ASTM E1918-06(2015)
(Test Method)Standard Test Method for Measuring Solar Reflectance of Horizontal and Low-Sloped Surfaces in the Field
Standard Test Method for Measuring Solar Reflectance of Horizontal and Low-Sloped Surfaces in the Field
SIGNIFICANCE AND USE
5.1 Solar reflectance is an important factor affecting surface and near-surface ambient air temperature. Surfaces with low solar reflectance (typically 30 % or lower), absorb a high fraction of the incoming solar energy which is either conducted into buildings or convected to air (leading to higher air temperatures). Use of materials with high solar reflectance may result in lower air-conditioning energy use and cooler cities and communities. The test method described here measures the solar reflectance of surfaces in the field.
SCOPE
1.1 This test method covers the measurement of solar reflectance of various horizontal and low-sloped surfaces and materials in the field, using a pyranometer. The test method is intended for use when the sun angle to the normal from a surface is less than 45°.
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Designation:E1918 −06 (Reapproved 2015)
Standard Test Method for
Measuring Solar Reflectance of Horizontal and Low-Sloped
Surfaces in the Field
This standard is issued under the fixed designation E1918; 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 3.2 Definitions of Terms Specific to This Standard:
3.2.1 solar spectrum—the solar spectrum at ground level
1.1 This test method covers the measurement of solar
extending from wavelength 0.3 to 3.5 µm.
reflectance of various horizontal and low-sloped surfaces and
materials in the field, using a pyranometer. The test method is
4. Summary of Test Method
intended for use when the sun angle to the normal from a
4.1 A pyranometer is used to measure incoming and re-
surface is less than 45°.
flected solar radiation for a uniform horizontal or low-sloped
2. Referenced Documents surface. The solar reflectance is the ratio of the reflected
radiation to the incoming radiation.
2.1 ASTM Standards:
E722 PracticeforCharacterizingNeutronFluenceSpectrain
5. Significance and Use
Terms of an Equivalent Monoenergetic Neutron Fluence
5.1 Solar reflectance is an important factor affecting surface
for Radiation-Hardness Testing of Electronics
and near-surface ambient air temperature. Surfaces with low
E903 Test Method for Solar Absorptance, Reflectance, and
solar reflectance (typically 30 % or lower), absorb a high
Transmittance of Materials Using Integrating Spheres
fractionoftheincomingsolarenergywhichiseitherconducted
3. Terminology
into buildings or convected to air (leading to higher air
temperatures).Useofmaterialswithhighsolarreflectancemay
3.1 Definitions:
result in lower air-conditioning energy use and cooler cities
3.1.1 low-sloped surfaces—surfaces with a slope smaller
and communities.The test method described here measures the
than 9.5°. The roofing industry has widely accepted a slope of
solar reflectance of surfaces in the field.
2:12 or less as a definition of low-sloped roofs. This corre-
sponds to a slope of approximately 9.5° (16.7 %).
6. Apparatus
3.1.2 pyranometer—an instrument (radiometer) used to
6.1 Sensor—A precision spectral pyranometer (PSP) sensi-
measure the total solar radiant energy incident upon a surface
tive to radiant energy in the 0.28–2.8 µm band is recom-
per unit time and unit surface area.
mended. A typical pyranometer yields a linear output of
–2
3.1.3 solar energy—the radiant energy originating from the
60.5 % between 0 and 1400W·m and a response time of one
sun. Approximately 99 % of solar energy lies between wave-
s. Specific characteristics can be obtained based on calibration
lengths of 0.3 to 3.5 µm.
by the manufacturer of the pyranometer. Other suitable pyra-
3.1.4 solar flux—for these measurements, the direct and
nometers are discussed in Zerlaut. The double-dome design of
diffuse radiation from the sun received at ground level over the
the PSP minimizes the effects of internal convection resulting
solar spectrum, expressed in watts per square metre.
fromtiltingthepyranometeratdifferentangles.Forthisreason,
the PSP is especially suitable for this test, since measurement
3.1.5 solar reflectance—the fraction of solar flux reflected
of solar reflectivity requires the apparatus to alternatively face
by a surface.
up and down.
6.2 Read-Out Instrument—Theanalogoutputfromthepyra-
This test method is under the jurisdiction ofASTM Committee D08 on Roofing
and Waterproofing and is the direct responsibility of Subcommittee D08.18 on nometer is converted to digital output with a readout meter
Nonbituminous Organic Roof Coverings.
(such as EPLAB Model 455 Instantaneous Solar Radiation
Current edition approved Feb. 1, 2015. Published February 2015. Originally
Meter) that has an accuracy of better than 60.5 % and a
approved in 1997. Last previous edition approved in 2006 as E1918 – 06. DOI:
–2
resolution of 1 W·m . The meter shall be scaled to the
10.1520/E1918-06R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Zerlaut, G., “Solar Radiation Instrumentation,” Solar Resources, R.L.
the ASTM website. Hulstrom, ed., MIT Press, Cambridge, MA, 1989, pp. 173–308.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1918−06 (2015)
sensitivity of the specific PSP by the manufacturer of the solar noon for that day. In winter months (when solar angle is
pyranometer. Alternatively, a precision voltmeter can be used. low), perform the tests between hours 10 a.m. and 2 p.m.
6.3 Pyranometer Stand—Thepyranometershallbemounted
9.3 Align the stand such that the arm points toward the sun
on an arm and a stand that places the sensor at a height of 50
(this eliminates the shadow of the people conducting the test
cm above the surface to minimize the effect of the shadow on
andminimizestheeffectoftheshadowfromequipment).There
measured reflected radiation. The arm and stand shall be
shall be no other shadow on the measurement area other than
strong, cast the smallest possible shadow, and allow the
theminimalshadowcastbythepyranometerandthestand.The
pyranometer to be turned upward and downward easily as
pyranometer shall be parallel to the surface where measure-
shown in Fig. 1.
ment is conducted.
