ASTM E1084-86(2003)
(Test Method)Standard Test Method for Solar Transmittance (Terrestrial) of Sheet Materials Using Sunlight
Standard Test Method for Solar Transmittance (Terrestrial) of Sheet Materials Using Sunlight
SIGNIFICANCE AND USE
Solar transmittance is an important factor in the admission of energy through fenestration, collector glazing, and protective envelopes. This test method provides a means of measuring this factor under fixed conditions. While the data may be of assistance to designers in the selection and specification of glazing materials, the solar transmittance is not sufficient to define the rate of net heat transfer without information on other important factors.
This test method has been found practical for both transparent and translucent materials, as well as for those with transmittance reduced by highly reflective coatings. This test method is particularly applicable to the measurement of transmittance of inhomogeneous, fiber reinforced, patterned, or corrugated materials since the transmittance is averaged over a large area.
This test method may be used to measure transmittance of glazing materials at angles up to 60° off normal incidence.
Note 1—A technique similar to the one described but using a pyrheliometer has been used for the measurement of specular solar reflectance; however, there is insufficient experience with this technique for standardization at present.
SCOPE
1.1 This test method covers the measurement of solar transmittance (terrestrial) of materials in sheet form by using a pyranometer, an enclosure, and the sun as the energy source.
1.2 This test method also allows measurement of solar transmittance at angles other than normal incidence.
1.3 This test method is applicable to sheet materials that are transparent, translucent, textured, or patterned.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E1084–86 (Reapproved 2003)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.1 solar flux, n—the total radiation from the sun, both
direct and diffuse.
1.1 This test method covers the measurement of solar
transmittance (terrestrial) of materials in sheet form by using a
4. Summary of Test Method
pyranometer, an enclosure, and the sun as the energy source.
4.1 Usingapyranometertomeasurethesolarirradiance,the
1.2 This test method also allows measurement of solar
test specimen is inserted in the path of the rays from the sun to
transmittance at angles other than normal incidence.
the pyranometer. An enclosure with a nonreflecting bottom is
1.3 This test method is applicable to sheet materials that are
used to avoid measuring flux from around the edges of the
transparent, translucent, textured, or patterned.
specimen or from multiple reflections between the box and the
1.4 This standard does not purport to address all of the
specimen. The transmittance is the ratio of the flux measured
safety concerns, if any, associated with its use. It is the
withthespecimeninthelightpathtothefluxmeasuredwithout
responsibility of the user of this standard to establish appro-
the specimen in the path.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents 5.1 Solar transmittance is an important factor in the admis-
sion of energy through fenestration, collector glazing, and
2.1 ASTM Standards:
protective envelopes. This test method provides a means of
E284 Terminology of Appearance
3 measuring this factor under fixed conditions. While the data
E772 Terminology Relating to Solar Energy Conversion
may be of assistance to designers in the selection and specifi-
2.2 Other Document:
4 cation of glazing materials, the solar transmittance is not
ASHRAE Handbook of Fundamentals
sufficient to define the rate of net heat transfer without
3. Terminology information on other important factors.
5.2 This test method has been found practical for both
3.1 Definitions:
transparent and translucent materials, as well as for those with
3.1.1 pyranometer, n—a radiometer used to measure the
transmittance reduced by highly reflective coatings. This test
total solar radiant energy incident upon a surface per unit time
method is particularly applicable to the measurement of
per unit area. This energy includes the direct radiant energy,
transmittanceofinhomogeneous,fiberreinforced,patterned,or
diffuse radiant energy, and reflected radiant energy from the
corrugated materials since the transmittance is averaged over a
background.
large area.
3.1.2 solar reflectance, n—the ratio of reflected to incident
5.3 This test method may be used to measure transmittance
solar flux.
of glazing materials at angles up to 60° off normal incidence.
3.1.3 solar transmittance, n—the ratio of transmitted to
incident solar flux.
NOTE 1—A technique similar to the one described but using a pyrhe-
3.2 Definitions of Terms Specific to This Standard:
liometer has been used for the measurement of specular solar reflectance;
however, there is insufficient experience with this technique for standard-
ization at present.
These test methods are under the jurisdiction of ASTM Committee E44 on
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
6. Apparatus
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems
6.1 Enclosure—The required apparatus is a box capable of
and Systems.
