FINAL DRAFT UGANDA 
STANDARD  FDUS 859
First Edition
2009-mm-dd
- 
Reference numbe  
r
FDUS 859: 2009
 © UNBS 2009 
  
Standard practice for exposure of cover materials for solar 
collectors to natural weathering under conditions simulating 
operational mode  
 FDUS 859: 2009 
ii © UNBS 2009 – All rights reserved
 Compliance with this standard does not, of itself confer immunity from legal obligations 
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS  2009  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, in cluding photocopying and microfilm, without prior written 
permission from UNBS. 
Requests for permission to reproduce this document should be addressed to 
The Executive Director 
Uganda National Bureau of Standards 
P.O. Box 6329 
Kampala  
Uganda 
Tel: 256 41 4505995 
Fax: 256 41 4286 123 
E-mail: unbs@infocom.co.ug 
Web: www.unbs.go.ug  FDUS 859: 2009 
© UNBS 2009 – All rights reserved  iii
 Contents Page 
Foreword………………………………………………………………………………………………..…………iv 
1   Scope ....................................................................................................................................................1  
2   Normative references ..........................................................................................................................1  
3   Terms and definitions .........................................................................................................................1  
4   Significance and use ...........................................................................................................................1  
5    Weathering box test fixture ................................................................................................................2  
5.2    Test Specimen .....................................................................................................................................3  
5.3    Sample mounting ............................................................................................................................... .7 
5.4    Assembly of weathering box ..............................................................................................................8  
6    Natural weathering exposure .............................................................................................................9  
7    Report ...................................................................................................................................................9  
 
 FDUS 859: 2009 
iv © UNBS 2009 – All rights reserved
 Foreword 
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry  of Tourism, Trade and 
Industry established under Cap 323, of the Laws of Uganda.  UNBS is mandated to co-ordinate the 
elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex A limentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT/SPS Agr eements of the World Trade Organisation (WTO). 
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a gi ven field or area and consists of representatives of 
consumers, traders, academician s, manufacturers, governme nt and other stakeholders. 
Draft Uganda Standards adopted by the Technical Committ ee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
Committee membership 
The following organisations were represented on su bcommittee on Solar Energy, SC 3 under the Energy 
management standards Technical Committee, UNBS/ TC 13 in the development of this standard: 
• Battery Masters (U) Limited 
• Equator-sun (U) Limited 
• Incafex Solar Systems 
• Makerere University 
• Renewable Energy Department, Minist ry of Energy and Mineral Development 
• Solar Masters 
• Sonnerkraft Solar Systems 
• Uganda Institute of Professional Engineers 
• Uganda National Bureau of Standards 
• Uganda National Plumbers Association 
• Ultratec (U) Limited 
•  
 FINAL DRAFT UGANDA STANDARD FDUS 859: 2009
 
