1、Designation: E 822 92 (Reapproved 2003)Standard Practice forDetermining Resistance of Solar Collector Covers to Hail byImpact With Propelled Ice Balls1This standard is issued under the fixed designation E 822; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1
3、.1 This practice covers a procedure for determining theability of cover plates for flat-plate solar collectors to withstandimpact forces of falling hail. Propelled ice balls are used tosimulate falling hailstones. This practice is not intended toapply to photovoltaic cells or arrays.1.2 This practic
4、e defines two types of test specimens,describes methods for mounting specimens, specifies impactlocations on each test specimen, provides an equation fordetermining the velocity of any size ice ball, provides a methodfor impacting the test specimens with ice balls, and specifiesparameters that must
5、be recorded and reported.1.3 This practice does not establish pass or fail levels. Thedetermination of acceptable or unacceptable levels of ice-ballimpact resistance is beyond the scope of this practice.1.4 The size of ice ball to be used in conducting this test isnot specified in this practice. Thi
6、s practice can be used withvarious sizes of ice balls.1.5 The categories of solar collector cover plate materials towhich 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, and1.5.3 Flexible membrane, such as plastic film.1.6 So
7、lar collector cover materials should be tested as:1.6.1 Part of an assembled collector (Type 1 specimen), or1.6.2 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 thestandard. The values given in parentheses are for informat
8、iononly.1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Sign
9、ificance and Use2.1 In many geographic areas there is concern about theeffect of falling hail upon solar collector covers. This practicemay be used to determine the ability of flat-plate solar collectorcovers to withstand the impact forces of hailstones. In thispractice, the ability of a solar colle
10、ctor cover plate to withstandhail impact is related to its tested ability to withstand impactfrom ice balls. The effects of the impact on the material arehighly variable and dependent upon the material.2.2 This practice describes a standard procedure for mount-ing the test specimen, conducting the i
11、mpact test, and reportingthe effects.2.2.1 The procedures for mounting cover plate materialsand collectors are provided to ensure that they are tested in aconfiguration that relates to their use in a solar collector.2.2.2 The corner locations of the four impacts are chosen torepresent vulnerable sit
12、es on the cover plate. Impacts nearcorner supports are more critical than impacts elsewhere. Onlya single impact is specified at each of the impact locations. Fortest control purposes, multiple impacts in a single location arenot permitted because a subcritical impact may still causedamage that woul
13、d alter the response to subsequent impacts.2.2.3 Resultant velocity is used to simulate the velocity thatmay be reached by hail accompanied by wind. The resultantvelocity used in this practice is determined by vector additionof a 20 m/s (45 mph) horizontal velocity to the vertical terminalvelocity.2
14、.2.4 Ice balls are used in this practice to simulate hailstonesbecause natural hailstones are not readily available to use, andice balls closely approximate hailstones. However, no directrelationship has been established between the effect of impactof ice balls and hailstones. Hailstones are highly
15、variable inproperties such as shape, density, and frangibility.2Theseproperties affect factors such as the kinetic energy delivered tothe 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 v
16、elocity near the rangeof hailstones, are the nearest hailstone approximation known at1These test methods are under the jurisdiction of ASTM Committee E44 onSolar, Geothermal and Other Alternative Energy Sources and is the direct respon-sibility of Subcommittee E44.05 on Solar Heating and Cooling Sys
17、tems andMaterials.Current edition approved March 10, 2003. Published June 1993. Originallyapproved in 1981. Last previous edition approved in 1996 as E 822 92(1996).2Gokhale, N. R., Hailstorms and Hailstone Growth, State University of NewYork Press, Albany, NY, 1975.1Copyright ASTM International, 10
18、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.this time. Perhaps the major difference between ice balls andhailstones is that hailstones are much more variable than iceballs. However, ice balls can be uniformly and repeatedlymanufactured to ensure a projectile wit
