Solar heating — Domestic water heating systems — Part 2: Outdoor test methods for system performance characterization and yearly performance prediction of solar-only systems
Describes test procedures for characterizing the performance of solar domestic water heating systems operated without auxiliary boosting and for predicting annual performance in any given climatic and operating conditions.Suitable for testing all types of systems including forced circulation, thermosiphon, freon-charged collektor systems.
Chauffage solaire — Systèmes de chauffage de l'eau sanitaire — Partie 2: Méthode d'essai en extérieur pour la caractérisation de la performance des systèmes "tout solaire" et la prédiction de leur performance annuelle
Standards Content (sample)
Solar heating - Domestic water heating
Outdoor test methods for System
Performance characterization and yearly
Performance prediction of solar--only Systems
Chauffage solaire - Systemes de chauffage de I’eau sanitaire -
Partie 2: Methode d’essai en extbrieur pour Ia caract&isation de Ia
Performance des systemes “tout solaire” et Ia prkdiction de leur
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ISO 9459-2: 1995(E)
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3 Def initions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 System classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7 Test procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Analysis and presentation of results
9 Prediction of long-term Performance ......................................
A Format sheets for test and annual Performance prediction for solar
domestic water heating Systems
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25B Computer programs for long-term Performance prediction . . 51
C Test for Systems with a midday draw-off
D Bibliography ............................................................................0 ISO 1995
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International Organization for Standardization
Case Postale 56 l CH-l 211 Geneve 20 l Switzerland
Printed in Switzerland
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ISO 9459-2: 1995(E)
ISO (the International Organization for Standardization) is a worldwide
federation of national Standards bodies (ISO member bodies). The work
of preparing International Standards is normally carried out through ISO
technical committees. Esch member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take patt in the work. ISO
collaborates closely with the International Electrotechnical Commission
(1 EC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
International Standard ISO 9459-2 was prepared by Technical Committee
lSO/TC 180, Solar energy, Subcommittee SC 4, Systems - Thermal
Performance, reliability and durability.
ISO 9459 consists of the following Parts, under the general title Solar
hea ting - Domestic water heating Systems:
- Part 1: Performance rating procedure using indoor test methods
- Part 2: Outdoof fest methods for System Performance character-
ization and yearly Performance prediction of solar-only Systems
- Part 3: Performance test for solar plus supplementary Systems
- Part 4: System Performance characteriza tion by means
ponent tests and Computer simulation
System Performance characterization
- Part 5: by means of whole-
tests and Computer simulation
Annex A forms an integral part of this part of ISO 9459. Annexes B, C and
D are for information only.
. . .
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ISO 9459-2: 1995(E) ’
International Standard ISO 9459 has been developed to help facilitate the
international comparison of solar domestic water heating Systems. Be-
cause a generalized performante model which is applicable to all Systems
has not yet been developed, it has not been possible to obtain an inter-
national consensus for one test method and one Standard set of test
conditions. lt has therefore been decided to promulgate the currently
available simple methods while work continues to finalize the more
broadly applicable procedures. The advantage of this approach is that each
part tan proceed on its own.
into five within three
ISO9459 is divided Parts broad categories, as de-
scri bed below.
ISO 9459-1 :1993, Solar heating - Domestic water heating Systems -
Part 1: Performance rating procedure using indoor test methods, involves
testing for periods of one day for a standardized set of reference con-
ditions. The results, therefore, allow Systems to be compared under
identical solar, ambient and load conditions.
Black box correlation procedures
ISO 9459-2 is applicable to solar-only Systems and solar-preheat Systems.
The performante test for solar-only Systems is a “black box” procedure
which produces a family of “input-output” characteristics for a System.
The test results may be used directly with daily mean values of local solar
irradiation, ambient air temperature and cold water temperature data to
predict annual System Performance.
