ICS 97.100.99; 27.160  
 
Reference number  
DRS 212: 2022 
© RSB 202 2 
  
 RWANDA 
STANDARD  DRS 
2022 
 
Second  edition  
2022-mm-dd 
 
 
 Domestic storage solar water heating 
systems — Requirements  for installation, 
maintenance, repair and replacement   
   
DRS 214: 2022 
©RSB 2022 - All rights reserved                 ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition 
 
 
 
 
 
 
 
 
© RSB 2022 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.r w 
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 214: 2022 
iii                ©RSB 202 2 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Requirem ents ................................ ................................ ................................ ................................  2 
4.1 General  ................................ ................................ ................................ ................................ ..........  2 
4.2 Assembly  ................................ ................................ ................................ ................................ ....... 6 
4.3 Operation of the system  ................................ ................................ ................................ ..............  6 
5 Installation  ................................ ................................ ................................ ................................ ..... 6 
5.1 Freeze protection  ................................ ................................ ................................ ..........................  6 
5.2 Solar collectors  ................................ ................................ ................................ .............................  7 
5.3 Solar storage tank  ................................ ................................ ................................ ........................  9 
5.4 Safety devices and controls  ................................ ................................ ................................ ........  9 
5.5 Pipe work  ................................ ................................ ................................ ................................ ..... 10 
6 Operation and maintenance  ................................ ................................ ................................ ...... 10 
7 Repair ................................ ................................ ................................ ................................ ...........  11 
Annex  A (normative)  Des ign considerations and positioning of solar collectors  ..........................  12 
 DRS 214: 2022 
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 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national st andards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 214 was prepared by Technical Committee RSB/TC 049, Solar energy  systems  and accessories . 
In the preparation of this standard, reference was made to the following standard s: 
1) SANS 1307, Domestic storage solar water heating systems  
2) RS ISO 9459 -1, Solar heating — Domestic water heating systems — Part 1: Performance rating 
procedu re using indoor test methods  
3) RS ISO 9459 -2, Solar heating — Domestic water heating systems — Part 2: Outdoor test methods for 
system performance characterization and yearly performance prediction of solar -only systems  
4) ISO 9459 -4, Solar heating — Domestic w ater heating systems — Part 4: System performance 
characterization by means of component tests and computer simulation  
5) ISO 9459 -5, Solar heating — Domestic water heating systems — Part 5: System performance 
characterization by means of whole -system tests and computer simulation  
6) ASTM E 1026, Installation and service of solar domestic water heating systems for one -and two -family 
dwellings  
The assistance derived from the above source is hereby acknowledged with thanks.   
Committee membership  
The following organizations were represented on the Technical Committee s on Solar energy  systems  and 
accessories  (RSB/TC 049) in the preparation of this standard.  
LE-GTSIM Ltd  
Ministry of Infrastructure  
Rwanda Energy Group/Energy Development Corporation Limited (EDCL)  
Rwanda Military Hospital (RMH)  
TEECCSM Ltd  
University of Rwanda - College of Science and Technology (UR -CST)  
Rwanda Standards Board (R SB) - Secretariat  DRS 214: 2022 
1                ©RSB 202 2 - All rights reserved  
 Domestic storage solar water heating systems  — Requirements  for 
installation, maintenance, repair and replacement  
1 Scope   
This Draft Rwanda Standard specifies the requirements for  installation, maintenance, repair and replacement  
of domestic storage solar water heating systems  with all the relevant and applicable control units . 
2 Normative references   
The following documents are referred to in the text in such a way that some or all of  their content constitutes 
requirements of this document.  For dated references, only the edition  cited applies. For undated references, the 
latest edition of t he referenced document (including any amendments) applies.  
DRS 212 , Domestic storage solar water heat ing systems  — Requirements  
3 Terms and definitions   
For the purposes of this standard, the terms and definitions given in DRS 212 and the following apply.  
3.1 
acceptable  
acceptable to the local authority in whose area of jurisdiction the system is installed, or to the body administering 
this standard  
3.2 
approved  
approved by the local authority in whose area of jurisdiction the system is installed, or by the authority 
administering this standard  
3.3 
competent person  
person who is able, by virtue of possessing a relevant professional qualification or applicable knowledge, 
training and experience, to solve or resolve problems that relate to the subject matte r 
energy output above mean inlet temperature of a collector (Ta − Tc = 10 °C) as determined by the thermal 
performance test, and normalized to a base of 20 MJ/ m2/d of solar energy input   
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 4 Requirements  
4.1 General  
4.1.1  The symbolic signs given in figure 1 are used to identify the type; nature and combination of the varieties 
of valves recommended for particular systems (see figures 2 - 7, inclusive) . 
 
