FINAL DRAFT UGANDA 
STANDARD  
  FDUS 853
First Edition
2009-mm-dd
 
Reference numbe r
FDUS 853: 2009
 © UNBS 2009 
  
Code of practice for solar wate r heating systems – Design, in stallation, testing, repair 
and maintenance FDUS 853: 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 sp ecified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, in cluding photocopying and microfilm, without prior written 
permission from UNBS. 
Requests for permission to reproduce this document should be addressed to 
The Executive Director 
Uganda National Bureau of Standards 
P.O. Box 6329 
Kampala  
Uganda 
Tel: 256 41 4505995 
Fax: 256 41 4286 123 
E-mail: unbs@infocom.co.ug 
Web: www.unbs.go.ug FDUS 853: 2009 
© UNBS 2009 – All rights reserved  iii
 Contents Page 
1 Scope .......................................................................................................................... ............................ 1 
2 Normative re ferences ........................................................................................................... ................... 1 
3 Definitions.................................................................................................................... ............................ 5 
4 Legal require ments............................................................................................................. ..................... 9 
5 Types of system ................................................................................................................ .................... 10 
6 Components for solar water heating systems ....................................................................... 25 
6.1 General........................................................................................................................ .......................... 25 
6.2  Collectors.................................................................................................................... .......................... 26 
6.3  Storage tanks ................................................................................................................. ...................... 29 
6.4  Pumps ......................................................................................................................... ......................... 32 
6.5  Piping........................................................................................................................ ............................ 33 
6.6  Controls ...................................................................................................................... .......................... 35 
6.7   Heat exchangers ............................................................................................................... ................... 38 
6.8  Heat-trans fer fluids .......................................................................................................... ..................... 43 
6.9  Expansi on tank................................................................................................................ ..................... 43 
6.10  Valves, gauges and meters  used in sola r syst ems.............................................................................. 44 
6.11  Air vent ...................................................................................................................... ........................... 45 
6.12  Temperature – pres sure relief valve........................................................................................... .......... 45 
6.13  Pressure re lief valve......................................................................................................... .................... 46 
6.14  Pressure  gauge ................................................................................................................ .................... 46 
6.15  Vacuum breaker ................................................................................................................ ................... 46 
6.16  Isolati on valv es.............................................................................................................. ....................... 47 
6.17  Drain valves.................................................................................................................. ........................ 48 
6.18  Check valves .................................................................................................................. ...................... 48 
6.19  Mixing or tem pering va lve ..................................................................................................... ............... 49 
6.20   Anti-scald valve ............................................................................................................. ...................... 50 
6.21   Freeze-prot ection valves ..................................................................................................... ................ 50 
6.22   Other component s............................................................................................................. .................. 51 
6.23  Water supply.................................................................................................................. ....................... 52 
7  Design considerations ......................................................................................................... .52 
7.1  General....................................................................................................................... .......................... 52 
7.2  Collector design considerations ............................................................................................... ............ 52 
7.3  System design considerations.................................................................................................. ............ 54 
7.4  Corrosion protection .......................................................................................................... ................... 56 
7.5  Heat transf er fluids .......................................................................................................... ..................... 57 
7.6  Controllers and te mperature sensors........................................................................................... ........ 57 
7.7  Other design  factors .......................................................................................................... ................... 58 
8  Thermal performance of solar water heating systems.......................................................... 58 
8.1  General....................................................................................................................... .......................... 58 
8.2  Collector class ............................................................................................................... ....................... 59 
8.3  Effective co llector area ...................................................................................................... ................... 59 
8.4  Hot wate r usage ............................................................................................................... .................... 60 
8.5  Preheat ve ssel size ........................................................................................................... ................... 60 
8.6  Collector mounti ng and location............................................................................................... ............ 60 
8.7  Climate ........................................................................................................................ ......................... 61 
8.8  Other fa ctors................................................................................................................. ........................ 61 
9  Electrical considerations..................................................................................................... ..62 
9.1  General....................................................................................................................... .......................... 62 FDUS 853: 2009 
iv © UNBS 2009 – All rights reserved
 9.2  Electrical installa tion ....................................................................................................... ..................... 62 
9.3  Electrical  safety............................................................................................................. ....................... 62 
9.4  Controls...................................................................................................................... .......................... 62 
9.5  Avoidance of electr ical interference.......................................................................................... ........... 62 
9.6  Testing ....................................................................................................................... .......................... 62 
10   Installation................................................................................................................. ........... 63 
10.1   General ...................................................................................................................... ......................... 63 
10.2   Pre-installa tion procedure................................................................................................... ................ 63 
10.3   Installation procedures ........................................................................................................ ............... 63 
10.4   Collector subsys tem installation ............................................................................................. ............ 64 
10.5.1    Collector positioning ........................................................................................................ ................... 65 
11   Component installation ....................................................................................................... .80 
11.1   General ...................................................................................................................... ......................... 80 
11.2   Piping, ducting and ancillary equipment ...................................................................................... ....... 80 
11.3   Storage tank installation .................................................................................................... ................. 83 
11.4   Pump, blowers a nd heat exchangers ............................................................................................ .....85 
11.5   Controls, sensors and safety  devices......................................................................................... ........ 86 
11.6   Freeze pr otection............................................................................................................ .................... 88 
11.7   Heat tran sfer fluids......................................................................................................... ..................... 89 
12   System installation checkout and start-up procedures ........................................................ 90 
12.1   General ...................................................................................................................... ......................... 90 
12.2    Pressure  testing............................................................................................................. ..................... 90 
12.3    Flushing the system.......................................................................................................... .................. 90 
12.4   Testing the pum p and co ntrols ................................................................................................ ........... 91 
12.5   Cleani ng up.................................................................................................................. ....................... 95 
12.6   Homeowner’s manual  and instructions.......................................................................................... .....95 
13   Commissioning and documentation..................................................................................... 96 
13.1   Filling t he syst em ........................................................................................................... ..................... 96 
13.2   Drain-down  systems ........................................................................................................... ................ 96 
13.3   Electrical and auxiliary eq uipment ........................................................................................... ........... 96 
13.4    Thermal insulati on for the system............................................................................................ ........... 97 
13.5    Making good .................................................................................................................. ..................... 97 
13.6    Start-up and  handing over .................................................................................................... .............. 97 
13.7    Recommended form of  user's da ta sheet........................................................................................ ...98 
13.8    Post-commissioning checks ...................................................................................................... ......... 99 
14    Problem assessment and system checkout ........................................................................ 99 
14.1    Problem assessment ........................................................................................................... ............... 99 
14.2    The initial service call..................................................................................................... ..................... 99 
14.3   System records............................................................................................................... .................. 100 
14.4    Warranty coverage ............................................................................................................ ............... 100 
14.5    Service history .............................................................................................................. .................... 101 
14.6    Contractor  liability ......................................................................................................... .................... 101 
14.7    Overall checkout ............................................................................................................. .................. 101 
14.8    Investigating consumer complaints — an exam ple .......................................................................... 102 
14.9    Lifestyle analysis............................................................................................................ ................... 102 
14.10    Common problems.............................................................................................................. .............. 102 
14.11    System checkout.............................................................................................................. ................. 105 
15  Troubleshooting checklist ................................................................................................... 113 
16  Maintenance ................................................................................................................... ....119 
17   Safety precautions............................................................................................................ ..120 
Annex A: Maintenance of weathe r-tightness………………………………………………………………….…….123 
Annex B:  Loads on coll ectors .................................................................................................. ....................... 124 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  v
 Annex C: Condensation and ventilation in roof spaces .................................................................................... 128 
Annex D: Method for calculat ing the thermal performance .............................................................................. 130 
Annex E: Methods of pressure and leak testing of absorber plates ................................................................. 134 
Annex F: Methods of type testing for collectors  .....................................................................................  135 
Annex G: Methods of test ing for differential temper ature contro l syst ems ..................................................... 136 
Annex H (informative) Solar therma l applications an d technol ogies ............................................................. ..136 
Annex I (informati ve) Solar basics............................................................................................. ....................... 135 
Annex J: Crome-dome collector si ting aid....................................................................................... ................. 135 
Annex K: Simplified sizing procedure fo r solar domestic hot water systems................................................... 135 
Annex L: Electric wate r heater ci rcuitry ...................................................................................... ..................... 136 
Annex M: Volt-ohmmeter (VOM) or multimeter  operation........................................................................... .....132 
Annex N: Solar syst em flow rates ............................................................................................... ..................... 133 
Annex P: Tools fo r service repair .............................................................................................. ....................... 136 
Bibliography................................................................................................................... ................................... 136 
 
 FDUS 853: 2009 
vi © UNBS 2009 – All rights reserved
 Foreword 
Uganda National Bureau of Standards (UNBS) is a pa rastatal 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 
 
 FINAL DRAFT UGANDA STANDARD FDUS 853: 2009
 
© UNBS 2009– All rights reserved  1
 Code of practice for solar water heating systems – Design, 
installation, testing, repair and maintenance 
1 Scope 
1.1 This code of practice provides recommendations for solar water heating syst ems having collectors with 
liquid heat transfer media for heating water to help ensure adequate operation and safety. Design 
consideration, manufacture, handling, installati on, operation and maintenance are included. 
1.2 This code of practice applies regardless of the fr action of heating requirements supplied by solar energy, 
the type of conventional fuel used in conjunction with solar, or the heat tr ansfer fluid (or fluids) used as the 
energy transport medium. However, where more stringent requirements are recommended by the 
manufacturer, these manufacturer requirements shall prevail. 
1.3 This code of practice does not apply to space heating and swimming pools. 
2 Normative references 
The following referenced documents are indispensable fo r the application of this Uganda Standard. For dated 
references, only the edition cited applies. For undated references, the latest edition of the referenced 
document (including any amendments) applies. 
ISO 9059:1990, Solar energy – Calibration of field pyrhelio meters by comparison to a reference pyrheliometer 
ISO 9060:1990, Solar energy – Specific ation and classification of inst ruments for measuring hemispherical 
solar and direct solar radiation ISO 9459 -1:1993, Solar heating – Domestic water heati ng systems – Part 1: Perf ormance rating procedure 
using indoor test methods 
ISO 9459-2:1995, Solar heating – Domestic water heating systems – Part 2: Outdoor test methods for system 
performance characterization and yearly performance prediction of solar –only systems 
ISO 9459-5:2007, Solar heating - Domestic water heat ing systems – Part 5:  System performance 
characterization by means of whole-system test and computer simulation ISO 9488:1999, Solar energy – Vocabulary ISO 9553:1997, Solar energy – Methods of testing pref ormed rubber seals and sealing compounds used in 
collectors ISO 9806-1:1994, Test methods for solar collectors – Part 1: Thermal performance of glazed liquid heating 
collectors including pressure drop 
ISO 9806-2:1995, Test methods for solar collector s – Part 2: Qualification test procedures 
ISO 9806-3:1995, Test methods for solar collectors – Pa rt 3: Thermal performance of unglazed liquid heating 
collectors (sensible heat transfer only) including pressure drop FDUS 853: 2009 
2 © UNBS 2009 – All rights reserved
 ISO 9808:1990, Solar water heaters — Elastomeric mate rials for absorbers, connecting pipes and fittings — 
Method of assessment 
ISO 9845-1:1992, Solar energy — Reference solar spectr al irradiance at the ground at different receiving 
conditions – Part 1: Direct normal and hemi spherical solar irradiance for air mass 1.5 
ISO 9846:1993, Solar energy — Calibration of  a pyranometer using a pyrheliometer 
ISO 9847:1992, Solar energy — Calibration of field pyr anometers by comparison to a reference pyranometer 
ISO/TR 9901:1990, Solar energy — Field pyranometers — Recommended practice for use ISO/TR 10217:1989, Solar energy — Wate r heating systems — Guide to material selection with regard to 
internal corrosion ISO 4952:2006, Structural steels with impr oved atmospheric corrosion resistance 
ISO 11303:2002, Corrosion of metals and alloys — Guidelines for selection of protection methods against 
atmospheric corrosion 
ISO 11972:1998, Corrosion-resistant ca st steels for general applications 
US 854-1, Thermal solar systems and components — Solar collectors — General requirements US 854-2, Thermal solar systems and components — Solar collectors — Test methods US 855-1:2009, Uganda Standard — Thermal solar systems and components — Factory made systems — 
General requirements US 855-2:2009, Thermal solar systems compone nts — Factory made systems — Test methods 
US 857-1:2009, Thermal solar systems and compone nts — Custom built syst ems —Part 3: General 
requirements 
US 857-2:2009, Thermal solar systems and components — Custom built systems — Part 2: Test methods 
US 857-3:2009, Thermal solar systems and component s — Custom built systems —Part 3: Performance 
characterization of stores for solar heating systems US 862, Standard test method for determination of so lar reflectance near ambient temperature using a 
portable solar reflectometer US 861, Standard practice for evaluating absorptive so lar receiver materials when exposed to conditions 
simulating stagnation in solar collectors with cover plates US 856, Standard guide for on-site inspection and veri fication of operation of solar domestic hot water 
systems ISO 559:1991, Steel tubes for water and sewage 
ASTM B42:2002, Standard specification for seamless copper pipe, standard sizes 
ISO 7598:1988, Stainless steel tubes suitable for scr ewing in accordance with ISO 7-1 
ISO 49:1994, Malleable cast iron fittings threaded to ISO 7-1 
ISO 4144:2003, Pipework — Stainless steel fittings threaded in accordance with ISO 7-1 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  3
 ASTM A126:2004, Standard specification for gray iron cast ings for valves, flanges, and pipe fittings 
BS 417-2, Specification for galvanized low carbon steel cister ns, cistern lids, tanks and cylinders — Part 2: 
Metric units 
ISO 12468-1:2003, External exposure of roofs to fire — Part 1: Test method 
ISO 12468-2:2005, External fire exposure to roofs — Part 2: Classification of roofs 
ISO 3008:2007, Fire-resistance tests — Door and shutter assemblies 
IEC 60364 (All parts), Low-voltage electrical installations 
ASTM E119:2007, Standard test methods for fire tests of  building construction and materials 
ASTM E861:1994(2007), Standard practice for evaluating thermal insulation materials for use in solar 
collectors ISO 9774:2004, Thermal insulation for building applications — Guidelines for selecting properties 
ISO 13787:2003, Thermal insulation products for building equipment and industrial installations —
Determination of declared thermal conductivity BS 864-2, Capillary and compression tube fittings of copper an d copper alloy — Part 2: Specification for 
capillary and compression fittings for copper tubes BS 864-3, Capillary and compression tube fittings of copper and copper alloy — Part 3: Compression fittings 
for polyethylene pipes ISO 9906:1999, Rotodynamic pumps — Hydraulic performance acceptance tests — Grades 1 and 2 
ISO 15783:2002, Seal-less rotodynamic pumps — Class II — Specification  
ISO 9908:1993, Technical specifications for centrifugal pumps — Class III 
ISO 9905:1994, Technical specifications for centrifugal pumps — Class I 
BS 1565-2, Galvanized mild steel indirect cylinders, annular  or saddle-back type — Part 2: Metric units 
BS 1566-1, Copper indirect cylinders for domestic purposes — Part 1: Specification for double feed indirect 
cylinders 
BS 1566-2, Copper indirect cylinders for domestic purposes — Part 2: Specification for single feed indirect 
cylinders BS EN 1057, Copper and copper alloys — Seamless, round copper tubes for water and gas in sanitary and 
heating applications BS 3198, Specification for copper hot water storag e combination units for domestic purposes 
ISO 4427-1:2007, Plastics piping systems — Poly ethylene (PE) pipes and fittings for water supply — Part 1: 
General 
ISO 4427-2:2007, Plastics piping systems — Poly ethylene (PE) pipes and fittings for water supply — Part 2: 
Pipes FDUS 853: 2009 
4 © UNBS 2009 – All rights reserved
 ISO 4427-5:2007, Plastics piping systems — Poly ethylene (PE) pipes and fittings for water supply — Part 5: 
Fitness for purpose of the system 
ISO 22391-1:2007, Plastics piping systems for hot and cold water installations — Polyethylene of raised 
temperature resistance (PE-RT) — Part 1: General ISO 22391-5:2007, Plastics piping systems for hot and cold water installations — Polyethylene of raised 
temperature resistance (PE-RT) — Part 5: Fitness for purpose of the system 
ISO 4422-1:1996, Pipes and fittings made of unplasticized poly(vinyl chloride) (PVC-U) for water supply —
Specifications — Part 1: General ISO 4422-2:1996, Pipes and fittings made of unplasticized poly(vinyl chloride) (PVC-U) for water supply — 
Specifications — Part 2: Pipes (w ith or without integral sockets) 
ISO 4422-3:1996, Pipes and fittings made of unplasticized poly(vinyl chloride) (PVC-U) for water supply — 
Specifications — Part 3: Fittings and joints ISO 4422-4:1997, Pipes and fittings made of unplasticized poly(vinyl chloride) (PVC-U) for water supply — 
Specifications — Part 4: Va lves and ancillary equipment 
ISO 4422-5:1997, Pipes and fittings made of unplasticized poly(vinyl chloride) (PVC-U) for water supply — 
Specifications – Part 5: Fit ness for purpose of the system 
EAS 205, Controls for household appliances 
BS 4213:2004, Cisterns for domestic use — Cold water storage and combined feed and expansion 
(thermoplastic) cisterns up to 500 L — Specification ISO 16422:2006, Pipes and joints made of oriented unplasticiz ed poly(vinyl chloride) (PVC-U) for the 
conveyance of water under pressure — Specifications BS 4814, Specification for expansion vessels using an in ternal diaphragm, for sealed hot water heating 
systems 
ISO 15874-1:2003, Plastics piping systems for hot and cold water installations — Polypropylene (PP) — Part 
1: General ISO 15874-2:2003, Plastics piping systems for hot and cold water installations — Polypropylene (PP) — Part 
2: Pipes ISO 15874-5:2003, Plastics piping systems for hot and cold water installations — Polypropylene (PP) — Part 
5: Fitness for purpose of the system ISO 6242-1:1992, Building construction — Expression of users' requirements — Part 1: Thermal requirements 
ISO 6242-2:1992, Building construction — Expression of user s' requirements — Part 2: Air purity 
requirements 
ISO 15493, Plastics piping systems for industrial applicat ions — Acrylonitrile-butadiene-styrene (ABS), 
unplasticized poly(vinyl chloride) (PVC-U) and chlorinat ed poly(vinyl chloride) (PVC-C) — Specifications for 
components and the system — Metric series 
ISO 727-1:2002, Fittings made from unplasticized poly(vinyl chloride) (PVC-U), chlorinated poly(vinyl chloride) 
(PVC-C) or acrylonitrile/butadiene/styre ne (ABS) with plain sockets for pipes under pressure — Part 1: Metric 
series FDUS 853: 2009 
© UNBS 2009 – All rights reserved  5
 IEC 61000-3-2, Electromagnetic compatibility (EMC) — Part 3- 2: Limits — Limits for harmonic current 
emissions (equipment input current ≤ 16 A per phase) 
ISO 22897:2003, Glass in building — Glazing and airborne sound insulation — Product descriptions and 
determination of properties 
ISO 16932:2007, Glass in building — Destructive-windstorm-resistant security glazing — Test and 
classification ISO 3934:2002, Rubber, vulcanized and thermoplastic — Preformed gaskets used in buildings — 
Classification, specifications and test methods ISO 9050:2003, Glass in building — Determination of light transmi ttance, solar direct transmittance, total solar 
energy transmittance, ultraviolet tr ansmittance and related glazing factors 
ISO 8873-1:2006, Rigid cellular plastics — Spray-applied polyurethane foam for thermal insulation — Part 1: 
Material specifications ISO 8873-2:2007, Rigid cellular plastics — Spray-applied polyurethane foam for thermal insulation — Part 2: 
Application ISO 24510, Activities relating to drinking water and wastewat er services — Guidelines for the assessment and 
for the improvement of the service to users ISO 24512, Activities relating to drinking water and wastewater services — Guidelines for the management of 
drinking water utilities and for the asse ssment of drinking water services 
ISO 2103:1986, Loads due to use and occupancy in residential and public buildings 
ISO 4354, Wind actions on structures 
ISO 12494, Atmospheric icing of structures 
ISO 9453, Soft solder alloys — Chemical compositions and forms 
ISO 9454-1, Soft soldering fluxes — Classification and requirements — Part 1: Classification, labelling and 
packaging 
ISO 9454-2:1998, Soft soldering fluxes — Classification and requirements — Part 2: Performance 
requirements ISO 12224-1, Solder wire, solid and flux cored — Specification and test methods — Part 1: Classification and 
performance requirements 
3  Definitions 
For the purpose of this Uganda Standard, the definitions  given in ISO 9488 and the following definitions apply. 
3.1   
absorber plate surface coating a coating the principal function of which is to absorb solar radiation 
3.2   
absorber plate (absorber) the element of a collector that receives and abso rbs the solar radiation and converts into heat 
3.3   FDUS 853: 2009 
6 © UNBS 2009 – All rights reserved
 absorptance 
the ratio of the solar radiation absorbed by a surface to that which falls on the surface 
3.4   
accessible, adj 
permitting close approach that may require removal or opening of an access pane, door, or similar obstruction 
3.5   
aperture 
that part of the outer surface of the collector which admi ts solar radiation to the absorber plate, including any 
glazing bars or supports over the absorber 
3.6   
aperture area 
the maximum area projected by the aperture 
3.7   
auxiliary energy subsystem, n 
in solar energy application, equipment using non-solar energy sources to supplemen t or backup the output 
provided by a solar energy system 
3.8   
collector (solar collector, solar panel) the general term for the device in which solar radiat ion is absorbed, converted to heat, and removed by the 
heat transfer fluid 
3.9   
differential temperature controller 
a device that is able to detect a temperature differenc e, and to control pumps and other electrical devices in 
accordance with this temperature difference 
3.10   
direct system 
a system in which the water that w ill ultimately be drawn from the hot taps passes thro ugh the collector 
3.11   
drainback system 
a system in which, as part of the nor mal working cycle, the collector is automatically drained and refilled with 
heat transfer fluid 
3.12   
draindown system a system in which the collector is drained to waste, ei ther manually or automatica lly, when freezing conditions 
are likely to occur 
3.13   
draw-off temperature (delivery temperature) 
the temperature at which domestic hot water is supplied 
3.14   
durability, n 
the ability (of a system or component) to operate properly as long as intended 
3.15   
effective area 
the area of the perfect collector that would collect the same amount of solar energy as the aperture area 
3.16   
emittance FDUS 853: 2009 
© UNBS 2009 – All rights reserved  7
 the ratio of the thermal radiation from the unit area of a surface to the radiation from the unit area of a full 
emitter (‘black body’) at the same temperature 
3.17   
flash point, n 
of a liquid, the minimum temperature at which it gives off vapour in sufficient concentration to form an ignitable 
mixture with air near the surface of the liquid within t he vessel as specified by appr opriate test procedure and 
apparatus 
3.18   
flat plate collector a collector that employs no concentration of the incident  solar radiation, and in which the absorber plate is 
essentially planar 
3.19   
gravity system (thermosyphon system ) 
a system in which circulation of the heat tran sfer fluid is achieved by natural convection 
3.20   
heat transfer fluid, n 
(i) in solar energy systems, a liquid or gas that passes through the solar collector and carries the absorbed 
thermal energy away from the collector 
(ii) any fluid that is used to transfer thermal energy between subsystems in solar energy systems 
3.21  indirect system a system in which a fluid other than the water ultima tely drawn from the hot passes through the collector 
3.22  open system a system in which the heat transfer fluid is  in extensive contact with the atmosphere 
3.23  
operating conditions, extreme , n 
unusual physical conditions to which a component or system may be exposed and for which it is not designed 
or intended to withstand, nor is it requir ed to withstand by a local regulatory agency 
3.24  
operating conditions, normal , n 
the usual range of physical conditions (for example, te mperature, pressure, wear and tear, weather) for which 
the component or system was designed 
3.25  
potable water, n 
water that is free of impurities in amounts sufficient to cause disease or harmful physiological effects and 
conforming in its bacteriological and chemical quality to  the regulations of the public health authority having 
jurisdiction 
3.26  
preheat vessel (solar store) 
a thermal store for the energy transferred from the collector 
3.27  
pumped system 
a system in which the heat transfer fluid is circulated by means of a pump 
3.28  
reliability, n FDUS 853: 2009 
8 © UNBS 2009 – All rights reserved
 the ability (of a system or component) to operate properly when required 
3.29  
SDHW, n 
solar domestic hot water 
3.30  
sealed system a system in which the heat transfer fluid is completely sealed from the atmosphere 
3.31  selective surface an absorber plate surface c oating that will decrease the radiative emission from the ab sorber plate whilst 
maintaining a high absorptance for solar radiation 
3.32  
shall, vi 
a mandatory requirement necessary to provide minimum operation and safety 
3.33  
should, vi 
a recommended method or component to prov ide improved perform ance and effectiveness 
3.34  solar energy system, active, n 
a solar energy system that uses me chanical equipment (pumps, fans), t hat is not an integral part of a 
structure, to collect and transfer thermal energy, either to the point of  use or to be stored for later use 
3.35  solar water heating systems, direct, n 
a solar water heating system in which the potable water passes directly from the water supply, through the 
collectors and storage, to t he residential hot water supply 
3.36  
solar energy system, drainback, n 
a solar energy system in which the heat transfer fluid is drained out of the collector and exposed piping, and 
into a storage tank, a holding tank, or expansion tank in  order to protect the collector and piping from damage 
due to freezing 
3.37  
solar energy system, draindowm, n 
a solar energy system in which the heat transfer fluid is  drained out of the collector and exposed piping to an 
external drain in order to protect the collector and piping from damage due to freezing 
3.38  
solar water heating system, indirect, n 
a solar water heating system in which a closed circulation loop isolates one fluid from contact with others in 
the system. This closed loop may contain a nonpotable fluid. 
3.39  
solar energy system, thermosiphon, n 
a solar energy system in which the heat transfer fluid circulates by convection as the less dense, warm fluid 
rises and is displayed by the denser, cooler fluid. 
3.40  
solar water heating system, tank absorber, n 
Solar Domestic Hot Water (SDHW) system in which sola r radiation is absorbed by the surface of the storage 
tank, which is usually installed in an insulated housing  whose sunward side is glazed. Such systems are also 
referred to as “batch” or “breadbox” heaters. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  9
 3.41  
toxic, adj 
any substance (other than a radioactive substance) that  has the capacity to produce personal injury or illness 
to man through ingestion, inhalation, or absorption thr ough any body surface, or any substance producing  a 
lethal close in half (LD50) of white rats when ingest ed as a single close of less than 10 g/kg of body mass. 
3.42  
trickle collector 
a flat plate collector in which the heat transfer fluid is  not contained within passage ways in the absorber plate 
but flows down the plate surface 
3.43  
vented system 
a system in which contact between the heat transfer fluid and the atmosphere  is restricted to the free surface 
of a feed and expansion cistern 
3.44  
weather conditions, extreme , n 
environmental conditions that are rare in a local clim atic region (which have occurred no more than once 
during the past 30 years) 
3.45  
weather conditions, normal,  n 
the (actual or anticipated) range of  environmental conditions (rain, snow, hail, wind, temperature, pollution) 
that typically occur in a local c limatic region over several years 
4   Legal requirements 
4.1 General 
The local authority and water supplier for the region in  which a proposed installation is to be sited should 
always be consulted concerning the requirements in re spect of planning, building regulations and water supply 
before the installation of a solar wa ter heating system is undertaken. 
4.2 Planning 
Planning permission may to be obtained from the local planning authority before carrying out any 
‘development’. Consequently application should be made to  the local planning authority to ascertain whether 
or not the proposed installati on constitutes ‘development’. 
4.3 Building regulations 
General regulations have been enacted concerning the design and construction of buildings. Solar heating 
systems incorporated into buildings have to comply with these regulations in so far as they effect such matters 
as the materials of construction, roof loading, we ather tightness, fire resi stance, insulation, etc. 
Advice on some of these matters is given in this c ode. However, responsibility for the application of the 
regulations in a particular area rests with the local aut hority, which may require plans to be deposited, showing 
how the regulations have been complied with. 
4.4 Water supply 
Water supply byelaws for preventing wa ste, undue consumption, misuse, or  contamination of water supplies 
have been made by water authorities and water supply  companies in respective local authorities. 
These byelaws require written notice to be made to the water supply authority before any installation of, or 
alteration to, a water fitting is made, if connected to  the authority’s supply. Where a water fitting has been 
installed, that can subsequently be found by the water supply authority to contravene its byelaws, the water FDUS 853: 2009 
10 © UNBS 2009 – All rights reserved
 supply can insist that the occupier remove it. The occupier of the pr emises will also, on summary conviction of 
such an offence, be liable to a fine in respect of each offence and, in the case of a continuing offence, to a 
further fine for each day during which the offence conti nues after such a conviction. It should be noted that, 
whilst the various sets of byelaw s are identical except in a few minor respects, the interpretation and 
enforcement of each set of byelaws will vary with the particular water supplie r concerned. Bearing this in mind, 
it is considered that to attempt to give meaningful gener al guidance on the application of water byelaws in this 
code of practice could be misleading. 
It is, however, in the interest of pros pective purchasers of solar heating sy stems to obtain the assurance of the 
installer/manufacturer of the system  that the recommendations given in 7. 3.3 and 7.5 of this code of practice 
have been followed. 
4.5 Other actions 
In addition to complying with the legal requirements detail ed in 4.1 to 4.4, it is recommended that he occupier/ 
owner inform the lessors, mortgagors, in surers, etc of the property as applicable. 
5      Types of system 
5.1 General 
A solar water heating system which incorporates arrangements for providing………… A hot water system incorporating solar water heating may contain arrangements for providing heat by other 
means such as a solid fuel, gas or oil fired boiler or an  electric immersion heater. This is necessary in places 
where the water cannot be heated to the required draw-off temperature at all times of the year by solar energy 
alone due to cloudy conditions. 
The working principle of solar hot water systems is shown schematically in Figure 5.1.  Water from the cold 
supply is led to the ‘cold store’ (the  feed cistern) whence it passes into the preheat vessel, forming the ‘warm 
store’ where it is heated by solar energy. The water pas ses then to the ‘hot store’ (the hot water cylinder) 
which is heated by a boiler or electric immersion heater. 
NOTE 
To discourage the growth of the organism responsible fo r Legionnaire’s disease, water in the hot store should 
be kept at a temperature of at least 55 oC.  
            Heat from    Heat from boiler or     
            s o l a r  c o l l e c t o r     i m m e r s i o n  h e a t e r  
              
             Cold supply 
                                                                                                                                                                             Taps 
       Feed cistern   Preheat vessel   hot water cylinder 
 NOTE Preheat vessel and hot water cylinder may be combined in one vessel 
Figure 5.1 – Working principle of solar hot water system 
5.2 System types 
5.2.1 General 
Many different designs of solar water heating systems are possible and they may be classified in several 
ways. Factors that influence the selection of a specific  system type include the amount of water that needs to Cold 
Store Warm 
StoreHot 
StoreFDUS 853: 2009 
© UNBS 2009 – All rights reserved  11
 be heated, relative cost  and efficiency, simplicity of  operation, and clim ate conditions in wh ich the system will 
be used. 
Solar water heating systems are classified into two general categories: 
- active systems, which use a pump to control water flow, and 
- passive systems, which use no pump. 
Both active and passive systems can be ei ther direct or indirect (Figure 5.2) 
- In a direct system, the portable water circulates fr om the tank to the collector and back to the storage 
tank. Thus, the heat collecting fluid is the same  potable water that is in the water heater. 
- In an indirect system, the fluid that circulates th rough the collector may be water or it may be another 
heat transfer fluid. This heat-collecting fluid nev er comes in contact with the potable water in the 
storage tank. Instead, it transfers heat to  the potable water through a heat exchanger. 
 
 
Figure 5.2 – Direct and indirect solar water heating systems 
Further, there are two types of solar water heating systems – active and passive – and each has two 
categories – direct and indirect. 
      Active    Passive  
      D i r e c t     D i r e c t  
      I n d i r e c t     I n d i r e c t  
Several design variations exist in each sys tem type. The types and variations include: 
1. Active direct systems 
- Active direct systems that us e different types of controllers 
2. Active indirect systems 
- Active indirect systems that use different type s of controllers, heat collecting fluids, and heat 
exchange mechanisms 
3. Passive direct and indirect systems 
- Passive direct systems in which the collector and storage are one and the same 
- Passive systems that circulate water through t hermosiphoning action and can be direct or indirect 
 FDUS 853: 2009 
12 © UNBS 2009 – All rights reserved
  
5.2.2 Active direct systems 
Active direct systems incorpor ate the following components: 
- Water storage tank 
- Solar collector 
- Controller to regulate pump operation 
- A pump or circulator to transfer water from the storage tank to the collector 
Several additional components ensure proper system oper ation. Each of these co mponents, listed below and 
in Figure 5.3, are described in Clause 6. 
1) Check valves to prevent thermosiphoning action 2) Isolation valves isolate subsystem components for service. 
3) Pressure relief valves relieve high pressure. 
4) Temperature and pressure relief valves  relieve high temperature and pressures 
5) Air vents release air that coul d cause air locks in the system 
6) Vacuum breakers allow proper collector loop drainage 7) Drain valves drain the collector loop and tank or other subsystem components 8) Freeze valves and sensors help to protect the co llector from being damaged by freezing temperatures 
9) Optional temperature indicators and flow meters monitor components. 
 
Figure 5.3- Additional system components FDUS 853: 2009 
© UNBS 2009 – All rights reserved  13
 Active direct systems are principally differentiated by their pump control or freeze protection scheme. 
Following are descriptions and illustrations of active di rect systems based on their method of pump control. 
5.2.2.1 Differential controlled 
In a differential controlled system (F igure 5.4), the circulating pump oper ates when sensors located at the top 
of the collector (hottest point) and bottom of the storage tank (coldest point) indicate a 5-20 oC temperature 
difference. When the temperature difference drops to about 3 – 5 oC, the pumps switches off. During the 
course of the day, the controller is constantly comparing the two sensor temperatures. In this way, water 
circulates through the collector only when sufficient solar energy is available to increase the water 
temperature. 
 
Figure 5.4 – Active direct system with differential controller FDUS 853: 2009 
14 © UNBS 2009 – All rights reserved
 5.2.2.2 Photovoltaic controlled 
The photovoltaic (PV) controlled system (Figure 5.5) uses a PV module to operate pump control functions. In 
a direct-coupled system, the PV module and pump are sized and matched to ensure that the pump will begin 
operating when sufficient solar energy for heating water is available and will stop operating when solar energy 
diminishes.  
 
Figure 5.5 – Active direct system with photovoltaic control 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  15
 5.2.2.3 Timer - controlled 
This control method is used in tropical climates where temperatures are mid year-round and significant 
amounts of solar energy are available almost everyday. In  a timer controlled system (Figure 5.6), a timer turns 
on a pump in mid morning and switches it off in late after noon. To ensure that the heated water stratifies at he 
top of the storage tank, the sy stem uses a very small ( ≤ 10W) pump. The collector feed and return lines are 
both connected through the use of a special valve at t he bottom of the storage tank so only the coldest water 
from the tank flows through the solar collector. 
Timer controlled systems could conceivably operate during rain or overcast conditions, so care must be taken 
to ensure the supply and return lines to the collector are located near the bottom of the storage tank. 
Therefore, if the pump operates duri ng a cloudy day, only a small amount of  the water at the very bottom of 
the tank will be circulated through the collector . This prevents potential major tank heat loss. 
 
Figure 5.6 – Active direct system with timer control 
 
 FDUS 853: 2009 
16 © UNBS 2009 – All rights reserved
 5.2.3  Active indirect systems 
Indirect systems are typically  used in areas of freezing temperatures or  areas that have water that is very high 
in mineral content. The combination of high dissolved minerals and high temperatures produced by the solar 
system can accelerate scale building in system piping, fittings, and valves. 
Like direct system, active indirect systems employ a solar collector, a circulating pump, a potable water 
storage tank and a variety of ancillary valves. Unlike dire ct systems, indirect system s also incorporate a heat 
exchange mechanism that transfers heat from the freeze-pr oof heat-collecting fluid to the potable water in the 
storage tank. Active systems are differentiated principa lly by the type of heat ex changer, controller, and heat 
collection fluid used. 
5.2.3.1 Indirect pressurized system 
In an indirect pressurized system (Figure 5.7), the heat transfer fluid provides freeze protection at low 
temperatures. A differential or PV controller activates t he circular to move the fl uid through the collector. A 
heat exchanger transfers the heat from  the heat transfer medium to the potable water. The heat exchanger 
may be external to the storage tank, coiled around the outside lower half of the tank, or immersed inside the 
tank. A double wall heat exchanger is always used in sy stems that se toxic heat transfer fluids. For systems 
using non-toxic heat transfer fluids, a single wall heat exchanger is acceptable. An expansion tank on the 
solar loop compensates for the heat transfer fluid’s expansion and contraction. In addition, these systems 
require fill and drain valves for adding and servicing heat transfer fluids. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  17
 
 
Figure 5.7 – Active indirect system with tank internal heat exchanger 
5.2.3.2 Drainback system 
Drainback systems offer freeze protection and high-limit  protection because the collectors empty by gravity 
when the system pump is not operating. Since these di fferentially controlled systems often use distilled water 
as the heat collection fluid, they offer improved heat transfer to the potable water. When installed correctly, 
these systems also provide a fail-safe method for prot ecting the collectors and piping from freeze damage. 
Each time the differentially controlled pump shuts off, all fluid in the slightly tilt ed collector and pipes drains 
into an insulated reservoir tank located in the building’ s interior. In some system s, the heat exchanger is 
incorporated in the drainback reservoir; in others, the heat exchanger may be external or inside the storage 
tank. This system does not require air vents or vacuum breakers; instead, the piping contains air that should 
not be added or released.  
Drainback systems have a measured amount  of air and a measured amount of water in the system. The air is 
transferred to the reservoir when the pump is running and the water fills the collector. The pump is never 
without water since water is returning from the collector loop. When the pump  shuts off, the air in the reservoir 
is forced up and into the top of the collector by the wa ter draining back into the reservoir from the bottom of 
the collector. Several other special charac teristics of drainback systems include: FDUS 853: 2009 
18 © UNBS 2009 – All rights reserved
 - Pimps must be sized correctly to overcome gravity and friction losses 
- Since the system is not pressurized, expansion tan ks, check valves or fill and drain valves are not 
required 
- Collectors and pipe drains must be installed to allow proper and unimpeded drainage back to the 
drainback reservoir 
5.2.4  Passive direct and indirect systems 
Passive systems use no pumps or controllers. Instead, t hey rely on convection either to move water between 
the collector and storage tank in a thermosiphon system or  to stratify heated water wi thin an integral collector 
system. Most passive systems are direct; that is, the potable water directly collects the sun’s heat in the 
collector.  
When a fluid in the collector is hotter than the water in the preheat vessel, flow occu rs by natural convection, 
transferring heat from the collector to the preheat vessel. This type of system has the following limitations: 
a) The collector has to be sited sufficiently below t he preheat vessel to promote natural circulation when 
the collector is hotter than the store. 
b) Freeze protection in the direct gr avity system cannot be readily achieved. 
c) All pipe work should be of minimal length and of sufficient bore to ensure adequate flow. 
d) There should be sufficient rise on a ll pipe runs to prevent air locks. 
e) A non-return valve fitted to prevent reverse circul ation would need to have a very low pressure drop 
for forward flow. 
Following are descriptions of the most  common types of passive systems. 
5.2.4.1 Thermosiphon system, direct or indirect 
In a thermosiphon system (Figure 5.8) the water storage tank is located abov e the collector. Cold water from 
the bottom of the thermosiphon system’s tank flows through a pipe to the bottom of the solar collector. As the 
sun shines on the collector, the heated water expands  slightly and becomes lighter than the cold water. 
Heavier, denser cold water from the tank flows into t he collector inlet, which pushes the lighter, heated water 
through the collector outlet and up into the top half of t he storage tank. This process of displacement provides 
a tank full of hot water at the end of the day. The sola r heated water is drawn from  the elevated tank either 
directly to the hot water service or to an interior auxiliary tank. Some thermo siphon systems (Figure 5.9) 
include a heat exchanger in or around the tank a nd an antifreeze solution to avoid freeze problems. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  19
 
 
Figure 5.8 – Direct thermosiphon system 
 
Figure 5.9 – Indirect thermosiphon system 
5.2.4.2 Integral collector storage (ICS) system 
In other solar water heating systems the collector an d storage tank are separate co mponents. In an integral 
collector storage system, (Figure 5. 10 and 5.11) both collection and solar storage are combined within a 
single unit. Most ICS systems store potable water inside seve ral tanks within the collect or unit. The entire unit FDUS 853: 2009 
20 © UNBS 2009 – All rights reserved
 is exposed to solar energy throughout the day. The result ing water is drawn off either directly to the service 
location or as replacement hot water to an aux iliary storage tank as water is drawn for use. 
 
