1、Designation: E 881 92 (Reapproved 2003)Standard Practice forExposure of Solar Collector Cover Materials to NaturalWeathering Under Conditions Simulating Stagnation Mode1This standard is issued under the fixed designation E 881; the number immediately following the designation indicates the year ofor
2、iginal adoption or, 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.1. Scope1.1 This practice covers a procedure for the exposure ofsolar co
3、llector cover materials to the natural weather environ-ment at elevated temperatures that approximate stagnationconditions in solar collectors having a combined back and edgeloss coefficient of less than 1.5 W/(m2 C).1.2 This practice is suitable for exposure of both glass andplastic solar collector
4、 cover materials. Provisions are made forexposure of single and double cover assemblies to accommo-date the need for exposure of both inner and outer solarcollector cover materials.1.3 This practice does not apply to cover materials forevacuated collectors, photovoltaic cells, flat-plate collectorsh
5、aving a combined back and edge loss coefficient greater than1.5 W/(m2 C), or flat-plate collectors whose design incorpo-rates means for limiting temperatures during stagnation.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsib
6、ility 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. Referenced Documents2.1 ASTM Standards:D 1435 Practice for Outdoor Weathering of Plastics2E 765 Practice for Evaluation of Cover Materia
7、ls for FlatPlate Solar Collectors3E 772 Terminology Relating to Solar Energy Conversion3E 782 Practice for Exposure of Cover Materials for SolarCollectors to Natural Weathering Under Conditions Simu-lating Operational Mode3G 7 Practice for Atmospheric Environmental ExposureTesting of Nonmetallic Mat
8、erials42.2 Other Documents:Federal Specification HH-I-558B, Amendment 3, InsulationBlocks, Boards, Felts, Sleeving (Pipe and Tube Covering),and Pipe Fitting Covering Thermal (Mineral Fiber, Indus-trial Type) August 197653. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refe
9、r to Terminology E 772.4. Significance and Use4.1 This practice describes a weathering box test fixture andestablishes limits for the heat loss coefficients. Uniform expo-sure guidelines are provided to minimize the variables encoun-tered during outdoor exposure testing.4.2 Since the combination of
10、elevated temperature and solarradiation may cause some solar collector cover materials todegrade more rapidly than either exposure alone, a weatheringbox that elevates the temperature of the cover materials is used.4.3 This practice may be used to assist in the evaluation ofsolar collector cover mat
11、erials in the stagnation mode. Nosingle temperature or procedure can duplicate the range oftemperatures and environmental conditions to which covermaterials may be exposed during stagnation conditions. Toassist in evaluation of solar collector cover materials in theoperational mode, Practice E 782 s
12、hould be used. Insufficientdata exist to obtain exact correlation between the behavior ofmaterials exposed in accordance with this practice and actualin-service performance.4.4 This practice may also be useful in comparing theperformance of different materials at one site or the perfor-mance of the
13、same material at different sites, or both.4.5 Means of evaluating the effects of weathering areprovided in Practice E 765, and in other ASTM test methodsthat evaluate material properties.4.6 Exposures of the type described in this practice may beused to evaluate the stability of solar collector cove
14、r materialswhen exposed outdoors to the varied influences that compriseweather. Exposure conditions are complex and changeable.Important factors are material temperature, climate, time ofyear, presence of industrial pollution, etc. Generally, because it1These test methods are under the jurisdiction
15、of ASTM Committee E44 onSolar, Geothermal, and Other Alternative Energy Sources and is the directresponsibility of Subcommittee E44.05 on Solar Heating and Cooling Subsystemsand Systems.Current edition approved Sept. 15, 1992. Published March 1993. Originallyapproved in 1982. Last previous edition a
16、pproved in 1996 as E 881 - 92 (1996).2Annual Book of ASTM Standards, Vol 08.01.3Annual Book of ASTM Standards, Vol 12.02.4Annual Book of ASTM Standards, Vol 14.02.5Available from the General Services Administration (3 FRI), Building 197,Navy Yard Annex, Washington, DC 20407.1Copyright ASTM Internati
17、onal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.is difficult to define or measure precisely the factors influencingdegradation due to weathering, results of outdoor exposuretests must be taken as indicative only. Repeated exposuretesting at different seasons
18、 over a period of more than one yearis required to confirm exposure tests at any one location.Control samples must always be used in weathering tests forcomparative analysis.5. Weathering Box Test Fixture5.1 Test Fixture Requirements:5.1.1 The weathering box test fixture shall be constructedsuch tha
19、t the combined back and edge loss coefficient is lessthan 1.5 W/(m2 C) (0.264 Btu/(ft2 h F) (Note 1). (Themethod for determining this coefficient is outlined in AppendixX1 of this practice.) The distance between the absorber and theclosest cover plate shall be between 13 and 38 mm (0.5 and 1.5in.).
