ASTM E881-92(2022)
(Practice)Standard Practice for Exposure of Solar Collector Cover Materials to Natural Weathering Under Conditions Simulating Stagnation Mode
Standard Practice for Exposure of Solar Collector Cover Materials to Natural Weathering Under Conditions Simulating Stagnation Mode
SIGNIFICANCE AND USE
4.1 This practice describes a weathering box test fixture and establishes limits for the heat loss coefficients. Uniform exposure guidelines are provided to minimize the variables encountered during outdoor exposure testing.
4.2 Since the combination of elevated temperature and solar radiation may cause some solar collector cover materials to degrade more rapidly than either exposure alone, a weathering box that elevates the temperature of the cover materials is used.
4.3 This practice may be used to assist in the evaluation of solar collector cover materials in the stagnation mode. No single temperature or procedure can duplicate the range of temperatures and environmental conditions to which cover materials may be exposed during stagnation conditions. To assist in evaluation of solar collector cover materials in the operational mode, Practice E782 should be used. Insufficient data exist to obtain exact correlation between the behavior of materials exposed in accordance with this practice and actual in-service performance.
4.4 This practice may also be useful in comparing the performance of different materials at one site or the performance of the same material at different sites, or both.
4.5 Means of evaluating the effects of weathering are provided in Practice E765, and in other ASTM test methods that evaluate material properties.
4.6 Exposures of the type described in this practice may be used to evaluate the stability of solar collector cover materials when exposed outdoors to the varied influences that comprise weather. Exposure conditions are complex and changeable. Important factors are material temperature, climate, time of year, presence of industrial pollution, etc. Generally, because it is difficult to define or measure precisely the factors influencing degradation due to weathering, results of outdoor exposure tests must be taken as indicative only. Repeated exposure testing at different seasons over a period of more than one year is req...
SCOPE
1.1 This practice covers a procedure for the exposure of solar collector cover materials to the natural weather environment at elevated temperatures that approximate stagnation conditions in solar collectors having a combined back and edge loss coefficient of less than 1.5 W/(m2·°C).
1.2 This practice is suitable for exposure of both glass and plastic solar collector cover materials. Provisions are made for exposure of single and double cover assemblies to accommodate the need for exposure of both inner and outer solar collector cover materials.
1.3 This practice does not apply to cover materials for evacuated collectors, photovoltaic cells, flat-plate collectors having a combined back and edge loss coefficient greater than 1.5 W/(m2·°C), or flat-plate collectors whose design incorporates means for limiting temperatures during stagnation.
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
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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: E881 − 92 (Reapproved 2022)
Standard Practice for
Exposure of Solar Collector Cover Materials to Natural
Weathering Under Conditions Simulating Stagnation Mode
This standard is issued under the fixed designation E881; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope E765Practice for Evaluation of Cover Materials for Flat
Plate Solar Collectors (Withdrawn 1991)
1.1 This practice covers a procedure for the exposure of
E772Terminology of Solar Energy Conversion
solar collector cover materials to the natural weather environ-
E782Practice for Exposure of Cover Materials for Solar
ment at elevated temperatures that approximate stagnation
CollectorstoNaturalWeatheringUnderConditionsSimu-
conditionsinsolarcollectorshavingacombinedbackandedge
2 lating Operational Mode
loss coefficient of less than 1.5 W/(m ·°C).
G7/G7MPractice for Natural Weathering of Materials
1.2 This practice is suitable for exposure of both glass and 4
2.2 Other Documents:
plastic solar collector cover materials. Provisions are made for
Federal Specification HH-I-558B, Amendment 3Insulation
exposure of single and double cover assemblies to accommo-
Blocks,Boards,Felts,Sleeving(PipeandTubeCovering),
date the need for exposure of both inner and outer solar
and Pipe Fitting CoveringThermal (Mineral Fiber, Indus-
collector cover materials.
trial Type), August 1976
1.3 This practice does not apply to cover materials for
3. Terminology
evacuated collectors, photovoltaic cells, flat-plate collectors
having a combined back and edge loss coefficient greater than
3.1 Definitions:
1.5 W/(m ·°C), or flat-plate collectors whose design incorpo-
3.1.1 For definitions of terms used in this practice, refer to
rates means for limiting temperatures during stagnation.
Terminology E772.