ISO 9459-3 applies to solar plus supplementary Systems. The Performance
test is a “black box” procedure which produces coefficients in a corre-
lation equation that tan be used with daily mean values of local solar
irradiation, ambient air temperature and cold water temperature data to
predict annual System Performance. The test is limited to predicting annual
Performance for one load Pattern.
Testing and Computer Simulation
ISO 9459-4, a procedure for characterizing annual System Performance,
uses measured component characteristics in the Computer Simulation
program “TRNSYS”. Procedures for characterizing the Performance of
System components other than collectors are also presented in this part
of ISO 9459. Procedures for characterizing the Performance of collectors
are given in other International Standards.
ISO 9459-5 presents a procedure for dynamic testing of complete sys-
tems to determine System Parameters for use in a Computer model. This
model may be used with hourly values of local solar irradiation, ambient
air temperature and cold water temperature data to predict annual System
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0 ISO ISO 9459-2: 1995(E)
The procedures defined in ISO 9459-2, ISO 9459-3, ISO 9459-4 and
ISO 9459-5 for predicting yearly Performance allow the ouput of a System
to be determined for a range of climatic conditions.
The results of tests performed in accordance with ISO 9459-1 provide a
rating for a Standard day.
The results of tests performed in accordance with ISO 9459-2 permit
Performance predictions for a range of System loads and operating con-
ditions, but only for an evening draw-off.
The results of tests performed in accordance with ISO 9459-3 permit an-
nual System Performance predictions for one daily load Pattern.
The results of tests performed in accordance with ISO 9459-4 or
ISO 9459-5 are directly comparable. These procedures permit perform-
ante predictions for a range of System loads and operating conditions.
System reliability and safety will be dealt with in ISO 11924:-, Solar
heating - Domestic water heating Systems - Test methods for the as-
sessment of reliability and safety.
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INTERNATIONAL STANDARD 0 ISO ISO 9459-2: 1995(E)
Solar heating - Domestic water heating Systems -
Outdoor test methods for System Performance
characterization and yearly Performance prediction of
This part of ISO 9459 establishes test procedures for characterizing the Performance of solar domestic water
heating Systems operated without auxiliary boosting, and for predicting annual Performance in any given climatic
and operating conditions, but only for an evening draw-off. A “black box” approach is adopted which involves no
assumptions about the type of System under test; the procedures are therefore suitable for testing all types of
Systems, including forced circulation, thermosiphon, freon-charged and integrated collector-storage Systems.
This part of ISO 9459 is not intended to be used for testing solar heating Systems which have an auxiliary heater
as an integral patt of the System, since the Operation of the auxiliary input may influence the Performance of the
solar heating System. To quantify the interaction between the energy inputs, the test procedure described inISO 9459-3 is recommended.
This part of ISO 9459 applies to solar-only domestic water heating Systems designed to heat potable water to be
supplied for domestic water usage and is not intended to be applied to other Systems. The test procedures areapplicable only to Systems of 0,6 m3 of solar storage capacity or less.
The test procedures in this part of ISO 9459 do not require the solar water heating System to be subjected to
freezing conditions. Consequently, the energy consumed or lost by a System while operating in the freeze-protection mode is not determined.
This part of ISO 9459 is not generally applicable to concentrating Systems.
lt is not intended to be used for testing the individual components of the System, nor is it intended to abridge anysafety or health requirements.
2 Normative references
The following Standards contain provisions which, through reference in this text, constitute provisions of this patt
of ISO 9459. At the time of publication, the editions indicated were valid. All Standards are subject to revision, and
Parties to agreements based on this patt of ISO 9459 are encouraged to investigate the possibility of applying the
most recent editions of the Standards indicated below. Members of IEC and ISO maintain registers of currentlyvalid International Standards.
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ISO 9459-2: 1995(E)
ISO 9060:1990, Solar energy - Specification and classification of ins trumen ts for measuring hemispherical solarand direct solar radiation.
