1、Designation: C1549 16Standard Test Method forDetermination of Solar Reflectance Near AmbientTemperature Using a Portable Solar Reflectometer1This standard is issued under the fixed designation C1549; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase 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.1. Scope1.1 This test method covers a technique for determining thesolar reflectance of flat opaque m
3、aterials in a laboratory or inthe field using a commercial portable solar reflectometer. Thepurpose of the test method is to provide solar reflectance datarequired to evaluate temperatures and heat flows across sur-faces exposed to solar radiation.1.2 This test method does not supplant Test Method E
4、903which measures solar reflectance over the wavelength range250 to 2500 nm using integrating spheres. The portable solarreflectometer is calibrated using specimens of known solarreflectance to determine solar reflectance from measurementsat four wavelengths in the solar spectrum: 380 nm, 500 nm,650
5、 nm, and 1220 nm. This technique is supported bycomparison of reflectometer measurements with measurementsobtained using Test Method E903. This test method is appli-cable to specimens of materials having both specular anddiffuse optical properties. It is particularly suited to themeasurement of the
6、solar reflectance of opaque materials.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the u
7、ser 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:2C168 Terminology Relating to Thermal InsulationE691 Practice for Conducting an Interlaboratory Study toDetermi
8、ne the Precision of a Test MethodE903 Test Method for Solar Absorptance, Reflectance, andTransmittance of Materials Using Integrating SpheresE1980 Practice for Calculating Solar Reflectance Index ofHorizontal and Low-Sloped Opaque Surfaces2.2 ANSI/CRRC Standard:3ANSI/CRRC S100 Standard Test Methods
9、for DeterminingRadiative Properties of Materials3. Terminology3.1 DefinitionsFor definitions of some terms used in thetest method, refer to Terminology C168.3.2 Definitions of Terms Specific to This Standard:3.2.1 air massair mass is related to the path length of solarradiation through the Earths at
10、mosphere to the site of interest.Air mass 1 is for a path of normal solar radiation at the Earthsequator while air mass 2 indicates two times this path length.3.2.2 solar reflectancethe fraction of incident solar radia-tion upon a surface that is reflected from the surface.3.3 Symbols:3.3.1 Aarea no
11、rmal to incident radiation, m2.3.3.2 Qabsrate at which radiant heat is absorbed per m2ofarea, W.3.3.3 qsolarsolar flux, W/m2.3.3.4 rsolar reflectance, dimensionless.4. Summary of Test Method4.1 This test method employs a diffuse tungsten halogenlamp to illuminate a flat specimen for two seconds out
12、of aten-second measurement cycle. Reflected light is measured atan angle of 20 from the incident angle with four detectors.Each detector is equipped with color filters to tailor itselectrical response to a range of wavelengths in the solarspectrum. Software in the instrument combines the outputs oft
13、he four detectors in appropriate proportions to approximate theresponse for incident solar radiation through air mass 0, 1, 1.5,1This test method is under the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.30 on ThermalMeasurement.Current
14、edition approved Nov. 1, 2016. Published November 2016. Originallyapproved in 2002. Last previous edition approved in 2014 as C1549 09 (2014).DOI: 10.1520/C1549-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Boo
15、k of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Cool Roof Rating Council (CRRC), 449 15th Street, Suite 400,Oakland, CA 94612, http:/www.coolroofs.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoh
16、ocken, PA 19428-2959. United States1or 2. The solar reflectance for the desired air mass is selectablefrom the instruments keypad. The reflectances measured bythe individual detectors are also available from the keypad anddigital readout. The instrument is calibrated using a black bodycavity for a r
17、eflectance of zero and one or more surfaces ofknown solar reflectance provided by the manufacturer. Asurface to be evaluated is placed firmly against the 2.5 cmdiameter opening on the measurement head and maintained inthis position until constant readings are displayed by the digitalreadout. A compa
18、rison of techniques for measuring solarreflectance is available.45. Significance and Use5.1 The temperatures of opaque surfaces exposed to solarradiation are generally higher than the adjacent air tempera-tures. In the case of roofs or walls enclosing conditionedspaces, increased inward heat flows r