19、h known properties.2.2.5 A wide range of observable effects may be producedby impacting the various types of cover plate materials. Theeffects may vary from no effect to total destruction. Somechanges in the cover material may be visible when there is noapparent functional impairment of the cover pl
20、ate material. Alleffects of each impact must be described in the report so that anestimate of their significance can be made.2.3 Data generated using this practice may be used: (1)toevaluate impact resistance of a single material or collector, (2)to compare the impact resistance of several materials
21、 orcollectors, (3) to provide a common basis for selection of covermaterials or collectors for use in various geographic areas, or(4) to evaluate changes in impact resistance due to environ-mental factors such as weather.2.4 This practice does not state the size(s) of ice ball(s) to beused in making
22、 the impact. Either the person requesting the testor the person performing the test must determine ice ball sizeto be used in the testing. Choice of ice ball size may relate tothe intent of the testing.2.4.1 If the testing is being performed to evaluate impactresistance of a single material or colle
23、ctor, or several materialsor collectors, it may be desirable to repeat the test using severalsizes of ice balls. In this manner the different effects of varioussizes of ice balls may be determined.2.4.2 The size and frequency of hail varies significantlyamong various geographic areas. If testing is
24、being performedto evaluate materials or collectors intended for use in a specificgeographic area, the ice ball size should correspond to the levelof hail impact resistance required for that area. Information onhail size and frequency may be available from local historicalweather records or may be de
25、termined from the publicationslisted in Appendix X1.2.5 The hail impact resistance of materials may change asthe materials are exposed to various environmental factors.This practice may be used to generate data to evaluatedegradation by comparison of hail impact resistance datameasured before and af
26、ter exposure to such aging.3. Apparatus3.1 LauncherA mechanism capable of propelling a se-lected ice ball at the corresponding resultant velocity. Theaiming accuracy of the launcher must be sufficient to propel theice ball to strike the cover plate within 25 mm (61 in.) ofthespecified impact points.
27、 See Fig. 1.NOTE 1A launcher that has proven suitable uses a compressed airsupply, an accumulator tank, a large-diameter quick-opening valve andinterchangeable barrels to accommodate the sizes of ice balls to be used.Barrels should be made from materials with low thermal conductivity toreduce meltin
28、g of the ice ball. Barrels should be sized such that the ice ballremains intact during loading and launching.3.2 Velocity Meter, for measuring the ice ball velocity withan accuracy of 62.0 %.3.3 Test BaseA structurally rigid support for mounting acomplete solar collector panel (Type 1 specimen), or
29、formounting a solar collector cover plate material (Type 2specimen) set in the cover holder.3.4 Cover Holder A rigid edging frame (see Fig. 1 andFig. 2) designed to hold an approximately 860 by 1930-mm (34by 76-in.) cover plate.NOTE 2Hardwood, such as oak, birch, maple, or hickory, is manda-tory if
30、wood is used for the cover holder.NOTE 3Corner straps, as shown in Fig. 3 and Fig. 4, have been founduseful to ensure the cover holder is rigid.3.5 Molds, for casting spherical crack-free ice balls ofappropriate diameter.NOTE 4Molds made from room-temperature vulcanizing rubber andexpanded polystyre
31、ne have been found suitable.3.6 FreezerA device controlled at 12 6 5C (106 9F)for making and storing ice balls.4. Test Specimen4.1 Type 1The test specimen shall consist of a completeglazing assembly or a complete solar collector panel withnecessary mounting brackets or fixtures.4.2 Type 2The test sp
32、ecimen shall consist of a section ofsolar collector cover plate material mounted in the coverholder.5. Mounting5.1 Type 1Position and support the test specimen on asuitable test base using necessary mounting brackets or fix-tures, or both. Do not obstruct the specified impact points bythe mounting f
33、ixtures.FIG. 1 Frame Dimensions and Location of Test Impact PointsFIG. 2 Cover Holder, Empty (Section A-A of Fig. 1)E 822 92 (2003)25.2 Type 2Secure the test specimen in the cover holder, asshown in Fig. 2 and Fig. 5, and mount the cover holder (withthe cover), on a suitable test base. Provide suffi
34、cient clearanceon the side opposite the impact surface to permit unobstructeddeflection of the cover material.5.2.1 Lay brittle sheet cover materials, approximately 860by 1930 mm (34 by 76 in.), on the elastomeric gasket (Type Adurometer rating 30 to 50) of one member of the cover holder.Put the shi