ISO 9459-3: -‘1, Solar hea ting - Domestic water heating Systems - Part 3: Performance test for solar plussupplementary Systems.
ISO 9846: 1993, Solar energy - Calibration of a pyranometer using a pyrheliometer.
ISO 9847:1992, Solar energy - Calibration of field pyranometers by comparison to a reference pyranometer.
lSO/TR 9901: 1990, Solar energy - Feld pyranometers - Recommended practice for use.
ISO 11924: -l) , Solar heating - Domestic water heating Systems - Test methods for the assessment of reliabilityand safety.
World Meteorological Organization, Guide to Meteorological Instruments and Methods of Observation, No. 8, 5thWorld Radiometric Reference, known as the WRR.
edition, WMO, Geneva, 1983, Chapter 9 -
each part of ISO 9459 has been conceived as a self-contained document. Therefore,As stated in the Introduction,
definitions given in this clause may also appear in other Part(s) of ISO 9459.
some of the terms with their
For the purposes of this International Standard, the following definitions apply.
3.1 absorber: Device within a solar collector for absorbing radiant energy and transferring this energy as heat intoa fluid.
3.2 accuracy: Ability of an instrument to indicate the true value of the measured phys’ical quantity.
3.3 ambient air: Air in the space (either indoors or outdoors) surrounding a thermal energy storage device, a solarcollector, or any Object being considered.
angle of incidence (of direct solar radiation): Angle between the solar radiation beam and the outward-drawn34 .
normal from the plane considered.
Angle of incidence is often termed “incidence angle” or “incident angle”. The use of these terms is deprecated.NOTE 1
3.5 aperture area: Maximum projected area through which the unconcentrated solar radiation enters a collector.
3.6 aperture plane: Plane at or above the solar collector through which the unconcentrated solar radiation isadmitted.
3.7 auxiliary energy: See auxiliary (heat) Source.
3.8 auxiliary (heat) Source: Source of heat, other than solar, used to Supplement the output provided by thesolar energy System.
3.9 collector: Device containing an absorber.
3.10 collector tilt angle: Angle between the aperture plane of a solar collector and the horizontal plane.
3.11 components: Parts of the solar hot water System including collectors, storage, Pumps, heat exchanger,controls, etc.
1) To be published.
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ISO 9459-2: 1995(E)
3.12 concentrating collector: Solar collector that uses reflectors, lenses or other Optical elements to redirect
and concentrate the solar radiation passing through the aperture onto an absorber, the surface area of which issmaller than the aperture area.
3.13 differential temperature controller: Device that is able to detect a small temperature differente, and to
control Pumps and other electrical devices in accordance with this temperature differente.3.14 domestic: For use in residential and small commercial buildings.
3.15 draw-off rate; water draw-off rate: Rate at which water is withdrawn from a water heating System.3.16 draw-off temperature: Temperature of hot water withdrawn from the System.
3.17 evacuated tube [tubular] collector: Solar collector employing transparent tubing (usually glass) with anevacuated space between the tube wall and the absorber.
The absorber may consist of an inner tube or another shape, with means for removal of the thermal energy. Thepressure in the evacuated space is usually less than 1 Pa.
3.18 flat plate collector: Non-concentrating solar collector in which the absorbing surface is essentially planar.3.19 fluid transport: Transfer of air, water, or other fluid between components.
3.20 gross collector area: Maximum projected area of a complete solar collector, excluding any integral meansof mounting and connecting fluid pipework.
For an array or assembly of flat plate collectors, evacuated tubes or concentrating collectors, the gross area in-cludes the entire area of the array, i.e. also borders and frame.
3.21 heat exchanger: Device specifically designed to transfer heat between two physically separated fluids.Heat exchangers tan have either Single or double Walls.
3.22 heat transfer fluid: Fluid that is used to transfer thermal energy between components in a System.
3.23 irradiance: Power density of radiation incident on a surface, i.e. the quotient of the radiant flux incident on
the surface and the area of that surface, or the rate at which radiant energy is incident on a surface, per unit areaof that surface.
lt is expressed in Watts per Square metre.
