1、Designation:E191806(Reapproved 2015)Standard Test Method forMeasuring Solar Reflectance of Horizontal and Low-SlopedSurfaces in the Field1This standard is issued under the fixed designation E1918;the number immediately following the designation indicates the year oforiginal adoption or,in the case o
2、f 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.1.Scope1.1 This test method covers the measurement of solarreflectance of various horizontal and low-sloped sur
3、faces andmaterials in the field,using a pyranometer.The test method isintended for use when the sun angle to the normal from asurface is less than 45.2.Referenced Documents2.1 ASTM Standards:2E722 Practice for Characterizing Neutron Fluence Spectra inTerms of an Equivalent Monoenergetic Neutron Flue
4、ncefor Radiation-Hardness Testing of ElectronicsE903 Test Method for Solar Absorptance,Reflectance,andTransmittance of Materials Using Integrating Spheres3.Terminology3.1 Definitions:3.1.1 low-sloped surfacessurfaces with a slope smallerthan 9.5.The roofing industry has widely accepted a slope of2:1
5、2 or less as a definition of low-sloped roofs.This corre-sponds to a slope of approximately 9.5(16.7%).3.1.2 pyranometeran instrument(radiometer)used tomeasure the total solar radiant energy incident upon a surfaceper unit time and unit surface area.3.1.3 solar energythe radiant energy originating f
6、rom thesun.Approximately 99%of solar energy lies between wave-lengths of 0.3 to 3.5 m.3.1.4 solar fluxfor these measurements,the direct anddiffuse radiation from the sun received at ground level over thesolar spectrum,expressed in watts per square metre.3.1.5 solar reflectancethe fraction of solar f
7、lux reflectedby a surface.3.2 Definitions of Terms Specific to This Standard:3.2.1 solar spectrumthe solar spectrum at ground levelextending from wavelength 0.3 to 3.5 m.4.Summary of Test Method4.1 A pyranometer is used to measure incoming and re-flected solar radiation for a uniform horizontal or l
8、ow-slopedsurface.The solar reflectance is the ratio of the reflectedradiation to the incoming radiation.5.Significance and Use5.1 Solar reflectance is an important factor affecting surfaceand near-surface ambient air temperature.Surfaces with lowsolar reflectance(typically 30%or lower),absorb a high
9、fraction of the incoming solar energy which is either conductedinto buildings or convected to air(leading to higher airtemperatures).Use of materials with high solar reflectance mayresult in lower air-conditioning energy use and cooler citiesand communities.The test method described here measures th
10、esolar reflectance of surfaces in the field.6.Apparatus6.1 SensorA precision spectral pyranometer(PSP)sensi-tive to radiant energy in the 0.282.8 m band is recom-mended.A typical pyranometer yields a linear output of60.5%between 0 and 1400 Wm2and a response time of ones.Specific characteristics can
11、be obtained based on calibrationby the manufacturer of the pyranometer.Other suitable pyra-nometers are discussed in Zerlaut.3The double-dome design ofthe PSP minimizes the effects of internal convection resultingfrom tilting the pyranometer at different angles.For this reason,the PSP is especially
12、suitable for this test,since measurementof solar reflectivity requires the apparatus to alternatively faceup and down.6.2 Read-Out InstrumentThe analog output from the pyra-nometer is converted to digital output with a readout meter(such as EPLAB Model 455 Instantaneous Solar RadiationMeter)that has
13、 an accuracy of better than 60.5%and aresolution of 1 Wm2.The meter shall be scaled to the1This 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 approv
14、ed Feb.1,2015.Published February 2015.Originallyapproved in 1997.Last previous edition approved in 2006 as E1918 06.DOI:10.1520/E1918-06R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume in
15、formation,refer to the standards Document Summary page onthe ASTM website.3Zerlaut,G.,“Solar Radiation Instrumentation,”Solar Resources,R.L.Hulstrom,ed.,MIT Press,Cambridge,MA,1989,pp.173308.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1
16、 sensitivity of the specific PSP by the manufacturer of thepyranometer.Alternatively,a precision voltmeter can be used.6.3 Pyranometer StandThe pyranometer shall be mountedon an arm and a stand that places the sensor at a height of 50cm above the surface to minimize the effect of the shadow onmeasured reflected radiation.The arm and stand shall bestrong,cast the smallest possible shadow,and allow thepyranometer to be turned upward and downward easily asshown in Fig.1.7.Sampling,Test Specimens,an