19、esult. In the case ofequipment or storage containers exposed to the sun, increasedoperating temperatures usually result. The extent to whichsolar radiation affects surface temperatures depends on thesolar reflectance of the exposed surface. A solar reflectance of1.0 (100 % reflected) would mean no e
20、ffect on surface tem-perature while a solar reflectance of 0 (none reflected, allabsorbed) would result in the maximum effect. Coatings ofspecific solar reflectance are used to change the temperature ofsurfaces exposed to sunlight. Coatings and surface finishes arecommonly specified in terms of sola
21、r reflectance. The initial(clean) solar reflectance must be maintained during the life ofthe coating or finish to have the expected thermal performance.5.2 The test method provides a means for periodic testing ofsurfaces in the field or in the laboratory. Monitor changes insolar reflectance due to a
22、ging and exposure, or both, with thistest method.5.3 This test method is used to measure the solar reflectanceof a flat opaque surface. The precision of the average of severalmeasurements is usually governed by the variability of reflec-tances on the surface being tested.5.4 Use the solar reflectanc
23、e that is determined by thismethod to calculate the solar energy absorbed by an opaquesurface as shown in Eq 1.Qabs5 Aqsolar1 2 r! (1)5.4.1 Combine the absorbed solar energy with conductive,convective and other radiative terms to construct a heat balancearound an element or calculate a Solar Reflect
24、ance Index suchas that discussed in Practice E1980.6. Apparatus6.1 This test method applies to solar reflectance tests con-ducted with a portable reflectometer. The instrument consistsof three major parts.6.1.1 Measurement HeadThe measurement head containsa tungsten halogen lamp used as the radiatio
25、n source, the filtersused to tailor the reflected radiation to specific wavelengthranges, and detectors for each of the four wavelength ranges.A2.5 cm diameter circular opening on the top of the measure-ment head serves as a port through which incident and reflectedradiation are transmitted to and f
26、rom the test surface.6.1.2 Connecting CableA connecting cable, connects themeasurement head to the readout module. The connectingcable transmits electrical signals from the four detectors to thereadout module.6.1.3 Readout ModuleThe readout module that is con-nected to the measurement head includes
27、a keypad for control-ling the functions of the software, software for interpreting thesignals from the measurement head, and a digital readout forsolar reflectivity or the display of input parameters or calibra-tion information. The resolution of the digital readout is 0.001.Detailed instructions fo
28、r use of the keypad to communicatewith the software are provided by the manufacturer of theapparatus.6.1.4 Reference StandardsThe calibration of the solarreflectometer is accomplished with a black body cavity that issupplied by the manufacturer and at least one high-reflectancestandard. The solar re
29、flectance of the high-reflectance standardor standards are programmed into the software to facilitatecalibration. The apparatus accommodates up to eight solarreflectance standards.6.1.5 Test SpecimensSpecimens to be tested for solarreflectance shall be relatively flat and shall have a minimumdimensi
30、on greater than 2.5 cm in order for the specimen tocompletely cover the measurement head opening. Test speci-mens of sufficient size are placed on top of the measurementhead. Position the measurement head against a surface forin-situ or large area solar reflectance measurements.7. Procedure7.1 Set-u
31、pThe instrument requires 110 volt AC power.Take into account necessary safety precautions when using theinstrument outside of conditioned spaces. Before power isapplied and the instrument is turned on, either end of the cablemust be connected to the socket on the measurement head. Theother end must
32、be connected to the socket on the readout andcontrol module. The instrument powers up, ready to estimatethe total solar reflectance through air mass 2. The instrument isdesigned to provide solar reflectances for air mass values of 0,1, 1.5, or 2.0. The instrument shall be calibrated after at least30
33、 min. of warm-up time to avoid drift from the calibration.Leaving the instrument on for extended periods of time with acover over the measurement head opening does not causedamage.7.2 Calibration (gain)At the end of the warm-up period,check and adjust the zero and gain. A zero reflectance black-body
34、 cavity and various high reflectance standard specimensare provided to check zero and gain. If the blackbody cavitycovers the opening of the measurement head and a non-zeroreading is noted, then depress calibration/zero key. The instru-ment detects the presence of the zero reflectance cavity andrese
