FINAL DRAFT UGANDA 
STANDARD  FDUS 857-2
First Edition
2009-mm-dd
 
Reference numbe  
r
FDUS 857-2: 2009
 © UNBS 2009 
  
Custom built systems- Part 2: Test methods  
 FDUS 857-2: 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 857-2: 2009 
© UNBS 2009 – All rights reserved  iii
 Contents Page 
Foreword………………………………………………………………………………………………..…………iv 
1   Scope ....................................................................................................................................................1  
2  Normative references ...........................................................................................................................2  
3  Terminology ..........................................................................................................................................2  
4    Summary of practice ...........................................................................................................................2  
5    Significance and use ...........................................................................................................................4  
6    Preconditioning ...................................................................................................................................4  
7    Procedures and computations ............................................................... Error! Bookmark not defined.  
8    Calculation ............................................................................................................................... ..........16  
8.1    Energy collected ............................................................................................................................... .16 
8.2    Solar radiation ......................................................................................... Error! Bookmark not defined.  
9    Reporting requirements ..........................................................................Error! Bookmark not defined.  
 
 FDUS 857-2: 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 by the Act of Parliament of 198 3, 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 Energy Management Subcommittee on Solar Energy, UNBS TC 13/SC 3, in the preparation of this standard: 
• Renewable Energy Department, Minist ry of Energy and Mineral Development 
• Makerere University 
• Incafex Solar Systems 
• Battery Masters (U) Limited 
• Equator-sun (U) Limited 
• Ultratec (U) Limited 
• Sonnerkraft Solar Systems 
• Solar Masters 
• Uganda National Plumbers Association 
• Uganda Institute of Professional Engineers 
• Uganda National Bureau of Standards 
 
 
 
 
 
 
 
 FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  v
 Factory Made and Custom Built solar heating systems 
The standards FDUS 855-1 as well as FDUS 855- 2 and the standards FDUS 857-1 to FDUS 857-3 
distinguish two categories of solar heating systems: Factory Made solar heating systems and Custom Built 
solar heating systems. The classification of a system as Factory Made or Cu stom Built is a choice of the final 
supplier, in accordance with  the following definitions. 
Factory Made solar heating systems  are batch products with one trade name, sold as complete and 
ready to install kits, with fixed configurations. Systems of this category are considered as a single product and 
assessed as a whole. If a Factory Made Solar Heating Sy stem is modified by changi ng its configuration or by 
changing one or more of its components, the modified system is considered as a new system for which a new 
test report is necessary. Requireme nts and test methods for Factory Made solar heating systems are given in 
DUS 855-1 and DUS 855-2. 
Custom Built solar heating systems  are either uniquely built, or assembled by choosing from an 
assortment of components. Systems of this category are regarded as a set of components. The components 
are separately tested and test results are integrated to  an assessment of the whol e system. Requirements for 
Custom Built solar heating systems are given in DU S 857-1; test methods are specified in DUS 857-2 and 
DUS 857-3. Custom Built so lar heating systems are subdiv ided into two categories: 
-  Large Custom Built systems are uniquely designed for a specific situation. In general HVAC    
engineers, manufacturers or other experts design them. 
-  Small Custom Built systems offered by a company are described in a so-called assortment file, in 
which all components and possible sy stem configurations, marketed by the company, are specified. 
Each possible combination of a system configuration with components from the assortment is 
considered as one Custom Built system. 
Table 1 shows the division for different system types: 
Table 1-Division for factory made and custom built solar heating systems 
Factory Made Solar Heating Systems (DUS 855-1, 
-2) Custom Built Solar Heating Systems (DUS 857-1,-2,-3) 
integral collector-storage for hot water preparation 
Thermosiphon systems for hot water preparation Forced-circulation systems for hot water preparation and/or space heating, assembled using components 
and configurations described in a documentation 
file(mostly small systems) 
forced-circulation systems as batch product with fixed 
configuration for hot water preparation Uniquely designed and assembled systems for hot water preparation and/or space heating (mostly large 
systems) 
 
NOTE 1 Forced circulation systems can be classified either as Factory Made or as Custom Built, depending on the market 
approach chosen by the final supplier. 
NOTE 2 Both Factory Made and Custom Built systems are perfo rmance tested under the same set of reference conditions 
as specified in Annex B of DUS 855-2 a nd Annex A of DUS 857-2. In practice, the installation conditions may differ from 
these reference conditions. 
NOTE 3 A Factory Made system for domestic hot wa ter preparation may have an option for space heating, 
however this option should not be used or cons idered during testing as a Factory Made system . 
 FINAL DRAFT UGANDA STANDARD FDUS 857-2: 2009
 
