FINAL DRAFT UGANDA 
STANDARD  FDUS 855-2
First Edition
2009-mm-dd
 
Reference numbe 
r
FDUS 855-2: 2009
    
  © UNBS 2009 
  
Thermal solar systems and components – Factory made 
systems – Part 2: Test methods 
 FDUS 855-2: 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: 256 414 505995 
Fax: 256 414 286 123 
E-mail: unbs@infocom.co.ug
Web: www.unbs.go.ug FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  iii
 Contents Page 
1 Scope ......................................................................................................................................................1  
2 Normative references ..............................................................................................................................1  
3 Terms and definitions ..............................................................................................................................1  
4 Symbols and abbreviations .....................................................................................................................1  
5  Testing ....................................................................................................................................................2  
5.1  Freeze resistance ...................................................................................................................................2  
5.2  Over temperature protection ..................................................................................................................3  
5.3   Pressure resistance ............................................................................................................................... 5 
5.4  Water contamination ............................................................................................................................... 6 
5.5  Lightning protection ............................................................................................................................... .6 
5.6  Safety equipment ....................................................................................................................................6  
5.7  Labelling .................................................................................................................................................7  
5.8  Thermal performance characterization ...................................................................................................7  
5.9  Ability of solar-plus-supplement ary systems to cover the load ............................................................11  
5.10  Reverse flow protection ........................................................................................................................13  
5.11  Electrical safety ............................................................................................................................... .....13  
Annex A  (normative)   Thermal performance presentation sheet .....................................................................1 4 
Annex B (normative)  Reference conditions for performance prediction ...........................................................1 6
Annex C (informative) Extreme climate test procedure fo r the assessment of the frost resistance of solar  
DHW systems with  outdoor tank .................................................................................................. .........20         
Annex D (informative) Ageing test for thermost atic valves ...................................................................... ..........35         
Annex E (informative) Lightning protection test for sola r heating sy stems ...................................................... ..37        
Annex F (informative)  Lightn ing protection te sting sh eet ..................................................................... .....40        1 
Bibliogr aphy .................................................................................................................. .....................................44         2
 
 FDUS 855-2: 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 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 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 855-2: 2009 
© UNBS 2009 – All rights reserved  v
  