NOTE 2 Solar irradiance is often termed “incident solar radiation intensity”, “instantaneous insolation”, “insolation” or “in-cident radiant flux density”; the use of these terms 1s deprecated.
3.24 Irradiation: lncident energy per unit area of a surface, found by integration of irradiance over a specifiedtime interval, often an hour or a day.
lt is expressed in megajoules per Square metre.
NOTE 3 Solar irradiation is often termed “radiant exposure” or “insolation”; the use of these terms is deprecated.3.25 load: Heat supplied to the User, for example in the form of hot water.
NOTE 4 Because of heat losses in the distribution System, the location of the heat delivery must be specified.
3.26 lang-wave radiation: Radiation at wavelengths greater than 3 Pm, typically originating from sources at
terrestrial temperatures (e-g. ground and other terrestrial objects); sometimes called “thermal radiation”.
3.27 precision: Measure of the closeness of agreement among repeated measurements of the same physicalquantity.
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ISO 9459-2: 1995(E) 0 ISO
3.28 pyranometer: Radiometer for measuring the irradiance on a plane receiver surface which results from the
radiant fluxes incident from the hemisphere above, within the wavelength range 0’3 Pm and 3 Pm.surface which results from the
3.29 pyrgeometer: Instrument for determining the irradiance on a plane receiving
Pm to 50 Pm.
radiant fluxes incident from the hemisphere above, within the wavelength range 3
NOTE 5 The given spectral range is similar to that of atmospheric long-wave radiation and is only nominal. Depending on the
material used for the domes which protect the receiving surface of a pyrgeometer, the spectral limits of its responsivity meetmore or less accurately the limits mentioned above.
3.30 pyrheliometer: Radiometer for measuring the irradiance which results from the solar radiant flux incident
from a weil-defined solid angle whose axis is perpendicular to the plane receiver surface.
NOTE 6 Pyrheliometers are used to measure direct solar irradiance at normal incidence. Typical field-of-view angles ofpyrheliometers range from 5” to IO".
radiant energy: Energy in the form of electromagnetic waves.
3.32 radiant flux: Power emitted, transferred or received in the form of radiation.radiation: Transfer of radiant energy in the form of electromagnetic waves.
3.34 radiometer: Instrument for measuring radiant energy.
Its output tan be either irradiance or irradiation.
3.35 solar (thermal) collector: Device designed to absorb solar radiation and to transfer the thermal energy sogained to a fluid passing through it.
NOTE 7 Sometimes called a solar “panel”. This term is deprecated to avoid potential confusion with photovoltaic Panels.
solar energy: Energy emitted by the sun in the form of electromagnetic radiation (primarily in the wave-3.36
length range of 0,3 Pm to 3 Pm) or any energy made available by the reception and conversion of solar radiation.3.37 solar contribution: Heat supplied by the solar part of a System.
solar noon: Local time of day at which the sun crosses the observer’s meridian.
NOTE 8 For the solstices, solar noon occurs when the sun is at its highest altitude for that day.
3.39 solar radiation: Radiation emitted by the sun, practically all of which is incident at the earth’s surface atwave lengths less than 3 Pm.
NOTE 9 lt is often termed “short-wave radiation”. Use of the term “insolation” to mean solar radiation is deprecated.
3.40 solar irradiance Simulator: Artificial Source of radiant energy simulating solar radiation, usually an electriclamp or an array of such lamps.
3.41 solar storage capacity: Quantity of sensible heat that tan be stored per unit volume of store for everydegree of temperature Change.
