ASTM C1549-16(2022)
(Test Method)Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer
Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer
SIGNIFICANCE AND USE
5.1 The temperatures of opaque surfaces exposed to solar radiation are generally higher than the adjacent air temperatures. In the case of roofs or walls enclosing conditioned spaces, increased inward heat flows result. In the case of equipment or storage containers exposed to the sun, increased operating temperatures usually result. The extent to which solar radiation affects surface temperatures depends on the solar reflectance of the exposed surface. A solar reflectance of 1.0 (100 % reflected) would mean no effect on surface temperature while a solar reflectance of 0 (none reflected, all absorbed) would result in the maximum effect. Coatings of specific solar reflectance are used to change the temperature of surfaces exposed to sunlight. Coatings and surface finishes are commonly specified in terms of solar reflectance. The initial (clean) solar reflectance must be maintained during the life of the coating or finish to have the expected thermal performance.
5.2 The test method provides a means for periodic testing of surfaces in the field or in the laboratory. Monitor changes in solar reflectance due to aging and exposure, or both, with this test method.
5.3 This test method is used to measure the solar reflectance of a flat opaque surface. The precision of the average of several measurements is usually governed by the variability of reflectances on the surface being tested.
5.4 Use the solar reflectance that is determined by this method to calculate the solar energy absorbed by an opaque surface as shown in Eq 1.
5.4.1 Combine the absorbed solar energy with conductive, convective and other radiative terms to construct a heat balance around an element or calculate a Solar Reflectance Index such as that discussed in Practice E1980.
SCOPE
1.1 This test method covers a technique for determining the solar reflectance of flat opaque materials in a laboratory or in the field using a commercial portable solar reflectometer. The purpose of the test method is to provide solar reflectance data required to evaluate temperatures and heat flows across surfaces exposed to solar radiation.
1.2 This test method does not supplant Test Method E903 which measures solar reflectance over the wavelength range 250 nm to 2500 nm using integrating spheres. The portable solar reflectometer is calibrated using specimens of known solar reflectance to determine solar reflectance from measurements at four wavelengths in the solar spectrum: 380 nm, 500 nm, 650 nm, and 1220 nm. This technique is supported by comparison of reflectometer measurements with measurements obtained using Test Method E903. This test method is applicable to specimens of materials having both specular and diffuse optical properties. It is particularly suited to the measurement of the solar reflectance of opaque materials.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 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.
General Information
Standards Content (Sample)
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
1
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
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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
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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:
2
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.
2
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.
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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.
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