ASTM E881-92(2009)

Standard Practice for Exposure of Solar Collector Cover Materials to Natural Weathering Under Conditions Simulating Stagnation Mode

SIGNIFICANCE AND USE
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.
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.
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 E 782 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.
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.
Means of evaluating the effects of weathering are provided in Practice E 765, and in other ASTM test methods that evaluate material properties.
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 required to confirm exposure t...
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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Mar-2009
• ICS: 27.160 - Solar energy engineering
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources

Relations

• Replaces: ASTM E881-92(2003) - Standard Practice for Exposure of Solar Collector Cover Materials to Natural Weathering Under Conditions Simulating Stagnation Mode
• Effective Date: 01-Apr-2009
• Referred By: ASTM E782-95(2022) - Standard Practice for Exposure of Cover Materials for Solar Collectors to Natural Weathering Under Conditions Simulating Operational Mode
• Effective Date: 01-Apr-2009
• Referred By: ASTM G179-04(2019) - Standard Specification for Metal Black Panel and White Panel Temperature Devices for Natural Weathering Tests
• Effective Date: 01-Apr-2009

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E881 − 92(Reapproved 2009)
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 lating Operational Mode
G7Practice for Atmospheric Environmental Exposure Test-
1.1 This practice covers a procedure for the exposure of
ing of Nonmetallic Materials
solar collector cover materials to the natural weather environ-
2.2 Other Documents:
ment at elevated temperatures that approximate stagnation
Federal Specification HH-I-558B,Amendment 3, Insulation
conditionsinsolarcollectorshavingacombinedbackandedge
2 Blocks,Boards,Felts,Sleeving(PipeandTubeCovering),
loss coefficient of less than 1.5 W/(m · °C).
and Pipe Fitting CoveringThermal (Mineral Fiber, Indus-
1.2 This practice is suitable for exposure of both glass and
trial Type) August 1976
plastic solar collector cover materials. Provisions are made for
3. Terminology
exposure of single and double cover assemblies to accommo-
date the need for exposure of both inner and outer solar
3.1 Definitions:
collector cover materials.
3.1.1 For definitions of terms used in this practice, refer to
Terminology E772.
1.3 This practice does not apply to cover materials for
evacuated collectors, photovoltaic cells, flat-plate collectors
4. Significance and Use
having a combined back and edge loss coefficient greater than
4.1 Thispracticedescribesaweatheringboxtestfixtureand
1.5 W/(m ·° C), or flat-plate collectors whose design incorpo-
establishes limits for the heat loss coefficients. Uniform expo-
rates means for limiting temperatures during stagnation.
sureguidelinesareprovidedtominimizethevariablesencoun-
1.4 This standard does not purport to address all of the
tered during outdoor exposure testing.
safety concerns, if any, associated with its use. It is the
4.2 Sincethecombinationofelevatedtemperatureandsolar
responsibility of the user of this standard to establish appro-
radiation may cause some solar collector cover materials to
priate safety and health practices and determine the applica-
degrade more rapidly than either exposure alone, a weathering
bility of regulatory limitations prior to use.
boxthatelevatesthetemperatureofthecovermaterialsisused.
2. Referenced Documents
4.3 This practice may be used to assist in the evaluation of
2.1 ASTM Standards: solar collector cover materials in the stagnation mode. No
single temperature or procedure can duplicate the range of
D1435Practice for Outdoor Weathering of Plastics
E765Practice for Evaluation of Cover Materials for Flat temperatures and environmental conditions to which cover
materials may be exposed during stagnation conditions. To
Plate Solar Collectors (Withdrawn 1991)
E772Terminology of Solar Energy Conversion assist in evaluation of solar collector cover materials in the
