1、Designation: E 1084 86 (Reapproved 2009)Standard Test Method forSolar Transmittance (Terrestrial) of Sheet Materials UsingSunlight1This standard is issued under the fixed designation E 1084; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, 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 solartransmittance (terrestrial) of materials in sheet
3、form by using apyranometer, an enclosure, and the sun as the energy source.1.2 This test method also allows measurement of solartransmittance at angles other than normal incidence.1.3 This test method is applicable to sheet materials that aretransparent, translucent, textured, or patterned.1.4 This
4、standard does not purport to address all of thesafety concerns, 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. Terminology2.1 Defini
5、tions:2.1.1 pyranometer, na radiometer used to measure thetotal solar radiant energy incident upon a surface per unit timeper unit area. This energy includes the direct radiant energy,diffuse radiant energy, and reflected radiant energy from thebackground.2.1.2 solar reflectance, nthe ratio of refle
6、cted to incidentsolar flux.2.1.3 solar transmittance, nthe ratio of transmitted toincident solar flux.2.2 Definitions of Terms Specific to This Standard:2.2.1 solar flux, nthe total radiation from the sun, bothdirect and diffuse.3. Summary of Test Method3.1 Using a pyranometer to measure the solar i
7、rradiance, thetest specimen is inserted in the path of the rays from the sun tothe pyranometer. An enclosure with a nonreflecting bottom isused to avoid measuring flux from around the edges of thespecimen or from multiple reflections between the box and thespecimen. The transmittance is the ratio of
8、 the flux measuredwith the specimen in the light path to the flux measured withoutthe specimen in the path.4. Significance and Use4.1 Solar transmittance is an important factor in the admis-sion of energy through fenestration, collector glazing, andprotective envelopes. This test method provides a m
9、eans ofmeasuring this factor under fixed conditions. While the datamay be of assistance to designers in the selection and specifi-cation of glazing materials, the solar transmittance is notsufficient to define the rate of net heat transfer withoutinformation on other important factors.4.2 This test
10、method has been found practical for bothtransparent and translucent materials, as well as for those withtransmittance reduced by highly reflective coatings. This testmethod is particularly applicable to the measurement oftransmittance of inhomogeneous, fiber reinforced, patterned, orcorrugated mater
11、ials since the transmittance is averaged over alarge area.4.3 This test method may be used to measure transmittanceof glazing materials at angles up to 60 off normal incidence.NOTE 1A technique similar to the one described but using a pyrhe-liometer has been used for the measurement of specular sola
12、r reflectance;however, there is insufficient experience with this technique for standard-ization at present.5. Apparatus5.1 EnclosureThe required apparatus is a box capable ofsupporting a 0.60 m (24 in.) square specimen. The box shallhave a square, clear aperture of no less than 0.50 m by 0.50 m(20
13、in. by 20 in.). The enclosure shall have provisions to holdspecimens planar across the aperture with the additionalcapability to remove and replace the specimen easily during themeasurement process. It shall also have the capability to movethe specimen across the aperture in a systematic way. Lightb
14、affled air vents at the top and bottom of the enclosure arerecommended to aid cooling of all components when aspecimen is in place.The inside of the box shall have side wallscovered with mirrors having specular, solar reflectance greaterthan 0.85 that extend from the opening down to the plane of the
15、sensor element. The rest of the inside of the box shall beblackened so that its solar reflectance is less than 0.10. Atypical unit is shown in Fig. 1.NOTE 2Mirrors having the necessary specular reflectance are brightanodized aluminum lighting sheet, aluminized polymer films, and con-ventionally mirr