Figure 5.10 – Integral collector storage (ICS) system 
 
Figure 5.11 – Cutaway of an ICS system 
5.2.4.3 Batch system 
The simplest of all solar water heating systems is a bat ch system (Figure 5.12). it is simply one or several 
storage tanks coated with a black, solar-absorbing materi al in an enclosure with glazing across the top and 
insulation around the other sides. It is  the simplest solar system to make and is quite poplar with do-it-
yourselves. When exposed to direct sun during the day, the tank transfers the heat it absorbs to the water it FDUS 853: 2009 
© UNBS 2009 – All rights reserved  21
 holds. The heated water can be drawn fo r service directly from the tank or  it can replace hot water that is 
drawn from an interior tank inside the residence. 
 
Figure 5.12 – Batch solar water heater 
5.3 Freeze protection 
Freeze protection mechanisms prevent damage to system components. There are four basic methods used to 
prevent freezing. These include: 
1. Indirect antifreez e fluid circulation 
2. Draining 
3. Water flow 
4. Thermal mass 
5. Auxiliary heater 
Except for solar systems in the tropics, all systems require some type of freeze protection method. The 
following examples are some of the more common met hods used to prevent freezing. Systems may employ 
one or more of the following methods of freeze protection. 
5.3.1 Indirect antifr eeze fluid circulation 
Indirect heat exchange systems use a heat-transfer fl uid that provides freeze protection in very low 
temperatures. The antifreeze solution circulates in a closed loop through the collector and heat exchanger. 
This provides protection to the collector and exterior piping during freezing temperatures. 
5.3.2 Draining 
Direct systems can be protected from freezing by re moving all the water from the collector and the exposed 
piping. This can be done manually or automatically by one of two methods: drain down or drain back. 
a) Automatic drain-down 
In a drain down system (Figure 5. 13), sensors and a controller activa te one or more automatic valves 
hat isolate the collector loop from the tank. The autom atic valve should be installed to allow collector FDUS 853: 2009 
22 © UNBS 2009 – All rights reserved
 loop drainage when power to the electrically operated  valve is interrupted. The collectors and piping 
for these systems must be installed so that no gravity traps or low pots occur so that the collector loop 
fluid will drain totally by gravity. 
 
Figure 5.13- Drain-down system configuration 
b) Manual drain-down 
Systems can also be designed to be manually dr ained. The system must have isolation valves 
between the collector and the storage tank and dr ain valves on the supply and return lines. The 
manual draining operation must include shut off of  any system controller and circulating pump. It is 
best to keep he drain valves open when the collectors are drained. A leak or failure of the isolation 
valve can provide a path for water to flow back to the solar collector and result in freeze damage. 
Complete draining requires both properly sloped piping and a means for air to enter the system. The 
use of a vacuum breaker will ensure that the collector loop drains properly. In turn, refilling after 
draining requires a method to allow air to escape at  the high point of the system. A properly installed 
air vent will provide a means of allowing air to be purged aut omatically from the system. 
c) Drain-back 
In drain-back systems (Fig ure 5.14), a reservoir collects the heat-t ransfer fluid (usually distilled water) 
that drains from the collector  loop each time the pump turns off. When th e pump turns on, it 
recirculates this same fluid. Generally, a drain ba ck system uses a heat exchanger to transfer heat 
from the collector fluid to the potable water. 
The pump used in these drain-back systems must be capable of overcoming fairly large static heads, 
since the collector may be mounted several storie s above the pump. The pump must be installed in 
such a way that it is below the low-water mark wh en liquid is not circulating. As in drain down FDUS 853: 2009 
© UNBS 2009 – All rights reserved  23
 systems, the collectors and piping for drain back systems must be insta lled in a way allows no gravity 
traps or low spots to prevent the drai n back of the heat-transfer fluid. 
 
Figure 5.14 – Drain-back system with internal tank heat exchanger 
 Water flow 
Freeze prevention may be provided by moving warm from the bottom of the tank through the collector. 
This movement can be accomplished by recircul ation or use of freeze-protection valves. 
a) Recirculation 
In direct systems, recirculation may be where the threat of freeze damage is infrequent. For 
recirculation, a freeze sensor is connected to  the controller to turn on the pump whenever the 
collector temperature approaches freezing. For sy stems that use a separate freeze sensor, the 
freeze sensor should be placed on the collector pl ate at the middle or bottom of the collector 
(away from the collector inlet) so that it will se nse the coldest temperature of the collector. Another 
option is to turn the pump on manually during freeze conditions. 
Because the pump requires electric power, th is method will fail when a power outage and freeze 
occur simultaneously. At such a time, the collector must be drained manually. 
b) Freeze protection valves 
A freeze protection valve (Figure 5.15), set to op en before freezing temperatures, is installed on 
the collector return plumbing line just beyond where the line penetrates the roof. When the valve 
registers a set temperature, it opens and warm water bleeds through the collector and out the FDUS 853: 2009 
24 © UNBS 2009 – All rights reserved
 valve to protect the collector and collector loop  piping from freezing. Once the valve registers 
warmer temperatures (from the tank water being circulated through the valve), it closes. This 
action is repeated throughout the freezing conditions. The valve may be controlled by a spring-
loaded thermostat or a bimetallic switch. Figure 5.16 shows where a freeze-protection valve is typically located on a solar DHW system. 
 
Figure 5.15 – Freeze protection valves 
 
Figure 5.16 – Location for freeze protection valve 
Freeze-protection valves require water pressure to force water through the valve (and in turn through the 
collector and associated piping) when activated. If these va lves are installed on well water or cistern systems, 
low-pressure relief valves should also be installed on  the system. The valve will  open and drain the collector 
and collector loop when power outages create low pressures. 
A check valve shall be used in all systems with freeze-p rotection valves. They are installed in the collector 
loop return line (See Figure 5.16). To protect the absorber  plate, water must flow through all the pipes. The 
check valve prevents tank water from flowing straight from  the tank to the freeze valve by way of the return 
line, thus bypassing flow through the collector.  FDUS 853: 2009 
© UNBS 2009 – All rights reserved  25
 5.3.4 Thermal mass 
When used in milder climates, inte gral collector storage and batch ty pe solar systems are protected from 
freezing by the large thermal mass in  their collectors. Nevertheless, spec ial care must be taken to protect 
exterior and attic collector loop piping. Any thermal mass protected system c an eventually lose heat and 
freeze. The size of the collector tanks, the climatic and geographical location, local winter temperatures, and 
the length of the freeze all play a factor in det ermining how effective thermal mass will be as a freeze 
protection option. 
5.3.5 Auxiliary heating  
A less commonly used freeze-protection option is to use he at tape or electrical devices that are incorporated 
in the collector and collector loop piping. During freezing periods, these are activated to provide warmth to the 
collector and piping. As in recirculation, this relie s on the continued availability of electric power during 
freezes. 
6  Components for solar water heating systems 
6.1  General 
This clause describes the system components and rela ted control functions that are required to collect, 
transport, store, and convert the sola r energy for typical domestic hot water systems. Active systems need 
controls for pump operation and valves for safety and proper operation. Passive systems utilize many of the 
same components but in some cases for different reasons. Table 6.1 shows the recommended system 
components and related control functi ons that are required for solar  hot water systems (see 5.2.2) 
Table 1 – Solar water heating system components 
Component Function 
1 Solar collector Convert radian t energy into thermal energy 
2 Solar storage tank Accumulate thermal energy in th e form of solar heated water to supply domestic 
needs 
3 Insulation Minimize thermal losses from components 
4 Piping fittings Interconnect compone nts and convey heat transfer fluid 
5 Mixing valve Limit temperature of domestic hot water delivered for personal use 
6 Temperature and pressure relief 
valve Automatically relieves pressure if temperature and/or pressure maxima are 
exceeded 
7 Auxiliary heat source Supplements solar energy to provide adequate hot water 
8 Pump Circulate liquid 
9 Controller Controls the collection and distribution of thermal energy within the solar domestic 
hot water system and may provide limited safety functions 
10 Auxiliary storage tank and heat 
source Supplements solar energy to provide hot water and storage 
11 Heat exchanger (internal or 
external) Transfer thermal energy between physically separated fluids 
12 Air duct Interconnect collect ors and heat exchanger in syst em employing air as transfer 
medium 
13 Blower Circulate air 
14 Expansion tank Protect system from pressure damage created by expansion of heat transfer liquid 
15 Heat transfer fluid Tr ansports thermal energy 
16 Pressure relief valve Automatically re lieves pressure if maximum is exceeded 
17 Check valve Prevent reverse liquid flow 
18 Vent valve Release trapped air 
19 Drain valve To drain fluid passages of liquid; manual or automatic 
20 Backflow preventer To prevent backflow of nonpotable fluid into potable water supply 
21 Vacuum breaker To relieve a vacuum by permitting air into a system 
22 Air damper Control air flow FDUS 853: 2009 
26 © UNBS 2009 – All rights reserved
 23 Shutoff valves To isolate components, manual or automatic 
24 Temperature sensor Senses fluid temperature to operate controller 
 
6.2   Collectors 
Solar collectors capture the sun’s electromagnetic energy and convert it to heat energy. While most direct and 
indirect active systems use flat-plate collectors, so me systems employ evacuated  tube collectors, or use 
collectors that incorporate one or more storage tanks. 
6.2.1 Flat-plate collectors 
Flat plate collectors are designed to heat wate r to medium temperatures (approximately 60 oC). As shown in 
Figure 6.1, flat-plate collectors typi cally include the following components: 
a) Enclosure – A box or frame that holds all the components together. The material is chosen for its 
environmental durability as well as its structural characteristics 
b) Glazing – A transparent cover ov er the enclosure that allows the sun’s rays to pass through the 
absorber. Most glazing is glass but some designs use clear plastic. In general, the sun’s heat energy 
passes quite easily through the glazing as short waves.  Heat energy that re-radiates from the collector 
absorber is in long waves. Glass glazing prevents long waves from passing back through the glazing. 
Glazing also blocks air motion across the absorbe r, thereby reducing heat loss through convection. 
The glazing also serves as a transparent insulation that can be single or multiple layers. The more the 
layers the greater the insulation value, but multiple layers also decrease the amount of light that is 
transmitted through the layers of glazing. 
c) Glazing flame – Attaches the glazing to the en closure. Glazing gaskets prevent leakage around the 
glazing frame and allow for contraction and expansion. 
d) Insulation – Material between the absorber and t he surfaces it touches that blocks heat loss by 
conduction thereby reducing the heat loss from the co llector enclosure. The insulation must be able to 
withstand extremely high temperatures, so insulations like Styrofoam are not suitable. 
e) Absorber - A flat, usually metal surface inside t he enclosure that, because of its physical properties, 
can absorb and transfer high levels of solar ener gy. The absorber material may be painted black with 
a semi-selective coating or it may be electroplated or chemically coated with a spectrally selective 
material (selective surface) that increases its sola r absorption capacity by preventing heat from the re-
radiating from the absorber. 
f) Flow tubes – Highly conductive metal tubes across the absorber through which fluid flows, transferring 
heat from the absorber to the fluid. The heat transf er fluid tubes remove heat from the absorber. The 
collector may also incorporate headers, which are the fluid inlet and outlet tubes. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  27
 
 
Figure 6.1 – Flat plate collector 
6.2.2 Evacuated- tube collectors 
Evacuated-tube collectors generally have a smaller sola r collecting surface because this surface must be 
encased by an evacuated gl ass tube. They are designed to deliver higher temperatures (approximately 150 
oC). The tubes themselves compri se of the following elements: 
- Highly tempered glass vacuum tubes, which function as both glazing and insulation. 
- An absorber surface inside the vacuum tube. The absorber is surrounded by a vacuum that greatly 
reduces heat losses. 
In “flooded” evacuated-tube collectors (Figure 6.2) the absorber itself forms a tube through which the heat 
collection fluid is pumped. Flooded evacuated-tubes are typically used in passive thermosyphon systems. 
In a “heat pipe” evacuated-tube collector (Figure 6.3), a flat absorber plate runni ng the length of the tube 
covers a heat pipe filed with a fluid that evaporates at relatively low temperatures. As the fluid is heated, it 
evaporates and rises to the top of t he tube. There it transfers the heat to water in a manifold. The condensed 
heat-collection fluid then returns by gravity to the botto m of the heat pipe. These systems can be active or 
passive. 
 
Figure 6.2 – Flooded evacuated-tube collector FDUS 853: 2009 
28 © UNBS 2009 – All rights reserved
 
 
Figure 6.3 – Heat pipe evacuated –tube collector 
6.2.3 Integral collectors 
In integral collector storage (ICS) and batch solar water- heating systems, the collector functions as both solar 
absorber and water storage. ICS collectors (Figure 6.4) generally incorporate 10 cm or  larger diameter horizontal metal tanks connected in 
series by piping from a water inlet at the bottom of the t ank to an outlet at the top. The tanks, which are coated 
with either a selective or moderately selective absorb er finish, are enclosed in a highly insulated box covered 
with multiple glazing layers. The mu ltiple glazing layers and selective coatings are designed to reduce the 
heat loss of water stored in the absorber. 
 
Figure 6.4 – ICS collector 
The simplest of all water-heating collectors, a batch co llector (Figure 6.5) usually is made of just one black – 
painted metal tank inside an insulated enclosure covered with some type of glazing. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  29
 
 
Figure 6.5 – Batch collector 
6.3   Storage tanks 
The storage tank holds the water that has been heated by  the collector. The water can be stored in any vessel 
suitable for high temperatures. The tanks can be pres sure rated depending on the application and whether or 
not a back-up heating system is used. 
In subtropical and tropical climates, solar water heating systems usually have a single solar storage tank. This 
tank usually incorporates an electric heating element. Gas water heaters are not usua lly for solar storage. The 
reason for this is that the gas burner is at the bottom of the tank. As cold water enters the tank and activates 
the gas burner, the whole tank is heated and the gas he at reduces the contribution from the solar system. 
When gas water heaters are used for back-up, a thermo syphon or ICS system that preheats water entering 
the gas back-up heater may be used. .A two-tank sys tem may be used where the solar tank preheats the 
water for the gas back-up tank. In colder regions and industrial applications, two tank s may be required to store sufficient solar-heated water 
over very cold or cloudy periods. In these cases a sola r storage tank, to which the solar loop is plumped, is 
connected in a series to an auxiliary water heater or bo iler that has “back-up” electric or gas heating. This 
auxiliary tank or boiler provides hot water in the event there is insufficient solar-heated water. Solar thermal 
systems that supply heated water for applications other than potable domestic water, such as space heating, 
may employ more than one storage tank. The most popular tanks are made of steel with an inner  glass, stone or epoxy lining to protect the steel from 
galvanic corrosion caused by the water’s chemistry. (Dissolved oxygen in the water becomes corrosive to 
untreated steel). Steel tanks also have an internal al uminium or magnesium “sacrificial” anode rod to attract 
the oxygen away from the steel. Stone-lined tanks and st ainless steel or copper tanks normally do not require 
anode rods. Where hard or highly conductive water will be stored in the tank, the anode rod should be replaced 
periodically. Even in areas with good quality water supp lies, the solar storage (an auxiliary) tank should be 
drained periodically to remove sediment build-up. 
Solar storage tanks should be well insulated, especially if they are installed in an air conditioned space. If they 
are installed outside a building, they should also be well protected from environmental conditions and FDUS 853: 2009 
30 © UNBS 2009 – All rights reserved
 corrosion, including ultraviolet degradation, by an ultraviole t (UV) resistant plastic, stainless steel or aluminium 
jacket. Painted steel or powder coated steel jacket ma terials on storage tanks require continuous maintenance 
in coastal or high moisture areas. If the system de sign requires that tanks be buried below ground, they 
should have additional insulation and accessible ports for valves and wiring connections. Heat loss from 
buried storage tanks is accelerated by high water tables or wet ground. Ground conditions should be 
considered in heat loss calculations. 
6.3.1 Single tank systems 
The design of conventional water heater tanks encourages mixing water in the tank, producing a tank full of 
water at the highest selected temperature. For this  reason, natural gas and propane system burners are 
located at the bottom of the tank and conventional electr ic units have heating elements located in both the top 
and bottom third of the tank. 
6.3.1.1 Electric 
Solar systems with single tanks (Fi gure 6.6) are designed to encourage temp erature stratification so that when 
water is drawn for service, it is supplied from the hottest  stratum in the tank (top of tank). For a solar system 
tank that normally contains a heating element, the elem ent is deliberately located at the upper third of the 
tank. The electric element functions as back-up when so lar energy is not available or when hot water demand 
exceeds the solar-heated supply. To fu rther encourage stratification of co ld and hot water in a storage tank, 
the cold supply water inlet is located at the bottom of the tank, as is the opening of  the collector feed tube. In 
addition, the collector return tube opens below the heat ing element, returning the solar heated water to the 
hottest stratum. 
6.3.1.2 Gas 
Gas back-up systems may use passive (thermosyphon or ICS) solar preheating plumbed in series for proper 
operation. Or two separate tanks may be used for acti ve solar systems with gas back-up heating systems. 
The solar storage tank is piped in series to the auxilia ry tank sending the hottest solar preheated water to the 
gas back-up tank. (See Figures 6.8a and 6.8b). 
 
Figure 6.6 – Vertical solar storage tank FDUS 853: 2009 
© UNBS 2009 – All rights reserved  31
 Depending on the system design, solar tanks may be vert ical, as shown in Figure 6.6, or horizontal as shown 
in Figure 6.7.  Stratification is generally better in a ve rtical tank than in a horizontal tank. Yet, aesthetics and 
mounting considerations favour the horizontal tank design if the tank is mounted on the roof as in a 
thermosiphon roof-mounted system. 
 
Figure 6.7 – Horizontal solar storage tank 
6.3.2 Multiple – tank systems 
In two-tank systems (Figures 6.8a a nd 6.8b), one tank provides storage fo r solar-heated water. It is plumbed 
directly to the solar collector and does not contain any back-up heating source. Th is solar storage tank is 
plumbed to a second tank, which cont ains an auxiliary power so urce that can be used when no so lar energy is 
available. This type of configuration is most commonl y used in residential and light commercial applications. 
Larger commercial and industrial solar system storage ta nk strategies can incorporate a single large solar 
storage tank or multiple sm aller solar storage tanks. In these system s, all the tanks are typically plumbed in 
parallel, thereby acting as a single storage mechanism. The fluid flow is balance so an equal amount of water 
enters each of the tanks as hot water is drawn for service. These storage ta nks supply hot water directly to the 
back-up (auxiliary) heater or conventi onal commercial boiler. In certain situations, multiple tank storage 
systems use parallel piping between mo st of the tanks and series piping to a single tank with back-up 
capabilities. 
 
Figure 6.8a – Two-tank solar water heater storage FDUS 853: 2009 
32 © UNBS 2009 – All rights reserved
 
 
Figure 6.8b – Two –tank solar water heater storage 
6.4   Pumps 
An active system uses a pump or circulator (Figure 6.8a)  to move the heat transfer fluid from the storage tank 
to the collector. In pressurized systems,  the system is full of fluid and a circ ulator is used to move hot water or 
heat transfer fluid from the collector to the tank. Pu mps are sized to overcome static and head pressure 
requirements in order to meet specific system design and performance flow rates. (It is advisable to refer the 
pump manufacturer’s pump curve to determine the proper pump size) 
Drain-back and other unpressurized solar water heati ng systems require a high head pump to lift the water 
from the storage vessel to the collector and force the air out  of the collector or collect or array. This requires a 
centrifugal pump or other pump t hat will provide a dequate pressure. 
Most active solar systems use centrifugal pumps . Pump selection depends on the following factors: 
- System type (direct or indirect) 
- Heat collection fluid - Operating temperatures 
- Required fluid flow rates - Friction losses 
The most common pump (circulator) used in solar systems is  the “wet rotor” type in which the moving part of 
the pump, the rotor, is surrounded by liquid. The liquid acts as a lubricant during pump operation, negating the 
need for manual lubrication. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  33
 
 
Figure 6.10 – Pumps used in solar water heating systems 
Pumps used on active direct systems must have bronze or stainless steel housings and impellers to prevent 
corrosion from water chemistry. Simply put, using cast iron pumps in systems in which the potable water 
comes into contact with the pump will cause the cast ir on to rust. Cast iron pumps can be used with certain 
heat transfer fluids used in indirect systems. T able 6.1 lists pump options for various applications. 
Table 6.1 – Pump applications 
Application Pump type and size 
Potable water, pressurized, direct active system Bronze or stai nless steel, low head 
Potable water, pressurized, direct active drain-
down system Bronze or stainless steel, low to medium head 
Potable fluids, unpressurized, drain-back Br onze or stainless steel, low to high head 
Glycol fluids, pressurized Cast iron, low head 
Glycol fluids, unpressurized Cast iron, medium to high head 
 
6.5  Piping 
Piping provides the path for fluid transport in the system. The piping must be compatible with system 
temperatures, pressures and other components. Most sy stems use copper piping because of its durability, 
resistance to corrosion and ability to withstand very high temperatures. Type L, K or M is commonly used, 
depending on the application, local codes and traditions. 
Copper, brass, and bronze are normally the only material s that should be used in active direct solar systems 
using potable water. In cases where galvanized piping already  exists, it should either be replaced, or dielectric 
unions should be used to isolate the different  metals. (refer to galvanised standard) 
6.5.1  Pipe hangers FDUS 853: 2009 
34 © UNBS 2009 – All rights reserved
 When installing-long system piping runs, pipe hanger s are commonly used for support. The piping, depending 
on the type, may be pliable due to high temperatures (t emp ranges shud be included) and therefore, must be 
supported. Since the slope of the piping must be ma intained for proper operation and drainage of many 
systems, pipe hanger are also required to properly orient the pipe runs. 
6.5.2 Solder 
Solder used in system piping shall comply with IS O 9453, ISO 9454 or ISO 12224 depending on the material 
to be soldered. Leaded solder should not be used in potable water system piping. 
6.5.3 Incompatible materials 
Corrosion caused by the contact between dissimilar metals is called galvanic corrosion. Such corrosion 
usually results in an accelerated rate of attack on only one of several dissimilar metals. In the language of the corrosion expert, the protected material – the one that remains virtually unattached – is called the cathode. 
The material that is attacked is called the anode. 
Metals can be listed in a galvanic series that is usef ul in predicting which metals are acceptable for use in 
contact with one another and which materials are likely to be corroded. The following is a simplified galvanic 
table that can be used as a reference source. 
  CORRODED END – ANODIC 
   Magnesium 
    Zinc, Galvanised Steel 
       A l u m i n i u m          M i l d  S t e e l ,  c a s t  i r o n  
         Lead, Tin 
          * B r a s s ,  C o p p e r ,  B r o n z e              *Nickel-Silver, Copper-Nickel Alloys 
             *Monel 
                S t a i n l e s s  s t e e l  
              PROTECTED END – CATHODIC 
The coupling of two metals from differ ent groups will result in accelerated corrosion of the metal higher in the 
series. The farther apart the metals are in the series , the greater the galvanic co rrosion tendency. Material 
groups marked with an asterisk (*) have no strong tendency to produce galvanic action and from a practical 
standpoint are safe to use in contact with one another. 
6.5.4 Pipe insulation 
The most common type of pipe insulation used in solar sy stems is the closed cell flexible elastomeric foam 
type (rubber)(Figure 6.11). Plastic insulation such as po lystyrene or polyethylene should never be used due to 
their low operating temperatures (Figure 6.12). All exterior piping insulation must be protected from 
environmental and ultraviolet ray degradation by using sp ecial ultraviolet ray resistant coatings, paints or 
shielded wraps. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  35
 
 
Figure 6.11 – Rubber insulation being    Figure 6.12 – Plastic insulation should not be used 
installed            used in high temperature or external applications 
6.6   Controls  
6.6.1 General 
In active solar water-heating systems, the controller ac ts as the “brains” of the system. When the controller 
determines that sufficient solar energy is available at the collector, it activates the pump to circulate water to 
the collector and back to the storage tank. The most fr equently used types of controllers include differential, 
photovoltaic and timer. 
Electronic differential temperature controllers are activa ted by sensors that detect the temperatures of the 
collector and the preheat vessel. The main co mponents of a typical control system are: 
a) a power source to provide supplies at the required voltages; 
b) an electrically operated switch to  control the supply to the pump; 
c) temperature sensors to provide signals for operating the control; 
d) a device, such as a bridge circuit, to com pare the signals received from the sensors and to 
operate the pump switch. Control sy stem functions may also include: 
1) preventing excessive cycling of the pump; 
2) operating draindown, mixing and by-pass valves; 3) limiting water storage temperatures to safe values.  
 FDUS 853: 2009 
36 © UNBS 2009 – All rights reserved
 6.6.2 Differential controller 
Differential controllers (Figure 6.13) work in conjunct ion with two sensors (Figure 6.14) – one at or near the 
hottest point of the collector and another near the bottom of the storage tank. When the temperatures 
measured by two sensors reach a preset difference of 5 to 20 oC, the controller starts the pump. On many 
controllers, the installer has the added option of selecti ng the differential setting. For instance, the installer can 
set the differential at 9, 12, 15 or 20 oC depending on the characteristics of the system. For systems with long 
pipe runs, it is suggested that higher temperature diff erentials be used, systems with short pipe runs can use 
smaller differentials. 
When the temperature difference between the sensors fall s to about 3 to 5 oC, the controller stops the pump. 
The off temperature differential is usually set at the factory and cannot be adj usted by the installer. 
 
Figure 6.13 – Differential controller 
Differential controllers commonly have an on, off and au to position switch. In the on position, the sensor 
signals (and their interaction with the controller) ar e ignored and the controller  operates the pump on a 
continuous basis. In the off position,  the sensor signals are also ignored  and the pump remains turned off. In 
the auto position, the sensors and controller in teract to control the operation of the pump. 
Many differential controllers also incorporate a freeze control to activate the pump during freezing conditions. 
A manual adjustment must be made by the installer to ac tivate the freeze control option. Always check the 
manufacturers instructions when installing solar contro llers. Installer selected features may be required to 
activate the controller functions designed into the unit. 
Some differential controller models also incorporate high temperature limit settings that turn the pump off 
when a preset tank temperature has been reached. It is important to remember this is the temperature of the 
sensor at the bottom of the tank – t he top of the tank may be even hotter. 
The sensors used with differential controllers are thermal resistors that change their electrical resistance with 
temperatures. They are commonly called thermistors. Un derstanding the relationship in a thermistor between 
electrical resistance and temperature is quite simple . It works in reverse. When the sensor’s temperature 
increases, its resistance goes down. When its temperature decreased, its resistance increases. 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  37
 
 
Figure 6.14 – Sensors 
Thermistors come in both 10K and 3K –ohm types (K=1000). At 25 oC, a 10K thermistor should have a 1000 
ohms resistance, while a 3K should have a 3000 ohms re sistance. Currently, most controller manufacturer 
use 10K thermistors. A few manufacturers have used  more accurate resistance temperature detectors 
(RTDs).  
Special care must be made to avoid installing sensor wi ring near sharp edges or close to 230V wiring as this 
could adversely affect the performance of the sensors and controller due to electrical interference. In addition, 
exterior runs of sensor wiring should also be protected from environmental degradation. 
6.6.3 Photovoltaic (PV) controller 
In this control scheme, a photovoltaic  module (Figure 6.15) is installed adja cent to the solar thermal collector 
and generates direct current (DC) electricity to pow er a DC pump motor. Because the PV module generates 
electricity only when the sun shines, the pump circulates water to the collector only when sufficient solar 
energy is available. 
 
Figure 6.15 – Photovoltaic module 
To maximize solar collection, some systems also incorporate a pump activator (linear booster) that 
electronically assi sts pump start-up. FDUS 853: 2009 
38 © UNBS 2009 – All rights reserved
 The use of a photovoltaic controller offers increased  heat collection efficiency, as the pump speed is 
proportional to the amount of power generated by the PV module. When more heat energy is available in the 
thermal collector due to increased so lar radiation, the module also rece ives more solar radiation, which 
increases the pump speed sending more heat collecting fluid through the collector. 
6.6.4 Timer controller 
A timer controller (Figure 6.16) turns the pump on onl y during the brightest portion of the day (from 
approximately 9 a.m. to 4:30 p.m.). To  keep the system from losing energy in cloudy weather, the collector 
feed and return lines are connected through a special valve installed in the tank’s common drain port, special 
care must be taken to ensure the valve’s feed and return ports do not accumulate a large amount of sediment 
and scale build-up which could eventually affect system  performance. Routine maintenance of the feed and 
return valve should be observed. 
 
Figure 6.16 – Timer 
6.7   Heat exchangers 
Indirect systems have heat exchangers  that transfer the ener gy collected in the heat-transfer fluid from the 
solar collector to the potable water. Heat exchangers can be either internal  or external to the storage tank. 
Common heat exchanger designs are the tube-in-tu be, shell-in-tube, coil- in-tank, wraparound-tube, 
wraparound-plate and side-arm designs. A technical di scussion of the design and performance of these heat 
exchangers follows. 
6.7.1 Tube in tube 
This type of heat exchanger, as its name implies, cons ists of a tube within in a tube (Figure 6.17). Heat 
transfer occurs when one fluid moves through the inner t ube while a second fluid moves in a different direction 
through the space between the inner and outer tubes. These heat exchangers are most commonly used in 
smaller systems. For example, in an  indirect system using a tube heat exchanger, the collector heat-transfer 
solution would be in the inner tube, while the potable water would be in the space between the inner tube and 
the outer tube. The heat gained at the collector by the heat-transfer fluid would be transferred to the potable 
water passing over the inner tube. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  39
 
 
Figure 6.17 – Tube-in-tube heat exchanger  
6.7.2 Shell in tube (becomes 6.7.1) 
Similar to the tube-in-tube is the shell-in-tube h eat exchanger (Figure 6.18) in which potable water flows 
through multiple tubes while the collect or loop heat-transfer fluid passes over  the tubes through the shell. This 
type of heat exchanger is used in numerous other te chnologies and available in single – or double-wall 
configurations. 
 
Figure 6.18 – Shell-in-tube heat exchanger 
The coil-in-tank heat exchanger (Figure 6.19) is imme rsed in the lower section of the storage tank. The 
wraparound-tube (Figure 6.20) heat exchanger uses tube s welded to the outside of the water vessel. It is 
located on the lower half of the storage tank. The wrapar ound-plate design (double jacket) is similar to the 
wraparound-tube but it uses a separate plate wel ded around the lower half of the storage tank. FDUS 853: 2009 
40 © UNBS 2009 – All rights reserved
 
 
 Figure 6.19 – Coil-in-tank type heat exchanger  Figure 6.20 – Wraparound type heat exchanger 
A side-arm heat exchanger is a tube-in-shell design that  can be installed on the side of the storage tank to 
allow thermosiphoning of the water from the storage t ank through the heat exchanger. The heat transfer fluid 
in the solar loop side of the heat exchanger heats the water in the shell side of the heat exchanger and heat 
exchange initiates the thermosiphon action between t he water storage (potable) and the heat exchanger. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  41
 
 
Figure 6.21 – Side-arm heat exchanger 
6.7.3 Single and double-wall heat exchangers 
Heat exchangers may have one or two walls (Figure 6.22) . Double-wall heat exchangers have two walls that 
separate the heat-transfer fluid from the potable water.  Double-wall heat exchangers often incorporate small 
passageways between the two walls to provide leak detec tion. An area between the two walls allows leaking 
fluid to pass outside, thereby revealing any leaks. In the event a leak occurs, system owners or service 
personnel can visually see the fluid flowing out from these passageways. 
Whether a single-or double-walled exchanger is used dep ends on the heat-transfer fluid used in the system. 
Nontoxic fluids such as propylene glycol can be us ed with a single-walled heat exchanger. But ethylene 
glycol, a toxic fluid, should be used only with a double-walled heat exchanger. FDUS 853: 2009 
42 © UNBS 2009 – All rights reserved
 
 
Figure 6.22 – Single – and double-wall heat exchangers Heat exchanger materials 
Heat exchanger materials must be compatible with the system’s fluid and piping. These materials can be 
steel, aluminium, bronze, stainless stee l or cast iron, but copper is by fa r the most common. Copper prevents 
corrosion and also acts as a good thermal conductor. Alloys of copper and nickel may also be used for 
aggressive or hard water areas. 
6.7.4 Plate Heat exchanger  
A plate heat exchanger is a type of he at exchanger that uses pressed corrugated metal plates to transfer heat 
between two fluids. These metal plates are fitted between  a thick, carbon steel fr ame.  Each plate flow 
channel is sealed with a gasket, a weld, or an alternati ng combination of the two.  Plate heat exchangers have 
overall heat transfer coefficients that are 3-4 ti mes those found in shell and tube heat exchangers. 
 
6.7.5 Heat exchanger efficiency 
Systems with heat exchangers can experience a 10 – 20 % loss  in total efficiency in the transfer of heat from 
the collection loop to the stored water. However, economic  savings and fail-safe freeze protection may offset 
that efficiency loss. For example, heat exchange systems c an use corrosion-inhibiting heat-transfer fluids that allow the use of 
less-expensive aluminium or steel in collectors, exchangers and piping. If aluminium is used anywhere in the 
system, no red metal (copper, brass or similar alloys) should be used unless the heat transfer fluid is non-ionic FDUS 853: 2009 
© UNBS 2009 – All rights reserved  43
 or an ion trap is placed upstream of each aluminium component to reduce galvanic corrosion. Ion traps 
require periodic servicing. 
6.7.6 Heat exchanger sizing 
Heat exchangers are sized ba sed on their heat-t ransfer capabilities, flow ra tes and the temperatures of 
incoming and outgoing fluids. For packaged and approved or  certified systems, the manufacturers have sized 
the heat exchanger and matched its performance to the collector array and flow rates of the system. Under 
sizing the heat exchanger is a comm on mistake of home-built systems. 
6.8  Heat-transfer fluids 
All solar systems use some types of heat -transfer fluid. Potable water is the heat-transfer fluid in active direct 
systems and is the most co mmon. Indirect systems in cold climates  use a non-potable solution that will freeze 
only at extremely low temperatures. The most common of these fluids are: 
- Propylene glycol 
- Ethylene glycol 
- Hydrocarbon oils 
- Synthetic oils such as silicone 
Glycols are the most commonly used heat-transfer solution s for indirect systems. Special inhibitors are added 
to the glycol during the manufacturing process to prevent the fluid from becoming corrosive. Thus glycol fluids 
must be checked periodically (follow manufacturers instru ctions) to ensure they rema in chemically stable. PH 
tests of the glycol can be conducted using either pH  test strips or standard pH testing color charts. 
When using glycol, materials, such as gaskets and s eals used in the various system parts (pumps, valves, 
expansion tank, etc), must be compatible. Glycol compatible materials include Teflon, Viton and EPDM. The 
use of certified systems will assure that all system components and materials are compatible. 
In some cases, the glycol is mixed or diluted with distilled or demineralised water during the system charging 
process. As always, follow the manufacturer’s reco mmendations. Some heat transfer fluids should not be 
diluted since dilution can change the level of freeze protection. 
Synthetic and silicon oils have unique characteristics.  Both have long lifetimes and require little maintenance. 
Their toxicity is also low. Nevertheless, the lower th ermal conductivity and viscosity of these oils increase 
pump and heat exchanger requirements. As in the ca se of glycol, one must pay special attention to 
component material selection and their compatibility with t he specific oils. The surface tension of oils is very 
low so sometimes leaks can be a recurring problem. Special care must be taken to avoid mixing any water 
with oils. 
 6.9  Expansion tank 
Most indirect systems that use a heat transfer fluid other than water also incorporate an expansion tank 
(Figure 6.23). As the heat-transfer fluid temperature rise s, it expands. The expansio n tank provides room for 
this change in volume. Inside the expansion tank, a flexible bladder maintains a constant pressure on the fluid 
while allowing it to expand and contract as it he ats and cools. The expansion tank prevents damage from 
over-pressurization and eliminates the potential creation of a vacuum inside the collector loop. 
Expansion tanks are normally pre-char ged by the manufacturer to a set pressure level. The system pressure-
relief devices provide overpressure protection. The size of the expansion tank depends on the volume of fluid 
in the system and the rate of fluid expansion at higher temperatures. The higher the temperature the more the 
fluid expands. The size of the expansion tank must a llow for the total potential expansion of the fluid or 
elevated pressures will be experienced causing the pressure relief valve to open and result in complete 
pressure loss in the solar loop. Some solar water heating systems have an expansion tank on the cold water 
supply line when a check valve or back-flow pr evention device is on the cold-water line. FDUS 853: 2009 
44 © UNBS 2009 – All rights reserved
 
 
Figure 6.23 – Expansion tank 
6.10  Valves, gauges and meters used in solar water heating systems 
As indicated in Figure 6.24, a variety of valves, gauges  and meters can be incorporated as part of a solar 
heating system’s design. T hese components serve to: 
- Expel and vent air from the system (air vents) 
- Safety limit excessive temperatures and pressu res (pressure relief and temperature-pressure relief 
valves) 
- Prevent vacuum locks during drainage (vacuum breakers) - Isolate parts of the sy stem (isolation valves) 
- Prevent thermosiphon heat losses and maintain flow direction (check valves-mechanical and 
motorized) 
- Provide freeze protection (freeze-prevention valve) 
- Monitor the system (pressure gauges, temperature gauges and flow meters). 
 
Figure 6.24 – Solar water heating syst em valves and monitoring equipment FDUS 853: 2009 
© UNBS 2009 – All rights reserved  45
 6.11  Air vent 
This valve (Figure 6.25) allows air that has entered the sy stem to escape, and in turn prevents air locks that 
would restrict flow of the heat-transfer fluid. An air vent must be positioned vertically and is usually installed at 
the uppermost part of the system. In active direct syst ems supplied by pressurized water, an air vent should 
be installed anywhere air could be trapped in pipes or colle ctors. Indirect systems that  use glycol as the heat-
transfer fluid use air vents to remove any dissolved ai r left in the system after it has been pressurized or 
charged with the heat-transfer fluid. (Once the air ha s been purged in these indirect  systems, the air vent 
mechanism is manually closed.) 
A popular option to using a separate air vent and vacuum  breaker, when both are required, is a combination 
air vent and vacuum breaker valve. 
Manual air vents should be used in indirect systems to avoi d any loss of heat-transfer fluid, which would affect 
the system’s pressurized. Using a man ual air vent that the installer opens during charging to relieve trapped 
air in the loop will not only vent trapped air, but once the air has been expelled and the installer then closes 
the vent, it will in turn prevent any additional venti ng from the system. If an autom atic, instead of manual air 
vent is used, the dissolved air bubbles that had accumu lated during the charging process will eventually vent 
through the automatic air vent causing the system l oop to lose pressure. Some automatic air vents have a 
dust cap that can be closed to prevent additional venting or loss of pressure. 
 
Figure 6.25 – Air vent 
6.12   Temperature – pressure relief valve 
A temperature-pressure relief valve is also called a pr essure-temperature relief valve or P&T valve or T&P 
valve. These names are used interchangeably in the i ndustry. This valve (Figur e 6.26) protects system 
components from excessive pressures and temperatures . A pressure-temperature relief valve is always 
plumbed to the solar storage (as well as auxiliary) ta nk. In thermosiphon and ICS systems, where the solar 
tanks are located on a roof, these tanks may also be equi pped with a temperature-pressure relief valve since 
they are in some jurisdictions considered storage vessel s. These valves are usually set by the manufacturer at 
1034 kPa and 100 oC. Since temperature pressure relief valves open at temperatures below typical collector 
loop operating conditions, they are not commonly install ed in collector loops. (See pressure relief valves 
below). Temperature-pressure relief valves located in side a building must drain to the outside. If uncertain, 
follow local code requirements. 
 
Figure 6.26 – Pressure-temperature relief valve FDUS 853: 2009 
46 © UNBS 2009 – All rights reserved
 6.13   Pressure relief valve 
A pressure relief valve (Figure 6.27) protects compon ents from excessive pressures that may build up in 
system plumbing. In any system where the collector l oop can be isolated from the storage tank, a pressure 
relief valve must be installed on the collector loop. The pr essure rating of the valve (t ypically 862 kPa) must be 
lower that the pressure rating of  all other system components, wh ich it is installed to protect. 
The pressure relief valve is usually installed at the collector. Because it opens only with high pressure, it 
operates less frequently than does a temper ature-pressure relief valve. For this reason, it offers a higher 
degree of reliability and is the valve of choice for protecting the solar collec tor. Indirect systems typically use 
pressure-relief valves with lower pressure settings. Pres sure relief valves located inside a building should be 
piped to discharge to a safe location. 
 
