1、Designation: E1918 16Standard 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 of revision, t
2、he 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 surfaces a
3、ndmaterials 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:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interla
4、boratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 low-sloped surfacessurfaces with a slope smallerthan 9.5. The roofing industry has widely accepted a slope of2:12 or less as a definition of low-sloped roofs. This corre-sponds to a slope of approximately 9.
5、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 from thesun. Approximately 99 % of solar energy lies between wave-lengths of 0.3 to 3.5 m.3
6、.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 flux reflectedby a surface.3.2 Definitions of Terms Specific to This Standard:3.2.1 so
7、lar 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 low-slopedsurface. The solar reflectance is the ratio of the reflectedradiation to th
8、e 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 highfraction of the incoming solar energy which is either conductedinto buildings
9、 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 thesolar reflectance of surfaces in the field.6. Apparatus6.1 SensorA precis
10、ion 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 be obtained based on calibrationby the manufacturer of the pyranome
11、ter. 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 suitable for this test, since measurementof solar reflectivity re
12、quires 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 an accuracy of better than 60.5 % and aresolution of 1 Wm2. Th
13、e 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 approved Nov. 1, 2016. Published January 2017. Originallyapproved
14、in 1997. Last previous edition approved in 2015 as E1918 06 (2015).DOI: 10.1520/E1918-16.2For 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 Summ
15、ary 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 StatesThis international standard was
16、 developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1sensitivity o
17、f 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
18、 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, and Test Units7.1 The test method described here applies to large (circleswith at least four metres in diam
19、eter or squares four metres ona side), homogeneous, low-sloped surfaces, such as roofs,streets, and parking lots. The measurements shall be performedon dry surfaces.8. Calibration and Standardization8.1 The pyranometer shall be checked to ensure its accu-racy. Most pyranometers are precalibrated by
20、manufacturers. Itis a good practice to recalibrate the pyranometer as specified bythe manufacturer (typically once every year or two years).Recalibration is done by the manufacturer of the pyranometer.9. Procedure9.1 Cloud cover and haze significantly affect the measure-ments. The tests shall be con
21、ducted on a clear sunny day withno cloud cover or haze during the individual measurements.See AnnexA1 for guidelines on determination of the suitabilityof the 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 sur
22、face 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 when solar radiation is at least 70 % of the value obtained atsolar noon for that day. In winter months (when solar angle islow), perform the t
23、ests 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 testand minimizes the effect of the shadow from equipment). Thereshall be no other shadow on the measurement area other thanthe minimal shadow cast
24、 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, looking directlyaway from the surface) to read incoming solar radiation. Flipthe pyranometer downward to read reflected solar radiation.Make su
25、re 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. Solarreflectance is the ratio of the reflected radiation to incomingradiation. Repeat the pairs of incoming and reflected measure-ments at lea
26、st 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 reflectance of most exterior surfaces is inher-ently variable due to variations in the materials themselves,weathering conditions, and a broad range
27、of environmentalcontaminants. To adequately represent the solar reflectance ofthese surfaces, a minimum of three measurements from widelyspaced (locations separated by more that 10 times the height ofthe sensor above the surface being measured) areas must becollected, and the detailed condition (sur
28、face condition,location, and surrounding objects) of each sample are recorded.For each location repeat 9.1 9.3.10. Report10.1 The report shall include the following:10.1.1 The place, date, and time of the test.FIG. 1 Schematic of the Pyranometer and its StandE1918 16210.1.2 General description of th
29、e 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.)10.1.4 The incoming solar radiation, the reflected solarradiation, and the calculated solar reflec
30、tance for all three pairsof acceptable measurements at each location. The solar reflec-tance is the average of the three acceptable values.11. Precision and Bias11.1 PrecisionThe precision of this test method is basedon an interlaboratory study of Practice E1918 conducted in2012. Each of seven labor
31、atories tested three different smoothsurfaced materials. Every “test result” represents the average ofthree determinations, and all participants were instructed toreport four replicate test results. Practice E691 was followedfor the design and analysis of the data; the details are given inASTM Resea
