ASTM_E_1980_-_11.pdf

Designation:E198011Standard Practice forCalculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces1This standard is issued under the fixed designation E1980;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe steady-state surface temperature(Ts)under the sun is strongly correlated to solar reflectivityand thermal emissivity of the surface.For equivalent conditions,the Tsof dark surfaces(with low solarreflectance)is higher than light-colored surfaces(with high solar reflectance);and surfaces with lowthermal emissivity have higher Tss than surfaces with high thermal emissivity.The procedurerecommended in this standard will allow a direct comparison of Tsof surfaces under the sun.Theprocedure defines a Solar Reflectance Index(SRI)that measures the relative Tsof a surface withrespect to the standard white(SRI=100)and standard black(SRI=0)under the standard solar andambient conditions.1.Scope1.1 This practice covers the calculation of the Solar Reflec-tance Index(SRI)of horizontal and low-sloped opaque sur-faces at standard conditions.The method is intended tocalculate SRI for surfaces with emissivity greater than 0.1.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2G173 Tables for Reference Solar Spectral Irradiances:DirectNormal and Hemispherical on 37 Tilted Surface3.Terminology3.1 Definitions:3.1.1 convective coeffcient(hc)the rate of heat transferfrom the surface to air induced by the air movement,expressedin watts per square metre per degree Kelvin,Wm2K1.3.1.2 low-sloped surfacessurfaces with a slope smallerthan 9.5 from the horizontal.3.1.3 reference black surface temperature(Tb)is thesteady-state temperature of a black surface with solar reflec-tance of 0.05 and thermal emissivity of 0.9,under the standardsolar and ambient conditions.3.1.4 reference white surface temperature(Tw)is thesteady-state temperature of a white surface with solar reflec-tance of 0.80 and thermal emissivity of 0.9,under the standardsolar and ambient conditions.3.1.5 sky temperature(Tsky)is the temperature of a blackbody that would radiate the same power toward the earth asdoes the sky.3.1.6 solar absorptance()the fraction of solar flux ab-sorbed by a surface.For an opaque surface =1 a.3.1.7 solar flux(I)is the direct and diffuse radiant powerfrom the sun received at ground level over the solar spectrum,expressed in watts per square metre,Wm2.3.1.8 solar reflectance(a)the fraction of solar flux re-flected by a surface.3.1.9 solar reflectance index(SRI)is the relative Tsof asurface with respect to the standard white(SRI=100)andstandard black(SRI=0)under the standard solar and ambientconditions.3.1.10 solar spectrumspectral distribution of typical ter-restrial sunlight at air mass 1.5 as defined in Tables G173.1This test method is under the jurisdiction ofASTM Committee D08 on Roofingand Waterproofing and is the direct responsibility of Subcommittee D08.18 onNonbituminous Organic Roof Coverings.Current edition approved Jan.1,2011.Published January 2011.Originallypublished in 1998.Last previous edition approved in 2001 as E198001,which waswithdrawn in January 2010 and reinstated in January 2011.DOI:10.1520/E1980-11.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.11 standard solar and ambient conditions for thepurpose of this calculation,is defined as a solar flux of 1000Wm2,ambient air temperature of 310 Kelvin(K),and skytemperature of 300 K.Three convective coefficient of 5,12,30Wm2K1,corresponding to low-(0 to 2 ms1),medium-(2to 6 ms1),and high-wind(6 to 10 ms1)conditions,respec-tively.3.1.12 steady-state surface temperature(Ts)is the tem-perature of the surface,in K,under the standard solar andambient conditions.3.1.13 thermal emissivity()the ratio of radiant flux emit-ted by a surface at a given temperature to that emitted by ablack body radiator at the same temperature.For thiscalculation,the thermal emissivity is for a temperature below150C.4.Summary of Practice4.1 For a surface exposed to the sun,when the conductioninto the material is zero,the steady-state surface temp