16、ored glass. For highly diffusing materials, a box with the1This test method is under the jurisdiction of ASTM Committee E44 on Solar,Geothermal and OtherAlternative Energy Sources and is the direct responsibility ofSubcommittee E44.05 on Solar Heating and Cooling Systems and Materials.Current editio
17、n approved April 1, 2009. Published June 2009. Originallyapproved in 1986. Last previous edition approved in 2003 as E 108486(2003).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.specified aperture and blackened side walls, the test
18、 method couldunderestimate the transmittance by up to 0.03. Using highly reflecting sidewalls on the interior of the enclosure reduces this error for such materialsto less than 0.01 transmittance unit. For highly specular materials, thiserror is negligible.NOTE 3For an enclosure with a highly reflec
19、ting bottom, the mea-sured transmittance could be greater than 0.05 too high due to multiplereflections.Ablackened bottom having less than 0.10 reflectance will holdthis error to less than 0.005 transmittance units.25.2 Tracking:5.2.1 The enclosure shall be mounted in a manner thatallows repositioni
20、ng approximately every 15 min in order totrack the sun. The use of an equitorial or altazmuth mount isrecommended and automatic solar tracker is optional.2Flat black paints are satisfactory for this purpose.Also, a lining of opaque blackvelvet cloth such as that available from photographic suppliers
21、 is suitable.(A) Specular mirror, 500 3 50 mm. (J) Standard 2 3 4 in. wood framing, 75 mm long (bottom to center of hole)(B) Nonreflecting, black bottom. Nontransmitting louvers or multiple layers of grillcloth that allow air circulation into the enclosure are preferable.(K) Rectangular,34 in. plywo
22、od, 500 3 75 mm.(C) Pyranometer (L)12 3 2 in. carriage bolt with wing and washer.(D) Support shelf for pyranometer. The height of the shelf will depend on thepyranometer used.(M)34 in. iron pipe.(E) Semicircular disk 538 mm diameter out of34 in plywood. (N) U-bolts.(F) Semicircular tracker with scal
23、e (P) Primary tracking axis, aligned parallel to earths axis of rotation. The axis shallmake an angle with the vertical equal to the local latitude and point toward theNorth Star.(G) Lip of flange turned up to 20 mm to help support specimens (Q) C-clamp attached to arm to lock equatorial angle durin
24、g measurements.(H) 50 mm flange bent out of sheet metal or cut from wood. Top surface ispainted back to prevent light entering enclosure due to multiple reflections fromaround the specimen edges.(R) Vertical support post approximately1mlong. Made from standard 2 3 6ftlumber.NOTE 1This apparatus cons
25、isting of enclosure, detector, and equatorial mount has been found acceptable for measuring solar transmittance of sheetmaterials. The majority of the pieces are cut from standard 2.4, 2 by 6, and34 in. plywood construction materials.FIG. 1 Apparatus Consisting of Enclosure, Detector, and Equatorial
26、 MountE 1084 86 (2009)25.2.2 For manual tracking, an alignment device shall beused. Several acceptable devices are shown in Fig. 2.5.3 Sensor:5.3.1 The sensing element of this apparatus is a pyranometerthat shall meet WMO Class 2 specifications (1, 2).3The mostimportant characteristics for the pyran
27、ometer are as follows:5.3.1.1 a flat spectral sensitivity (62 %) over the regionfrom 300 nm to 3000 nm that encompasses nearly all theterrestrial solar flux;5.3.1.2 sensitivity that is isotropic except for the usualcosine response with altitude angle; and5.3.1.3 output linear to within 62 % from 0 t
28、o 1000 W/m2or calibration curves accurate to within 62 % over the samerange. Additional desirable characteristics are relative short-time constants of a few seconds and good temperature stability.NOTE 4When using pyranometers meeting WMO Class 2 specifica-tions in this procedure, the inaccuracies du
29、e to these sources are expectedto be less than 1 %. This is because relative, rather than absolute, readingsare made over a dynamic range that is small compared to the range of thesensor. The procedure and apparatus specified in this test methodminimize the thermal drift during the measurements.5.3.
