ASTM E822-92(1996)
(Practice)Standard Practice for Determining Resistance of Solar Collector Covers to Hail by Impact With Propelled Ice Balls
Standard Practice for Determining Resistance of Solar Collector Covers to Hail by Impact With Propelled Ice Balls
SCOPE
1.1 This practice covers a procedure for determining the ability of cover plates for flat-plate solar collectors to withstand impact forces of falling hail. Propelled ice balls are used to simulate falling hailstones. This practice is not intended to apply to photovoltaic cells or arrays.
1.2 This practice defines two types of test specimens, describes methods for mounting specimens, specifies impact locations on each test specimen, provides an equation for determining the velocity of any size ice ball, provides a method for impacting the test specimens with ice balls, and specifies parameters that must be recorded and reported.
1.3 This practice does not establish pass or fail levels. The determination of acceptable or unacceptable levels of ice-ball impact resistance is beyond the scope of this practice.
1.4 The size of ice ball to be used in conducting this test is not specified in this practice. This practice can be used with various sizes of ice balls.
1.5 The categories of solar collector cover plate materials to which this practice may be applied cover the range of:
1.5.1 Brittle sheet, such as glass,
1.5.2 Semirigid sheet, such as plastic, and
1.5.3 Flexible membrane, such as plastic film.
1.6 Solar collector cover materials should be tested as:
1.6.1 Part of an assembled collector (Type 1 specimen), or
1.6.2 Mounted on a separate test frame cover plate holder (Type 2 specimen).
1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.8 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
Relations
Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: E 822 – 92 (Reapproved 1996)
Standard Practice for
Determining Resistance of Solar Collector Covers to Hail by
Impact With Propelled Ice Balls
This standard is issued under the fixed designation E 822; 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 2. Significance and Use
1.1 This practice covers a procedure for determining the 2.1 In many geographic areas there is concern about the
ability of cover plates for flat-plate solar collectors to withstand effect of falling hail upon solar collector covers. This practice
impact forces of falling hail. Propelled ice balls are used to may be used to determine the ability of flat-plate solar collector
simulate falling hailstones. This practice is not intended to covers to withstand the impact forces of hailstones. In this
apply to photovoltaic cells or arrays. practice, the ability of a solar collector cover plate to withstand
1.2 This practice defines two types of test specimens, hail impact is related to its tested ability to withstand impact
describes methods for mounting specimens, specifies impact from ice balls. The effects of the impact on the material are
locations on each test specimen, provides an equation for highly variable and dependent upon the material.
determining the velocity of any size ice ball, provides a method 2.2 This practice describes a standard procedure for mount-
for impacting the test specimens with ice balls, and specifies ing the test specimen, conducting the impact test, and reporting
parameters that must be recorded and reported. the effects.
1.3 This practice does not establish pass or fail levels. The 2.2.1 The procedures for mounting cover plate materials
determination of acceptable or unacceptable levels of ice-ball and collectors are provided to ensure that they are tested in a
impact resistance is beyond the scope of this practice. configuration that relates to their use in a solar collector.
1.4 The size of ice ball to be used in conducting this test is 2.2.2 The corner locations of the four impacts are chosen to
not specified in this practice. This practice can be used with represent vulnerable sites on the cover plate. Impacts near
various sizes of ice balls. corner supports are more critical than impacts elsewhere. Only
1.5 The categories of solar collector cover plate materials to a single impact is specified at each of the impact locations. For
which this practice may be applied cover the range of: test control purposes, multiple impacts in a single location are
1.5.1 Brittle sheet, such as glass, not permitted because a subcritical impact may still cause
1.5.2 Semirigid sheet, such as plastic, and damage that would alter the response to subsequent impacts.
1.5.3 Flexible membrane, such as plastic film. 2.2.3 Resultant velocity is used to simulate the velocity that
1.6 Solar collector cover materials should be tested as: may be reached by hail accompanied by wind. The resultant
1.6.1 Part of an assembled collector (Type 1 specimen), or velocity used in this practice is determined by vector addition
1.6.2 Mounted on a separate test frame cover plate holder of a 20 m/s (45 mph) horizontal velocity to the vertical terminal
(Type 2 specimen). velocity.