 FINAL DRAFT UGANDA STANDARD FDUS 855-2: 2009
 
© UNBS 2009– All rights reserved 1
 Thermal solar systems and components – Factory made 
systems – Part 2: Test methods 
1 Scope 
This Uganda Standard specifies test methods for validat ing the requirements for Factory Made Thermal Solar 
Heating systems as specified in DUS 855-1. The standard also includes two test methods for thermal 
performance characterization by means of whole system testing. 
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. 
DUS 854-2, Thermal solar syst ems and components – Solar collectors – Part 2: Test methods 
IEC 60335-1, Household and similar electrical applia nces – Safety – Part 1: General requirements 
IEC 60335-2-21, Household and similar electrical appliances – Safety – Part 2-21: Particular requirements for 
storage water heaters 
ISO 9488, Solar energy – Vocabulary 
ISO 9459-1, Solar heating – Domestic water heating syst ems – Part 1: Performance rating procedure using 
indoor test methods 
ISO 9459 -2, Solar heating - Domestic water heating sy stems – Part 2: Outdoor test methods for system 
performance characterization and yearly performance prediction of solar-only systems 
ISO 9459-5, Solar heating – Domestic water heating syst ems – Part 5: System performance characterization 
by means of whole-system tests and computer simulation 
EN 1717, Protection against pollution of potable wate r in water installations and general requirements of 
devices to prevent pollution by backflow 
3 Terms and definitions 
For the purposes of this Uganda standard, the terms and definitions given in ISO 9488 and DUS 855-1 apply. 
4 Symbols and abbreviations 
Qaux,net  net auxiliary energy demand of a solar heating syst em delivered by the auxiliary heater to the 
store or directly to the dist ribution system (see 5.8.3.2) 
Qd   heat demand FDUS 855-2: 2009 
2 © UNBS 2009 – All rights reserved
 QL   energy delivered at the outle t of the solar heating system 
Qpar   parasitic energy (electricity) for the collector loop pump(s) and control unit 
Hc  hemispherical solar irradiation in the collector plane 
Ql  Store heat loss 
Qohp  heat diverted from the store as ac tive overheating protection, if any 
Qsol  heat delivered by the collector loop to the store 
5  Testing  
5.1  Freeze resistance 
5.1.1 General  
The following checks are given to ensure that the prot ective antifreezing provisions are operating properly. 
There are many possible forms of protective provisions, and testing authority shall first identify which method 
has been employed. 
The provision shall then be checked in accordance with appropriate section of the following list (see 5.1.2 to 
5.1.6) in accordance with the manufacturer’s recommendations.  
5.1.2 Systems using antifreeze fluid 
The system components which are exposed to low ambien t temperature are filled with an antifreeze fluid, 
usually a glycol/water mixture, having a low enough freezing point. 
For these systems, no freezing test is performed. Howe ver, if no sufficient data is available on the freezing 
point of the antifreeze fluid, the freezing point shall be measured and checked against the minimum system 
temperature as given by the manufacturer. 
NOTE In general, the minimum allowed temperature of the system is equal to the freezing point of the antifreeze fluid. 
If the concentration of some antifreeze fl uids – like glycols – exceeds a certain limit, they can freeze without damaging the 
system. In this case the minimum allowed temperature c an be lower than the freezing po int of the antifreeze fluid.  
Check the freezing point by measuring the glycol conc entration (e.g. using a portable refractometer). The 
freezing point should be as recommended by the manufac turer in agreement with local climate (minimum 
expected air temperature, radiativ e cooling of the collectors). 
The composition of the fluid shall be checked to see whether it is accordance with the manufacturer’s 
specifications. 
5.1.3 Drain-back systems 
The fluid in the system components, which are exposed to low ambient temperature, is drained into a storage vessel for subsequent reuse when freezing danger occurs. 
The collector loop piping should be in accordance with  the manufacturer’s recommendation in the installer 
manual and if there is no instruction, accordin g to reference conditions given in Annex B. 
Filing may be observed gauge or from water level indicator. Switch the pump on, and observe the pressure gauge or water level indicator. If the system does not in clude a pressure gauge or level indicator, other means 
for checking filing provided by the manufacturer shall be used in accordance with the instruction manual. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  3
 Drain-back may be observed from the decreasing reading of the pressure gauge or water level indicator. 
Switch the pump OFF, and observe the pressure gauge or water level indicator. If the system does not include 
a pressure gauge or level indicator, other means for ch ecking drain-back provided by the manufacturer shall 
be used in accordance with the instruction manual. It might be necessary to repeat the check at high storage temperature (90 
oC) in order to insure drain-back in all situations (see 5.2). 
5.1.4 Drain-down systems 
The fluid in the system components, which are exposed to low ambient temperature, is drained and run to 
waste when freezing danger occurs. 
Check the proper opening and closing of the vacuum relief valve. 
If there is a solenoid drain valve independent of the control unit, simulate the opening temperature. 
If there is a non-electrically operated freeze-protection valve, a check can be made using a freezing spray. 
The temperature-sensing element shall be sprayed. T he measured temperature of the valve opening is to be 
compared with the nominal value given by the manufacture r. It is important that the sensing part of the freeze-
protection valve be properly placed. 
The collector loop piping should be in accordance with  the manufacturer’s recommendations in the installer 
manual and if there is no instruction, accordin g to reference conditions given in Annex B. 
Open drain-down valve manually and measure the drain rate with vessel and a stop-watch. 
If the system uses an electrically operated freez e-protection valve, drain down shall be checked while 
interrupting the power.  
5.1.5 Freeze protection and control functions combined 
For systems where the freeze-protection and control func tions are combined, the control unit shall be checked 
as follows: 
Set the simulated temperature of the freeze-protection sensor to a value deactivating the freeze protection. 
Decrease the simulated temperatur e slowly. Measure the temperature TFP (freeze-protection)  of the related actuator. 
Compare it with the nominal va lue given by the manufacturer. 
5.1.6 Other systems 
For all other systems, the pump control system, drain-down valve or any other freeze protection device or system shall be checked to the manufacturer’s specific ation and the minimum allowed temperature specified 
by the manufacturer. For ICS system s, or other SDHW systems with the tank placed outside, special frost 
resistance test should be carried out, as described in C.1. 
5.2  Over temperature protection 
5.2.1  Purpose 
The purpose of this test is to determine whether the solar water heating system is protected against damage 
and the user is protected from scalding hot water delivery after a period of no hot water draw and failure of 
electrical power. 
5.2.2  Apparatus  
The following apparatus is required: 
a) A pyranometer having the minimum characterist ics specified in DUS 854-2, to measure the 
hemispherical solar irradiance, or the short wave irradi ance form a solar simulator lamp if the test is 
to be conducted inside a solar simulator chamber. FDUS 855-2: 2009 
4 © UNBS 2009 – All rights reserved
 b) Equipment to measure the temperature, flow rate  and volume of hot water drawn from the system. 
c) An outdoor or an indoor test stand for installing the solar hot water system with the collector array at 
the manufacturer’s specified angle of inclination. 
d) A temperature and pressure controlled water supply within the range of 5 oC to 25 oC and 200 kPa to 
600 kPa or the manufacturer’s maximum working pressure whichever is less. 
This test may be conducted using a solar simulator or outdoors. 
5.2.3 Procedure 
The system, both as described in the installation manual  and as installed on the test facility, shall be first 
checked on overheating safety, e.g. if safety valves and other overheating protection devices are present and 
installed at the right place, if there are no valves between components and relief valves etc. For systems 
containing antifreeze fluids, it shall be checked whether  sufficient precautions have been taken to prevent the 
antifreeze fluid from deterioration as a result of high temperature conditions (see also 5.6) 
Furthermore, if non-metallic materials are used in any circuit, the highest temperature in the circuit shall be 
measured during the overheating temp erature protection test, for use in the pressure resistance test. 
The procedure of testing shall be as follows: 
a) Assemble the solar water heating system according to the installation instruct ions with the collector 
array oriented towards solar noon for the outdoor test, or the simulator lamp may be adjusted to 
normal incidence for the indoor test. 
b) Charge the system from the water supply and, for pressurized storage tanks, maintain the water 
supply pressure. 
c) Energize the system as per installation instructions. 
d) (i) For the outdoor test, operate the system fo r a minimum of 4 consecut ive days without any hot 
water withdrawal and until the collector array has been subjected to 2 consecutive days in which the 
solar, temperature on the plane of the collector array has exceeded 20MJ/m2 per day and the 
ambient temperature has exceeded 20 oC during solar noon. 
(ii) For the indoor test, operate the system without any hit water withdrawal at an ambient temperature of (25 ± 2) 
oC and a minimum solar lamp irradiance of 1000 W/m2 at the plane of the 
collector array, measured and with uniformity as specified in ISO 9459-1, 6.3.1.2  for a 5 h period or 
until the collector array drains. 
e) (i) For the outdoor test, disconnect all electrical  power to the system and continue to operate the 
system until the solar irradiation on the plane  of the collector array has exceeded 20 MJ/m2 per day 
or until the collector array drains. 
 (ii) For the indoor test, disconnect all electric al power to the system and subject the system to a 
solar lamp irradiance of 1000 W/m2 at the plane of  the collector array for an addition 4 h or until the 
collector array drains. 
f) Immediately begin to withdraw a volume of water gr eater than the total volume of water in the system 
at a rate of 2 x 10-4 ± 3 x 10-5 m3/s (10 ± 1 L/min) 
5.2.4 Reporting requirements 
The following results shall be reported: 
a) The make and model id entification of the system including ancillary scald and over temperature 
protection devices fitted. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  5
 b) The inclination of the collector array. 
c) A record of temperature of the hot water withdrawn from the system versus time and the total volume 
of water withdrawn. Note the pr esence of stem if observed. 
d) Details of the condition of the system and indi vidual components following the test or any failure 
modes during the test with  particular regard to any defects which may affect the serviceability of the 
system such as the swelling of pipes and components or fluid leakages. 
5.3   Pressure resistance 
5.3.1 Purpose 
The purpose of this test is to evaluate hydraulic pres sure rating of all components and interconnections of a 
solar water heating system when installed ac cording to the manufacturer’s instructions. 
5.3.2 Apparatus 
The apparatus shall consist of the following: 
a) suitable platform and support struct ure for installation of the system 
b) pressure regulated hydraulic pressure source 
c) pressure gauge suitable to determine the test pressure to within 5 % 
d) bleed valve 
e) isolation valve 
5.3.3 Safety precaution 
An explosion safe enclosure is recommended when test ing systems that have an int egral expansion space or 
tank that contains entrapped air. 
5.3.4 Procedure 
The system, both as described in the installation manual  and as installed on the test facility, shall be first 
checked on pressure safety, e.g. if safety valves and other overheating protec tion devices are present and 
installed at the right place, if there are no valves between components and relief valves etc. 
The duration of the test is 15 min for metallic material. If a non-metallic material is used in any circuit, this 
circuit shall be pressure tested for 1 h at the high est temperature measured during the over temperature 
protection test +10 oC. 
a) Install the solar water heating system on the test  platform in accordance with the manufacturer’s 
instructions. 
b) Disable the pressure relief valves, if applic able, to prevent their opening during testing. 
c) Connect the pressure gauge and bleed valve at the hot water outlet of the system. 
d) Connect the isolation valve and hydraulic pressure source, using water as the test fluid, to the cold 
water inlet of the system. 
e) Fill the potable water side of the system using t he hydraulic pressure source  and bleed all air, as 
possible, out of the system through the bleed va lve at the hot water outlet of the system. 
f) Apply a hydraulic pressure equal to 1.5 times t he manufacturer’s stated maximum working pressure. FDUS 855-2: 2009 
6 © UNBS 2009 – All rights reserved
 g) Isolate the pressure source by  closing the isolation valve and record the readings of the pressure 
gauge at the beginning and end of the next 15 min interval. 
h) Release the system pressure through the bleed valve and record any visible permanent deformation 
and water leakage from system components and inter connections. 
i) Disconnect the bleed valve, pressure gauge, isol ation valve and hydraulic pressure source from the 
system. 
For those systems not constructed with a heat excha nger and a separate pressurized heat transfer loop, 
the following procedural steps are to be omitted. 
j) Connect the bleed valve and pressure gauge to the drain port of the system ’s heat transfer loop and 
connect the isolation valve and hydraulic pressu re source, using the manufacturer’s stated heat 
transfer fluid, to the fill port of the heat transfer loop. 
k) Fill the heat transfer loop of the system using the hydraulic pressure source and bleed all air, as 
possible, out of the loop through the bleed valve at the drain part of the top of the collector array. 
l) Apply a hydraulic pressure equal to 1.5 times t he manufacturer’s stated maximum individual working 
pressures. 
m) Isolate the pressure source by  closing the isolation valve and record the readings of the pressure 
gauge at the beginning and end of the next 15 min interval. 
n) Release the system pressure through the bleed valve and record any visible permanent deformation 
and heat transferor fluid leakage from system components and interconnections. 
5.3.5 Reporting requirements 
Report the maximum test pressures applied, the pres sure readings at the beginning and end of the 15 min 
Test intervals and any visible permanent defor mation or leakage from system components and 
interconnections. Note if the applied test pressures are lower than 1.5 times the manufacturer’s stated 
maximum working pressure. 
5.4  Water contamination 
See EN 1717. 
5.5  Lightning protection 
Annexes E and F give information to assist manufactu rers in meeting the requirements given in IEC 61024-1. 
5.6  Safety equipment 
5.6.1 Safety valves  
Check the system documentation to verify that each collector circuit or group of collector circuits is fitted with 
at least one safety valve. 
Check the specification of the safety  valves, whether the materials conform to requirements given in 4.4.1 of 
DUS 855-1. 
Check whether the size of the safety valve is correct in conformity with requirem ents given in 4.4.1 of DUS 
855-1. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  7
 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. 
To check the applicability of the specified maintenance fr equency of a thermostatic valve, the ageing test for 
thermostatic valves should be carrie d out, as described in Annex D. 
5.6.2 Safety lines and expansion lines 
Check the hydraulic scheme and system documentation to verify that safety and expansion lines, if any, 
cannot be shut-off. 
Check the internal diameter of the ex pansion line, if any, with respect to  the requirements given in 4.4.2 of 
DUS 855-1 
Check the system documentation to verify that the ex pansion line and the safety line, if any, are connected 
and laid in such a way that any accumulation of  dirt, scale or similar impurities are avoided. 
5.6.3 Blow-off lines 
Check the hydraulic scheme and system documentation to  verify that the blow-off lines, if any, conform to 
requirements given in 4.4.3 of DUS 855-1 
5.7  Labelling 
Check the marking plate or Label of the solar heating sy stem and examine if all item s of the labelling list are 
completed (as specified in 4.7 of DUS 855-1) 
5.8  Thermal performance characterization  
5.8.1 Introduction 
In this clause the methods for performance testing ar e described. The thermal performance of the system 
shall be characterized as described in 5. 8.2 and presented as specified in 5.8.3. 
NOTE The performance of a solar heatin g system depends on the individual installation and actual boundary 
conditions. With regard to the heat losses of the store besides  deficits in the thermal insulation, badly designed 
connections can increase the heat loss capacity rate of the stor e due to natural convection that occurs internally in the 
pipe. In order to avoid this effect t he connections of the pipes should be designed in such a way that no natural convention 
inside the pipe occurs. This can e.g. be achieved if the pipe is directly going downwards after leaving the store or by using 
a siphon. 
5.8.2 Test procedure 
One of the following test methods shall be used, as described in Table 2. 
a) Test method in accordance with ISO 9459-2. Th is test method maybe applied on “solar only” or 
“preheat systems”. 
b) Test method in accordance with ISO 9459-5. th is test method may be applied on all types of systems 
Table 2 – Selection of the performance test method 
Test method Solar-plus-supplementary sy stems *) Solar-only and preheat systems 
ISO 9459-2 (CSTG) No Yes 
ISO 9459-5 (DST) Yes Yes FDUS 855-2: 2009 
8 © UNBS 2009 – All rights reserved
 NOTE1.  Some systems have allowances for variations in t he installation instructions that  may affect the performance of 
the systems. In cases where the circum stances are not uniquely defined by the Reference Conditions given in Annex B, 
the most unfavourable conditions should be chosen for test ing and reporting of the system  performance. For example, 
systems without forced circulation should be tested with t he lowest position of the storage above the collector and the 
longest pipe length between collector and storage specified by the manufacturer. 
NOTE2.  In October 1999, the EU-SMT project team “Bri dging the Gap” reported on the comparability between CSTG 
(ISO 9459-2) and DST (ISO 9459-5) and conversion factors were successfully established. The relation between the 
performance predictions of both test methods is given by: 
 QDST   = (α ±    a) Q CSTG
The ‘a-values’ are represented in Table 3: 
Table 3 – Parameter a values for different load volumes 
Type of system Condition α a
Forced circulation 
Thermosyphon system 
ICS system Vload  ≥ Vstore a
All V load
All V load1.004 
1.056 
1.037 0.004 
0.004 
0.003 
a In case V load < V store    (forced circulation systems), the determined ‘a-values’  are higher. This indicates 
a stronger tendency for overesti mation of the DST test method. 
 
5.8.3 Prediction of yearly performance indicators 
5.8.3.1 General     
NOTE  In the following, performance indicators for solar heating systems for hot water preparation only are 
specified. The text of these paragraphs is identical for this standard and for Cust om Built Systems (DUS…-2). 
Performance Indicators for space heating systems are presently excluded, since there is not yet enough 
experience available. This is a preliminary step for the standardisation of this  procedure. After enough 
experience has been gained, also the performance indi cators for space heating systems will be elaborated. 
Uniform reference conditions for the calculation of the performance are specified in the identical Annex B of this standard derived from the performance test results: 
For “solar-plus-supplementary systems” 
a) the net auxiliary energy demand Q aux,net 
b) parasitic energy Q par 
For “solar-only” and “preheat systems” 
c) the heat delivered by the solar heating system Q L 
d) the solar fraction f sol 
e) the parasitic energy, Q par if any 
 
 5.8.3.2 Calculation of the net auxiliary energy demand for solar-plus-supplementary systems FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  9
 Calculate the yearly net auxiliary energy demand Q aux,net  directly by computer simulation (long term 
performance prediction) as specified in 5.8.2 of this standard (for Factory Made syst ems) or 7.5.1 of DUS 857-
2 (for Custom Built Systems). Additional indication  on the quantities entering the energy balance of a one-
store solar-plus-supplementary heati ng system may be found 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 y early heat demand, this shall be in the test report. 
NOTE The energy delivered to the user can be le ss 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. 
 
