FINAL DRAFT UGANDA 
STANDARD  FDUS 885
First Edition
2009-mm-dd
 
Reference numbe  
r
FDUS 885: 2009
 © UNBS 2009 
  
Standard practice for generating all-day thermal performance 
data for solar collectors  
 FDUS 856: 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  
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permission from UNBS. 
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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 885: 2009 
© UNBS 2009 – All rights reserved  iii
 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 885: 2009
 
© UNBS 2009– All rights reserved 1
 Standard practice for generating all-day thermal performance 
data for solar collectors 
1 Scope 
This Final Draft Uganda Standard practice covers a mean s of generating all-day thermal performance data for 
flat-plate collectors, concentrating collectors, and tracking collectors. 
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. 
FDUS 854-1: 2009, Thermal solar systems and components — Solar collectors — General requirements   
FDUS ISO 9488, Solar energy - Vocabulary 
ISO 9806-1:1994,  Test methods for solar collectors — Part 1: Thermal performance of glazed liquid heating 
collectors including pressure drop  
ISO 9806-2:1995, Test methods for solar collectors — Part  2: Qualification test procedures 
ISO 9806-3:1995, Test methods for solar collectors — Part 3:  Thermal performance of unglazed liquid heating 
collectors (sensible heat transfer only) including pressure drop 
3 Terms and definitions 
For the purposes of this standard, the terms and definitions given in FDUS ISO 9488 and the following apply . 
3.1. 
area, aperture, A a  
maximum projected area of a solar thermal collector, th rough which the unconcentrated solar radiant energy is 
admitted, measured in square metres (m2) 
NOTE For concentrating collectors, the gross aperture area in cludes any area of the reflector or refractor shaded by 
the receiver and its supports and including gaps between re flector segments within a collector module. Net aperture 
excludes any shaded area or gaps between reflector segment s and is sometimes called effective aperture area. (see 
FDUS ISO 9488). 
3.2  
heat transfer fluid , η, in solar energy systems, 
i) liquid or gas that passes through the solar collect or and carries the absorbed thermal energy away  from 
the collector 
ii) any fluid that is used to transfer thermal energy between subsystems in solar energy systems (see FDUS 
ISO 9488)  DUS 885: 2009 
2 © UNBS 2009 – All rights reserved
 3.3 
non-operational mode exposure  
condition that exists when the collector has been  filled, then purged of heat transfer fluid (if a liquid) and 
capped (but not sealed) to prevent introduction of fore ign substances, mounted on a test rack, and exposed to 
solar radiation (see FDUS ISO 9488) 
3.4  
stagnation conditions  
conditions (that is, temperature and pressure) exis ting when an energy system has attained a quasi-steady 
state after the flow of heat transfer fluid has stopped,  but the absorber continues to receive significant solar 
irradiance(see FDUS ISO 9488) 
3.5 
tilt angle  
in solar energy applications, angle in between the ho rizontal and the plane of the detector (collector, 
photovoltaic array, instrument ) surface(see FDUS ISO 9488) 
3.6 
time constant  
time required for the temperature change in the fluid leav ing a solar collector to attain 63.2 % of its equilibrium 
value following a step change in the solar irradiance  or inlet fluid temperature. (see FDUS ISO 9488) 
NOTE The step change involved should be thoroughly described in the procedure. 
3.7 
useful energy (removed) 
time integral of the product of mass flow rate, specific heat, and temperature difference across the collector 
when the outlet temperature is greater than the inlet temperature 
4 Summary of practice  
The solar collector is mounted in accordance with t he manufacturer's instructions. A constant flowrate and 
inlet temperature, and the transfer fluid, is pre-sele cted and specified. The temperature, fluid flowrate, 
irradiance, and wind parameters are recorded througho ut the daylight hours. Data  are collected at 1-min 
intervals or more frequently, and the average values are reported for each 5-min interval of the test day. All-
day thermal performance is determined from the summation of energy outputs for all intervals of the test day.   
5 Significance and use 
5.1 This practice may be employed for a relative determi nation of the useful energy collected by different 
solar collectors tested side-by-side under the same operating and environmental parameters, in the same 