Figure 6.27 – Pressure relief valve 
6.14   Pressure gauge 
A pressure gauge (Figure 6.28) is used in indirect syst ems to monitor pressure within the fluid loop. In both 
direct and indirect systems, such gauges can readily indi cate if a leak has occurred in the system plumbing. 
 
Figure 6.28 – Pressure gauge 
6.15   Vacuum breaker 
A vacuum breaker (Figure 6.29) admits atmospheric pressu re into system piping, which allows the system to 
drain. This valve is usually located at the collector outlet plumbing but also may be installed anywhere on the 
collector return line. The vacuum breaker ensures prop er drainage of the collector loop pluming when it is 
either manually or automatically drained. A valve t hat incorporates both air vent and vacuum breaker 
capabilities is also available. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  47
 
 
Figure 6.29 – Vacuum breaker 
6.16   Isolation valves 
These valves are used to manually isol ate various subsystems. Their primary use is to isolate the collectors or 
other components before servicing. Two common types of isolation valves are ball valves (Figure 6.30) and 
gate valves (Figure 6.31) 
 
Figure 6.30 – Ball valve 
 
Figure 6.31 – Gate valve FDUS 853: 2009 
48 © UNBS 2009 – All rights reserved
 Ball valves provide a complete flow barrier and are less likely than gate valves to l eak, corrode or stick. Ball 
valves may also be used as flow balancing valves in multiple collector arrays. Three-way ball valves may be 
used for both isolation and draining at the collector loop. An isolation valve is also required in the cold-water 
service line in the event water flow to th e storage tank and system must be stopped. 
6.17   Drain valves 
These valves (Figure 6.32) are used to drain the collect or loop, the storage tank and, in some systems, the 
heat exchanger or drain-back reservoir. In indirect sy stems, they are also used as fill valves. The most 
common drain valve is the standard boiler drain or hose bib. 
 
Figure 6.32 – Drain valve 
6.18   Check valves 
Check valves allow fluid to flow in only one direction. In solar systems, these valv es prevent thermosiphorning 
action in the system plumbing. Without a check valve, water that cools in the el evated (roof-mounted) collector 
at night will fall by gravity to the st orage tank, displacing lighter, warmer water out of the st orage tank and up 
to the collector. Once begun, this thermosiphoning acti on can continue all night, continuously cooling all the 
water in the tank. In many cases, it may lead to the activation of the backup-heating element, thereby causing 
the system to lose even more energy. 
The various types of check valves include motorized, ve rtical and horizontal swing. A motorized check valve 
(Figure 6.33) is wired to the pump. When the pump is  on, the valve opens; when the pump is off, the valve 
closes and forms a positive seal. 
 
Figure 6.33 – Motorized check valve 
Vertical check valves (Figure 6.34) must open easily wi th activation of low-flow, low-head PV-powered pumps 
used in some solar systems. The seat of these va lves should resist scal e and high temperatures. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  49
 Horizontal swing check valves (Figure 6.35) must be installed horizontally becau se gravity and the flapper’s 
weight close the valve. 
 
Figure 6.34 – Vertical check valve 
Corrosion and scale may build up on the internal compone nts of any (motorized, vertical or horizontal) check 
valve; therefore, a regular service schedule should be maintained. The chemical makeup of the local water 
supply is a major determinant in how sc ale build-up affects system components. 
 
Figure 6.35 – Horizontal swing check valve 
6.19   Mixing or tempering valve 
This valve will mix cold water with the hottest wate r from the storage tank, de livery water at a preset 
temperature. Such a valve increases the total amount of hot water available. The intended use of this valve is 
to conserve hot water – not as a safety device (Figure 6.36). 
 
Figure 6.36 – Tempering valve FDUS 853: 2009 
50 © UNBS 2009 – All rights reserved
 6.20   Anti-scald valve 
An anti-scald valve (Figure 6.37) also mixes cooler water with hot water to deliver water at a preset 
temperature. However, unlike a mixing valve, an anti-scald valve also functi ons as a safety device, closing off 
the flow into the house if the hot or cold mixing supply fails. 
 
Figure 6.37 - Anti-scald valve 
6.21   Freeze-protection valves 
Freeze-protection valves (Figure 6.38), are set to open at near freezing temperatures, and are installed on the 
collector return line in a location close to where the line penetrates the roof. Warm water bleeds through the 
collector and out this valve to protect the collector a nd pipes from freezing. A spring-loaded thermostat or a 
bimetallic switch may control the valv e. Figure 6.39 shows wher e a freeze-protection valve is typically located 
on a solar system. 
 
Figure 6.38 – Freeze-protection valves 
 
Figure 6.39 – Location for freeze-protection valves FDUS 853: 2009 
© UNBS 2009 – All rights reserved  51
 A check valve must be used in all systems with freeze-p rotection valves. This check valve prevents tank water 
from going straight from the tank to the freeze valve, thus bypassing flow through the collector. 
If these valves are installed on well water or cistern sys tems, low-pressure valves should also be installed, 
which enable freeze protection to function when power outages create pressures. 
6.22   Other components 
The following components are not as crucial to system operation as the previously listed valves, but they do 
provide the homeowner and service tec hnician with important information. 
6.22.1 Temperature gauges 
These gauges (Figure 6.40) provide an indication of sys tem fluid temperatures. A temperature gauge at the 
top of the storage tank indicates the temperature of th e hottest water available for use. Temperature wells 
installed at several points in the system will allow t he use of a single gauge in ev aluating system operation. 
 
Figure 6.40 – Temperature gauge 
6.22.2 Flow meters Flow meters (Figure 6.41) enable the owner and service person to determine if the pump is operating and, if 
so, at what flow rate. The flow mete r is usually located in the collector feed line above the pump to protect the 
meter from extreme temperatures. 
 
Figure 6.41 – Flow meter FDUS 853: 2009 
52 © UNBS 2009 – All rights reserved
  
6.23  Water supply 
While not necessarily a component of a solar water heat ing system, the method for cold water supply to the 
system can influence both system se lection and operation. Most solar water heating systems must operate 
under pressure. Pressure is supplied though the servic e water entering from the municipality, a pressure 
pump on the water system of the building (well, cistern), or pressurized by an elevated cold-water supply tank 
mounted above the solar heating system. 
NOTE:  The water supply tank should be mounted at least two meters from solar heating system. 
7   Design considerations 
7.1  General 
The main requirements of a solar heatin g system are that it should absorb solar energy efficiently and transmit 
the heat so generated with a minimum of loss to a storage unit ready for use.  In addition, it should be 
sufficiently durable to have a useful life comparable with that of other building services equipment, and require 
a minimum of maintenance. This clause mainly covers  those features of component and system design that 
promote durability and reliability. Design factors that affect the thermal performance of a system are discussed 
in Clause 8. System design considerations are similar to those concerning other parts of hot water systems in 
respect of compatibility of materials, freedom from le akage and air locks, and other matters on which good 
practice is already well established. Additional consider ations that apply to solar heating systems are mainly a 
consequence of the exposure of part s of them to the outdoor environment and the extremes of temperature 
that result from this. Freezing and boiling in collector s are hazards to which refe rence has already been made. 
A further consequence is the high temperature that ma y be reached by an absorber at times when there is no 
fluid flow through it. This may occur on drainback duri ng normal operation, on shut-down for maintenance, or 
even during installation. Under these conditions the plat e temperature may approach 150 °C if it has a neutral 
black absorbing finish or 200 °C if the finish is hi ghly selective, and these values are recommended for design 
purposes. The corresponding temperature for the front cover may approach 100 °C, and when more than one 
cover is fitted, the inner ones may re ach temperatures greater than this. 
Having an exposed surface, the collector of  a solar heating system is subject to wind loading. The fixtures that 
support the collector shall withstand these loads, together  with the weight of the collector. They shall also 
transfer the loads safely to the roof members or other foundations without impairing the weather tightness or 
strength of the stru cture. (See Annex B.) 
7.2   Collector design considerations 
7.2.1 Materials 
Properties of importance in the selection of materials for collectors are thermal properties and durability. Of 
the thermal properties, the thermal conductivity deter mines such design features as the absorber plate 
thickness and fluid passage spacing, whilst the heat ca pacity affects the rate of response to intermittent 
sunshine (see also Clause 8). Durability requirements will need to take account of the effects of the outdoor 
environment (solar radiation, wind loading, hail impact, et c.), thermal effects (expansi on and contraction, frost, 
etc.), corrosion and stressing (in situ and handling duri ng installation, etc.). Capillary fittings employing low 
temperature soft solders are not suitable for use when directly attached to, or in contact with, collectors. 
Manufacturers should be consulted on suitable high temperatur e solders for this duty. Absorber plates shall be 
leak and pressure tested as described in Annex E. Each  absorber plate or collector shall be marked with the 
maximum working pressure (see E.2.1). 
Methods of type testing for assessing the resistance of collectors to adverse conditions are described in 
Annex F. NOTE: Materials used should be environmentally friendly. 
7.2.2 Heat transfer and flow rates FDUS 853: 2009 
© UNBS 2009 – All rights reserved  53
 The collection efficiency of a solar collector decreases with increasing temperature and therefore systems are 
generally designed to give good heat transfer to the fluid and rapid thermal response. 
To ensure adequate efficiency of heat removal, flow rate s in the region of 0.01 to 0.02 kg/s per square metre 
of collector area are found to be satisfactory, when the flui d is water or water based. For other fluids, the flow 
rate is likely to be higher, and the manufacturer of  the fluid should be consulted. (See also Clause 8.) 
7.2.3 Insulation 
The reverse side of an absorber plate often has a bright surface of low emittance, but it is desirable to provide 
additional insulation to reduce heat loss. Since solar absorber plates can, under shut-down conditions, reach 
temperatures approaching 200 °C, care should be taken to select insulating materials that will tolerate these 
temperatures without degradation. Some insulating mate rials give off vapours at el evated temperatures which 
can condense on the underside of the cover and reduce tr ansmission of solar radiation. As a design rule-of-
thumb, the total thermal conductance between the back of the absorber plate and the rear of the collector 
should not be more than 1.5 W/(m2.K); appreciably lower values could be justified for collectors having 
selective absorber coatings or more than one cover. W here collectors are built into roof spaces, it may be 
necessary to provide sufficient back and side insulation to  protect the other roofing material (such as wooden 
roof trusses, boarding and felts) and, in  addition, to ens ure that the insulation properties of the roof continue 
to comply with the requirements of building regulations. 
7.2.4 Absorber coatings 
Paints are often used to provide the surface finish on abs orber plates. Some form of pre-treatment of the plate 
surface is usually necessary to ensure satisfactory paint adhesion during the repeated thermal cycling that 
occurs in service. The paint manufacturer's advice sha ll be sought so that the pre-treatment and finish are 
compatible with the expected service conditions. 
7.2.5 Collector box 
An externally-mounted collector shall be weather tight and sufficiently strong and stiff to withstand the forces 
applied to it in service and during installation withou t mechanical failure, breakage of glass or damage to 
weather seals. 
Methods of calculating the forces applied to the collect or box by wind and snow l oads are given in Annex B. 
Arrangements for supporting the covers shall include adeq uate provision for thermal expansion, and particular 
care shall be taken to ensure that cove rs will not be caused to fail from t hermal stress due to cooling at the 
points of support. The collector box shall be so designed as to prevent  the retention of excessive  quantities of internal 
condensation, which can impair the effectiveness of insulation and lead to corrosion or degradation of the 
absorbing surface.  Unless special provision has been made to ensure that the collector will remain 
hermetically sealed throughout its workin g life, the internal spaces shall be vented to the atmosphere by holes 
situated at the lowest portion of the box, so as to allow drainage of any condensed moisture. In addition to the 
drainage holes at the bottom, other holes may be require d to provide ventilation of the insulation and of the 
space below the cover. Holes should be so placed or shiel ded as to preclude the ingress of wind-driven rain or 
snow. 
7.2.6 Covers for solar collectors 
The following physical and chemical properties are desi rable in materials used for the construction of covers 
for solar collectors: 
a) high transmission of visible and near in fra-red radiation of wavelength up to 2.4 µm in order to 
maximize the input of solar radiation; 
b) low transmission of infra-red radiation of wavele ngth exceeding 3 µm in order to minimize heat losses; 
c) good resistance to degradation by sunlight FDUS 853: 2009 
54 © UNBS 2009 – All rights reserved
 d) good resistance to chemical degradation and env ironmental stress cracking when subjected to 
contact with rainwater, atmospheric pollutants, detergents used for cleaning, or any other materials 
with which the cover may reasonably be expected to come into contact (e.g. sealant, paint splashes); 
e) tolerance to high and low temperatures wit hout significant embrittlement or softening; 
f) hard surface (to facilitate cl eaning without surface damage); 
g) high impact resistance (to resist  accidental or malicious damage); 
h) appropriate  fire resistance; 
i) sufficient strength to withstand wind a nd hailstorms as indicated in Annex B. 
Glass or appropriate plastics materials may be used as  cover materials. Many variants of basic plastics have 
been formulated to satisfy special requirements. The manufacturers/suppliers should always be consult ed to ensure that materials used for covers are of a 
suitable type and grade in relation to factors (a) to (i) in this clause. 
7.3  System design considerations 
7.3.1 Plumbing and flow rates 
Some of the components used in a solar preheati ng system may be selected from existing products 
developed for other heating applications, but care shoul d be exercised. Help should be sought from 
manufacturers to ensure that the components will be suitable for the temperatures, pressures and other 
conditions found in solar heating system s. Particular attention is drawn to the high temperatures that may be 
experienced by cisterns and float valv es connected to the collector circuit. 
The system plumbing should be designed to ensure t hat there is an approximately equal fluid flow through 
each collector in an array, and that adeq uate air bleeding facilities are provided. 
Flow velocities shall be less than 1 m/s and in any event  they shall not exceed 2 m/ s, since excessive flow 
velocity can give rise to noise and erosion (Note: m/s – meters per second). 
7.3.2 Pressure relief and venting 
Vent pipes, pressure relief valves and automatic ai r bleeding devices on the collector circuit shall be so 
arranged that vapour or heat transfer fluid esc aping from the system c an be safely discharged. 
A free fluid path from the collectors to a safety valve or expansion vessel shall be provided. This path shall not 
contain a non-return valve, and if it is  necessary that it should contain a sh ut-off device, this shall be protected 
from accidental closure (e.g. by means of a wire and seal). 
Sealed systems shall be fitted with a pressure relief valve and a pressure gauge.  
7.3.3 Components and fittings All materials, fittings and components used shall comp ly with the requirements of the relevant Uganda 
Standards listed in Clause 2 and those given in the Bibliography. Among the standards relating to the potable 
water side of the system are those listed in Table 7.1, though the list  is not exhaustive. 
In direct systems, where t he heat transfer fluid is mains water, the metals and connectors used in the solar 
collector circuit shall be wholly suitable for potable wate r applications and no other less suitable materials shall 
be used. 
7.3.4 Collector mounting  FDUS 853: 2009 
© UNBS 2009 – All rights reserved  55
 Collectors are mounted in various ways, the most co mmon arrangement being mounting above, and parallel 
to, a slated or tiled roof, with clearance between the botto m of the collector and roof cladding to allow rain to 
run off normally and to avoid accumulation of leaves and other debris at the upper edge. Mounting in direct 
contact with tiles and slates may be convenient, but this  provides less clearance for the runoff of rain and 
debris and can impose loads on the cladding which it has not been designed to accept. Sometimes, the 
cladding is removed or omitted and collectors are mount ed with the exposed surface more-or-less flush with 
the roof. Collectors are also sometimes bu ilt into the roof behind patent glazing. 
7.3.5 Patent glazing 
Where collectors are integrated into roof structures u nder patent glazing, reference should be made to ISO 
16932. Particular regard should be paid to minimization of thermal stress in the glass, which will be subject to 
a wider range of operating temperature than in normal us e. Consultation on this point with the manufacturers 
is advised. (See also 7.2.6(e).) 
7.3.6 Weather resistance 
Where the system is attached to, or forms an integral part of, a wall or roof, the positioning and method of 
attachment to the building shall be such as not to im pair the weather tightness and resistance of the building 
to moisture penetration into any part that would be adversely affected by such moisture. (See Annex A.) 
7.3.7 Structural safety 
The method of fixing and the fixtures used to attach the system to the building shall be adequate for their 
purpose during the life of the building. The forces t hat the wind exerts on a collector depend on how it is 
installed on the roof. Procedures are outlined in Annex B for determining the highest loads likely to be 
experienced by collectors installed in various ways. It should be recognized that the collector fixtures can be 
subjected to a component of force tending to lift the co llector from the roof. However, it will usually be the 
components acting parallel to the roof that determine the strength and type of fixtures required. Fixtures shall 
need no maintenance during the service life of the collector. In addition to the primary loads referred to in this clause, they shall be designed to withstand other effect s such as bending due to variation in wind forces and 
differential thermal movement, abrasion against roof t iles and other nearby materials, and corrosion due to 
rain and accumulated debris. 
The addition of the system to a building shall in no wa y impair the ability of the building structure to withstand 
the combined dead load, wind load and imposed loads expe cted during the building life. (See Annexes A and 
B.)  
Table 7.1 – Some relevant standards for components and fittings 
Feed and expansion cisterns and ex pansion vessels BS 417, BS 4213, BS 4814 
Tanks and cylinders BS 1566-1, BS 1565, BS 3198 
Pumps                                                                           ISO 9906 
Valves                                                                           BS EN 12288 
Pipework and fittings 
British Standards applicable to pipes and pipe fittings include the following  
Form and material BS designation Type and application 
Tubes 
Copper 
Plastics 
    ABS  
BS EN 1057 
 
ISO 15493  
Hot and cold water services 
 
Cold water services FDUS 853: 2009 
56 © UNBS 2009 – All rights reserved
     PP 
    Unplasticized PVC 
    HDPE 
Stainless steel ISO 15874 
ISO 4422 
ISO 4427 
ISO 7598 Hot and cold water services 
Cold water services 
Cold water services 
Hot and cold water services 
Fittings 
Copper and copper alloy 
Malleable cast iron and cast copper 
alloy 
Unplasticized PVC 
ABS 
  
BS 864-2 
ISO 49 and ISO 4144 
 ISO 16422 
ISO 727-1  
(capillary and compression) 
Hot and cold water services (compression) 
Cold water services (screwed pipe fittings) Hot and cold water services 
Cold water services 
Cold water services 
 
7.3.8 Fire resistance 
The addition of the system on to the walls or roof of a building should in no way impair the fire resistance of 
the element to which it is attached. Where the collector forms an integral part of an element of a building, the 
following minimum requirements apply. 
a) When wall-mounted, the collector, together with  any back-up walling, is required to have a fire 
resistance of a specified period. 
b) When roof-mounted, the collector, in conjunction with any back-up r oof construction, is required to 
comply with ISO 3008. 
c) Where pipes pass through a separating wall or floor, protected structure or cavity barrier, they shall be 
adequately fire-stopped, without inhibiting movement due to thermal expansion. 
7.3.9 Thermal insulation 
Where the system forms an integral part of either the r oof or external wall of a building, it shall be thermally 
insulated to a standard not less than that of the surrounding  parts of the roof or wall in which it is situated. In 
addition, where the system is installed in a roof spac e above a heavily insulated ceiling, the pipe insulation 
should protect the system from fros t conditions. Selection of thermal in sulation for building applications and 
equipment shall be done in accordance with ISO 9774 and ISO 13787. (See also Annex C.) All tanks, 
cisterns, cylinders, pipes, etc. should be well insulat ed using insulation board, petal jackets, or other 
conventional or proprietary  systems. (See ISO 8873.) 
7.3.10 Bio-deterioration 
The system should be constructed and installed in such a way as to inhibit the entry of small mammals, birds 
and large insects. Particular care will be required at collector vent holes and at holes where pipes or wires 
pass through the building fabric and the collector box. Ma terials which are likely to be adversely affected or 
attacked by organisms such as fungi, mosses, bacteria an d insects should be used only if suitably treated in 
accordance with the relevant standards listed in Clause 2. 
7.4  Corrosion protection 
7.4.1 General  
Corrosion in metals in a solar water heating system may occur both internally within the fluid passages of the 
collector and system pipe work and externally on the su rfaces of the collector box  and absorber plate. Two 
main forms of corrosion need to be guarded against in solar heating systems: bimetallic corrosion and pitting 
corrosion. External components should be of corrosion-resistant materials, and liability to bimetallic corrosion 
should be reduced wherever possible. (See ISO/TR 10217, ISO 4952, ISO 11303, ISO 11972.) FDUS 853: 2009 
© UNBS 2009 – All rights reserved  57
 7.4.2 Bimetallic corrosion 
Bimetallic corrosion normally occurs at the interfac e between two dissimilar metals when in contact with an 
electrolyte. Internal corrosion rates can be slowed subs tantially by using a non-electrolyte fluid or by using 
suitable inhibitors. Insulated couplings are sometimes used also to reduce external corrosion at joints between 
dissimilar metals. Their action will be adversely affect ed if there are external co nducting paths between the 
dissimilar metals. The possibility of this occurring through earth bondi ng should not be overlooked (see 9.2). 
7.4.3 Pitting corrosion 
Pitting corrosion normally occurs where the fluid transpor ts particles of one metal, either in suspension or 
solution, and deposits them on to another metal in the presence of an electrolyte. This type of corrosion can 
be reduced by using suitable corrosion inhibitors or by using a non-electrolyte fluid. Pitting corrosion may also 
be caused by the effects of microorganism growth, and th is can be reduced by the use of suitable biocides. 
7.5   Heat transfer fluids 
7.5.1 General 
Temperatures in solar heating systems using flat plate co llectors can vary from about -15 °C to as high as 200 
°C when the heat transfer fluid is not circulating. Th e possibility of such a range of temperatures should be 
taken into account in the design of solar heating syst ems and in the selection of the heat transfer fluid. 
Agreement of the Environment and Water supply authorit ies to the use of fluids other than potable water 
should be obtained. 
7.5.2 Aqueous fluids 
Water has good heat transfer characteristics and is often used as a base for heat transfer fluids in solar 
heating systems. Supply waters, however, vary greatly in  corrosion properties, and it is sometimes necessary 
to use distilled or deionised water. It may be necessary to add i nhibitors, formulated to protect all metals in the 
system from corrosion. These inhibitors deteriorate in  use and need to be renewed from time to time. Some 
inhibitors may be liable to degradation due to boiling.  Anti-freeze additives are also used, but it should be no ted that certain of these are toxic and/or corrosive and 
may not be acceptable to the water undertaker. 
7.5.3 Non-aqueous fluids 
Non-aqueous fluids, such as oils, can be used as the heat transfer fluid. The fluids shall be chosen to be 
compatible with the materials used in the collector ci rcuit and should contain de-oxidants, dehydration agents 
and biocides as necessary. Compatibility with pump gl ands and seals shall be determined. Because of the 
wide range of specific requirements of non-aqueous fluids , particularly in respect of the use of appropriate 
expansion vessels, the operating temp erature range and protection of potable water from contamination, it is 
recommended that the manufacturer's advice be sought w hen selecting these fluids.(standards on these fluids 
should be referenced) 
7.6  Controllers and temperature sensors 
7.6.1 Safety aspects 
Controllers for solar water heating systems shall be capabl e of meeting the safety requirements specified in 
EAS 205. 
7.6.2 Performance 
The switching temperature differentials shall remain with in the manufacturer's specif ication over both the full 
operating temperature range of the sensors and the range of ambient temperatures. Details of test methods 
for checking the performance of differential temper ature control systems are given in Annex G. FDUS 853: 2009 
58 © UNBS 2009 – All rights reserved
 NOTE  A controller may be called upon to perform at many as 100 000 operations and an ancillary valve 10 
000 operations during the life of the system. 
7.6.3 Electrical interference 
Electrical noise picked up through the sensor leads, the mains leads or otherwise shall not alter the specified 
switching temperature differentials. 
Control systems shall not generate an am ount of electrical interference (see 9.5) which is sufficient to affect 
other electrical equipment. 
7.6.4 Indicators 
Control systems should preferably be fitted with indicato r lights showing the status  of each control function 
(see 6.6). 
7.6.5 Marking and information 
A controller shall comply with the marking requirements given in EAS 205. 
7.6.6 Temperature sensors 
Methods of attachment of temperatur e sensors shall ensure that  the sensor is in good thermal contact with the 
component the temperature of which is to be sens ed, and that the attachment will remain secure. 
It is recommended that sensors shoul d not be directly immersed in water unless specially designed for 
immersion. 
Temperature sensors attached to water stores shall be able to withstand temperatures in the range of 5 °C to 
100 °C. 
Collector temperature sens ors and their associated wiring shall be able to withstand the temperature 
recommended in 7.1, without long term deterioration or dr ift in calibration. Connections in sensor leads should 
preferably not be made outdoors. However,  if outdoor connections are unavoi dable, waterproof junction boxes 
shall be used. Where matched sensors are supplied, these need to be used together. If failure of one occurs, 
replacement of both may be necessary. 
7.7  Other design factors 
Design features that affect the overall thermal perform ance of the system are disc ussed in Clause 8, where 
recommendations are given on such matters as component si zing, collector orientation, tank insulation etc. It 
should be noted that the expected benefits of solar h eating may not be fully realized if the arrangements for 
raising the water to the final draw-off temperature are i nefficient. It is important that the conventional parts of 
the system should be in good order, the cylinder suitably insulated and thermostats and other controls 
properly adjusted. 
 8   Thermal performance of solar water heating systems 
8.1   General 
Thermal performance of collectors shall be determined in  accordance with the methods of test given in ISO 
9806 and DUS 854-2. 
The factors affecting performance which shall be taken into account include the following:  
- collector class; FDUS 853: 2009 
© UNBS 2009 – All rights reserved  59
 - collector area; 
- average daily  hot water usage; 
- the size of the preheat vessel; 
- collector mounting and location; 
- solar irradiation; 
- air temperature; 
- cold water feed temperature; - hot water draw-off temperature. 
Full details are given in Annex D. Clauses 8.2 to 8. 9 indicate how the performance depends on the various 
factors. Figures 8.1 and 8.2 illustrate th e performance of typical system s.(check for t hese figures) 
8.2  Collector class 
The characteristics of the collector are of primary importance in determining the thermal performance of the 
system. 
ISO 9806 provides methods for obtaining the collector's performance characteristics. These are the zero-loss 
collector efficiency ηo (mainly a measure of the collector's optical properties) and the collector heat loss 
coefficient U (a measure of the collector's thermal properties). The ratio U/ηo is a useful parameter by which to 
classify collectors and the classes defined for this standard are shown in Table 8.1. The boundaries have 
been chosen to correspond approximately to the main divisions of collector technology, which however are 
shown for guidance only. 
Table 8.1 – Solar collector classification 
Collector class Range of collector 
characteristics U/ηo (in W-m-2-K-1) Typical collector technology for the 
class 
B 
C D 
E 
F less than 3 
3 to 6 6 to 9 
9 to 13 
greater than 13 advanced 
vacuum insulated single glazed with selective coating 
single glazed with matt black coating 
unglazed 
(check for testing component equipment from project) 
8.3   Effective collector area 
No solar collector collects all the solar radiation incide nt upon it. Because of this, the collector area required to 
collect a certain amount of  solar energy will be larger if the collec tor were perfectly efficient. For design 
purposes, it is useful to think in terms of the e ffective area of a collector, although it will obviously be 
necessary to obtain its real dimensions when planni ng an installation. The quant itative relationship between 
the effective area A' and the aperture area A of a collector is given by the equation: 
A' = ηo × A 
The gross area of a collector will of course be gr eater than the aperture area because of the surrounding 
frame. FDUS 853: 2009 
60 © UNBS 2009 – All rights reserved
 8.4   Hot water usage 
The solar energy supplied by a given system depends on the amount of hot water, used. In sizing a system, 
the occupancy for which the house is designed should be borne in mind as well as the number and ages of 
the actual occupants at the time of installation. T he average daily consumption in three to five person 
households is about 30 L per person at 55 °C, rising to between 35 L and 40 L per person in one to two 
person households.(its most preferably to use a flexible shower than a fixed shower). 
8.5   Preheat vessel size 
Calculations show that, provided the volume of the preheat vessel exceeds about 80 % of the average daily 
hot water usage; its size does not si gnificantly affect the annual solar energy  supplied. However, if the preheat 
vessel is made smaller, then the annual solar energy s upplied may be reduced considerably, especially if the 
hot water is used after sunset or before mid-morning. In Annex D a method is given to estimate the variation in 
annual solar energy supplied as a function of the size of  the preheat vessel, for the case where most of the 
hot water is used in the evening. When the hot water is used predominantly during hours of sunlight, the 
annual solar energy supplied becomes much less sensitive to reducing preheat vessel size. Calculations also 
suggest that a small increase in the solar energy suppli ed can be realized if stratification (a variation in 
temperature from the top to the bottom of the vessel) occurs, and it is recommended that the preheat vessel 
be designed to encourage this. 
8.6  Collector mounting and location 
8.6.1 General 
The way in which a collector is mounted will influence t he results of thermal performa nce tests. Collectors to 
be tested shall therefore be mounted in accordance with 8.6.2 to 8.6.8. Full-size collector modules shall be 
tested, because the edge losses of small collectors may significantly reduce t heir overall performance. 
8.6.2 Collector mounting frame 
The collector mounting frame shall in no way obstruct t he aperture of the collector, and shall not significantly 
affect the back or side insulation. Unless otherwise spec ified (for example, when the collector is part of an 
integrated roof array), an open mounting structure shall be  used which allows air to circulate freely around the 
front and back of the collector. The collector shall be m ounted such that the lower edge is not less than 0.5 m 
above the local ground surface. Currents of  warm air, such as those which rise  up the walls of a building, shall 
not be allowed to pass over the collector. Where collector s are tested on the roof of a building, they shall be 
located at least 2 m away from the roof edge. 
8.6.3 Tilt angle 
The collector shall be tested at tilt angles such that th e incidence angle modifier for the collector varies by no 
more than ±2 % from its value at normal incidence. Fo r single glazed flat plate co llectors, this condition will 
usually be satisfied if the angle of incide nce of direct solar radiation at the collector aperture is less than 20°. 
NOTE For many collectors, the influence of tilt angle is small, bu t it can be an important variable for specialized collectors 
such as those incorporating heat pipes.  
8.6.4 Collector orientation outdoors 
The collector may be mounted outdoors in a fixed position facing the equator, but this will result in the time 
available for testing being restricted by the acceptance range of incide nce angles. A more versatile approach 
is to move the collector to follow the sun in  azimuth, using manual or automatic tracking. 
8.6.5 Shading from direct solar irradiance 
The location of the test stand shall be such that no shadow is cast on the collector during the test. 
8.6.6 Diffuse and reflected solar irradiance FDUS 853: 2009 
© UNBS 2009 – All rights reserved  61
 For the purposes of analysis of outdoor test results, so lar irradiance not coming directly from the sun's disc is 
assumed to come isotropically from the hem ispherical field of view of the collector. 
In order to minimize the errors resulting from this app roximation, the collector sha ll be located where there will 
be no significant solar radiation reflected onto it from su rrounding buildings or surfaces during the tests, and 
where there will be no significant obstructions in the field of view. With some collector types, such as 
evacuated tubular collectors, it may be equally important to minimize reflections on both the back and the front 
fields of view. 
Not more than 5 % of the collector's field of view sha ll be obstructed, and it is particularly important to avoid 
buildings or large obstructions subtending an angle of greater than approximately 15° to the horizontal in front 
of the collectors. The reflectance of most rough surfaces  such as grass, weathered concrete or chippings is 
usually low enough so no problem is caused during collector testing. 
Surfaces to be avoided in the collector's field of view include large expanses of glass, metal or water. In most 
solar simulators the simulated beam approximates direct solar irradiance only. In order to simplify the 
measurement of simulated irradiance, it is necessary to  minimize reflected irradiance. This can be achieved 
by painting all surfaces in the test chamber with dark (low reflectance) paint. 
8.6.7 Thermal irradiance 
The performance of some collectors is particularly sensitive to the levels of thermal irradiance. The 
temperature of surfaces adjacent to the collector shall be as close as possible to that of the ambient air in 
order to minimize the influence of thermal radiation. Fo r example, the outdoor field of view of the collector 
shall not include chimneys, cooling towers or hot exhausts . For indoor and simulator testing, the collector shall 
be shielded from hot surfaces such as radiators, air-conditioning ducts and machinery, and from cold surfaces 
such as windows and external walls. Shielding is im portant both in front of and behind the collector. 
8.6.8 Airspeed 
The performance of many collectors is  sensitive to air speeds. In order to maximize the reproducibility of 
results, collectors shall be mounted such that air ca n freely pass over the aperture, back and sides of the 
collector. The average value of air speed parallel to the collector aperture, taking into account spatial 
variations over the collector and temporal variations during the test period, shall be 3 ms-1 ± 1 ms-1. Where 
necessary, artificial wind generators shall be used to achieve these air speeds. Collectors designed for 
integration into a roof may have their backs protected from  the wind; if so, this shall be reported with the test 
results. 
8.7     Climate 
The change in weather from year to year has been show n to cause variations of up to ±10 % in the annual 
solar energy supplied in a given system. 
In a given year, variations in performance between sim ilar systems in the same locality may occur because of 
varied local conditions, for example, exposure to wind; cold water feed temperature, etc. 
The effect of latitude may also be significant. Annex D provides information on calculating the annual solar 
energy supplied at various locations. 
8.8   Other factors 
There are several other factors that will affect system  performance, not leas t of which is adeq uate insulation of 
the preheat vessel, hot water cylinder and the pipes leading to and from the solar collector. It is recommended 
that the insulation applied to the preheat vessel and cy linder should be not less t han the equivalent of 80 mm 
of glass fibre and not less than 19 mm on the pipes. Water contained in the pipework between the preheat 
vessel and the hot water cylinder may lose much of it s heat to the surroundings when no draw-off is taking 
place. The distance between the two vessels should therefore be kept to a minimum and the connecting 
pipework should be well insulated. The temperatur e differences (between the collector and the preheat 
vessel) at which the circulating pump is switched on and off can affect the amount of solar energy supplied. FDUS 853: 2009 
62 © UNBS 2009 – All rights reserved
 For a typical flow rate of water through the collector, sa y 0.02 kg/s per square metre of collector area, it is 
desirable that the temperature difference at which th e pump is switched off should not exceed about 1.5 K, 
and the temperature difference at which it is  switched on should not exceed about 4 K. 
Provided that the flow rate of water through the collect or exceeds the equivalent of 0.01 kg/s per square metre 
of collector area, the thermal perform ance of the system is not signific antly affected by the value chosen (see 
Clause 7). Solar heating systems may be designed in a variety of ways (see Clause 5 for examples) and the 
type of design may influence the thermal performance. For instance, within the general class of systems 
having a preheat vessel, one factor that might significantly  affect thermal performance is the incorporation of a 
heat exchanger (as in an indirect system). Provided t hat the heat exchanger is large enough, however, the 
performance will be similar to that of a direct system. Computations show that the energy supplied will be at 
least 95 % of the figures quoted in this clause, if the heat exchanger is at least as large in relation to the 
preheat vessel as those specified in BS 1566. 
The thermal capacity of the collector when full of  fluid has a small effect on the system performance. 
9   Electrical considerations 
9.1  General 
The electrical component of the system shall be des igned and installed in accordance with relevant 
regulations and standards.(check with the Editor on this) 
9.2   Electrical installation 
All wiring and apparatus shall be installed in ac cordance with the requirements of  IEC 60364.  
9.3   Electrical safety 
The Uganda Wiring Regulations require any wiring and apparatus to be properly installed and protected to 
ensure safety, particularly from the effects of fire  and shock. This protection is achieved by adequate 
insulation of all conductors and apparatus and the provis ion of effective earthing arrangements to ensure that, 
in the event of a fault, the installa tion is automatically disconnected fr om the supply to prevent danger. In 
conventional household plumbing systems, all items t hat may be touched, i.e. taps and pipework, shall be 
effectively bonded to earth. Solar water heating systems vary  in their design and construction and, particularly 
in a mixed metal system; advice should be sought from the component manufacturers for the most 
appropriate protection technique to be applied. 
9.4   Controls 
Controls shall be in accordance with  the requirements set out in EAS 205. 
9.5   Avoidance of electrical interference 
Where applicable, the requirements given in IEC CI SPR 14 and IEC 61000-3-2 shall be complied with, to 
avoid interference with other systems. 
9.6  Testing 
All electrical wiring and apparatus associated with a solar water heating system shall be inspected and tested 
in accordance with IEC 60364-6 to determine the co rrect polarity, effectivenes s of earthing and adequacy of 
the insulation. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  63
 10   Installation 
10.1   General 
Firms marketing solar water heating sy stems shall ensure that a potential customer is provided with adequate 
information about the layout and expect ed performance of systems similar to  that proposed to be installed. It 
is suggested that literature describi ng typical systems should include information of the kind recommended in 
Clause 13 to be provided about a particular installation a fter completion. The attention of potential customers 
shall be drawn to the statutory requirements mentioned in Clause 4. 
10.2   Pre-installation procedure 
The installer of solar heating systems may expect to meet either of two basic situations as follows. 
a)  Installations that form part of the construction of a new building, where the solar heating system is part of 
the specification. 
b)  Installations added to existing buildings. 
In each case the installer s hall ensure the availability of  the following information. 
1)  The required location on the outside of the structur e for the collector. This should preferably be in the 
form of a drawing. 
2)  The methods of fixing to be employed, as recomm ended by the manufacturer or the designer, to ensure 
security and weather tightness. 
3)  Drawings showing the general layout of the sola r water heating system and, in the case of existing 
buildings, details of the existing hot water supply and its interconnection with the new equipment. 
4)  A schedule of the components required to be fitted. 5)  A specification of the heat transfer fluid to be used. 
6)  The suitability of existing or  proposed roof st ructure to accommodate t he installation reliably. 
7)  The system size should meet the estima ted hot water consumption of the facility. 
8)  Confirmation that clearance of the statutory requirements ha s been obtained (see Clause 4). 
10.3         Installation procedures 
10.3.1 General 
The installer should comply with statutory codes  applicable to the works determined to be carried out.(contact 
the Min works) 
10.3.2 External work 
The fixing position should be inspected by a person exper ienced in such operations or works, and suitably 
qualified for the purpose. Fixings commensurate in spec ification with the weight and dimensions of the 
collector should be prepared in situ, in accordance with  the manufacturer's recommendations, prior to raising 
the collector up to the fixing position. Many solar collectors are supplied to site unglazed, the fitting and water 
sealing being left to be carried out by the installer. It is recommended that, where possible, these processes 
be carried out at ground level prior to raising and fixing.  The installer should satisfy himself that the glazing 
seals are sound, whether or not the collector is suppli ed glazed. This also is best determined at ground level. 
In view of the difficulties of handling collectors on a roof in adverse weather conditions, suitable practices 
should be employed to permit installation to be carried out with due regard to the maintenance of the health FDUS 853: 2009 
64 © UNBS 2009 – All rights reserved
 and safety of all concerned. Attention should be paid to  special lifting requirements which may be detailed by 
the manufacturer. Solar collectors ar e specifically designed to convert t he solar radiation into heat and may 
become extremely hot when exposed to sunlight. During in stallation and before the circulating liquid is added, 
temperatures well in excess of the boiling point of water may be attained. Care should be taken to avoid 
contacting the metal parts with bare skin because, apar t from the risk of burns, the shock may dislodge the 
installer from his foothold. It is recommended that collectors should be shaded with a removable cover (e.g. heavy paper secured by adhesive tape) during installation to  reduce the risk of burns, and also to reduce the 
risk of damage to the collector. 
10.3.3 Internal procedures 
With a new building, the installation of the additional plum bing services relating to the solar heating system will 
normally form part of the plumbing and heating spec ifications. Components can therefore be installed and 
hydraulically tested through at the same time. With insta llations to existing systems, the plumbing services will 
require the draining down of the existing hot water se rvices. All procedures should comply with ISO 6242- 1 
and with any additional manufacturer's instructions. 
10.4  Collector subsystem installation 
10.4.1  Collectors shall be installed in  accordance with the instructions provided by the collector 
manufacturer or system designer, or both, and in comp liance with requirements of the applicable building 
codes and standards. 
10.4.2  Structural supports shall be constructed to suppor t the collector under anticipated extremes of 
environmental conditions and to withstand local conditions  and anticipated loads, such as wind, seismic, rain, 
snow, and ice so that the solar system does not impair t he resistance to damage of the building. Neither wind 
loading nor the additional mass of filled collectors sh all exceed the live and dead load ratings of the building, 
roof, foundation, or soil. 
10.4.3  Structural supports shall be constructed to mainta in collector tilt and orientation within design 
conditions throughout the life of the SHW system. 
10.4.4  Joints between support structures and the building s hall be caulked or flashed, or both, to prevent 
water leakage. Access should be provided to permit minor  repairs to flashing and caulking without disturbing 
roof, collector supports , or collector panels. 
10.4.5  Collectors shall be installed so as not to contribute to moisture build-up, rotting, or other accelerated 
deterioration of roofing materials. 
10.4.6  Collectors and suppo rts shall be installed in a manner that wate r flowing off the co llector surface will 
not increase the potential for ice dams or cause water dam age, or both, to the building or premature erosion of 
the roof. 10.4.7  Provisions should be taken to minimize build-up of snow upon collectors which may reduce their 
effectiveness. 10.4.8  Structural supports shall be selected and installed in  such a manner that thermal expansion of the 
collector subsystem will not cause damage to the collector, structural frame, or building. 
10.4.9  Collectors and supports shall not create a hazard by blocking any means of egress. 
10.4.10  Safe access to components subject to deterioration or failure, such as rubber hoses, joint sealants, 
and cover plates, shall be provided to allow for main tenance or repair. For roof-mounted collectors, work 
space adjacent to collectors and provisions for sa fe placement of ladders should be considered.  
10.4.11  Collectors should be installed giving consider ation to minimizing objectionable glare. 
10.4.12  Protection of collectors and components shall be pr ovided during handling and installation to prevent 
damage. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  65
 10.4.13  Frames, braces, and fasteners used in collector in stallation shall be made of materials suitable for 
exterior location. 
10.4.14  Collectors shall not reduce the fire rating of t he roof as prescribed in applicable building codes. 
10.4.15  Roof penetrations necessitated by a collector array should be kept to a minimum. 
10.4.16  The collector array should not move with fros t heave unless adequate provisions for flexing have 
been provided. 
10.4.17  In thermosiphon systems, the bottom of the stor age tank should be above the top of the collector. 
10.4.18 The supply storage tank should be hi gher than the water heater by at least 2m. 
10.5   Collector Installation 
10.5.1  Collector positioning 
Collectors for solar water heating are generally mounted on  a building or the ground in a fixed position at 
prescribed angles. The angle will vary according to geographic location, collector type and use of the 
absorbed heat. 
The collector should be positioned to maximize sunli ght energy collection during the worst weather periods, 
receiving sunshine during the middle six to eight day light hours of each day. Mi nimize shading from other 
buildings, trees or other collectors. Plan for lengthening shadows, as the sun's path changes significantly with 
the seasons (Figure 10.1). 
 
