ASTM E881-92(1996)

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

SCOPE
1.1 This practice provides 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/(m [dot]°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/(m [dot]°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 problems, 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-Dec-1995
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources

Relations

• Replaced By: ASTM E881-92(2003) - Standard Practice for Exposure of Solar Collector Cover Materials to Natural Weathering Under Conditions Simulating Stagnation Mode
• Effective Date: 15-Sep-1992
• Referred By: ASTM G179-04(2019) - Standard Specification for Metal Black Panel and White Panel Temperature Devices for Natural Weathering Tests
• Effective Date: 01-Jan-1996
• 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-Jan-1996

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 881 – 92 (Reapproved 1996)
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 E 881; 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.
1. Scope Federal Specification HH-I-558B, Amendment 3, Insulation
Blocks, Boards, Felts, Sleeving (Pipe and Tube Covering),
1.1 This practice covers a procedure for the exposure of
and Pipe Fitting Covering Thermal (Mineral Fiber, Indus-
solar collector cover materials to the natural weather environ-
trial Type) August 1976
ment at elevated temperatures that approximate stagnation
conditions in solar collectors having a combined back and edge
3. Terminology
loss coefficient of less than 1.5 W/(m · °C).
3.1 Definitions—For definitions of terms used in this
1.2 This practice is suitable for exposure of both glass and
practice, refer to Terminology E 772.
plastic solar collector cover materials. Provisions are made for
exposure of single and double cover assemblies to accommo-
4. Significance and Use
date the need for exposure of both inner and outer solar
4.1 This practice describes a weathering box test fixture and
collector cover materials.
establishes limits for the heat loss coefficients. Uniform expo-
1.3 This practice does not apply to cover materials for
sure guidelines are provided to minimize the variables encoun-
evacuated collectors, photovoltaic cells, flat-plate collectors
tered during outdoor exposure testing.
having a combined back and edge loss coefficient greater than
2 4.2 Since the combination of elevated temperature and solar
1.5 W/(m ·° C), or flat-plate collectors whose design incorpo-
radiation may cause some solar collector cover materials to
rates means for limiting temperatures during stagnation.
degrade more rapidly than either exposure alone, a weathering
1.4 This standard does not purport to address all of the
box that elevates the temperature of the cover materials is used.
safety concerns, if any, associated with its use. It is the
4.3 This practice may be used to assist in the evaluation of
responsibility of the user of this standard to establish appro-
solar collector cover materials in the stagnation mode. No
priate safety and health practices and determine the applica-
single temperature or procedure can duplicate the range of
bility of regulatory limitations prior to use.
temperatures and environmental conditions to which cover
materials may be exposed during stagnation conditions. To
2. Referenced Documents
assist in evaluation of solar collector cover materials in the
2.1 ASTM Standards:
2 operational mode, Practice E 782 should be used. Insufficient
D 1435 Practice for Outdoor Weathering of Plastics
data exist to obtain exact correlation between the behavior of
E 765 Practice for Evaluation of Cover Materials for Flat
3 materials exposed in accordance with this practice and actual
Plate Solar Collectors
3 in-service performance.
E 772 Terminology Relating to Solar Energy Conversion
4.4 This practice may also be useful in comparing the
E 782 Practice for Exposure of Cover Materials for Solar
performance of different materials at one site or the perfor-
Collectors to Natural Weathering Under Conditions Simu-
3 mance of the same material at different sites, or both.
lating Operational Mode
4.5 Means of evaluating the effects of weathering are
G 7 Practice for Atmospheric Environmental Exposure
4 provided in Practice E 765, and in other ASTM test methods
Testing of Nonmetallic Materials