© UNBS 2009 – All rights reserved  1
 Custom built solar systems – Part 2: Test methods 
1 Scope 
This Final Draft Uganda Standard applies to small and la rge custom built solar heating systems with liquid 
heat transfer medium for residential buildings and similar applications, and gives test methods for verification 
of the requirements spec ified in FDUS 857-1. 
This Uganda Standard includes also a method for thermal performance characterization and system 
performance prediction of small custom built systems by  means of component testing and system simulation. 
Furthermore, the Uganda Standard contains methods fo r thermal performance characterization and system 
performance prediction of la rge custom built systems. 
This Uganda Standard applies to the following types of small custom built solar heating systems: 
- systems for hot water preparation only; 
- systems for space heating only; 
- systems for domestic hot water preparation and space heating. 
This Uganda Standard applies to large custom built solar heating systems; primarily to solar preheat systems, 
with one or more storage vessels, heat exchangers, pipi ng and automatic controls and with collector array(s) 
with forced circulation of fluid in the collector loop. 
This Uganda Standard does not apply to: 
-  systems with a store medium other than water (e.g. phase-change materials); 
- systems for space heating with a distribution fluid other than water for the space heating subsystem 
(e.g. air systems); 
-  small custom built systems with a circulation line entering any store having a feedback on the solar 
heated store. 
Principally, systems with circulation line may be tested in accordance to the methods described in this Uganda Standard, if the connecting port for the circulation line is  kept closed during the tests. This should, however, 
stated in the test report. 
-  thermosiphon systems; 
-  integral collector-storage (ICS) systems. 
The test procedure of Annex C cannot be applied to so lar heating systems with co ncentrating collectors. 
NOTE  The two test methods presented in annex C ("Short-te rm system testing") have only been validated, so far, two 
laboratories, at the Danish Technologica l Institute DTI and at the Chalmers Univer sity of Technology Goteborg ([9], [14]). 
DTI is confident that the proc edures are promising and very efficient. However, the full verification and a round robin test 
within Europe are urgently needed . FDUS 857-2: 2009 
2 © UNBS 2009 – All rights reserved
 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 9488, Solar energy – Vocabulary 
EN 806-1, Specifications for installations inside buildings  conveying water for human consumption — Part 
1:General 
ISO 15783, Seal-less rotodynamic pumps — Class II — Specification 
ISO 9906, Rotodynamic pumps — Hydraulic performance acceptance tests — Grades 1 and 2 
EN 1717, Protection against pollution of potable water in drinking water installations and general requirements 
of devices to prevent pollution by backflow 
ISO 6612, Windows and door height windows — Wind resistance tests 
ISO 16528, Boilers and pressure vessels 
IEC 60335-1, Safety of household and similar electrical appliances — Part 1: General requirements 
IEC 60335-2-21, Safety of household and similar electrical applia nces — Part 2: Particular requirements for 
storage water heaters 
ISO 9459-5, Solar heating — Domestic water heating systems — Part 5: System performance by means of 
whole system testing and computer simulation  
US 854-1: 2009, Uganda Standard — Thermal solar systems and components — Solar collectors — General 
requirements   
US 854-2: 2009, Thermal solar systems and components — Solar collectors — Part 2: Test methods 
US 855-1:2009, Thermal solar systems and components — Fact ory made systems — Part 1: General 
requirements 
US 855-2, Thermal solar systems and components — Factor y made systems — Part 2: Test methods 
DUS 857-1, Thermal solar systems and components — Custom built systems — Part 1: General requirements 
DUS 857-3, Thermal solar systems and components — Custom built systems — Part 3: Performance 
characterization of stores for solar heating systems 
3  Terms and definitions 
For the purposes of this Uganda Standard, the terms and definitions given in ISO 9488 and ISO 9459-5 as 
well as US 854-1, US 855-1 and DUS 857-1 apply. 
4   Symbols and abbreviations 
al     algebraic constant for the determinatio n of the collector heat loss coefficient 
Ac     collector reference area FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  3
 Cc      collector array heat capacity 
fsol   solar fraction 
G   solar irradiance 
Gd   diffuse irradiance 
Gg   global irradiance (i.e. horizontal) 
Gh   hemispherical irradiance, e.g. on tilted plane 
Hc   hemispherical solar irradiation in collector plane 
Kατ   incidence angle modifier 
Paux   power of the auxiliary heater 
Pc   thermal power of the collector or collector array 
Prc   circulation heat loss power 
Qsol   heat delivered by the collector loop to the store 
Qaux  net auxiliary energy demand of a solar heating system delivered by the auxiliary heater to the store 
or directly to the heat dist ribution system (see 7.5.3) 
QL   energy delivered at the outle t of the solar heating system 
Qd   heat demand 
Ql   store heat losses 
Qohp  heat diverted from the store as ac tive overheating protection, if any 
Qpar   parasitic energy (electricity) for the collector loop pump(s) and control unit 
ϑaverage   yearly average cold water temperature on reference location 
ϑc,mb  collector ambient air temperature 
ϑs,amb  store ambient air temperature 
