ASTM E1980-98e1

Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces

SCOPE
1.1 This practice covers the calculation of the Solar Reflectance Index (SRI) of horizontal and low-sloped opaque surfaces at standard conditions. The method is intended to calculate SRI for surfaces with emissivity greater than 0.1.
1.2 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.

General Information

• Status: Historical
• Publication Date: 09-Apr-2001
• ICS: 17.180.20 - Colours and measurement of light
• Technical Committee: E06 - Performance of Buildings
• Drafting Committee: E06.21 - Serviceability

Relations

• Replaced By: ASTM E1980-01 - Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces (Withdrawn 2010)
• Effective Date: 10-Apr-2001
• Referred By: ASTM E2813-18 - Standard Practice for Building Enclosure Commissioning
• Effective Date: 10-Apr-2001
• Referred By: ASTM C1549-16(2022) - Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer
• Effective Date: 10-Apr-2001
• Referred By: ASTM D3794-22 - Standard Guide for Testing Coil Coatings
• Effective Date: 10-Apr-2001

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e1
Designation: E 1980 – 98
Standard Practice for
Calculating Solar Reflectance Index of Horizontal and Low-
Sloped Opaque Surfaces
This standard is issued under the fixed designation E 1980; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—An editorial change was made to this standard in August 2000.
INTRODUCTION
The steady-state surface temperature (T ) under the sun is strongly correlated to solar reflectivity
s
and thermal emissivity of the surface. For equivalent conditions, the T of dark surfaces (with low solar
s
reflectance) is higher than light-colored surfaces (with high solar reflectance); and surfaces with low
thermal emissivity have higher T ’s than surfaces with high thermal emissivity. The procedure
s
recommended in this standard will allow a direct comparison of T of surfaces under the sun. The
s
procedure defines a Solar Reflectance Index (SRI) that measures the relative T of a surface with
s
respect to the standard white (SRI = 100) and standard black (SRI =0) under the standard solar and
ambient conditions.
1. Scope 3.1.1 convective coeffıcient (h )—the rate of heat transfer
c
from the surface to air induced by the air movement, expressed
1.1 This practice covers the calculation of the Solar Reflec-
–2 –1
in watts per square metre per degree Kelvin, W· m ·K .
tance Index (SRI) of horizontal and low-sloped opaque sur-
3.1.2 low-sloped surfaces—surfaces with a slope smaller
faces at standard conditions. The method is intended to
than 9.5° from the horizontal.
calculate SRI for surfaces with emissivity greater than 0.1.
3.1.3 reference black surface temperature (T )—is the
b
1.2 This standard does not purport to address all of the
steady-state temperature of a black surface with solar reflec-
safety concerns, if any, associated with its use. It is the
tance of 0.05 and emissivity of 0.9, under the standard solar
responsibility of the user of this standard to establish appro-
and ambient conditions.
priate safety and health practices and determine the applica-
3.1.4 reference white surface temperature (T )—is the
w
bility of regulatory limitations prior to use.
steady-state temperature of a white surface with solar reflec-
2. Referenced Documents
tance of 0.80 and emissivity of 0.9, under the standard solar
and ambient conditions.
2.1 ASTM Standards:
3.1.5 sky temperature (T )—is the temperature of a black
E 408 Test Methods for Total Normal Emittance of Surfaces sky
body that would radiate the same power toward the earth as
Using Inspection-Meter Techniques
does the sky.
E 772 Terminology Relating to Solar Energy Conversion
3.1.6 solar absorptance (a)—the fraction of solar flux
E 891 Tables for Terrestrial Direct Normal Solar Irradiance
absorbed by a surface. For an opaque surfacea=1- a.
for Air Mass 1.5
3.1.7 solar flux (I)—is the direct and diffuse radiant power
E 903 Test Method for Solar Absorption, Reflectance, and
from the sun received at ground level over the solar spectrum,
Transmittance of Materials Using Integrating Spheres
–2
expressed in watts per square metre, W · m .
E 1918 Test Method for Measuring Solar Reflectance of
3.1.8 solar reflectance (a)—the fraction of solar flux re-
Horizontal and Low-Sloped Surfaces in the Field
flected by a surface.
3. Terminology
3.1.9 solar reflectance index (SRI)—is the relative T of a
s
surface with respect to the standard white (SRI = 100) and
3.1 Definitions:
standard black (SRI = 0) under the standard solar and ambient
conditions.
This test method is under the jurisdiction of ASTM Committee E-6 on
3.1.10 solar spectrum—spectral distribution of typical ter-
Performance of Building Construction and is the direct responsibility of Subcom-
mittee E06.21 on Serviceability.
restrial sunlight at air mass 1.5 as defined in Tables E 891.
Current edition approved Sept. 10, 1998. Published March 1999.
3.1.11 standard solar and ambient conditions— for the
Annual ASTM Book of Standards, Vol 15.03.
3 purpose of this calculation, is defined as a solar flux of 1000 W
Annual ASTM Book of Standards, Vol 12.02.
–2
·m , ambient air temperature of 310 Kelvin (K), and sky
Annual ASTM Book of Standards, Vol 04.07.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1980
temperature of 300 K. Three convective coefficient of 5, 12, 30 5. Significance and Use
–2 –1 –1
W· m ·K , corresponding to low- (0 to 2 ms ), medium- (2
5.1 Solar reflectance and thermal emittance are important
–1 –1
to6ms ), and high-wind (6 to 10 ms ) conditions, respec-
factors affecting surface and near-surface ambient air tempera-
tively.
ture. Surfaces with low solar reflectance, absorb a high fraction
3.1.12 steady-state surface temperature (T )—is the tem-
of the incoming solar energy. A fraction of this absorbed energy
s
perature of the surface, in K, under the standard solar and
is conducted into ground and buildings, a fraction is convected
ambient conditions.
to air (leading to higher air temperatures), and a fraction is
3.1.13 thermal emissivity (e)—the ratio of radiant flux radiated to the sky. For equivalent conditions, the lower the
emitted by a surface at a given temperature to that emitted by emissivity of a surface the higher its steady-state temperature.
a black body radiator at the same temperature. For this Surfaces with low emissivity cannot effectively radiate to the
calculation, the thermal emissivity is for a temperature below sky and, therefore, get hot. Determination of
...