32、rch Report No. RR:D08-1018.4This precisionstatement is not applicable to materials which surface iscovered with mineral granules such as modified bitumen capsheets. A new interlaboratory study is under way to determinethe precision of this test method with such materials.11.1.1 Repeatability (r)The
33、difference between repetitiveresults obtained by the same operator in a given laboratoryapplying the same test method with the same apparatus underconstant operating conditions on identical test material withinshort intervals of time would in the long run, in the normal andcorrect operation of the t
34、est method, exceed the followingvalues only in one case in 20.11.1.1.1 Repeatability can be interpreted as maximum dif-ference between two results, obtained under repeatabilityconditions, that is accepted as plausible due to random causesunder normal and correct operation of the test method.11.1.1.2
35、 Repeatability limits are listed in Tables 1-3.11.1.2 Reproducibility (R)The difference between twosingle and independent results obtained by different operatorsapplying the same test method in different laboratories usingdifferent apparatus on identical test material would, in the longrun, in the n
36、ormal and correct operation of the test method,exceed the following values only in one case in 20.11.1.2.1 Reproducibility can be interpreted as maximumdifference between two results, obtained under reproducibilityconditions, that is accepted as plausible due to random causesunder normal and correct
37、 operation of the test method.11.1.2.2 Reproducibility limits are listed in Tables 1-3.11.1.3 The above terms (repeatability limit and reproduc-ibility limit) are used as specified in Practice E177.11.1.4 Any judgment in accordance with statements 11.1.1and 11.1.2 would have an approximate 95 % prob
38、ability ofbeing correct.11.2 The precision statement was determined through sta-tistical examination of 208 results, from seven laboratories, onthree smooth surfaced materials, using three different instru-ment types (described below).(1) Instrument A: second-class pyranometer (CMP3)(2) Instrument B
39、: first-class pyranometer (upper CMP6pyranometer on CMA6 albedometer)(3) Instrument C: first-class albedometer (CMA6)11.3 To judge the equivalency of two test results, it isrecommended to choose the material closest in characteristicsto the test material.11.4 BiasAt the time of the study, there was
40、no acceptedreference material suitable for determining the bias for the testmethod, therefore no statement on bias is being made.12. Keywords12.1 pyranometer; solar energy; solar reflectance4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research
41、Report RR:D08-1018. ContactASTM CustomerService at serviceastm.org.TABLE 1 Solar Reflectance Instrument AAMaterialBAverageCxRepeatability StandardDeviationSrReproducibility StandardDeviationSRRepeatability LimitrReproducibility LimitRBlack EPDM 0.0653 0.0039 0.0102 0.0108 0.0286White TPO 0.7125 0.00
42、65 0.0159 0.0182 0.0446Beige Metal 0.3822 0.0049 0.0084 0.0139 0.0236APlease note that measurements from Instrument A have been included only as supplementary information since Instrument A (second-class pryanometer) does not meetthe hardware requirements of Test Method E1918.BThis precision stateme
43、nt is not applicable to materials which surface is covered with mineral granules such as modified bitumen cap sheets.CThe average of the laboratories calculated averages.E1918 163ANNEX(Mandatory Information)A1. GUIDELINES ON DETERMINATION OF THE SUITABILITY OF THE ATMOSPHERIC CONDITIONS FOR CONDUCT-
44、ING 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 measurementscan be performed with reasonable accuracy.A1.1.2 CloudsThe impact of
45、 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-minute period), and make sure that thecalculated solar reflectance is re
46、peatable within the period ofthe measurement (see 9.4).BIBLIOGRAPHY(1) Akbari, H., Bretz, S., Taha, H., Kurn, D., and Hanford, J., “PeakPower and Cooling Energy Savings of High-albedo Roofs,” Energyand Buildings, Vol 25, No. 2, 1997, pp. 117126.(2) Rosenfeld, A., Akbari, H., Bretz, S., Fishman, B.,
47、Kurn, D., Sailor,D., and Taha, H., “Mitigation of Urban Heat Islands: Material, UtilityPrograms, Updates,” Energy and Building, Vol 22, 1995, pp.255265.(3) Taha, H., Sailor, D., and Akbari, H., “High-Albedo Materials forReducing Building Cooling Energy Use,” Lawrence Berkley Labo-ratory Report LBL-3
48、1721, Berkeley, CA., 1992.(4) Florida Solar Energy Center (FSEC), “Laboratory Testing of Re-flective Properties of Roofing Materials,” Contract Report FSEC-CR-670-93, August, 1993.(5) Reagan, J. A. and Acklam, D. M. A., “Solar Reflectivity of CommonBuilding Materials and its Influence of the Roof He
49、at Gain of TypicalSouthwestern USA Residences,” Energy and Buildings, Vol 2, 1979,pp. 237248.(6) Yarbrough, D. W. and Anderson, R. W., “Use of Radiation ControlCoatings to Reduce Building Air-Conditioning Loads,” EnergySource, Vol 15, 1992, pp. 5966.TABLE 2 Solar Reflectance Instrument BMaterialAAverageBxRepeatability StandardDeviationSrReproducibility StandardDeviationSRRepeatability LimitrReproducibility LimitRBlack EPDM 0.0694 0.0033 0.0088 0.0091 0.0246White TPO 0.7021 0.0056 0.0192 0.0157 0.0536Beige Metal 0.3884 0.0020 0.0112 0.0057
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