 
Figure 10.1 – Solar window 
The collector should face directly south in the no rthern hemisphere and directly  north in the southern 
hemisphere. However, facing the collector within 30° to 45° either east or west of due south or north reduces 
performance by only about 10 %. A compass may be used to determine true south or north. The closer to the 
equator, the less the need to maintain the orientation and direction of the collector, but be aware of the 
seasonal position of the sun in the sky and how it may affect the seasonal performance of the system. 
The optimum tilt angle for the collector is about the sa me as the site's latitude plus or minus 15°. An 
inclinometer will aid in determining tilt angles. If colle ctors will be mounted on a slope d roof, check the roof's 
inclination to determine whether the collectors should be mounted parallel to the roof or at a different tilt. FDUS 853: 2009 
66 © UNBS 2009 – All rights reserved
 Collectors should be mounted parallel to the plane of a sloped roof unless the perf ormance penalty is more 
than 30 %. The mounted collector should not det ract from the appearance of the roof. 
Total length of piping from collector to storage should not exceed 30 m. The longer the pipe run, the greater 
the heat loss and pressure drop. If a greater length is nec essary, an increase in piping diameter or pump size 
may be required. 
If the collectors will be roof-mounted, they should not bloc k drainage or keep the roof surface from properly 
shedding rain. Water should not gather or pool arou nd roof penetrations. Roof curbs may be required. 
10.5.2 Wind loading 
A mounted collector is exposed not only to sunlight and the rigors of ultraviolet light but also to wind forces. 
For example, in parts of the world that is vulnerable to hurricanes or extreme wind storms, the collector and its 
mounting structure need to be able to withstand intermi ttent wind loads up to 240 km/h (Figure 10.2). This 
corresponds to a pressure of about 110 Pa. Wind s, and thermal contraction and expansion may cause 
improperly installed bolts and roof seals to loosen over time. As always, follow local code requirements for 
wind loading. 
 
Figure 10.2 – Conceptual drawing of wind loading 
Do not mount collectors near the ridge of a roof or ot her places where the wind load may be unusually high. 
Figure 10.3 shows a desirable location for a roof-mounted collector. Mountin g collectors parallel to the roof 
plane helps reduce wind loads and heat loss. 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  67
 Figure 10.3 – Collector mounted down from roof ridge to reduce wind loading and heat losses 
Determining the actual wind-load effect on collector anc hors and fasteners is difficult, and most collector 
suppliers employ professional engineers to approve co llector-mounting details. This  may be required by some 
local code jurisdictions. 
10.5.3 Ground mounting 
In an alternative to roof mounting, the collector fo r a solar water heating system may be mounted at ground 
level. The lower edge of the collector should be at le ast one foot above the ground so it will not be obstructed 
by vegetation or soaked by standing water.  Figure 10.4 depicts ground-mounting details. 
 
 
Figure 10.4 – Ground mounting 
Important points to keep in mind when using ground mounting include: 
1.  Keep threads protected with masking tape when setting anchor bolts in concrete. 
2.  Avoid the use of dissimilar metals. If they must  be used, isolate them with neoprene pads or silicone. 
3.  Coat threads with durable elastic material  before tightening the nuts to prevent rusting. 
4.  When possible, use galvanized anchors, which are ve ry durable. Before installing these bolts, check the 
threads — hot dip galvanizing sometimes puddles in the grooves. 
10.5.4 Roof mounted collectors 
There are four ways to mount flat-plate collectors on roof: 
1. Rack mounting  – This method is used on homes with fl at roofs. Collector s are mounted at the 
prescribed angle on a structural frame (Figure 10.5 ). The structural connect ion between the collector 
and frame and between the frame and building, or si te must be adequate to resist maximum potential 
wind loads. FDUS 853: 2009 
68 © UNBS 2009 – All rights reserved
 
 
Figure 10.5 - Rack-mounted collector 
2. Standoff mounting  – Standoffs separate the collector from the finished roof surface; they allow air 
and rainwater to pass under the collector and minimize problems of mildew and water retention 
(Figure 10.6). Standoffs must have adequate struct ural properties. They are sometimes used to 
support collectors at slopes that di ffer from that of the roof angle.  This is the most common mounting 
method used.  
 
Figure 10.6 – Standoff-mounted collector 
3. Direct mounting  – Collectors can be mounted directly on the roof surface (Figure 10.7). Generally, 
they are placed on a waterproof membrane coveri ng the roof sheathing. Then the finished roof 
surface, the collector’s structural attachments,  and waterproof flashing are built up around the 
collector. A weatherproof seal must be maintained between the collector and the roof to avoid leaks, 
mildew and rotting. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  69
 
 
Figure 10.7 – Direct-or flush-mounted collector 
4. Integral mounting  – Integral mounting places the collector within the roof construction itself. The 
collector is attached to and supported by the stru ctural framing members (Figure 10.8). The top of the 
collector serves as the finished roof surface. W eather tightness is crucial in avoiding water damage 
and mildew. Only collectors designed by the manufac turer to be integrated into the roof should be 
installed as the water/moisture barrier of buildings. The roofing materials and solar collectors expand 
and contract at different rates and have the potential  for leaks. A well sealed flashing material allows 
the expansion and contraction of the materials to maintain a water seal. 
 
Figure 10.8 – Integral-mounted collector 
10.5.5 Roof work considerations 
The most demanding aspects of installing roof-mount ed collectors are the actual mounting and roof 
penetrations. Standards and codes are sometimes ambiguo us about what can and cannot be done to a roof. 
Always follow accepted roofi ng practices, be familiar with local buildi ng codes, and communica te with the local 
building inspector. These are prime roof work considerations: 
1. Perform the installation in a safe manner. 
2. Take precautions to avoid (or minimize) damage to the roof area. FDUS 853: 2009 
70 © UNBS 2009 – All rights reserved
 3. Position collectors for the maximum performance compatible with acceptable mounting practices. 
4. Seal and flash pipe and sensor penetrations in  accordance with good roofing practices. Use 
permanent sealants such as silicone, urethane or butyl rubber. 
5. Locate collectors so they ar e accessible for needed maintenance. 
10.5.5.1 Site preparation 
Roof-mounted collectors often are placed on supports  or brackets. Preparation of the roof area and 
procedures for anchoring to the roof members must be done carefully to avoid causing leaks or weakening the 
roof. In a new home installation, much of the mounting work can be performed after the roof has been framed 
and sheathed, but before the waterproof membrane is applied. 
The best position for a collector is over the roof rafters  or trusses (Figure 10.9). Avoid placing it at the roof 
ridge and areas where the roof slope changes, as wind loading and heat loss are greater there.  
 
Figure 10.9 – Roof structures 
The collector or its supports should be anchored to the r oof rafters or trusses, not the sheathing. Following are 
recommended procedures: 
1.  Choose an appropriate site for the collector. 
2. Locate the specific rafters to be used for mounting. 
3.  Measure and mark the roof penetration points for the anchor bolts. 
4. Prepare the roof surface and install pro per flashing or other waterproofing devices. 
5.  Properly anchor the mounting brackets to the rafters. 
6.  Reseal the roof (retrofit) or complete the installation of the roof (new construction). 
In retrofit situations, rafters or roof trusses may be lo cated from inside an attic if the space is large enough to 
permit access. Very small galvanized nails may be dr iven up beside the rafter at the desired anchoring points; 
this locates the points for the workers on the roof, and roof preparation can begin. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  71
 If access to the attic is not adequate, trusses can be lo cated by looking for nails in the fascia board. They 
indicate the location and spacing of the trusses. Locate the mounting points by measuring across the roof 
ridge and popping a chalk line between the ridge and the fasc ia along the run of the truss (Figure 10.10). The 
truss may not be perfectly straight, so the chalk line will be close to (but not precisely on ) the truss run. Many 
installers use the variation in tone associated with exte rnal hammer blows to locate the run of the truss. A 
mechanical or digital truss finder can also be used to locate the position of the truss. 
After the anchoring points have been select ed, prepare the roof for penetration. 
 
 
Figure 10.10 – A method of locating mounting points 
10.5.5.2 Roof penetration 
Modern roof finish materials cover a wide range. The most commonly used materials are asphalt or fibreglass 
shingles, clay or concrete tile, iron sheets  tar and gravel. 
Shingles are applied in an overlapping pattern, nailed, or stapled to the roof sheathing below. Old, brittle 
shingles may break underfoot. Use care until the conditi on of the shingles is ascertained. Brackets can be 
mounted directly over pliable shingles; no special prepar ation is necessary. Holes for the mounting bolts may 
be drilled through the shingles. The entire penetration shall then be sealed. 
Tile roofs require extensive preparation. When walking on these roofs, care must be taken not to break the 
tiles or slip on loose tiles. On ba rrel tiles, never walk on the crowns. Br oken tiles must be replaced, increasing 
installation time and cost. Tiles in the area of the anchoring spots should be sawed out. Remove as few tiles 
as possible, because the area must be sealed later to  protect the underlying watertight membrane. When the 
tiles are removed, the exposed waterproof membrane may be treated as if it were an asphalt shingle roof. The 
area where tile was removed may be filled with cem ent that is colored and molded to correspond to the 
undamaged roof configuration. 
There are many ways to penetrate t ile roofs. Most methods used to seal the tile will depend on the type, 
shape and base material of the tile. Cement, clay, cera mic rounded, or flat tiles may require different methods 
of attaching the collector to the stru cture and sealing the roof penetrations. 
For example, installation methods can include penetrati ng the tile and attaching the mounting hardware to the 
roof truss assembly and flashing the riser as shown in Figure 10.11 or attaching the mounting hardware to the 
roof and using a flashing that allows installa tion of the tile around the mounting hardware. FDUS 853: 2009 
72 © UNBS 2009 – All rights reserved
 
 
 
 
Figure 10.11 – Tile roof mount 
Or, the solar collectors may be supported above the tile  on a rack or bracket as shown in Figure 10.12. 
 
 
Figure 10.12 – Tile roof-bracket mounting 
Yet another method may include using lead roof vent stack flashing that can be shaped to the style and 
contour of the tile and sealed on the top with a cap or the mounting hardware support base as shown in Figure 
10.13. 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  73
 
 
Figure 10.13 – Vent stack flashing 
A built-up, roof is composed of alternating layers of w eather-resistant membrane (such as roofing felt) and tar, 
which is covered with loosely bound gravel that reinforc es the semi-viscous roof tar and protects it from 
excessive heat and ultraviolet rays. This roof finish is ty pically used on flat roofs. The rafters in this case can 
be located by hammering on the roof surface — the roof pebbles will not jump when a rafter is struck. 
Remove all of the gravel under the mounting bracket and fo r a space of at least four inches in each direction 
from its edges. When bolts penetrate the waterproof memb rane, pitch pans will be required. Pitch pans can be 
made from six-ounce sheet copper, galvanized ir on or lead. Figure 10.14 shows a pitch pan. 
 
Figure 10.14 – Pitch pan detail 
Use high quality roof cement and four -inch strips of asphalt-impregnated r oofing to waterproof the penetration. 
Also, avoid creating any "pools" in the pitch pan seali ng material where water can accumulate. Then cover it 
with gravel. 
10.5.5.3  Bracket mounting and sealing 
Brackets attach the collector to the roof. The brackets  themselves must be securely attached to the underlying 
rafters or trusses. 
If the site has working room in an attic or crawl space, wood or angle iron spanners can be used to secure the 
mounting brackets, acting as an anchor for a threaded r od. Spacers must be pre-drilled and placed directly 
under the threaded rod to relieve any tension pulling down on  the roof deck. A clip angle or collector mounting 
bracket is attached on the "roof" end of the threa ded rod. Figure 10.15 illustrates spanner mounting FDUS 853: 2009 
74 © UNBS 2009 – All rights reserved
 
 
Figure 10.15 – Spanner mounting 
If under-roof access is not available, J-bolts or lag bo lts may be required. J-bolts must be long enough to grip 
under a rafter and still leave enough threading outside the ro of sheathing for easy brac ket and nut installation. 
(Follow the collector manufacturer's length and diameter recommendation to the letter.) 
To mount a lag bolt: 
1. Drill a pilot hole of 50 – 75 % of the bolt diameter into  the centerline of the truss to the actual length of bolt 
penetration. 2. Liberally apply a high quality sealant around the pilot hole opening. 
3. Place the pre-drilled sealing pad and mounting bracket angle on the roof. 
4. Apply the flat washer, lock washer and bolt with a high quality sealant between the bracket and flat washer. 
Figure 10.16 shows an acceptable se quence in lag bolt mountings. 
  FDUS 853: 2009 
© UNBS 2009 – All rights reserved  75
 
 
Figure 10.16 – Lag-bolted mounting assembly 
 
For J-bolt mounting as illustrated in Figure 10.17: 
1. Drill a hole directly beside the rafter; the hol e size must be slightly larger than the bolt 
diameter. 
2. Fit the bolt through the mounting bracket (angle) 
3. Insert the bolt (hook side first) through the hole in the roof. 
4. Work the hook underneath the rafter. 
5. Pull the hook snug against the rafter before tightening the nut. 6. Use double nuts or lock washers to secu rely fasten the mounting bracket t the J-bolt. FDUS 853: 2009 
76 © UNBS 2009 – All rights reserved
 
 
Figure 10.17 – J-bolt mounting 
10.5.5.4 Collector attachment 
If the collector is to be rack-mounted make sure the rack  (if adjustable) is tilted to the desired angle and the 
collector (when mounted) will drain by  gravity. Follow the co llector manufactu rer's guidelines regarding rack 
adjustment and attachment. Make sure the rack is struct urally sound and firmly secu red and not skewed. If it 
is skewed, tightening the collector in place may break  its glass cover. If collector and rack are made of 
dissimilar metals, provisions must be made to prevent galvanic corrosion. 
If the collector is to be mounted with standoffs, allow at least one inch of clearance between the collector 
bottom and roof surface to prevent water or material bui ld-up. The bracket-to-collector attachment must be 
strong enough to withstand the maximum expected wi nd loads. Follow the manufacturer's instructions. 
After the collector has been mounted, check the entire asse mbly for rigidity. As a rule of thumb, if you can 
shake it by hand, it is not fastened securely enough. 
10.5.5.5 Roof piping and penetrations 
Select the spots to penetrate the roof for the piping runs  close to the mounted collector. In some cases it may 
be necessary to pipe both the feed and the return lines through the same penetration. In gravity drain 
systems, the feed line should penetrate  the roof below the collector. Pitch all lines at least 0.635 cm per 0.3 m 
of pipe run to allow proper drainage. Make roof penetrations between trusses to allow for thermal expansion and slight flexing of the pipe from wind buffeting. 
There are several methods of roof penetration that comp ly with accepted practices of building codes. If there 
are any conflicts between the recomme ndations made here and those of building codes, follow the building 
codes. 
One method of providing a watertight penetration uses a st andard plumbing roof vent  stack flashing (Figure 
10.18). Remember to protect the rubber or plastic boot from the sun. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  77
 
 
Figure 10.18 – Penetration with vent stack flashing 
Another method is to make a flat copper flashing with an oversize collar that is penetrated by the fluid line 
(Figures 10.19 thru 10.21). Note the base of t he flashing should be mounted under the shingle above. A 
flashing cap is then soldered to the pipe at their junction.  This type of flashing is available for both pipe only 
(Figure 10.20), and pipe and wire penetrations (Figure 10.21). 
 
Figure 10.19 – Penetration with flat flashing 
 
 
Figure 10.20 – Copper flashing for pipe only FDUS 853: 2009 
78 © UNBS 2009 – All rights reserved
 
 
Figure10.22 – Copper flashing for both pipe and wiring 
A less desirable method brings both pipes up through a pitch pocket (Figure 10.22). Such an open bottom 
pitch pocket requires periodic maintenance and inspections over the life of the solar system. 
 
 
Figure 10.22 – Penetration with pitch pocket 
For larger commercial installa tions on flat, built-up roofs, the installe r should follow specific recommendations 
of the most current NRCA R oofing and Waterproofing Manual. 
10.5.5.6 Valves 
Most solar systems may have valves on the roof for venting, f illing, freeze protection  and other aspects of 
operation. In order to eliminate air trap s, air-vent valves must be at all hi gh points in the system where air is 
most likely to accumulate (Figure 10.23). FDUS 853: 2009 
© UNBS 2009 – All rights reserved  79
 
 
 
Figure 10.23 – Elimination of an air trap with an automatic air vent 
If multiple collector arrays are used, an air vent shoul d be installed on each array.  The system must be piped 
to prevent air traps and allow fo r gravity draining (Figure 10.24). 
 
 
Figure 10.24 – Piped and vented collector array 
By code, a pressure relief valve is required in any port ion of the system that can be isolated that contains a 
pressure producing fixture. For example, a circulating pump might have isolation valves so it can be removed 
for maintenance, but it is not c onsidered a pressure producing fixtur e from the standpoint of the risk of 
bursting the system, so you don't ne ed a pressure relief valve on this part of the system. However, the 
collector, or tanks with heater elements (connected or not), and even tankless water heaters are pressure 
producing fixtures, so if any can be isolated, there must  be a pressure relief valve somewhere in that portion 
of the isolated loop that contain t hem. Most solar water heaters have the pr essure relief valve for the collector 
loop installed at the collector. Special care should be ta ken to ensure the hot overflow  from this valve does not 
come into contact with people or pets; some codes specify how this should be accomplished. The discharge FDUS 853: 2009 
80 © UNBS 2009 – All rights reserved
 pipe must be large enough to safely handle the overfl ow volume from indirect antifreeze systems, which 
usually operate at low pressure. S pecial low-pressure relief valves are often used on these systems. 
10.5.5.7 Piping collector arrays 
Cover all roof piping with insulation. Protect the insu lation from degradation through exposure to ultra violet 
(UV) light by completely covering it with UV-resistant paint, or metallic or vinyl tape. Painted insulation will 
need to be repainted periodically, as the paint will deteriorate over time. 
Slip the pipe through the insulation sleeve before solderi ng, or slit and re-glue insulation in difficult areas. 
Insulation that has been slit must be glued or taped proper ly because it will shrink from the pipe as it ages. 
Insulate joints only after the entire syst em has been pressure-tested for leaks. 
The collectors in multiple-collector arrays should be  plumbed in parallel unless the manufacturer specifies 
otherwise. Parallel, reverse-return piping (Figure 10.25) en sures a fairly uniform flow in a collector array with 
no more than four collectors. Use 1.9 cm pipe for the interconnections. A parallel connection without reverse 
return leads to uneven flow throughout the collector array. 
If the array cannot be piped in parallel with reverse return, use flow-balancing valves to reduce the flow in the 
collector of least resistance, equalizing the flow ra te through the entire array (Figure 10.25 b). A balancing 
valve is a fairly expensive valve with which accurate flow adjustment may be made. Gate valves should not be 
used for this purpose, as they will not allow accurate  flow equalization over time, but ball valves have been 
used successfully for balancing. 
 
 
Figure 10.25 – Multiple collector piping arrangements 
Avoid flexible connectors from the array header to the i ndividual collectors, as they have been shown to fail or 
leak over time. However, flexible hoses may be accept able in indirect antifreez e systems, which are not 
subject to high operating pressures. 
11   Component installation 
11.1   General 
This clause outlines recommended installation and servicing minimum practices needed to provide an 
effective SDHW system operation. 
11.2   Piping, ducting and ancillary equipment 
11.2.1  Piping, ducting, and equipment shall be located so as not to interfere with normal operation of 
windows, doors, or other exit openi ngs. Piping, ducting, and equipment shall be installed in a manner to 
prevent damage to such piping, ducting, and equipment; pr event injury to persons; and in accordance with the 
manufacturer's instructions and the applicable building codes. 
11.2.2  Piping and ductwork shall be selected and insta lled to withstand the ex pected operating and 
stagnation temperatures and pressures without excessive air leaking, saggi ng, or corrosion. Piping shall not 
leak. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  81
 11.2.3  Pipe hangers, supports, and expansion devices shall be provided to compensate for thermal 
expansion effects and to provide adequate support. Care shall be exercised during their installation to prevent 
damage to connections on the collector or the collector casing. Pipe hangers shall not short circuit insulation 
by creating a thermal bridge. Expans ion devices shall not prevent draining. Pipe supports should not 
compress the insulation. 
11.2.4  Standard pipe fittings should be used wherever possible. 
11.2.5   Pipe and duct runs should be as short as practical with as few ells and bends as possible. 
11.2.6  Joints shall be made with materials selected for durability within the expected operating temperatures 
and pressures for the fluid selected. Soft solder may not be adequate for joints near collectors under 
stagnation conditions. Soldering fluxes shall be water soluble. 
11.2.7  Underground piping shall be installed below the fros t line. Underground piping subject to vehicular 
traffic shall be installed to withstand the anticipated stat ic and dynamic loads. The trench shall be free of sharp 
objects surrounding the pipe. 
11.2.8  Piping shall be installed to facilitate drainage of  liquid systems. Piping shall be pitched at the 
minimum rate of '/s in./ft (1  cm/m) towards the drain. 
11.2.9  Suitable connections shall be provided for filling, draining, and flushing liquid systems. 
Interconnecting piping or ducting shall be installed to mi nimize flow restrictions, prevent air blocks, and to 
provide a balanced flow. 
11.2.10  Where trapped air could impair the performance of a system or prevent drainage, air bleed 
provisions shall be provided at those high point s so that air can be purged from the system. 
11.2.11  Where heat losses may occur, insulation shall be provided on piping and ductwork. Insulation shall 
be suitable for the application and location. Insulation shall be protected against degradation due to weather 
or environmental conditions. Underground installations sh all be protected to prevent deterioration of insulating 
properties by compression, water penetration, or bacterial action. 
11.2.12  Piping shall be leak tested before en closing, backfilling, or insulati ng. Caution shall be exercised so 
that excessive pressure is not applied to the system. 
11.2.13  In an SDHW systems the air tightness of  the ductwork is critical to system  efficiency. All joints in rigid 
and in flexible ductwork shall be sealed. Brackets or hangers shall be used to securely support, suspend, or 
hang ducts. At no time shall duct supports penetrate the duct itself. 11.2.14 The direct joining of dissimilar metals in liquid syst ems that may result in accelerated corrosion should 
be avoided. Where it is necessary to joint dissimilar me tals in the same system, they should be separated by 
electrically insulated joints or  suitable intermediate metals. 
11.2.15  When a liquid is used as the heat transfer fluid in a SDHW system and quick-closing valves are 
employed in the design, the piping system shall be abl e to control or withstand potential "water hammer." 
Water hammer arresters shall be in compliance with local codes. 11.2.16  Grounding electrical systems to SDHW system piping shall not be employed. 
11.2.17  Auxiliary (nonsolar) heating equipm ent shall be sized and located to  provide the residence with the 
required water temperature and flow whenever solar ener gy is inadequate. It shall be compatible with the 
solar system with regard to such items as out put, temperatures, flow volume, and fluid types. 
11.2.18  Where air needs to enter the system to allow drainage, a vacuum breaker should be located at the 
high point of the system. 11.2.19  Piping from the tank to the collectors should be as short as possible and insulated to reduce heat 
loss. Increase the pipe insulation if the collect ors are a long distance from the storage tank. FDUS 853: 2009 
82 © UNBS 2009 – All rights reserved
 For direct residential systems, use 1. 25 cm or 1.9 cm copper pipe. Smaller sizes tend to become constricted 
by boiler scale when the water contains salts with reversed solubility char acteristics. Use 1.9 cm or larger feed 
and return lines for multiple collector systems containing three or more collectors piped in parallel to prevent 
unwanted pressure drops between collector connections. 
Copper tubing, like all piping materials, expands and c ontracts with temperature changes (about 37.8 °C in 
most solar systems). Using expansion loops or offsets can accommodate this expansion. A typical piping run 
(for a domestic water heater) will increase in length ab out 1.25 cm when hot. This expansion can be absorbed 
by a one foot in diameter loop on each run, a U-bend, or  an offset of the same length for each run (Figure 
11.1). An alternative is to use soft copper tubing in each  line. Prevent air traps or low spots in systems when 
installing expansion loops, and allow for thermal expansion of the pipes. 
 
Figure 11.1 – Expansion loops – Systems must be able to drain 
The following installation practices should be observed: 
1. If possible, utilize an electric-operated (motor ized) check valve to pr event back-siphoning. As 
a second choice, use a vertical spring-check va lve with a high temperature (e.g., Teflon, not 
neoprene) seal. Use of a horizontal swing-check valve is not highly recommended. 
2. The solar system must have isolation valves – one on each side of the solar loop. An isolation 
valve should be provided between the pump and the tank on the feed line and between the 
check valve and the tank on the return line. 
3. Drain valves should be provided on both side s of the collector loop. Drain valves should 
always be readily accessible. When install ed above the check valve it can be used to back 
flush the collector and when installed below the pump it can be used to drain the pump for 
service. 
4. If a vertical spring-check va lve is utilized, the drain valve pl aced between the check valve and 
the tank can be used to test the check valve at lo w pressure to determine if it closes properly. 
In order to back flush the collector loop, the drain valve must be above the check valve. The 
location used for the drain valve is based on installer preference. 
5. Use only nontoxic heat transfer fluids with  single-walled heat excha nger systems. Label the 
heat exchanger so that it can be identified as a single-walled unit. 
6. Thermometer wells on both inlet and outle t sides of the solar loop are desirable. 
7. Before leaving the premises, check the flow th rough the collector loop to make sure there are 
no major obstructions. Recommended flow rate: about 1/2 gallon per minute (gpm) for each 
40 ft2 of panel area (unless the manufactu rer specifies to the contrary). FDUS 853: 2009 
© UNBS 2009 – All rights reserved  83
 8.  For residential forced circul ation systems, use a minimum of 1.25 cm pipe for total runs over 
100 feet, or when the flow requirement is greater than one gpm and the pump is less than 
1/20 hp, use 1.9 cm pipe. For a thermosiphon system, use of 1.9 cm piping helps eliminate 
undesirable resistance to fluid flow. If two or more collectors are to be connected in parallel, 
use 1.9 cm pipe for interconnections. 
9. Use 1.25 cm thickness (minimum) rubber type insulation on all piping and make sure the    
insulation is protected from environmental degradation, especially ultraviolet rays. 
10.   Minimize piping distances wherever possible. 
11.  Install all piping with a continuous slope of 0.6 cm for 30 cm toward the drains. 
12.  Pipe runs should use hangers to maintain  their slope and stability. When constructing 
hangers, use wide plumbing straps. (Do not us e wire.) Follow plumbing code requirements 
for hanger spacing. 
13.  Install collectors so internal piping will drain itself completely by gravity. 
14.  Use lead-free solder for soldering system joints and components. Follow local code 
requirements. 
15.  If piping requires high points, inst all air vents at those locations. 
11.3   Storage tank installation 
11.3.1 General 
Because of their size and weight, solar storage tanks mu st be carefully sited in new installations, and finding 
suitable locations sometimes challenges the solar contract or's ingenuity on retrofit installations. Since it will 
eventually require replacement, locate the tank so it c an be removed with the least possible effort. Make sure 
it is placed where a leak will not cause damage, there is adequate working room for making piping 
connections, and it is protected from detrimental environmental conditions. 
New wiring is a job for the electrical contractor, but the solar installer will want to tell the electrician whether a 
230 VAC is needed for operating the pump, controller and electric water heater. Amperage information can be 
found in the installation brochures fo r the pump and the tank controller. 
Configurations for two-tank system piping with electr ical backup are shown in Figure 11.2. Gas water heaters 
should be used with the system shown in Figure 11.3. Gas water heaters do not work well in single-tank solar systems because the gas tank's burner  heats the entire tank of stored water from the bottom up. Gas water 
heaters should be used with passive solar systems whic h preheat water or with auxiliary solar storage tanks 
(See Figure 11.3). (By contrast, electric tanks can be configured to heat only the top portion of the stored 
water.) 
The following installation practices should be observed: 
1. If possible, provide a separate switch, convenien tly located, to turn on and off the hot water heating 
element(s) on the tank. (This will require a doubl e pole, 230 VAC switch). Also point out to the 
homeowner the hot water heater circuit breaker switch. 
2. If a dual element tank is used for solar storage, disconnect the lower tank element wires at the upper 
thermostat. Or, turn the bottom t hermostat to its lowest setting. 
3. Maintain enough clearance to t he tank's heating element/thermostat  plate(s) so the thermostat 
setting device can be accessed and the heating element can be replaced. 
4.  Install a heat trap on the cold-water inlet line and the hot water line to the building, as required. FDUS 853: 2009 
84 © UNBS 2009 – All rights reserved
 5.  Add an insulating blanket to a conventional electric  water heater tank (a minimum of 5 to 7.5 cm of 
fiberglass equivalent is needed). Do not cover the th ermostat access doors. To  prevent heat loss, set 
all tanks on 1.3- to 1.9-cm plywood (preferably wi th a layer of insulation board between the plywood 
and the floor). 
6.  Add insulation to the temperature and pressure  relief valve and any other tank mounted pipe or 
fittings. (Don't restrict the pressure temp erature relief valve test lever movement.) 
7.  The solar return on a standard electric water heater should have a dip tube to return heated water 
approximately 15 cm below the upper element's thermostat. 
8.  If a standard "mixing" valve is to be installed,  be sure it is below the top of the tank. Remove the 
element when soldering if the valve utilizes soldered  fittings. Specific models of "anti-scald" valves 
can be installed in the piping above the tank. 
9.  Pressure temperature relief valve piping should be piped to the outside and/or into a suitable drain 
six inches above ground level. Follow local code requirements. 
10.  For thermosiphon systems the hot water storage tank  should be located at least one foot above the 
solar panel (except in the case of factory-made unitized systems). 
11.  Insulate both the hot water fixture line and t he cold water supply line at the top of the tank. 
 
 
 
Figure 11.2 – Multiple tank connection 
 
 
 
 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  85
 
 
Figure 11.3 – Gas heater connection 
11.3.2  Requirements for thermal storage devices 
11.3.2.1 Where heat losses may occur, thermal insulation shall be provided on the storage devices and 
related piping. Insulation shall be suitable for the application, site, and occupancy conditions. 
11.3.2.2 Care shall be exercised during the installation of  the storage device to prev ent damage to the device, 
lining, and insulation material during handling, mounting or other installation procedures. 11.3.2.3 If liquid storage devices are provided with overflows, the outlets shall be located so that spillage will 
not damage the premises. 
11.3.2.4 Storage devices installed in an attic shall be provided with a drip pan whose outlet is piped to an 
adequate drain. 
11.3.2.5 Fill devices shall be installed with air gaps, ba ckflow preventers, or some method to prevent 
contamination of potable water supplies as prescribed by applicable codes.  
11.4  Pump, blowers and heat exchangers  
11.4.1 In  many solar water-heating applications, inexpensi ve, low-horsepower pumps will circulate enough 
liquid through the heat collectors for efficient operation. When the entire circulation l oop of a collector system 
is full of liquid, as is the case with most pressurize d systems, only the friction re sistance of the piping and 
valves must be overcome. 
11.4.2 Drain -back systems must use higher head pumps to li ft the water (overcome the static head) between 
the storage water level and the highest point in t he system. That same pump must have enough reserve 
pressure capacity to overcome t he friction head. Fortunately, the fric tion head is usually very low when 
compared to the static head. 
 FDUS 853: 2009 
86 © UNBS 2009 – All rights reserved
 11.4.3 The  location of the pump is also important in a drain- back system. Since most solar pumps are not self-
priming, the impellers must be below liquid level at all times. Pumps may be mounted in any orientation unless 
the position prevents air from escaping from the volute ( pump cavity). Pump rotation must push the fluid in the 
right direction. Some pump motors may require lubrication, and the homeowner should be shown how and 
when to lubricate the pump motor. 
11.4.4 Pumps and blowers shall be installed in accordance with the manufacturer's instructions and so that 
the flow is in the proper direction. 
11.4.5 Pumps and blowers should be installed with consideration to access for maintenance. 
11.4.6 Pumps and blowers shall be installed to allow sufficien t air circulation to prevent motor overheating. 
11.4.7 Pumps and heat exchangers shall be adequately suppor ted for their mass and to minimize vibration. 
Minimize noise and vibration by mounting the base solidly or allowing the pump to be supported by its 
mounting flanges from a secured section of pi pe. All pumps and motors must be UL-listed. 
11.4.8 Heat exchangers shall be installed in accor dance with the manufacturer's instructions. 
11.4.9 Materials of construction used in pumps and heat exchangers should be compatible with other SDHW 
system components and the heat transfer fluid. 
11.5   Controls, sensors and safety devices 
11.5.1 Controls and safety devices shall be selected and inst alled in a manner that, in the event of a failure 
of any system component, such failure will not result in serious damage to the rest of  the system or any part 
thereof. Installation shall be in accordance with the manufacturers’ instructions and applicable building code 
requirements. 
11.5.2  Differential controller 
The differential controller is usually boxed and mounted insi de the building to protect it from the weather and 
tampering. It often is connected directly to the pum p with preformed conduit and equipped with 230 VAC wire 
and a wall plug. 
The low-temperature sensor of the differential control is  usually attached near the bottom of the storage tank. 
The high-temperature sensor may be placed: 
1.  On the outlet pipe of the solar collector. 
2.  In the air space between the collector absorber and the transparent cover. 
3.  Against the absorber surface. 
Follow the instructions from the controller manufacturer s. In any one of the three sensor locations, the basic 
on-off modes are the same. When the collector sensor senses temperatures 5-20 °C hotter than the tank 
sensor, the pump is turned on. When that differenc e is reduced to about 3 °C, the pump is turned off. 
This method of controlling the pump's operation guarant ees water circulates through the collectors only when 
such circulation will result in an energy gain to the storage tank. 
There is no guarantee water returning to the tank will be hotter than the water stratified at the top of the tank; 
therefore, solar tanks introduce the returning water about  one-third of the way down the side of the tank. This 
is done with a sideported tank or with a short dip tube, as shown in Figure 11.4. 
 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  87
 
 
Figure 11.4- Side port and “dip tube” arrangement of collector return port 
The following installation practices should be observed: 
1.  The tank sensor should be located on the storage t ank as close as possible to the bottom. If the tank 
is not accessible, it should be located on the colle ctor supply pipe as close as possible to the tank 
outlet. All sensors should be insu lated from the surrounding air. 
2.  Perform a controller checkout procedure before leaving to be sure collector and tank sensors are 
calibrated. This procedure sh ould utilize a digital ohm mete r and/or a controller tester. 
3.  Check all freeze sensors before installation. Th is can be done by placing them in an ice water bath. 
They must activate the pump or freeze contro l strategy above 0 °C (usually 3 – 5.6 °C). 
4.  For adequate freeze protection, use at least two methods of freeze protection. Connect the collector 
sensor and freeze sensor in parallel if the freeze se nsor closes on temperature fall, series if it opens 
on temperature fall. (The sensors must be used with  a controller that responds to a closing or 
opening freeze signal as required). 
5.  A collector sensor mounted on piping should be well  covered with insulation and thermally in contact 
with the piping. 
6.  All sensors must be mounted accord ing to manufacturer's specifications. 
7.  Connections for sensors should be made with silic one-filled wire nuts or telephone style waterproof 
connections. They should be coated weather tight  with sealant and protected from exposure to 
sunlight. 
8.  Use Teflon (or other high-temperature insulation) in sulated wire within or close to the solar collector. 
9.  Do not run low voltage sensor lines near higher voltage 230 VAC lines. The controller may be 
affected by induced voltage fluctuations. When running se nsor wiring in the attic, secure it at regular 
intervals overhead, stringing it from one rafter to the next or along piping insulation to prevent 
potential damage by people moving about or storing objec ts in the attic. Near the tank, run sensor 
wiring along piping insulation and tape it in pl ace. Do not leave any wire dangling anywhere. FDUS 853: 2009 
88 © UNBS 2009 – All rights reserved
 10.  Do not stretch sensor wires taut before securing them to supports. Thermal expansion and 
contraction may cause premature failure of the circuit because of damaged insulation and the 
resulting short circuits. 
11.  Check completed circuits for unwanted grounding.  Some controller sensor's circuits contain one 
grounded leg. Observe proper polarity in such cases. 
12. It is recommended that 24 VDC or less be used fo r all sensor circuits. If 230 VAC circuits must be 
used, follow local electrical codes. 
 
