ASTM C1549-16(2022)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:C1549 −16 (Reapproved 2022)
Standard Test Method for
Determination of Solar Reflectance Near Ambient
Temperature Using a Portable Solar Reflectometer
This standard is issued under the fixed designation C1549; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers a technique for determining the
C168 Terminology Relating to Thermal Insulation
solar reflectance of flat opaque materials in a laboratory or in
E691 Practice for Conducting an Interlaboratory Study to
the field using a commercial portable solar reflectometer. The
Determine the Precision of a Test Method
purpose of the test method is to provide solar reflectance data
E903 Test Method for Solar Absorptance, Reflectance, and
required to evaluate temperatures and heat flows across sur-
Transmittance of Materials Using Integrating Spheres
faces exposed to solar radiation.
E1980 Practice for Calculating Solar Reflectance Index of
1.2 This test method does not supplant Test Method E903
Horizontal and Low-Sloped Opaque Surfaces
which measures solar reflectance over the wavelength range
2.2 ANSI/CRRC Standard:
250 nm to 2500 nm using integrating spheres. The portable
ANSI/CRRC S100 Standard Test Methods for Determining
solar reflectometer is calibrated using specimens of known
Radiative Properties of Materials
solar reflectance to determine solar reflectance from measure-
3. Terminology
ments at four wavelengths in the solar spectrum: 380 nm, 500
nm, 650 nm, and 1220 nm. This technique is supported by
3.1 Definitions—For definitions of some terms used in the
comparison of reflectometer measurements with measurements
test method, refer to Terminology C168.
obtained using Test Method E903. This test method is appli-
3.2 Definitions of Terms Specific to This Standard:
cable to specimens of materials having both specular and
3.2.1 air mass—airmassisrelatedtothepathlengthofsolar
diffuse optical properties. It is particularly suited to the
radiation through the Earth’s atmosphere to the site of interest.
measurement of the solar reflectance of opaque materials.
Air mass 1 is for a path of normal solar radiation at the Earth’s
1.3 The values stated in SI units are to be regarded as equator while air mass 2 indicates two times this path length.
standard. No other units of measurement are included in this
3.2.2 solar reflectance—the fraction of incident solar radia-
standard.
tion upon a surface that is reflected from the surface.
1.4 This standard does not purport to address all of the
3.3 Symbols:
safety concerns, if any, associated with its use. It is the
3.3.1 A—area normal to incident radiation, m .
responsibility of the user of this standard to establish appro- 2
3.3.2 Q —rate at which radiant heat is absorbed per m of
abs
priate safety, health, and environmental practices and deter-
area, W.
mine the applicability of regulatory limitations prior to use.
3.3.3 q —solar flux, W/m .
solar
1.5 This international standard was developed in accor-
3.3.4 r—solar reflectance, dimensionless.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
4. Summary of Test Method
Development of International Standards, Guides and Recom-
4.1 This test method employs a diffuse tungsten halogen
mendations issued by the World Trade Organization Technical
lamp to illuminate a flat specimen for two seconds out of a
Barriers to Trade (TBT) Committee.
ten-second measurement cycle. Reflected light is measured at
1 2
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Measurement. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Sept. 1, 2022. Published October 2022. Originally the ASTM website.
approved in 2002. Last previous edition approved in 2016 as C1549 – 16. DOI: Available from Cool Roof Rating Council (CRRC), 449 15th Street, Suite 400,
10.1520/C1549-16R22. Oakland, CA 94612, http://www.coolroofs.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1549−16 (2022)
an angle of 20° from the incident angle with four detectors. 6. Apparatus
Each detector is equipped with color filters to tailor its
6.1 This test method applies to solar reflectance tests con-
electrical response to a range of wavelengths in the solar
ducted with a portable reflectometer. The instrument consists
spectrum. Software in the instrument combines the outputs of
of three major parts.
thefourdetectorsinappropriateproportionstoapproximatethe
6.1.1 Measurement Head—The measurement head contains
response for incident solar radiation through air mass 0, 1, 1.5,
a tungsten halogen lamp used as the radiation source, the filters
or 2. The solar reflectance for the desired air mass is selectable
used to tailor the reflected radiation to specific wavelength
from the instrument’s keypad. The reflectances measured by
ranges, and detectors for each of the four wavelength ranges.A
the individual detectors are also available from the keypad and
2.5 cm diameter circular opening on the top of the measure-
digital readout.The instrument is calibrated using a black body
mentheadservesasaportthroughwhichincidentandreflected
cavity for a reflectance of zero and one or more surfaces of
radiation are transmitted to and from the test surface.
known solar reflectance provided by the manufacturer. A
6.1.2 Connecting Cable—A connecting cable, connects the
surface to be evaluated is placed firmly against the 2.5 cm
measurement head to the readout module. The connecting
diameter opening on the measurement head and maintained in
cable transmits electrical signals from the four detectors to the
this position until constant readings are displayed by the digital
readout module.
readout. A comparison of techniques for measuring solar
6.1.3 Readout Module—The readout module that is con-
reflectance is available.
nected to the measurement head includes a keypad for control-
ling the functions of the software, software for interpreting the
5. Significance and Use
signals from the measurement head, and a digital readout for
5.1 The temperatures of opaque surfaces exposed to solar solar reflectivity or the display of input parameters or calibra-
radiation are generally higher than the adjacent air tempera- tion information. The resolution of the digital readout is 0.001.
tures. In the case of roofs or walls enclosing conditioned Detailed instructions for use of the keypad to communicate
spaces, increased inward heat flows result. In the case of with the software are provided by the manufacturer of the
equipment or storage containers exposed to the sun, increased apparatus.