Key 
1 Collector 
2 Pump 
3 Store 
4 Auxiliary heater 
5 Control unit 
6 Cold water 
Figure 1 – Energy balance for one-store solar-plus-supplementary systems (example) 
5.8.3.3 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 B of this standard 
or Annex A of DUS 857-2.  
Qd  heat demand; 
QL  heat delivered by the solar heating system (load) 
Q  parasitic energy (electricity) for pump and controls parFDUS 855-2: 2009 
10 © UNBS 2009 – All rights reserved
  shall be calculated according to 5.8.3.4. The parasitic energy Q par
NOTE 1 The reference locations for calculating the load Q L are the store ports or the load-side heat 
exchanger ports, if provided. The reference temper ature for calculating the loads is the cold water 
temperature. Heat losses of the circul ation line are not included in the loads. 
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 system 
itself. Hence, for this type of the system the energy delivered by the solar heating system Q L is calculated at 
the outlet of the solar heating sy stem and the store heat loss Q l is the heat loss of the solar store itself (see 
Figure 3)  
NOTE 3  The yearly heat demand is calculated using the load volume, cold water temperature and the desired 
temperature as specified in Annex B. 
 
Key 
1 Collector 
2 Pump 
3 Solar store 
4 Auxiliary heater 
5 Control unit 
6 Cold water 
7 Solar preheat system 
8 Series connected auxiliary heating system 
Figure 3  - Energy balance for solar preheat systems 
Calculate the solar fraction, f  by using the definition of ISO 9488. sol
Solar fraction f: The energy supplied by the solar part of a system divided by the total system load (Q sol d = 
heat demand). 
   f = Qsol L / Q dFDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  11
  
5.8.3.4 Calculation of the parasitic energy 
Calculate the yearly parasitic energy needed by pumps, cont rollers etc, in conformity with 4.6.3 h) 3) of DUS 
855-1-general 
5.8.3.5 Presentation of performance indicators 
The results from 5.8.3.2 to 5.8.3.4 shall be presented for the load volume(s) as specified in Annex B or Annex 
A of DUS 857-2.  For Factory Made Systems, the reporting form given in Annex A shall be used, for Custom 
Built systems the table given in 7.6 of DUS 857-2 shall be used. 
5.9  Ability of solar-plus-supplementary systems to cover the load 
5.9.1 General 
The test described in this clause shall be carried out in order to ensure that the solar-plus-supplementary system is able to cover the maximum daily load without solar contribution. If recommended by the 
manufacturer, this test can be performed for a daily load higher than the maximum daily load related to the 
reported performance prediction (5.9.3).  if the system fails to cover the maximum daily load, this shall be 
stated in the test report together with the results of the performance prediction related to this maximum daily 
load. The test shall be repeated for a lower maximum daily load. 
The ability of the system to cover the maximum daily  load shall be determined for the boundary conditions 
given in 5.9.2 and 5.9.3. 
For systems with auxiliary heater, which are tested in ac cordance with the test method given in ISO 9459-5 
(see 5.9.2), the ability of the system to cover the maximum daily load without solar contribution shall be 
determined either by the test described in 5.9.4 or by m eans of numerical simulations as described in 5.9.5. 
5.9.2 Boundary conditions for auxiliary heating 
The auxiliary heater shall be mounted and  operated during the test in accordan ce with the settings in Annex B 
for the yearly performance prediction. 
In the case of an emergency heater  the apparatus shall be made fully ope rational in accordance with the 
manufacturers specifications. 
When several types of heating devices can be installed,  the heating device with a heating power fitted for the 
maximum “daily load volume” shall be used. The manufacturer  shall in this case select the appropriate type of 
heating device. 
For systems with auxiliary heating by means of heated water (e.g. directly or with an immersed heat 
exchanger inside the store) the “flowrate through aux iliary heat exchanger’ shall be stated in Table B.1. 
The following specifications shall be reported: 
- the control setting for the temperatur e of the integrated auxiliary heater; 
- the type of control, if availabl e the serial number of the device and if applicable the setting of the 
hysteresis; 
- the power of the electrical aux iliary heating element or thermal power delivered to the store as 
applicable; 
- if applicable the flowrate through the heating device. FDUS 855-2: 2009 
12 © UNBS 2009 – All rights reserved
  
5.9.3 Boundary conditions for daily load 
The “maximum daily load conditions” are characterized by: 
- volume, as being the highest daily load volume for which the yearly performance is reported (Table 
B.1); 
- flowrate, in accordance with Table B.1; 
- cold water temperature, in accordance  with the lowest value in table B.4. 
if the cold water inlet temperature during the test in accordance with 5.9.4 differs from the minimum cold water 
inlet temperature in accordance with Table B.4, the draw -off flow rate shall be adjusted in order to perform a 
discharge with the same power as calculated with the defined settings. 
One “daily load cycle” consists of t he following draw-offs based on the cold  water temperature (the cycle starts 
at t o): 
- at t = (to + 12)h withdraw of 40% of the daily load volume; 
- at t = (to + 17)h withdraw of 40% of the daily load volume; 
- at t = (to + 22)h withdraw of 40% of the daily load volume; 
If repeated tests are necessary the cycle starts again at 24 h after the last to
NOTE Some kinds of stores with an integrated domesti c hot water heat exchanger where the flow inside the 
store depends on certain thermosiphonic effects sometimes require a certain temperature in the lower part of 
the store in order to reach their full performance with re spect to hot water preparation. In this case it is 
recommended to repeat the daily load several times. 
5.9.4 Determination of the ability to cover the maximum daily load by means of testing the 
system 
The system shall be mounted, fully operational, but with: 
- the collector circuit disabled or the collector covere d in such a way that there is no contribution from 
the solar collector to the store; 
- the mixing valve installed, and set as described in the product specifications, only if it is an integral 
part of the system. At the beginning of the test at  least three store volumes shall be withdrawn while 
the auxiliary is disabled. 
After this initial conditioning ( t = t0) the auxiliary heating is set into operat ion. Discharges in accordance with 
the daily load cycle as described in 5.9.3 shall be performed. 
During each draw off the temperature of the hot water drawn from the store and t he thermal power discharged 
form the store shall be measured and recorded. 
The test with duration of one daily load cycle is consider ed as valid, if during 95% of the draw-off time the hot 
water temperature does not drop below 45 oC. 
5.9.5 Determination of the ability to cover the maximum daily load by means of numerical 
simulations 
For the determination of the ability to cover the maximu m daily load by means of numerical simulations the 
model given in ISO 9495-5, with the boundary conditions  described in 5.9.2 and 5.9.3 shall be used. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  13
 The calculation procedure for the determination of the ability to cover the maximum daily load (without solar 
contribution) by means of numerical simulations is in pr inciple similar to the test procedure described in 5.9.4. 
During the calculation process the solar irradiation shall be set to zero. 
The power for the heating element used in the DST- model shall be determined as the mean value of the 
measured power delivered to the store during the first heating up of the auxiliary part within the test sequence 
Saux. The test with duration of one daily load cycle is cons idered as valid, if during 95 % of the draw-off time 
the hot water temperature does not drop below 45 oC. 
5.10  Reverse flow protection 
Visual inspection shall be performed on the existence of a check valve or other provisions. 
5.11  Electrical safety 
If the system contains any electrical device, these s hall be tested in accordance with IEC 60335-1 and IEC 
60335-2-21. FDUS 855-2: 2009 
14 © UNBS 2009 – All rights reserved
 Annex A 
(normative) 
 
Thermal performance presentation sheet 
Name and type                                                :…………………….Factory Made/Custom Built Systema
Derived from test report                                  : 
By test institute                                               : 
This table filled in by                                       : 
Date                                                                : 
Test method used                                           : Factory made systems ISO 9449–5a
                                                                       : Custom Built System: DUS …..-2a
Integrated auxiliary heater                             : Electric / Indirect /Direct Gas / None / Other. 
NOTE. In case of solar heating systems with emergency heaters, instructions should be issued that this 
emergency heater shall only be us ed for emergency heater purposes. 
a Select appropriate option 
Figure A.1 – Thermal performance presentation sheet 
 
Table A.1 – Presentation of the system performance indicators for solar-plus-supplementary 
systems 
Performance indicators for solar-plus-supplementary systems on annual base for a demand 
volume of …..Ld-1
Location  
(latitude) Qd  
MJ Qaux,net   
MJ Qpar  
MJ 
Stockholm 
 (59.6 oN) -   
Wurzburg 
 (49.5 oN) -   
Davos  
(46.8 oN) -   
Athens  
(38.0 oN) -   
a 
-    
a For a location free to choose 
 
 
 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  15
  
 
 
Table A.1 – Presentation of the system performance indicators for solar-only and solar 
preheat systems 
Performance indicators for solar-only and solar preheat systems on annual base for a demand 
volume of …..Ld-1
Location 
(latitude) Qd  
MJ QL  
MJ fsol  
% Qpar  
MJ 
Stockholm 
 (59.6 oN) -    
Wurzburg  
(49.5 oN) -    
Davos 
 (46.8 oN) -    
Athens  
(38.0 oN)  -    
a 
-     
a For a location free to choose 
 
 FDUS 855-2: 2009 
16 © UNBS 2009 – All rights reserved
 Annex B  
(normative) 
 