35、m in place. Lay the other member of the coverholder on top. Tighten the bolts or C-clamp screws until theelastomeric gaskets are compressed and the shim is firmly held,as shown in Fig. 5.(Note 5). Mount the specimen firmly on thetest base for testing.NOTE 5If the cover plate material will be damaged
36、 by the procedurespecified herein, the bolts or C-clamp screws should be tightenedsufficiently to hold the specimen in the frame, but not tightened to theextent that permanent deformations are made in the cover plate material.5.2.2 Clamp semirigid sheet (plastic) cover materials in thecover holder i
37、n the same manner as brittle sheet covermaterials.5.2.3 Flexible Membrane:5.2.3.1 Mount the material in accordance with the manufac-turers recommendations on a suitable rigid subframe approxi-mately 860 by 1930 mm (34 by 76 in.). Mount the subframe inthe cover holder in the same manner as described
38、for brittlesheet in 5.2.1.5.2.3.2 Alternatively, set flexible membrane cover materialsin the holder and place under biaxial tension (normal to lengthand width).NOTE 6This may be accomplished by cutting the films oversize,notching the four corners to the dimensions of the holder frame, anddraping the
39、 four flaps with suitable mass attached over the frame. Themass must be located to uniformly distribute the tension over the area ofthe film. Experience has shown that a 0.13-mm (0.005-in.) film requires amass of approximately 9 kg/m (6 lb/linear foot) of perimeter. Aftertightening the clamps to pre
40、vent slippage during testing, the flaps andexcess material may be trimmed away, and the clamped specimensmounted as described in 5.2.1.NOTE 1Slot corner as indicated to fit steel corner straps. Straps shouldbe flush with surface.FIG. 3 Slots for Corner Straps of Cover HolderFIG. 4 Detail of Corner S
41、traps for Cover HolderNOTE 1Bolts may be used in place of C-clamps if the bolt does not penetrate the test specimen (that is, for rigid sheet).FIG. 5 Cover Holder, LoadedE 822 92 (2003)36. Preconditioning6.1 Precondition Type 1 test specimen or the test materialfor the Type 2 test specimen at 23 6 2
42、C (73.4 6 4F) and 506 5 % relative humidity for not less than 24 h prior to testing.7. Safety Considerations7.1 The operation of the described equipment may exposethe operator to risk of injury from the propelled or reboundedice ball, fragments of the broken test specimen, and from thenoise that may
43、 develop. Eye and ear protection should beconsidered as the minimum protection for the operator.8. Procedure8.1 Using the ice ball mold(s), make sufficient quantities ofice balls of the size(s) anticipated for testing.8.2 Precondition theType 1 test specimen or the material forthe Type 2 test specim
44、en as described in 6.1.8.3 Determine the ice ball size to be used in the test.NOTE 7The size of the ice ball shall be determined by the sponsor ofthe test or the testing facility personnel.8.4 Calculate the resultant velocity corresponding to the iceball diameter. Determine the resultant velocity as
45、 follows:Vr5 = Vt21 Vw2(1)where:Vw= 20 m/s or 66 ft/s (45 mph), andVt= 14.04=dcmor 73.4=din.where:Vr= resultant velocity of ice ball,Vt= terminal velocity of ice ball,Vw= wind velocity of 20 m/s (66 ft/s), andd = ice ball diameter.8.5 Mount the test specimen as described in Section 5.8.6 Mark the fo
46、ur target impact points shown in Fig. 1 onthe cover plate material. Each impact point is located in acorner 150 mm (6 in.) from both supporting edges.NOTE 8Care should be taken to ensure that the marking does not reactwith the cover material or influence test results.8.7 Position the launcher as nec
47、essary to ensure that the pathof the propelled ice ball at impact will be essentially perpen-dicular (906 5) to the surface of the cover plate material.NOTE 9The apparatus may be designed so that the path of the ice ballis horizontal or vertical, as long as the other requirements of the test aremet.
48、NOTE 10This practice may also be used to evaluate collector coverplates that are not flat. Due to the many configurations in nonflat coverplates, considerable judgment and knowledge of the particular configura-tions are necessary in applying this practice.8.8 Aim the launcher at a target impact poin
49、t (as shown inFig. 1) not previously impacted. Impact each impact point onetime only.8.9 Position the velocity meter such that the ice ball velocitywill be measured between the launcher and the test specimen.The ice ball should leave the velocity meter not more than 1.0m (3.1 ft) in front of the impact location. Prepare the velocitymeter for the test.8.10 Remove from the freezer an ice ball of the sizedetermined in 8.3. Inspect the ice ball to ensure it is uncracked,uniform, and spherical. Measure and record the nominaldiameter and mass of the ice ball. Re