11.5.3 Timer controller 
1.  Use a certified timer incorp orating battery back-up capability. 
2.  Provide the homeowner with t he timer instructi on booklet. This will become very important during 
battery changes and if the homeowner ever has to reset the timer. 
11.5.4 Photovoltaic controller 
1.  Follow the photovoltaic manufacturer's recommendations for gauge size of wiring. 
2.  Follow the differential controller wiring guidelin es regarding securing wiring runs and stretching of 
wiring. 
3.  The photovoltaic module should be covered befo re the DC pump is connected to avoid an electrical 
spike to the motor. 
11.5.5  Where systems are designed to drain out automatica lly, the automatic drain valves shall be piped to 
a suitable drain. 
11.5.6  Adequately sized pressure relief or temperature and pressure relief devices shall be provided in 
those parts of the solar system that can be isolated and contain a heat source (see 17.2). 
11.5.7  Devices (for example, dampers) s hall be installed to prevent cold air from freezing any air to water 
heat exchanger. Care should be taken during installation to ensure a positive air seal. 
11.5.8  Expansion tanks shall be provided as part of the SDHW system to provide for thermal expansion of 
heat transfer liquids in closed loops. Expansion tan ks shall be sized for the expected operating and stagnation 
temperature and pressure ranges a nd the type of heat transfer fluid. 
11.5.9  Control circuit wiring and terminals should be i dentified so that wires are readily traceable. 
11.5.10 Isolation valves should be provided so that t he major components of SDHW systems can be 
maintained or serviced. If collectors can be isolated, t hey shall be protected by a pressure relief valve. 
11.5.11  Check valves may be used to prevent flow in the opposite direction within the solar energy system. 
They shall be installed according to manufacturer's di rections and never in place of backflow preventers. 
11.5.12  Controls, sensors, dampers, and valves should be ma rked to identify their function. Any control that 
serves as an emergency shutdown device shall be so indicated by conspicuous and permanent labels. 
11.5.13  Systems should include means by wh ich the owner can be alerted that a portion of the system or the 
entire system has ceased to function  and that repairs are necessary (f or example, pump pilot lights, 
thermometers, flow indicators, etc.). 
11.6   Freeze protection 
11.6.1   SDHW systems installed in climates where freezing can occur shall be protected. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  89
 11.6.1.1 Antifreeze chemicals 
Freeze protection may be accomplished through the use of chemicals either as or in the heat transfer fluid. 
11.6.1.2 Automatic draining Freeze protection may be accomplished through the use of  system controls which automatically allow heat 
transfer fluids to drain from parts of the system ex posed to freezing temperatures, as in the draindown or 
drainback systems. Electrically oper ated valves shall drain the system when there is a power outage (that is, 
fail safe). 
11.6.1.3 Automatic recirculation 
Freeze protection may be accomplished through the use of system controls which automatically circulates 
heat transfer fluids through the syst em when outdoor temperatures reach predetermined levels. This freeze 
protection does not operate during periods of power out age unless an auxiliary source of power is provided. 
This freeze protection system is not recommended for us e in areas with frequent or severe freeze conditions, 
and may increase the heat loss of the system during off periods. 
11.6.1.4 Manual draining 
Freeze protection may be accomplished through the us e of system controls which allow an operator to 
manually drain the system of heat transfer fluids. Caution should be exercised when depending on this 
method of freeze protection since it requires human att ention for proper operation. Failure to operate the 
system properly may result in considerable damage. 
11.6.1.5 Low wattage electric resistance heating 
Freeze protection for tank absorber systems may be ac complished through the use of low wattage (less than 
300 W) electrical resistance heaters and system cont rols that supply heat to the tank and adjacent 
piping/fittings only when temperatures inside the system  reach 2 + 1 °C. This freeze protection system does 
not operate during periods of power outage unl ess an auxiliary source power is provided. 
11.6.1.6 Freeze tolerant materials 
Freeze protection may be accomplished through the us e of materials which are not damaged by repeated 
cycles of freezing and thawing while filled with potabl e water, provided evidence that the material can 
withstand such cycling is supplied. 
11.7    Heat transfer fluids 
11.7.1  Heat transfer fluids shall be added and maintained in accordance with the manufacturers' 
instructions. 
11.7.2  Toxic heat transfer fluids shall be separated from the potable water supply by means of a double 
walled heat exchanger or equivalent protection (see 17.3). 11.7.3  Heat transfer fluids shall be selected for normal operating temperatures, as well as maximum (no-
flow) and minimum temperatures. 
11.7.4  Heat transfer fluids should not accelerate corrosion . Similar metals, corrosion inhibitors, inert fluids, 
or sacrificial anodes should be used. 11.7.5  Heat transfer fluids shall be disposed of in a manner acceptable to local health authorities. FDUS 853: 2009 
90 © UNBS 2009 – All rights reserved
 12   System installation ch eckout and start-up procedures 
12.1   General 
12.1.1  This clause presents recommended steps for checking out and starting up a newly installed solar 
water heating system. In most cases, the manufacturer of the system will have included specific instructions. If 
the following recommendations differ, follow the manufacturer's instructions. The general steps for activation 
and start-up include pressure testing and flushing the system, testing the operation of individual components, 
cleaning up the work area, and instructing the owner on system operat ion and maintenance. 
12.1.2  After the system has been installed, it shall be test ed in all modes of operation to the extent practical 
to ensure that it is functioning properly. 
12.2    Pressure testing 
Direct systems should be pressurized to the maximum pr essure they will encounter plus the safety factor 
specified by any local codes. Indirect systems should be pressurized to their design pressure. Use a charging 
or testing kit that includes a tank of compressed gas,  charging fittings, charging liquid and a pressure gauge. 
Some indirect systems require pressurization and testing with a liquid other than water. Follow the 
manufacturer's recommended procedure. 
When the system is full of liquid and pressurized, chec k for any leaks. Check the collector, joints and valve 
stem seals. If any leaks are detected, correct them  and then retest before applying insulation over those 
areas. 
12.3    Flushing the system 
12.3.1  All liquid loops of a SDHW system shall be fl ushed and leak tested. If hydrostatically tested, 
pressurized systems shall be isolated and tested at the maximum working pressure of its lowest rated 
component as specified by the manufacturer. If air te sted, the maximum test pressure shall not exceed 40 
psig (275 kPa). Care should be exercised to purge comple tely fluids used in flushing. During flushing of the 
system, the collectors may be disco nnected or by-passed to  prevent the passage of debris through the 
collector. 
An important factor to note after flushing and checking t he collector loop with water is that some heat-transfer 
fluids, such as silicone and synthetic oils, must not be mixed with water. Ensure that all water has been 
removed from the system piping and that the piping is  dry before adding the oils. Blowing dry compressed air 
through the system for a time can do this. Most glycols can be mixed with water, thereby, the system piping 
does not have to be dry before introducing the glycols. 
Isolate and flush the collector loop, preferably in the re verse direction of normal flow. If the check valve is 
located on the collector supply, use the cold-water service pressure to back flush the collector return. If the 
check valve is located below the collector return hose bib drain, use a garden hose with a double female 
adaptor connected to both an outside faucet  and the collector return drain. 
In both cases, force water out the collector supply drai n through an attached hose leading to a point of safe 
discharge. Check this water for dirt, scale or other  signs of blockage. Stop when the discharge no longer 
contains any debris. 
Except in the case of drain-back systems, it is impor tant that all air be vented out of the collection loop; 
otherwise, it may accumulate in a column of sufficient height to stop or seriously impede circulation. The air 
vent at the high point in the piping is installed for th is purpose. When water reaches the air vent, the vent 
should close quickly, without leaking. Many vent valves  have a stem that can be depressed to allow fluid to 
escape, flushing the valve seat clean. 
12.3.2 All air loops of a SDHW system should be ex amined to confirm compliance with 11.2.13. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  91
 Manual air vents should be used to purge air from the co llector indirect systems using glycol or oil heat 
transfer solutions. Once the air has been purged, the air v ent should be sealed tightly to prevent loss of fluid 
or fluid vapors. 
12.4   Testing the pump and controls 
1.  Check the operation of the pump.  Confirm it is plugged in or wired correctly and power is available. If 
the system's controller has an on/off automatic switch , manually place the switch "on" to activate the 
pump. In systems so equipped, an LED will signal if the pump is on. In systems without such an 
indicator, check for other signs of pump operati on, as an audible hum, motor fan rotation, slight 
vibration, or temperature differences in the feed and return piping. 
a).  Sunny day . On a sunny day, the pump should run most of the time. If the system has a differential or 
direct PV controller, passing clouds may cause the pump to cycle on and off occasionally. 
b).  Cloudy day . On a heavily overcast day or at night, t he pump should not run. To determine if a pump 
powered by 230V residential power is working, unplug it from the controller and plug it directly into a 
wall outlet. If the pump does not have its own plug, direct wire the pump to power (bypassing the 
controller and/or switches). 
CAUTION: Do not attempt this procedure if y ou are not familiar with safe electrical practices. 
It is generally easier and safer to "fool" the c ontroller into turning on the pump. See item 3c, 
Differential controller test. 
2.  Check for flow in the collecto r loop. If there is a flow meter or  indicator in the collector loop, 
determine if fluid is actually moving. If the system  has no flow indicator, use the following methods: 
a).  Sunny day . If it is a sunny day and the pump is runni ng, pull back a portion of the insulation on 
both the collector supply and return pipes (at points a few feet from the tank). Carefully feel (or 
measure with a thermometer) the pipe to make sure  that the return line from the collector is 
hotter than the supply line going to the collector. On a sunny day, such a temperature difference 
(usually 5-15°F) indicates fluid is flowing in the collector loop. 
If you cannot detect a temperature difference, turn the pump off by disconnecting its power 
supply. Leave the pump off for a few minutes - long enough for the fluid in the collector to heat 
up. Then restart the pump and feel the pipes again.  Within several seconds, you should feel the 
hotter fluid from the collector pass through the co llector return line into the tank. If you do not 
feel this surge of hot fluid on a sunny day, ther e is probably some blockage in the collector, the 
pump, the valves or the pipes. 
b).  Cloudy day or at night . On a very cloudy day or at night, you can still use the above procedure to 
check for flow in the collector loop. However, make sure the pump has been off for a long time, 
so the fluid in the collector is relatively cool. Then, when you turn on the pump again, you should 
feel a surge of cool fluid pass from the collector  into the tank. Note that this method works best 
on colder nights. 
To determine the actual flow rate through the solar collectors, use a flow meter or one of the 
methods discussed in Annex N. 
3.  Test control system operation. Conduct t he following tests to check the control system. 
WARNING! For any procedure involving electrical equipment, always turn off or disconnect t
 he unit from the power supply before making any adjustments or resistance measurements.  
a).  Detailed controller test.  A complete method of checking the controller involves the use of a 
differential controller test set. Containing fixed and/or variable resistances, the test set is 
generally calibrated for a specific manufacturer's lin e of controllers, though it can be adapted to 
test other brands of controllers. Instructions for its use are usually supplied with the tester. FDUS 853: 2009 
92 © UNBS 2009 – All rights reserved
 The test set enables you to determine the exact "turn-on" and "turn-off temperatures of the 
controller. Compare these differ ential temperatures to the manufacturer's specifications. If the 
measured temperatures do not match the specificat ions, and if the setting is adjustable, you can 
change the setting to match the manufacturer's recommendations, 
b).  Sensor test . To check the temperature sensors of a differential controller, measure their 
resistance. Disconnect the sensors from the cont roller terminals or lead wires and use a volt-
ohmmeter to measure the resistance across the sensor wires. (See A nnex M.) For thermostats 
and metal film sensors, compare their resistan ce to the manufacturer's temperature-versus-
resistance specifications. 
Table 12.1 – Temperature and thermistor resistance 
Temperature (oF) 3000-Ω 
Thermistor 10,000-Ω 
Thermistor Temperature 
(oF) 3000-Ω 
Thermistor 10000-Ω 
Thermistor 
Thermistor open Infinite Infinite 92 2100 7000 
Thermistor shorted 0 0 94 2010 6683 
30 10400  96 1920 6383 
32 9790 32660 98 1830 6098 
34 9260 30864 100 1750 5827 
36 8700 29179 102 1670 5570 
38 8280 27597 104 1600 5326 
40 7830 26109 106 1530 5094 
42 7410 24712 108 1460 4873 
44 7020 23399 110 1400 4663 
46 6650 22163 112 1340 4464 
48 6300 21000 114 1280 4274 
50 5970 19906 116 1230 4094 
52 5660 18876 118 1180 3922 
54 5370 17905 120 1130 3758 
56 5100 16990 124 1040 3453 
58 4840 16128 128 953 3177 
60 4590 15315 132 877 2925 
62 4360 14548 136 809 2697 
64 4150 13823 140 748 2488 
66 3940 13140 144 689 2298 
68 3750 12494 148 637 2124 
70 3570 11885 152 589 1966 
72 3390 11308 156 546 1820 
74 3230 10764 160 506 1688 
76 3080 10248 165 461 1537 
77 3000 10000 170 420 1402 
78 2930 9760 175 383 1280 
80 2790 9299 180 351 1170 
82 2660 8862 185 321 1071 
84 2530 8449 190 294 982 
86 2420 8057 195 270 901 
88 2310 7685 200 248 828 
90 2200 7333 210 210 702 
 
Generally, differential controllers now have 10000 oh m thermistor sensors or an RTD. In the past, 
3000 ohm sensors were more prevalent. Sensor resistance should match the measured temperature 
as closely as possible, as shown in  Table 1. Refer to the manufacturer's installation guide for specific 
instructions and specifications. 
For example, the table shows that  when the environment temperatur e is 25 °C, the 3000 ohm sensor 
should read 3000 ohms, and the 10,000 ohm sensor should read 10000 ohms. As the temperature FDUS 853: 2009 
© UNBS 2009 – All rights reserved  93
 increases, the resistance dec reases. At 32.2 °C, a 3000 ohm sensor reads 2200 ohms and a 10000 
ohm sensor reads 7333 ohms. 
The general range of solar system temperatures is  21.1 — 60 °C for the tank sensor and 100- 150°F 
for the collector sensor, depending on the time and co nditions of day. If an "open" or "short" condition 
is indicated, check the wiring between the controller and sensor. 
A common cause for an "open" condition is a broken connection between the wiring and the sensor. 
A "short" may be caused by a piece of metal pinching  the sensor wire and conducting it to ground. 
For temperature-actuated switches, such as freeze  sensors and upper limit sensors, you can also 
check the switch position with a volt-ohmmeter. The switch is either normally open or normally closed 
and changes position at a particular temperature. Check the freeze sensor by placing it in ice water and determining that the switch changes position. 
c. Differential controller test. Follow the manufacture r's checkout procedures if they are provided. 
However, if the procedure is unavailable, follow th ese steps to check differential controllers with 
thermistor sensors that have a negative temperature coefficient in which resistance decreases as the 
temperature increases. 
i.  Disconnect and separate all sensor inputs. I dentify the sensor wires for proper reconnection. 
ii.  With the controller in its normal operation or automatic switch position, short the collector sensor 
input wires or terminals together. This simulates a very hot collector. The control should turn on 
(indicated by the LED and/or pump operation). 
iii.  Remove the short and the control should turn off. Be aware that some controllers may utilize a 
time delay circuit to keep the pump from cycling on and off too often. 
iv.  The controller is (probably) in good condition if  it responds correctly to these steps. Test the 
temperature sensors next before proceeding to  a more detailed test of the controller. 
For the differential controllers that use resistance  temperature devices (RTDs), which are positive 
temperature coefficient sensors, t he tank sensor input should be sh orted in Steps iii and iv above. 
Shorting the collector sensor i ndicates a low temperature, and th e pump should stay off. Shorting the 
tank should turn the pump on. If freeze protection and the collector sensor functions are combined, 
shorting the collector terminals simulates a freeze condition. The pump should again turn on. Use a 
volt-ohmmeter to ensure that temperature ma tches resistance as shown in Table 2. 
d. Photovoltaic (PV) controller test. Use the follo wing procedure to check the voltage and current output 
of the photovoltaic module on a sunny day: 
i.  Disconnect the pump from the wires co ming from the PV module or pump starter box. 
ii.  With a volt-ohmmeter, check the voltage bet ween the positive and negative terminals of the PV 
module. Given almost any amount of sunligh t, this open-circuit voltage should be between 14 
and 22 volts. 
You should also check the PV modules  short-circuit current with a volt-ohmmeter that has milliamp 
measurement capability. Under su nny conditions, the short-circuit current should be between 200 
and 1000 milliamps, depending on the voltage rating of the PV module. 
If there is no amperage at good sun conditions, the PV module or the connecting wiring may be 
defective. In this case, check the amperage of the modul e at its roof location to eliminate the effect of 
connecting wiring.  
 FDUS 853: 2009 
94 © UNBS 2009 – All rights reserved
 Table 12.2 – Temperature and RTD resistance 
Temperature (oF) Resistance Temperature (oF) Resistance 
30 861.8 35 876.1 
40 890.5 45 905.1 
50 919.2 55 933.9 
60 948.7 65 963.7 
70 978.2 75 993.4 
80 1008.7 85 1024.0 
90 1039.0 95 1054.6 
100 1070.3 10 1086.1 
110 1101.5 115 1117.5 
120 1133.6 125 1149.9 
130 1165.6 135 1182.1 
140 1198.7 145 1215.4 
150 1231.5 155 1248.4 
160 1265.4 165 1282.5 
170 1299.1 175 1316.5 
180 1333.9 185 1351.4 
190 1368.5 195 1386.2 
200 1404.1 205 1422.0 
210 1439.5 215 1457.7 
 
iii.  To check the DC-powered pump,  use a 12-volt power supply or two 6-volt lantern batteries 
connected in series (12V). Disconnect the PV panel from the pump and connect the pump to the 
proper terminals of the batteries. If the pump does not operate off the batteries, the pump is 
defective. If the pump does run off the batteries, the PV module or connecting wire is defective. 
e.  Check valve test. Use the hose bib drains and se rvice water pressure to check these two valves: a 
horizontal swing check valve or a ve rtical in-line ring check valve. 
Send water against the normal flow direction. Water flowing past the valve indicates a faulty seat or 
stuck hinge that will not seal under the lo w back flow of unwanted thermosiphoning. 
Check a solenoid-actuated or motorized ball valve by using the manual lever (if it is present) to open 
and close the valve while checking for flow. Some motorized valves are not designed to close off 
against municipal water pressure. 
After you have tested these valves, verify their normal operation by listening to and watching the 
valve open and close as the pump turns on and o ff. Check valves are prone to problems from 
sedimentation build-up, so they  should be inspected periodically. 
If the check valve cannot be test ed by the above back flow procedur e and it is suspected it might 
cause night-time thermosiphoning, ex amine the system at night. When the fluid in the collector has 
cooled to a temperature sufficiently below that of t he fluid in the tank, feel the collector supply and 
return pipes a few feet from the heat of the tank . If one pipe is warm, the check valve might not be 
sealing. Sometimes a leaking check valve can cause the diffe rential control to cycle the pump at night. To 
confirm this speculation, unplug the pump from th e differential controller and plug a clock into the 
controller instead. Note the clock's time. Note the time again the next morning before the solar 
system would normally start. If the clock has adva nced because the controller supplied power to it, 
the check valve is not sealing and needs to be replaced. 
f.  Mixing valve test. To check a mixing valve, feel or measure the temperature of the service hot water 
at the closest hot water faucet. As you measure, adjust the mixing valve over its range of motion, 
moving it to the desired temperature setting. Thes e valves may stick open or closed after prolonged 
use, in which case they must be repaired, replaced or eliminated. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  95
 12.5  Cleaning up 
Collect and remove all tools. Dispose of any debris cr eated during the installation. Make sure arrangements 
have been made to repair any damage that may have occurr ed during installation (such as broken roof tiles). 
Ask the owner to look things over and approve the installation and clean up. 
12.6   Homeowner’s manual and instructions 
12.6.1  Written operating instructions fo r the SDHW system shall be giv en to the owner for retention. 
12.6.2  Complete operating instructions, including seq uence of operation, wiring diagrams, and flow 
diagrams, shall be provided with the SD HW system. Installers shall provide written instructions to the building 
occupant for proper operating, safety, and em ergency shutdown procedures of the devices. 
Carefully instruct the owner on the op eration of the solar wa ter heater. This reduces "false alarm" callbacks 
and enables the owner to make minor adjustments. With  active systems, the owner should understand the 
pump and "pump operating" indicator on the control system. 
12.6.3  Where hazardous fluids are used in the system , suitable warning labels shall be permanently 
mounted in a conspicuous place, with instructions for emergency treatment. 
12.6.4  The owner shall be provided with written instructio ns for routine required maintenance, including 
operations that should be performed by service personnel. Instructions shall include collector glazing cleaning 
(see 6.10.7), draining and refilling, air venting of liquid systems, cleaning  of components, corrosion control, 
and other maintenance procedures, in t he system's operating instructions. 
12.6.5 A periodic maintenance program is recommended. 
12.6.6  Service check lists and logs should be provided with system operating instructions. 
12.6.7  Periodic cleaning of the collector glazing may be n eeded to maintain optimum efficiency. Operating 
instructions should recommend the proper cleaning agents and methods of cleaning that are compatible with 
collectors. 12.6.8  Valves should be checked periodically for proper operation. 
12.6.9  Periodic inspection of the storage tank pan drains  should be made to ensure their ability to drain 
adequately when needed. 
Carefully explain any freeze protection devices. Demons trate the steps for manually draining the collectors 
and piping, if that is a freeze protection mechanism fo r the system. Also, show them how to reactivate the 
system. 12.6.10 Devices such as pumps, valves, and controls shou ld be accessible for repair and maintenance. 
12.6.11   Show the owner how the back-up electric element may be turned off during warm months. Explain 
that the system should provi de some hot water on its own. If the system shortly runs out of hot water, consider 
if it could have been subjected to a temporary abnormal  load or lack of sunshine. Otherwise, it may need 
service. 12.6.12   Demonstrate how to isolate the storage tank from  the collector loop. Then show the owner how to 
drain several gallons of water from the tank to remove bu ilt-up sedimentation. Instruct  the owner to follow this 
procedure at least annually. Advise the owner that hot water use patterns can affect system efficiency. Let 
them know the system will provide the hottest water du ring late afternoon and early evening. Suggest they 
adjust their hot water use to accommodate the solar cycle. 
12.6.13   Affix the name and contact information of the installi ng firm and installation mechanic to the tank or 
controller so the homeowner can contact the right people quickly if service is required. If possible, make 
arrangements with the owner for periodic professional inspection and maintenance of the system. Make sure FDUS 853: 2009 
96 © UNBS 2009 – All rights reserved
 that the owner has a copy of the system manual and t hat the manual is kept in an accessible location for 
future reference. 
13   Commissioning and documentation 
13.1   Filling the system 
With direct systems, and with indirect systems where wa ter is the heat transfer fluid, all new work, and also 
the existing system, as necessary, should be thoroughly flushed out with water, pressurized if necessary, and 
suitably isolated from the mains to prevent back siphonage. 
Indirect systems using non-aqueous and certain aqueous ba sed heat transfer fluids have to be flushed out in 
accordance with the fluid manufactu rer’s instructions. This stage of commissioning may afford an early 
opportunity to check that all unions and glands are wate rtight and free of weeps. However, some liquids are 
more searching than water and, particularly in systems w here a circulating pump is employed, the circuits will 
require a second inspection when finally filled and with the pump operating. The installer should ensure that all non-return valves  and the pump are connected the right way round (usually 
indicated by an arrow) for the direction of flow, and that  non-return valves and motorized or solenoid valves 
are operative. The system should then be drained and refilled with the final charge of flui d, preferably when the collector is 
cold rather than hot. It is important to ensure that air pockets are remove d from sealed and vented systems, and special attention 
should be given to this at the time of commissioning.  The design of the system should allow for subsequent 
automatic release of air. 
13.2   Drain-down systems 
Solar heating systems that are susceptible to freezing may be expected to incorporate in their design a frost 
sensing device that will monitor either freezing conditions at the collector, or the am bient temperature adjacent 
to the array, or both. 
Frost control devices can be of a simple 'yes/no' l ogic or they can monitor the differential temperature 
irrespective of ambient temperature and drain the system  when no temperature differential exists between the 
collectors and the preheat vessel. 
Where drainback systems are employed, it is recommended t hat provision is made for the installer to test that 
the installation is operating correctly by the provision of a test button fac ility. Where no such provision is made, 
the manufacturer should provide instruct ions for overriding the control so that the arrangements for drainback 
may be tested. 
13.3   Electrical and auxiliary equipment 
Pumps of a lower wattage than domestic central heating pum ps are available for solar heating installations. 
However, special attention to pump selection will be needed when non-aqueous fluids are used. The pump's 
setting will have to be made to suit the flow rate requir ed. The installer should ensure that the pump is vented 
of air and that it operates quietly. If a flow meter is fitted to the circuit, the pump flow control should be 
adjusted to give the design flow rate. 
Differential temperature controllers may be preset at a suit able differential at the factory, or they may require 
setting and testing on site in accordance with the manufacturer's instructions. 
Correct functioning of all indicator lights and other electr ical devices should be confirmed. Correct functioning 
of temperature indicators (if fitted) should be confirmed wh en the system is first filled and, if possible, at a later 
date when the system is hot. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  97
 The manufacturer's instructions should also be follo wed for any frost protection equipment installed. 
13.4    Thermal insulation for the system 
It is recommended that all testing and inspection of the system is conducted before  the system connections 
are thermally insulated in order to  ensure that these are not weeping. 
13.5     Making good 
Before an installation can be regarded as being satisfacto rily completed, the installer has to ensure that all 
damage to the structure caused by th e fitting of pipes, tanks, mounting br ackets, etc. is restored and made 
good. 
Particular attention should be paid to repairing and seali ng any damage to the roof lining, resulting from the 
installation of fixing brackets and pipes, etc. passing through the roof cover. Damage to guttering, walls, 
garden and lawn by ladders, scaffolding,  hoists, etc. should also be made good. 
13.6     Start-up and handing over 
Once the installer has completed the installation, dependi ng upon the time of year and on the instructions of 
the client, the system may be either switched on and left operating, or left in a safe condition for later handing-
over. 
In either event the installer should present an appropriate document to t he client, certifying that the system 
has been installed and commissioned satisfactorily. 
At handing-over, the client should be supplied with a user's information envelope, containing the following: 
a)  The handing-over document described in paragraph 2 of 10.6. 
b)  Descriptive literature, prepared by the designer, relating to the operational principle of the system, and 
giving technical data on the main system components. This information may be provided on a data sheet, 
and a suggested format providing the mi nimum information is given in 10.7. 
c)  Warranties or guarantees issued by the manufac turers of the components, or by the installer. 
d)  A set of operating instructions, describing start-up,  normal running and shut-down procedures in a form 
readily intelligible to the non-technical user. These sh ould also include details of protection provided 
against overheating and frost. 
e)  A schematic diagram of the syst em and a circuit diagram of the electrical controls. A warning should be 
given against tampering with any of the electrical controls or other equipment. 
f)  A user's data sheet (see 10.7). 
g)  Details should be provided of any equipment that has been fitted to check system operation. The purpose 
of all indicator lights should be clearly explained. If a flow meter is fitted, the design flow rate (and 
permissible variations) should be stated. Informat ion should be given on the expected normal behaviour 
of instruments and on how they may be used to detect incorrect system operation. Details of action to be 
taken in the event of apparent faults  should be provided. If special additives are used in the heat transfer 
liquid, durable identifying labels providing the necess ary information as to the formulation, solution 
strength, and specific hazards, source of supply and  expected life of the liquid should be attached to the 
appropriate system components in a conspicuous manne r for future reference. A separate label should 
also record the date of the installation and the name and address of the installer. 
 