Reference conditions for performance prediction 
B.1  General 
The conditions given in Table B.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 Except the specification in respect of the status of the auxiliary heat er for solar-plus-supplementary systems 
(see Table A.1 in DUS 857-2), the following reference conditions  are identical for testing and simulating of Factory Made 
Systems in this standard and Cust om Built Systems in DUS 857-2. 
For systems tested according to ISO 9459-2, the Long Term Performance Prediction, will be in agreement 
with the reference conditions of this annex provided t hat the following changes in the calculation procedure 
are implemented: 
Changes in Clause 9 of ISO 9459-2:1995 (pages 21, 22, 23 and 24), step 3 (Energy drawn off): 
Calculations for Day 1: 
  Q  (1) is calculated according to: c
   ∫='
0) ( ) 1 ( ) 1 (v
c dV V f Q Q
where V’ is determined by two conditions: 
Q(1) ≤ Vρ c load wCpw(t - t load main) and V’ ≥  Vload
Calculations for Day 2 and subsequent days : 
  Q  (2:part 1) is calculated according to: c
   ∫=v
dV V f part Q part Qc
0) ( ) 1 : 2 ( ) 1 : 2 (
  And Q(2 :part 2) is calculated according to : c
   ∫='
0) ( ) 1 : 2 ( ) 2 : 2 (v
dV V g part Q part Qc
The value V’ is determined when the total energy extracted is calculated according to: 
Q(2) = Q (2:part1) + Q (2:part 2) ≤  Vρ c c c load wCpw(t - t load main)  and  V’ ≤  Vload
The calculations done according to this procedure give lower values than with one load volume extracted 
everyday, but will give higher va lues than will the c onsideration of a minimum load temperature. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  17
 Table B.1 – Reference conditions for performance presentation 
Reference condition Value Remarks 
SYSTEM 
Collector orientation South   
Collector Tilt Angle 45 oFor 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 B.2 If piping is not delivered with the system or 
specified by the manufacturer. 
Location of collector circuit pipes Indoor, for systems with 
store situated indoors; outdoors, for systems with store situated outdoors As far as possible at the test rig 
Store ambient temperature 15 oC For systems where the store is located 
outside, the ambient temperature from the climate data shall be used. 
For systems with indirect (hydraulic) auxiliary heating: 
Power to be applied on auxiliary 
heat exchanger (100 ± 30)W per litre 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 modeled as an 
ideal heat source with no heat capacity and 
constant heating power. 
Flowrate through auxiliary heat exchanger The flowrate through the heat exchanger shall be chosen such that the temperature difference between the inle t and outlet of t he auxiliary heat 
exchanger is (10 ± 2) K under steady  state conditions, unless specifies 
otherwise by the manufacturer. 
For systems with electrical auxiliary heating: Power of 
electrical element If an electrical element is normally deliv ered with system or specified by the 
manufacturer, this element shall be used. Otherwise, (25 ± 8) W per litre of store volume above the electrical element. 
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, Wirzburg, Davos, 
Athens  
Climate Data For Stockholm: CEC Test Reference Year, for Davos, Wirzburg and Athens: 
Test Reference specified in the test procedure. 
HEAT LOAD 
Daily load pattern For all systems: 100 % at 6h after solar noon For testing, the load patterns 
shall be as specified in the test procedure. 
Cold water supply temperature See B.3 For te sting, the temperature shall be specified 
in the test procedure 
Desired (mixing valve) temperature 45 oC If the daily or yearly loads are calculated I 
terms of energy, this energy shall be calculated using the cold water supply 
temperature and the desired temperature. 
Daily load volume The load volumes in litres per day shall be chosen from the following series: 
50 l/d, 80 l/d, 110 l/d, 140 l/d, 170 l/d, 200  l/d, 250 l/d, 300 l/d, 400 l/d, 600 l/d. 
if larger loads are required, the series may be extended by repeatedly 
multiplying by V2 and rounding to the ne arest multiple of 10. the manufacturer 
shall give a design load for the system. The nearest value given in the above 
series shall be used, as well as the next lower and higher values. It is 
recommended to use all lower and higher values from the series, which lie 
between 0.5 times and 1.5 times the design load. 
NOTE Fixed load volumes have been chosen to facilitate comparison of the 
performance of different systems. 
For testing, the load volumes as specif ied in the test procedures shall be 
used. FDUS 855-2: 2009 
18 © UNBS 2009 – All rights reserved
 Draw – off flow rate 101/min If the maximal design draw-off flow rate of the 
system is less than 10 l/min, the maximum 
design draw-off rate of the system shall be 
used. 
 
B.2  Pipe diameter and insulation thickness 
If the pipe and insulation for the collector circuit are delivered with the system, or the pipe diameter and the 
insulation thickness to be used for the collector circuit are clearly specified in the insulation manual for the 
system, the delivered hardware or the specified values shall be used. 
When piping and insulation are not delivered with the syst em or clearly specified, the pipe diameter, thickness 
and insulation thickness given in table B. 1 shall be used for thermosiphon systems. 
The material for the collector circuit piping shall be copper, unless specified otherwise in the installation manual. 
B.3  Calculation of cold water temperature at reference location 
The cold water temperature shall be calculated in accordance with: 
ϑ cw = ϑ average  + Δϑamplit Sin (2π([Day] – D s) / 365) 
where 
ϑ cw   is the cold water temperature to be used for performance presentation 
ϑ average   is the yearly average cold wate r temperature on reference location 
Δϑamplit  is the average amplitude of seasonal variations on reference location 
[Day]  is the day number of the year  
Ds   is Shift term 
The yearly average cod water temper ature, average amplitude of  seasonal cold water temperature variations 
and shift term given in Table B.4 shall be used for reference locations. 
Table B.2 – Pipe diameter and insulation thickness for forced- circulation systems 
Flow rate in collector 
circuit 
l/h 
 External pipe diameter 
mm Pipe thickness 
mm Thickness of one layer 
insulation 1
mm 
<90 10 ±1 1 20 ± 2 
≥90 and ≤140 12±1 1 20 ± 2 
≥140and ≤ 235 15±1 1 20 ± 2 
≥235 and ≤ 405 18 ±1 1 20 ± 2 
≥405 and ≤ 565 22 ±1 1 20 ± 2 
≥565 and ≤880 28±1 1.5 30 ± 2 
≥ 880 and ≤ 1445 35 ±1 1.5 30 ± 2 
≥1445 and ≤ 1500 42 ± 1 1.5 39 ± 2 
>1500 Such that the flow velocity is approximately 
0.5 m/s 1.5 Same as internal pipe diameter 
1 based on a thermal conductivity of 0.04  W/mK ± 0.01 for temperature of 10 oC FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  19
  
Table B.3 – Pipe diameter and insulation thickness for thermosiphon systems 
Collector array aperture 
area  
m2External pipe diameter 
mm Pipe thickness 
mm Thickness of one layer 
insulation 
 mm 
≥1 and < 2 15 ± 1 
 1 20 ± 2 
 
≥2and < 6 
 18± 1 
 1.5 30 ± 2 
 
≥6and < 10 22 ± 1 1.5 39 ± 2 
1 Based on a thermal conductivity of 0.04  W/mK ± 0.01 for temperature of 10 oC 
 
Table B.4 – Data for calculation of the cold water temperature at the reference locations 
Reference location ϑ average   
oC Δϑamplit  
oC Ds 
d 
Stockholm 8.5 6.4 137 
Wurzburg 10.0 3.0 137 
Davos 5.4 0.8 137 
Athens 17.8 7.4 137 FDUS 855-2: 2009 
20 © UNBS 2009 – All rights reserved
 Annex C  
(informative)  
 
Extreme climate test procedure fo r the assessment of the frost 
resistance of solar DHW systems with outdoor tank 
C.1 Indoor test procedure for assessment of the frost resistance of solar DWH systems 
with outdoor tank  
C.1.1 Objective and applicability 
The purpose of this test is to determine whether extreme frost condition s for a certain climate region will                        
damage a solar domestic hot water (DHW) system or influence the proper functioning of such a system. 
The test is applicable to ICS systems and other sola r DHW systems with the stor age tank place outdoors, and 
takes into account the connecting piping and freeze prot ection device(s). it is suited for systems with or 
without active freeze protection devices (like a small internal heater). 
C.1.2 Apparatus and mounting of the system 
The solar DHW system is mounted in a climate chamber which is large enough to contain the complex system 
and the necessary mounting construction, and which is ca pable of generating the necessary test conditions 
with regard to temperature, wind sp eed and irradiation. The lamps to provide irradiation do not need to have a 
spectrum similar to the solar spectrum, however appr opriate measures should be taken to avoid excessive 
infrared radiation to the solar DHW system (for in stance, a transparent screen between the lamps and the 
solar DHW system which absorbs infrared radiation and which is cooled by a fan). Installation should be 
similar to realistic conditions, taking into account the most  severe conditions that are allowed in the installation 
manual. 
The system should be mounted in accordance with the installation instruction. S pecial attention should be 
given to the following points: 
- the mounting and installation of the piping into and from solar DHW system, including check valve and 
any freeze protection measures. 
- Any freeze protection measures required in the installation manual 
- The way the solar DHW system is mounted on the roof. 
If installation instruction allow the system to be mount ed on a flat roof, or otherwise in such a way that no 
thermal contact with the indoor climate is established , the system should be mounted in such a way that all 
components are exposed to the cold air temperature in the climate chamber as much as allowed. If however, 
in accordance with the installation instruction, the sys tem may only be integrated into the roof or otherwise 
being in contact with the indoor ambient air temperature,  the system should accordingly be mounted on a test 
roof. The test roof should be placed at the lowest tilt angle allowed in the installation instruction. Figures C.1 to 
C.4 give some examples of mounting, while Figure  C.5 gives an overview of the test chamber.  
 
 
 
 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  21
 
 
  Key            Key 
1 SDHW system         1 SDHW system 
2 Titled roof          2 Flat roof support 
3 Indoor (Attic) temperature ϑ1      3  D H W  p i p e s  
4 DHW pipes          4 Flat roof 
 
Figure C.1 — Solar DHW system mounted in a tilt ed   Figure C.2 – Solar DHW system mounted 
r o o f               o n  a  f l a t  
 
 
K e y               K e y  
1  S D H W  s y s t e m            1  S D H W  s y s t e m  
2 Titled roof            2 Closed extension to flat roof 
3 DHW pipes through roof opening       3 Indoor (Attic) temperature  ϑi  
4 Indoor (Attic) temperature ϑi        4 DHW pipes through roof opening 
 
Figure C.3 — Solar DHW system mounted on a tilt ed  Figure C.4 – Solar DHW system mounted 
roof with thermal contact to indoor ambient air   on a tilted extension of a flat roof with  
thermal contact to indoor ambient air  
 
 
 FDUS 855-2: 2009 
22 © UNBS 2009 – All rights reserved
 
 
  
 
 
Key 
1  Light source 
2  Infrared absorption screen 
3  SDHW system 
4  Fan 
5  Expansion tank 
6  Transparent mains water tank enables detection of small flows 
7  Safety valve (installed ace. to installers instructions) 
8  Draw-off valve 
9  Check valve 
10  Insulated, climatised test chamber with test roof 
 
  Pyranometer 
       Anemometer   
  Fluid thermometer (ϑ ), flow meter ( V) or pressure sensor ( P) 
  Air thermometer  
Figure C.5―Schematic of test set-up 
 