ϑci/co  collector or collector array inlet/outlet fluid temperature 
ϑcw   mains water temperature 
ϑd   desired hot water temperature 
ϑm   mean collector fluid temperature; ϑm = (ϑci + ϑco) / 2 
ϑrci   fluid temperature at circulation loop inlet 
ϑrce   fluid temperature at circulation loop outlet 
θreq   required temperature for sensor hi gh-temperature resistance (see annex B) FDUS 857-2: 2009 
4 © UNBS 2009 – All rights reserved
 ϑS   store outlet fluid temperature 
θsens  sensor temperature (see annex B) 
ϑstart/stop  temperature for which controller operation starts/stops (see annex B) 
ϑtank  temperature of the storage tank (see annex B) 
T*   reduced temperature of collector; T* = (ϑm - ϑc,amb) /Gh
(UA)hx  heat transfer rate of a heat exchanger 
(UA)S  store heat loss rate 
UL   overall heat loss coefficient of collector array 
Vd   demanded (daily) load volume 
VS   store volume 
VC   volume flow rate in collector loop 
Vrc   volume flow rate in circulation loop 
Vs   volume draw-off flow rate from storage 
v   surrounding air speed 
Δϑ   temperature difference 
Δϑamplit  average amplitude of seasonal variations on reference location 
η   zero-loss collector efficiency (efficiency at T* = 0) 
5    System classification  
See clause 5 of DUS 857-1. 
6    Test methods 
Subsequent test methods refer to the requirements given in DUS 857 -1. 
NOTE The numbering of the following clauses is kept in  direct correspondence to the numbering in DUS 857-1. 
6.1 General 
6.1.1 Suitability for drinking water 
See EN 806-1. 
6.1.2 Water contamination 
For small custom built systems see EN 1717. FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  5
 Large custom built systems: Check the hydraulic scheme or any other pa rt of the documentation of the 
system according to 6.7.3 of DUS 857-1. 
6.1.3 Freeze resistance 
See 5.1 of DUS 855-2 
6.1.4 Overheating protection  
6.1.4.1 Scald protection 
If the temperature of the hot wate r in the system can exceed 60 oC, check the design plan or the system 
documentation to see whether the system is provided with an automatic cold water mixing device or any 
other device capable for limiting the water temperature to 60 oC at most. 
6.1.4.2 Overheating protection of materials 
Ensure by checking the hydraulic scheme and/or by calculation and taki ng into account the most adverse 
conditions for the materials of all parts of the system , that the maximum temperatures which may occur do not 
exceed the maximum permissible temperatures for the respective materials. 
NOTE  Both transients (high-temperature peaks of short du ration) and stagnation of longer duration may create adverse 
conditions for the respective material. 
6.1.5 Reverse flow prevention 
Check the hydraulic scheme included in the documentat ion (see 6.7) to ensure that no unintentional reverse 
flow will occur in any hydraulic loop of the system . 
6.1.6 Pressure resistance 
See ISO 16528. 
If any component of the system is not covered by IS O 16528 or US 854-1, check the technical data to see 
whether the component for the part of the system in which it is used will withstand the lowest of the following 
pressures 
- 1.5 times the manufacturer's stated maximum working pressure 
_  the manufacturer's stated maximum test pressure 
In addition, for large custom built systems only: 
-  Regarding safety valves, check the hydraulic sche me or any other part of the documentation of the 
system according to 6.7.3 of DUS 857-1. 
-  Regarding pressure resistance, check whether the collector array can withstand short and high 
pressure peaks. Calculate the highest pressure that  can occur in the individual loops in the system 
and compare it with the maximum allowed pressure of the individual loops (see also NOTE 2 in 6.1.6 
of DUS 857-1). Alternatively, an experimental test with 1, 3 times the maximum allowed pressure of 
each loop may be applied.  
6.1.7 Electrical safety 
See US IEC 60335-1 and US IEC 60335-2-21 FDUS 857-2: 2009 
6 © UNBS 2009 – All rights reserved
 6.2  Materials 
Check the work certificates provided by the manufacturer whether t he requirements on UV radiation and 
weather resistance as well as on the choice of materials for the collector  loop are fulfilled. For small custom 
built systems this check shall in any case be performed, for large ones as far as applicable. 
6.3  Components and pipework 
6.3.1  Collector and collector array 
The collector shall be tested according to DUS 854-2. 
In addition, the maximum disparity of the mass flow rate in parallel collector rows should be calculated by 
means of the corresponding pressure drops. 
6.3.2  Supporting frame 
Check the calculation proving the resistance of t he frame to wind loads in accordance with ISO 6612. 
6.3.3  Collector and other loops 
The optional collector loop test comprises the following steps: 
-   Determination of the nominal power needed by the collector loop pump 
- Calculation of the highest heat power wh ich can be delivered by the collector array P c,max: 
 P c,max = η 0AcGref                   ( 1 )  
where Gref is the reference irradiance of 1000 W/m2 (for other symbols see Clause 4). 
- Check of the values calculated by formula (1) in co mparison with the values listed in Table 4 of DUS 
871-1. 
For other heat transfer loops, the nominal parasitic pow er of their pump(s) should be directly compared with 
the calculated highest transmitted heat  power, based on Table 4 of DUS 857-1. 
6.3.4  Circulation pump 
See ISO 9906 and ISO 15783. 
6.3.5  Expansion vessel 
For drain-back systems without a separate expansi on vessel, check both by ca lculation and the hydraulic 
scheme to see whether the drain-back facility is able to fulfill its additional task as an expansion vessel. 
