1、Designation: E 424 71 (Reapproved 2007)Standard Test Methods forSolar Energy Transmittance and Reflectance (Terrestrial) ofSheet Materials1This standard is issued under the fixed designation E 424; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 These tes
3、t methods cover the measurement of solarenergy transmittance and reflectance (terrestrial) of materials insheet form. MethodA, using a spectrophotometer, is applicablefor both transmittance and reflectance and is the refereemethod. Method B is applicable only for measurement oftransmittance using a
4、pyranometer in an enclosure and the sunas the energy source. Specimens for Method A are limited insize by the geometry of the spectrophotometer while Method Brequires a specimen 0.61 m2(2 ft2). For the materials studied bythe drafting task group, both test methods give essentiallyequivalent results.
5、1.2 This standard does not purport to address all of thesafety problems, 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 D
6、ocuments2.1 ASTM Standards:2E 259 Practice for Preparation of Pressed Powder WhiteReflectance Factor Transfer Standards for Hemisphericaland Bi-Directional GeometriesE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near-Infrared Spectrophotom-etersE 308 Practice fo
7、r Computing the Colors of Objects byUsing the CIE System3. Terminology Definitions3.1 solar absorptancethe ratio of absorbed to incidentradiant solar energy (equal to unity minus the reflectance andtransmittance).3.2 solar admittancesolar heat transfer taking into ac-count reradiated and convected e
8、nergy.3.3 solar energy for these methods the direct radiationfrom the sun at sea level over the solar spectrum as defined in3.2, its intensity being expressed in watts per unit area.3.4 solar reflectancethe percent of solar radiation (watts/unit area) reflected by a material.3.5 solar spectrum for t
9、he purposes of these methods thesolar spectrum at sea level extending from 350 to 2500 nm.3.6 solar transmittancethe percent of solar radiation(watts/unit area) transmitted by a material.4. Summary of Methods4.1 Method AMeasurements of spectral transmittance, orreflectance versus a magnesium oxide s
10、tandard, are made usingan integrating sphere spectrophotometer over the spectral rangefrom 350 to 2500 nm. The illumination and viewing mode shallbe normal-diffuse or diffuse-normal. The solar energy trans-mitted or reflected is obtained by integrating over a standardsolar energy distribution curve
11、using weighted or selectedordinates for the appropriate solar-energy distribution. Thedistribution at sea level, air mass 2, is used.4.2 Method BUsing the sun as the source and a pyranom-eter as a detector the specimen is made the cover of anenclosure with the plane of the specimen perpendicular to
12、theincident radiation; transmittance is measured as the ratio of theenergy transmitted to the incident energy. (The apparatus ofMethod B has been used for the measurement of solar-energyreflectance but there is insufficient experience with this tech-nique for standardization at present.)1These test
13、methods are under the jurisdiction of ASTM Committee E44 onSolar, Geothermal and Other Alternative Energy Sources and is the direct respon-sibility of Subcommittee E44.05 on Solar Heating and Cooling Systems andMaterials.Current edition approved March 1, 2007. Published April 2007. Originallyapprove
14、d in 1971. Last previous edition approved in 2001 as E 424-71(2001).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 w
15、ebsite.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 Solar-energy transmittance and reflectance are importantfactors in the heat admission through fenestration, most com-monly through glass or plastics. (
16、See Appendix X3.) Thesemethods provide a means of measuring these factors underfixed conditions of incidence and viewing. While the data maybe of assistance to designers in the selection and specificationof glazing materials, the solar-energy transmittance and reflec-tance are not sufficient to defi
17、ne the rate of heat transferwithout information on other important factors. The methodshave been found practical for both transparent and translucentmaterials as well as for those with transmittances reduced byhighly reflective coatings. Method B is particularly suitable forthe measurement of transm
18、ittance of inhomogeneous, pat-terned, or corrugated materials since the transmittance isaveraged over a large area.6. Method ASpectrophotometric Method6.1 Apparatus:6.1.1 SpectrophotometerAn integrating sphere spectro-photometer, by means of which the spectral characteristics ofthe test specimen or