1.7 The values stated in SI units are to be regarded as the 2.2.4 Ice balls are used in this practice to simulate hailstones
standard. The values given in parentheses are for information because natural hailstones are not readily available to use, and
only. ice balls closely approximate hailstones. However, no direct
1.8 This standard does not purport to address all of the relationship has been established between the effect of impact
safety concerns, if any, associated with its use. It is the of ice balls and hailstones. Hailstones are highly variable in
responsibility of the user of this standard to establish appro- properties such as shape, density, and frangibility. These
priate safety and health practices and determine the applica- properties affect factors such as the kinetic energy delivered to
bility of regulatory limitations prior to use. the cover plate, the period during which energy is delivered,
and the area over which the energy is distributed. Ice balls,
with a density, frangibility, and terminal velocity near the range
of hailstones, are the nearest hailstone approximation known at
These test methods are under the jurisdiction of ASTM Committee E44 on
this time. Perhaps the major difference between ice balls and
Solar, Geothermal, and Other Alternative Energy Sources and is the direct
hailstones is that hailstones are much more variable than ice
responsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystems
and Systems.
Current edition approved Sept. 15, 1992. Published June 1993. Originally
Gokhale, N. R., Hailstorms and Hailstone Growth, State University of New
published as E 822 – 81. Last previous edition E 822 – 81(1987).
York Press, Albany, NY, 1975.
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 822
balls. However, ice balls can be uniformly and repeatedly
manufactured to ensure a projectile with known properties.
2.2.5 A wide range of observable effects may be produced
by impacting the various types of cover plate materials. The
effects may vary from no effect to total destruction. Some
changes in the cover material may be visible when there is no
apparent functional impairment of the cover plate material. All
effects of each impact must be described in the report so that an
estimate of their significance can be made.
2.3 Data generated using this practice may be used: (1)to
evaluate impact resistance of a single material or collector, (2)
to compare the impact resistance of several materials or
collectors, (3) to provide a common basis for selection of cover
materials or collectors for use in various geographic areas, or
FIG. 1 Frame Dimensions and Location of Test Impact Points
(4) to evaluate changes in impact resistance due to environ-
mental factors such as weather.
Fig. 2) designed to hold an approximately 860 by 1930-mm (34
2.4 This practice does not state the size(s) of ice ball(s) to be
by 76-in.) cover plate.
used in making the impact. Either the person requesting the test
or the person performing the test must determine ice ball size
NOTE 2—Hardwood, such as oak, birch, maple, or hickory, is manda-
to be used in the testing. Choice of ice ball size may relate to
tory if wood is used for the cover holder.
the intent of the testing. NOTE 3—Corner straps, as shown in Fig. 3 and Fig. 4, have been found
useful to ensure the cover holder is rigid.
2.4.1 If the testing is being performed to evaluate impact
resistance of a single material or collector, or several materials
3.5 Molds, for casting spherical crack-free ice balls of
or collectors, it may be desirable to repeat the test using several
appropriate diameter.
sizes of ice balls. In this manner the different effects of various
NOTE 4—Molds made from room-temperature vulcanizing rubber and
sizes of ice balls may be determined.
expanded polystyrene have been found suitable.
2.4.2 The size and frequency of hail varies significantly
3.6 Freezer—A device controlled at − 12 6 5°C (106 9°F)
among various geographic areas. If testing is being performed
for making and storing ice balls.
to evaluate materials or collectors intended for use in a specific
geographic area, the ice ball size should correspond to the level
4. Test Specimen
of hail impact resistance required for that area. Information on
4.1 Type 1—The test specimen shall consist of a complete
hail size and frequency may be available from local historical
glazing assembly or a complete solar collector panel with
weather records or may be determined from the publications
necessary mounting brackets or fixtures.
listed in Appendix X1.
4.2 Type 2—The test specimen shall consist of a section of
2.5 The hail impact resistance of materials may change as
solar collector cover plate material mounted in the cover
the materials are exposed to various environmental factors.
holder.
This practice may be used to generate data to evaluate
degradation by comparison of hail impact resistance data
5. Mounting
measured before and after exposure to such aging.
5.1 Type 1—Position and support the test specimen on a
3. Apparatus
suitable test base using necessary mounting brackets or fix-
3.1 Launcher—A mechanism capable of propelling a se-
tures, or both. Do not obstruct the specified impact points by
lected ice ball at the corresponding resultant velocity. The
the mounting fixtures.
aiming accuracy of the launcher must be sufficient to propel the
5.2 Type 2—Secure the test specimen in the cover holder, as
ice ball to strike the cover plate within 25 mm (61 in.) ofthe
shown in Fig. 2 and Fig. 5, and mount the cover holder (with
specified impact points. See Fig. 1.
the cover), on a suitable test base. Provide sufficient clearance
NOTE 1—A launcher that has proven suitable uses a compressed air
supply, an accumulator tank, a large-diameter quick-opening valve and
interchangeable barrels to accommodate the sizes of ice balls to be used.
Barrels should be made from materials with low thermal conductivity to
reduce melting of the ice ball. Barrels should be sized such that the ice ball
remains intact during loading and launching.
