1、Designation: E 1918 06Standard Test Method forMeasuring Solar Reflectance of Horizontal and Low-SlopedSurfaces in the Field1This standard is issued under the fixed designation E 1918; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 surface
3、s 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:2E 722 Practice for Characterizing Neutron Energy FluenceSpectra in Terms of an Equivalent Monoenergetic Neutr
4、onFluence for Radiation-Hardness Testing of ElectronicsE 903 Test Method for Solar Absorptance, Reflectance, andTransmittance of Materials Using Integrating Spheres33. Terminology3.1 Definitions:3.1.1 low-sloped surfacessurfaces with a slope smallerthan 9.5. The roofing industry has widely accepted
5、a slope of2:12 or less as a definition of low-sloped roofs. This corre-sponds to a slop 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 ene
6、rgy originating from 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 reflectancet
7、he fraction of solar flux 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
8、uniform horizontal or low-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
9、 30 % or lower), absorb a highfraction 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
10、method described here measures thesolar 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 tim
11、e of ones. Specific characteristics can be obtained based on calibrationby the manufacturer of the pyranometer. Other suitable pyra-nometers are discussed in Zerlaut.4The double-dome design ofthe PSP minimizes the effects of internal convection resultingfrom tilting the pyranometer at different angl
12、es. For this reason,the PSP is especially suitable for this test, since measurementof solar reflectivity requires the apparatus to alternatively faceup and down.6.2 Read-Out InstrumentThe analog output from thepyranometer is converted to digital output with a readout meter(such as EPLAB Model 455 In
13、stantaneous Solar RadiationMeter) that has 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
14、Organic Roof Coverings.Current edition approved Aug. 15, 2006. Published September 2006. Originallyapproved in 1997. Last previous edition approved in 1997 as E 1918 97, whichwas withdrawn in January 2006 and reinstated in August 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.
15、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.3Withdrawn.4Zerlaut, G., “Solar Radiation Instrumentation,” Solar Resources, R.L. Hul-strom, ed., MIT Press, Cambridge, MA, 19
16、89, pp. 173308.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.sensitivity of the specific PSP by the manufacturer of thepyranometer. Alternatively, a precision voltmeter can be used.6.3 Pyranometer StandThe pyranometer shall bemount
17、ed on an arm and a stand that places the sensor at aheight of 50 cm above the surface to minimize the effect of theshadow on measured reflected radiation. The arm and standshall be strong, cast the smallest possible shadow, and allowthe pyranometer to be turned upward and downward easily asshown in
18、Fig. 1.7. Sampling, Test Specimens, and Test Units7.1 The test method described here applies to large (circleswith at least four metres in diameter or squares four metres ona side), homogeneous, low-sloped surfaces, such as roofs,streets, and parking lots. The measurements shall be performedon dry s
19、urfaces.8. Calibration and Standardization8.1 The pyranometer shall be checked to ensure its accu-racy. Most pyranometers are precalibrated by manufacturers. Itis a good practice to recalibrate the pyranometer as specified bythe manufacturer (typically once every year or two years).Recalibration is
20、done by the manufacturer of the pyranometer.9. Procedure9.1 Cloud cover and haze significantly affect the measure-ments. The tests shall be conducted on a clear sunny day withno cloud cover or haze during the individual measurements.SeeAnnexA1 for guidelines on determination of the suitabilityof the
21、 atmospheric conditions for conducting the tests.9.2 The test shall be done in conditions where the angle ofthe sun to the normal from the surface of interest is less than45. For flat and low-sloped surfaces, this limits the test tobetween the hours of 9 a.m. and 3 p.m. local standard time; thisis w
22、hen solar radiation is at least 70 % of the value obtained atsolar noon for that day. In winter months (when solar angle islow), perform the tests between hours 10 a.m. and 2 p.m.9.3 Align the stand such that the arm points toward the sun(this eliminates the shadow of the people conducting the testa
23、nd minimizes the effect of the shadow from equipment). Thereshall be no other shadow on the measurement area other thanthe minimal shadow cast by the pyranometer and the stand. Thepyranometer shall be parallel to the surface where measure-ment is conducted.9.4 Face the pyranometer upward (that is, l
24、ooking directlyaway from the surface) to read incoming solar radiation. Flipthe pyranometer downward to read reflected solar radiation.Make sure the readings are constant for at least 10 s. Themeasurements of incoming and reflected radiation shall beperformed in a time interval not to exceed 2 min.