operating temperatures usually result. The extent to which 6.1.4 Reference Standards—The calibration of the solar
solar radiation affects surface temperatures depends on the reflectometer is accomplished with a black body cavity that is
solar reflectance of the exposed surface. A solar reflectance of supplied by the manufacturer and at least one high-reflectance
1.0 (100 % reflected) would mean no effect on surface tem- standard. The solar reflectance of the high-reflectance standard
perature while a solar reflectance of 0 (none reflected, all or standards are programmed into the software to facilitate
absorbed) would result in the maximum effect. Coatings of calibration. The apparatus accommodates up to eight solar
specific solar reflectance are used to change the temperature of reflectance standards.
surfaces exposed to sunlight. Coatings and surface finishes are 6.1.5 Test Specimens—Specimens to be tested for solar
commonly specified in terms of solar reflectance. The initial reflectance shall be relatively flat and shall have a minimum
(clean) solar reflectance must be maintained during the life of dimension greater than 2.5 cm in order for the specimen to
completely cover the measurement head opening. Test speci-
the coating or finish to have the expected thermal performance.
mens of sufficient size are placed on top of the measurement
5.2 The test method provides a means for periodic testing of
head. Position the measurement head against a surface for
surfaces in the field or in the laboratory. Monitor changes in
in-situ or large area solar reflectance measurements.
solar reflectance due to aging and exposure, or both, with this
test method.
7. Procedure
5.3 This test method is used to measure the solar reflectance
7.1 Set-up—The instrument requires 110 volt AC power.
ofaflatopaquesurface.Theprecisionoftheaverageofseveral
Take into account necessary safety precautions when using the
measurements is usually governed by the variability of reflec-
instrument outside of conditioned spaces. Before power is
tances on the surface being tested.
applied and the instrument is turned on, either end of the cable
5.4 Use the solar reflectance that is determined by this
must be connected to the socket on the measurement head.The
method to calculate the solar energy absorbed by an opaque
other end must be connected to the socket on the readout and
surface as shown in Eq 1.
control module. The instrument powers up, ready to estimate
the total solar reflectance through air mass 2.The instrument is
Q 5 A·q ·~1 2 r! (1)
abs solar
designed to provide solar reflectances for air mass values of 0,
5.4.1 Combine the absorbed solar energy with conductive,
1, 1.5, or 2.0. The instrument shall be calibrated after at least
convectiveandotherradiativetermstoconstructaheatbalance
30 min. of warm-up time to avoid drift from the calibration.
around an element or calculate a Solar Reflectance Index such
Leaving the instrument on for extended periods of time with a
as that discussed in Practice E1980.
cover over the measurement head opening does not cause
damage.
7.2 Calibration (gain)—At the end of the warm-up period,
Petrie, T. W., Desjarlais, A. O., Robertson, R. H., and Parker, D. S.,
check and adjust the zero and gain. A zero reflectance black-
“Comparison of Techniques for In Situ Nondamaging Measurement of Solar
body cavity and various high reflectance standard specimens
Reflectances of Low-Slope Roof Membranes,” International Journal of
Thermophysics, Vol 22, No. 5 , 2001, pp. 1613-1628. are provided to check zero and gain. If the blackbody cavity
C1549−16 (2022)
TABLE 1 Solar Reflectances (%) of Roofing Materials—Precision
covers the opening of the measurement head and a non-zero
Statistics
reading is noted, then depress calibration/zero key. The instru-
Material Average S S rR
ment detects the presence of the zero reflectance cavity and r R
A 5.79 0.10 0.15 0.29 0.43
resets the output reflectance to zero.
B 13.85 0.06 0.17 0.17 0.48
7.2.1 The gain or calibration adjustment requires that the
C 28.93 0.17 0.72 0.47 2.01
reflectance of a known standard be coded into the instrument.
D 35.57 0.15 0.23 0.41 0.65
E 49.53 0.12 0.46 0.34 1.27
Three standards provided with the instrument are prepro-
F 76.00 0.14 0.51 0.38 1.42
grammed into the memory. Memory for five additional stan-
G 84.69 0.21 0.43 0.59 1.21
dards is provided. A selection key on the keypad allows the
user to select which of eight standards will be used. If the
desired standard covers the opening of the measurement head
8.2 Includeinthetestreportthemanufactureroftheproduct
and its reflectance is not noted on the display, then depress the
being tested. Include any information about the history or age
calibration/zero key should be depressed. When a calibration
of the material in the test report.
standard is in position over the measurement head opening and
8.3 The temperature and relative humidity of the room or
the calibration/zero key is depressed, the instrument automati-
environment in which the measurements were conducted shall
cally detects that a high reflectance object is in place and resets
be reported.
the output reflectance to the selected standard’s preset value.
Zero is very stable but is conveniently checked by using the 8.4 The measured solar reflectances, arithmetic average of
blackbodycavitytocoverthemeasurementheadbetweentests. the measured reflectances, and if appropriate, the standard
Repeat the gain or calibration adjustment described above deviation of the set of measurements shall be reported.
every 30 min.
8.5 The air mass to be associated with the measured solar
7.3 Solar Reflectance Measurement—A surface area of suf- reflectance shall be reported.
ficient size to cover the 2.5 cm diameter circular port on top of
8.6 The date of the test shall be reported.
the measurement head is required. The flat specimen is placed
8.7 A statement of compliance with this standard shall be
on top of the circular port and either held in place by hand or
part of the report. Any exceptions to the procedure shall be
by a weight that will hold the specimen firmly agains
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