9.4 Face the pyranometer upward (that is, looking directly
7. Sampling, Test Specimens, and Test Units
away from the surface) to read incoming solar radiation. Flip
7.1 The test method described here applies to large (circles
the pyranometer downward to read reflected solar radiation.
with at least four metres in diameter or squares four metres on
Make sure the readings are constant for at least 10 s. The
a side), homogeneous, low-sloped surfaces, such as roofs,
measurements of incoming and reflected radiation shall be
streets, and parking lots.The mea
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1918 − 06 E1918 − 06 (Reapproved 2015)
Standard Test Method for
Measuring Solar Reflectance of Horizontal and Low-Sloped
Surfaces in the Field
This standard is issued under the fixed designation E1918; 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
1.1 This test method covers the measurement of solar reflectance of various horizontal and low-sloped surfaces and materials
in the field, using a pyranometer. The test method is intended for use when the sun angle to the normal from a surface is less than
45°.
2. Referenced Documents
2.1 ASTM Standards:
E722 Practice for Characterizing Neutron Fluence Spectra in Terms of an Equivalent Monoenergetic Neutron Fluence for
Radiation-Hardness Testing of Electronics
E903 Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres
3. Terminology
3.1 Definitions:
3.1.1 low-sloped surfaces—surfaces with a slope smaller than 9.5°. The roofing industry has widely accepted a slope of 2:12
or less as a definition of low-sloped roofs. This corresponds to a slopslope of approximately 9.5° (16.7 %).
3.1.2 pyranometer—an instrument (radiometer) used to measure the total solar radiant energy incident upon a surface per unit
time and unit surface area.
3.1.3 solar energy—the radiant energy originating from the sun. Approximately 99 % of solar energy lies between wavelengths
of 0.3 to 3.5 μm.
3.1.4 solar flux—for these measurements, the direct and diffuse radiation from the sun received at ground level over the solar
spectrum, expressed in watts per square metre.
3.1.5 solar reflectance—the fraction of solar flux reflected by a surface.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 solar spectrum—the solar spectrum at ground level extending from wavelength 0.3 to 3.5 μm.
4. Summary of Test Method
4.1 A pyranometer is used to measure incoming and reflected solar radiation for a uniform horizontal or low-sloped surface. The
solar reflectance is the ratio of the reflected radiation to the incoming radiation.
5. Significance and Use
5.1 Solar reflectance is an important factor affecting surface and near-surface ambient air temperature. Surfaces with low solar
reflectance (typically 30 % or lower), absorb a high fraction of the incoming solar energy which is either conducted into buildings
or convected to air (leading to higher air temperatures). Use of materials with high solar reflectance may result in lower
air-conditioning energy use and cooler cities and communities. The test method described here measures the solar reflectance of
surfaces in the field.
This test method is under the jurisdiction of ASTM Committee D08 on Roofing and Waterproofing and is the direct responsibility of Subcommittee D08.18 on
Nonbituminous Organic Roof Coverings.
Current edition approved Aug. 15, 2006Feb. 1, 2015. Published September 2006February 2015. Originally approved in 1997. Last previous edition approved in 19972006
as E1918 – 97E1918 – 06., which was withdrawn in January 2006 and reinstated in August 2006. DOI: 10.1520/E1918-06. DOI: 10.1520/E1918-06R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1918 − 06 (2015)
6. Apparatus
6.1 Sensor—A precision spectral pyranometer (PSP) sensitive to radiant energy in the 0.28–2.8 μm band is recommended. A
–2
typical pyranometer yields a linear output of 60.5 % between 0 and 1400 W·m and a response time of one s. Specific
characteristics can be obtained based on calibration by the manufacturer of the pyranometer. Other suitable pyranometers are
discussed in Zerlaut. The double-dome design of the PSP minimizes the effects of internal convection resulting from tilting the
pyranometer at different angles. For this reason, the PSP is especially suitable for this test, since measurement of solar reflectivity
requires the apparatus to alternatively face up and down.
6.2 Read-Out Instrument—The analog output from the pyranometer is converted to digital output with a readout meter (such
as EPLAB Model 455 Instantaneous Solar Radiation Meter) that has an accuracy of better than 60.5 % and a resolution of 1
–2
W·m . The meter shall be scaled to the sensitivity of the specific PSP by the manufacturer of the pyranometer. Alternatively, a
precision voltmeter can be used.
6.3 Pyranometer Stand—The pyranometer shall be mounted on an arm and a stand that places the sensor at a height of 50 cm
above the surface to minimize the effect of the shadow on measured reflected radiation. The arm and stand shall be strong, cast
the smallest possible shadow, and allow the pyranometer to be turned upward and downward easily as shown in Fig. 1.
7. Sampling, Test Specimens, and Test Units
7.1 The test method described here applies to large (circles with at least four metres in diameter or squares four metres on a
side), homogeneous, low-sloped surfaces, such as roofs, streets, and parking lots. The measurements shall be performed on dry
surfaces.
8. Calibration and Standardization
8.1 The pyranometer shall be checked to ensure its accuracy. Most pyranometers are precalibrated by manufacturers. It is a good
practice to recalibrate the pyranometer as specified by the manufacturer (typically once every year or two years). Recalibration is
done by the manufacturer of the pyranometer.
9. Procedure
9.1 Cloud cover and haze significantly affect the measurements. The tests shall be conducted on a clear sunny day with no cloud
cover or haze during the individual measurements. See Annex A1 for guidelines on determination of the suitability of the
atmospheric conditions for conducting the tests.
9.2 The test shall be done in conditions where the ang
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