6.3.5.1  Open expansion vessel 
Check the volume and design of the open expansion ve ssel by calculation and by checking the hydraulic 
scheme. 
In addition, check the connection of the vessel to the atmosphere, the spill line and the expansion lines on the 
hydraulic scheme. 
6.3.5.2  Closed expansion vessel 
For small custom built systems only: Check the fulfillment of the requireme nts given in 6.3.5.2 of DUS 857-1 
by calculation and by visual check of the hydraulic scheme and operating instruction. FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  7
 6.3.6  Heat exchangers 
Apart from the tests in compliance with ISO 16528, check the design of the heat exchanger(s) with respect to 
scaling or the availability of cleaning facilities. 
In addition, the drop in system efficiency Δη induced by a heat exchanger in the collector loop of a small 
custom built system should be estimated by formula (2): 
()% 1001 0× = Δ
hxc
UAa Aηη                  ( 2 )  
where η0 and a , are given from the collector performance test of DUS 854-2. For small systems ( UA) l hx is 
delivered by the store performance test of DUS 857-3 (( UA)hx to be chosen for fluid temperatures of 20 °C). 
For large systems ( UA)hx is taken from the heat exchanger performance data sheet provided by the 
manufacturer. 
NOTE 1  In the latter case, since performance data of external heat exchangers (which are mostly used in large custom 
built systems) are generally quite reliable , no additional measurements are needed. 
For heat exchangers in other loops (e.g., a load side heat exchanger), the mean temperature rise on the 
primary side Δϑ which is induced by the presence of the heat exchanger should be estimated by calculation. 
The drop in efficiency may then be estimated by: 
() % 100 / 1× Δ = Δ refG aϑη                 ( 3 )  
where the reference irradiance Gref is set to 1000 W/m2. 
NOTE 2  More accurate calculation methods are given in [1]. In special cases the thermal stratification in the store should 
be taken into account, to obtain an accurate figure for the efficiency drop. 
6.3.7  Store 
With the exception of the heat loss rate, stores for drinking water shall be tested according to ISO 16528. For 
small custom built systems, this test applies in any ca se, for large custom built systems as far as applicable. 
In addition, for small custom built systems only: 
-  the performance of their hot water stores sh ould be characterized according to DUS 857-3. 
-  the heat loss rate of these hot water stores, obta ined from performance characterization according 
to DUS 857-3, should be compared with the requirements given in 6.3.7 of DUS 857-1. 
6.3.8  Pipework 
Check the design plan, manufacturer's works certificates and system docu mentation in respect of design and 
material of pipes and fittings. 
6.3.9  Thermal Insulation 
Check the design plans and system documentation. 
6.3.10  Control system 
6.3.10.1  Controller 
For small custom built systems only: The optional controller test is described in annex B. 
6.3.10.2  Temperature sensors FDUS 857-2: 2009 
8 © UNBS 2009 – All rights reserved
 The design plans and components shall be visually checked in respect of location, installation and insulation 
of the sensors according to the r equirements in 6.3.10.2 of DUS 857-1. 
Additionally: 
- For small custom built systems: Test the sensor re sistance to high temperature as described in B.3. 
This test is, however, not necessary  if a documentation delivered with the sensor indicates that it can 
withstand 100 °C or stagnation conditions (whichever  the greatest) without altering by more than 1 K. 
-  For large custom built systems: Check the suit ability of the temperature sensors in respect of 
stagnation conditions or maximum temperatures in connection with the quality declaration given by 
the supplier. 
6.4    Safety equipment and indicators 
6.4.1   Safety valves 
Check the design plan and the system documentation to verify that each collector or group of collectors is 
fitted with at least one suitable safety valve. 
Check the specification of the safety valves, whether the materials fulfil the requirements given in 6.4.1 of 
DUS 857-1. 
Check whether the size of the safety valve is correct, in compliance with the requirements given in 6.4.1 of 
DUS 857-1. 
Check whether the temperature of t he heat transfer medium at the release pressure of the safety valve 
exceeds the maximum allowed temperat ure of the heat transfer medium. 
Additionally, for large custom built systems: For testi ng the system behavior after release of one or more 
safety valves according to the requirements given in 6.4.1 of DUS 857-1, check t he electric and hydraulic 
schemes or any other part of the document ation according to 6.7.3 of DUS 857-1. 
6.4.2  Safety lines and expansion lines 
Check the hydraulic scheme and system documentation to verify that safety and expansion lines cannot be 
shut-off. 
Check the internal diameter of the safety and the expansion line with respect to the requirements given in 6.4.2 of DUS 857-1. 
Check the hydraulic scheme and system documentation to verify that the expansion line and the safety line 
are connected and laid in such a way that any accumulati on of dirt, scale or similar impurities is avoided. 
6.4.3  Blow-off lines 
Check the hydraulic scheme and system documentation to verify that the blow-off lines fulfil the requirements given in 6.4.3 of DUS 857-1. 
6.4.4   Store shut-off valve 
For large systems only: Verify the existence of a shut-off valve by ch ecking the system documentation in 
accordance with 6. 7.3 of DUS 857-1. 