 FDUS 853: 2009 
98 © UNBS 2009 – All rights reserved
 13.7   Recommended form of user's data sheet 
System description 
Instrumentation provided for checking system operation ……………………………………………………………. 
Circuit design  
*Direct system/Indirect system 
Heat transfer fluid in collector circuit  
*Water and inhibitors/water and antifreez e/mains supply water/non-aqueous/other  
Manufacturer's recommended replacement fluid…………………………………………………………………. 
Method of circulation  
*Pumped (pump rating ……………………………………………………………………….W)/ thermosiphon 
Means of accommodating fluid expansion  
*Feed and expansion cistern/pressurize d accumulator/other………………………………………………. 
Means of accommodating 'no-load' condition in summer weather  *Drainback/special fluid/pressurized system/other ………………………………………………………………. 
Method of frost protection  
*Antifreeze/special fluid/drai nback/other……………………………………………………………….. 
Method of system control  
*Differential temperature controller /time clock/other…………………………………………………………. 
*Other controlled functions………………………………………………………………………..m
2 
System performance 
Aperture area of collector …………………………………………………………………m2 
Collector inclination to horizontal ………………………………………………….degrees 
Collector orientation ……………………………… ……....... degrees east/west of south 
Collector performance classification in accordance with BS 5918 *B/C/D/E/F1 
Design hot water demand.…………./day Preheat storage tank volume……………………………………... 
Combined preheat/hot cylinder volume …………………………. 
Design hot water delivery temperature ……………………………….°C 
Estimated annual solar energy supplied…………………………………………. (MJ per year) 
Maintenance 
Recommended frequency for heat transfer fluid inspection …………………………………………………….. Recommended frequency for heat transfer fluid replacement …………………………………………………. 
Other servicing requirements ……………………………………………………………………………………… 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  99
 13.8  Post-commissioning checks  (see also Clause 16 (a) and (b)) 
Depending on the terms of contract agreed, a post-commissioning visit within a few weeks may be included in 
the supply and fixing cost, or it may form part of a maintenance contract, or be by arrangement with the 
installer. It is recommended that at least the following checks should be made: 
a)  that all unions and glands are free of weeps; 
b)  that the glazing seals are weathertight and sound; 
c)  that all air has been expelled from the collector circuit; 
d)  that the levels in cisterns are correct or that  sealed systems are at the correct pressure and volume; 
e)  that electrical controls and warning indicators are operating correctly, according to the manufacturer's test 
instructions; 
f)  that the circulating pump (if fi tted) is operating without undue noise; 
g)  that all insulation is firmly attached; h)  that all cistern covers are properly in place, i)  that no condensation or damp spots are apparent, particularly around the pipes and fixings in the roof 
space; 
j)  that roof fixings are firm, and that the roof co vering is free from cracks and abrasions beneath the 
collectors; 
k)  that the weathering is prop erly protecting the structure. 
A suitable check list should be provided by the supplier for the inspection, and it should be signed and dated 
by the person making the inspection. A copy should be left with the client. 
14    Problem assessment and system checkout 
14.1    Problem assessment 
To diagnose system problems, y ou must not only understand the syst em type and its components and how 
they work, but you must also know what questions to  ask to determine the problem and find out when and why 
it occurred. The more experi ence you have servicing solar systems, t he more you will learn what questions to 
ask the customer. 
14.2    The initial service call 
When you first receive a service call, record the caller's name, address and telephone number and be sure to 
get directions to the service location. Also, verify th e caller is the system owner and is authorized to have you 
service the system. 
Determine what kind of service the call er is requesting. Is it a routine se rvice call or is the system not working 
properly? If the system is not working,  what exactly is wrong? Is there no hot water? Is the system leaking? If 
it is leaking, where is the leak — on the roof or at the storage tank? The more you know about the system, the 
better prepared you will be when you arri ve at the site. For example, if t he system has an ex pansion tank and 
the system is over two years old, yo u will want to take new glycol with you to replace the old glycol. If the 
system has a drainback tank, you will w ant to have distilled water with you. 
 FDUS 853: 2009 
100 © UNBS 2009 – All rights reserved
 Avoid any misunderstanding by making your payment policy clear at the outs et. For example, if the caller is 
renting the home, clarify whether or not you expe ct to be paid at the time service is rendered. 
Find out the type of system, who installed it, how old it  is and what previous service has been performed. Also, 
find out if the caller has a manual, a schematic, and a parts list for the system and what, if any, service 
contracts, warranties and insurance policies cover the system or its components. 
14.3  System records 
All collectors and systems sold or marketed shall be certif ied. As part of the certif ication requirements, each 
system must include a homeowner's manual that lists system components and desc ribes the system design, 
operation and maintenance requirements. In addition to the manual, each system should have a freeze 
protection information label displayed at a prominent location on the system — on the storage tank, heat 
exchanger or controller. This label describes the syst em's freeze protection mechanism and any actions the 
homeowner must take when freezing occurs. 
14.4   Warranty coverage 
Find out if the system or its components are covered by warranties. Typically, t he term of the collector 
warranty will be from 5 to 20 years, with other components varying from 90 days to 5 years. It is also important 
to know whether the warranties are full or limited. This designation is required to appear on the warranty 
document. A full warranty is required by law to provide the following: 
-  A defective product will be fixed (or replaced) fr ee, including removal and reinstallation if necessary. 
-   The product will be fixed within a reas onable time after the customer complains. 
-  The customer will not have to do anything unreasonable to get warr anty service (such as shipping 
components back to the factory). 
-  The warranty is good for anyone who owns  the product during the warranty period. 
-  If the product cannot be fixed (or has not been after a reasonable effort to do so), the customer may 
choose to receive a new product or a refund. 
Limited warranties provide less pr otection than the full warranty. For example, a limited warranty may: 
-  Cover only parts, not labor 
-  Allow only a prorated refund on credit 
- Require the customer to return the product to the manufacturer for service 
-  Cover only the original buyer 
-  Charge for handling the service order 
Be aware, too, that some companies include a provisio n that unauthorized service may void their warranties. 
In these cases, be sure to contact the manufacturer fo r approval. If you provide unauthorized service, you may 
be held liable and be forced to take over that warranty. 
Typically, a solar water heating system has a system or  installation warranty separate from the individual 
component manufacturer warranties. Be prepared to explai n this to the customer if necessary. Some service 
problems that arise during the warranty period may not be covered by the warranty for the item in need of 
repair or replacement. For example, if a component fails because of faulty installation rather than a product  
defect, the manufacturer of the product may not be required to repair the component. In this case, the 
contractor's system warranty, if still in force,  should cover the cost to repair the problem. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  101
 Another potential gap in warranty coverage falls in the ar ea of freeze damage. Some collector warranties will 
specifically exclude damage as a result of freezing. In  addition, the freeze protection component will typically 
exclude coverage of incidental damages. If the freeze protection device fails, causing damage to the collector, 
this exclusion normally relieves the manufacturer of t he component of liability for re pair or replacement of the 
collector. The customer can usually seek recourse from the homeowner's policy to recover these costs. 
If the customer has warranties that appear to be in force,  but the company is no longer in business, all hope is 
not necessarily lost. If the system was financed, the fi nance company may be liable for all warranty claims as 
a "holder in due course."  A review of the instalment sales contract will us ually specify what ri ghts the customer 
may have in this regard. 
Even when the warranty is no longer in force, some cont ractors replace components at no cost as a goodwill 
gesture toward the customer. But they are not obligated to absorb this expense. Ask about warranties at the 
outset so neither you or the customer is su rprised when you prepare the repair estimate.  
14.5   Service history 
Many contractors offer service contracts to their custom ers, providing either the la bor or materials for free, 
depending on the type of contract. So it is important to  determine whether or not you are doing something you 
do not need to do because the customer has a service contract with another company. 
Find out about past service and repairs on the system. If you know a system is five years old, you may think 
the controller is no longer under warranty. But if the controller was replaced just 90 days ago and is under a 
one-year warranty, you can take the controller back to the supplier for exchange. The customer will appreciate 
not having to pay for another controller and will call you back the next time service is needed. 
14.6   Contractor liability 
Some contractors give customers adv ice over the telephone about how to correct a problem. If you do this, be 
aware of potential liability. For example, pushing the reset button on the storage tank is a very simple 
procedure, and you may suggest that  your customers do this themselves. It saves you time and saves them 
the cost of a service call. But tell them first to turn of f the circuit breaker. Emphasize that they should never 
remove the front plate on the tank until they have turned off the power. 
You might rather not give any instru ctions over the telephone. Even if yo u only need to reset the heater you 
can make the visit worthwhile for the customer and fo r yourself by performing a routine service check while 
you are there. 
14.7   Overall checkout 
You should always check the entire system while you are on a servic e call because many times more than 
one problem exists. For example, you may replace a def ective pump. Later, when this new pump also fails, 
you find that a defective valve was preventing water from  getting to the pump, causing the pump failure. Keep 
in mind that a "system" requires proper perform ance of all the components working together. 
While you check the system, consider ways you can improve its performance. For example, open-loop 
systems can include an air vent, a vacu um breaker, a pressure  relief valve and a freeze valve. You will find 
many direct systems do not have all of these component s, even though each one has a definite function. You 
can give the customer a better working sy stem by adding these useful components. 
At the same time, do not change the system for c hange's sake. Some contractors do not like or do not 
understand controllers or PV systems. So rather than make repairs, they change the whole system. If you do 
not want to work on one type of system, refer the job to someone else. 
When you first look at a system, prepare an estimate fo r the customer including the cost, the results and the 
benefits of the repairs. After you complete the repairs, test the system completely once again. Be sure that it is 
right. If you have to go back on a second or third call, y ou lose whatever money you made on your first call. 
And finally, point out your work so t he customer knows what you have done. FDUS 853: 2009 
102 © UNBS 2009 – All rights reserved
 14.8   Investigating consumer complaints — an example 
Suppose a collector loop pipe has burst, but the customer  manually drained the sy stem to prevent freeze 
damage. The collectors were drained using the proper is olation and drain valves; yet the next morning water 
was trickling from the collector and a pipe was ruptur ed. Somehow water had gathered in the collector. You 
should check several possible causes. 
First, is the homeowner sure all the water was drained from the collector? Is the system installed to prevent 
water being trapped when the collectors are drained? Inve stigation reveals the system contains a vacuum 
breaker at the collectors and the drain valves are installe d in such a manner that one is at a higher level than 
the other. You determine the amount of water the homeow ner says was drained represents what would have 
been in the collectors and piping — unless, of course, there is a small water trap in the collector or collector 
piping. If the collector is large and mounted in a horizontal position, are the flow tubes bending in the 
midsection (creating a water trap)? Investigation reveals no trap. 
There could be another culprit — the isolation valve.  Although the valve was cl osed by the homeowner, 
sedimentation build-up or a malfunction could have caused t he valve to leak, allowing water to slowly seep to 
the collectors, freeze and rupture the pipe. 
14.9   Lifestyle analysis 
Some people think when they acquire a solar DHW syst em, they have an unlimited supply of hot water. Be 
sure they understand the DHW system storage can prov ide the hottest water during the late afternoon and 
early evening hours. Keeping this in mind, they should use hot water during these periods to achieve the best 
results from the system. To minimize their back-up h eating expense, they could, for example, take showers 
and use the dishwasher during the evening and use only sm all amounts of hot water in the morning. Here are 
some questions that you may want to ask if the compla int is "not enough hot water" or "high electric use": 
1.  How many people are using the hot water? 2.  Have recent guests added to the water use? How many guests? 
3.  Have extra washing (clothes or dish es) demands recently been put on the system? 
4.  When is the family's major use of hot water? 
5.  Has the weather been clear, allowing the maximum solar heating? Or has it been overcast, 
especially around the middle of the day? 
6.  Are water bills higher than usual (perhaps indica ting a leak in the system — perhaps a leak under the 
slab)? 
NOTE Remember, this is only a sample of the questions service personnel might ask. 
14.10  Common problems 
Some common problems are easy to identify and corr ect. Other problems, such as "not getting enough hot 
water" require investigating numerous components, the system design and location, as well as the 
homeowners' lifestyle. This section first discusses probl ems that are easy to identify and then describes 
problems that demand more investigation. A detailed and concise listing of these problems, the components 
to check, the possible causes, and the corrective acti ons are listed in Section 4, Module: Troubleshooting 
Checklist. 
The simplest way to find out if the system is working is  by turning off or disconnecting the electric back-up 
element (or other source of back-up heat). Some insta llers provide a switch near the storage tank for this 
purpose. In most cases it is necessary to turn off the appropriate circuit breaker at the electrical load center. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  103
 Certain symptoms are obvious, but you may find more  than one problem. Therefor e, once you identify the 
initial symptoms, continue the diagnostic procedure. 
Before you begin the diagnostic procedure, ask the owne rs to describe any sympto ms they have noticed (for 
example, insufficient hot water, pump running at night, noi sy pump or leaking collectors). Use this information 
and the Troubleshooting Checklist Module to quickly identif y the causes. Then follow this procedure to identify 
other, less obvious problems. 
The most common problems are related to the following: 
-  Controls and sensors 
-  Pumps and flow rates 
-  Thermosiphoning and check valves -  Freeze damage 
-  Collector shading 
-  System sizing and consumer lifestyle 
14.10.1  Controls and sensors 
If the pump operates constantly or does not operate at  all, the problem may be in the control system. 
The controller itself, a sensor or the wiring might hav e been damaged by lightning strikes, line voltage surges 
or short circuiting from water, rust or abrasion. Ea ch of these components should be examined. But if the 
pump does not operate, the problem could also be in the pump itself or the piping. 
14.10.2  Pumps and flow rate 
If the system controls are working correctly, an inope rative pump may be due to a stuck impeller, a burned-out 
motor or a broken shaft. These types of problems ma y be expected over the lif etime of any component 
subjected to the temperature and cyclin g stresses of a solar system pump. 
Even though a solar pump is operating and is being contro lled correctly, there still may be problems with the 
actual flow rate in the collector loop. If the pump has b een sized to just barely overcome the pressure head of 
the collector loop, an unexpected added resistance can stop all flow through the collector. For example, air in 
the fluid may, over a period of time, collect in a secti on of piping, especially if it  cannot escape through a vent 
to the atmosphere. This "air lock" can prevent any flow if the pump does  not have the capacity to compress 
the air completely and force it through the system. 
In an indirect system, loss of collector  fluid pressure can also prevent flow in the collector loop. The pump is 
generally not sized to overcome the static head or pres sure due to the difference in height between the top 
and bottom of the collector loop. It is usually sized to maintain the desired flow against the dynamic head or 
pressure due to the resistance to flow in the pipes, fi ttings and valves. If the fluid pressure to overcome the 
static head is lost, then the pump may not be able to maintain flow against the combined static and dynamic 
head of the system. 
14.10.3  Thermosiphoning and check valves 
As the liquid in the active system collector loop beco mes cooler in the evening or in colder weather, it 
becomes denser and heavier, flowing down into the storage tank. In turn, it forces less dense, heated liquid up 
into the collector where this heated liquid cools. This  action, if not stemmed with a properly operating check 
valve, can result in excessive loss of heat. In addition,  this action often deceives the collector sensor and 
controller into believing the collector is hot and thereby  activating the pump intermittently during the evening 
and colder nights. FDUS 853: 2009 
104 © UNBS 2009 – All rights reserved
 The most common check valve utilized in active solar syst ems is the vertical ring check valve. Unfortunately, 
scale and sedimentation build up over time may prevent this valve from seating co mpletely. Defective valves 
must be cleaned of all sedimentation and corrosion or r eplaced. A simple and relatively accurate method of 
determining if the check valve is defective is to check the operation of the pump at night. If the pump is turning 
on and off (on differential controlled systems), leaking th rough the check valve and thermosiphon heat loss is 
indicated. 
14.10.4  Freeze damage 
Burst collector tubes and piping are a result of an im properly functioning freeze protection system. In a 
differential controlled system, the fault may lie in the freez e sensor operation, in the se nsor's location or in the 
controller itself. If the system has a freeze sensor but no freeze protection valve, a power failure during a 
freeze could result in pipe rupture. It is not uncommon to have a power failure during a freeze. 
In a system using an automatic freeze  prevention valve, the valve or its lo cation may be at fault. This type of 
valve often fails to reseat properly after opening. Extr eme temperatures during summer conditions can affect 
the calibration and internal components of the valve, whic h in time may lead to failure or leakage. A leaking 
valve should be removed, serviced and recalibrated per manufacturer's recommendations or replaced to 
ensure proper operation during the winter season. 
Freeze damage can also occur when the collector is "dra ined." (Some systems have "traps" in the piping that 
prevent complete drainage.) 
14.10.5  Other potential problems 
The common problems discussed above are fairly eas y to diagnose. The following problems require more 
investigation because they cannot readily be seen. 
14.10.5.1 Shading the collector 
Collector shading may not be a problem in the summer months, but during winter months, the sun is at a 
lower position in the sky and shading from adjacent tr ees or man-made structures may occur. Relocation of 
the collector or trimming vegetation causing the shade are the only solutions. In both cases, use the Crome-
Dome Collector Siting Aid provided in the Appendix or an appropriate site selection device to make sure that 
shading of the collector does not occur. 
14.10.5.2 Pipe insulation degradation 
Ultraviolet (UV) rays and extreme system temperatures accelerate degradation of many materials, especially 
exterior pipe insulation. Although many manufacturers clai m their pipe insulation contains ultraviolet inhibitors 
and does not require a protective coating, sustained exposure appears to degrade almost every unprotected 
material. 
Therefore, all insulation should be inspected for degradat ion and be replaced as necessary. Exterior insulation 
should be coated with UV resistant material. Several insu lation manufacturers offer a coating for this purpose. 
Latex paint that matches the roof color and has pigmen ts that inhibit UV degradation is also available. 
Insulation that has degraded due to high temperatures must be replaced with a brand  that can withstand such 
temperatures. This is critical for insulation that is us ed on the collector return line directly adjacent to the 
collector. When replacing exterior insulation on the roof area valves, take care not to restrict the operational 
parts of these valves. 14.10.5.3 Equipment sizing 
If solar system equipment is sized im properly, the homeowner might not hav e enough hot water or might have 
excessive utility costs. Use Annex K to determine proper system sizing. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  105
 14.11  System checkout 
Use the following procedures to diagnose system probl ems and can also be used to verify that new systems 
are installed correctly and working properly. 
The simplest way to find out if the system is working is  by turning off or disconnecting the electric back-up 
element (or other source of back-up heat). Some insta llers provide a switch near the storage tank for this 
purpose. In most cases it is necessary to turn off the appropriate circuit breaker at the electrical load center. 
With the electric back-up element o ff, the system - if it has been prop erly sized to th e owner's demand - 
should provide ample hot water on bright, sunny days and even on days with a modest amount of cloud cover. 
If the system fails to provide enough hot  water, or if the water is not hot enough (lower than 115°F), something 
may be wrong with the system operation. Use the followi ng procedure to identify the problem and its cause. 
Certain symptoms are obvious, but you may find more  than one problem. Therefor e, once you identify the 
initial symptoms, continue the diagnostic procedure. 
Before you begin the diagnostic procedure, ask the owne rs to describe any sympto ms they have noticed (for 
example, insufficient hot water, pump running at night, noi sy pump, or leaking collectors). Use this information 
and the Troubleshooting Checklist Module, to quickly i dentify the causes. Then follow this procedure to 
identify other, less obvious problems. 
1.  Collectors . Standing on the ground outside and looking at  the collectors, verify these details: 
a.  They receive very little shading , if any, from three hours before solar noon to three hours 
after, for all seasons of the year. (Appendix: Cr ome-Dome Collector Siting Aid gives a method 
for estimating the sun's location in relation to the collector for all seasons of the year.) 
b.  They face approximately south (within 45° east or west of s outh). If they are oriented outside 
of this range, collector surface area should be increased above normal sizing requirements. 
c. They have a reasonable tilt . To maximize solar system performance in the winter, proper tilt is 
latitude plus 10°-15° from horizontal. For example, in  Orlando, Florida, optimum tilt is 43° (28° + 
15° = 43°). 
d.  They are not leaking . Water running off the roof or collector fluid stains from the collector area 
indicates an obvious leak. 
e.  For systems utilizing PV modules as the control method , the PV module is not shaded or 
covered with dirt. 
Any of these problems reduces the performance of  the system. However, avoid climbing on the 
roof at this stage unless you have determined t he exact problem and need to perform repairs or 
service. 
2.  Back-up heating element . At the storage tank, check to see if the electric back-up element is on or 
off. Solar tanks usually have only one element, loca ted in the upper area of the tank. The element 
may be wired to a separate switch, but by code, it  must also be controlled by a 230 VAC breaker at 
the house load center. If it has been off for some time an d the area has just experienced a period of cloudy weather, the 
storage tank won't contain much hot water. If it is  on and it is also a bright sunny day, turn the 
element off so only the solar system operates for the rest of the procedure. For your own safety, 
make sure that it stays off for the remainder of the procedure. 
If the symptoms warrant it, remove the elemen t cover plate and check the setting on the tank 
thermostat. Set it to the lowest necessary temperature (u sually about 120-125°F). Finally, make sure 
the bottom element, if any, is properly disabled or if a conventional tank is used, set to a low temperature. Sometimes, the over-temperature breaker above the thermo stat has deactivated the FDUS 853: 2009 
106 © UNBS 2009 – All rights reserved
 element. To reset this breaker, simply press the reset button. (See Appendix: Electric Water Heater 
Circuitry for a description of the operation of an electric water heater.) 
3.  Plumbing attached to the tank . Inspect the plumbing attached to t he tank(s). Identify and verify the 
proper connection of each of the following element s according to the system manual or the plumbing 
schematics in this publication. (I n some cases, the tank may be different from the one diagrammed in 
the manual and have different plumbing connections. Note these variations.) 
a.  Hot and cold water service connections . If there is a tempering valve, is it connected 
properly? Generally, the hot, cold and mixed ports of the valve are marked, as are the 
connections to the tank. The mixing valve should also be located below th e top of the tank so it is not continuously 
exposed to the hottest water of the system. Check the temperatur e setting of the valve. (Keep in 
mind that some anti-scald valves can be installed above the top of the tank.) 
b.  Collector supply and return connections . Does the supply line run from the bottom of the 
tank and the return line from the collector deliv er water below the thermostat of the back-up 
heating element? Systems that utilize a timer as  the pump control method can have collector 
supply and return lines located at the bottom of the storage tank. 
Finally, note where the pipes penetrate the ceili ng/roof so the lines may be traced for proper 
connection at the collectors). 
c.  Control valves and their settings . A serious problem can sometimes be traced to a valve 
being incorrectly open or closed or havi ng been installed in the wrong location. 
d.  Pump and check valve . Generally an arrow or some other symbol on the pump and the check 
valve indicates the direction of water flow. Be su re these devices have been installed so flow is 
in the right direction. (The check valve may be co vered by insulation. You can usually find it by 
feeling the pipes through the insulation.) 
e.  Piping insulation . Check the insulation around the tank. Ensure there are no uninsulated pipes 
or valves. At least two feet of the "cold-in" and "hot-out" lines should be insulated. If convenient, 
check for pipe insulation in the attic. Note deficiencies for later service. 
Pressurized indirect systems only: 
f.  Expansion tank . Check the expansion tank location. T he commonly used diaphragm type tank 
may be installed anywhere in the collector loop and in any position. However, for the most 
efficient pump operation, it should be located on the suction side of the pump with the distance 
between the pump and expansion tank as short as possible. 
An expansion tank may also be used in the water si de of an indirect solar system if a back-flow 
preventer is installed on the cold-water supply  line. The tank must be sized to accommodate any 
expansion in the total storage capa city of the hot water system. 
g. Pressure gauge . The system fluid is generally charged to a static pressure (pump not running) 
of 10-30 psig. If the collectors are locate d more than one story above the pump, system 
pressure will be increased. On the discharge side of the pump, the pressure gauge normally 
registers additional pressure (about 3-5 psig) when the pump is running. The pressure also 
fluctuates depending on the temperat ure of the collector fluid. 
4.  Control system . Locate the control sensors, temperature sensors and the electronic controller box 
(if one is present). Determine which type of control system is used: 
a.  Thermosiphon and integral collector storage (ICS) systems . Controls and sensors are not 
needed. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  107
 b.  Snap-switch (absolute) . These sensors are attached to the pipes with #14 to #18 gauge wire 
connected to the 115 VAC supply to the pump mo tor. Although usually this type of control 
system does not have a control box, occasionally  a control box houses a step-down transformer 
to supply low voltage to the collector snap-switch. 
c.  Timer . The pump is connected to a simple clock timer plugged into an electrical outlet. Check 
the time and on/off settings and that the timer functions properly. 
d.  Differential temperature . Sensors are attached to a contro ller by two small wires. The 
controller is plugged into a 115 VAC electrical ou tlet. Once you have located everything in the 
control system, consult the manufacturer's informat ion or controller labels to ensure everything 
is connected properly. 
e.  Photovoltaic (PV) . The PV module is generally wired directly to a DC motor pump with from 
#14 to #18 gauge wire. Sometimes an electronic pump starter is connected in between the PV 
module and the pump to facilitate current matching. There may also be an on/off switch. Check 
the switch position and all connections. 
5.  Pump operation . Check the operation of the pump. Confirm t hat it is plugged in or wired correctly 
and power is available. Some controllers have an on/off automatic switch and you can manually 
place the switch "on." You can usually hear a sli ght hum when the pump is running. You might also 
be able to see the motor fan moving or feel a slight vibration. 
WARNING! Many pump motors are very hot after operating continuously for some time. 
In some systems, an indicator lamp on the contro ller signals when power is supplied to the pump. 
When this indicator is on, the pump should run. 
a.  Sunny day . On a sunny day, the pump should run mo st of the time. If the system has a 
differential temperature controller or PV module, passing clouds may cause the pump to cycle 
on and off occasionally. 
If the system has a snap-switch control, the pump tends to turn on and off more often. 
b.  Cloudy day . On a heavily overcast day or at night, th e pump should not run. To see if an AC-
powered pump is defective, unplug it from the contro ller and plug it directly into a wall outlet. If 
the pump does not have its own plug, direct wire  the pump to power (bypassing the controller 
and/or switches). 
CAUTION: Do not attempt this procedure if you are not familia r with safe electrical practice. 
It is generally easier and safer to "fool" the controller into turning on the pump. See item 7a, 
Differential controller test . 
6.  Flow in the collector loop . If there is a flow meter or indicator in the collector loop, determine if the 
fluid is actually moving. If there is no flow indicator, use the following methods: 
a.  Sunny day . If it is a sunny day and the pump is r unning, pull back a portion of the insulation on 
both the collector supply and return pipes (at points a few feet from the tank). Carefully feel (or 
measure with a thermometer) the pipes to make su re that the return line from the collector are 
hotter than the supply line going to the collector. On a sunny day, such a temperature difference 
(usually 5-15°F) indicates fluid is flowing in the collector loop. 
If you cannot detect a temperature difference, turn the pump off by disconnecting its power 
supply. Leave the pump off for a few minutes; long enough for the fluid in the collector to heat 
up. Then restart the pump and feel the pipes again. FDUS 853: 2009 
108 © UNBS 2009 – All rights reserved
 Within several seconds, you should feel the hotter fluid from the collector pass through the 
collector return line into the tank. If you do not f eel this surge of hot fluid on a sunny day, there is 
probably some blockage hi the collector, the pump, the valves or the pipes. 
b.  Cloudy day or at night. On a very cloudy day or at night, you can still use the above procedure to 
check for flow in the collector loop. However, make sure the pump has been off for a long time, 
so that the fluid in the collector is relatively cool. 
Then, when you turn on the pump again, you should  feel a surge of cool fluid pass from the 
collector into the tank. Of course, th is method works best on colder nights. 
To determine the actual flow rate through the so lar collectors, use a flowmeter or one of the 
methods discussed in Annex N. Check the contro ller operation before determining the exact flow 
rate. 
7.  Control system operation . Conduct the following tests to check the control system. 
WARNING: For any procedure involving electrical equipment, always turn off or disconnect the unit 
from the power supply before making any adjustments or resistance measurements. a.  Differential controller test. You may need to fo llow the manufacturer's checkout procedures to 
not void the warranty. If their procedure is unava ilable, you can follow these steps to check most 
differential controllers with thermistor sensors. i). Disconnect and separate all sensor input s. Identify the sensor wires for proper 
reconnection. 
ii).  On drain-down controls that use normally closed freeze sensors, short the freeze sensor 
input wires or terminals at the control. 
iii).  With the controller in its no rmal operation or automatic swit ch position, short the collector 
sensor input wires or terminals together. The control should turn on (indicated by lights 
and/or pump operation). 
iv).  Remove the short and the control should turn off. (Some older-model  controllers may utilize 
a time delay circuit to keep the pump from cycling on and off too often.) 
v).  The controller is probably in good condition if it responds correctly to these steps. Test the 
temperature sensors next before proceeding to  a more detailed test of the controller. 
For the differential controller that uses resi stance/temperature devices (RTDs) — positive 
temperature coefficient sensors — the tank se nsor input should be shorted in Steps iii and 
iv. Shorting the collector sensor indicates a low temperature and the pump should stay off. 
Shorting the tank sensor should turn the pump on. If freeze protection and the collector 
sensor functions are combined, shorting the colle ctor terminals simulates a freeze condition. 
The pump should turn on if recirc ulation freeze protection is used. 
b.  Sensor test. To check the temperature sensors of a differential controller, measure their 
resistance. Disconnect the sensors from the cont roller terminals or lead wires and use a volt-
ohmmeter to measure the resistance across the sensor wires. 
For thermistors and metal film sensors, co mpare their resistance to the manufacturer's 
temperature versus resistance specifications. Also, see Annex M. 
Generally there are two types of thermistor sensors: a 3,000 ohm sensor and a 10,000 ohm 
sensor. Sensor resistance should match the measured temperature as closely as possible. (See 
Table 1 in Annex M.) FDUS 853: 2009 
© UNBS 2009 – All rights reserved  109
 For example, when the environment temperature is 25 °C, the 3,000 ohm sensor should read 3,000 
ohms, and the 10,000-ohm sensor should read 10,000 ohms. As the temperature increases, the 
resistance decreases. At 32.2 °C, a 3,000 ohm sensor reads 2,200 ohms; a 10,000 ohm sensor 
reads 7,333 ohms. 
The general range of solar system temperatures is 21.1 – 60 °C for the tank sensor and 100- 150°F 
for the collector sensor depending on the time and condi tions of day. If an "open" or "short" condition 
is indicated, check the wiring between the controller and sensor. 
A common cause for an "open" condition is a broken connection between the wiring and the sensor. 
A "short" may be caused by a piece of metal pinching  the sensor wire and conducting it to ground or 
causing it to short across the wires. 
For temperature-actuated switches (freeze sensors,  upper limit sensors, an d snap-switch controls), 
you can also check the switch position with a volt -ohmmeter. The switch is either normally open or 
normally closed, and changes position at a particular temperature. You can ch eck the freeze sensor 
by placing it in ice water and measuring with the VOM to see that the switch changes position. 
c.  Detailed controller test. A complete method of  checking the controller involves the use of a 
differential controller test set. Containing fixed and/or  variable resistances, the test set is generally 
calibrated for a specific manufacturer's line of co ntrollers, though it can be adapted to test other 
brands of controllers. Instructions for it s use are usually supplied with the tester. 
The test set enables you to determine the exact "turn- on" and "turn-off temperatures of the controller. 
Compare these differential temperatures to the manufacturer's specifications. If the measured 
temperatures do not match the sp ecifications, and if the setting is  adjustable, you can change the 
setting to match the manufacturer's recommendations. 
d.  Photovoltaic (PV) module controller test. Us e the following procedure to check the voltage and 
current output of the photovoltaic module on a sunny day: i.  Disconnect the pump from the wires co ming from the PV module or pump starter box. 
ii.  With a volt-ohm-meter, check the voltage bet ween the positive and negative terminals of the PV 
module. This open-circuit volt age should be between 14 and 22 volts,  in almost any amount of 
sunlight.  
You should also check the PV modules short-circui t current with a volt-ohm-meter (with milliamp 
measurement capability). Under sunny conditions , the short-circuit current should be between 
200 and 1000 milliamps, depending on the voltage rating of the PV module. If there is no 
amperage at good sun conditions, the PV modul e or the connecting wiring may be defective. 
(Do not exceed the amperage measurem ent capacity of your meter.) 
If there is no amperage at the pump, check the amperage of the module at its roof location to 
determine if there is a break in the connecting wiring. 
iii.  To check the DC-powered pump, use two 6-volt  lantern batteries connected in series (12V). 
Disconnect the PV panel from the pump and conn ect the pump to the proper terminals of the 
batteries. If the pump does not operate off the batteries, the pump is defective. If the pump does 
run off the batteries, the PV module or connective wiring is defective. 
8.  Heat-transfer fluids and the collector loop. 
For indirect systems, inspect the heat transfer fluids ; for direct systems, inspect the collector loop. 
Perform item 8a for pressuri zed indirect systems only: 
a.  Evaluate heat-transfer fluids . All heat-transfer fluids must be inspected and evaluated 
periodically. Most fluid manufacturers and syst em vendors recommend periodic inspections. To FDUS 853: 2009 
110 © UNBS 2009 – All rights reserved
 check the fluid, remove a few ounces from a fill or drain point. (Be careful not to spill any fluid 
and do not allow air to enter the system.) 
To determine the average condition of the fluid, take the sample from a point above the bottom 
of the collector loop, during a per iod when the system is operating. 
Examine the sample for rust, scale, water depo sits, sludge and gummy materials. Rust or scale 
accumulation is probably the result of degradati on of iron in the system. If you find water in the 
sample, look for system or heat exchanger leaks. 
Sludge in the sample indicates heat transfer fluid degradation, which in time can lead to clogs in 
the collector and heat exchanger loop. Fluids ca n deteriorate some plastic seals and gaskets. 
Gummy materials in the sample usually indi cate this deterioration is occurring. 
Test the various fluids using the specific manufacturer's recommended procedures. Be sure to obtain the fluid manufacturer's recommendations for filling, flushing and refilling of various heat-
transfer fluids. Some fluids must be completely dr ained and the system recharged with new fluid. 
Other fluids may not need to be drained, only more fluid added. In addition, systems using one 
type of fluid can be flushed with water while other  systems must be flushed with specified fluids. 
Perform items 8b-f for direct systems only: 
b.  Drain the collector loop . Disconnect the pump and controller from the power supply. 
CAUTION: The PV module can be disconnected from the pump only for short periods of 
time (4-5 hours). 
Isolate and drain the collector l oop, if drains are available. 
CAUTION: If you drain the collector loop on a sunny day, direct the hot water to a safe 
point of discharge. 
A loop that drains easily indicates properly pitche d (or tilted) pipes and a path for air to enter the 
system. A vacuum breaker valve or a system air ve nt at the top of the collector loop may supply 
this path. Sometimes air enters during draining on ly through a second drain valve at the bottom 
of the loop. 
c.  Flush the collector loop . Isolate and flush the collector loop , preferably in the reverse direction 
of normal flow. If the check valve is located on the collector supply, use the cold-water service 
pressure to back flush the collect or return. If the check valve is located below the collector return 
hose bib drain, use a garden hose with a doubl e female adaptor connected to both an outside 
faucet and the collector return drain. 
In both cases, force water out the collector su pply drain and through an attached hose leading to 
a point of safe hot-water dischar ge. Check this water for dirt, sc ale and other signs of blockage. 
Stop when the discharge no longer contains any debris. 
If sedimentation build-up in the tank is a problem,  isolate the tank and drain several gallons of 
water to remove any sedimentation. Advise t he owner this draining should performed at least 
once per year and preferably every six months. 
d.  Test the check valve . Use the hose bib drains and service water pressure to check these two 
valves: a horizontal swing check valve or  a vertical in-line ring check valve. 
Send water against the normal flow direction. Water flowing past the valve i ndicates a faulty seat 
or stuck hinge that will not s eal under the low backflow of  unwanted ther-mosiphoning.  
Check a solenoid-actuated or motorized ball valve by  using the manual lever (if it is present) to 
open and close the valve while checking for flow . Some motorized valves are not designed to FDUS 853: 2009 
© UNBS 2009 – All rights reserved  111
 close off against normal city water pressure. Ve rify the normal operati on of these valves by 
listening to and watching the valve open and cl ose as the pump is turned on and off. Since 
check valves are very prone to problems from sedimentation build-up, t hey should be inspected 
periodically. 
If the check valve cannot be tested by the above backflow procedure and it is suspected of 
being the cause of night-time thermosiphoning, you need to examine the system at night. When 
the fluid in the collector has cooled to a temperature sufficiently below the fluid in the tank, feel 
the collector supply and return pipes a few feet from the heat of the tank. If one pipe is warm, the 
check valve might not be sealing. 
Sometimes a leaking check valve can cause a differ ential control to cycle the pump at night. To 
confirm this speculation, unplug the pump from the differential controller and plug a clock into 
the controller instead. Note t he clock's time. Note the time again the next morning before the 
solar system would normally start. If the cloc k has advanced because the controller supplied 
power to it, the check valve is not sealing and needs to be replaced. To check a mixing valve, feel or measure the tem perature of the service ho t water at the closest 
house hot water faucet. As you measure, adjus t the mixing valve over its range of motion, 
leaving it at the desired temper ature setting. Sometimes these valves stick open or closed after 
prolonged use and must be repaire d, replaced or eliminated. 
e.  Purge air from the system . With the collector supply isolat ion valve open, close the collector 
return isolation valve. Force water out of the collector return line drain (and hose). Close the 
return line drain when air no longer bubbles out the drain hose. Open the collector return 
isolation valve. 
f.  Plug the pump and controller back in . Check for proper operation and return the electric 
heating element switch (if provided) to its original on/off position.  
9.  Inspect the collectors up close 
Caution: Some roofs can be damaged by a person's weight. Walk slowly and make sure the roof can support you wherever you move. Be careful that you do not break concrete tiles or brittle asphalt shingles. 
Look for the following items: 
a.  Dirty glazing . Rain generally does a good job of keeping co llectors clean, but occasionally in very 
dry and dusty weather they will gather a visible layer of dirt  and dust. If so, they should be cleaned 
with mild soap and water. Clean the collectors only when they are not hot to the touch, in the early 
morning or late evening. Spraying the collectors with a garden hose during early morning or late 
evening hours is also effective. 
b.  Condensation or outgassing on the inside of the glazing . A major part of the solar energy 
striking the collector may be blocked by moisture  or chemical deposits from outgassing of the 
collector insulation on the inside of the collector box. 
To remove extreme and lasting condensation, take off the glazing, wipe it dry and dry the box. To 
minimize future water collection, drill small holes (weep holes) in the frame - a few in the bottom of 
the frame for drainage and two at the top corners to allow warm moist air to escape. Screen the holes to keep out insects. 
To clean off inner outgassing deposits, the glaz ing will have to be removed and the glazing cleaned 
with a detergent or a solvent su ch as alcohol. (Depending on the amount of time they have been on 
the glazing, these deposits may be difficult to remove.) 
c.  Leaking connections . Repair small leaks around fittings and pipes to minimize heat loss from the 
system. Freeze damage causes many leaks. Generally, leaks appear in the collector flow tubes. FDUS 853: 2009 
112 © UNBS 2009 – All rights reserved
 d.  Temperature-pressure relief valve . Look for stains on the roof around this valve, indicating 
repeated discharge of collector fluid from ove r-temperature conditions. This symptom generally 
indicates a lack of flow in the collector loop ev en though solar heat is avail able. (Note that most 
installations now use pressure relie f valves in the collector loop.) 
Over temperature of the collector may be due to a lo w use of hot water, a faul ty upper limit sensor, or 
air in the collector loop that prevents the pump from maintaining flow. An air vent at the highest point 
should discharge this air from the system. 
WARNING: Lifting the test lever of the temperature pressure relief valve may cause the valve 
to fail. Be prepared to replace the valve before manipulating the test lever. 
e.  Air vent . When you fill the system, you mi ght hear and even f eel a stream of air leaving a properly 
operating air vent. Most air vent caps must  be loose (to permit the air to escape). 
NOTE The cap should be in place to prevent dirt from en tering the valve or insects from plugging it, but it should 
not be completely tightened. 
When water reaches the air vent, the vent should close fast, without leaking. Many valves have a 
stem that can be depressed to allow fluid to  escape, flushing the valve seat clean. 
CAUTION: When filling a system that has been solar heated, the escaping air may be 
extremely hot and contain steam until the system reaches normal operation. 
f.  Vacuum breaker . When draining the collector loop, you should be able to hear air entering the 
valve, permitting water drain-down.  
NOTE In reference to air vents and vacuum breakers, the interior valve seats and float pivots may collect 
deposits and become inoperative. Disassemble the valve, if possible, and clean it thoroughly to ensure proper 
operation and to eliminate air pockets and drainage problems. 
g. Pipe insulation . Look for cracks or splits, opened joints or deteriorating insulation. Most closed cell 
foam insulation should be wrapped or covered with a protective paint to shield it from ultraviolet 
radiation. Plasticized vinyl lacq uer and exterior latex with a white pigment both protect well and may 
be found at air conditioning supply stores. 
h.  Sensor location . Sensors placed on the collector outlet need to be in good thermal contact with the 
pipe and insulated from the surrounding air. Sensor s placed inside the collector box generally do not 
require the same intimate contact and may even have to be separated from the absorber plate. Refer 
to the manufacturer's recommendations. 
Check the wire leads to these interior sensors to  ensure they are not crimped or exposed to the 
metal of the box. Sensor wires t hat cross over the meta l edges of the box will wear through and short 
due to weather induced movement of the box and wires. Also, if a freeze sensor is used, check that it is indeed a freeze-actuated switch, different from the 
actual collector sensor, and is either wired separa tely or according to the controller manufacturer's 
recommendations. The freeze sensor also needs to be in good thermal contact with the pipe or 
collector plate and to be insulated from the surrounding air. 
i.  Collector anchoring . While not directly affecting the efficient  operation of the solar system, improper 
mounting of the collectors can cause serious problems, such as roof leaks or building damage from high winds. 
Supports should be durable, materials tightly fast ened, and mountings strong enough to resist the 
near-hurricane force winds to be expected in Flori da. Roof penetrations should be well sealed with a 
durable roofing sealant to prevent leaks and interior water damage. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  113
 j.  Collector piping . When the system has two or more collectors, they should be plumbed in a parallel 
configuration, unless the manufacturer suggests ot herwise. The pipes and interior collector tubes 
should all have a continuous slope (1/4 inch per foot). 
They should not contain any low pockets that do not drain or high pockets that capture air. Use a 
builder's level to correctly determine proper pipe sl ope, as the roof or shingle line may not be level.  
k.  Photovoltaic (PV) module . Ensure the PV module is securely mounted and properly oriented for the 
geographical area and collector mounting. Check that all electrical connections are secure and wiring 
is protected from environmental degradation.  
15  Troubleshooting checklist 
When the symptoms for problems have been identified, the following checklist can be used to determine the 
probable causes and the appropriate corrective actions . During system evaluation, the complete system 
should be checked to identify any ot her situations that might lead to mo re problems. A well-maintained system 
is the best insurance against future problems. 
Solar system problems are difficult to organize because no problem is more important than another — to the 
solar system owner, any problem is important. 
The checklist begins with problems relating to water te mperature. It continues with general system problems 
and problems relating specifically to the cont roller, and then system leaks and drainage. 
Problem Check item Possible cause Corrective action 
Auxiliary heater 
(electric) No power to aux iliary back-up 
heating element Check high temperature protection and push reset button above thermostat. 
(Use caution when dealing 
with electricity) 
Failure to ignite Check pilot light mechanism 
Safety switch malfunctioning Check and replace 
Defective automatic pilot valve Check and replace 
Pilot wont stay lit:  
Too much primary air Adjust pilot shutter 
Dirt in pilot orifice Clean and open orifice 
Pilot valve defective Replace 
Loose thermocouple connection Tighten 
Defective thermocouple Replace Auxiliary heater (gas) 
Improper pilot gas adjustment Adjust 
Auxiliary heater 
thermostat Thermostat defective Replace 
Improper adjustment Check water temperature at 
house faucet and adjust 
valve setting Mixing and/or anti-scald valve 
Valve defective Replace or remove from 
system plumbing No hot water 
Distribution piping Leak (under slab or  in walls) Locate leak and correct 
Undersized for hot water demand load Replace 
Storage tank losses Insulate tank Not enough hot water Auxiliary heater 
Thermostat set too low Increase set point 
temperature 
Element failure Replace element 
Thermostat failure Replace thermostat   
Lower element disconnected in 
conventional rank system Reconnect element and set thermostat to low FDUS 853: 2009 
114 © UNBS 2009 – All rights reserved
 temperature 
Check valve Heat loss due to defective or 
improperly installed check valve Inspect valve and repair or 
replace 
Solar return dip tube Missing, wrong location, 
defective Replace dip tube 
Cold water supply dip tube Missing or wrong location Install in proper location 
Absorber coating degradation Recoat or replace absorber 
(contact manufacturer) 
Area undersized Increase collector area 
Excessive condensation Inspect and repair glazing 
seal, pipe gaskets and weep 
holes and vents at bottom 
Glazing dirty Clean as required 
Leaks Repair 
Orientation Check orientation. Face 
collector 45 oC east or west 
of south 
Outgassing inside collector 
glazing Clean surface and contact manufacturer 
Plastic glazing deteriorating Replace 
Reduction of glazing 
transmission Replace glazing 
Shaded by tree(s) or building(s) Remove obstacle and 
shading or relocate 
collector(s) Collector(s) 
Improper plumbed Check tilt for geographic 
area. Set 15 oC of latitude 
Improper operation (cycling, late turn on) Compare with system schematic in installation manual 
Faulty sensors or controller Conduct resistance 
measurement or check by placing sensors against hot 
and cold-water glasses and 
watching pump function. 
Replace defective units. 
Improper wiring or loose 
connections Compare with system schematic. Check for proper 
connections. Seal all splices against moisture.  
Differential controller 
Shorted sensor wiring Check wiring for breaks, 
metal contact, water 
exposure and corrosion. 
Sized too small Replace with properly sized 
heat exchanger. Insulate. Heat exchanger 
Scaling, clogging Back flush, clean 
Isolation valves Closed Open 
Mixing/ Anti-scald 
valve Improperly adjusted Reset temperature indicator 
Owner High water usage Check system size and 
discuss solar system and 
owner’s lifestyle 
Clogged with corrosion or 
sediment Replace excessively corroded components  
Piping 
Insufficient insulation Add insulation where 
required 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  115
 Troubleshooting checklist ( cont.)  
Problem Check item Possible cause Corrective action 
High heal losses Check insulation for splits, 
deterioration, absence 
Nighttime thermosiphoning Check for pump operation at night 
Improperly plumbed Compare with system schematic. 
Check flow direction. 
Isolation valve closed Open valves 
Isolation valve failure after 
closing Replace valve 
Flow blockage Flush system. Check effluent for 
dirt/scaling.  
Low system pressure Check pressure gauge. Refer to 
owner’s manual for correct 
pressure 
No power Check breaker, pump, and 
controller. Repair or replace 
Flow rate too high or too low Adjust flow rate 
Defective Check and replace 
Activation switch off Check for switch on PV to pump 
wiring 
No power Check breaker, pump cord, 
controller fuse, if any. Replace if 
necessary. 
Faulty pump Listen for irregular noises in pump 
operation. Feel collector feed and 
return pipes for temperature 
difference. 
Runs continuously Check c ontrol system for breaks 
and shorts Pump 
Improperly installed Compar e with system schematic 
Sensors Improper wiring, cuts, or 
loose connections Check and correct 
Sensor wiring Shorted wiring Check repair 
Too small Install larger tank Not enough 
hot water 
(Cont.) 
Storage tank 
Storage losses Insulate tank with insulation 
blanket 
Check valve Stuck open or does not seat Replace check valve 
Controller Sensor wires reversed Check wiring and reconnect 
Water heater circuit 
breaker Water heater circuit breaker shutoff Turn breaker back on 
Freezing conditions at 
night Recirculation freeze protection (with back-up power off) Turn back-up power back on (circuit breaker) No hot water 
in morning 
Occupants Excessive consumption Discuss hot water usage. Check 
system size and auxiliary heater 
status 
Auxiliary heater Thermostat set point too high Reduce set point temperature 
High limit sensor Improper calibration Check, recalibrate and replace 
Occupants No hot water use (vacation, 
etc.) Run hot water to reduce tank 
temperature 
Mixing or anti-scald 
valve Temperature set too high Adjust Water too hot 
Mixing/anti-scald valve Valv e failure Replace valve 
No water Cold-water supply 
valve Valve closed Open valve 
    FDUS 853: 2009 
116 © UNBS 2009 – All rights reserved
 Problem Check item Possible cause Corrective action 
Piping, hot water 
distribution Leak Repair leak 
Tank In dual element tank, lower 
heating element Turn to low setting or disconnect 
Thermostat set too high Check setting and adjust to 
desired temperature Tank thermostat 
Inaccurate temperature dial Recalibrate or replace 
Tank dip tubes Collector return above tank 
thermostat Increase length of dip tube High electric use 
Piping  collector return above tank Check tank plumbing. Contact 
installer, if necessary. 
Controller switch in “off” position Turn to “automatic” or normal operating position. 
Unplugged Return power to controller 
On and/or off temperature 
differential set points too high Reset according to specifications 
Loose contacts Clean contacts and tighten 
connections or replace Differential controller 
Defective components Replac e components or controller 
Controller circuitry Sensors connected to wrong 
terminal Correct per manufacturer’s 
recommendations 
DC pump Loss of circuit continui ty Check and repair or replace 
On/off switch is “off” Turn to “on” 
Blown fuse or breaker tripped 
on overload Determine cause and replace fuse or reset breaker Electrical power supply 
Brownout Await resumption of utility power Pump does 
not start 
Photovoltaic module Shaded Relocate or eliminate shade 
 Defective Check and replace, if required 
Photovoltaic wiring Improper wiring, cuts or 
loose connection Check and repair 
Motor failure Check brush holders and other 
mechanical components that may 
be loose, worn, dirty or corroded. Replace as appropriate and 
reasonable. Check for thermal 
overload. 
Pump motor runs when 
started by hand. Capacitor 
failure Replace capacitor 
No power Check breaker, cord and 
controller 
Stuck shaft, impeller, or 
coupling Replace 
Frozen bearings Replace  
Defective sensor(s) Replace  
Improper installation Clean and reinstall properly Pump  
Sensors out of calibration Recalibrate or replace 
Defective sensor wiring Repair or replace 
Open collector sensor wiring Clean wiring continuity. Repair or 
replace Sensor wiring 
Shorted tank sensor wiring Check wiring for continuity. Repair 
or replace 
Defective Replace   
Timer 
Wrong on and/off time Reset, check battery. 
Pump starts, 
but cycles 
continuously Differential controller On and off temperature 
differential set points are too close together Reset according to specifications FDUS 853: 2009 
© UNBS 2009 – All rights reserved  117
 Freeze protection setting too 
high Reset according to specifications  
Faulty controller Use controller test set to perform 
operation check. Repair or 
replace. 
Piping  Reversed connections to 
collector Reconnect  properly 
Improper location Relocate sensors as per system 
design or manufacturer’s 
requirements 
Not properly secured Secure properly and insulate from 
air  
Sensors  
Faulty  Test sensors. Replace if 
necessary. 
Interference from radio or 
garage door opener, etc. Use shielded sensor wire Sensor wiring 
Radio frequency interference 
from close proximity to 
antenna. Use shielded sensor wire Pump cycles 
after dark 
Check valve Does not seat Replace  
Off temperature differential set point too low Reset according to specifications 
Lightning damage Replace controller Controller  
Controller in “on” position Turn to “automatic” or normal run 
position 
Sensor(s) out of calibration Recalibrate 
Defective sensor Replace Sensor(s) 
Improper installation reinstall 
Interference fro radio/garage door opener, etc.  Shielded cable may be necessary 
Shorted collector sensor 
wiring Check wiring for continuity. Check wiring connections for weather 
tightness. Repair or replace. Pump runs 
continuously 
Sensor wiring 
Open tank sensor wiring Check wiring for continuity. Check 
wiring connections for weather 
tightness. Repair or replace. 
System air-locked. Air vents 
closed. Disassemble and clean seat and seal. Replace if necessary. 
Improper location Install at the highest point. Install 
at all high points if possible air 
trap locations exist. Install in true 
vertical position. Air vent 
Air vent cap tight Loosen J/4 turn 
Check valve Installed improperly  Check flow arrow on valve to 
ensure direction is per system 
design 
Collector Flow tubes clogged Flush collector tubing 
Drain-down valve Drain-down valve stuck in 
drain position Clean cause of sticking. Check 
power to valve. 
No fluid in direct system Open cold-water supply valve 
Loss of fluid indirect syst em Locate leak and refill Fluid  
Loss of fluid in drain-back 
system Cool system, locate leak, refill properly 
Isolation valves Valves in closed position Open valves Pump 
operates but no fluid flows 
from collector  
Piping  Clogged or damaged piping Unblock piping or repair damaged 
piping 
 