19、material may be determined throughoutthe solar spectrum. For some materials the spectrum regionfrom 350 to 1800 nm may be sufficient. The design shall besuch that the specimen may be placed in direct contact with thesphere aperture for both transmission and reflection, so that theincident radiation
20、is within 6 of perpendicularity to the planeof the specimen.36.1.2 Standards:6.1.2.1 For transmitting specimens, incident radiation shallbe used as the standard relative to which the transmitted lightis evaluated. Paired reflecting standards are used, prepared induplicate as described below.6.1.2.2
21、For reflecting specimens, use smoked magnesiumoxide (MgO) as a standard as the closest practicable approxi-mation of the completely reflecting, completely diffusingsurface for the region from 300 to 2100 nm. The preferredstandard is a layer (at least 2.0 mm in thickness) freshlyprepared from collect
22、ed smoke of burning magnesium (Rec-ommend Practice E 259). Pressed barium sulfate (BaSO4)orMgO are not recommended because of poor reflecting proper-ties beyond 1000 nm.6.1.3 Specimen Backing for Reflectance MeasurementTransparent and translucent specimens shall be backed by alight trap or a diffusi
23、ng black material which is known toabsorb the near infrared. The backing shall reflect no more than1 % at all wavelengths from 350 to 2500 nm as determinedusing the spectrophotometer.6.2 Test Specimens:6.2.1 Opaque specimens shall have at least one planesurface; transparent and translucent specimens
24、 shall have twosurfaces that are essentially plane and parallel.6.2.2 Comparison of translucent materials is highly depen-dent on the geometry of the specific instrument being used. Itis recommended that the specimen be placed in direct contactwith the sphere to minimize and control loss of scattere
25、dradiation.6.2.3 For specularly reflecting specimens the sphere condi-tions, especially where the reflected beam strikes the spherewall, shall be known to be highly reflecting (95 % or higher).It is recommended that a freshly coated sphere be usedespecially when measuring translucent or specularly r
26、eflectingspecimens.6.3 Calibration:6.3.1 Photometric The calibration of the photometricscale shall be done as recommended by the manufacturer. Itshall be carefully executed at reasonable time intervals toensure accuracy over the entire range.6.3.2 WavelengthPeriodic calibrations should be made ofthe
27、 wavelength scales. Procedures for wavelength calibrationmay be found in Recommended Practice E 275. A didymiumfilter has also been used for this purpose. Although theabsorption peaks have been defined for specific resolution inthe visible spectrum it also has peaks in the near infrared;however, the
28、 wavelength of the peaks must be agreed upon,using a specific instrument.6.4 Procedure:6.4.1 Transmittance Obtain spectral transmittance datarelative to air. For measurement of transmittance of translucentspecimens, place freshly prepared matched smoked MgOsurfaces at the specimen and reference port
29、s at the rear of thesphere (Note 1). The interior of the sphere should be freshlycoated with MgO and in good condition.NOTE 1Magnesium oxide standards may be considered matched if oninterchanging them the percent reflectance is altered by no more than 1 %at any wavelength between 350 and 1800 nm.6.4
30、.2 Reflectance Obtain spectral directional reflectancedata relative to MgO. Include the specular component in thereflectance measurement. Back the test specimen with a blackdiffuse surface if it is not opaque. Depending on the requiredaccuracy, use the measured values directly or make correctionsfor
31、 instrumental 0 and 100 % lines (see Method E 308).6.5 Calculation Solar energy transmittance or reflectanceis calculated by integration. The distribution of solar energy asreported by Parry Moon4for sea level and air mass 2 shall beused.6.5.1 Weighted OrdinatesObtain the total solar energytransmitt
32、ance, Tse, and reflectance, Rse, in percent, by integrat-ing the spectral transmittance (reflectance) over the standardsolar energy distribution as follows:Tseor Rse5 (l5350nml52100 nmTlor Rl! 3 El(1)El for air mass 2, at 50-nm intervals, normalized to 100, isgiven in Appendix X1.6.5.1.1 This integr
33、ation is easily programmed for automaticcomputation.6.5.2 Selected OrdinatesIntegration is done by readingthe transmittance or reflectance at selected wavelengths and3For additional apparatus specifications see Recommended Practice E 308.4Journal of the Franklin Institute, Vol 230, 1940, p. 583, or
34、SmithsonianPhysical Tables, Table 1, Vol 815, 1954, p. 273.E 424 71 (2007)2calculating their average. Appendix X2 lists 20 selected ordi-nates for integration.56.6 ReportThe report shall include the following:6.6.1 Complete identification of the material tested, andwhether translucent, clear, or spe