Figure 1 — Symbolic signs  
NOTE  The figures are for information only and do not represent all the systems in the market place.  
4.1.2  Solar water heaters consist basically of an absorber unit that collects the incident solar radiation during 
the day, and a storage tank to contain the heated water. These two main components a re separate in most 
conventional systems, as shown in figures 2, 3, 4 and 5, but can also be combined to form a single absorber 
and storage unit . 
DRS 214: 2022 
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Figure 2 — Thermosiphonic hot water system  
NOTE  H is the hot water pipe and HR is the hot water reserve pipe . 
 
Figure 3 — Pumped direct solar hot water system  
 
 
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Figure 4 — Pumped indirect solar water system  
 
 
Figure 5 — Solar water heater used for preheating in a hot water system  
DRS 214: 2022 
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Figure 6 – Solar water heater used as pre -heater in a hot water s ystem  
 
Figure 7 — Thermoscopic hot water system with no supplemental heat source  
 
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 4.1.3  The type of system to be used should be determined from the average efficiencies of different types of 
solar absorbers as given by the manufacturer.  
4.2 Assembly  
4.2.1  All components used in an assembly shall be of an approved type.  
4.2.2 The system assembly shall comprise:  
a) fittings and components, of which the type and quality shall comply with appropriate acceptable standards;  
b) solar water heater that complies with RS 2 12; 
c) solar collectors; and  
d) for systems with a storage tank installed under the roof, a drip tray.  
NOTE Additional power supply and valves are required to control the circulation of the heated fluid. To achieve independency 
from the mains supply, a solar pho tovoltaic panel is used to power the circulation pump . 
4.2.3  In systems where the storage tank is below the absorber unit, a non -return valve shall be installed in the primary return 
pipe.  
4.2.4  The system shall be fitted with a drain pipe and a circulatio n pump with intelligent controls (pump, valves and 
temperature sensors) if the bottom of the storage tank is less than 300 mm above the top of the panels.  
4.3 Operation of the system  
All the components of the system shall be installed in accordance with the manufacturer’s instructions and in 
such a manner and position as to ensure:  
a) the safe and effective operation of the system and of each individual component part;  
b) that shut -off valves are installed to enable the easy, effective and correct removal and repla cement of 
component parts or spare parts during maintenance, replacement or repair; and  
c) the effective discharge and drainage of water from the system.  
5 Installation  
5.1 Freeze protection  
Domestic solar water heaters installed in areas where freezing is known to  occur, shall be protected against 
freezing.  DRS 214: 2022 
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 5.1.1  Antifreeze chemicals   
Freeze protection may be accomplished through the use of chemicals either as or in the heat transfer fluid.  
5.1.2  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 exposed to freezing temperatures, as in the drain down or drain 
back systems. Electrically operated valves shall drain the system when there is a power outage (that is, fail 
safe).  
5.1.3  Automatic recirculation  
Freeze protection may be accomplished through the use of system controls which automatically circulates heat 
transfer fluids through the system when outdoor temperatures reach predetermined levels. This freeze 
protection does not operate during periods of power outage unless an auxiliary source of power is provided. 
This freeze protection system is not recommended for use in areas with frequent or severe freeze conditions, 
and may increase the heat loss of the s ystem during off periods.  
5.1.4  Manual draining  
Freeze protection may be accomplished through the use 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 fr eeze 
protection since it requires human attention for proper operation. Failure to operate the system properly may 
result inconsiderable damage.  
5.1.5  Low wattage electric resistance heating  
Freeze protection for tank absorber systems may be accomplished through  the use of low wattage (less than 
300 W) electrical resistance heaters and system controls that supply heat to the tank and adjacent piping/fittings 
only when temperatures inside the system reach 35 °F + 2 °F (2 °C + 1 °C). This freeze protection system d oes 
not operate during periods of power outage unless an auxiliary source power is provided.   
5.1.6  Freeze tolerant materials  
Freeze protection maybe accomplished through the use of materials which are not damaged by repeated cycles 
of freezing and thawing while  filled with potable water, provided evidence that the material can withstand such 
cycling is supplied.  
5.2 Solar collectors  
5.2.1  Solar collectors shall be installed in accordance with the manufacturer's instructions.  
5.2.2  Before installation, an assessment of the roof structure that will support the solar collector and its related 
(i.e. wind and rain) and anticipated loads shall be carried out by a competent person, in accordance with the 
requirements of Rwanda Building Co de, relevant  standards and solar water heating regulations .  
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 5.2.3  Structural supports shall be constructed to support 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 the resistance to damage of the building. Neither wind 
loading nor the additional mass of filled collectors shall exceed the live and dead load ratings of the building, 
roof, foundatio n, or soil.  
5.2.4  The solar collectors shall be provided with supports to maintain collector tilt and orientation within the 
design conditions.  
5.2.5  The orientation of the solar collectors and the tilt angle shall be determined by a competent person.  
NOTE  See Annex A for design considerations and positioning of solar collectors.  
5.2.6  The collectors shall be installed in a manner that will ensure that they do not contribute to the acceleration 
of roofing material deterioration.  
5.2.7  Access to components t hat require maintenance and repair shall be provided without disturbing roof, 