3.42 solar hot water System: Complete assembly of Subsystems and components necessary to convert solar
energy into thermal energy for the heating of water; may include an auxiliary heat Source.
storage device (thermal): Container(s) plus all contents of the Container(s) used for storing thermal energy.3.43
NOTE 10 The transfer fluid and sories such as heat exchangers, flow switching devices, valves and baffles which aree thermal storage conta iner
firmly fixed to th are considered a part of the storage device.
surrounding air Speed: Air Speed measured in a specified location near a collector or System.3.44
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3.45 tank capacity: Measured volume of the fluid in the tank when full.
3.46 temperature, ambient air: Temperature of the air surrounding the thermal energy storage device or solarcollectors being tested.
NOTE 11 Significant differentes in ambient occur over short distances; therefore, in a paair temperature tan appli-
cation the method of measurement should be specif ied.
3.47 time constant: Time required for a System, whose Performance tan be approximated by a first-Order dif-
ferential equation, to Change output by 63,2 % of its final Change in output, following a step Change in input.
3.48 thermopile: Set of thermocouples connected in series which tan measure small temperature differentesby means of enhancement of the voltage Signal per unit temperature Change.
The Symbols given in ISO 9459-1 and the following Symbols apply.
coefficients used in equation (2) (System Performance)
q , a2, a3
coefficients used in equation (3) (water temperature increase)
b, / b2t b3
specific heat capacity of water, in joules per kilogram kelvin [J/(kg.K)]
normalized draw-off temperature Profile, dimensionless
normalized mixing draw-off temperature Profile, dimensionless
daily solar irradiation (radiance exposure) in the collector aperture, in megajoules per Square metre
daily diffuse solar irradiation in the collector aperture, in megajoules per Square metre
monthly average daily solar irradiation on a horizontal plane, in megajoules per Square metre
monthly average daily solar Irradiation on a tilted plane, in megajoules per Square metreHtilt
useful energy extracted from the System, in megajoules
energy contained in a volume of water Vc, in megajoules
thermal loss from the store, in megajoules
energy remaining in the store, in megajoules
ambient or surrounding air temperature, in degrees Celsius
t ambient air temperature adjacent to the store, in degrees Celsius
water temperature of load drawn off, in degrees Celsius
final water temperature [equation (1)], in degrees Celsius
required hot water temperature, in degrees Celsius
initial water temperature [equation (i)], in degrees Celsius
t cold water supply temperature, in degrees Celsius
average ambient air temperature during the night, in degrees Celsius
average temperature of water in the store, in degrees Celsius
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ISO 9459-2: 1995(E)
surrounding air Speed, in metres per second
storage tank heat loss coefficient, in Watts per kelvin
volume of daily hot water consumption, in litres
volume of water drawn off, in cubic metres
fluid capacity of the store, in litres
At time interval, in seconds
density of water, in kilograms per cubic metre
average (mean) value of Parameter
average (mean) value of Parameter during the period 6 h before solar noon to 6 h after solar noonMay)
maximum value of Parameter
5 System classifications
Solar domestic hot water Systems are classified by seven attributes, each divided into two or three categories.The categories of each attribute are defined as shown in table 1.
5.1 Attribute 1
a) Solar only - System designed to provide solar heated domestic water without use of supplementary energyother than that required for fluid transport and control purposes.
b) Solar preheat - System not incorporating any form of supplementary heating and installed to preheat coldwater Prior to its entry into any other type of household water heater.
c) Solar plus supplementary - System which utilizes both solar and auxiliary energy sources in an integrated
way and is able to provide a specified hot water Service independently of solar energy availability.Table 1 - Classification of solar domestic hot water Systems
a b C
1 Solar only Solar preheat Solar plus supplementary
2 Direct Indirect
3 Open Vented Closed
4 Filled Drainback Draindown
5 Thermosiphon Forced
6 Circulating Series-connected
7 Remote storage Close-coupled collector storage Integral collector storage
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0 ISO ISO 9459-2: 1995(E)
5.2 Attribute 2
a) Direct - System in which the heated water that wi ultimately be consumed Passes through the collector.
b) Indirect (heat exchange) - System in which a heat ransfer fluid other than the heated water ultimately con-sumed Passes through the collector.