location, and on the same test day. Variations in inle t temperature and transfer fluid flow rate should be 
minimized for best results. 
5.2 Caution should be exercised when comparing the all-day thermal performance data for collectors tested 
by this practice to the performance of other collectors  not tested at the same time and the same location, or 
with the same test conditions. The data collected by this practice represent the behavior of the tested collectors only under the conditions occurring on the day of test and at the specific inlet temperature and fluid 
flow rate employed during the test. 
In the case of low-temperature collectors (operating below 100 °C), consideration must be given to the relationship of inlet temperature to ambient temper ature when analyzing or interpreting the test data. 
5.3 Data collected in this test have not been shown to  provide the overall comparison of collectors or 
collector concepts that would be required to support a nationally accepted rating or certification program .  DUS 885: 2009 
© UNBS 2009 – All rights reserved  3
 6 Preconditioning  
Prior to starting the all-day thermal performance test in ac cordance with this practice, the solar collectors shall 
be preconditioned. Preconditioning shall consist of stagnat ion conditions in a non-operational mode and in a 
dry (or drained) condition for a minimum of three days. The minimum radiant exposure measured in the plane 
of the collector during preconditioning shall be 17 MJ/m2.day. 
NOTE If the preconditioning procedure above can be expected to cause either structural or material failure, the 
procedure should be deleted or modified to a method agreeable to the client to preclude t hermally induced problems prior 
to performance testing.   
7 Procedures and computations  
7.1 General  
7.1.1 Mounting  
Mount the solar collectors in accordance with the manufacturer's instructions at a tilt and azimuth that is 
commensurate with the end-use application, if known. Otherwise, for non-tracking collectors, the tilt shall be 
that of the local latitude minus the seasonal decli nation angle and the azimuth shall be 180° (true south). 
If the test is intended to compare collector types for which an array of two or more will be used in normal 
applications, then test a collector assembly consisting of two or more collectors of each type, together with 
any required external manifolding. Include a description of the manifolding in the report, giving the pipe length, 
diameter, and material and the insulation type and thickness used. It shall be stated whether collectors were 
joined in series or parallel. 
7.1.2 Time constant 
Determine the collector time constant at the mass flow ra te utilized in this test meth od and in accordance with 
FDUS 854-2/ISO 9806.  
7.2 Test conditions  
7.2.1 Exposure conditions 
Precondition the solar collectors in accordance with Clause 6. 
7.2.2 Operating conditions 
Pump the specified transfer fluid through the collectors  at a constant preselected mass flow rate and inlet 
temperature specified by the manufactu rer. The selected flow rate should be the projected flow rate for the 
anticipated end-use application, and the inlet temperatur e should be selected to provide the anticipated end-
use temperature. Maintain the inlet temperatures with in ± 0.5 °C during each 5-min measurement interval and 
within ± 2.5 °C during the test day. Maintain the fl ow rate within ± 1.0 % during each 5-min measurement 
interval. Variations in inlet temperature and mass fl ow rate should be minimized for best test results. 
7.2.3 Measurements 
7.2.3.1 Temperature and flow rate measurements 
Make temperature and flow rate measurements in ac cordance with US 854-2/ISO 9806 or US 854-2/ISO 
9806-3 where applicable. Mount inlet and outlet temperat ure sensors at the locati on where the heat transfer 
fluid first enters the collector assembly and leaves the collector assembly, respectively. Average the transfer 
fluid temperature measurements and the flow rate meas urement over the 5-min test interval and record.  DUS 885: 2009 
4 © UNBS 2009 – All rights reserved
 7.2.3.2 Solar radiation measurements 
Make solar radiation measurements in accordance with US 854-2/ISO 9806 and record at 1-min intervals. 
More frequent intervals or continuous recording are permissible. Average the readings over each 5-min 
interval and report the averages.  
7.2.3.3 Area measurements 
Measure both gross and aperture areas and report for each collector tested. 
7.2.4 Recorded data 
7.2.4.1  Record ambient temperature, collector inlet temperatures, mass flow rate, solar irradiance 
(measured in the plane of the collector), and wind dat a beginning at local sunrise and terminating at local 