25、Solarreflectance is the ratio of the reflected radiation to incomingradiation. Repeat the pairs of incoming and reflected measure-ments at least three times. The calculated solar reflectance fromall the measurements shall agree within 0.01 in a reflectivityscale of 0.00 to 1.00.9.5 The solar reflect
26、ance of most exterior surfaces is inher-ently variable due to variations in the materials themselves,weathering conditions, and a broad range of environmentalcontaminants. To adequately represent the solar reflectance ofthese surfaces, a minimum of three measurements from widelyspaced (locations sep
27、arated by more that 10 times the height ofthe sensor above the surface being measured) areas must becollected, and the detailed condition (surface condition, loca-tion, and surrounding objects) of each sample are recorded. Foreach location repeat 9.1-9.3.10. Report10.1 The report shall include the f
28、ollowing:10.1.1 The place, date, and time of the test.10.1.2 General description of the surface (surface condition,dirt on surface, age, if available).10.1.3 Aqualitative assessment of cloud cover or haze. (Themeasurements may need to be repeated if taken under cloudyor hazy conditions.)FIG. 1 Schem
29、atic of the Pyranometer and its StandE191806210.1.4 The incoming solar radiation, the reflected solarradiation, and the calculated solar reflectance for all three pairsof acceptable measurements at each location. The solar reflec-tance is the average of the three acceptable values.11. Precision and
30、Bias11.1 A precision and bias statement has not been estab-lished. However, most surfaces are non-uniform and their solarreflectances may vary both from one location to another andwith time.12. Keywords12.1 pyranometer; solar energy; solar reflectanceANNEX(Mandatory Information)A1. GUIDELINES ON DET
31、ERMINATION OF THE SUITABILITY OF THE ATMOSPHERIC CONDITIONS FORCONDUCTING THE TESTSA1.1 The following criteria shall be used to establish thesuitability of the measurement conditions:A1.1.1 HazeAs long as the solar disk is visible and solarflux is not changing rapidly during the test, the measuremen
32、tscan be performed with reasonable accuracy.A1.1.2 CloudsThe impact of clouds close to the sun islarger than clouds in the horizon. It is important to make themeasurements in a stable solar condition. The best way ofdetermining stability is to make several measurements (eachperformed within a two-mi
33、nute period), and make sure that thecalculated solar reflectance is repeatable within the period ofthe measurement (see 9.4).APPENDIX(Nonmandatory Information)X1. BIBLIOGRAPHY(1)Akbari, H., Bretz, S., Taha, H., Kurn, D., and Hanford, J.,“Peak Power and Cooling Energy Savings of High-albedoRoofs,” En
34、ergy and Buildings, Vol 25, No. 2, 1997, pp.117126.(2) Rosenfeld, A., Akbari, H., Bretz, S., Fishman, B., Kurn,D., Sailor, D., and Taha, H., “Mitigation of Urban Heat Islands:Material, Utility Programs, Updates,” Energy and Building, 22,1995, pp. 255265.(3) Taha, H., Sailor, D., and Akbari, H., “Hig
35、h-AlbedoMaterials for Reducing Building Cooling Energy Use,”Lawrence Berkley Laboratory Report LBL-31721, Berkeley,CA., 1992.(4) Florida Solar Energy Center (FSEC), “ LaboratoryTesting of Reflective Properties of Roofing Materials,” Con-tract Report FSEC-CR-670-93, August, 1993.(5) Reagan, J. A. and
36、 Acklam, D. M. A., “Solar Reflectivityof Common Building Materials and its Influence of the RoofHeat Gain of Typical Southwestern USA Residences,” Energyand Buildings, 2, 1979, pp. 237248.(6) Yarbrough, D. W. and Anderson, R. W., “Use ofRadiation Control Coatings to Reduce Building Air-Conditioning
37、Loads,” Energy Source, Vol 15, 1992, pp. 5966.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, a
38、nd the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revis
39、ion of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you s
40、houldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E1918063