20、For a double-cover exposure the separation between theinner and outer cover shall be between 13 and 38 mm (0.5 and1.5 in.). Not more than 10 % of the absorber plate area shall beshaded when the sun is at a 30 angle with the plane of the frontsurface of the exposure box.NOTE 1A good flat-plate solar
21、collector has a combined back andedge loss coefficient of less than about 1.5 W/(m2 C) (0.264 Btu/(ft2hF).5.1.2 Boxes that meet the requirements of 5.1.1 are de-scribed in Table 1. Fig. 1 and Fig. 2 illustrate the weatheringbox test fixtures. Although Fig. 1 shows a square box, anyshape is permitted
22、 if the requirements in 5.1.1 are met.Appendix X1 of this practice describes the method for deter-mining the combined back and edge loss coefficient.5.2 Contents of the Weathering Box Test Fixture: (1) a box,( 2) insulation, (3) absorber, ( 4) box top, (5) spacer, ( 6)glazing frame, and (7) adhesive
23、 tapes.5.2.1 The box may have any dimensions and be made of anymaterial as long as the requirements in 5.1.1 are met. A weephole shall be drilled at the lower end of the bottom of the boxto provide drainage and to minimize moisture accumulation.NOTE 2It is desirable that the box and box top be made
24、of a materialthat will be unaffected by the exposure environment. A metal resistant tocorrosion encountered in the environment would be suitable. If wood isused, it should be painted or treated on the exterior to make it resistant tomoisture. In certain climates only rot-resistant wood should be use
25、d tominimize deterioration during exposure.5.2.2 The insulation shall be a material suitable for use at ahigh temperature (for example, 150C (302F).6NOTE 3Insulation materials having resins or binders should not beused because elevated temperatures may cause the resin or binder todeteriorate and out
26、gas. Outgassing products condense on the covermaterial causing changes in the solar transmittance of the solar collectorcover material.5.2.3 The absorber shall be of an adequate size to cover theinterior surface of the weathering box aperture. The absorbershall have a flat black nonselective coating
27、 having an absorp-tance not less than 0.90 after exposure.5.2.4 The box top shall be of an adequate size to fit over thebox.NOTE 4The box top is intended to protect the edges of the testspecimen in contact with the box from reaching excessively hightemperatures, to minimize exposure of the adhesive
28、tape to sunlight, andto minimize moisture penetration into the exposure test fixture.5.2.5 The glazing frame is intended to hold the cover platematerial. The glazing frame shall have dimensions similar tothe perimeter of the box. For a double-cover exposure theframe shall provide a separation betwee
29、n the two cover platesof not less than 13 mm (0.5 in.) or greater than 38 mm (1.5 in.).Exact dimensions of the frame are related to the requirementsin 5.1.1. A vent hole may be drilled at one end of the glazingframe to provide drainage and to minimize moisture accumu-lation.6Federal Specification HH
30、-I-558B has several classes of insulation materialintended for high-temperature use.TABLE 1 Examples of Weathering Box Test Fixtures with Combined Heat Loss Coefficient for Back and Edge Losses Less than1.5 W/(m2C) (0.264 Btu/(ft2hF)Example 1 Example 2Box material steel aluminumInsulation material g
31、lass fiber glass fiberl, 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 coverplate0.013 m (0.5 in.) 0.038 m (1.5 in.)Aa, area of aperture of test fixtu
32、re Aa=(l 3 w) 0.033 m2(51 in.2) 0.372 m2(576 in.2)Ab, area of back insulation Ab=(l 3 w) 0.033 m2(51 in.2) 0.372 m2(576 in.2)Ae, area of edge insulation Ae=2(l + w)h 0.01 m2(15 in.2) 0.093 m2(144 in.2)db, thickness of back insulation 0.077 m (3 in.) 0.05 m (2 in.)dc, thickness of box 0.001 m (0.04 i
33、n.) 0.002 m (0.08 in.)de, thickness of edge insulation 0.013 m (0.5 in.) 0.025 m (1 in.)Kb, conductivity of back insulation 0.038 W/(mC) (0.22 Btu/(ft2hF) 0.038 W/(mC) (0.022 Btu/(ft2hF)Kc, conductivity of box 43 W/(mC) (24.9 Btu/(ft2hF) 204 W/(mC) (118 Btu/(ft2hF)Ke, conductivity of edge insulation
34、 0.038 W/(mC) (0.022 Btu/(ft2hF) 0.038 W/(mC) (0.022 Btu/(ft2hF)Ab/Aa11Ae/Aa0.305 0.25db/Kb2.03 m2C/W (11.4 (ft2hF)/Btu) 1.32 m2C/W (7.5 (ft2hF)/Btu)dc/Kc2.33 3 105m2C/W (1.32 3 104(ft2hF)/Btu) 9.8 3 106m2C/W (5.6 3 105(ft2hF)/Btu)de/Ke0.342 m2C/W (1.94 (ft2hF)/Btu) 0.658 m2C/W (3.74 (ft2hF)/Btu)UL,
35、 back + UL, edge 1.38 W/(m2C) (0.243 Btu/(ft2hF) 1.14 W/(m2C) (0.201 Btu/(ft2hF)E 881 92 (2003)25.2.6 The spacer shall provide a separation of 13 to 38 mm(0.5 to 1.5 in.) between the absorber and the closest cover plate.Exact dimensions of the spacer are related to the requirementsin 5.1.1.NOTE 5Cer
