt Shingle White Cement Coat. Al Roof Coat. Green Asphalt Shingle Black Paint Solar Absorptance 3

4 F 92 What Is a Heat Island? Sketch of an Urban Heat-Island Profile C Late Afternoon Temperature Rural Suburban Residential Commercial Downtown Urban Residential Park Suburban Residential Rural Farmland 4

5 White is cool in Bermuda 5

6 and in Santorini, Greece 6

7 Cool roofs programs Cool roofs in DC. Al Gore and NYC Mayor Bloomberg kick off NYC s Cool Roofs Initiative. Goal: 1 million sq. ft. of cool roofs installed in Philadelphia s RetroFIT PHILLY Coolest Block contest. Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change. Steven Chu, US Energy Secretary and in Tucson 7

8 Cool roofs in Hyderabad, India 8

9 U.S. Cool roof saves 10%-20% air-conditioning for area under the roof Japan Europe Asia Middle East China India (Hyderabad demos; see graph at right) 9

10 Cool roof technologies Old New flat, white pitched, cool & colored pitched, white 10

11 Cool colored roofs are in market cool concrete tile R 0.40 standard concrete tile (same color) Courtesy American Rooftile Coatings solar reflectance gain = cool clay tile R 0.40 Courtesy MCA Clay Tile cool metal R 0.30 Courtesy BASF Industrial Coatings cool fiberglass asphalt shingle R 0.25 Courtesy Elk Corporation 11

12 Cool paving materials: needs more development 12

13 Cool surfaces also cool the globe Cool roofs, cool pavements, and shade trees save energy, improve air quality, and improve comfort; we estimate savings of > $50B/year Reflective roofs and pavements also directly cool the globe, independent of avoided CO 2 Geo-engineering

14 The Earth s radiation budget Source: Kiehl and Trenberth,

15 CO 2 offset of cool roofs and pavements World-wide CO 2 offset of cool roofs and pavements = GT CO 2 Equal to 1-2 years of the world 2025 emission of 37 GT CO 2 At a growth rate of 1.5% in the world s CO 2 - equivalent emission rate, GT CO 2 would offset the effect of the growth in CO 2 -equivalent emissions for years Would offset emissions from all cars for years 15

16 Value of CO 2 offset CO 2 emissions currently trade at ~$25/tonne GT worth $1100B-$2000B, for changing albedo of roofs and paved surfaces Cooler roofs alone worth $600B - $1100B Cooler roofs also save air conditioning (and provide comfort) and improve air quality worth over $5000B over the next 100 years 16

17 The white revolution The idea of painting surfaces white to conserve energy is being actively pursued by the US. Earlier this month, Barack Obama's chief scientific adviser, John Holdren, received a scientific memorandum on the subject. Scientists estimate that making roofs and pavements white or more light-coloured would counter global warming with "negative radiative forcing" reflecting sunlight back into space. They said that retrofitting urban roofs and pavements in tropical and temperate regions with solar-reflective materials would offset about 44 billion tonnes of carbon dioxide. The scientists said it would lower the cost of air conditioning, making buildings more comfortable and mitigate the "urban heat island" effect caused by the concentration of concrete surfaces in cities. 17

18 Global Cool Cities Alliance (GCCA) Non-profit international cooperation launched in 2009 Mission: Advance policies and actions to increase solar reflectance of urban surfaces as a low- or no-cost way to Cool buildings Cool cities Cool the world Membership: Open to all cities in the world 18

19 GCCA objectives & programs 100 Cool Cities Corporate leadership Building codes and pavement specifications Financial mechanisms Research and development In response to the sweeping climate change issues, and actions to curb the urban heat island effect, Taipei City is honored to be part of this Cool Cities program. - Lung-Bin Hau, Mayor of Taipei 19

20 GCCA cities network Charter members of 100 Cool Cities: Athens, Chicago, New York, Singapore, Taipei 20

21 We envision a future world in which our urban environments are dramatically more reflective than at present and the earth is noticeably cooler as a result. Join us! GlobalCoolCities.org 21