 
 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  23
 The water flow rate and volume to the solar DHW system should be measured in the mains water pipe and 
monitored throughout the test. Also the volume of wa ter discharged through the hot water pipe as well as 
though freeze protection devices or safety valves sh ould be measured and monitored. The measurement 
equipment should be able to detect water volumes at very low flow rates, with an accuracy of 5 ml. for outlets, like the domestic hot water outlet and safety device outlets; this may be done by capturing the water in an 
open vessel and weighing it. For the mains water pipe, a transparent vessel with expansion vessel is 
recommended; the water fed to the system can then be me asured by reading the water level. In that case, the 
expansion vessel should allow for pressure of the mains water which does not differ more than 10000 Pa from 
usual mains pressure. When ne cessary, the vessel can be kept at the mains water temperature by refilling. 
Water pressure sensors should be placed in the mains water and outlet pipes, in order to obtain extra pressure information during the test, if any freeze protec tion requires electricity or any other external energy 
source, the consumption of energy should be measured throughout the test. It is recommended to include a means of detecting or handling excessive leakage during the test in order to protect the climate chamber. 
 The system is filled with mains wa ter in accordance with the installa tion instruction and  checked for any 
leakage. The hot water outlet pipe is then shut off, and the cold water pipe  is kept at mains pressure. The 
system is energized as specified by the manufactur er, including any freeze protection equipment. If the 
system contains an auxiliary heating whic h plays a role in freeze protection (as specified by the manufacturer), 
the auxiliary heater is switched on, otherwise kept switched off. The temper ature of the mains cold water at 
the inlet to the climate chamber is kept at 5 oC. 
C.1.3 Test procedure 
The test procedure consists of three periods, which are described below in the order they have to be carried out. The values of the parameters mentioned in this description are given in C.1.4. 
C.1.3.1 Test period I 
C.1.3.1.1 General  
Test period I consists of n days with low solar irradi ation and ambient air temperature to induce ice growth 
and/or low solar DHW system temperatures, simulating av erage values of extreme climate conditions for the 
climate region considered; see C.1.4.1. 
The test starts after the system has been filled as desc ribed above, the domestic hot water draw-off flow rate 
has been measured and the hot water valve has been shut off. 
C.1.3.1.2 Procedure          
Conduct the test as follows. 
a) Reduce the air temperature of the test cell to ϑ a,1 the indoor ambient air temperature to ϑ i,1 (if 
applicable) and apply a wind speed level of  V w,1 
b) Condition the system by drawing off at least th ree times the system volume while keeping the mains 
water temperature at (5 ± 1) oC. Keep the system under these te mperature and wind conditions for a 
period of n days ± 1 h, starting from the above draw-off. 
c) During these n days, periodically apply an irradiance level of G sol,1 during a time interval  f sol,1. The 
start of the first irradiation period may be chosen within  the first 18 h of the test  period. The start of the 
second irradiation period should be (24 ± 1) h after the start of the first irradiation period. The third irradiation period should start (48 ± 1) h after the st art of the first irradiation period, and so on in a 
daily cycle. 
d) During the test 
- Visually inspect the solar DHW system for leakage or  frost damage at least every four days. No water 
should be withdrawn from the system; FDUS 855-2: 2009 
24 © UNBS 2009 – All rights reserved
 - especially record the consumption of water whic h is not equalled by corresponding discharge through 
the outlet pipe or any safety device. 
e) At the end of the period I, visually inspect the solar DHW system for any leakage or frost damage. 
C.1.3.2 Test period II 
C.1.3.2.1 General 
Test period II consists of a number of hours with no solar irradiation as well as absolute minimum air 
temperature and maximum wind speed for the climate region considered. 
C.1.3.2.2 Procedure 
Conduct the procedure as follows: 
a)  Immediately after test period I, reduce the air temperature to ϑ a, 2x and set the wind speed to V w, 2x and 
maintain this condition during t2 h (starting from the moment when the air temperature reaches ϑ a, 2x without 
any irradiation. No water shall be withdrawn from the system 
b)  Record the pressure read out of the pressure sensors at least every two hours 
c)  Record the moment and quantity of any water consumpt ion or use of electricity or  other external sources. 
d)  Record especially the consumption of water, wh ich is not equalled by corresponding discharge through 
the outlet pipe or any safety device. 
e)  At the end of the period II, open the draw-off valve fo r (10 ± 1) s and measure t he quantity of water drawn 
off. This may be done by accumulating the drawn off water and weighing it. 
When this tapping shows the dom estic hot water line of the system is not blocked by ice, the test period III is 
not necessary. 
NOTE  indications for possible pressure bu ild-up in the system are the following: 
- ice formation blocking the domestic hot water line (as indicated by no or very low water flow rate 
during the final draw-off; 
- the pressure relief valve was frozen during the test. In many system s, the pressure valve will start  
leaking during the test periods I or II, to release t he volume increase caused by ice formation in the 
systems. When at later stage, i.e. after several daily cycles, the pressure valve stops leaking. This is 
an indication of the valve being blocked by ice. A further indication is pressure build-up beyond the 
release pressure of the pressure relief valve, regist ered by one of the pressure sensors. However, it is 
also possible that an ice block is loca ted between the system and the sensor. 
If ice is blocking the domestic hot water line or the pressu re relief valve is blocked,  there is a possibility of 
pressure build-up in the solar DH W system, and the test period III is  recommended to in vestigate whether 
repeated pressure build-up could damage the system 
f)  If period III is carried out, vi sually inspect the solar DHW system for any leakage or frost damage 
immediately after period II. During this inspection, t he temperature in the test chamber should not rise 
more than 5 K above the temperature ϑ a, 2x, for a period of no longer than 1 h.  Then immediately (see 
C.1.3.3.2a)) continue with test period III. 
g)  If period III is not carried out, wi thdraw at least three times the syst em volume while keeping the mains 
water temperature at (5 ± 1) oC. Record the flow rate and the tem perature of the drawn off water during 
this draw-off. Again visually inspect the solar DHW sy stem for any leakage, frost damage or permanent 
deformation. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  25
  