© UNBS 2009– All rights reserved 1
 Standard practice for exposure of cover materials for solar 
collectors to natural weathering under conditions simulating operational mode 
1 Scope 
1.1 This standard practice provides a procedure for t he exposure of cover materials for flat-plate solar 
collectors to the natural weather env ironment at temperatures that ar e elevated to approximate operating 
conditions. 
1.2 This standard practice is suitable for exposure of bot h glass and plastic solar collector cover materials. 
Provisions are made for exposure of single and doubl e cover assemblies to accommodate the need for 
exposure of both inner and outer solar collector cover materials. 
1.3 This standard practice does not apply to cover mate rials for evacuated collectors or photovoltaics. 
2 Normative references  
The following referenced documents are indispensable fo r the application of this Uganda Standard. For dated 
references, only the edition cited applies. For undated references, the latest edition of the referenced 
document (including any amendments) applies. 
ISO 291, P lastics — Standard atmospheres for conditioning and testing   
FDUS ISO 9488, Solar Energy- Vocabulary 
FDUS 858, Method of test for exposure of solar collector  cover materials to natural weathering under 
conditions simulating stagnation mode  
FDUS 861, Method of test for e valuating absorptive solar receiver materials when exposed to conditions 
simulating stagnation in solar collectors with cover plates 
3 Terms and definitions 
For purposes of this Uganda standard, the following terms and definitions given in FDUS ISO 9488 apply. 
4 Significance and use  
4.1 This practice describes a weathering box test fi xture and provides uniform exposure guidelines to 
minimize the variables encountered during outdoor exposure testing. 
4.2 This practice may be useful in comparing the perf ormance of different materials at one site or the 
performance of the same material at different sites, or both. FDUS 859: 2009 
2 © UNBS 2009 – All rights reserved
 4.3 Since the combination of elevated temperature an d solar radiation may cause some solar collector 
cover materials to degrade more rapidly than either al one, a weathering box that elevates the temperature of 
the cover materials is used. 
4.4 This practice is intended to assist in the evaluation of solar collector cover materials in the operational, 
not stagnation mode. Insufficient data exists to obtain exact correlation between the behaviour of materials 
exposed according to this practice and actual in-service performance. 
4.5 Means of evaluation of effects of  weathering are provided in FDUS 861, and in other test methods that 
evaluate material properties. 
4.6 Test of the type described in this practice may be used to evaluate the stabilit y of solar collector cover 
materials when exposed outdoors to the varied influen ces which comprise weather. Exposure conditions are 
complex and changeable.  Important factors are solar radi ation, temperature, moisture, presence of pollutants 
etc. these factors vary from site to site and should be considered in selecting locations for exposure. Control 
samples must always be used in weathering test for comparative analysis. Outdoor exposure for at least two 
years is required to make evident changes, such as  surface degradation without  the use of sophisticated 
analytical equipment. 
4.7 Temperature conditions attained with this box may not exactly duplicate those that occur under 
operational conditions with fluid flow. Dependent on environmental exposure conditions, the cover plate 
temperatures obtained with this box may be higher or lower than those obtained under operational conditions. 
Additional testing under stagnation conditions, although not covered by this practice should be conducted. 
NOTE 1 Research has shown that exposure outdoors at sites having the combination of high levels of humidity, solar 
energy, and ambient temperature can cause more severe degradat ion of some polymeric cover materials, (for example, 
microcracking and leaching of UV radiation screen ing additives) than exposure in arid climates. 
NOTE 2 Stagnation conditions are a normal occurrence for so lar collectors, for example, during operation when the 
storage is fully charged; when the collectors are initially installed, befor e system start-up; or when the system is shut down 
for maintenance or seasonal considerations such as heating-only systems in the summer. 
5 Weathering box test fixture 
5.1 General 
5.1.1 Weathering box test fixture, consisting of a box, ra ils, a box top, a glazing frame, and adhesive tapes. 
The weathering box test fixture should be cons tructed in accordance with figures 1 – 5. 
5.1.2 The box and box top should be made in metal that is suitably resistant to co rrosion encountered in the 
exposure environment. A weep hole should be drilled at the lower end of the bottom of the box to provide drainage and to minimize moisture accumulation. 
NOTE The box top is intended to protec t the edges of the test specimen in contact with the box from reaching 
excessively high temperatures, to minimize exposure of the ad hesive to sunlight, and to minimize mo isture penetration 
into the exposure test fixture. 
5.1.3 The box interior shall be a flat black nonselective coating having an absorptance of not less than 0.90 
after exposure. Organic absorber coatings should be he ated in an oven at 150 °C for 24 h before the test 
fixture is assembled. This should minimize outgassi ng, which result from deterioration of the organic 
components exposed to elevated temperatures. 
5.1.4 The adhesive tapes should be stable when exposed to moisture and elevated temperatures. They 
should be compatible with the specific materials from  which the box, glazing frame, box top, and cover plate 
are made. FDUS 859: 2009 
© UNBS 2009 – All rights reserved  3
 5.1.5 Organic materials are potential sources for outgassin g and should be eliminated from the interior of 
the weathering box where possible. Fo r example, metallic parts should be cle aned to remove traces of grease 
or other foreign matter. Other possible sources of out gassing include coatings and sealants. 4.1.2 addresses 
outgassing of absorber coatings. 
5.2 Test Specimen 
5.2.1 The test specimen shall be of an adequate size to co ver the aperture of the box or glazing frame, and 
consideration given to dimensional changes due to temperature. 
5.2.2 The test specimen identification marks shall not interf ere with either the exposure or the subsequent 
testing. FDUS 859: 2009 
4 © UNBS 2009 – All rights reserved
  
 
NOTE 1 Material: metal suitably corrosion-resistant for exposure. A typical material would be 24-gauge galvanized 
steel. 
NOTE 2 Dimension tolerance ± 1mm 
NOTE 3 Box must be watertight when weep hole is covered. 
NOTE 4 Paint interior of box black, bake 1h at 150 oC. 
NOTE 5 Use lead solder on corner joints. 
Figure 1 – Natural weathering box - Box 
 FDUS 859: 2009 
© UNBS 2009 – All rights reserved  5
 
 
 
NOTE 1 Make: 4 per box 
NOTE 2 Material: metal suitably corrosion-resistant for exposure, typical material would be 24-gauge galvanized steel. 
NOTE 3 Dimension tolerance ± 1 mm. 
Figure 2 – Natural weathering box - Rolls 
 FDUS 859: 2009 
6 © UNBS 2009 – All rights reserved
  