operational mode, Practice E782 should be used. Insufficient
E782Practice for Exposure of Cover Materials for Solar
data exist to obtain exact correlation between the behavior of
CollectorstoNaturalWeatheringUnderConditionsSimu-
materials exposed in accordance with this practice and actual
in-service performance.
This practice is under the jurisdiction of ASTM Committee E44 on Solar,
4.4 This practice may also be useful in comparing the
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof
performance of different materials at one site or the perfor-
Subcommittee E44.05 on Solar Heating and Cooling Systems and Materials.
Current edition approved April 1, 2009. Published June 2009. Originally
mance of the same material at different sites, or both.
approved in 1982. Last previous edition approved in 2003 as E881–92(2003). DOI:
4.5 Means of evaluating the effects of weathering are
10.1520/E0881-92R09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
provided in Practice E765, and in other ASTM test methods
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
that evaluate material properties.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
The last approved version of this historical standard is referenced on Federal Specification HH-I-558B has several classes of insulation material
www.astm.org. intended for high-temperature use.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E881 − 92 (2009)
4.6 Exposures of the type described in this practice may be 5.2 Contents of the Weathering Box Test Fixture: (1) a box,
used to evaluate the stability of solar collector cover materials (2) insulation, (3) absorber, (4) box top, (5) spacer, (6) glazing
when exposed outdoors to the varied influences that comprise frame, and (7) adhesive tapes.
weather. Exposure conditions are complex and changeable.
5.2.1 Theboxmayhaveanydimensionsandbemadeofany
Important factors are material temperature, climate, time of
material as long as the requirements in 5.1.1 are met. A weep
year,presenceofindustrialpollution,etc.Generally,becauseit
hole shall be drilled at the lower end of the bottom of the box
isdifficulttodefineormeasurepreciselythefactorsinfluencing
to provide drainage and to minimize moisture accumulation.
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
is required to confirm exposure tests at any one location.
used, it should be painted or treated on the exterior to make it resistant to
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
closestcoverplateshallbebetween13and38mm(0.5and1.5
shall have a flat black nonselective coating having an absorp-
in.). For a double-cover exposure the separation between the
tance not less than 0.90 after exposure.
inner and outer cover shall be between 13 and 38 mm (0.5 and
1.5in.).Notmorethan10%oftheabsorberplateareashallbe 5.2.4 Theboxtopshallbeofanadequatesizetofitoverthe
shadedwhenthesunisata30°anglewiththeplaneofthefront box.
surface of the exposure box.
NOTE 4—The box top is intended to protect the edges of the test
specimen in contact with the box from reaching excessively high
NOTE 1—A good flat-plate solar collector has a combined back and
2 2
temperatures, to minimize exposure of the adhesive tape to sunlight, and
edge loss coefficient of less than about 1.5 W/(m · °C) (0.264 Btu/(ft ·
h·°F). to minimize moisture penetration into the exposure test fixture.
5.1.2 Boxes that meet the requirements of 5.1.1 are de- 5.2.5 The glazing frame is intended to hold the cover plate
scribed in Table 1. Fig. 1 and Fig. 2 illustrate the weathering material. The glazing frame shall have dimensions similar to
box test fixtures. Although Fig. 1 shows a square box, any the perimeter of the box. For a double-cover exposure the
shape is permitted if the requirements in 5.1.1 are met. frame shall provide a separation between the two cover plates
Appendix X1 of this practice describes the method for deter- ofnotlessthan13mm(0.5in.)orgreaterthan38mm(1.5in.).
mining the combined back and edge loss coefficient. Exact dimensions of the frame are related to the requirements
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 0.013 m (0.5 in.) 0.038 m (1.5 in.)
plate
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 (2009)