collector supports, or collector panels  
5.2.8  Collectors and supports shall be installed in such a manner that water flowing off the surface of the 
collector does not cause water  collection on certain parts of the roof.  
5.2.9  The solar collectors shall not be positioned (located) where they are likely to be shaded between the hours 
of 09:00 and 15:00.  
NOTE  The shadows of tall objects nearby can severely limit the satisfactory operation of a solar system.  
5.2.10  Solar collectors to be installed on thatched roofs shall be approved by a competent person.  
5.2.11  Structural supports shall be selected and installed i n such a manner that thermal expansion of the 
collector subsystem will not cause damage to the collector, structural frame, or building.  
5.2.12  Collectors and supports shall not create a hazard by blocking any means of egress.  
5.2.13  Protection of collecto rs and components shall be provided during handling and installation to prevent damage.  
5.2.14  Frames, braces, and fasteners used in collector installation shall be made of materials suitable for exterior location.  
5.2.15  Collectors shall not reduce the fire rating of the roof as prescribed in applicable building codes.  
5.2.16  Roof penetrations necessitated by a collector array should be kept to a minimum.  
5.2.17  The collector array should not move with frost heave unless adequate provisions for flexing have been provided.  
5.2.18  In thermosiphon systems, the bottom of the storage tank should be above the top of the collector  
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 5.3 Solar storage tank  
5.3.1  The minimum storage capacity of a container in any solar hot water system shall, unless otherwise 
required, be as follows:  
a) if no supplementary energy source is provided, a storage capacity of 20 % in excess of the daily hot 
water demand under winter condi tions; and  
b) if a supplementary energy source is provided  for: 
1) an integral solar heater system, a storage capacity of at least 100 % of the daily hot water demand 
under summer conditions; and  
2) an integral solar heater and supplementary storage container syste m, a storage capacity of:  
i) in the case of the solar container, at least 25 % of the daily hot water demand under summer 
conditions; and  
ii) in the case of the supplementary container, at least 75 % of the daily hot water demand under 
summer conditions.  
5.3.2  Where heat losses might occur, the storage tanks shall be thermally insulated in an acceptable manner to 
prevent heat loss.  
5.3.3  When the storage tank (complete with its ancillary components) is installed in a manner and position where 
any leakage from the storage tank and its ancillary components can cause any damage to property, it shall be 
furnished with a drip tray:  
a) such a drip tray shall be fitted with a discharge pipe connected to the discharge connection of the drip 
tray and be led through an external  wall in a visible position in order to discharge on the outside of the 
building; and  
b) the joint between the discharge pipe and discharge connection of the tray shall be made leaktight.  
5.3.4  Where the storage tank is fitted with an overflow valve, the outl et thereof shall be directed to where it 
shall not cause damage to the building.  
5.4 Safety devices and controls   
5.4.1  Control systems components shall comply with the relevant national, regional or international standards.  
5.4.2  Pressure relief and temperature relief valves shall be installed in those parts of the system which can be 
isolated and contain a heat source.  
5.4.3  The system shall incorporate a means of alerting the user of the malfunctioning of the system.   
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 5.4.4  Systems that rely on air to facilitate drainage shall be fitted with vacuum breakers that comply with the 
requirements of relevant approved standards for functional -control valves and safety valves for domestic hot 
and cold  water supply systems.  
5.4.5  Where the temperature of the stored water is not set to 60 °C, the system shall be fitted with a mixing 
valve.  
5.4.6  If necessary, pressure either to the working pressure of the system incorporated in the installation or to 
the maximum permissible pressure al lowed in the installation. The pressure control valve shall be situated at a 
convenient position in the incoming cold water supply pipeline.  
5.5 Pipe work  
5.5.1  Pipe work shall be designed to withstand the expected working pressures and temperatures.  
5.5.2  The pipe network layout for both hot and cold  water systems shall be such that length and directional 
changes are minimized  
5.5.3  Where heat loss might occur, the piping shall be acceptably insulated.  
5.5.4  Copper pipes shall comply with the requirements of r elevant approved standard for copper tubes for 
potable water.  
5.5.5  Unless galvanic action is unlikely to occur, or unless effective measures are taken to prevent such 
deterioration, metal pipes of different materials shall, as far as possible, not be conn ected to one another.  
NOTE 1 Galvanic action will be reduced when the sequence of metals, in relation to the normal direction of flow, is galvanize d 
steel (zinc) to uncoated iron to copper.  
NOTE 2 A copper supply pipe connected to a galvanized steel storag e tank or coated steel storage water heater will result 
in galvanic action occurring in the tank or heater.  
6 Operation and maintenance  
6.1 On completion of the installation, the installer shall furnish the owner with an operation manual that contains:  
a) proper operating and safety procedures; and  
b) emergency shutdown procedures . 
6.2 The owner shall also be provided with written and schematic ins tructions for routine maintenance.  
6.3 The maintenance of the system shall include:  
a) cleaning of the solar collector glazing ; 
b) cleaning of components ; and DRS 214: 2022 
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 c) recommended maintenance intervals.  
7 Repair  
7.1 Repair of solar water heating systems shall be carried out by a competent person, or under his personal 
supervision.  
7.2 Repair of a solar water heating system shall ensure that the system is restored to full and effective 
operational readiness and that it complies with the requirements of the original manufacturer.   
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 Annex  A 
(normative)  
 