 
NOTE 1 Make: 1 per box 
NOTE 2 Material: metal suitably corrosion-resistant for exposure, typical material would be 24-gauge galvanized steel. 
NOTE 3 Top must fit over box with rails in place 
Figure 3 – Natural weathering box - Top 
 
 FDUS 859: 2009 
© UNBS 2009 – All rights reserved  7
  
 
 
NOTE 1 Make: 1 per box. 
NOTE 2 Material: metal suitably corrosion-resistant for ex posure. A typical material would be 24-gage galvanized steel. 
NOTE 3  Glazing frame must fit into box. 
Figure 4 — Natural weathering box — Glazing frame 
5.3 Sample mounting 
5.3.1 Rigid and semi- rigid glazings 
5.3.1.1 Lay test specimens for single cover exposure di rectly on the glazing frame and place the frame 
on the rails in the weathering box (see Figure 5). 
5.3.1.2 Lay test specimens for inner cover exposure on a double cover assembly on the rails before the 
glazing frame is put in place (see Figure 5). FDUS 859: 2009 
8 © UNBS 2009 – All rights reserved
 5.3.1.3  Lay test specimens for outer cover exposure on  a double cover assembly on the glazing frame 
(see Figure 5). 
 
 
Figure 5 — Natural weathering box assembly — Rigid glazing 
5.3.2 Films 
Place film test specimens on the glazing frame using adh esive transfer tape to hold the test specimens taut. 
Then place the frame in the box (see Figure 5)  similar to 5.3.1.1, 5.3.1.2, and 5.3.1.3. 
5.4 Assembly of weathering box 
5.4.1 Slide the various parts of the weat hering box test fixture into position. The outer glazing must be 
roughly flush with the top side of the box. The position of an inner glazing, if used, will be nearest the bottom 
of the box. If an inner glazing of substantial thickness is used, the frame may protrude above the box edge by 
an amount equal to the thickness of the glazing. FDUS 859: 2009 
© UNBS 2009 – All rights reserved  9
 5.4.2 After assembly, seal the frame and outer glazing in  place with an adhesive tape to prevent moisture 
intrusion. Then place the cover on the box covering the tape (see Figure 5). 
6 Natural weathering exposure 
6.1 Mount the weathering boxes in a backed condition (using 13-mm,exterior grade plywood) on weathering 
racks. The racks should be capable of having the angles adjusted and have their axis of rotation on an east-
west line. 
6.2 Use a variable-angle exposure to maximize solar radiation upon the weathering box. Adjust the racks in 
accordance with one of the schedules contained in Annex B of FDUS 858. 
6.3 When a number of weathering boxes are exposed simultaneously, mount the boxes side by side with 
the sides not touching. 
6.4 Do not clean the solar collector cover materials during exposure. 
7 Report 
7.1 The report shall include the following: 
a) complete identification of the solar collector cover material, 
b) whether the solar collector cover materials are exposed as a single or double cover configuration and 
whether the test specimen was the inner or outer cover, 
c) material used for the absorber coating, 
d) description of the test specimen attachment and mounting procedures, 
e) latitude, longitude, altitude, and address of the test ing site including a description of the type of 
climate, 
f) exposure data, 
g) climatological data, 
i) radiant exposure (GJ/m2) measured in the plane of  the weathering boxes, 
ii) monthly maximum, minimum, and mean temperatures, 
h) visual inspection of test specimens, noting any obv ious changes in appearance should be made at 
regular scheduled intervals (once per month minimum), 
i) description of control specimens, and 
j) any deviation from this practice. 
7.2 Other data that are desirable to report, if available, are: 
a) optional climatological data, 
i) daily maximum, minimum, and mean percent relative humidity, 
ii) daily hours of wetness, both dew and rain, FDUS 859: 2009 
10 © UNBS 2009 – All rights reserved
 iii) daily total mm (inches) of rainfall, 
iv) daily maximum and minimum ambient temperature, 
v) daily radiant energy, 
vi) wind direction and velocity, 
b) type of atmosphere, for example, indu strial, and level of air pollutants, 
c) ultraviolet radiation, and 
d) maximum absorber plate temperature. 
 
 
 
 
 
 
  
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 Certification marking 
Products that conform to Uganda standards may be  marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The use of the UNBS Certification Mark is gove rned by the Standards Act, and the Regulations made 
thereunder. This mark can be used only by those licens ed under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in co njunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relation to a product is an assurance that the goods comply with the 
requirements of that standard under a system of supervision, control and  testing in accordance with the 
certification mark scheme of the Uganda National  Bureau of Standards. UNBS marked products are 
continually checked by UNBS for conformity to that standard.  
Further particulars of the terms and conditions of  licensing may be obtained from the Director, Uganda 
National Bureau of Standards.  
 
 
2009 – DUS 
 
ICS 885: 2009 
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