FIG. 1 Top View of Weathering Box Test Fixture
FIG. 2 Assembled Weathering Box Test Fixture
in 5.1.1. A vent hole may be drilled at one end of the glazing 5.2.7 The adhesive tapes shall be stable when exposed to
frame to provide drainage and to minimize moisture accumu- moisture and elevated temperatures. They shall be compatible
lation.
with the specific materials from which the box, glazing frame,
5.2.6 The spacer shall provide a separation of 13 to 38 mm box top, and cover plate are made.
(0.5to1.5in.)betweentheabsorberandtheclosestcoverplate.
5.2.8 Organic materials are potential sources of outgassing
Exact dimensions of the spacer are related to the requirements
andshallbeeliminatedfromtheinterioroftheweatheringbox
in 5.1.1.
where possible. For example, metallic parts shall be cleaned to
remove traces of grease or other foreign matter. Other possible
NOTE 5—Certain designs of weathering boxes may eliminate the need
for the spacer. sources of outgassing include coatings and sealants. Test
E881 − 92 (2009)
TABLE 2 Variable-Angle Rack Adjustment Schedule Using Four
fixture components containing organic materials (for example,
A,B
Changes Per Year
absorber coatings or insulation) shall be heated in an oven at
Calendar Period
150°C (302°F) for 24 h before the test fixture is assembled.
Rack Tilt Angle, °
Dates Days of Year
Thisshouldminimizeoutgassingthatresultsfromdeterioration
Latitude ±2.5 3/2 to 4/11 61 to 101
of the organic components exposed to elevated temperatures.
Latitude − 16) ±2.5 4/12 to 8/31 102 to 243
Latitude ±2.5 9/1 to 10/10 244 to 283
5.3 Test Specimen:
(Latitude + 16) ±2.5 10/11 to 3/1 284 to 60
5.3.1 Thetestspecimenshallbeofanadequatesizetocover
A
This exposure schedule may be used in both northern and southern hemi-
the aperture of the box or glazing frame and to permit suitable
spheres.Thelatitudeinthesouthernhemisphereisnegative.Positiverackangles
face south.
attachment.
B
Theincidentangleofbeamradiation(θ)atsolarnoonforasouth-facingcollector
is#8°.
NOTE 6—Adequate allowances should be made for materials that will
undergo dimensional changes due to temperature.
5.3.2 The test specimen identification marks shall not inter-
6.3 When a number of weathering boxes are exposed
fere with either the exposure or the subsequent testing.
simultaneously,mounttheboxessidebysidewiththesidesnot
5.4 Sample Mounting: touching.
5.4.1 Rigid and Semirigid Glazings:
6.4 Do not clean the solar collector cover materials during
5.4.1.1 Lay the test specimen for single cover exposure exposure.
directly on either the spacer or the glazing frames. If used, the
6.5 Visually inspect the test specimens at intervals of not
frame is then placed on the spacer in the weathering box (see
more than one month. Record all changes in appearance.
Fig. 2).
7. Report
5.4.1.2 Lay the test specimen for inner cover exposure of a
double cover assembly on the spacer or attach it to the glazing
7.1 The report shall include the following:
framebeforetheglazingframeisplacedinthebox(seeFig.2).
7.1.1 Description of the weathering box test fixture and its
5.4.1.3 Lay the test specimen for outer cover exposure of a
calculated combined back and edge loss coefficient,
doublecoverassemblyonthetopoftheglazingframe(seeFig.
7.1.2 Whether the solar collector cover materials are ex-
2).
posed as a single- or double-cover configuration and whether
the test specimen was the inner or outer cover,
5.4.2 Films—Placefilmtestspecimensontheglazingframe
7.1.3 Complete identification of the solar collector outer
usingadhesivetransfertapetoholdthetestspecimentaut.Itis
cover material(s),
essential that uniform tensioning be obtained prior to applying
7.1.4 Complete identification of the solar collector inner
the tape. Then place the frame in the box similar to 5.4.1.1,
cover material(s) (if any),
5.4.1.2, and 5.4.1.3.
7.1.5 A description of the test specimen attachment and
5.5 Assembly of Weathering Box:
mounting procedures,
5.5.1 Slide the various parts of the weathering box test
7.1.6 Latitude,longitude,altitude,andaddressofthetesting
fixture into position. The outer glazing must be roughly flush
site including a description o
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