6.4.5  Indicators 
6.4.5.1  Indicators for collector loop flow FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  9
 Check the hydraulic scheme and system documentation in respect of the position and installation of the 
recommended indicators for the collector loop flow. 
6.4.5.2  Pressure gauge 
Check the hydraulic scheme and system documentation in respect of the position and the installation of the 
pressure gauge or, in the case of some drain-back systems without pressure gauge, of the other means 
provided for checking drain-back and the fluid level in the collector loop. 
6.4.5.3  Heat meter 
If the collector loop of a large cust om built system is equipped with a heat  meter (see 6.4.5.3 of DUS 857-1), 
this should be mentioned in  the system documentation. 
6.5    Installation 
Check the design plans and the system documentation to  see whether the leak tightness of the roof may be 
affected by the installation of the collector. 
6.5.1  Lightning 
For small custom built systems see 5.5 of DUS 855-2. 
For large custom built systems verify the compliance wi th the requirements given in 6.5.1 of DUS 855-1 by 
checking the documentation included in 6.7.3 of DUS 855-1. 
6.5.2  Wind loads 
See ISO 6612. Moreover, check the documents for the inst aller whether they comply with 6.5.2 of DUS 855-1. 
6.6    Initial operation, inspection and commissioning 
This clause applies to large systems only. 
Before initial operation: 
- Check whether the system layout and compon ents are as described in the documentation. 
- Check the record of the adjustments for the corresponding fittings. For each fitting a recorded 
adjustment shall exist. 
- If there is a supervisor of the system, ensure that he has been sufficiently instructed. 
The procedure for short-term system testing referred to  in 6.6 of DUS 857-1 (only if needed or required) is 
given in annex C. 
The procedure for long-term system monitoring referred to  in 6.6 of DUS 857-1 (only if needed or required) is 
given in annex D. 
6.7    Documentation 
Check all documents, as to whether they fulfil the re quirements given in 6.7 of DUS 857-1 and whether they 
are complete and understandable. 
6.8    System performance 
This clause applies to small systems only. FDUS 857-2: 2009 
10 © UNBS 2009 – All rights reserved
 The optional performance test methods for small custom  built systems are described in Clause 7. The test 
results shall be presented in a test report as described in clause 8. 
7    Optional performance test of sm all custom built solar heating systems 
The test method is based on component tests of the so lar collector, the store(s), the controller and other 
components as necessary. These component tests are de scribed in 7.1, 7.2 and 7. 3. The whole system is 
then simulated using a validated simulation program as described in 7.4. The long-term performance of the 
whole system is predicted for referenc e conditions as described in 7.5. 
If the carrying out of this performance test is required, the specification included in 7.4 and 7.5 shall be 
adhered to. 
In general, the system does not need to be installed as a whole for testing. 
For systems for hot water preparation only (class A) the full tests should be carried out including the long-term 
performance prediction for reference conditions. 
For systems for space heating only (class B) and syste ms for combined domestic hot water preparation and 
space heating (class C) the components should be te sted and the results be stated in the test report. The 
long-term performance prediction is a further option. If the performance prediction is carried out, the results 
should be stated in the test report stating also the chosen boundary conditions for the simulation. The 
following remark should be added to the results of pe rformance predictions for systems of class B and C: 
Intercomparison of the results of the long-term perfor mance prediction is only possible, if validated simulation 
models and the same boundary conditions are used. 
NOTE 1  The procedure for space heating systems as described above allows national solutions with respect to the 
definition of reference conditions. This is  a preliminary step for the standardization of this procedure within the CEN 
countries. After enough experience has been gained on national level, the reference conditions for all CEN countries can 
be elaborated . 
Before starting the performance testing all tests specifi ed in 6.1 to 6.7 shall be completed. In case a system 
fails one or more of these tests, the malfunction or defect shall be eliminated by the manufacturer prior to 
performance testing. If this is not possible 
- the malfunction shall be stated in the performance test report, 
- the performance of the system shall be determined with the method as described in this clause. 
However, the reduction of the system performance  induced by the malfunction or defect shall be 
estimated and the results of the perfo rmance test corrected accordingly. 
NOTE 2  If the system fails one of the following tests descr ibed in clause 6, a significant reduction of the system 
performance can be expected: 
- Collector array: balanced flow (see 6.3.1) 
- Temperature sensors: thermal contact of the sensors to the part of which the tem perature is measured           
(see  6.3.10.2) 
- Reverse flow prevention (see 6.1.5) 
- Thermal insulation (see 6.3.9) 
7.1    Separate test of the solar collector  
For the collector test according to DUS 854-2, all data for dynamic simulation of the thermal behaviour of the collector as listed below should be determined: FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  11