Current edition approved Feb. 21, 1986. Published April 1986. Originally
supporting a 0.60 m (24 in.) square specimen. The box shall
approved in 1986. Last previous edition approved in 1996 as E1084–86(1996)
have a square, clear aperture of no less than 0.50 m by 0.50 m
Annual Book of ASTM Standards, Vol 06.01.
(20 in. by 20 in.). The enclosure shall have provisions to hold
Annual Book of ASTM Standards, Vol 12.02.
specimens planar across the aperture with the additional
Available from American Society of Heating, Refrigerating, and Air Condi-
tioning Engineers, 1791 Tullie Circle N.E., Atlanta, GA 30329.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1084–86 (2003)
capabilitytoremoveandreplacethespecimeneasilyduringthe blackened so that its solar reflectance is less than 0.10. A
measurement process. It shall also have the capability to move typical unit is shown in Fig. 1.
the specimen across the aperture in a systematic way. Light
NOTE 2—Mirrors having the necessary specular reflectance are bright
baffled air vents at the top and bottom of the enclosure are
anodized aluminum lighting sheet, aluminized polymer films, and con-
recommended to aid cooling of all components when a
ventionally mirrored glass. For highly diffusing materials, a box with the
specimenisinplace.Theinsideoftheboxshallhavesidewalls
specified aperture and blackened side walls, the test method could
covered with mirrors having specular, solar reflectance greater
underestimatethetransmittancebyupto0.03.Usinghighlyreflectingside
than0.85thatextendfromtheopeningdowntotheplaneofthe
sensor element. Therest of the inside of the box shall be
(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 grill (K) Rectangular, ⁄4 in. plywood, 500 3 75 mm.
cloth that allow air circulation into the enclosure are preferable.
(C) Pyranometer (L) ⁄2 3 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 ⁄4in 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 36ft
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 (2003)
walls on the interior of the enclosure reduces this error for such materials
6.3.1 Thesensingelementofthisapparatusisapyranometer
to less than 0.01 transmittance unit. For highly specular materials, this
that shall meet WMO Class 2 specifications (1, 2). The most
error is negligible.
important characteristics for the pyranometer are as follows:
NOTE 3—For an enclosure with a highly reflecting bottom, the mea-
6.3.1.1 a flat spectral sensitivity (62%) over the region
sured transmittance could be greater than 0.05 too high due to multiple
from 300 nm to 3000 nm that encompasses nearly all the
reflections.Ablackenedbottomhavinglessthan0.10reflectancewillhold
terrestrial solar flux;
this error to less than 0.005 transmittance units.
6.3.1.2 sensitivity that is isotropic except for the usual
6.2 Tracking:
cosine response with altitude angle; and
6.2.1 The enclosure shall be mounted in a manner that
6.3.1.3 output linear to within 62% from 0 to 1000 W/m2
allows repositioning approximately every 15 min in order to
or calibration curves accurate to within 62% over the same
track the sun. The use of an equitorial or altazmuth mount is
range. Additional desirable characteristics are relative short-
recommended and automatic solar tracker is optional.
timeconstantsofafewsecondsandgoodtemperaturestability.
6.2.2 For manual tracking, an alignment device shall be
used. Several acceptable devices are shown in Fig. 2. NOTE 4—When using pyranometers meeting WMO Class 2 specifica-
tions in this procedure, the inaccuracies due to these sources are expected
6.3 Sensor:
tobelessthan1%.Thisisbecauserelative,ratherthanabsolute,readings
are made over a dynamic range that is small compared to the range of the
sensor. The procedure and apparatus specified in this test method
Flat black paints that are satisfactory for this purpose are 3M brand ECP-2200
available from 3M Company; Parson’s Black available from Eppley Laboratories,
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
Newport, RI; or Krylon Flat Black. Other flat black paints may also be satisfactory.
this standard.
Also, a lining of opaque black velvet cloth such as available from photographic
suppliers is suitable.
(a) Semicircle with scale (b) 12.7mm( ⁄2 in.) ID pipe by 195 mm (7.67 in.) long.
1 3
(A) Semicircle with 143 mm radius cut out of 150 300 mm piece of ⁄2 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
E1084–86 (2003)
minimize the thermal drift during the measurements.
8.7 Compute the estimated standard deviation of the aver-
age transm
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