35、ts the output reflectance to zero.7.2.1 The gain or calibration adjustment requires that thereflectance of a known standard be coded into the instrument.4Petrie, T. W., Desjarlais, A. O., Robertson, R. H., and Parker, D. S.,“Comparison of Techniques for In Situ Nondamaging Measurement of SolarReflec
36、tances of Low-Slope Roof Membranes,” International Journal ofThermophysics, Vol 22, No. 5 , 2001, pp. 1613-1628.C1549 162Three standards provided with the instrument are prepro-grammed into the memory. Memory for five additional stan-dards is provided. A selection key on the keypad allows theuser to
37、 select which of eight standards will be used. If thedesired standard covers the opening of the measurement headand its reflectance is not noted on the display, then depress thecalibration/zero key should be depressed. When a calibrationstandard is in position over the measurement head opening andth
38、e calibration/zero key is depressed, the instrument automati-cally detects that a high reflectance object is in place and resetsthe output reflectance to the selected standards preset value.Zero is very stable but is conveniently checked by using theblackbody cavity to cover the measurement head bet
39、ween tests.Repeat the gain or calibration adjustment described aboveevery 30 min.7.3 Solar Reflectance MeasurementA surface area of suf-ficient size to cover the 2.5 cm diameter circular port on top ofthe measurement head is required. The flat specimen is placedon top of the circular port and either
40、 held in place by hand orby a weight that will hold the specimen firmly against the rimof the port. Position the measurement head manually against asurface such as a roof or wall. It is important that the rim of thespecimen port be in contact with the specimen around theentire circumference of the p
41、ort. The escape of radiationbetween the rim of the specimen port and the specimen willresult in inaccurate solar reflectance values.7.3.1 Atest specimen shall be maintained in the test positionfor at least three ten-second cycles or until a consistent readingis observed on the digital readout. The r
42、eadout gives eithersolar reflectance or solar absorptance (one minus solar reflec-tance). In the event of a reading that fluctuates between twovalues the average of the two values shall be recorded.7.4 Evaluation of a SurfaceQuantify the variability of thesolar reflectance with position on a test sp
43、ecimen by measuringsolar reflectance at three or more locations on the surface. If asurface is cleaned before testing, then the surface shall beallowed to dry completely before the reflectance test isundertaken.7.5 CalculationThe set of individual solar reflectancemeasurements for a test surface sha
44、ll be averaged and reported.If the set contains three or more measurements, then thestandard deviation of the measurement set shall be reported. Inany event, all of the individual measurements for a test surfaceshall be recorded and reported.8. Report8.1 Include in the test report a physical descrip
45、tion of thesurface being reported and indicate if the surface has beencleaned prior to the test. The test report shall include adescription of the specimen substrate in the case of coatingsand the thickness of the coating. The source or location of thetest specimen shall be reported.8.2 Include in t
46、he test report the manufacturer of the productbeing tested. Include any information about the history or ageof the material in the test report.8.3 The temperature and relative humidity of the room orenvironment in which the measurements were conducted shallbe reported.8.4 The measured solar reflecta
47、nces, arithmetic average ofthe measured reflectances, and if appropriate, the standarddeviation of the set of measurements shall be reported.8.5 The air mass to be associated with the measured solarreflectance shall be reported.8.6 The date of the test shall be reported.8.7 A statement of compliance
48、 with this standard shall bepart of the report. Any exceptions to the procedure shall bestated in the report.8.8 An estimated uncertainty in the reported solar reflec-tance shall be part of the report.9. Precision and Bias9.1 PrecisionPrecision statistics for seven roofing materi-als that were deter
49、mined by an interlaboratory study involvingsix laboratories are shown in Table 1. Each laboratory reportedthree replicates on the same specimen. The repeatability, Sr,and the reproducibility standard deviations, SR, were calculatedfrom the data using Practice E691. The 95 % repeatability, r,and the reproducibility, R, limits were calculated from thefollowing expressions: 2.8 Srand 2.8 SR, respectively. Thecalculations for r and R were made before Srand SRwererounded to two significant figures.9.2 BiasSolar reflectance values at air mass 1.5 wereobtained f