that evaluate material properties.
2.2 Other Documents:
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
These test methods are under the jurisdiction of ASTM Committee E44 on
weather. Exposure conditions are complex and changeable.
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems Important factors are material temperature, climate, time of
and Systems.
year, presence of industrial pollution, etc. Generally, because it
Current edition approved Sept. 15, 1992. Published March 1993. Originally
published as E 881 - 82. Last previous edition E 881 - 82 (1988).
Annual Book of ASTM Standards, Vol 08.01.
3 5
Annual Book of ASTM Standards, Vol 12.02. Available from the General Services Administration (3 FRI), Building 197,
Annual Book of ASTM Standards, Vol 14.02. Navy Yard Annex, Washington, DC 20407.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 881
NOTE 2—It is desirable that the box and box top be made of a material
is difficult to define or measure precisely the factors influencing
that will be unaffected by the exposure environment. A metal resistant to
degradation due to weathering, results of outdoor exposure
corrosion encountered in the environment would be suitable. If wood is
tests must be taken as indicative only. Repeated exposure
used, it should be painted or treated on the exterior to make it resistant to
testing at different seasons over a period of more than one year
moisture. In certain climates only rot-resistant wood should be used to
is required to confirm exposure tests at any one location.
minimize deterioration during exposure.
Control samples must always be used in weathering tests for
5.2.2 The insulation shall be a material suitable for use at a
comparative analysis.
high temperature (for example, 150°C (302°F)).
5. Weathering Box Test Fixture
NOTE 3—Insulation materials having resins or binders should not be
used because elevated temperatures may cause the resin or binder to
5.1 Test Fixture Requirements:
deteriorate and outgas. Outgassing products condense on the cover
5.1.1 The weathering box test fixture shall be constructed
material causing changes in the solar transmittance of the solar collector
such that the combined back and edge loss coefficient is less
cover material.
2 2
than 1.5 W/(m · °C) (0.264 Btu/(ft · h ·° F)) (Note 1). (The
5.2.3 The absorber shall be of an adequate size to cover the
method for determining this coefficient is outlined in Appendix
interior surface of the weathering box aperture. The absorber
X1 of this practice.) The distance between the absorber and the
shall have a flat black nonselective coating having an absorp-
closest cover plate shall be between 13 and 38 mm (0.5 and 1.5
tance not less than 0.90 after exposure.
in.). For a double-cover exposure the separation between the
5.2.4 The box top shall be of an adequate size to fit over the
inner and outer cover shall be between 13 and 38 mm (0.5 and
box.
1.5 in.). Not more than 10 % of the absorber plate area shall be
shaded when the sun is at a 30° angle with the plane of the front
NOTE 4—The box top is intended to protect the edges of the test
specimen in contact with the box from reaching excessively high
surface of the exposure box.
temperatures, to minimize exposure of the adhesive tape to sunlight, and
NOTE 1—A good flat-plate solar collector has a combined back and
to minimize moisture penetration into the exposure test fixture.
2 2
edge loss coefficient of less than about 1.5 W/(m · °C) (0.264 Btu/(ft ·
5.2.5 The glazing frame is intended to hold the cover plate
h·°F).
material. The glazing frame shall have dimensions similar to
5.1.2 Boxes that meet the requirements of 5.1.1 are de-
the perimeter of the box. For a double-cover exposure the
scribed in Table 1. Fig. 1 and Fig. 2 illustrate the weathering
frame shall provide a separation between the two cover plates
box test fixtures. Although Fig. 1 shows a square box, any
of not less than 13 mm (0.5 in.) or greater than 38 mm (1.5 in.).
shape is permitted if the requirements in 5.1.1 are met.
Exact dimensions of the frame are related to the requirements
Appendix X1 of this practice describes the method for deter-
in 5.1.1. A vent hole may be drilled at one end of the glazing
mining the combined back and edge loss coefficient.
frame to provide drainage and to minimize moisture accumu-