3.2 Velocity Meter, for measuring the ice ball velocity with
an accuracy of 62.0 %.
3.3 Test Base—A structurally rigid support for mounting a
complete solar collector panel (Type 1 specimen), or for
mounting a solar collector cover plate material (Type 2
specimen) set in the cover holder.
3.4 Cover Holder— A rigid edging frame (see Fig. 1 and FIG. 2 Cover Holder, Empty (Section A-A of Fig. 1)
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 822
NOTE 6—This may be accomplished by cutting the films oversize,
notching the four corners to the dimensions of the holder frame, and
draping the four flaps with suitable mass attached over the frame. The
mass must be located to uniformly distribute the tension over the area of
the film. Experience has shown that a 0.13-mm (0.005-in.) film requires a
mass of approximately 9 kg/m (6 lb/linear foot) of perimeter. After
tightening the clamps to prevent slippage during testing, the flaps and
excess material may be trimmed away, and the clamped specimens
mounted as described in 5.2.1.
6. Preconditioning
6.1 Precondition Type 1 test specimen or the test material
for the Type 2 test specimen at 23 6 2°C (73.4 6 4°F) and 50
NOTE 1—Slot corner as indicated to fit steel corner straps. Straps should
6 5 % relative humidity for not less than 24 h prior to testing.
be flush with surface.
FIG. 3 Slots for Corner Straps of Cover Holder 7. Safety Considerations
7.1 The operation of the described equipment may expose
the operator to risk of injury from the propelled or rebounded
ice ball, fragments of the broken test specimen, and from the
noise that may develop. Eye and ear protection should be
considered as the minimum protection for the operator.
8. Procedure
8.1 Using the ice ball mold(s), make sufficient quantities of
ice balls of the size(s) anticipated for testing.
8.2 Precondition the Type 1 test specimen or the material for
the Type 2 test specimen as described in 6.1.
8.3 Determine the ice ball size to be used in the test.
NOTE 7—The size of the ice ball shall be determined by the sponsor of
the test or the testing facility personnel.
8.4 Calculate the resultant velocity corresponding to the ice
ball diameter. Determine the resultant velocity as follows:
2 2
FIG. 4 Detail of Corner Straps for Cover Holder
V 5 = V 1 V (1)
r t w
on the side opposite the impact surface to permit unobstructed
where:
deflection of the cover material.
V = 20 m/s or 66 ft/s (45 mph), and
w
5.2.1 Lay brittle sheet cover materials, approximately 860
V = 14.04 dcm or 73.4 din.
= =
t
by 1930 mm (34 by 76 in.), on the elastomeric gasket (Type A
durometer rating 30 to 50) of one member of the cover holder. where:
Put the shim in place. Lay the other member of the cover V = resultant velocity of ice ball,
r
V = terminal velocity of ice ball,
holder on top. Tighten the bolts or C-clamp screws until the
t
V = wind velocity of 20 m/s (66 ft/s), and
elastomeric gaskets are compressed and the shim is firmly held, w
d = ice ball diameter.
as shown in Fig. 5. (Note 5). Mount the specimen firmly on the
8.5 Mount the test specimen as described in Section 5.
test base for testing.
8.6 Mark the four target impact points shown in Fig. 1 on
NOTE 5—If the cover plate material will be damaged by the procedure
the cover plate material. Each impact point is located in a
specified herein, the bolts or C-clamp screws should be tightened
corner 150 mm (6 in.) from both supporting edges.
sufficiently to hold the specimen in the frame, but not tightened to the
extent that permanent deformations are made in the cover plate material.
NOTE 8—Care should be taken to ensure that the marking does not react
with the cover material or influence test results.
5.2.2 Clamp semirigid sheet (plastic) cover materials in the
cover holder in the same manner as brittle sheet cover
8.7 Position the launcher as necessary to ensure that the path
materials.
of the propelled ice ball at impact will be essentially perpen-
5.2.3 Flexible Membrane: dicular (906 5°) to the surface of the cover plate material.
5.2.3.1 Mount the material in accordance with the manufac-
NOTE 9—The apparatus may be designed so that the path of the ice ball
turer’s recommendations on a suitable rigid subframe approxi-
is horizontal or vertical, as long as the other requirements of the test are
mately 860 by 1930 mm (34 by 76 in.). Mount the subframe in
met.
the cover holder in the same manner as described for brittle
NOTE 10—This practice may also be used to evaluate collector cover
sheet in 5.2.1. plates that are not flat. Due to the many configurations in nonflat cover
plates, considerable judgment and knowledge of the particular configura-
5.2.3.2 Alternatively, set flexible membrane cover materials
tions are necessary in applying this practice.
in the holder and place under biaxial tension (normal to length
and w
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