 FDUS 853: 2009 
118 © UNBS 2009 – All rights reserved
 Troubleshooting checklist ( cont.) 
Problem  Check item Possible cause Corrective action 
Broken impeller shaft Replace shaft 
Impeller broken or 
separated from shaft Replace impeller and/or shaft or replace pump 
Improperly installed Install to ensure correct flow 
Not vented properly Install in correct orientation Pump  
Undersized Check pumps specifications. 
Change pump if required. Pump operates but 
no fluid flows from collector 
(Cont.) 
Valves Valves closed Open valves 
Pump cycles on and off 
after  dark Check valve Corroded or defective 
check valve Repair or replace 
Defective  Change sensor 
Improper location Relocate Pump runs 
after dark, 
but 
eventually shuts off Sensors  
Sensor not insulated Insulate  
Sensor (freeze) Open circuits  Check sensor and wiring. Repair 
or replace  No power to 
pump with 
switch on Controller output relay Weak or failed relay Replace relay or controller 
Air vents Air trapped in syst em Open automatic air vent 
Pump bearings Dry or excessive wear Lubricate or replace 
Pump impeller Loose impeller Tighten or replace impeller 
Pump enclosed in small 
room (closet) None Pump location 
Pump attached to wall-wall 
acts as amplifier Relocate pump if noise is 
unacceptable 
Pump volute Corrosion or particles in 
volute Clean volute and impeller. 
Replace if required Noisy pump 
Vent port on pump (if 
applicable) Air trapped in pump Open vent port and/or vent valve 
and bleed air 
Bearings need lubrication 
(if applicable) Oil per manufacturer’s recommendation Pump  
Air locked Bleed air 
Entrapped air (direct 
systems only) Purge system by running water up supply pipe and out drain on return line (isolation valves 
closed) Noisy system 
Piping  
Pipe vibration Isolate piping from walls 
Controller  Defective  Conduct function check and repair 
or replace  
Defective sensors; 
resistance problem; 
sensors off scale Check with multimeter (ohm). 
Correct or replace sensors. 
Improper contact or insulation Ensure proper contact is made. Insulate sensors. Sensors  
Improper location Relocate  Controller does not turn on or off in 
the 
“automatic” 
mode but 
operates in 
the “manual” 
mode Wiring  Short or open Replace or splice wire 
Collector  Defective  Repair or replace 
Defective sensor Check with multimeter(ohm) and 
replace System shuts 
off at wrong 
high limit or 
continues to 
run Sensors  
Improper location Relocate  
Collector(s) Pipe burst due to freeze or 
defective joint Repair or replace. Check freeze-
protection mechanisms. System leaks 
Freeze-protection valve Did not reseal a fter opening Recalibrate, if required, or 
replace. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  119
 Valve out of calibration Recalibrate per manufacturer’s 
instructions or replace 
  Normal operation (most 
open at 42 oF) No action 
Hose connection Clamps not tightly se cured Tighten clamps, replace clamp or 
hose. 
Thermal expansion and 
contraction. Replace and provide for flexibility 
Joint improperly made Reassemble Pipe joints 
Improper seal in system 
using glycol solution Make a good seal. Use recommended sealer. Note: glycol 
will leak through joints where 
water would not. 
Did not reseal after opening Replace  
Defective  Replace  Pressure-temperature 
relief valve 
Improper pressure or 
temperature setting Reset, if possible, or replace 
Valve gland nuts loose Tighten nuts. Replace seal or 
packing if necessary.  
Valves  
Seats deteriorating  Replac e seat washers. Redress 
seat. Replace valve if necessary. 
Defective seal Replace  Pressure-temperature 
relief valve Activates due to no 
circulation through collector 
(s) Check flow in collector loop. (See 
“Pump does not start” and “Pump 
operational but no flow to 
collector”.) 
Out of calibration Calibrate, if possible, or replace. 
Defective seal Repair or replace Freeze-prevention valve 
Normal operation (most 
open at 42 oF) No action 
Ruptured piping due to 
freeze Repair or replace Collector piping 
Defective piping Repair or replace Water comes 
off the roof  
Low-pressure valve 
installed on collector 
supply line Power loss. Pressure loss 
from well. No action required. 
Collector (parallel) Fins and tubes are 
horizontal and are sagging, 
preventing drainage from occurring Straighten fins and tubes. Realign 
collector so it will drain completely 
Collector (serpentine) Serpentine design prevents 
drainage Blow water out of tubes with air compressor 
Piping Insufficient slope for 
drainage Check and ensure piping slopes 
¼” per foot of piping System does 
not drain 
Vacuum breaker Does not open. Defective 
due to internal mechanism 
or corrosion. Clean or replace 
 
16   Maintenance 
While a properly designed and installed solar heating system should be expected to give a service life 
comparable with that of other types of domestic he ating system, some maintenance may be necessary to 
maintain the efficiency of the installation. 
During a maintenance inspection at least the following  checks should be added to the items listed in 10.8. FDUS 853: 2009 
120 © UNBS 2009 – All rights reserved
 a)  Outside the building 
1)  that the glazing of the collectors is clean; 
2)  that the glazing is sound and free of cracks; 
3)  that there is no evidence of serious corrosion; 4)  that any paintwork is sound. 
b) Inside the building 
1)  that the sensing devices are fi rmly and properly in place (this may also form part of the external  
examination); 
2)   that there are no signs of corrosion; 
3)   that labels are in position and up dated at the time of the service visit; 
4)  that the life of the heat transfer fluid has not expired. 
17    Safety precautions 
17.1   This section covers the safety aspects of the SDHW system. It describes the use of accepted 
practices that are common in many existing building and plumbing codes. Its purpose is to ensure the safe 
operation of the system with regard for human safety. 
17.2  Release of hot or hazardous fluids 
17.2.1  All parts of the SDHW system that are isolated, or  are capable of being isol ated by valves or other 
means, shall have a pressure relief valve set to open at the maximum recommended working pressure of that 
part of the system. The rating of the relief valve shall exceed the heat input of the collector(s) or other heat 
source. 
17.2.2  Relief valve discharges shall not damage structural  members, contaminate potable water sources, 
or create risk of fire, and shall not pose a hazard to heal th or safety, and shall drain to locations acceptable to 
local codes and ordinances. 
17.2.3  All liquid containment components shall be capabl e of withstanding a minimum pressure 1 and ½ 
times the rated maximum working pressu re of the system without rupture. 
17.2.4  All systems shall be provided with an approved self-closing (levered) pressure relief valve and 
temperature relief valve or combination thereof. Such valv e shall be installed in the shell of the water heater 
tank or in the hot water outlet, provided that the thermo-e lement of the valve shall be installed within the top 6 
in. (150 mm) of the tank. For installa tions with separate storage tanks, the valves shall be installed on both 
tanks. Pressure relief valves may be located adjacent to the equipment they serve. There shall be no check 
valve or shut-off valve between a relief valve and the heater(s) or tank (s) that it serves. 
17.2.5  All automatically controlled syst ems shall be equipped with an energy cut-off device that will interrupt 
the supply of energy to the water tank before the temper ature of the potable water in the tank exceeds 88 °C 
or 12 °C less than the temperature setting of the tem perature relief valve. This energy cut-off device shall be 
in addition to the temperature and pressure relief valve. 
17.2.6  Temperature and pressure relief valves, or combinat ions thereof, shall comply with the requirements 
of ANSI Z 21.22 with a temperature setting of not mo re than 99 °C and a pressure setting not to exceed the 
tank or heater manufacturer's rated working pressure. The relieving capacity of these devices shall equal or 
exceed the heat input to the water heater or storage tank. 
17.2.7  To avoid fluid damage or scalding due to relief valv e discharge, drain pipe shall be connected to the 
valve outlet and run to a safe place of disposal. Drain pi pe shall be as short as possible and be the same size 
as the valve discharge connection throughout its entire l ength. Drain line shall pitch downward from the valve 
and terminate at least 6 in. (150 mm) above the floor dr ain where any discharge w ill be clearly visible. The 
drain line shall terminate plain, not threaded, of materi al serviceable for 120 °C, or greater. Excessive length 
(over 15 in. (4m)) or use of more than two elbows can cause a restriction of flows and reduce the discharge FDUS 853: 2009 
© UNBS 2009 – All rights reserved  121
 capacity of the valve. Shut-off valves shall not be inst alled between the relief valve and tank, or in the drain 
line. 
17.2.8  All pressurized storage tank s shall be capable of withstanding a hydrostatic test pressure in 
accordance with accepted criteria applicable to t he usage and maximum working pressures recommended by 
the manufacturer. 
17.2.9  All piping materials used in interconnections shall be capable of withstanding the temperatures and 
pressures anticipated in the system. 
17.2.10  In the event that temperature of the stored potable water is not limited to 60 °C, a mixing valve shall 
be provided to limit the water for personal use to not mo re than 60 °C. Maximum water temperature shall be in 
conformance with local codes. 
17.3  Contamination of potable water supplies 
17.3.1  Double wall heat exchangers should be provided with means to detect leakage through one of the 
walls (see 11.6.2). 
17.3.2  Materials that come into direct physical contact wi th the potable water shall be acceptable for that 
use under the applicable codes. 17.3.3  No direct connection between the potable wate r supply and a non-potable piping system shall be 
allowed, unless separated by an approved backflow preventer.  
17.3.4  Each system shall be clearly and permanently marked near the filling port(s) with a label specifying 
the fluids approved by the designer or  manufacturer for use in the system. 
17.4  Falling or flying objects 
17.4.1  Collectors employing glass in thei r construction should be located so that in the event of glass 
breakage by any cause, glass fragments will not create an undue safety hazard. 
17.4.2  Collectors should be located in such a way to minimi ze melting snow from sliding onto walkways or 
driveways. 
17.5  Electrical hazards 
Electrical equipment shall conform to the requirements  of the applicable electrical code. Electrical equipment 
and wiring shall not be located in spaces having temper atures higher than the thermal rating of the wire or 
equipment. 
17.6  Fire Hazards 
17.6.1  Solar collector system 
17.6.1.1  Assemblies and materials used in the SDHW system shall comply with the requirements of the 
applicable codes for fire safety under all anticipated operating and no-flow conditions. 
17.6.1.2  Solar collectors shall be constructed and installed in such a way that any nearby or adjacent 
combustible material shall not be heated to temperatur es in excess of 90 °C during periods of maximum 
temperature under no-flow conditions. Wood structur al components should be protected from prolonged 
exposure to temperatures over 65 °C. 
17.6.2  Heat transfer fluids—Liquid flash point 
The flash point of a liquid heat transfer fluid shall e qual or exceed the higher temperature determined from: (A) 
a temperature of 28 °C above the design maximum flow temperature of the heat transfer fluid in the solar 
system, and (B) the design maximum no-flow temperature of the fluid. FDUS 853: 2009 
122 © UNBS 2009 – All rights reserved
 17.6.2.1 Exception 
When the collector manifold assembly is located outside of the building and exposed to the weather, and 
provided that the relief valves locat ed adjacent to the collector or collect or manifold do not discharge directly 
or indirectly into the building and such discharge is  directed away from flames and ignition sources, only A 
applies. 
17.6.3 Insulating materials 
Materials used for insulating piping and storage tanks shall be of a fire resistance as specified in the local 
codes and appropriate to the location and use. 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  123
 Annex A 
 
Maintenance of weather-tightness 
When considering the design of flashings and seals around joints between the roof or wall and the collector, 
fixings or pipework, it is necessary to cons ider the effects of driving rain and snow. 
For low pitched roofs in particular, where high speed airf lows up the roof slope can be expected, rainwater can 
be blown upwards through lapped joints. The design of pitched roofing components (slates, tiles, shingles, 
etc.) takes this into account in both design and practice. If rain or snow can be driven up between a collector and a roof, all joints in the roof should be made we ather-tight, even if sheltered from direct rainfall. 
The severity of driving rain varies widely over the country and depends on the exposure of the site. Care 
should therefore be taken in applying experience gained in one area to another. It is important to understand 
the functions performed by an underlay. This is placed  under slates or tiles to  prevent powdery snow being 
blown into the loft, and to carry away temporary accumulation of water under the slates or tiles due to melting 
snow; it also reduces the air flow through the laps and any consequent risk of rain  penetration. Lastly, it 
reduces the wind uplift on the slates or tiles. 
It is important that any holes made in the underlay wh ilst fixing a solar collector are made good so that the 
underlay can still perform these function s. The underlay will receive considerable wind forces which all joints 
should be able to resist.  FDUS 853: 2009 
124 © UNBS 2009 – All rights reserved
 Annex B 
 
Loads on collectors 
B.1  Introduction 
Collectors and their fixtures have to be designed with  due consideration given to the magnitudes, directions 
and lines of action of forces applied to the collector. These forces comprise dead and imposed loads (due to 
the weight of the collector and of snow  lying on it) and loads due to the wind. 
In determining the design case for fixings, it shou ld be assumed that the dead and snow loads can act 
together, and that the dead and wind loads can act togethe r, but not all three simultaneously. This is because 
the highest accumulation of snow is not likely to occur when the wind speed is also at its highest. 
The loads applied to the collector vary with the loca tion and orientation of the roof and how the collector is 
mounted on it. Reference should be made to the relev ant standards for the determination of wind and snow 
loading (see B.3.2 and B.4.1) when an installation is bei ng designed for a particular location. It will be usual for 
a collector and its fixings to be designed so as to be safe for use in given situations (for example, on specified 
types of roof) throughout particular regions of the country. The designer will thus have to examine a number of 
possible situations, in order to determine the maximum combination of loads likely to be encountered, which 
defines the design case. For this purpose it will be f ound convenient for the various forces to be resolved into 
components, normal to the plane of the roof and parallel to it. In this annex, methods are given for calculating 
the highest values of the various forces and their components likely to be encountered in some common 
situations. These will provide general guidance to designers on the magn itude of the forces involved and on 
the use of the relevant standards when other cases are being considered. 
B.2   General 
Methods are given here for determining the maximum va lues of the components of dead, imposed and wind 
loads on collectors mounted in various ways on typical roofs having pitches in the range 20° to 45°. It is 
assumed that the collector has a simp le box-like shape and is mounted not closer than a metre to the edges 
of the roof or to projections such as parapets, ch imneys and dormer windows. When an installation in those 
regions is contemplated, or the collector has a more  complex shape, specialist advice should be obtained, 
since the loads could be greater than those indicat ed here. The components into which the forces are 
resolved for present purposes and the di rections taken to be positive are defined and illustrated in Figure B.1. 
Loads are related to presented areas of the collect or box shown in Figure B.1 and defined as follows: 
-  area of the top surface of the box   At, 
-  area of exposed side of the box   As; 
-  area of exposed end of the box     Ae. 
B.3    Dead and imposed loads 
B.3.1  Dead load 
Dead load is due to the weight W of the collector and its fluid contents. 
The components PX, normal, and PY, parallel, to the roof plane are respectively Wcosα and Wsinα. For roof 
pitches in the range 20° to 45°, the maximum values of the load components are as given in Table B.1. 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  125
 Table B.1 – Maximum dead load components for roof pitches in the range 20o to 45o 
PX P Y P Z 
0.94 W 0.71 W 0 
 
 
Figure B.1 – Components of force in a solar collector 
B.3.2  Imposed loads 
Snow loads are related to a characteristic value of the snow load on the ground s0 determined in accordance 
with ISO 12494. The designer needs to select a value of S0 based on a judgement of possible locations for the 
collector. The load on an exposed object, such as a sola r collector, is expressed in terms of one or more 
shape coefficients μ, which give the intensity of the loads sd on a particular surface as a fraction of the basic 
snow load: FDUS 853: 2009 
126 © UNBS 2009 – All rights reserved
 sd = μso 
Values of shape coefficient are given in ISO 12494. The snow load is assumed to act vertically and to be the 
product of the intensity and the area of  the horizontal projection of the su rface. For a collector of upper surface 
area At, the projected area is Atcosα, so that the components normal and parallel to the roof plane are 
respectively μs0.Atcos2α and μso.At cosαsinα. The shape coefficient μ is a function of roof pitch. For roof 
pitches in the range 20° to 45°, the maximum values of the components are as given in Table B.2. 
Tale B.2 – Maximum snow load components for roof pitches in the range 20o to 45o 
PY Roof type P X 
Lying snow Sliding snow PZ 
  
 
Mono-pitch roof   
0.71soAt   
0.35s
oAt   
o.35s
owel   
0 
  
Duo-pitch roof  
0.90s oAt  
0.52s oAt  
0.52s owel  
0 
 
Included in the parallel component is an allowance fo r the load applied by the sliding of snow which has 
accumulated on the part of the roof between the ridge and  the top edge of the collector. For this component, it 
is assumed that the load will be increased as if th e area of the upper surface of the collector had been 
increased by we×l, where we is the width of the collector and l the distance to the ridge of the roof (see Figure 
B.1). Table B.2 gives the load due to sliding snow. It should be included in the load calculations if the collector 
projects more than 50 mm above the plane of the roof. 
B.4   Wind load 
B.4.1    Determination of wind loads 
Wind loads are related to the dy namic pressure of the wind q, determined in accordance with ISO 4354. In the 
procedure given in ISO 4354 for determining q for a particular case, the value taken for the factor S1, should 
be that for class A at a height equal to that of the collector, and S3 should be taken to be equal to 1.0. 
The load on an object exposed to the wind, such as a so lar collector, is expressed in terms of one or more 
pressure coefficients, C p, which gives the pressure p on a particular surface as a fraction of the dynamic 
pressure of the wind q as shown by the following equation: 
p = C Pq 
Pressure coefficients vary with the shape and location of the surface concerned and the direction of the wind 
relative to it. They are convenient because they do not va ry much with wind speed; that variation is expressed 
in q. The resultant normal force on a solar collector is determined by the difference of the pressure on the 
bottom and top surfaces. These pressures may be expr essed separately by appropri ate coefficients. If the 
collector is mounted within a roof so that its top surf ace does not project much above it, the coefficients may 
be obtained from ISO 4354. 
A difference in pressure between the top and bottom su rfaces of a collector produces a load which is 
uniformly distributed. When the collector projects a bove the plane of the roof, flow separations produce 
additional loads which can be approximated by a localiz ed normal load with a line of action through the centre 
of the upstream edge of the collector and a drag load in the direction of the wind across the roof, through the 
centre of the upstream face of the collector. For the pur poses of design, it should be assumed that the wind 
may blow in any direction across the roof, so t hat any edge of the collector could be the upstream one. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  127
 B.4.2   Cases considered 
In this annex, values of the wind loads are given for three common situations: 
a)  collectors mounted into the roof, with the top surface in the plane of the roof surface; 
b)  collectors mounted into the roof, with the top surfac e projecting above the plane of the roof surface by up 
to 150 mm; 
c)  collectors mounted above the roof surface and parallel to it, with a gap of not more than 150 mm between 
the bottom of the collector and t he plane of the roof surface. 
Since in different circumstances, the resultant normal  component of force on the collector can be either 
outward or inward, the maximum values likely to be enc ountered in both directions are required to enable the 
design case to be determined. 
B.4.3   Maximum wind loads 
For roof pitches in the range 20° to 45°, the maximu m values of the load components are as given in Table 
B.3. For the normal component PX, the first column gives expressions fo r the distributed part of the load and 
the second column represents the localized load at t he upstream edge of the coll ector, where appropriate. 
Table B.3 – Maximum wind components for roof pitches in the range 20o to 45o 
PX 
Maximum outward Maximum inward PY P Z  
Distributed Localized at leading edge Distributed Distri buted Distributed 
Case (a) -1.2qA t 0 +1.0qA t 0 0 
Case (b) -1.5qA t -3.6qA e (or -3.6qA s) +1.0qA t ±1.6qA e ±1.6qA s 
Case ( c) -0.5qA t -3.6qA e (or -3.6qA s) +1.1qA t ±3.0qA e ±3.0qA s 
B.5   Free-standing collectors 
A free-standing collector is one mounted on a framewor k above the roof and inclined at amounted on a frame 
work above the roof and inclined at an angle different from the roof pitch. Less information is available on the 
loads experienced by free-standing collectors, but fo r design purposes, the following maximum values are 
recommended: 
a)  dead load:     W, applied vertically; 
b)  imposed (snow) load:   0.3 soAt, applied vertically; 
c)  wind load     ±3.0 qAt, applied normal to the plane of the collector; and 
±3.0qAe (or 3.0 qAs (3.0 qAs), applied parallel to the plane of the collector 
through any edge. 
Free-standing collectors mounted on flat roofs or on t he ground are not subjected to the accelerated air flow 
produced by a pitched roof. For those cases, the loads are similar to those experienced by monopitch canopy 
roofs, which may be obtained by reference to t he pressure coefficients given in of ISO 12494. 
B.6   Worked example of load calculation 
Fixings are to be designed for a collector with overall dimensions 1.5 m long × 1 m wide × 0.15 m deep and 
mass 45 kg when full of fluid. The collector will be a standard type for installations on roofs with pitches 
between 20o and 45o anywhere up to an altitude of 200 m wi thout undue exposure to wind. The long 
dimension of the collector will lie up the roof  slope. The worked ex ample is as follows: 
a)  Collector properties 
From the data given: FDUS 853: 2009 
128 © UNBS 2009 – All rights reserved
 we = 1 m, 
At = 1.5 m2, As = 0.23 m2, Ae = 0.15 m2, W = 441 N. 
b)  Dead load 
From the Table 4 the maximum dead load components are: 
PX = 415 N, PY = 313 N, PZ = 0 
c)  Snow load 
From ISO 12494, the maximum characteristic value of now load is: s
o = 800 + 160 = 690 N/m2 
From Table B.2 the maximum snow load components are: 
PX = 1296 N, PY = 749 N (lying snow) + 1498 N (sliding snow), = 2247N, 
PZ = 0 
(i is assumed here to be 3 m). 
d)  Wind load 
From ISO 12494, the design wind speed is 48m/s ( S1 = 1.0, S3 = 1.0) giving q = 1410 m2 
From Table B.3, case c), the maximum wind load components are: P
X (distributed) = -1058 N (outward); 2327 N (inward); 
PX (at upper/lower edge) = -1167 (side); -761 N (upper/lower edge) 
PY = ±635 N; PZ = ±973 N 
e)  Load combination 
Since loads determined under (b) and (c) or under (b) and (d) can act together, the worst cases for 
the design of fixings are: 
PX: 2742 N (inward); -643 N (outward), with -1167 N (at either side) or -761 N (at upper or lower 
edge); 
PY: 2560 N (down roof plane); -322 N (up roof plane); 
PZ: ±973 N (across roof plane) 
B.7   Effects of the roof structure 
The loads applied to the collector fixings are normally  transmitted to the roof st ructure. Traditional roof 
construction may have larger safety factors than thos e of modern trussed rafter roofs, where additional 
loading may be critical. The applied loads not only incr ease the magnitude of forces in the members of the 
trussed, but by being applied asymmetr ically, may cause a member or joint designed for compression to be 
put in tension (or vice versa). It may be necessary to strengthen timber members and joints and/or to provide 
additional members to distribute the loads more widely among the rafters. It is often necessary also to support 
an additional water tank in the loft space. The additional load may be troublesome, especially where there are 
no internal load-bearing walls. Modifications to the roof structure may then be necessary . FDUS 853: 2009 
© UNBS 2009 – All rights reserved  129
 Annex C 
 
Condensation and ventilation in roof spaces 
If the solar collectors are fixed to roofs with metal straps or bolts that pass through the tiles, it is possible that 
condensation may form on these fixings since they may be at a lower temperature than the air in the roof 
space. Excessive condensation could result in decay of the timbers to which the stra ps or bolts are attached, 
and if persistent dripping occurred this could le ad eventually to dampness of the ceilings. Whether 
condensation is likely to occur depends essentially upon thre e factors: the amount of thermal insulation in the 
loft space, the amount of air leakage from the inhabited space of the house  into the loft space, and the amount 
of ventilation in the loft space. If the thermal insulati on is situated on top of, and between, the ceiling beams, 
and if it is of sufficient thickness, then the loft space w ill rarely be significantly warmer than the fixing straps 
and there is, consequently, little increas ed risk of condensation occurring. 
If there is excessive air leakage from the inhabited space into the loft, this will result in exce ssive amounts of 
moist warm air entering the loft and the risk of condens ation occurring is high (even in the absence of solar 
collectors' fixing bolts); such leakage should be minimiz ed. An adequate amount of ventilation of loft spaces is 
necessary in order to prev ent decay of timber, and this is espec ially important near the eaves, where 
dampness may eventually give rise to timber decay while  the rest of the roof re mains sound. If the natural 
ventilation rate is sufficient to prevent any condensation in the absence of solar collector s, it is unlikely that the 
addition of these units will cause problems. Condensation on cold pipework may be prevented by insulation. 
Where a vapour barrier has been installed, care shoul d be taken to maintain its integrity, ISO 5268-2 gives 
further information. 
 
      
 
      
 
 FDUS 853: 2009 
130 © UNBS 2009 – All rights reserved
 Annex D 
 
Method for calculating the thermal performance 
D.1   Introduction 
The method used to calculate the annual solar energy supplied by the system is applied through the 
information given in D.2. Then the equations shown in D.3 are used to calculate the collector area parameter 
M, the collector type parameter K and the storage parameter R. These three parameter s are used, as shown 
in D.4, to obtain the solar energy supplied Q. 
D.2   Collection of  basic information 
The sequence for collection of basic information is as follows. 
a)  From climatical maps, estimate the annual mean daily  irradiation on a horizontal  surface at the site of 
interest, H (in MJ/m2). 
b)  From rainfall maps, estimate the annual mean air temperature T (in °C) at the site of interest. 
c)  For the particular site, estimate the annual mean daytime air temperature, Ta (in °C), and the annual 
mean cold water supply temperature Tc (in °C). If no data are available on these, assume that they are 
given respectively by the following equations: 
Ta = T + 1; 
Tc = T + 2; 
d)  Knowing the orientation and tilt  of the collectors, use Figures D.1 and D.2 to estimate the orientation 
factors Ch and Cg respectively. 
e)  From the collector specification, obtain its performance parameters U (collector heat loss coefficient, in 
W/(m2-K) and η0 (zero-loss collector efficiency). 
f)  Either specify the effective area A' (in m2) of the collector, or obtain it from the specified aperture area A 
(in m2), using the equation: 
A’ = η0A 
g)  Estimate the daily mean hot water requirement V (in L/day) and specify the de sired hot water draw-off 
temperature Td (in °C). 
h)  From the system specification, obtain the volume Vs (in L) of the preheat vessel. 
 
 
 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  131
 
 
 
 
 
 
 
Figure D.1 – Orientation f actor Ch for irradiation 
 
 
 
 
 
 
Figure D.2 – Orientation fact or Cg for pea irradiance 
D.3  Calculation of parameters M, K and R 
Substitution of the values of the quant ities obtained in D.2 into the followi ng equations will provide the values 
of M, K and R: 
 FDUS 853: 2009 
132 © UNBS 2009 – All rights reserved
   ()⎥⎦⎤
⎢⎣⎡− + = c a h TTUHCLAM
00432.0'
η 
  ()
()⎥⎦⎤
⎢⎣⎡−+−=
c a gc d
TTUGCTT UK
00
ηη 
  VVRs=  
  Where 
  L = 0.00418.V (T a-Tc) 
  G  =  4 0 H  
D.4   Estimation of the annual solar energy supplied Q 
Two methods for estimating the annual solar energy supplied, Q, are as follows. 
a)  Graphical method 
Use Figure D.3 with the calculated values of M and K to estimate the value of the parameter E. Use 
Figure D.4 with the calculated values of R and K to estimate the value of the parameter CR. 
Then Q is given (in MJ/year) by the equation: 
Q = 365 EC RL 
NOTE  If R is less than 0.8, the energy supplied may be greater than Q, if the hot water is drawn off predominantly 
during hours of sunlight. In favourable cases it may be as great as that obtain ed with the assumption that CR equals 
1. 
b)  Numerical method 
Substitute the calculated values of K and R into the following equations to obtain the values of the 
parameters F, B and λ. 
F = 0.554 + 0.342 R - 0.097 R2 
B = 0.383 K - 0.066 K2 
λ = 1.121 +0.212/0 for K < 1, or 
λ = 0.71 (1 + K), for K > 1 
Then Q is given (in MJ/year) by the equation: 
Q = 365 L (F - B) [1 - exp (- λM)] 
NOTE  If fl is less than 0.8, t he energy supplied may be greater than Q, if the hot water is drawn off predominantly 
during hours of daylight. In favourable cases it may be as  great as that calculated with the assumption that F is equal 
to 0.8. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  133
 D.5   References 
[1]  A parametric study of open loop solar heating sy stems, J.P. Kenna, Solar Energy, 32, 1984, 687-706. 
[2]  Meteorological Office tables for H. 
[3]  Meteorological Office tables for T a 
 
 
 
 
 
Figure D.3 – Graphical estimation of parameter f from calculated values of the collector area 
parameter M and the collector type parameter K 
 
  
 
 
Figure D.4 – Graphical estimation of parameter C R from calculated values of the storage parameter R 
and the collector type parameter K FDUS 853: 2009 
134 © UNBS 2009 – All rights reserved
 Annex E 
 
Methods of pressure and leak testing of absorber plates 
E.1   General 
Manufacturers of absorber plates for solar heating sys tems are required to perform a type test for pressure 
(see E.2.1) on each design or modification, and a leak test (see E.3) on each absorber plate. 
E.2   Pressure test 
E.2.1  Pressure test (at elevated temperature ) 
A hydraulic test pressure of 1.25 × the maximum work ing pressure (see the note) is applied to the absorber 
plate when it is at the maximum temperature to which it is liable to be subjected when working at maximum 
pressure in a solar heating system. 
NOTE  Maximum working pressure means the maximum pressure  to which the absorber plate is liable to be subjected 
in service. For example: 
a)  the pressure which will exist in the absorber plate instal led in a system when the pressure-relieving device starts to 
relieve, or the set pressure of the pressure -relieving device, whichever is higher; or 
b)  the maximum pressure which can be attained in the absorber  plate in service, where this pressure is not limited by a 
relieving device. 
The test is carried out using either aqueous or non-aque ous heat transfer fluid, as appropriate, and with the 
temperature of the fluid stabilized with  that of the absorber plate. The pr essure supply equipment should be 
fitted with a pressure limiting device, e.g. a reducing va lve with pressure gauge, or other device for preventing 
a pressure higher than that selected being applied. 
E.2.2   Hydraulic tests 
Manufacturers will be required to perform a hydraulic pres sure test at ambient temp erature and at twice the 
maximum working pressure as declared by the manufacture r in order to satisfy the pressure test requirements 
of the water byelaws in respect of fittings which may be located in positions to which access is difficult (see 
4.4). 
E.3   Leak test 
A test for leaks should be effected by means of a low pr essure pneumatic test at an internal pressure of not 
more than 0.5 bar above atmospheric pressure. The test is made at ambient temperature, with the absorber 
plate submerged under fluid in a suitable tank. In the course  of the test, all surfaces of the absorber plate need 
to be visible in turn to the operator. 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  135
 Annex F 
 
Methods of type testing for collectors 
F.1   General 
The type tests described in F.2 to F.4 are for assessing the resistance of collectors to adverse conditions, 
including extreme weather conditions. 
The tests are intended to identify weak  design features rapidly without the need to wait for adverse conditions 
to occur in service. 
F.2   High temperature test 
The empty collector is mounted at an inclination of between 20° and 60° to the horizontal and subjected to 
solar or simulated solar irradiance at a level sufficient to raise the temperature of the absorber plate to the 
relevant temperature indicated in 6.1. 
This temperature should be maintained for not less than 4 h. By stripping and inspecting the collector 
components, checks are made for distortion, cracking or other failures. 
F.3   Thermal shock test 
The empty collector is brought to the high temperature as described in F.2. This temperature should be 
maintained for not less than 1 h. Water or other heat transfer fluid at a temperature of 10 ± 5 °C is then 
introduced into the collector fluid inlet at a rate of a pproximately 0.02 kg/s per square metre of collector area. 
Care should be taken to allow the safe venting of any vapour produced. The flow is maintained for about 5 min 
after the collector has been filled. 
By stripping and inspecting the collector components, checks are made for distor tion, cracking or other 
failures. 
F.4   Water ingress test 
The purpose of this test is to ident ify whether or not the collector is able to withstand heavy rainfall conditions; 
it will not demonstrate resistance to driving rain. The empty collector is mounted at angles of 20° and 60° to 
the horizontal and subjected to a vertical water spray for a period of about 5 min. The total water flow rate is 
approximately 0.06 kg/s per square metre of collector area and this is produced by an array of water jets 
placed above the collector. 
The spray nozzles should produce a dropl et velocity of approximately 7 m/s to simulate impact spray, and the 
water should be spread evenly over the collector aperture. The collector is inspected for ingress of water. FDUS 853: 2009 
136 © UNBS 2009 – All rights reserved
 Annex G  
 
Methods of testing for differential temperature control systems 
G.1   General 
In these tests, the complete differential temperature c ontrol system comprising the c ontroller, the sensors, the 
mounting, the inter-connecting wiring and all other items, is tested for performance. 
G.2   Apparatus 
G.2.1  Test chamber , suitable for enclosing the controller is required. The chamber is substantially sealed 
during testing and is fitted with means for heating and c ooling to enable the relevant temperatures (see Table 
G.1) to be maintained, and with temperature measur ing devices having an accuracy of at least ±2 °C. 
NOTE  For reasons of economy it may be des irable to place a number of controllers si multaneously in the test chamber for testin g. 
Table G.1 – Test Temperature ranges 
Temperature range   
(in oC) Examples of conditions of service 
-15 to 45 Components mounted externally (i.e . open air mounting) or components mounted 
inside a loft space, e.g. controllers 
-15 to 35 
-15 to 200 
 
 
-15 to 150 
 5 to 100 Components mounted inside the heated spac e of a house, e.g. controllers 
Components mounted in contact with a sele ctively coated absorber plate, e.g. 
collector temperature sensors Components mounted in contact with a non-se lectively coated absorber plate, e.g. 
collector temperature sensors Components mounted in contact with any par t of a domestic hot water system, e.g. 
store temperature sensors 
 
G.2.2  Two temperature,  controlled baths, one for simulating the solar store temperature, and the other 
for simulating the absorber plate temperature. Thermome ters having an accuracy of at least ± 0.05 °C, and a 
means of heating and cooling the temperature controlled baths are required together with a control device to 
ensure that reference temperatures can be held stable to ±0.1 °C. 
G.2.3  Simulated electrical load,  consisting of a means of simulating the loads to be switched by the 
controller, e.g. a variable inductor and/or a variable resistor. 
G.3   Test procedures 
G.3.1   Setting up apparatus and components for test 
The controller is adjusted in accordance with the manufacturer's instructions. If 'user' adjustments are 
available for the temperature differential settings, t hese are set to the minimum temperature difference 
positions. The controller is installed in the test cham ber, and the temperature sens ors are installed in their 
respective temperature controlled baths. 
The electrical load is connected to the controller and adjusted to the maximum load rating declared by the 
manufacturer. FDUS 853: 2009 
© UNBS 2009 – All rights reserved  137
 G.3.2  Collector sensor maximum temperature check 
A check is carried out for approximately 15 min with the store sensor at about 30 °C and the collector sensor 
at 150 °C or 200 °C, depending on its maximum temperature sp ecification. This is to ensure that the controller 
can accommodate the sensor signal under collector st agnation conditions, and that the resistance to 
temperature of the sensor  and its leads is adequate. 
G.3.3  Switching tests 
A sequence of switching tests is made for each of th ree controller temperatures, e.g. 15 °C, 20 °C and 45 °C. 
The controller should be allowed about 30 min to reach equilibrium prior to each testing sequence with its 
power supply ON in order to ensure that any self-heating is taken into account. 
A typical switching test begins with the controller in its OFF condition and with both sensors at low 
temperature, e.g. 5 °C. 
The collector sensor is then slowly raised in temperat ure until the controller switc hes to the ON condition. The 
temperature at which this occurs is recorded, and the sensor is stabilized at a new temp erature slightly above 
the switching temperature. The store sensor is then slowly raised in temperatur e until the controller switches to the OFF condition again. 
This temperature is recorded, and the sensor temperature stabilized. 
This procedure of raising the temperature of each sensor in turn is repeated to give at least five recordings of 
switching OFF events spaced over the range of store temperatures between 5 °C and 80 °C. 
NOTE 1  Before performing switching tests, a check shoul d be made to ensure that sw itching of the temperature 
controlled baths does not affect t he performance of the controller. 
NOTE 2  When testing controllers which employ a time delay circuit, sufficient time should be allowed to elapse between 
switching tests to ensure that the resu lts are not affected by the time delay. 
The results for each controller temperature can be record ed in the form of tables showing the temperature at 
which switching took place, or graphically as shown in Figure G.1. 
G.3.4  Mains voltage sensitivity check 
With the store sensor at about 30 °C, the switch-on and switch-off temperature differentials are measured at 
the nominal mains voltage (say 230 V), and again at 10 % above and 15 % below the nominal mains voltage. 
 
 
 
 
Figure G.1 – Controller operating curves FDUS 853: 2009 
138 © UNBS 2009 – All rights reserved
 Annex H 
(informative)  
 
Solar thermal applications and technologies 
A wide variety of applications can benefit from the use of  solar technologies. Currently, solar technologies are 
used for a myriad of applications, including standard water and pool heating as well as space heating, crop 
drying, cooking, and water distillation, to name but a few. 
This annex provides a general overview of the various  applications that can benefit from the use of these 
technologies. 
Residential applications 
-  Domestic hot water 
-  Swimming pool and spa heating -  Space heating 
-  Water purification/distillation 
-  Air Conditioning 
Commercial applications 
-  Hotels -  Schools -  Apartment and condominium complexes 
-  Recreation areas and campgrounds 
-  Hospitals/Nursing homes -  Restaurants 
-  Laundries 
-  Car washes -  Beverage manufacturing 
-  Cane sugar refining 
-  Canning facilities -  Food processing 
-  Meat packing facilities 
-  Poultry farms 
-  Light commercial businesses 
-  Summer camps 
- Recreation areas and campgrounds -  Industrial process heat 
Agricultural applications 
-  Crop drying -  Green houses 
-  Dairy processing 
-  Meat processing -  Aqua-culture 
-  Food processing 
  
 
 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  139
 Annex I 
(informative)  
 
Solar basics 
Understanding solar thermal systems requires the knowle dge of several energy terms and physical principles. 
This chapter presents important terms and principles and shows how they apply in solar thermal systems. 
Terms and principles 
Insolation is the amount of the sun's electromagnetic energy that "falls" on any given object. Simply put, when 
we are talking about solar radiation, we are referring to insolation. In Florida (at about sea level), an object will 
receive a maximum of around 950 watts/meter2 at hi gh noon on a horizontal surface under clear skies on 
June 21 (the day of the summer equinox). 
Sun path 
On the surface of the earth, insolation varies over time  because of the planet's daily rotation, tilted axis and 
elliptical orbit around the sun. Imagine the sky as a dome  (sky dome) with the horizon as its edge. From this 
perspective, the sun's path describes an arc across the sky from dawn until dusk. This perceived path and its 
variations over time can be plotted as in Figure I.1, which shows the annual sun path from the perspective of 
28 degrees north latitude. This figure illustrates the s easonal changes in the sun's path for a given location. It 
shows that the winter the sun rises in the Southeast, sets in the Sout hwest, has a relatively short path and 
rises to a shallow 39 degree angle above the horizon at noon. In the summertime, the sun rises in the 
Northeast, sets in the Northwest, has a longer path and rises to a much higher angle above the horizon. 
 
 
Figure I.1 – Annual sun path for 28oN latitude (Orlando, Florida) 
 
Atmosphere 
The atmosphere absorbs certain wavelengths of light more  than others. The exact spectral distribution of light 
reaching the earth’s surface depends on how much atmosphere the light passes through, as well as the 
humidity of the atmosphere. In the morning and evening, the sun is low in the sky and light waves pass 
through more atmosphere than at noon. The winter s unlight also passes through more atmosphere versus 
summer. In addition, different latitudes on the earth hav e different average “thickness es” of atmosphere that 
sunlight must penetrate. Figure I.2 illustrates the atmosp heric effects on solar energy reaching the earth. 
Clouds, smoke and dust reflect some solar insolation back up into the atmosphere, allowing less solar energy 
to fall on a terrestrial object. These conditions also di ffuse or scatter the amount of solar energy that does 
pass through . 
 FDUS 853: 2009 
140 © UNBS 2009 – All rights reserved
 
 
Figure I.2 – Atmospheric effects on the solar energy reaching earth 
Angle of incidence 
The sun’s electromagnetic energy travel s in a straight line. The angle at which these rays fall on an object is 
called the angle of incidence (See Figure I.3). A flat surface receives more sola r energy when the angle of 
incidence is closer to zero (normal, perpendicular) and therefore receives signific antly less in early morning 
and late evening. Because the angle of incidence is so large in the morning and evening on earth, about six 
hours of “usable” solar energy is available daily. This is called the “solar window.” 
 
 
Figure I.3 – Angle of incidence 
Absorptance vs. reflectance 
Certain materials absorb more insolation than others. More absorptive materials are generally dark with a 
matte finish, while more-reflective materials are generally lighter colored with a smooth or shiny finish. A golf 
ball covered with black matte paint plac ed in sunlight w ill absorb more solar insolation than a plain white golf 
ball. 
The materials used to absorb the su n’s energy are selected for their ability to absor b a high percentage of 
energy and to reflect a minimum amount of energy. T he solar collector’s absorber and absorber coating 
efficiency are determined by the rate of absorption versus the rate of reflectance. This in turn, affects the 
absorber and absorber coating’s ability to retain heat and minimize emissivity and reradiation. High 
absorptivity and low reflectivity improves the potential for collecting solar energy . 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  141
 Heat transfer 
Because all natural systems seek a balance, heat alwa ys moves from warm (more energy) to cool (less 
energy). Heat moves by thr ee methods: conduction, convection and radiation. 
Conduction 
Conduction occurs when a solid material is heated. Molecules exposed to a heat source become energized. 
These energetic molecules collide with  neighbouring, less-energetic molecu les, transferring their energy. The 
greater the energy transfer ability of the solid’s molecules, the more ener gy they can transf er and the better 
the solid’s conductivity. Copper has high conductivity while glass has low conductivity. If you place a heat 
source at the bottom of a copper tube and a glass tube at the same time, the top of the copper tube will 
become hotter quicker than t he top of the glass tube. 
Convection 
Like conduction, convection occurs by molecular motion but in a fluid (such as a gas or liquid), rather than in a 
solid. When a gas or liquid is heated, the energized mole cules begin to flow. On earth, where gravity is a 
factor, the heated, less-dense fluid flows upward as cooler, more compact fluid moves down. This process of 
displacement continues as long as the heat source remains. 
Radiation 
Radiation occurs not by molecular action but rather by  emission of electromagnetic waves, generally in the 
invisible, infrared spectrum. Because radiation does not rely on the presence of matter (molecules) for 
transport, it can occur in a vacuum. Ju st as the sun radiates to the earth,  a warm object on earth will radiate 
infrared waves at night to objects in deep space. All obje cts with heat radiate to objects with less heat that are 
in a direct path. 
 