5.3 Attribute 3
Open - System in which the heat transfer fluid is in extensive contact with the atmosphere.
NOTE 12 In the USA the term “open System” encompasses both open and vented Systems as herein defined.
b) Vented - System in which contact between the heat transfer fluid and the atmosphere is restricted either
to the free surface of a feed and expansion cistern or to an open vent pipe only.
c) Closed (sealed or unvented) - System in which the heat transfer fluid is completely sealed from the atmos-phere.
5.4 Attribute 4
Filled - System in which the collector remains filled with the heat transfer fluid.
b) Drainback - System in which, as part of the normal working cycle, the heat transfer fluid is drained from thecollector into a storage vessel for subsequent reuse.
System in which the heat transfer fluid tan be drained from the collector and run to waste.c) Draindown -
5.5 Attribute 5
a) Thermosiphon - System which utilizes only density changes of the heat transfer fluid to achieve circulationbetween collector and storage.
b) Forced - System in which heat transfer fluid is forced through the collector either by mechanical means orby externally generated pressure.
5.6 Attribute 6
a) Circulating - System in which heat transfer fluid circulates between the collector and a storage vessel or heatexchanger during operating periods.
Series-connected - System in which the water to be heated Passes directly from a supply Point through thecollector to a storage vessel or to a Point of use.
5.7 Attribute 7
a) Remote storage - System in which the storage vessel is separate from the collector and is located at somedistance from it.
Close-coupled collector storage - System in which storage vessel abuts the collector, and is mounted ona common support frame.
System in which the functions of collection and storage of solar energy are
c) Integral collector storage -
performed within the same device.
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ISO 9459-2: 1995(E)
6.1 System requirements
6.1.1 System type
Before applying the test procedure to a System with an auxiliary heater the following must be considered.Systems with separate auxiliary heating
Only the solar part of the System shall be tested using the test procedure. The solar Performance of Systems
which have an auxiliary heater separated from the solar-heated storage tank will not be influenced by the auxiliary
heater. However, the load size will be influenced by the presence of the auxiliary heater. Therefore, if the System
is to be tested with both the solar preheater and separate auxiliary heater considered as par-t of the same System,the test procedure described in ISO 9459-3 shall be used.
126.96.36.199 Systems with manual auxiliary heater control
Systems which have an auxiliary heater integrated in the solar-heated storage tank, and in which the auxiliary
heater is provided only for irregular intermittent Operation (manually operated switch), shall be tested with theauxiliary heater switched off.
6.1 .1.3 Systems with integrated auxiliary boosting
The test procedure does not apply to Systems which have a continuous or nighttime-use auxiliary heater integrated
in the solar-heated storage tank. Such Systems should be assessed using the test procedure defined in ISO 9459-3or other suitable International Standard.
6.1.2 Test System installation
Tests shall be performed with the System components installed in accordance with the manufacturer’s installation
instructions. Any controller included in the System shall be set in accordance with the manufacturer’s instructions.
In the absence of specific instructions from the manufacturer, the System shall be installed as follows.
The System shall be mounted in a manner such as to ensure safety to personnel. Due consideration shall be paid
to the likelihood of glass failure and the leakage of hot liquids. Mountings shall be able to withstand the effectsof wind gusts.
Whenever possible the System shall be mounted on the mounting structure provided by the manufacturer. If no
mounting is provided then, unless otherwise specified (for example when the System is part of an integrated roof
array), an open mounting System shall be used. The System mounting shall in no way obstruct the aperture of the
collectors and the mounting structure shall not significantly affect the back or side insulation of the collectors orstorage vessel.
Except for Systems where the storage vessel is fixed to the collectors in some way (for example integral
collector-storage Systems and close-coupled thermosiphon Systems), the store shall be installed in the lowestPosition allowed in the manufacturer’s installation instructions.
For Systems where the hot water store is separate from