C.1.3.3 Test period III 
C.1.3.3.1 General 
Test period III consists of 7-day period that simulates da ily cycles of frost and defrost. The goal of this test is 
to establish a cumulative effect of cycles of wa ter freezing, expanding and thereby possibly deforming the 
system, then thawing (during which some extra water could be consumed by the system to compensate 
the decrease in volume of the melted water), and then freezing again. 
C.1.3.3.2 Procedure 
Conduct the procedure as follows: 
a) Start test period III within 2 h after the end of te st period II, during which time the temperature in the 
test chamber should not rise more than 5 K above the temperature ϑ a, 2x. 
b) Set the wind speed to V w,3 and start applying the following daily cycle to the system. 
c) In the first period with length f sol,3, raise the temperature to ϑ a, 3x  within the first hour and apply a 
solar irradiance level of G sol,3 in the plane of the solar DHW system cover. 
d) In the second period with length (24 – t sol,3) h, lower the temperature to ϑ a, 3x within the first hour and 
without applying irradiance. 
e) Repeat the steps a) to d) 7 times and continue with f) 
f) At the end of period III, 
- visually inspect the solar DHW system for any leakage or frost damage 
- withdraw at least three times the system volume wh ile keeping the mains water temperature at (5 ± 1) 
oC. 
- record the flow rate and the temperature of the drawn off water during this draw-off. 
- Again visually inspect the solar DHW system  for any leakage, frost damage or permanent 
deformation. 
C.1.4 Test conditions 
C.1.4.1 General 
C.1.4.2 to C.1.4.4 describe procedures to obtain the test conditions from local weather data. In C.1.4.5, the 
test conditions are given for the climate region of the Netherlands. 
All test conditions are determined from a series of weather data, which includes extreme weather conditions 
for a representative location. The series should consis t of weather data, which contain the five most severe 
cold waves ever; 10 days before and 10 days after eac h cold wave period should be included. If these data 
are not available, a representative w eather data file of at least 10 consec utive years should be taken. In this 
case, the specified penalties as given apply. 
C.1.4.2 Determination of the test conditions for period II 
The conditions for test period I are represented by: 
Hsol,1  total daily diffuse solar irradiation, in MJ/m2; FDUS 855-2: 2009 
26 © UNBS 2009 – All rights reserved
 Gsol,1  corresponding solar irradiance during a specific time interval fv in W/m2; 
ϑ a, 1 ambient air temperature applied to the parts of  the solar DHW system that would normally be 
located outdoors , in oC; 
Vw,1   wind speed, in m/s; 
ϑ I,1 indoor ambient air  temperature applied to the parts of the solar DHW system that would normally  
be located indoors, in oC; 
n   length of the period, in d; 
tsol,1  irradiation period, in h. 
The quantities n, Hsol,1, Gsol,1, ϑ a, 1, Vw,1,  ϑ I,1 and tsol,1  are determined from the climate data described in 
C.1.4.1 in accordance with the following consecutive st eps. In consultation with the manufacturer, more 
severe conditions may be chosen, which should then be reported with the test result. 
a) Search all possible periods of n consecutive days in the climate data set, with the average ambient 
air temperature below zero for ea ch day in the period and period length n = 7d, 8d, 9d,…..,19d, 20d 
and 21d. For each period, determine hourly values of the quantity – H sol,1 t ϑ I,1 and the average value 
of that quantity. 
b) Detect the absolute minimum of all averaged - H sol,1 t ϑ I,1 values found under a) and the date and 
length n of the corresponding period. 
c) For this period, calculate the average values of the irradiation, temperature,  duration of the daylight 
period and wind speed to obtain, H sol,1,   ϑ I,1 , tsol,1  and V w,1 respectively. 
d) If weather data from an arbitrary decade is used, penalty ϑ p, 1 should be applied to correct ϑ a, 1  for 
more extreme temperatures than found in the decade  investigated. The penalty is a summation of the 
following temperature differences: 
- Temperature difference between the minimum n-days average temperature value of the decade 
considered and the average temperature value of the most severe cold wave in the region 
considered. 
- Temperature difference correction fo r nightly radiation as the infrared radiation in the test facility is 
less than for real outdoor conditions. 
e) The solar irradiance Gsol,1 to be used is calculated from the following equation: 
G sol,1  = (106 / 3600) x τsnow × τiam × H sol,1/ t sol,1 
  Where: 
  τ snow    = 0.2 the transmission factor of snow layer on the system; 
  τ iam  = 0.7, the average incidence angle modifier of the system. The value given here is an 
approximation; when a measure value is known this may also be used. This shall be reported with the test results. 
f) If the system is mounted in thermal connection to a test roof as described in C.1.2, the air 
temperature to be maintained under the test roof ϑ I,1  should be equal to the minimum air 
temperature specified in the instruction manual. If no  minimum air temperature is specified, the air 
temperature under the roof  ϑ I,1   should be equal to ( ϑ a, 1  + 5) K.  FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  27
 These values are used for period I of the freeze protection test. 
C.1.4.3 Determination of the test conditions for period III  
The conditions for this period are represented by: 
ϑ i,2 indoor ambient air temperature, in °C; 
ϑa,2 daily average outdoor ambient air temperature, in °C; 
ϑ a,2x minimum hourly ambient air temperature, in °C; 
Vw,2 wind speed, in m/s; 
t 2 test period, in h. 
From the climate data set as specified in C.1.4.1, find the day with the minimum hourly temperature ϑa,2x . For 
the same day, determine the daily average temperature ϑa,2 . 
If weather data from an arbitrary decade is used, penalty ϑp,2 should be applied to correct ϑa,2x for more  
extreme temperatures than found in the decade (see C.1.4.1) investigated. The penalty is a summation of the 
following temperature differences: 
-  Temperature difference between the minimum hourly temperature ϑa,2x and the absolute minimum hourly  
value in the region considered. 
-  Temperature difference correction fo r nightly radiation as the infrared r adiation in the test facility is less 
than for real outdoor conditions. 
Select the absolute maximum hourly average wind speed V w,2 during a period of frost. Calculate the test 
duration from: 
t2 = 24 × ϑa,2 /ϑa,2x
where 
ϑa,2x is the value without the penalty ϑp,2 described above. 
There is no solar irradi ation during period II. 
If the system is mounted in thermal connection to a test  roof as described in C.1. 2, the air temperature to be 
maintained under the test roof $ p2 should be equal to the minimum air temperature specified in the instruction  
manual. If no minimum air temperature is specified, the air temperature under the roof ϑ i,2 should be equal to 
(ϑa,2 + 5) K. Again, more severe conditions, e.g., longer test duration, may be chosen in consultation with the 
manufacturer . 
C.1.4.4  Determination of th e test conditions for period III 
The conditions for this period are represented by: 
ϑ 1,3a indoor ambient air temperature duri ng the irradiation period, in °C; 
ϑ 1,3b indoor ambient air temperature during the cold period, in °C; 
ϑ a,3a outdoor ambient air temperature duri ng the irradiation period, in °C; FDUS 855-2: 2009 
28 © UNBS 2009 – All rights reserved
 ϑ a,3b outdoor ambient air temperature during the cold period, in °C; 
Hsol,3 solar irradiation in the plane of the solar DHW system cover, in MJ/(m2.d); 
Gsol,3 solar irradiance in the plane of the solar DHW system cover, in W/m2; 
Vw,3 wind speed, in m/s; 
f sol,3 duration of the irradiation period, in h. 
Apart from the conditions for period III obtained by the following steps, different conditions in consultation with 
the manufacturer may be chosen. The conditions used should be reported with the test results. 
From the climate data set as specifi ed in C.1.4.1, select a consecutive 21-days period around the day with the 
absolute minimum daily average temperature already found in C.1.3.2. The 21-days period should comprise 
the 10 days before this day, the day itself and the ten consecutive days. 
Find in that period the day with the maximum daily average solar irradiation Hsol,3. From that day, also obtain 
the maximum solar irradiance Gsol,3.
Calculate fsol,3 from the following equation: 
t sol,3 = (106 /3600)× Hsol,3 /Gsol,3
and find, in the 21-days period, the period with length t sol,3 which has the highest average temperature ϑ a,3a. 
Also find, in the 21-days period, the period with length (24 – t sol,3) h that has the lowest average temperature 
ϑ a,3b . 
The value of V w,3 should be taken equal to vw,1. 
If the system is mounted in thermal connection to a test roof as described in C.1.2, the ambient air 
temperature to be maintained under the test roof ϑ i,3 should be equal to the minimum air temperature 
specified in the instruction manual. If no minimum air temperature is specified, the ambient air temperature 
under the roof ( ϑ a,3a or ϑ a,3b ) should be equal to the ambient air temperature ( ϑ a,3a or ϑ a,3b ) + 5K. 
C.1.4.5  Test conditions ela borated for specific locations 
The procedures given in C.1.4.2 to C.1.4.4 have been elaborated for the climate of the Netherlands. The 
results are: 
For test period I: H sol,1 = 0.3 MJ/(m2.d); G sol,1 = 10 W/m2; ϑa,1 = -9 °C; V w,1 = 5 m/s; n = 14d; t1 = 8.3 h. 
For test period II: ϑa,2x = -30 °C; V w,2 = 10 m/s; t 2 = 10 h. 
For test period III, no values are available yet. 
Climate data used involve the years 1961 to 1980. 
C.1.5  Results 
The following results should be reported: 
a)  make and model identification of the system in cluding auxiliary freeze protection devices fitted. 
b)  details of installation of the solar DHW system: mounting on or in the test roof, inclination, connections, 
lay-out, insulation of piping, etc. A sketch or photo of the installation should be included. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  29
 c)  location and time span of the climate data co nsidered for determination of the test conditions. 
d)  all test conditions as determined from the climate data. 
e)  record of draw-off flow rate and water temperature during initial conditioning of the solar DHW system at 
the start of period I. 
f)  volume of water discharged through freeze protection devices. 
g)  record of the time of activati on of auxiliary freeze protection devices. 
h)  record of the water flow rate to the solar DHW system. If the system consumed more water than the 
amount obtained by draw-offs or discharged through fr eeze protection or other safety devices, this could 
be an indication of internal deformation of  the system and it shall be reported. 
i)  record of consumption of electricity or other  external sources by freeze protection devices. 
j)  results of all visual inspections, includi ng any evidence of ice formation or leakage. 
k)  record of water pressure as measured by the pressure sensors. 
I)  volume of water drawn off at the end of period II (only when period  III is carried out). 
m)  record of the draw-off flow ra te and water temperature during the draw-off at the end of period II (if 
possible; only when period III is not carried out). 
C.2  Indoor test procedure for assessment of the reliability of solar DWH systems in 
respect of overheating protection  
C.2.1  Objective and applicability 
The purpose of this test is to assess if a solar DHW system is able to withstand extreme overheating 
conditions without being damaged. 
The test is applicable to solar DHW systems, in cluding connecting piping and overheating protection 
device(s). It is especially suited for systems that  do not have an active overheating protection device; 
however, for systems that do hav e such a device, the capability of that device to protect the system is tested. 
C.2.2  Apparatus and mounting of the system 
The solar DHW system is mounted in a solar simulator (similar to the solar simulators used for efficiency determination of solar collectors), capable of generati ng the necessary test conditions with regard to 
temperature, wind speed and irradiation (see Figure C. 6). The installation should be similar to realistic 
conditions, taking into account the most severe cond itions that are allowed in the installation manual. The 
system slope should be 45°, unless specifi ed otherwise in the installation manual. 
The system should be mounted in accordance with the in stallation instructions. Special attention should be 
given to the following points: 
-  The mounting and installation of the piping to and from the solar DHW system, including check valve and 
any overheating protection measures. 
-  Any overheating protection measures required in the installation manual. 
-  The way the solar DHW system is connected to the roof. 
 
 FDUS 855-2: 2009 
30 © UNBS 2009 – All rights reserved
 
  
  
  
 
Key 
1   Solar simulator 
2   SDHW system 
3   Safety valve (installed according to installers instructions) 
4   Draw-off valve A 
5   Heater 
6   Pump 
7   Valve C 
8   Non-return 
9   Valve B 
10   Fan 
  Pyranometer 
  Anemometer 
   Fluid thermometer ( ϑ), flow meter ( V) or pressure sensor ( P) 
  Air thermometer 
Figure C.6 — Scheme of the test set-up 
 