1.4 This standard does not purport to address all of the
4. Significance and Use
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 4.1 Thispracticedescribesaweatheringboxtestfixtureand
priate safety, health, and environmental practices and deter- establishes limits for the heat loss coefficients. Uniform expo-
mine the applicability of regulatory limitations prior to use. sureguidelinesareprovidedtominimizethevariablesencoun-
1.5 This international standard was developed in accor- tered during outdoor exposure testing.
dance with internationally recognized principles on standard-
4.2 Sincethecombinationofelevatedtemperatureandsolar
ization established in the Decision on Principles for the
radiation may cause some solar collector cover materials to
Development of International Standards, Guides and Recom-
degrade more rapidly than either exposure alone, a weathering
mendations issued by the World Trade Organization Technical
boxthatelevatesthetemperatureofthecovermaterialsisused.
Barriers to Trade (TBT) Committee.
4.3 This practice may be used to assist in the evaluation of
solar collector cover materials in the stagnation mode. No
2. Referenced Documents
single temperature or procedure can duplicate the range of
2.1 ASTM Standards:
temperatures and environmental conditions to which cover
D1435Practice for Outdoor Weathering of Plastics
materials may be exposed during stagnation conditions. To
assist in evaluation of solar collector cover materials in the
operational mode, Practice E782 should be used. Insufficient
This practice is under the jurisdiction of ASTM Committee E44 on Solar,
data exist to obtain exact correlation between the behavior of
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof
materials exposed in accordance with this practice and actual
Subcommittee E44.20 on Optical Materials for Solar Applications.
in-service performance.
Current edition approved Oct. 1, 2022. Published October 2022. Originally
approved in 1982. Last previous edition approved in 2015 as E881–92 (2015).
DOI: 10.1520/E0881-92R22.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The last approved version of this historical standard is referenced on
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM www.astm.org.
Standards volume information, refer to the standard’s Document Summary page on Federal Specification HH-I-558B has several classes of insulation material
the ASTM website. intended for high-temperature use.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E881 − 92 (2022)
4.4 This practice may also be useful in comparing the 5.1.2 Boxes that meet the requirements of 5.1.1 are de-
performance of different materials at one site or the perfor- scribed in Table 1. Figs. 1 and 2 illustrate the weathering box
mance of the same material at different sites, or both. test fixtures.Although Fig. 1 shows a square box, any shape is
permittediftherequirementsin5.1.1aremet.AppendixX1of
4.5 Means of evaluating the effects of weathering are
this practice describes the method for determining the com-
provided in Practice E765, and in other ASTM test methods
bined back and edge loss coefficient.
that evaluate material properties.
5.2 Contents of the Weathering Box Test Fixture: (1) a box,
4.6 Exposures of the type described in this practice may be
(2) insulation, (3) absorber, (4) box top, (5) spacer, (6) glazing
used to evaluate the stability of solar collector cover materials
frame, and (7) adhesive tapes.
when exposed outdoors to the varied influences that comprise
5.2.1 Theboxmayhaveanydimensionsandbemadeofany
weather. Exposure conditions are complex and changeable.
material as long as the requirements in 5.1.1 are met. A weep
Important factors are material temperature, climate, time of
hole shall be drilled at the lower end of the bottom of the box
year,presenceofindustrialpollution,etc.Generally,becauseit
to provide drainage and to minimize moisture accumulation.
isdifficulttodefineormeasurepreciselythefactorsinfluencing
degradation due to weathering, results of outdoor exposure
NOTE 2—It is desirable that the box and box top be made of a material
tests must be taken as indicative only. Repeated exposure
that will be unaffected by the exposure environment.Ametal resistant to
testingatdifferentseasonsoveraperiodofmorethanoneyear
corrosion encountered in the environment would be suitable. If wood is
used, it should be painted or treated on the exterior to make it resistant to
is required to confirm exposure tests at any one location.
moisture. In certain climates, only rot-resistant wood should be used to
Control samples must always be used in weathering tests for
minimize deterioration during exposure.
comparative analysis.