Design considerations and positioning of solar collectors  
A.1 Solar heaters effectively absorb heat from the sun from about 10:00 until about 16:00. Solar irradiance is at 
its peak between about 12:00 and 14:00. However , sufficient quantities of hot water have to be stored for use 
after 16:00.  
A.2 A critical factor in the installation of solar heating systems is the position of the collector relative to the 
movement of the sun. In the southern hemisphere, collectors shou ld be pointed true north and tilted at an angle 
above the horizontal equal to the latitude of the site plus 10°. This angle is chosen mainly to favour the collection 
of solar heat during winter when the sun is fairly low in the sky, to obtain year round ef ficiency. A deviation of 
up to 45° east or west of north may, however, be acceptable in many cases.  
A.3 The design of the absorber unit can vary from a simple flat plate to an evacuated tube reflector type 
absorber. Ideally, the exposed surface of the coll ector should absorb the maximum amount of incident solar 
radiation with a minimum of heat loss.  
A.4 The transparent cover over the collector prevents ingress of rain, reduces the cooling effect of outside air 
movement over the collector and restricts re -radiation losses, the latter probably being the most important. This 
means that the incident solar radiation has to be transmitted through the transparent cover with a minimum loss 
of heat energy due to absorption.  
A.5 Thermosiphonic circulation can be creat ed by placing the absorber at the lowest point of the system. The 
resulting circulation pressure is fairly small and any obstruction or an accumulation of air bubbles in the system 
can impede the natural flow of the water. The absorber and all pipes are th erefore sloped in such a way that air 
can escape to the tank to be vented off.  
A.6 While the thermosiphonic system, as shown in figure 2, is the most popular one for domestic applications, 
pumped systems permit greater freedom in the placement of the absor ber(s), which can then be situated either 
above or below the storage tank. A typical pumped system is shown in figure 3. Pumped systems can be direct 
(where the potable water itself circulates through the solar collector) or indirect as shown in figure 4, where the 
potable water is heated via a heat exchanger.  
A.7 In an indirect system, additives can be added to the solar panel water (or primary circulating water) to control 
corrosion. Figure 5 shows a more complex arrangement in which a solar installation is used to preheat the feed 
tester for the main hot water storage tank.  
A.8 Indirect systems are less efficient than direct systems, owing to losses from the heat exchanger. Indirect 
systems do, however, have the following advantages over both thermosiphon ic and pumped direct systems:  
a) frost damage can be prevented by the use of a suitable heat transfer fluid, usually water with an antifreeze 
additive;  
b) damage due to boiling can be prevented if a suitable heat transfer fluid with a high boiling  
c) temperature is  selected;  DRS 214: 2022 
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 d) corrosion within the primary system can be minimized by the use of a corrosion -inhibited heat  
e) transfer fluid; and  
f) scale formation within the primary system can be more effectively controlled.  
 
 
 
 
 
 
 
 DRS 214: 2022 
 
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