30、2 The pyranometer shall be located so that the sensingthermopile (not the dome) is centered approximately 50 mm (2in.) below the plane of the rim of the box. Normally pyranom-eters have a 180 viewing angle, but when placed as described,the field angle to the midpoint of the edges of the test specime
31、nis 157.5.3.3 For pyranometers with thermal control shields havinghigh reflectance, for example, the Eppley P.S.P.) it is importantthat the reflection from the pyranometer back toward the sheetmaterial under test be minimized. This can be done by coveringthe shield with a nonreflecting material or b
32、y mounting thepyranometer outside the enclosure with only the dome andsensor element projecting into the box.NOTE 5Mounting the pyranometer outside of the enclosure alsoreduces the heating load and cooling requirements for the pyranometer.6. Specimens6.1 The test specimens shall not be less than 0.6
33、0 by 0.60 m(24 by 24 in.). Care must be taken to prevent light leaks at the3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.(a) Semicircle with scale (b) 12.7mm(12 in.) ID pipe by 195 mm (7.67 in.) long.(A) Semicircle with 143 mm radius cut out of 150 3
34、00 mm piece of12 to34 in.plywood.NoteRealign when direct from the solar disk no longer traverses the pipe.(B) Tape with 1 cm scale attached to inside of semicircle.(C) This opaque sheet (preferably metal) with 3 mm aperture centered abovesemicircle.NoteA displacement of the light beam coming through
35、 the aperture of 1 cm onthe circumference of the semicircle equals 4 misalignment. This tracker is conve-nient for determining angles for off normal incidence measurements.(c) 9 mm diameter rod by 500 mm long centered on 80 mmdiameter white disk.NoteRealign when shadow of rod falls outside of white
36、disk.NOTE 1The dimensions are chosen to provide 6 4 limits on deviations from normal to the sun. In (b) and ( c) care must be taken to mount the rodor pipe perpendicular to the surface of the enclosure.FIG. 2 Alignment Devices for EnclosureE 1084 86 (2009)3edges, especially if the cross-sectional sh
37、ape of the specimen isnot flat. Also, if the cross-sectional shape is not flat or if thespecimen is patterned, a specimen enough larger to allowtranslation across the pyranometer by at least one period of theshape or pattern is required.7. Procedure7.1 Conduct the tests on a sunny day with no cloud
38、coverwithin 615 of the sun and a minimum normal solar irradianceof 700 W/m2 and constant to within 1 % during the individualtests. Conduct testing as close to solar noon as possible but nomore than 3 h before or after solar noon.7.2 Set up apparatus at a location where no prominentstructure or veget
39、ation is nearby in the pyranometers field ofview.7.3 Align the box aperture to within 4 of the normal to thesuns rays, and measure the solar flux with no specimen inplace.Allow adequate time for the trace or reading to stabilize.7.4 Place the test specimen on the box and measure thetransmitted solar
40、 flux, again allowing adequate time for thetrace or reading to stabilize.NOTE 6Operate the pyranometer as directed by its manufactureexcept that horizontal mounting requirements must be ignored. Longresponse times are undesirable because of the potential measurement errordue to changing irradiance a
41、nd the inconvenience of slow samplethroughput. The manufacturer shall be consulted if response times otherthan original provided are desired.7.5 Compute the solar transmittance of the test specimen asthe ratio of the flux measured when the test specimen is placedbetween the sun and the sensor to the
42、 flux measured by thesensor with no test specimen in place.NOTE 7For a sensor with linear response, the ratio is equal to the ratioof the output signals with and without the specimen in place.7.6 Repeat the steps in 7.3 and 7.4 a minimum of five timesor until the estimated standard deviation of the
43、average valuefor the calculated transmittance is acceptable. Make eachmeasurement with the specimen in a different location.7.7 Compute the estimated standard deviation of the aver-age transmittance of the specimen using the following equa-tion:Sr5(j 5 1nt 2tj!2n!n 2 1!(1)where:Sr= the estimated sta
44、ndard deviation of the average,t = the average transmittance,j = the jth individual measurement of the transmittance,andn = the number of individual measurements made.7.8 Align the apparatus, at least every 15 min.7.9 When measuring corrugated or nonuniformly transmit-ting specimens, translate the s
45、pecimen in such a way as toobtain an average value for the transmittance. Since a system-atic translation over one period of structure is required, it ispermissible to perform the step in 7.3. Then take severalmeasurements with sample on the box (8.4) before repeatingthe step in 7.3, provided these
46、before and after readings are inclose agreement.NOTE 8Do not leave the specimens on the box for periods longer than10 min since it may cause overheating of the sensor, resulting in nonlinearresponse or even permanent damage.7.10 Measurement of the solar transmittance of sheet mate-rials at angles up
47、 to 60 off normal incidence is also permittedby this test method. To do this, align the box aperture withrespect to the solar angle to provide the desired incidenceangle, and follow the steps in 7.4 to 7.7.8. Report8.1 The report shall include the following information:8.1.1 The source and identity
48、of the test specimen,8.1.2 A complete description of the test specimen, that is,thickness, cross-sectional shape, color, size, translucent ortransparent, type of material.8.1.3 The orientation of the sample based on any nonuni-formity or anisotropy such as surface coatings, exposed surfacefiber orie
49、ntation, color bands, etc. during each measurement.8.1.4 For each angle of incidence used, report the followinginformation.8.1.4.1 The angle of incidence.8.1.4.2 The solar transmittance as the average of the five ormore measurements to the nearest 0.01 transmittance unit.8.1.4.3 The estimated standard deviation of the averagecalculated as in 7.7.8.1.4.4 The number of measurements used in the computa-tion.8.1.5 The place, date, and time of the test.8.1.6 The solar irradiance as measured in 7.3.8.1.7 Type, model, serial number, and current cal