5.2.2 The insulation shall be a material suitable for use at a
5. Weathering Box Test Fixture high temperature (for example, 150°C (302°F)).
5.1 Test Fixture Requirements:
NOTE 3—Insulation materials having resins or binders should not be
5.1.1 The weathering box test fixture shall be constructed used because elevated temperatures may cause the resin or binder to
deteriorate and outgas. Outgassing products condense on the cover
such that the combined back and edge loss coefficient is less
2 2
material, causing changes in the solar transmittance of the solar collector
than 1.5 W/(m ·°C) (0.264 Btu/(ft ·h·°F)) (Note 1). (The
cover material.
methodfordeterminingthiscoefficientisoutlinedinAppendix
5.2.3 The absorber shall be of an adequate size to cover the
X1ofthispractice.)Thedistancebetweentheabsorberandthe
interior surface of the weathering box aperture. The absorber
closest cover plate shall be between 13 and 38 mm (0.5 and
1.5in.). For a double-cover exposure the separation between shall have a flat black nonselective coating having an absorp-
tance not less than 0.90 after exposure.
the inner and outer cover shall be between 13 and 38 mm (0.5
and 1.5 in.). Not more than 10% of the absorber plate area
5.2.4 Theboxtopshallbeofanadequatesizetofitoverthe
shall be shaded when the sun is at a 30° angle with the plane box.
of the front surface of the exposure box.
NOTE 4—The box top is intended to protect the edges of the test
NOTE 1—A good flat-plate solar collector has a combined back and specimen in contact with the box from reaching excessively high
edge loss coefficient of less than about 1.5 W/(m ·°C) (0.264 Btu/ temperatures, to minimize exposure of the adhesive tape to sunlight, and
(ft ·h·°F). to minimize moisture penetration into the exposure test fixture.
TABLE 1 Examples of Weathering Box Test Fixtures with Combined Heat Loss Coefficient for Back and Edge Losses Less Than
2 2
1.5 W/(m ·°C) (0.264 Btu/(ft ·h·°F))
Example 1 Example 2
Box material steel aluminum
Insulation material glass fiber glass fiber
l, length of aperture inside edge insulation 0.25 m (9.8 in.) 0.61 m (24 in.)
w, width of aperture inside edge insulation 0.13 m (5.2 in.) 0.61 m (24 in.)
h, distance from top of absorber to bottom of cover plate 0.013 m (0.5 in.) 0.038 m (1.5 in.)
2 2 2 2
A , area of aperture of test fixture A =(l × w) 0.033 m (51 in. ) 0.372 m (576 in. )
a a
2 2 2 2
A , area of back insulation A =(l × w) 0.033 m (51 in. ) 0.372 m (576 in. )
b b
2 2 2 2
A , area of edge insulation A =2(l + w)h 0.01 m (15 in. ) 0.093 m (144 in. )
e e
d , thickness of back insulation 0.077 m (3 in.) 0.05 m (2 in.)
b
d , thickness of box 0.001 m (0.04 in.) 0.002 m (0.08 in.)
c
d , thickness of edge insulation 0.013 m (0.5 in.) 0.025 m (1 in.)
e
2 2
K , conductivity of back insulation 0.038 W/(m·°C) (0.22 Btu/(ft ·h·°F)) 0.038 W/(m·°C) (0.022 Btu/(ft ·h·°F))
b
2 2
K , conductivity of box 43 W/(m·°C) (24.9 Btu/(ft ·h·°F) 204 W/(m·°C) (118 Btu/(ft ·h·°F))
c
2 2
K , conductivity of edge insulation 0.038 W/(m·°C) (0.022 Btu/(ft ·h·°F)) 0.038 W/(m·°C) (0.022 Btu/(ft ·h·°F))
e
A /A 11
b a
A /A 0.305 0.25
e a
2 2 2 2
d /K 2.03 m ·°C/W (11.4 (ft ·h·°F)/Btu) 1.32 m ·°C/W (7.5 (ft ·h·°F)/Btu)
b b
−5 2 −4 2 −6 2 −5 2
d /K 2.33 × 10 m ·°C/W (1.32 × 10 (ft ·h·°F)/Btu) 9.8 × 10 m ·°C/W (5.6 × 10 (ft ·h·°F)/Btu)
c c
2 2 2 2
d /K 0.342 m ·°C/W (1.94 (ft ·h·°F)/Btu) 0.658 m ·°C/W (3.74 (ft ·h·°F)/Btu)
e e
2 2 2 2
U , back + U , edge 1.38 W/(m ·°C) (0.243 Btu/(ft ·h·°F)) 1.14 W/(m ·°C) (0.201 Btu/(ft ·h·°F))
L L
E881 − 92 (2022)
FIG. 1 Top View of Weathering Box Test Fixture
FIG. 2 Assembled Weathering Box Test Fixture
5.2.5 The glazing frame is intended to hold the cover plate 5.2.6 The spacer shall provide a separation of 13 to 38 mm
material. The glazing frame shall have dimensions similar to (0.5to1.5in.)betweentheabsorberandtheclosestcoverplate.