 - standard steady-state parameters 
  - collector heat capacity 
- incidence angle modifier for beam and diffuse irradiance 
- wind speed dependence of the collector heat loss c oefficients (for collectors with non-selective 
absorbers or unglazed collectors) 
- influence of flow rate if relevant 
- influence of collector tilt angle if relevant 
If a solar collector is offered in different dimensions, the performance parameters of the smallest unit may be 
used as representative for the whole series of collectors. 
7.2    Separate test of the hot water store 
The store should be tested in accordance with DUS 857-3. Thereby all data for dynamic simulation of the 
thermal behaviour of the store as described in DUS 857-3 should be determined. 
7.3    Separate test of the control system 
The control system should be tested according to the methods described in annex B. Thereby all data for 
dynamic simulation of the behaviour of the control sy stem as described in annex B should be determined. 
7.4    System simulation model 
The modelling of the system should be carried out using a detailed transient  simulation programme in which it 
is possible to model the different system and store configurations involved, and in which all parameters 
determined in the component tests can be adjusted. 
The component models for collector and store used in t he system simulation shall be respectively the same as 
for the characterization of the collector according to  DUS 854-2, and for the characterization of the store 
according to DUS 857-3. The store model shall be able to adequately simulate thermal stratification in the 
store. 
The control concept tested according to annex B shall be included in the simulation programme. 
For other components, e.g. pi pework or external heat ex changer, the level of detail in the simulation model 
shall correspond to the available technical data. 
The following features shall be implemented in the model: 
NOTE 1 The computation of the irradiance on the tilted plane should be as  detailed as possible. Up-to-date models and 
any simplified tools should be avoided. A radiation model is given in [2], [3,] [4 ], and [5]. (See Bibliography) 
- A thermostat mixer which reduces the store outlet  temperature i9s to the desired temperature $, 
during draw-offs. For solar preheat systems and sola r-only systems this thermostat mixer shall be 
located directly at the outlet of the solar part of the system. 
- The collector loop operation shall be stopped when the store temperature exceeds 100 °C if no other 
temperature is specifie d by the manufacturer. 
The system simulation model shall have been previously validated. FDUS 857-2: 2009 
12 © UNBS 2009 – All rights reserved
 7.5    Long-term performance prediction 
The recommended long-term system performance predicti on is described only for system class A (domestic 
hot water preparation only). However, for system classes B and C the same general principles apply . 
7.5.1  Calculation procedure 
Use the simulation model selected according to 7.4. T he component parameter values used for the simulation 
are those given by the separate component tests accordi ng to 7.1 to 7.3. Data on other components of the 
system, e.g. pipework or external heat exchanger , should be used as given by the manufacturer. 
The reference conditions as specified in annex A shall be used when calculating or reporting the performance 
of a system by computer simulation. 
7.5.2  Prediction of yearly system performance indicators 
NOTE  In the following paragraphs, performance indicators for solar heating systems for hot water preparation only are 
specified. The text of these paragraphs is identical for this Uganda Standard and for Factory Made Systems (DUS 855-2), 
except that the calculation of  the performance indicators is mandatory for Factory Made Systems, be ing, on the contrary, 
optional here. Performance indicators for space heating syst ems are presently excluded, since there is not yet enough 
experience available. This is a preliminary step for the stand ardization of this procedure. After enough experience has 
been gained, the performance indicators fo r space heating systems will be determined . 
Uniform reference conditions for the calculation of the performance are specified in the identical annexes, 
Annex A of this standard or Annex B of DUS 855-2. Fo r these conditions, the following performance indicators 
should be derived from the performance test results: 
For solar-plus-supplementary systems: 
- the net auxiliary energy demand Qaux, net
- the parasitic energy Qpar
For solar-only and preheat systems: 
- the heat delivered by the solar heating system QL
- the solar fraction fsol
- the parasitic energy Qpar if any 
7.5.3  Calculation of the net auxiliary energy demand for solar-plus-supplementary systems 
Calculate the yearly net  auxiliary energy demand Q aux,net  directly by computer simulation (long-term 
performance prediction) as specified in 7.5.1 of this Ug anda Standard (for Custom Built  Systems) or 5.9.3.2 of 
DUS 855-2 (for Factory Made Systems). Additional indica tion to the quantities entering the energy balance of 
one-store and two-stores solar- plus-supplementary heating syst ems is given in Figure 1. 
If a solar-plus-supplementary system cannot meet the heat demand to such a degree that the energy 
delivered to the user is less than 90 % of the yearly heat demand, this should be stated in the test report. 
NOTE  The energy delivered to the user can be less than the heat demand for example when the power of 
the auxiliary heater is not sufficient or when str ong mixing occurs in the store during draw-offs. 
 