35、cularly reflecting,6.6.2 Solar T percent or Solar R percent, or both, to thenearest 0.1 %,6.6.3 Specimen thickness,6.6.4 Identification of the instrument used, and6.6.5 Integration method.7. Method BPyranometer MethodNOTE 2The pyranometer is used to measure total global (sun and sky)radiation (previ
36、ously designated a 180 pyroheliometer; presently thelatter word refers to a normal incidence measurement of direct solarradiation). See IGY Instruction Manual, Part VI, Radiation Instruments,Pergamon Press, New York, NY.7.1 Apparatus:7.1.1 EnclosureThe apparatus that has been used success-fully is a
37、 box capable of supporting a 0.61-m2(24-in.2)specimen. The box, which would normally be about 0.66-m2(26-in.2) outside, should be capable of being faced in anydirection, as on a universal mount. The inside of the box shouldbe painted flat black.3A typical unit is shown in Fig. 1.7.1.2 Sensor:7.1.2.1
38、 The sensing element of this instrument is a pyra-nometer consisting of concentric rings, or wedges of thermo-piles, colored alternately black and white. The voltage outputof this sensor is proportional to the intensity of the totalincident solar irradiation. The spectral sensitivity of thisinstrume
39、nt extends from the ultraviolet to infrared wavelengths(280 to 2800 nm), thus encompassing all the solar spectrum.The pyranometer should be located inside the box so that thesensing thermopile is approximately 50 mm (2 in.) from thecenter of the bottom plane of the sample.7.1.2.2 The pyranometer has
40、 a viewing area of 180. AnEppley pyranometer with its 25-mm (1-in.) diameter sensingdisk, when placed in the center of the box, views the midpointof the edges of the test specimen as a cone of 160; thediagonal of the specimen is viewed as a cone of 166 when thethermopile is 50 mm (2 in.) below the b
41、ottom of the specimen.7.1.2.3 Read-Out InstrumentationA recorder, or a nonre-cording meter capable of indicating in the 0.2 to 15-mV rangeare permissible for use. The output voltage of the pyranometerwill be affected by the input impedance of the meter to whichit is connected. Thus, the meter used t
42、o indicate solar intensityshould have a very high input impedance, such as a precisionvacuum-tube voltmeter, or a meter which has been calibratedfor one particular sensing element, thus compensating for anyloading effects on that element.7.2 SpecimensThe test specimens should be not less than0.61 by
43、 0.61 m (24 by 24 in.). If the cross-sectional shape ofthe specimen is not flat, care must be taken to prevent thepossibility of light leaks at the edges such as are caused by theuse of oversize specimens.7.3 Procedure:7.3.1 Conduct the tests on a clear sunny day with no cloudcover interruptions dur
44、ing the individual tests. Conduct testingbetween the hours of 9 a.m. and 3 p.m. local standard time; thisis when the solar radiation is at least 80 % of the value obtainedat solar noon for that day. In the Northern hemisphere takereadings between November and February only between 10a.m. and 2 p.m.
45、Expose the test specimen approximatelynormal to the sun for 15 min prior to testing. Next, align thebox normal to the suns rays and take the average incidentsolar-energy reading over a period of time (normally severalminutes) until a steady trace, or reading is obtained. Then placethe test specimen
46、on the box and again record the average solarenergy reaching the sensor. When the test specimen has acorrugated or irregular surface move it across the sensingelement, and take readings at 10-mm (12-in.) intervals for thewidth of one corrugation or irregularity, and average thereadings. Also measure
47、 corrugated specimens with the corru-gations in the North-South direction and in the East-Westdirection.7.3.2 The solar energy transmittance of the test specimens isthe ratio of the energy measured when the test specimen isplaced between the sun and the sensor and the energy measuredby the sensor wi
48、th no test specimen in place.7.4 ReportThe report shall include the following:7.4.1 The source and identity of the test specimen,7.4.2 A complete description of the test specimen, that is,thickness, cross-sectional shape, color, size, translucent ortransparent, type of material,7.4.3 The percent sol
49、ar energy transmittance to the nearest1%,7.4.4 The place, date, and time of the test,7.4.5 The intensity of the solar radiation,7.4.6 Type of sensing unit used, and7.4.7 Ambient air temperature.5Olson, O. H., “Selected Ordinates for SolarAbsorptivity Calculations,” AppliedOptics, Vol 2, No. 1, January 1963.FIG. 1 Typical Unit with Pyranometer Mounted in Black BoxE 424 71 (2007)38. Keywords8.1 pyranometer; reflectance; solar energy; spectrophotom-eter; terrestrial reflectance; transmittanceAPPENDIXES(Nonmandatory Information)X1. SOLAR ENERGY TRANSMITT