The water flow rate into the solar DHW system should be measured in the mains water pipe and monitored 
throughout the test. Also the volume of water discharg ed through overheating protection devices or safety 
valves should be measured and monitored. FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  31
 If any overheating protection requires electricity or any  other external energy source, the consumption of 
energy should be measured throughout the test. A water pressure sensor should be placed in the mains water 
line. 
The cold water inlet and the hot water outlet of the so lar DHW system are also connected to a circuit including 
a water heater and a pump, which has the purpose of heat ing up the solar DHW syst em water content at the 
start of the test period. This extra circ uit is fitted with two valves to make it possible to separate the circuit from 
the normal mains water connection and outlet pipe. Furthermore, a connection is pres ent to enable a pressure 
test to be made on the solar DHW system. 
The system and test circuit are filled with mains water in accordance with the installation instruction. The hot 
water outlet pipe is then shut off. 
C.2.3  Test procedure 
Ensure that the solar simulator is switched off. 
Carry out a pressure safety valve test by gradually rais ing the water pressure in the solar DHW system to the 
opening pressure of the safety valve. Read the pressure  at which the valve opens, and check the system for 
any leakage or damage. 
Restore the system to normal mains water pressure. Energize the system according to the manufacturer 
instruction, including any ov erheating protection equipment and auxiliary thermal sources. 
Connect the water heater circuit to the solar DHW syst em. Switch on the pump and heat the water in the solar 
DHW system using the water heater until the water in the solar DHW system reaches (75 ± 2) °C. 
NOTE1  If the solar DHW system is not des igned ever to reach a temperature of 75 °C or if it will never reach that 
temperature during normal operation, a lower temperature may be  chosen. This should be reported with the test results . 
Disconnect the water heater circuit and switch the solar DHW system back to mains water supply. Set the 
ambient air temperature in the chamber to ϑ i,4 and the wind speed to vw,4. 
NOTE 2  ϑ i,4 and V w,4 are defined in C.2. 
Keep the system under these temperature and wind condi tions for a period of 5 days +1 h. During these 5 
days, periodically apply an irradiation of Gsol,4 during a time t sol,4. The daily irradiation should be equal to H sol,4. 
The start of the first irradiation period may be chosen wi thin the first 6 h of the test period. The start of the 
second irradiation period should be (24 ± 1) h after the st art of the first irradiation period. The third irradiation 
period should start (48 + 1) h after the start of the fi rst irradiation period, and so on in a daily cycle. 
Record the temperature and amount of the water discharged to prevent overheating. 
At the end of the 5-days period, wit hdraw at least three times the system volume while keeping the mains 
water temperature constant to 1 °C around a value between 10 °C and 20 °C. Record the temperature of the 
drawn off water during this draw-off. Visually inspect the solar DHW sy stem for any dama ge or permanent 
deformation. 
C.2.4   Test conditions  
C.2.4.1  General 
In C.2.4.2 a procedure is described to obtain the test conditions from loca l weather data. In C.2.4.3 the test 
conditions are given for the climate region of the Netherlands. 
All test conditions are determined from a series of weather data, which includes extreme weather conditions 
for a representative location. The series should consis t of weather data, which contain the five most severe 
heat waves ever. If these data are not ava ilable, a representative weather data file of at least 10 consecutive 
years should be taken. In this case, the spec ified penalty as given below should be applied. FDUS 855-2: 2009 
32 © UNBS 2009 – All rights reserved
 C.2.4.2  Determination of test conditions 
The conditions for the te st are represented by: 
ϑ i,4   indoor ambient air temperature, in °C; 
ϑa,4   outdoor ambient air temperature, in °C; 
Hsol,4  5-days average solar irradiation in the pl ane of the solar DHW system cover, in MJ/(m2day); 
Gsol,4  peak hourly average solar irradiance in the plane of the solar DHW system cover within the 5-days 
period, in W/m2; 
Vw,4   lowest hourly average wind speed within the 5-days period, in m/s; 
t sol,4  duration of the irradiation period, in h. 
The quantities H sol,4, G sol,4, tsol,4, ϑa,4 , ϑi,4 and V w,4 are determined from the clim ate data described in C.2.4.1 
as follows: 
a)  Select a 5-days period with an average daily irradiation in the plane of the solar DHW system cover H sol,4 
and an average daily temperature ϑa,4 , which holds the absolute maximum product of Hsol,4 × ϑa,4 . 
b)  For the selected period, determine ϑa , ϑa,x , ϑa,max , H sol,4, G sol,4 and Vw,4 where: 
-  ϑa is the 5-days average outdoor ambient air temperature, in °C; 
-  ϑa,x is the peak hourly average outdoor ambient air temperature within the 5-days period, in °C 
-  ϑa,max is the peak hourly average outdoor ambient  air temperature ever registered, in °C; 
Investigate the local weather for ϑa,max as well. 
c)  Calculate the outdoor ambient air temperatur e for the test from the following equation: 
ϑa,4 = ϑa +ϑp,4 with 
 ϑp,4 = 0.5× (ϑa,max −ϑa,x) 
where ϑp,4 is the penalty for correction of ϑa for more severe temperatures than those found in the decade 
(see C.2.4.1) investigated: 
d)  Next, the duration of the irradiation period will be determined. If the solar DHW system to be tested is 
equipped with a TIM (Translucent Insulation Ma terial) one should account for an incidence angle 
dependent transmittance. In that case, the H sol (not the G sol) should be corrected with a factor cor sol in 
accordance with the integrated incidence angle modifier (IAM) function of the Tl material: 
cor sol = 0.5 I [IAM]( ϕ) × cosϕ 
where ϕ is the incidence angle, taken from 0 to 90°. 
For a number of TIM's, IAM functions are already known. Typical range of cor so| based on the IAM 
function for realistic Tl materials is from 0.90 to 0.75. For a cover having an incidence angle independent 
transmittance, the corsol is 1.0. Apart from the cover material , the construction of the solar DHW system FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  33
 (deep-seated box structures, parabolic mirrors, etc.) may influence the value of the IAM function and 
cor sol. Therefore, it is recommended to use a me asured IAM function of the solar DHW system. 
Taking into account the incidence angle correction, the duration of the daily insolation period is calculated 
by: 
 tsol,4 = 277.8 × cor sol × H sol,4/Gsol,4x.
In order to take into account properties of common solar simulators, a solar irradiance lower than G sol,4x 
by at most 20 % can be used to calculate the corresponding tsol,4. 
e)  If the system is mounted in thermal connection to  a test roof as described in C.1.2, the ambient air 
temperature to be maintained under the test roof ϑi,4 should be equal to the maximum ambient air 
temperature specified in the instruction manual. If no maximum ambient air temperature is specified, the 
ambient air temperature under the roof ϑ i,4 should be equal to ( ϑ a,4 + 5) K. 
C.2.4.3  Test conditions ela borated for specific locations 
The procedure given in C.2.4.2 has been elaborated for t he climate region of the Neth erlands. The results are: 
ϑa,4 = 27 °C;  Hsol,4 = 30 MJ/(m2.day);  G a, 4 = 1000 W/m2;  Vw,4 = 0 m/s;  tsol,4  =  8.3 h. 
C.2.5  Results 
The following results should be reported: 
a)  make and model identification of the system  including auxiliary overheating protection devices 
b) details of installation of the solar DHW system: mounting on or in the test roof, inclination, connections, 
lay-out, insulation of piping, etc. A sketch or photo of the installation should be included; 
c)  location and time span of the climate data co nsidered for determination of the test conditions; 
d)  all test conditions as determined from the climate data; 
e)  volume of water discharged through over heating protection devices and/or safety valves; 
f)  record of the time of activation of  auxiliary overheating protection devices; 
g)  record of consumption of electricity or other external sources by overheating protection devices; 
h)  results of all visual inspections, in cluding any evidence of damage or leakage; 
i)  record of water pressure as measured by the pre ssure sensor. If during the pressure test the pressure 
valve did not open, or if it opened at a pressure higher than its rated pressure, this should be reported. If 
the pressure at any time exceeded the pressure rating of the pressure valve, this should also be reported; 
j)  record of the draw-off water temperature during the draw-off at the end of the test. If at any time the water 
temperature exceeded 100 °C, this should be reported. 
 
 
 
 FDUS 855-2: 2009 
34 © UNBS 2009 – All rights reserved
 Annex D  
(informative)  
 
Ageing test for thermostatic valves 
D.1  General 
This accelerated ageing test has the goal to assess t he applicability of the specified maintenance frequency of 
a thermostatic valve, which is used as overheating protection valve in a solar heating system. Water of 
specified hardness is used in a cycle of operation and cooling down (closing). The correct functioning is 
regularly checked. When too large sedi ments of chalk are observed, the te st duration is recalculated to an 
expected period in normal use. Therefore, the assumpti on is made that the valve will operate 250 times per 
year (This number has been estimated based on model simulations for Dutch climate with ICS and 
thermosiphon systems). 
D.2  Test arrangement 
The test arrangement (see Figure D.1) consists of a mixing vessel V1 with sufficient volume. The vessel can 
be filled with drinking water through valve 1. Via the open lid, substances can be added. The water in the 
vessel is stirred using a stirring device R. In the ve ssel V1, the water is conditioned to the required hardness 
by adding a mixture of calcium and magnesium salts. Using a pump H, the conditioned water can be pumped into test vessel V2 where it can be heated electrically. On top of V2 there is a connection where the valve being tested (labelled T&P) is mounted. A flow meter F is used to register the amount of water drained by 
T&P. 
 
Figure D.1 – Test arrangement for thermostatic valve test 
D.3  Test Procedure 
D.3.1   Find out the specified maintenance frequency fm [year-1] of the thermostatic valve. If the 
maintenance frequency is not specified, assume a system lifetime of 15 years: f = 1/15 [year-1]. mFDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  35
                                                      D.3.2  Determine the number of cycles necessary for the test as n = 250 / f m
D.3.3  Start up the test rig: 
a)  Rinse V1 with domestic hot water and subsequently fill it. 
b)  Add magnesium carbonate and calcium sulphate until the desired hardness is  reached. Measure the 
hardness in accordance with ISO 6059. Start the stirring device and the pump. When refilling the store 
during the test, the amounts of salts to be added may be calculated from the amount of water refilled and 
the amounts of salts used to condition the first store volume. 
NOTE 1   The EN 60734 standard specifies procedures  to obtain 'hard water to be used for testing the 
performance of some household electrical appliances'.  This standard is however very labour intensive and 
expensive. Therefore a simplified method is given here to achieve the same result. 
NOTE 2   At TNO, with drinki ng water in Delft (hardness 8.5 °D1 ) and a volume of V1 of 600 I, 180 gram of 
magnesium carbonate and 290.4 gram of  calcium sulphate is needed to obtain the desired hardness of about 23 °D . 
c)  Open valve 2, 3 and 4 to fill V2 with hard water. Close valve 4. 
d)  Start heating V2 using the electrical heater. At a ce rtain point the valve will open and water will flow from 
V2 to the drain. Cold water is supplied from V1 . After a certain time the temperature has dropped 
sufficiently for the valve T&P to close again. 
e)  When V1 is almost empty, close all valves and s hut off the stirring device and the pump, refill V1 with 
water and restart at b). 
D.3.4  After every 30th to 35th cycle, check visually if the valve is still functioning. When the valve does not 
function any more after less than n cycles, the number of cycles completed is reported. 
D.3.5  After n cycles, report whether th e valve is still functioning. Remove the valve and visually inspect the 
amount of sediments on the valve. 
D.3.6  If n cycles have been completed with the valve functi oning, the specified maintenance frequency is 
sufficient for the valve. Else, convert the number of  test cycles to an expected operation period: 
expected operating period = number of cycles / 250 [year]. 
D.4   Results 
Report n, the number of cycles completed and, if applicable, the expected operating period. 
 