5.2 Contents of the Weathering Box Test Fixture: (1) a box,
lation.
( 2) insulation, (3) absorber, ( 4) box top, (5) spacer, ( 6)
5.2.6 The spacer shall provide a separation of 13 to 38 mm
glazing frame, and (7) adhesive tapes.
(0.5 to 1.5 in.) between the absorber and the closest cover plate.
5.2.1 The box may have any dimensions and be made of any
material as long as the requirements in 5.1.1 are met. A weep
hole shall be drilled at the lower end of the bottom of the box 6
Federal Specification HH-I-558B has several classes of insulation material
to provide drainage and to minimize moisture accumulation. intended for high-temperature use.
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 3 w) 0.033 m (51 in. ) 0.372 m (576 in. )
a a
2 2 2 2
A , area of back insulation A =(l 3 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 3 10 m ·°C/W (1.32 3 10 (ft ·h·°F)/Btu) 9.8 3 10 m ·°C/W (5.6 3 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
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 881
FIG. 1 Top View of Weathering Box Test Fixture
FIG. 2 Assembled Weathering Box Test Fixture
Exact dimensions of the spacer are related to the requirements 5.2.7 The adhesive tapes shall be stable when exposed to
in 5.1.1. moisture and elevated temperatures. They shall be compatible
with the specific materials from which the box, glazing frame,
NOTE 5—Certain designs of weathering boxes may eliminate the need
box top, and cover plate are made.
for the spacer.
5.2.8 Organic materials are potential sources of outgassing
3M Weather-Resistant Adhesive Tape No. 838, or equivalent, has been found
suitable for attaching the box top to the box. 3M Adhesive Transfer Tape and Densil
Silicone Pressure Sensitive Tape No. 2078 or equivalent, have been found suitable
for attaching glazings to the glazing frame in solar collectors. The 3M tape is
available from the 3M Co., 3M Center, St. Paul, Minn. 55101. The Densil tape is
available from the Dennison Manufacturing Co., Coated Paper Div., Framingham,
MA 01701.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 881
TABLE 2 Variable-Angle Rack Adjustment Schedule Using Four
and shall be eliminated from the interior of the weathering box
A,B
Changes Per Year
where possible. For example, metallic parts shall be cleaned to
Calendar Period
remove traces of grease or other foreign matter. Other possible
Rack Tilt Angle, °
sources of outgassing include coatings and sealants. Test Dates Days of Year
fixture components containing organic materials (for example,
Latitude 62.5 3/2 to 4/11 61 to 101
Latitude − 16) 62.5 4/12 to 8/31 102 to 243
absorber coatings or insulation) shall be heated in an oven at
Latitude 62.5 9/1 to 10/10 244 to 283
150°C (302°F) for 24 h before the test fixture is assembled.
(Latitude + 16) 62.5 10/11 to 3/1 284 to 60
This should minimize outgassing that results from deterioration
A
This exposure schedule may be used in both northern and southern hemi-
of the organic components exposed to elevated temperatures.
spheres. The latitude in the southern hemisphere is negative. Positive rack angles
face south.
5.3 Test Specimen:
B
The incident angle of beam radiation (u) at solar noon for a south-facing
5.3.1 The test specimen shall be of an adequate size to cover
collector is #8°.
the aperture of the box or glazing frame and to permit suitable
attachment.
6.3 When a number of weathering boxes are exposed
NOTE 6—Adequate allowances should be made for materials that will
simultaneously, mount the boxes side by side with the sides not
undergo dimensional changes due to temperature.
touching.
5.3.2 The test specimen identification marks shall not inter-
6.4 Do not clean the solar collector cover materials during
fere with either the exposure or the subsequent testing.
exposure.
5.4 Sample Mounting:
6.5 Visually inspect the test specimens at intervals of not
5.4.1 Rigid and Semirigid Glazings:
more than one month. Record all changes in appearance.
5.4.1.1 Lay the test specimen for single cover exposure
directly on either the spacer or the glazing frames. If used, the
7. Report
frame is then placed on the spacer in the weathering box (see
7.1 The report shall include the following:
Fig. 2).
7.1.1 Description of the weathering box test fixture and its
5.4.1.2 Lay the test specimen for inner cover exposure of a
calculated combined back and edge loss coefficient,
...