ASTM E1084-86(2009)

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Designation: E1084 − 86(Reapproved 2009)
Standard Test Method for
Solar Transmittance (Terrestrial) of Sheet Materials Using
Sunlight
This standard is issued under the fixed designation E1084; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope specimen or from multiple reflections between the box and the
specimen. The transmittance is the ratio of the flux measured
1.1 This test method covers the measurement of solar
withthespecimeninthelightpathtothefluxmeasuredwithout
transmittance (terrestrial) of materials in sheet form by using a
the specimen in the path.
pyranometer, an enclosure, and the sun as the energy source.
1.2 This test method also allows measurement of solar
4. Significance and Use
transmittance at angles other than normal incidence.
4.1 Solar transmittance is an important factor in the admis-
1.3 This test method is applicable to sheet materials that are
sion of energy through fenestration, collector glazing, and
transparent, translucent, textured, or patterned.
protective envelopes. This test method provides a means of
measuring this factor under fixed conditions. While the data
1.4 This standard does not purport to address all of the
may be of assistance to designers in the selection and specifi-
safety concerns, if any, associated with its use. It is the
cation of glazing materials, the solar transmittance is not
responsibility of the user of this standard to establish appro-
sufficient to define the rate of net heat transfer without
priate safety and health practices and determine the applica-
information on other important factors.
bility of regulatory limitations prior to use.
4.2 This test method has been found practical for both
2. Terminology
transparent and translucent materials, as well as for those with
2.1 Definitions:
transmittance reduced by highly reflective coatings. This test
2.1.1 pyranometer, n—a radiometer used to measure the
method is particularly applicable to the measurement of
total solar radiant energy incident upon a surface per unit time
transmittanceofinhomogeneous,fiberreinforced,patterned,or
per unit area. This energy includes the direct radiant energy,
corrugated materials since the transmittance is averaged over a
diffuse radiant energy, and reflected radiant energy from the
large area.
background.
4.3 This test method may be used to measure transmittance
2.1.2 solar reflectance, n—the ratio of reflected to incident
of glazing materials at angles up to 60° off normal incidence.
solar flux.
NOTE 1—A technique similar to the one described but using a
2.1.3 solar transmittance, n—the ratio of transmitted to
pyrheliometer has been used for the measurement of specular solar
incident solar flux. reflectance; however, there is insufficient experience with this technique
for standardization at present.
2.2 Definitions of Terms Specific to This Standard:
2.2.1 solar flux, n—the total radiation from the sun, both
5. Apparatus
direct and diffuse.
5.1 Enclosure—The required apparatus is a box capable of
supporting a 0.60 m (24 in.) square specimen. The box shall
3. Summary of Test Method
have a square, clear aperture of no less than 0.50 m by 0.50 m
3.1 Usingapyranometertomeasurethesolarirradiance,the
(20 in. by 20 in.). The enclosure shall have provisions to hold
test specimen is inserted in the path of the rays from the sun to
specimens planar across the aperture with the additional
the pyranometer. An enclosure with a nonreflecting bottom is
capabilitytoremoveandreplacethespecimeneasilyduringthe
used to avoid measuring flux from around the edges of the
measurement process. It shall also have the capability to move
the specimen across the aperture in a systematic way. Light
baffled air vents at the top and bottom of the enclosure are
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof
recommended to aid cooling of all components when a
Subcommittee E44.05 on Solar Heating and Cooling Systems and Materials.
specimenisinplace.Theinsideoftheboxshallhavesidewalls
Current edition approved April 1, 2009. Published June 2009. Originally
covered with mirrors having specular, solar reflectance greater
approvedin1986.Lastpreviouseditionapprovedin2003asE1084–86(2003).DOI:
10.1520/E1084-86R09. than0.85thatextendfromtheopeningdowntotheplaneofthe
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1084 − 86 (2009)
to less than 0.01 transmittance unit. For highly specular materials, this
sensor element. The rest of the inside of the box shall be
error is negligible.
blackened so that its solar reflectance is less than 0.10. A
NOTE 3—For an enclosure with a highly reflecting bottom, the
typical unit is shown in Fig. 1.
measured transmittance could be greater than 0.05 too high due to
multiple reflections.Ablackened bottom having less than 0.10 reflectance
NOTE 2—Mirrors having the necessary specular reflectance are bright
will hold this error to less than 0.005 transmittance units.
anodized aluminum lighting sheet, aluminized polymer films, and con-
ventionally mirrored glass. For highly diffusing materials, a box with the
specified aperture and blackened side walls, the test method could
underestimatethetransmittancebyupto0.03.Usinghighlyreflectingside Flatblackpaintsaresatisfactoryforthispurpose.Also,aliningofopaqueblack
walls on the interior of the enclosure reduces this error for such materials velvet cloth such as that available from photographic suppliers is suitable.