sunset plus three collector time constants. 
7.2.4.2  Record solar radiation over the sunrise-to-sunse t test day including those measurement intervals 
during which the collector does not produce useful energy.  
NOTE  As defined in this practice, the collector can operate during a measurement interval of the test day in such a 
manner that useful energy is not generated. In actual oper ation, flow to the collector would normally be shut off during 
these intervals. 
8 Calculation 
8.1 Energy collected 
8.1.1 Useful energy rate 
Calculate the useful rate of energy collection, qu, in W(Btu/h) as follows: 
  qu  = mCpΔ T                   ( 1 )  T
where: 
m is the mass flow rate, kg/s 
Cr is the specific heat of transfer fluid, J/(kg.oC) 
ΔT is the difference between outlet temperature, To, and inlet temperature, Ti- ΔT has the value zero 
when  Ti ≤ Ti oC 
8.1.2 Useful energy in the data interval 
Calculate the useful ener gy collected during the ith 5 min data interval, in J (Btu), as follows: 
  Q i = ∫mC=min 5 ti
tipΔTd t                 ( 2 )  
8.1.3 Useful energy for the test day 
Calculate total energy collected during the test day, in J (Btu), as follows: 
  Q D = ∑ Q
=n
i1i                   ( 3 )  DUS 885: 2009 
© UNBS 2009 – All rights reserved  5
 where the summation is made over all 5-min intervals of the day . 
8.2 Solar radiation 
8.2.1 Available energy rate 
Measure available solar power, E, W/m2, as follows:  
• total solar irradiance in the plane of the collector, or 
• direct beam irradiance normal to the aperture of the collector for collectors that do not accept diffuse 
radiation. 
8.2.2 Available energy in the data interval 
Calculate total solar energy available during the 5-min interval, in J/m2 as follows: 
  Hi = Ed t                  (4) ∫=min 5 ti
ti
8.2.3 Available energy for the test day 
Calculate the total solar energy available between sunrise and sunset,  
  HD = H∑
=n
i1i                  ( 5 )  
9 Reporting requirements 
9.1 The collector identification and associated informat ion shall be reported as shown in Figure 1. DUS 885: 2009 
6 © UNBS 2009 – All rights reserved
 Client…………………………………………………………………………………………………………… 
Date of test……………………………………………………………….……………………………………. 
Collector manufacturer……………………………………………………………………………………….. 
Model number……………………………………………………………….………………………………… 
Geographical location of test………………………………………………………………………………… 
Tilt angle, o …………………………………………………………………………………………………… 
Azimuth angle. o……………………………………………………………………………………………… 
Number of preconditioning days…………………………………………………………………………… 
Number of exposure days for precondi tioning requirement…………………….………………………. 
Heat transfer fluid designation…………………………………………………….……………………….. 
Mass flow rate, kg/s………………………………………………………………..………………………… 
Collector inlet temperature, oC……………………………………………………………………………… 
Collector time constant………………………………………………………………………………………. 
Miscellaneous: 
 Mounting details; description or figure attached. 
 Heat transfer fluid: C p versus T graph or table attached. 
Tracking collector wiring and control details; figure attached. 
Sky conditions; description attached. 
Figure 1 – Reporting format 
9.2 Test data and associated information shall be reported as shown in Figure 2. DUS 885: 2009 
© UNBS 2009 – All rights reserved  7
 The test report shall include the following: 
 Aperture dimensions and area, m and m2   ………………………………………………………………….…. 
 Gross dimensions and area, m and m2  ………………………………………… …………………………….... 
 Weight, dry; kg……………………………………………………………………………………………………… 
Sunrise-to-Sunset data report s for each time interval: 
 Date, beginning time……………………………………………………………………………………………….. 
  Averages of: 
  Ambient temperature, oC…………………………………………………………………………………….. 
  Collector mass flow rate, kg/s………………………………………………………………………………… 
  Irradiance, W/m2   .
  Average wind speed and direction, m/s (mph)…………………………………………………………….. 
  Collector inlet temperature, oC………………………………………………………………………………… 
  Collector outlet temperature, oC………………………………………………………………………………. 
  Sun incident Angle (at the begi nning at each test interval), o    ,…………………………………………. 
A plot of irradiance, E and useful energy rate, qu versus time, or plot of Hi and Qi versus time. 
A table showing for each 5-min interval, average values of Qi and Hi. 
All-day test results: 
 Useful energy collected, QD
 Available solar energy, HD, J/m2
Figure 2 – Data format 
 
 
 
 
 
  
© UNBS 2009– All rights reserved 
 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.  
 
 DUS 
 
ICS 27.160 885: 2009 
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© UNBS 2009– All rights reserved