 
 FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  13
 
 
Key 
1 Collector     4 Auxiliary heater 
2 Pimp      5 Control Unit 
3 Store       6 Cold Water 
a) Energy balance for one-store solar-plus-supplementary systems 
 
Key 
1 Collector     4 Auxiliary heater 
2 Pimp      5 Control Unit 
3 Solar store      6 Cold Water     7 Auxiliary store 
b) Energy balance for two-store-solar-plus-supplementary systems 
Figure 1 – Energy balance for one-store and two-stores-solar-plus-supplementary systems FDUS 857-2: 2009 
14 © UNBS 2009 – All rights reserved
 7.5.4  Calculation of the solar fraction for solar-only and preheat systems 
Compute the system energy balance on a yearly bas is. This includes the following energy quantities (see 
Figure 2 and Figure 3), calculated using the reference data and conditions given in annex A of this Uganda 
Standard or Annex B of DUS 855-2 
Qd   heat demand; 
QL   heat delivered by the solar heating system (load) 
Q  parasitic energy (electricity) for pump and controls; par
The parasitic energy Q shall be calculated according to 7.5.5 par
NOTE 1  The reference location for calculating the load Q L are the store ports or the load- side heat exchanger ports, if 
provided. The reference temperature for calc ulating the loads is the cold water temperature. Heat losses of the circulation 
line, if any, are not included in the loads, as the test is carried  out with this line kept closed. 
NOTE 2  According to ISO 9488, a solar preheat system is a solar system to preheat water or air prior to its entry into any 
other type of water or air heater. This water or air heater is not part of the solar preheat syst em itself. Hence, for this typ e 
of system the energy delivered by the solar heating system QL is calculated at the outlet of the solar heating system and 
the store heat loss QL is the heat loss of the sola r store itself (see Figure 3). 
NOTE 3  The yearly heat demand is calculated using the load volume, cold water temperature and the desired 
temperature for hot water as  specified in annex A. 
 
 
 
 
Key 
1 Collector     4 Cold water 
2 Pump      5 Control unit 
3 Store 
Figure 2 – Energy balance for solar-only systems 
 
 FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  15
 
 
 
 
 
 
Key 
1 Collector     5 Cold water 
2 Pump      6 Control unit 
3 Store      7 Solar preheated system 
4 Auxiliary heater    8 Series -connected auxiliary heating system 
Figure 3 – Energy balance for solar preheat systems 
Calculate the solar fraction, f sol by using the definition of ISO 9488: 
Solar fraction, f: The energy supplied by the solar part of a system divided by the total system load ( Q sol d = 
heat demand). 
 = Qfsol L/Qd
7.5.5  Calculation of the parasitic energy 
Calculate the yearly parasitic energy Qpar needed by pumps, controllers etc, in conformity with 4.6.3 h) 3) of 
DUS 855-1. 
7.6   Presentation of performance indicators 
The results from 7.5.1 to 7.5.5 shou ld be presented for the load volume(s) as specified in Annex A in the way 
shown in Table 2 and Table 3. 
 