22 100m 2 of a white roof, replacing a dark roof, offset the emission of tonnes of CO 2 22

23 References Akbari and Mathews PALENC2010 Akbari et al Climatic Change, 95, 3-4 Akbari et al Landscape and Urban Planning, 63 (1-14) Kiehl and Trenberth Bull. Am. Meteo. Soc, 78, 2 ( ) Menon et al Environ. Res. Lett. 5, 1 Rose et al LBNL-51448, Berkeley, CA Takebayashi and Moriyama. Solar Energy, 38(8) 23

24 Annual High Temperature Temperature trends in downtown Los Angeles F From Orchards to Blacktops Eruption of Krakatau, August 27, Year 24 Slope = (6 F/50 yr)/(3.3 C/50 yr) = (1 F/8 yr)/(1 C/14 yr) C

25 Measured temperature trends in selected cities (3-8 Decades) 1.0 Rate of Global Warming from 2005 to 2075 ( ppm CO 2 ) Degrees/ Decade 25

26 Effect of temperature rise on utility peak load 1 C = 600 MW 26

27 Japan: High temperatures cause peak demand Source: Hiroji Ohta, FEPC Chairman, 10 September C = 5 GW 27

28 Effect of temperature rise on peak ozone concentration 28

29 And are gaining traction now across the US Al Gore and NYC Mayor Bloomberg kick off NYC s Cool Roofs Initiative. Goal: 1 million sq. ft. of cool roofs installed in Philadelphia s RetroFIT PHILLY Coolest Block contest. Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of 29

30 Cool roofs in DC. and in Tucson 30

31 Cool roofs in Japan Nissan Facilities 31

32 Cool colors reflect invisible near-infrared sunlight 32

33 Cool and standard brown metal roofing panels Solar reflectance ~ 0.2 higher Afternoon surface temperature ~ 10ºC lower Courtesy BASF Coatings 33

34 Cool black: Dioxazine purple over various undercoats Two-layer system top coat: thin layer of dioxazine purple (14-27 µm) undercoat or substrate: aluminum foil (~ 25 µm) opaque white paint (~1000 µm) non-opaque white paint (~ 25 µm) opaque black paint (~ 25 µm) purple over aluminum foil purple over opaque white paint purple over non-opaque white paint purple over opaque black paint 34

35 Dioxazine purple reflectances over aluminum R solar = 0.41 over opaque white R solar = 0.42 over non-opaque white R solar = 0.30 over opaque black R solar =

36 Cooling vs. heating: Rule of thumb Anywhere in the world, if you need cooling in summer A cool roof saves you money The heating penalty is less than 30% of cooling energy saving If you do not have cooling and summer comfort is not an issue, cool roofs will not save you money If you are considering buying AC, first consider a cool roof A cool roof may result in a down-size in air-handling units and actually save you electricity in heating season Cool roofs also cool the globe 36

37 Why winter heating penalty is low? Days are shorter Sun angle on a roof is lower Sky is cloudier Most heating happens in the early morning or evening hours, when there is no Sun Roofs are covered by snow 37

38 Cool is cool: From cool-color roofs to cool-color cars and cool jackets Toyota experiment (surface temperature 10K cooler) Ford is also working on the technology Courtesy: BMW ( 38

39 Cooling saving and heating penalty: Commercial Buildings 39

40 Pavement Temperature vs. Albedo Pavement Temperature ( F) San Ramon, 8/7/98 Berkeley, 9/13/ Albedo 40

41 Temperature effect on rutting 20 Rut Depth (mm) C (122 F) failure criterion 40 C (104 F) 4 507RF: 50 C RF: 40 C Repetitions (thousands) Source: Dr. John Harvey, UC B Civil Engineering, Inst. Transpo. Studies 41

42 Pavement studies in Japan: Source: Takebayashi and Moriyama 42

43 Roof gardens Energy benefits similar to cool roofs Dirt on rooftops provides additional insulation: good for winter, not so good for summer Provides gardens to enjoy Design is complicated May cost significantly more than cool roofs Better suited for low-sloped roofs Potentially higher maintenance cost An expensive option in arid climates 43