(A) Specular mirror, 500 × 50 mm. (J) Standard 2 × 4 in. wood framing, 75 mm long (bottom to center of hole)
(B) Nonreflecting, black bottom. Nontransmitting louvers or multiple layers of grill (K) Rectangular, ⁄4 in. plywood, 500 × 75 mm.
cloth that allow air circulation into the enclosure are preferable.
(C) Pyranometer (L) ⁄2 × 2 in. carriage bolt with wing and washer.
(D) Support shelf for pyranometer. The height of the shelf will depend on the (M) ⁄4 in. iron pipe.
pyranometer used.
(E) Semicircular disk 538 mm diameter out of ⁄4 in plywood. (N) U-bolts.
(F) Semicircular tracker with scale (P) Primary tracking axis, aligned parallel to earth’s axis of rotation. The axis shall
make an angle with the vertical equal to the local latitude and point toward the
North Star.
(G) Lip of flange turned up to 20 mm to help support specimens (Q) C-clamp attached to arm to lock equatorial angle during measurements.
(H) 50 mm flange bent out of sheet metal or cut from wood. Top surface is (R) Vertical support post approximately1mlong. Made from standard 2 × 6 ft
painted back to prevent light entering enclosure due to multiple reflections from lumber.
around the specimen edges.
NOTE 1—This apparatus consisting of enclosure, detector, and equatorial mount has been found acceptable for measuring solar transmittance of sheet
materials. The majority of the pieces are cut from standard 2.4, 2 by 6, and ⁄4 in. plywood construction materials.
FIG. 1 Apparatus Consisting of Enclosure, Detector, and Equatorial Mount
E1084 − 86 (2009)
(a) Semicircle with scale (b) 12.7mm( ⁄2 in.) ID pipe by 195 mm (7.67 in.) long.
(A) Semicircle with 143 mm radius cut out of 150 300 mm piece of to ⁄4 in. Note—Realign when direct from the solar disk no longer traverses the pipe.
plywood.
(B) Tape with 1 cm scale attached to inside of semicircle.
(C) This opaque sheet (preferably metal) with 3 mm aperture centered above semicircle.
Note—A displacement of the light beam coming through the aperture of 1 cm on the 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 mm
diameter white disk.
Note—Realign when shadow of rod falls outside of white disk.
NOTE 1—The 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 rod
or pipe perpendicular to the surface of the enclosure.
FIG. 2 Alignment Devices for Enclosure
5.2 Tracking: range. Additional desirable characteristics are relative short-
5.2.1 The enclosure shall be mounted in a manner that timeconstantsofafewsecondsandgoodtemperaturestability.
allows repositioning approximately every 15 min in order to
NOTE 4—When using pyranometers meeting WMO Class 2 specifica-
track the sun. The use of an equitorial or altazmuth mount is
tions in this procedure, the inaccuracies due to these sources are expected
recommended and automatic solar tracker is optional.
tobelessthan1%.Thisisbecauserelative,ratherthanabsolute,readings
are made over a dynamic range that is small compared to the range of the
5.2.2 For manual tracking, an alignment device shall be
sensor. The procedure and apparatus specified in this test method
used. Several acceptable devices are shown in Fig. 2.
minimize the thermal drift during the measurements.
5.3 Sensor:
5.3.2 The pyranometer shall be located so that the sensing
5.3.1 Thesensingelementofthisapparatusisapyranometer
thermopile(notthedome)iscenteredapproximately50mm(2
that shall meet WMO Class 2 specifications (1, 2). The most
in.) below the plane of the rim of the box. Normally pyranom-
important characteristics for the pyranometer are as follows:
etershavea180°viewingangle,butwhenplacedasdescribed,
5.3.1.1 a flat spectral sensitivity (62%) over the region
thefieldangletothemidpointoftheedgesofthetestspecimen
from 300 nm to 3000 nm that encompasses nearly all the
is 157°.
terrestrial solar flux;
5.3.3 For pyranometers with thermal control shields having
5.3.1.2 sensitivity that is isotropic except for the usual
high reflectance, for example, the Eppley P.S.P.) it is important
cosine response with altitude angle; and
that the reflection from the pyranometer back toward the sheet
5.3.1.3 output linear to within 62% from 0 to 1000 W/m2
materialundertestbeminimized.Thiscanbedonebycovering
or calibration curves accurate to within 62% over the same
the shield with a nonreflecting material or by mounting the
pyranometer outside the enclosure with only the do
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