Figure I.4 – Illustration of conduction, convection and radiation 
Temperature differential or delta T (ΔT) 
The greater the difference in temperature between two poi nts of an object or between two objects, the greater 
the driving force to move heat from the warmer to the cooler point. This applies whether the heat transfer 
method is conduction, convection or radi ation. Consider the following examples: 
Conduction 
Applying a 260 °C heat source to the bottom of a coppe r tube will make the top of the tube hotter and it will 
heat faster than if the heat source were at 250 °F. 
Convection 
A hot air balloon will rise faster if its air is 121 °C rather than at 67 °C. 
 FDUS 853: 2009 
142 © UNBS 2009 – All rights reserved
 Radiation 
A camper sitting before a raging bonfire will feel mu ch warmer than a camper sitting by the fire’s glowing 
embers. 
Thermal mass 
Thermal mass is the measure of a material’s molecule s ability to hold thermal energy. The higher the thermal 
mass, the material’s energy capacity, the more effici ently the material can store sensible heat. Rock and 
masonry are two such materials that have high thermal mass and are solids. Water is a fluid with good energy 
capacity, making it a good thermal mass medium for energy storage. 
Applying the basics 
The purpose of a solar heating system is to collect so lar energy, convert it to heat, store the heat, and provide 
the stored heat for an intended purpose. The efficiency  of the system depends on how well the solar basics 
are applied. 
Collecting and converting solar energy 
Solar collectors capture the sun’s electromagnetic ener gy and convert it to heat energy. The efficiency of a 
solar collector depends not only on its materials and de sign but also on its size, orientation and tilt. 
Daily variations 
Available solar energy is at its maxi mum at noon, when the sun is at its high est point in its daily arc across the 
sky. The sun’s daily motion across the sky has an impac t on any solar collector’s efficiency and performance 
in the following ways. 
-  Since the angle of incidence of the solar energy — measured from the normal (right angle) surface of the 
receiving surface — changes throughout the day, solar power is lower at dawn and dusk. In reality, there 
are only about 6 hours of maximum energy available daily. 
-  The total energy received by a fixed surface duri ng a given period depends on its orientation and tilt and 
varies with weather conditions and time of day and season. 
Aiming the solar device to track the sun’s rays to strike it at right angles (normal) all day seems logical, but 
solar collectors are large and heavy and must be strong to withstand weather conditions. Tracking the sun 
requires considerably more hardware than does fixed mount ing. Most practical designs accept the loss of 
energy suffered through fixed mounting and use an orientation close to that which collects the most solar 
energy possible. 
Consequently, fixed solar collectors are best positioned to face true south in the northern hemisphere and true 
north in the southern hemisphere. If the collector w ill be unavoidably shaded in the morning when installed at 
its best solar location, it can be oriented slightly we st in the northern hemisphere and slightly east in the 
southern hemisphere. 
Seasonal variations 
The dome of the sky and the sun’s path at various times of the year are shown in Figure I.5 (note that 28° is 
about the latitude of Orlando, Florida). The top illustration shows the paths projected on a flat surface. In mid- 
June the days are long; the sun rises well north of due east and sets well north of due west. It also passes 
almost directly overhead (86°) so t hat at solar noon on June 21 a horizontal plate will almost collect a 
maximum amount of solar energy (see Figure I.6a). But in  December, the sun rises later — south of due east 
— to a noon elevation of less than 40°. It sets early on the west-southwest horizon. So, to get about the most 
solar power at noon in December, a fixed collector sh ould face south and be tilted up at an angle of about 50° 
to the horizontal, as shown in Figure I.6b 
 
 FDUS 853: 2009 
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Figure I.5 – Sun path diagrams for 28o N latitude FDUS 853: 2009 
144 © UNBS 2009 – All rights reserved
 
 
Figure I.6a and I.6b – Collected energy varies with time of year and tilt 
For many solar applications, we want maximum annual  energy harvest. For others, maximum winter energy 
(or summer energy) collection is important. To orient t he flat-plate collector properly, the application must be 
considered, since different angles will be "best" for each different application. 
Collector orientation 
Collectors work best when facing due so uth. If roof lines or other factors dictate different orientations, a small 
penalty will be paid, as shown in Figure I.7. As an exampl e: for an orientation 20° east or west of due south, 
we must increase the collector area to 1.06 times the size needed with due south orientation (dashed line on 
Figure 7) to achieve the same energy output. The orient ation angle away from due south is called the azimuth 
and, in the Northern Hemisphere, is plus if the collect or faces toward the east and minus if toward the west. 
Correction factors may be used to properly size solar collectors which cannot face due south. Closer to the 
equator, this can change. The lower the tilt of the collector,  the less the direction affects it. A collector at 5-10° 
tilt is almost flat to the sun. At 5° latitude and at  a 5° tilt, the collector could be in any direction. 
We have assumed that nothing shades the collector du ring any part of the day. If tall trees, for example, 
shade a collector until 10 a.m., an orient ation west of south (so that the a fternoon sun will provide the bulk of 
the energy collected each day) would enable maximum solar energy collection. Moving the collector or 
increasing its size will correct disruptions to solar insola tion. To help the installer determine shading problems, 
solar pathfinders are available from several manufact urers, or use the Crome- Dome provided with this 
manual. 
 
 
  
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  145
 
 
Figure I.7 - Glazed collector orientations 
Tilt angle 
The best tilt angle will vary not only with the collector's  geographical location but also with seasonal function. 
Solar water heating systems are de signed to provide heat year-round. 
Figure I.8 below shows results for various collector tilt angles for Central Florida. For the slope angles shown 
in the figure, we observe these effects: 
a)  Mounting at an angle equal to the lati tude works best for y ear-round energy use. 
b)  Latitude minus 15° mounting is best for summer energy collection. 
c)  Latitude plus 15° mounting is best for winter energy collection. 
 
Figure I.8 – Various collector tilt angles 
Table I.1 illustrates the effect of various tilt angles on a flat/plate solar collector installed in Miami, Florida . FDUS 853: 2009 
146 © UNBS 2009 – All rights reserved
 Table I.1 – Solar radiation for flat-plate co llectors facing south at a fixed tilt (kWh/m2/day average) in 
Miami, Florida (25.80 oN latitude) 
Tilt angle Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr 
0 3.5 4.2 5.2 6 6 5.6 5.8 5.6 4.9 4.4 3.7 3.3 4.8 
Latitude -15 4.1 4.7 5.5 6.2 5.9 5. 5 5.7 5.6 5.1 4.7 4.2 3.9 5.1 
Latitude 4.7 5.2 5.7 6.1 5.6 5.1 5.4 5.5 5.1 5.1 4.7 4.5 5.2 
Latitude +15 5.0 5.4 5.6 5.7 5.0 4.5 4.8 5 4.9 5.1 4.9 4.9 5.1 
90 4.1 3.9 3.4 2.6 1.9 1.6 1.7 2.1 2.7 3.5 3.9 4.1 3 
 
Methods exist to move a collector so the sun's rays stri ke it at a right angle all day  and in all seasons. Use of 
such sun-tracking mechanisms increase the amount of ener gy a collector receives, but it also increases the 
system's cost, complexity and future maintenance require ments. Most practical designs accept the loss of 
energy suffered through fixed mounting and use an orientation and tilt to colle ct the most usable solar energy 
possible. 
Therefore, for year-round use, a collect or tilt of about 25° for south Florid a or about 30° in North Florida works 
best. On a final note, installers must also keep in mind  the aesthetics of the collector mounting on the plane of 
the roof. 
Heat storage 
Most solar thermal systems employ a material with high energy capacity to store sensible heat until it is 
needed for a specific purpose. Water, masonry and even iron are all such thermally massive materials with 
high energy capacities. When the purpose  of the solar thermal system is to provide heated water, the water 
itself is the thermal mass that stores the heat generated by the solar collector. 
For these solar water heating system s, the water itself may be the fluid heated in the collector and then 
delivered directly to the tank. In areas where fr eezing temperatures are common during winter, the heat 
collecting fluid may be glycol or another heat transfer fluid with high energy capacity that can withstand 
freezing temperatures. Such systems employ heat exchan gers at the storage tank to  transfer the heat from 
the collector fluid to the potable water. 
In solar water heating systems, the storage is sized with generous proport ions to hold as much heated water 
as may be needed for a given purpose during times of low solar insolation. The tanks are also highly insulated 
to reduce heat losses. 
Further from the equator, inlet water temperatures are colder, while in many cases, the insolation may be 
close to the same during some periods of the year. On a given day, if the amount of insolation is about the 
same, one might think solar systems in Toronto or  Miami would perform about the same. The total heat 
energy collected and stored in the tank may be about t he same, but the end-of-the-day tank temperatures will 
be different. 
The Toronto storage tank will be colder than the Miami storage tank due to the difference in cold water supply 
temperatures. The cold water supply water temperature in Miami is approximately 24 °C, while the cold supply 
in Toronto is approximately 7 °C. More total solar ener gy is required to increase the Toronto system to the 
same end-of-the-day tank temperature. 
To achieve the same end-of-the-day tank  temperatures in Toronto you must increase the size of collector area 
to increase the energy gain of the system. Simply put, more collectors are required in order to increase the 
total degrees of the water being heated. 
Additional system considerations 
To meet its intended purpose, a solar thermal system mu st meet criteria beyond simply collecting and storing 
solar energy. 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  147
 Safety 
A solar thermal system must not contaminate the medi um used to store or provide the system's energy 
output. For example, solar water heating systems must not contaminate water that may be used in food 
preparation or in human contact activities. For th is reason, solar water h eaters with heat exchangers 
frequently employ two walls to isolate the potentially dangerous heat collecting fluid from the water to be 
heated. 
Mechanical safety must also be assured in designing and installing solar collectors. A 1.2-m-by-3-m solar 
collector can act like an airplane wing in strong winds, so  it must be structurally well connected and securely 
attached to its mounting surface. 
Affordability 
Affordability can be defined as perfor mance balanced by price. A solar th ermal system with collectors that 
track the sun's path will perform better than one with fi xed collectors. However, the tracking mechanisms can 
double the cost of the system. In the same way, a so lid gold absorber will perform better than a copper one, 
but the cost would be astronomical. To be affordable, a solar thermal system must balance performance and 
cost. Because solar therma l systems produce kilowatt -hour, kW-h/$ is a good measure of affordability. 
Materials used 
Materials for solar energy systems must be chosen carefully. The most important factors are safety, 
performance, durab ility and cost. 
The materials must retain their shape and strength duri ng repeated thermal expansion and contraction-all the 
while being exposed to the weather. Collector materials lead hard lives. The collector is exposed to wind, rain, 
hail, temperature extremes and ultraviolet radiati on. Untreated plastics, woods and synthetic boards 
deteriorate rapidly under such conditions. Even steel mu st be protected by plating, galvanizing or painting. 
The collectors must be able to tolerate stagnation temperatures. This can be as high as 205 °C for some solar 
collectors. Durability is important in all materials used in a solar system because t he cost effectiveness varies 
directly with their life expectancy. 
 
 
 FDUS 853: 2009 
148 © UNBS 2009 – All rights reserved
 Annex J 
 
Crome-dome collector siting aid 
The Crome-Dome is designed to determine the best loca tion for a solar collector. It will work well for any 
location in Florida, but it is not appropriate for use farther north than 31°N latitude (southern Georgia). 
A collector should be mounted in an area receiving su nshine during the entire year. The sun's path drops 
closer to the horizon during winter, and is higher in th e sky during summer. The sun's lowest path, its highest 
path, and its position three hours before and after sola r noon define the solar window. (See Figure J.1.) The 
solar window is shown on the Crome-Dome by  the heavy black lines on the sun path diagram . 
 
To use the Crome-Dome, stand a few feet in front of  the proposed collector si te facing south.* (Use a 
compass to determine south.) Holding the Crome-Dome base as level as possible, and several inches from 
your eye, look upward through the sighting circle. Align t he cross hairs within the sighting circle with the lower 
edge of the solar window. If you can see any objects (tre es, buildings) through the viewer that are within the 
solar window, these objects w ill shade the collector site. 
 
By aligning the collector location, your  eye, cross hairs and object, (see Fi gure J.2) you can read from the sun 
path diagram the times of day and times of year a par ticular object will shade the collector location. When 
checking for high angles (summer), tilt your head all the way back and peer through the viewer on the base of 
the Crome-Dome. The summer sun pat h goes almost directly overhead. 
*If you are on a roof, it is safer to squat or  sit at the base of the collector location. 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  149
 
 
 
  
 FDUS 853: 2009 
150 © UNBS 2009 – All rights reserved
 Annex K  
 
Simplified sizing procedure for solar domestic hot water systems 
The following procedure was developed to size resident ial Solar Water heating systems in Florida. See last 
page for limitation and assumptions. 
Hot water demand and tank size 
Step 1. Using Table 1, Estimate daily hot water use ( litres) and select a nominal tank size (TANK SIZE). 
                     L / d a y  
                 L I T R E S    ( 1 )  
                 T A N K  S I Z E   L  
Table K.1- Hot water demand and tank size 
Average LITRES1 and minimum TANK SIZE based upon number of people: 
     People      LITRES     Minimum TANK SIZE (Gallons) 
      1      75        151 
      2      151        151 
      3      208        250 
      4      265        303 
      5      322        303 
      6      378        378 
      7      435        450 
  (Add 57 litres per person for each additional person) 
Step 2. Use meteorological maps to determine the proper  cold water temperature (COLD TEMP) for location. 
Step 3.  Calculate how much energy is needed (BTUNEED) to heat the water to 50 oC. 
BTUNEED = 8.34 x LITRES x (50-COLD TEMP) x Standby loss factor 
BTUNEED = 8.34 x              x (50-                   ) x                                              Btu/day (3) 
     (Step 1)            (Step 2)             (Table 2)         BTUNEED 
Table K.2 – Standby heat loss from storage 
Type of tank installation …………                Standby loss factor  
25-mm foam or 63.5-mm fibreglass (R = 8-9)    1.20 
50-mm foam (R =16-17) 
(Use linear interpolation to obtain standby loss factor fo r insulation materials having other R-values.) Table K.2 
is to be used for sizing systems with FSEC ratings. If SRCC rating is used and if there are no other backup 
tanks use a standby loss factor or 1.0. 
Example: A thermosiphon water heater with its stor age tank containing a back-up element has an SRCC 
rating. There are not other back-up tanks for the system. In this case use a standby loss factor = 
1.0. 
                                                      
1 1 Gallon [u.s.liquid] = 3.785 412 liter [metric] FDUS 853: 2009 
© UNBS 2009 – All rights reserved  151
 Example:  The same thermosiphon water heater system  is used as a preheat to another back-up tank. The 
element in the thermosiphon tank may not be connect ed. In this case use a standby loss factor 
from Table K.2 corresponding to back-up tank insulation level. 
 
Collector sizing 
Step 4.   Determine penalty factors that affect sizing.  
   a. Select the system Factor form T able K.3.     System Factor   (4a) 
   b. Select the proper Tilt Factor fr om Table K.4.    Tilt Factor   (4b) 
   c. Select the Orientation Factor from Table K.5.    Orientation Factor  (4c) 
Calculate the overall penalty factor (PENALTY) for the combination of all the three individual 
effects:  
   PENALTY = System Factor x Tilt Factor x Orientation Factor 
   PENALTY =                        x                     x            
(Step 4a)  (Step 4b)      (Step 4c)     PENALTY   (c ) 
 
Table K.3 – System Factor   
   System configuration            System Factor 
   Direct system with no heat water exchanger.         1.29 
   Indirect system with a heat exchanger  between collector and storage tank.  1.30 
   Systems with SRCC sy stem certification and Q NET rating.      1.00 
Table K.4 – Tilt factor 
Collector tilt 
Tilt angle (o)         R o o f  p i t c h      R o o f  t i l t  
0  t o  3        0        0o 
 3 to 7      1 in 12      4.8o 
 7 to 12      2 in 12      9.5o 
12 to 16       3 in 12      14.0o 
16 to 20       4 in 12      18.4o 
20 to 25        5 in 12      22.6o 
25 to 30       6 in 12      26.2o 
30 to 37       8 in 12      33.7o 
37 to 43      10 in 12      39.8o 
        43 to 59        12 in 12         45.0o  
Table K.5 – Orientation Factors 
Collector orientation     Orientation Factor 
        South or nearly south       1.00 
        Southeast or southwest         1.15 
        East or West             1.40 
 
 FDUS 853: 2009 
152 © UNBS 2009 – All rights reserved
  
Step 5  Calculate the rating requirem ents of the solar system (RATREQD) 
   To provide 70 % of the annual hot water energy needs using the formular:    RATREQD = BTUNEED x 0.70 x PENALTY 
   RATREQD =                    x 0.70 x                      BTU/Day 
       (Step 3)        (Step 4)       RATREQD                (5) 
Step 6  For the collector selected, record the thermal performance rating at the intermediate 
temperature (BTURATING) in Btu/day and the gross collecto r area (GROSSAREA) in square 
feet form the required FSEC label. 
   Collector manufacturer 
   Model No. 
   Thermal Performance rating at the intermediate temperature (Btu /day)                            Btu/day 
                    B T U R A T I N G   ( 6 a )     Or SRCC Q
NET or Q NET equivalent* 
   Estimate the number of collectors needed using: 
       
   NUMBER =  RATREQD     =     (Step 5)          
      B T U R A T I N G             N U M B E R  ( 6 c )  
          ( S t e p  6 )  
Step 7  Select the actual number of collectors to be used. This is nearest 
                        N O . C O L L E C T R O S  ( 7 a )  
   Whole number (6c) 
   The total area of the number of collector array is  
   TOTAL AREA = NO. COLLECTORS x GROSSAREA 
 
   TOTAL AREA =                        x           m2 
        (Step 7a)              (Step 6b)       TOTAL AREA (7b) 
 
For those systems that are SR CC certified use the SRCC Q NET rating here. Systems with only FSEC test and 
certification may bet an equivalent SRCC Q NET from Testing & Operations on request. 
 
 
 
 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  153
  
Based upon the actual number of collectors to be us ed, compute the solar fraction (SOLAR FRACTION): 
              0 . 7 0  x  
SOLAR FRACTION = 0.70 x NO. COLLECTORS =      (Step 7a)             =  
       N U M B E R              S O L A R  F R A C T I O N  ( 7 c )  
             ( S t e p  6 c )  
 If the solar fraction (Step 7c) is less than 0.65, the collector array is undersized. Consider either adding 
another collector or using a different model/size collector.  This procedure has several constraints: 
1. The procedure is valid only for Florida 
2.  The procedure is based on sizing solar system s to provide between 65% and  75% of the heating load; 
i.e., a solar fraction of between 0.65 and 0.75. A solar fraction of 0.7 is estimated to be optimum for most 
installations and, in particular, for solar collectors with a tilt angle of approximately 20° — 25° (mounted 
parallel to the 10 cm in 30 cm or 12.5 cm in 30 cm pitched roofs that are common in Florida). The 20° — 
25° collector tilt angle provides for an aesthetic in stallation and meets 100% of the hot water needed in 
summer and 50 % in winter. Systems can be sized to ma ximize lifetime saving by providing a larger solar 
collector that will produce a solar fraction of 0.9 or  higher. At high annual solar fractions however, the 
production and waste of excess heat during the summertime needs to be considered. To minimize 
collector size for high annual solar fractions, the collec tors can be installed at a tilt angle of between 40° 
and 40°. Optimization of these types of systems is beyond the scope of th is simplified sizing procedure. 
To achieve this solar fraction, the collectors will need to be installed at a tilt angle of between 40° and50° 
3.  The hot water delivery temperature of 50 °C in st ep 3 was obtained by FSEC from analysis of two years 
of actual experimental data. The 50 °C delivery te mperature is consistent with Florida Law, which 
requires that hot water thermostats be set no higher than 50.7 °C. It is also consistent with electric water 
heater energy consumption data as measured by Florida Power and Light Co. 
Automatic dishwashers may not clean dishes very well at 50 °C. However, most dishwashers have a 
cycle that uses an electric element in the dish washer to boost water temperature to about 60 °C. FDUS 853: 2009 
154 © UNBS 2009 – All rights reserved
 Annex L  
 
Electric water heater circuitry 
The following illustration shows the electrical con nections in a standard hot water tank with two heating 
elements. Each electrical supply line has a potential of 230 volts measured to ground and 400 volts measured 
across the two lines. The illustration shows where the high- limit protector is located in the circuit. It also shows 
how the upper thermostat is used to prevent oper ation of both heating elements simultaneously. 
First, power travels through the high-limit protector: a double-pole, single-throw (DPST) snap-action device. 
When the water reaches a predetermined temperature (ab out 82 °C), this device ope ns both contacts of both 
lines at the same time, which cuts all power to th e heater. To restore operation, the reset button must be 
pressed. 
At the output side of the high-limit protector, the circuit splits and forms the parallel circuits that lead to the two 
elements through their respective ther mostats. The upper thermostat is a double-pole, double-throw (DPDT) 
bimetal type, designed so that when one of the contacts is closed, the other is open, and vice versa. This 
thermostat is always in operation. Depending on the dem and for hot water, it supplies power to either the 
upper or lower element, but never to both elements at the same time. The lower thermostat is a single-po le, single-throw (SPST) type and controls  the lower element. Before this 
lower element can be energized, the upper thermostat mu st be "satisfied" (even though the lower thermostat 
contacts may be closed). 
 
Figure L.1 – Typical electrical connections in a tank with two heating elements FDUS 853: 2009 
© UNBS 2009 – All rights reserved  155
 Annex M  
 
Volt-ohmmeter (VOM) or multimeter operation 
The volt-ohmmeter (VOM) measures voltage and resistan ce. (Some VOMs also measure current but current 
measurements are not needed in controll er troubleshooting.) VOMs have either an analog or a digital readout. 
The analog display uses a needle pointer on a scale. The digital display gives an LCD numerical reading. Both 
types of meters operate from batteries and usually have a battery low indicator to signal when new batteries are needed. 
The meter contains two probes with wire leads, o ne black (the common or ground lead) and one red (the 
positive lead), which plug into color-coded receptacles on the meter. For detailed information about operation 
of the meter, refer to the VOM manual. 
Check the VOM before each use: 
1.  Turn on the power switch. If the battery replacement indicator signals low batteries, replace them 
before continuing. 
2.  Set the function switch to "ohms," and set the range switch to a mid range around 0 to 20K ohms. 
(Note: K equals 1 000 and V refers to volts.) Conn ect the probe wires to the proper receptacles and 
touch the red probe to the black pr obe without contact with your body. 
The meter should read zero (0) or 0.00 (digital), showing continuity. If it does not, adjust to zero. If the meter 
doesn't respond, check the battery supply for a blown fuse. 
Two types of thermistors (sensors t hat change resistance with changing temperature) are generally used in 
control systems — the 3 000 (3K) ohm and the 10 000 (1 0K) ohm. Table M.1 lists the usual VOM settings for 
measuring resistance; Table M.2, for measuring AC  voltage; and Table M.3, for measuring DC voltage. 
Thermistor resistance should match temperature as cl osely as possible, as shown in Table M.4. To be 
accurate, disconnect the thermistor from the circuit before measuring it. 
Table M.5 lists the resistance setting for a positive te mperature coefficient resistance temperature device 
(RTD) that uses 1 000 (1K) ohm sensors. 
Resistance measurements with the VOM 
Remember any circuit must be disconnected to measure its resistance. 
Table M.1 – Measuring resistance with the volt –ohmmeter 
In the Range of Measuring 
Minimum Maximum Function 
switch at Range switch 
at Multiply 
reading by 
Resistance  0 199 Ohms 20 000 1 
Resistance  200 1 999 Ohms 2K 1 000 
Resistance  2 000 19 999 Ohms 20 K 1 000 
Resistance  20 000 199 999 Ohms 200 K 1 000 
Resistance  200 000 1 999 999 Ohms 2M 1 000 000 
Resistance  2 000 000 19 999 999 Ohms 20 M 1 000 000 
 
AC Voltage Measurements with the VOM 
-  Never measure circuits containing over 700 volts AC. 
-  Always make measurements from one line to the other (this is measuring in parallel). 
-  Never insert probes in series with a line. 
-  If the voltage is unknown, start with the highest range on the VOM. FDUS 853: 2009 
156 © UNBS 2009 – All rights reserved
 Table M.2 – Measuring AC voltage with the volt-ohmmeter 
In the Range of AV voltage 
Minimum Maximum Function 
switch at Range switch 
at Multiply 
reading by 
AV Voltage 0 0.19 AC 0.7 kV 200 mV 0.01 
AV Voltage 0.2 1.9 AC 0.7 kV 2V 1 
AV Voltage  2 19.9 AC 0.7 kV 20 V 1 
AV Voltage 20  199.9 AC 0.7 kV 200 V 1 
AV Voltage 200  700.0 AC 0.7 kV 2kV 1 000  
 
DC voltage measurements with the VOM 
- Never measure circuits containing over 1 000 volts DC. 
-  Always measure in parallel with the lines. 
-  Never insert probes in series with the circuit. -  If the voltage is unknown, start with the highest range on the VOM. 
Table M.3 – Measuring DC voltage with the volt-ohmmeter 
In the Range of 
DC voltage 
Minimum Maximum Function 
switch at Range switch 
at Multiply 
reading by 
DC Voltage 0 0.19 DC 1 kV 200 mV 0.01 
DC Voltage 0.2 1.9 DC 1 kV 2V 1 
DC Voltage  2 19.9 DC 1 kV 20 V 1 
DC Voltage 20  199.9 DC 1 kV 200 V 1 
DC Voltage 200  700.0 DC 1 kV 2kV 1 000  
 
Current measurements with the VOM 
Amperage measurements are not needed in the troublesho oting of controllers. Even if your VOM measures 
only up to 1 A safely, do not use it as an ammeter plac ed in series with the pump or motor valves. Some 
VOMs have extended 10 A ranges, but even these may be dam aged if the circuit has a low-resistance short. 
Possible causes for thermistor malfunction 
To check the thermistors in a solar DHW system, disconnect the thermistor leads at the controller. Remember 
also, a change in temperatur e changes thermistor resistance. Make sure the pump is not cycling on and off, 
changing measurement conditions. 
Open Circuit 
If the VOM measures an open circuit (an infinite resistance reading), either the sensor  is bad or the associated 
wiring is broken somewhere along its length. A break may occur where the wire crosses a sharp edge of the 
building or where it has been bent. Run new wi res if the break cannot be found and repaired. 
High resistance 
A high, but not infinite, resistance may also indicate a bad sensor or lead wire. Disconnect the sensor from the 
lead wire and check the resistance at or near room tem perature. The resistance should measure at or near 3K 
or 10K, depending on thermistor rating. 
Short Circuit 
A shorted circuit can also indicate a bad sensor or cont act in the associated wiring. This is indicated on the 
VOM by a zero reading, which shows continuity between the lines. 
Drift 
On rare occasions, thermistor resistance drifts to th e wrong value for its temperatur e and it must be replaced. 
This drift is usually due to aging and can be checked with the VOM. Refer to Table M.4 of thermistor 
temperatures. When resistance readings are correct or nea rly correct for various temperatures, the thermistor 
is working properly. There may be resistance in the wiri ng. To check the associated wiring, use a jumper to 
short across the sensor. The ohm resi stance of the wiring itself should go  near zero. If the resistance still FDUS 853: 2009 
© UNBS 2009 – All rights reserved  157
 exists, make sure all connectors are clean and no break s with resistance contact are found. If none of these 
are found, to eliminate the wiring  resistance, replace the wiring. 
Table M.4 – Temperature and thermistor resistance 
Temperature 
(oC) 3 000 -Ω 
Thermistor 10 000 -Ω 
Thermistor Temperature 
(oC) 3 000 -Ω 
Thermistor 10 000 -Ω 
Thermistor 
Thermistor 
open Infinite Infinite 33.3 2100 7000 
Thermistor 
shorted 0 0 34.4 2010 6683 
-1.1 10400  35.6 1920 6383 
0 9790 32660 36.7 1830 6098 
1.1 9260 30864 37.8 1750 5827 
2.2 8700 29179 38.9 1670 5570 
3.3 8280 27597 40.0 1600 5326 
4.4 7830 26109 41.1 1530 5094 
5.6 7410 24712 42.2 1460 4873 
6.7 7020 23399 43.3 1400 4663 
7.8 6650 22163 44.4 1340 4464 
8.9 6300 21000 45.6 1280 4274 
10.0 5970 19906 46.7 1230 4094 
11.1 5660 18876 47.8 1180 3922 
12.2 5370 17905 48.9 1130 3758 
13.3 5100 16990 51.1 1040 3453 
14.4 4840 16128 53.3 953 3177 
15.6 4590 15315 55.6 877 2925 
16.7 4360 14548 57.8 809 2697 
17.8 4150 13823 60.0 746 2488 
18.9 3940 13140 62.2 689 2298 
20.0 3750 12494 64.4 637 2124 
21.1 3570 11885 66.7 589 1966 
22.2 3390 11308 68.9 546 1820 
23.3 3230 10764 71.1 506 1688 
24.4 3080 10248 73.9 461 1537 
25.0 3000 10000 76.7 420 1402 
25.6 2930 9760 79.4 383 1280 
26.7 2790 9299 82.2 351 1170 
27.8 2660 8862 85.0 321 1071 
28.9 2530 8449 87.8 294 982 
30.0 2420 8057 90.6 270 901 
31.1 2310 7685 93.3 248 828 
32.2 2200 7333 98.9 210 702 
 
 
 
 
 
  
 FDUS 853: 2009 
158 © UNBS 2009 – All rights reserved
 Table M.5 – Temperature and RTD resistance 
 
Temperature (oC) Resistance Temperature (oC) Resistance 
-1.1 861.8 1.7 876.1 
4.4 890.5 7.2 905.1 
10.0 919.2 12.8 933.9 
15.6 948.7 18.3 963.7 
21.1 978.2 23.9 993.4 
26.7 1008.7 29.4 1024.0 
32.2 1039.0 35.0 1054.6 
37.8 1070.3 40.6 1086.1 
43.3 1101.5 46.1 1117.5 
48.9 1133.6 51.7 1149.9 
54.4 1165.6 57.2 1182.1 
60.0 1198.7 62.8 1215.4 
65.6 1231.5 68.3 1248.4 
71.1 1265.4 73.9 1282.5 
76.7 1299.1 79.4 1316.5 
82.2 1333.9 85.0 1351.4 
87.8 1368.5 90.6 1386.2 
93.3 1404.1 96.1 1422.0 
98.9 1439.5 101.7 1457.7 
 FDUS 853: 2009 
© UNBS 2009 – All rights reserved  159
 Annex N  
 
Solar system flow rates 
Determining flow rate 
Determining approximate flow rate through the collector  loop can help you identify problems in the system 
such as faulty pump operation, clogged or restricted pipes or failure of the check valve to open properly. Here 
are two simple methods for checking the solar system flow rate . 
Method A 
This method uses the "siphon principle" to keep water in the collector loop when the city water pressure is 
shut off. First, you must purge air from the collector loop. Also, you must vent the storage tank to the 
atmosphere to prevent a va cuum from forming during the following step s. Refer to the following illustration. 
a.  Turn off the back-up heating element (to avoid burn ing out the element should the water level drop to the 
element's level). 
b.  Ensure all air is purged from the collector loop  and close or plug any valves (air vents or vacuum 
breakers) that may admit air into the pipes. 
c.  Close the shutoff valve in the cold water supply line to the tank, 
d.  Open the PT relief valve on the storage tank. 
e.  Attach a hose to the boiler drain on the return line fr om the collector(s). Drain off a few gallons of water so 
the standing water level is below the top of the tank and not in the hot and cold supply pipes. If you have 
a clear plastic hose, you can easily see the water le vel. When the level is about 25 mm below the top of 
the tank, stop the draining proc ess by elevating the open end of t he hose above the top of the tank. 
Leave the boiler drain open. 
f.  Close the isolation valve between t he return line boiler drain and the tank. 
g.  Lower the open end of the hose to just above the standing water level in the tank. Allow the level to come 
to equilibrium. 
h.  Place a vessel of known volume where it can re ceive all the discharge from the hose attached to the 
return line boiler drain. Keep this container as close to the water level line as possible to minimize static head influences on the flow rate. 
i.  Manually turn on the pump and use a stopwatch to measure the time required to fill the vessel, 
j.  Turn off the pump. Use this formula to calculate the flow rate: 
Flow rate   =    Volume  
       T i m e  k.  Close the return line boiler drain. Open the shutoff valve in the cold water supply to refill the tank. Bleed 
off the entrapped air through the PT relief va lve, and close it when the tank is full. 
l.  Open the remaining valves to return the system to normal operation. This avoids prolonged stagnation in 
the collector loop. 
 
 FDUS 853: 2009 
160 © UNBS 2009 – All rights reserved
 
 
 
Figure 5.1 – Determination of flow rate 
Method B 
Another less accurate method can be used when the syst em is plumbed in such a way that you cannot follow 
Method A. 
a.  Determine the volumetric capacity of the collector. 
b.  Turn off the pump and allow the collector loop pipes to cool down to equilibrium (and the collector to heat 
up). 
c.  Put your hand on the return pipe near the tank and turn on the pump. When you feel the "slug" of hot 
water warm the area under your hand,  start timing. Use a stopwatch. C ontinue timing until the pipe starts 
to cool down again. 
d.  Calculate the approximate flow rate by divi ding the volumetric capacity by the time measured 
(litres/minute or litres/second). 
  FDUS 853: 2009 
© UNBS 2009 – All rights reserved  161
 Flow rates and water stratification in solar tanks 
Flow rates also have a direct correlation to system perf ormance. Low flow rates in single-tank direct systems 
result in better overall system performance. Low circulation does not mix up the water in the solar tank and 
thereby enhances stratification. 
When water circulates through the collectors and returns at a low flow rate, the hottest water will migrate to 
the upper portion of the tank. The colder water at t he bottom of the tank will not mix with the returning 
collector-heated water. Thus, the bottom water being fed to the collector is the coldes t water in the tank. This 
in turn improves the collector's efficiency because t he colder the inlet temperature, the more efficient the 
collector panel. To improve system performance by using lower flow ra tes and better stratification, follow these guidelines: 
a.  Use a flow rate of approximatel y 0.04 l/min (0.0006 l/s) square metre of collector panel (e.g. 3.71612 
square metre of panel × 0.01 = 2 l/min (0.03 l/s)). 
b.  Use dip tube diffusers on your cold and hot ports. You can make these by heat closing the end of the dip 
tube and drilling holes near the end — so the water exits sideways instead of downward. 
c.  Return the solar heated water at least 200 to 250 mm below the top heating element. 
 FDUS 853: 2009 
162 © UNBS 2009 – All rights reserved
 Annex P  
 
Tools for service and repair 
To avoid costly delays, repair and service personnel must arrive at the scene fully prepared and outfitted. 
Listed below are the recommended tools and equipment for diagnosis and repair of DHW systems. 
Bucket, 5-gallon plastic 
Brush, flux Brush, wire 
Chalk-line reel 
Compass Crimping tool 
Cutter, copper and PVC 
Drill, battery operated Drill, electrical 
Drill bits, assorted size set, high speed steel twist 
Drill bits, 19 mm to 75 mm set, steel hole saw 
Drill bits, 9 mm to 25 mm size set, power wood 
Extension drill Extension cord, 30 m 
Extinguisher, fire (A: B: C: rated) 
Flashlight, industrial Glasses, safety 
Gloves, work 
Gun, caulking Gun, soldering 
Hacksaw 
Hammer, claw Hand pump, or small air compressor 
Hex key sets, standard and metric 
Hose, rubber 7.5 m Inclinometer 
Knife, utility 
Ladder, extension 7.2 m Lamp, heavy duty trouble 
Level, 610 mm 
Level, magnetic torpedo 
Mask, dust 
Mirror, inspection Multimeter or voltmeter FDUS 853: 2009 
© UNBS 2009 – All rights reserved  163
 Nut driver set, standard and metric 
Pliers, diagonal cutting 150 mm 
Pliers, locking 25 mm 
Pliers, needle nose 203 mm Pliers, 150 mm 
Pliers, slip joint 203 mm 
Plumb bob Pop riveter 
Pressure gauge, testing 
Putty knife Rope, safety 9.5 mm × 30 m 
Saw, hand 8 point, general purpose 
Saw, skill 
Saw, miter 
Screwdriver, angle Screwdriver set, electronic 
Screwdriver set, Phillips 
Screwdriver set, standard Sensor stimulator 
Slate, nail cutter 
Shears, industrial Shoes, non-skid 
Socket wrench set 
Torch, acetylene Torch, propane 
Vise, mechanics 
Vise grips, 25 mm Water meter key 
Wire strippers 
Wrench set, Alien Wrench, adjustable 
Wrench, pipe 25 mm 
Wrenches, open-end kit, 8 mm to 18 mm 
 
 
 
 FDUS 853: 2009 
164 © UNBS 2009 – All rights reserved
 Bibliography 
23.040.01: Pipeline components and pipelines in general 
[1]  ISO 6708:1995, Pipework components — Definition and selection of DN (nominal size) 
[2]  ISO 7268:1983, Pipe components — Definition of nominal pressure 
[3] ISO 9311-1:2005, Adhesives for thermoplastic piping system s — Part 1: Determination of film 
properties 
[4] ISO 9311-2:2002, Adhesives for thermoplastic piping system s — Part 2: Determination of shear 
strength 
[5] ISO 9311-3:2005, Adhesives for thermoplastic piping syst ems — Part 3: Test method for the 
determination of resistance to internal pressure 
[6] ISO 9356:1989, Polyolefin pipe assemblies with or without jointed fittings — Resistance to internal 
pressure — Test method 
[7] ISO/TS 10465-1:2007, Underground installation of flexible glass-reinforced pipes based on 
unsaturated polyester resin (GRP-UP) — Part 1: Installation procedures 
[8] ISO/TR 10465-2:2007, Underground installation of flexible glass-reinforced pipes based on 
unsaturated polyester resin (GRP-UP) — Part 2: Comparison of static calculation methods 
[9] ISO/TR 10465-3:2007, Underground installation of flexible glass-reinforced pipes based on 
unsaturated polyester resin (GRP-UP) — Part 3:  Installation parameters and application limits 
[10]  ISO 10802:1992, Ductile iron pipelines — Hydrostatic testing after installation 
[11] ISO 10804-1:1996, Restrained joint systems for ductile iron pipelines — Part 1: Design rules and 
type testing 
[12] ISO 10931:2005, Plastics piping systems for industrial applications — Poly (vinylidene fluoride) 
(PVDF) -- Specifications for components and the system 
[13] ISO/TR 11295:1992, Techniques for rehab ilitation of pipeline systems by the use of plastics pipes 
and fittings 
[14] ISO 13845:2000, Plastics piping systems — Elastomeric-seal ing-ring-type socket joints for use with 
unplasticized poly (vinyl chloride) (PVC-U) pipes — Test method for leaktightness under internal 
pressure and with angular deflection 
[15] ISO 13951:2001, Plastics piping systems -- Test method for the resistance of polyolefin pipe/pipe or 
pipe/fitting assemblies to tensile loading 
[16] ISO 15493:2003, Plastics piping systems for industrial applic ations — Acrylonitrile-butadiene-styrene 
(ABS), unplasticized poly(vinyl ch loride) (PVC-U) and chlorinated po ly(vinyl chloride) (PVC-C) — 
Specifications for components an d the system — Metric series 
[17] ISO 15494:2003, Plastics piping systems for industrial app lications — Polybutene (PB), polyethylene 
(PE) and polypropylene (PP) — Specifications for components and the system — Metric series 
[18] ISO/TS 15874-7:2003, Plastics piping systems fo r hot and cold water installations — Polypropylene (PP) 
— Part 7: Guidance for the assessment of conformity  FDUS 853: 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 853: 2009 
 
ICS 27.160 
Price based on 172 pages 
© UNBS 2009– All rights reserved