44 Energy and air-quality benefits of trees Shading of buildings Evaporative cooling Wind shielding Smog reduction PM10 deposition Dry deposition Direct carbon sequestration 44

45 Other measures Roof gardens Green walls Anthropogenic heat reduction District cooling Outdoor evaporative cooling Energy efficient community design 45

46 Geo-engineering technologies Solar radiation management Atmospheric projects (Cloud seeding) Terrestrial albedo modification Land management / Bio-geoengineering Space projects Greenhouse gas remediation Carbon sequestration Biological processes Physical processes Chemical techniques Other schemes (black moon, white bubbles) 46

47 Cool urban surfaces: Methodology Changing albedo of urban surfaces and changing atmospheric CO 2 concentrations both result in a change in radiative forcing (RF) Comparing these two radiative forcings relates changes in solar reflectance of urban surfaces to the changes in atmospheric CO 2 content 47

48 GCM simulations (GEOS-5) 48

49 CO 2 offset of cool roofs and pavements Low-sloped roofs albedo for aged white roofs = 0.40 Emitted CO 2 offset for white roofs = -100 kg CO 2 /m 2 It takes about 10 m 2 of white roof to offset 1 T CO 2 emitted Sloped roofs albedo for typical residential and non-residential cool roofs = 0.25 Emitted CO 2 offset for cool roofs = -63 kg CO 2 /m 2 Pavements albedo for cool pavement = 0.15 Emitted CO 2 offset for cool pavements = -38 kg CO 2 /m 2 Source: Akbari et al,

50 World-wide CO 2 offset of cool roofs and pavements Typical urban area is 25% roof and 35% paved surfaces World-wide urban areas = 1.5x10 12 m 2 (1.5 M km 2 ) World-wide roof area = 3.8x10 11 m 2 (0.38 M km 2 ) World-wide paved area = 5.3x10 11 m 2 (0.53 M km 2 ) Emitted CO 2 offset for cool roofs = 24 GT CO 2 Emitted CO 2 offset for cool pavements = 20 GT CO 2 Total for cool roofs and cool pavements = 44 GT CO 2 Note: Menon, Akbari et al (2010) estimate 57 GT CO 2 Akbari and Matthews (2010) estimate 78 GT CO 2 50

51 Time series of CO2 offset effect of 0.10 albedo increase in urban areas Source: Akbari and Matthews (2010) 51

52 Implementation elements for 100 Cool Cities Tall buildings Cool roofs Cool roofing materials Roof gardens Cool walls Green walls Cool wall materials Shades Cool pavements Urban parks? Street misters Low-rise buildings Cool roofs Cool roofing materials Roof gardens? Cool walls Cool wall materials Shades Green walls? Shade trees Cool pavements 52

53 Research Elements for 100 Cool Cities What needs to be done? An initial list Perform detailed analysis (Energy and AQ impacts) Develop a detailed land use database Develop implementation programs (roofs, pavements, trees) Coordinate work with national governments, regional agencies, municipalities and communities Develop a feedback system Develop regional energy codes, standards, guidelines Develop demonstration projects 53

54 100 Cool Cities initiative needs Initial list of cities your help NYC, Taipei, Tokyo, Osaka, Tallahassee, Rome, Milano, Athens, Sao Palo, Hyderabad, Delhi, Los Angeles, Toronto, Montreal, Philadelphia, Chicago, Singapore Where are other cities (?) Join me to contact city officials and recruit more cities Industry needs to co-lead? 54

55 A global action plan: The big picture Develop an international program to install cool roof/pavement in world s100 largest cities This is a simple measure that we hope to organize the world to implement AND WE D BETTER BE SUCCESSFUL We can gain practical experience in design of global measures to combat climate change 100 Cool Cities 55

56 GCCA Objectives & Programs 100 Cool Cities Corporate leadership Building codes and pavement specifications Financial mechanisms Research and development In response to the sweeping climate change issues, and actions to curb the urban heat island effect, Taipei City is honored to be part of this Cool Cities program. - Lung-Bin Hau, Mayor of Taipei 56