 
 
 
 
 FDUS 857-2: 2009 
16 © UNBS 2009 – All rights reserved
 Table 2 – Presentation of system performance indicators for solar-plus-supplementary systems 
Performance indicators for solar-plus-supplementary  systems on annual base for a volume demand of 
…..l/d 
location (latitude) Qd  
MJ Qaux,net   
MJ Qpar 
MJ 
Stockholm (69.6o N) ……   
Würzburg (49.5oN) ……   
Davos (46.8oN)    
Athens (38.0oN) ……   
……….1)   
1) For a location free to choose 
 
Table 3 – Presentation of system performance indicators for solar-only and solar preheat systems 
Performance indicators for solar-only and solar preheat systems on annual base for a volume demand 
of …..l/d 
location (latitude) Qd  
MJ QI  
MJ fsol 
% Qpar
MJ 
Stockholm (69.6o N)     
Würzburg (49.5oN) …..    
Davos (46.8oN) ……    
Athens (38.0oN)     
……….1)    
1) For a location free to choose  
8     Performance test report 
This clause describes the report of results from the op tional tests performed according to Clause 7. This test 
report applies to small custom built systems only as also the system performance test methods given in 
Clause 7 are applicable to small custom built systems only (see 6.8). 
The test report shall include: 
- a detailed description of components and system configuration 
- the prediction method used. The simulation programme  shall be specified and an input file shall be 
enclosed. 
- the complete reference conditions used as specified in Annex A including information about the  
location for which the performance prediction is made and the reference weather data used. FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  17
 - for the reference conditions as specified in Annex A, the performance indicators on a yearly base as 
specified in 7.5.2. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FDUS 857-2: 2009 
18 © UNBS 2009 – All rights reserved
 Annex A 
(normative)  
 
Reference conditions for performance prediction  
A.1   General 
The conditions given in Table A.1 shall be used when calc ulating, reporting or comparing the performance of a 
system, either from a test or from a computer simu lation. These conditions should also be applied to the 
system during any system performance  test, if not specified otherwise. 
NOTE  The following reference conditions are identic al for testing and simulating of Factory Made Systems 
in US 855-2 and Custom Built Systems in this Uganda Standard. However, some aspects related to systems 
considered in only one of the two standards,  have been deleted from the other standard. 
Table A.1 – Reference conditions for performance presentation 
Reference Condition value Remarks 
SYSTEM  
Collector orientation South  
Collector tilt angle 45oFor testing. (45 5)o if not fixed for the system 
or specified by the manufacturer. 
Total length of collector circuit 20m = 10m + 10m If piping is not delivered with the system or 
specified by the manufacturer 
Pipe diameter and insulation 
thickness of collector circuit See A.2 If piping is not delivered with the system or 
specified by the manufacturer. 
Location of the collector circuit pipes Indoors, for systems with the store located indoors: for 
systems with the store 
located outdoors As far as possible at the test rig 
Store ambient temperature 15oC For systems where the store is located 
outside, the ambient temperature from the 
climate shall be used. 
For systems with indirect 
(hydraulic) auxiliary heating: Power to be applied on 
auxiliary heat exchanger (100 ± 30)W per liter of store 
volume above the lowest end of heat exchanger If the auxiliary heater is not delivered with the system and no restrictions have been given in the documentation. The auxiliary 
heater shall be modelled as an ideal heat 
source with no heat capacity and constant heating power. 
Flow rate through auxiliary 
heat exchanger  The flow rate through the heat exchanger 
shall be chosen such that the temperature 
difference between the inlet and outlet of the auxiliary heat exchanger is (10 ± 2)K under 
steady state conditions, unless specified 
otherwise by the manufacturer. FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  19
 For systems with electrical 
auxiliary heating: Power of 
electrical element If an electrical element is normally deliv ered with the system or specified by 
the manufacturer, this element shall be us ed. Otherwise, (25 ±  8) W per liter 
of store volume above the electrical element apply. 
For solar-plus-supplementary 
systems: Status of the auxiliary heater Permanently activated This is for performance prediction 
Temperature of integrated 
auxiliary heating 52.5 oC (minimum 
temperature of hysteresis) Or a higher temperature, if recommended by the manufacturer 
CLIMATE 
Reference locations Stockholm, Wurzburg, Davos. 
Anthens In the reporting form, the performance of a 
different location of choice may also be given. 
Climate Data For Stockholm: CEC Test Re ference Year; for Davos, Wurzburg and 
Anthens: Test Reference Year. 
HEAT LOAD 
Daily load pattern   
Cold water supply temperature   
Desired (mixing valve) temperature   
Daily load volume   
   
   
 
 
 
 
 
 
 
 
 FDUS 857-2: 2009 
20 © UNBS 2009 – All rights reserved
 Annex A 
(normative)  
 
Schematics for durabilit y and reliability tests 
 
 
 
 
 
 
 
 
 
 
 FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  21
 Annex A 
(normative)  
 
Schematics for durabilit y and reliability tests 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FDUS 857-2: 2009 
22 © UNBS 2009 – All rights reserved
 Annex A 
(normative)  
 
Schematics for durabilit y and reliability tests 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FDUS 857-2: 2009 
© UNBS 2009 – All rights reserved  23
  
  
© 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.  
 
 FDUS 885: 2009 
 
ICS 27.160 
Price based on nn pages 
© UNBS 2009 – All rights reserved