Advances in developing standards for accelerated aging of cool roofing materials Hashem Akbari, Professor Concordia University, Montreal, Canada
Acknowledgement The research on developing methods to estimate the effect of aging on solar reflectance and thermal emittance of roofing materials is primarily performed at Lawrence Berkeley National Laboratory, Berkeley, CA and the principal researchers include: Mohamad Sleiman Thomas W. Kirchstetter Haley E. Gilbert Paul H. Berdahl Hugo Destaillats Ronnen Levinson
Needs for accelerated aging standards Understand the effect of weathering and aging on solar reflectance and thermal emittance Allow manufacturers to develop and test new products Expedite market introduction of new products Reduce cost and time associated with testing materials in weathering farms
Aging = soiling + weathering wet deposition: soot, salts, organics 2010 dry deposition: mineral dust 2012 microbiological growth: fungi, mold, bacteria 4
Aging markedly decreases solar reflectance of conventional roofs Aged solar reflectance 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 OHIO (n=586) OHIO (n = 573) CA Title 24 no change 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Initial solar reflectance running mean fieldapplied coating clay tile metal roofing single-ply membrane factoryapplied coating concrete tile asphalt shingle modified bitumen Sleimanet al. (2011) Solar Energy Materials and Solar Cells, 95, 3385. 5
Coupons of 27 products naturally exposed at the three CRRC sites are collected & characterized quarterly temperate (Cleveland, OH) hot & dry (Phoenix, AZ) hot & humid (Miami, FL) 45 tilt 2011 2012 2013 JANUARY APRIL JULY OCTOBER 5 tilt 6
30 20 10 0 Factory-applied coating -10 Fractional difference in aged solar reflectance (%) Field-applied coating Metal Modified bitumen Shingle Single-ply membrane Tile 7 Fluctuations in aged solar reflectance with respect to CRRC 3-site average are moderate (R k R CRRC ) R CRRC Sleimanet al. Solar Energy Materials and Solar Cells. 2011;95:3385-20 -30 Florida Arizona Ohio 124 173 33 71 13 34 27
Roofing products used in this study We screened 100 roofing materials from 40 industrial partners Selected 28 materials from the following categories: fieldapplied coating clay tile single-ply membrane asphalt shingle factoryapplied coating concrete tile metal roofing modified bitumen Selection criteria: diversity of products & colors, market presence, sample uniformity and availability of aged samples. 8
Chemical composition of soiling on building envelopes How to mimic natural soiling in the lab? Dust 28 66% Salts 23% Salts 18 27% Dust 53% Favezet al, Soot 6% POM 18% Soot 4 12% Particulate Organic Matter 8 36 % soot core salts and organic coating Atmos. Environ, 2006 9
Soiling surrogates used in our laboratory method Salts Clays + Ironoxide Humic acid Soot hydrosol 10
Soiling apparatus and laboratory method Pressure gauge 2-way Valve Spraying nozzle Unexposed Compressed dry air Aqueous Soiling mixture Spraying vessel Coupon of a roofing product Soiled Spraying the soiling mix (5 30 sec) Drying w/ir lamp (1 2 min) Measurement of R ( 5-10 min)
Accelerated aging standard protocol
Our method reproduces CRRC s 3-year-aged solar reflectance ratings in 3 days Field applied coating (n=7) Metal or factoryapplied coating (n=8) Single-ply membrane (n=11) Clay tile (n=2) Asphalt shingle (n=4) Modified bitumen (n=3) 13
June 2012 -June 2014 Status of the standards A draft standard was balloted twice ASTM task group finalized the draft standard Working on to finalize the process at ASTM September 2012 Draft standard presented at ISO TC-163: Thermal performance and energy use in the built environment No activity since then 14
Trends in cool roof technologies Cool roof materials White Cool colored Directionally reflective Retro-reflective Thermochromics 15
White is the coolest
Cool colored roofs are in market cool concrete tile R 0.40 standard concrete tile (same color) Courtesy American Rooftile Coatings solar reflectance gain = +0.37 +0.26 +0.23 +0.15 +0.29 +0.29 cool clay tile R 0.40 Courtesy MCA Clay Tile cool fiberglass asphalt shingle R 0.25 Courtesy Elk Corporation cool metal R 0.30 Courtesy BASF Industrial Coatings 17
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 18 Courtesy: BMW (http://www.ips-innovations.com/solar_reflective_clothing.htm)
Applications: Directionally reflective materials 19
Directionally reflective materials 20
Application: Retro-reflective coatings 21
Thermo-chromic coatings 22
Application: New cool tiles Self-cleaning tiles by TOTO, Inc. 23
Application: Self-cleaning tent ordinary white tent photocatalytic white tent 24
Application: Self cleaning 25
Announcement 26
References Sleimanet al. 2014. Soiling of building envelope surfaces and its effect on solar reflectance Part II: Development of an accelerated aging method for roofing materials. Solar Energy Materials and Solar Cells 122, 271 281. CRRC. 2014. Rated Products Directory. Cool Roof Rating Council, Oakland, California. http://coolroofs.org. Favezet al. 2006. Crossed optical and chemical evaluations of modern glass soiling in various European urban environments. Atmospheric Environment 40 (37), 7192-7204.
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Contact Information Hashem Akbari, Professor Building, Civil and Environmental Engineering Concordia University, Montreal, Canada 1-514-848-2424 x3201 Hashem.Akbari@Concordia.CA