the perimeter of the box. For a double-cover exposure the
Exact dimensions of the spacer are related to the requirements
frame shall provide a separation between the two cover plates
in 5.1.1.
ofnotlessthan13mm(0.5in.)orgreaterthan38mm(1.5in.).
NOTE 5—Certain designs of weathering boxes may eliminate the need
Exact dimensions of the frame are related to the requirements
for the spacer.
in 5.1.1. A vent hole may be drilled at one end of the glazing
frame to provide drainage and to minimize moisture accumu-
lation.
E881 − 92 (2022)
TABLE 2 Variable-Angle Rack Adjustment Schedule Using Four
5.2.7 The adhesive tapes shall be stable when exposed to
A,B
Changes Per Year
moisture and elevated temperatures. They shall be compatible
Calendar Period
with the specific materials from which the box, glazing frame,
Rack Tilt Angle, °
Dates Days of Year
box top, and cover plate are made.
Latitude±2.5 3/2to4/11 61to101
5.2.8 Organic materials are potential sources of outgassing
Latitude − 16) ± 2.5 4/12 to 8/31 102 to 243
andshallbeeliminatedfromtheinterioroftheweatheringbox
Latitude ± 2.5 9/1 to 10/10 244 to 283
where possible. For example, metallic parts shall be cleaned to (Latitude + 16) ± 2.5 10/11 to 3/1 284 to 60
A
remove traces of grease or other foreign matter. Other possible This exposure schedule may be used in both northern and southern hemi-
spheres.Thelatitudeinthesouthernhemisphereisnegative.Positiverackangles
sources of outgassing include coatings and sealants. Test
face south.
fixture components containing organic materials (for example, B
Theincidentangleofbeamradiation(θ)atsolarnoonforasouth-facingcollector
absorber coatings or insulation) shall be heated in an oven at is#8°.
150°C (302°F) for 24 h before the test fixture is assembled.
Thisshouldminimizeoutgassingthatresultsfromdeterioration
of the organic components exposed to elevated temperatures.
face south. Choose the angles so that the weathering boxes are
5.3 Test Specimen:
never closer to the horizontal than by 5°. Other variable
5.3.1 Thetestspecimenshallbeofanadequatesizetocover
exposure schedules requiring more than four adjustments per
the aperture of the box or glazing frame and to permit suitable
year may be used. The method for determining the variable-
attachment.
angle exposure schedule is described in Appendix X2 of this
practice.
NOTE 6—Adequate allowances should be made for materials that will
undergo dimensional changes due to temperature.
6.3 When a number of weathering boxes are exposed
5.3.2 The test specimen identification marks shall not inter-
simultaneously,mounttheboxessidebysidewiththesidesnot
fere with either the exposure or the subsequent testing.
touching.
5.4 Sample Mounting:
6.4 Do not clean the solar collector cover materials during
5.4.1 Rigid and Semirigid Glazings:
exposure.
5.4.1.1 Lay the test specimen for single-cover exposure
6.5 Visually inspect the test specimens at intervals of not
directly on either the spacer or the glazing frames. If used, the
more than one month. Record all changes in appearance.
frame is then placed on the spacer in the weathering box (see
Fig. 2).
7. Report
5.4.1.2 Lay the test specimen for inner cover exposure of a
7.1 The report shall include the following:
double-cover assembly on the spacer or attach it to the glazing
7.1.1 Description of the weathering box test fixture and its
framebeforetheglazingframeisplacedinthebox(seeFig.2).
calculated combined back and edge loss coefficient,
5.4.1.3 Lay the test specimen for outer cover exposure of a
7.1.2 Whether the solar collector cover materials are ex-
double-cover assembly on the top of the glazing frame (see
posed as a single or double-cover configuration an
...
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