 
 
 
 
 
 
 
1 German index of hardness of water. T he SI unit is mmol/l; 1 mmol/l = 5.6 oD FDUS 855-2: 2009 
36 © UNBS 2009 – All rights reserved
 Annex E  
(informative)  
 
Lightning protection test for solar heating systems 
E.1   Field of application 
This test for lightning protection should be applied only to those parts of Factory Made solar heating systems 
that are normally exposed to outdoo r weather/environment conditions. 
Systems that contain few or no metallic parts may be excluded from this test. 
Test methods for special devices, components and other items that may be applied to Factory Made solar heating systems or connected to solar heating systems on th e roof with LPS installation are not covered by 
this standard.  
The outdoor parts of the system may be considered as " natural components" on roof constructions and should 
be treated as "natural air termination components" in accordance with the relevant lightning protection standards. 
NOTE  This test is based on IEC 61024-1, modified for the needs of thermal solar heating systems. It is included in this 
standard to assist the manufacturers  in meeting these requirements. 
E.2   Purpose 
The purpose of this test is to assess the relative re sistance of the Factory Made solar heating systems and to 
evaluate whether the solar heating system is adequately manufactured to ensure sufficient connections and 
protection against lightning in case of connecting with  a Lightning Protection System (LPS) in the building . 
The solar heating systems and components mounted on the roof  surface should only be used as a part of the 
existing LPS with the agreement of the structure engineer or the owner. 
The connection with LPS cannot guarantee absolute pr otection to structures, solar heating systems and 
components or person s, but will significantly reduce risk of damage caused by lightning. 
E.3   Requirements 
The system should conform to the requirements given in IEC 61024-1. 
When the water tank is mounted outdoors, the separation distance St (see E.5. 4) should either fulfill 
St > D t
or there should be at least one connection (bonding c able or strip) between the tank and the outer cover 
sheet(i.e. in front and rear bottom). This bonding cable or strip should have at least t he sizes as given in Table 
F.1, when measured in accordance with E.5.5. 
where 
Dt is the minimum separation distance (K × K c / K m) x L t  =  0.044L t 
Lt is the overall length of the tank, in millimetres; 
Ki =0.05 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  37
 Kc = 0.44 
Km = 0.50 
When the tank is mounted outdoors, the bridging between the tank and the supports should have a total 
contact (connection) area of at least 100 cm2 (overlapping surface bolted or sp ot welded), when measured in 
accordance with E.5.6. 
The bridging between the collectors and supports (as deter mined in E.5.7) should have a contact (connection) 
surface of at least 100 cm2 (overlapping surface bolted or welded). 
E.4   Apparatus 
No special apparatus is required except: 
-  a platform on which the complete solar heating system can be installed in accordance with the 
manufacturer's instructions and 
-  measuring instruments for distances,  etc. (see test procedures below). 
E.5   Test procedure 
E.5.1  Test conditions 
The test is normally carried out on solar heating system s, which are installed in a testing structure in 
accordance with the manufacturer's instructions. 
E.5.2  Solar heating system installation 
Install the Factory Made solar water heating system in a ccordance with the manufacturer's instructions, using 
his material for connections on the testing base stand and between components. Fill up the solar heating system and the close loop, for indire ct systems, with water and take care for removing air from all parts 
through the air vents. 
E.5.3  Separation distance St
Measure the overall length Lt of the tank, in millimetres. 
Measure the existing separation distance St between the tank and the outer metal cover in the front and rear 
bottom. 
Calculate the minimum permitted separation distance Dt. 
E.5.4  Size of the bonding cable or strip 
Check the existence of the above mentioned bonding connections. 
Measure the size of bonding and calcul ate the cross section surf ace (or determine the size from electric cable 
tables). 
E.5.5  Bridging between tank and supports 
Check if there are bolts or rivets etc. between tank and supports. 
Measure and calculate the overlapping surface between these parts. Compare the results with the lower limit 
of 100 cm2, overlapping surface. 
 FDUS 855-2: 2009 
38 © UNBS 2009 – All rights reserved
 E.5.6  Bridging between collectors and supports 
Check if there are bolts or rivets etc. between collect ors and supports. Measure and calculate the overlapping 
surface between these parts. Compare the results with the lower limit of 100 cm2, overlapping surface. 
E.5.7  Bridging between collectors and tank 
No special inspections. There is sufficient electrical continuity via metal supports. 
E.5.8  Connecting terminal with Lightning Protection System (LPS) 
Check the existence of the holes and measure the sizes d , I and h. 
E.5.9  Metal sheets covering parts of the solar heating system 
The electrical continuity check is not covered by this standard, but the relevant standards should be applied. 
Check the thickness of metal sheet. 
E.5.10  Heating effects due to lightning currents 
The heating effects are considered as negligible. 
E.5.11  Mechanical durability due to lightning mechanical loads 
The mechanical loads in considered as negligible 
The mechanical loads in the solar components are too low and the influence on durability and stability is 
considered as negligible. 
E.6   Report 
Report the results of the tests, measurements and calcul ations in a formal Lightning Protection Testing Sheet 
given in Annex F. 
E.7   Conclusions 
The conclusions include the final evaluation that t he Factory Made solar heating system is adequately 
manufactured and capable of connecting with an existing Li ghtning Protection System (LPS) on the roof of a 
building. In this way it should be protected against damage due to lighting effects. 
Final conclusions are reported and included in the Lighting Protection Testing Sheet. 
 
 
 
 
 
 
 
 
 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  39
 Annex F  
(informative)  
 
Lightning Protection testing sheet 
Table F.1 – Size of bonding cable 
Cable cross-section F c  
mm2Protection level Cable Material  
Large load of lightning Non large load lighting  
Copper (Cu) 16 6 
Aluminium (Al) 25 10  
I-II-III-IV 
Steel (Fe) 50 16 
 
Table F.2 – Size of metal cover sheets 
Metal cover sheet Minimum thickness  
mm 
Galvanized steel 0.50 
Stainless steel 0.40 
Copper 0.30 
Aluminium 0.70 
Zinc 0.70 
Lead  2.00 
 
 
 
 
 
 
 
 
 
 
 FDUS 855-2: 2009 
40 © UNBS 2009 – All rights reserved
 Lightning protection testing sheet (Continued) 
Laboratory                                      :………………………………………………………………………………….. 
No of Test                                       :………………..……………………………………………………………….. 
Date                                                :………………………………………………………………………………….. 
Standard                                         :…………………………………………………..………………………………… 
Solar heating system No                :………………………………..…………………………………………………. 
 
Manufacturer                            :………………………………………………………………………… . 
(From manufacturer specifications and by  laboratory examination of the sample) 
Open system  :                                Yes                       No 
Closed system:                                Yes                       No 
Tank Capacity:                                …….                          Collector area  :           m 2
Construction Materials 
Solar Tank  
Tank walls                                         :………………………………………………………………………………. 
Internal coating                                 :………………………………………………………………………………… 
Flange and sealings                          :………………………………………………………………………………… 
Heating element                                :………………………………………………………………………………… 
Pipes                                                 :………………………………………………………………………………… 
Heat exchanger                                 :……………………………………………………………………………….. 
Safety devices                                   :……………………………………………………………………………….. 
Welding / soldering                            :……………………………………………………………………………….. 
Other materials                                  :……………………………………………………………………………….. 
Solar Collector  
Absorber pipes                                  :……………………………………………………………………………….. 
Connecting pipes                               :………………………………………………………………………………. 
Sealing                                               :……………………………………………………………………………… 
Welding / soldering materials             :……………………………………………………………………………… 
Other materials                                  :………………………………………………………………………………. 
Supports  
Materials                                            :………………………………………………………………………………. 
Bolts/rivets/welding                            :………………………………………………………………………………. 
Coating                                              :…………………………………………………………………………………. 
Other materials                                  :…………………………………………………………………………………. 
Connecting pipes  
Pipes                                                 :………………………………………………………………………………… 
Welding/soldering materials              :………………………………………………………………………………… 
Other materials                                  :………………………………………………………………………………… 
 
 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  41
  
1.  Special components for connection with IPS :                                           Yes                           No 
2.  Test in accordance with other standards        :                                           Yes                           No  
3.   Installation on testing platform                       :                                           Yes                           No 
4.    Length of tank Lt                                           :……..mm 
       Separation distance S t                                  :……..mm 
       Calculation for Dt                                          :………mm    
       Comparison                                                  :            S t > Dt                                Yes                           No 
                                                                            :………..S t < Dt                                 Yes                          No 
       Need for bonding                                         :                                             Yes                          No 
       Number of bonding cable                             :………..Items 
5.   Existence of bonding  cable                          :                                              Yes                         No 
       Number of cables or strips                           :………..items 
       Dimensions of cable                                     :………mm 
       Cross section surface Fc                              :………  mm2
       Comparison                                                  : Fc >……mm2 (from Table F.1) 
                                                                            : Fc < …….mm2 (from Table F.1) 
6.   Tank support bridging 
       Existence of bolts etc                                   :                                              Yes                        No 
       Dimensions of overlapping                          :……..cm.         Surface of overlapping Fov :…..cm2
        Comparison                                                : Fov > 100 cm2                       Yes                        No 
                                                                           : Fov  < 100 cm2                       Yes                        No 
7.     Collector supporting bridging 
        Existence of bolts etc                                :                                                Yes                        No 
         Dimensions of overlapping                       :……cm.            Surface of overlapping Fov : ……cm2
         Comparison                                              : Fov > 100 cm2                        Yes                        No 
                                                                           : Fov  < 100 cm2                       Yes                        No 
8.      Existence of 2 Holes Ö10                           : 
         Dimensions                     d = 12mm:        d = ……..mm                            Yes                        No 
                                                 l = 22mm:          l = …….mm                             Yes                        No 
                                                h = 200mm         h = …….mm                            Yes                        No 
9.      Cover sheet thickness t                            :…………mm 
         Comparison (Table F.2)                           : t  > …….mm                           Yes                       No 
                                                                          : t  < …….mm                           Yes                        No 
 
 
 FDUS 855-2: 2009 
42 © UNBS 2009 – All rights reserved
 Lightning protection testing sheet (concluded) 
 
Laboratory                           :………………………………………………………………………………… 
No of Test                            :………………………………………………………………………………… 
Date                                     :………………………………………………………………………………… 
Standard                              :………………………………………………………………………………… 
Solar heating system No     :………………………………………………………………………………….. 
 
 
Final Conclusions 
 
 
 
 
 
Needs for special labelling –identification: 
 
 
 
Remarks: 
 
 
 
Tested by: 
 
 
Issued by: 
 
 
 FDUS 855-2: 2009 
© UNBS 2009 – All rights reserved  43
 Bibliography 
 [1]  IEC 60734, Household electrical appliances — Performance — Hard water testing 
[2]  ISO 6059, Water quality — Determination of the sum of calcium and magnesium — EDTA titrimetric 
method 
[3]  EN 1717, Protection against pollution of potable water in water installations and general requirements 
of devices to prevent pollution by backflow 
[4]  US 857-1, Thermal solar systems and compo nents — Custom built systems — Part 1: General 
requirements 
[5]  US 857-3, Thermal solar systems and component s — Custom built systems — Part 3: Performance 
characterization of stores for solar heating systems 
[6]  IEC 60343, Recommended test methods for determini ng the relative resistance of insulating materials 
to breakdown by surface discharges 
[7]  IEC 61024-1, Protection of structures agai nst lighting — Part 1: General principles 
 FDUS 855-2: 2009 
© 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 855-2: 2009 
 
ICS 27.160 
Price based on nn pages 
© UNBS 2009– All rights reserved