36、tain designs of weathering boxes may eliminate the needfor the spacer.FIG. 1 Top View of Weathering Box Test FixtureFIG. 2 Assembled Weathering Box Test FixtureE 881 92 (2003)35.2.7 The adhesive tapes7shall be stable when exposed tomoisture and elevated temperatures. They shall be compatiblewith the
37、 specific materials from which the box, glazing frame,box top, and cover plate are made.5.2.8 Organic materials are potential sources of outgassingand shall be eliminated from the interior of the weathering boxwhere possible. For example, metallic parts shall be cleaned toremove traces of grease or
38、other foreign matter. Other possiblesources of outgassing include coatings and sealants. Testfixture components containing organic materials (for example,absorber coatings or insulation) shall be heated in an oven at150C (302F) for 24 h before the test fixture is assembled.This should minimize outga
39、ssing that results from deteriorationof the organic components exposed to elevated temperatures.5.3 Test Specimen:5.3.1 The test specimen shall be of an adequate size to coverthe aperture of the box or glazing frame and to permit suitableattachment.NOTE 6Adequate allowances should be made for materi
40、als that willundergo dimensional changes due to temperature.5.3.2 The test specimen identification marks shall not inter-fere with either the exposure or the subsequent testing.5.4 Sample Mounting:5.4.1 Rigid and Semirigid Glazings:5.4.1.1 Lay the test specimen for single cover exposuredirectly on e
41、ither the spacer or the glazing frames. If used, theframe is then placed on the spacer in the weathering box (seeFig. 2).5.4.1.2 Lay the test specimen for inner cover exposure of adouble cover assembly on the spacer or attach it to the glazingframe before the glazing frame is placed in the box (see
42、Fig. 2).5.4.1.3 Lay the test specimen for outer cover exposure of adouble cover assembly on the top of the glazing frame (see Fig.2).5.4.2 FilmsPlace film test specimens on the glazing frameusing adhesive transfer tape to hold the test specimen taut. It isessential that uniform tensioning be obtaine
43、d prior to applyingthe tape. Then place the frame in the box similar to 5.4.1.1,5.4.1.2, and 5.4.1.3.5.5 Assembly of Weathering Box:5.5.1 Slide the various parts of the weathering box testfixture into position. The outer glazing must be roughly flushwith the top side of the box. The position of an i
44、nner glazing,if used, shall be nearest the bottom of the box.5.5.2 After assembly, seal the frame and outer glazing inplace with an adhesive tape to prevent moisture intrusion.Place the box top on the box (see Fig. 2).6. Natural Weathering Exposure6.1 Mount the weathering boxes in a backed condition
45、 using13-mm (0.5-in.) exterior grade plywood on weathering rackssuch as those described in Practice D 1435. The racks shall becapable of having the angles adjusted and have their axis ofrotation on an east-west line.6.2 Use a variable angle exposure to maximize solar radia-tion incident upon the wea
46、thering box. Adjust the racksaccording to the schedule given in Table 2. Positive rack anglesface south. Choose the angles so that the weathering boxes arenever closer to the horizontal than by 5. Other variableexposure schedules requiring more than four adjustments peryear may be used. The method f
47、or determining the variableangle exposure schedule is described in Appendix X2 of thispractice.6.3 When a number of weathering boxes are exposedsimultaneously, mount the boxes side by side with the sides nottouching.6.4 Do not clean the solar collector cover materials duringexposure.6.5 Visually ins
48、pect the test specimens at intervals of notmore than one month. Record all changes in appearance.7. Report7.1 The report shall include the following:7.1.1 Description of the weathering box test fixture and itscalculated combined back and edge loss coefficient,7.1.2 Whether the solar collector cover
49、materials are ex-posed as a single- or double-cover configuration and whetherthe test specimen was the inner or outer cover,7.1.3 Complete identification of the solar collector outercover material(s),7.1.4 Complete identification of the solar collector innercover material(s) (if any),7.1.5 A description of the test specimen attachment andmounting procedures,7.1.6 Latitude, longitude, altitude, and address of the testingsite including a description of the type of climate
