Solar heating — Domestic water heating systems — Part 3: Performance test for solar plus supplementary systems

Gives test procedures for characterizing the performance of solar domestic water heating systems and for predicting annual performance under climatic conditions. Applies to solar domestic water heating systems designed to heat potable water. It is not applicable to concentrating systems.

Chauffage solaire — Systèmes de chauffage de l'eau sanitaire — Partie 3: Essai de performance pour systèmes solaires comportant des systèmes d'appoint

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ISO 9459-3:1997 - Solar heating -- Domestic water heating systems
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Standards Content (Sample)

First edition
1997-01-I 5
Solar heating - Domestic water heating
systems -
Part 3:
Performance test for solar plus supplementary
Chauffage solaire -
Syst&mes de chauffage de I’eau sanitai-e -
Partie 3: Essai de performance pour systemes solaires comportan t des
sys tkmes d ‘appoin t
Reference number
IS0 9459-37 997(E)
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IS0 9459-3:1997(E)
........................... 1
Scope ........................................................
.......................................................... 1
Normative references

Definitions ............................................................................

Symbols ................................................................................

System classifications ..........................................................

Requirements ....................................................................... 4

Test procedure ..................................................................... 8

.................................... 11
Analysis and presentation of results
Format sheets for description of solar domestic water
heating system and test results
Format sheets for annual performance prediction
Conventional water heater energy consumption
Computer program for annual performance prediction
0 IS0 1997

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 permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
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IS0 9459=3:1997(E)
@ IS0
IS0 (the International Organization for Standardization) is a worldwide fed-
eration of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
technical committees. Each 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 part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are cir-
culated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 9459-3 was prepared by Technical Committee
lSO/TC 180, Solar energy, Subcommittee SC 4, Systems - Thermal
performance, reliability and durability.
IS0 9459 consists of the following parts, under the general title Solar
Domes tic water heating:
heating -
Part 7: Performance rating procedure using indoor test methods
- Part 2: Outdoor test methods for system performance
characterization and yearly performance prediction of solar-only
- Part 3: Performance test for solar plus supplementary systems
Part 4: System
- performance characterization by means of
component tes ‘ts and computer simulation
- Part 5: System performance characterization by means of whole-
system tests and computer simulation
Annexes A and B form an integral part of this part of IS0 9459. Annexes C
to E are for information only.
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IS0 9459=3:1997(E) 0 IS0
International Standard IS0 9459 has been developed to help facilitate the
international comparison of solar domestic water heating systems.
Because a generalized performance model which is applicable to all
systems has not yet been developed, it has not been possible to obtain an
international consensus for one test method and one standard set of test
conditions. It 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 can proceed on its own.
IS0 9459 is divi ded into five parts within three broad categories, as
described below.
Rating test
IS0 9459-l involves testing for periods of one day for a standardized set of
reference conditions. The results, therefore, allow systems to be
compared under identical solar, ambient and load conditions.
Black box correlation procedure
IS0 9459-Z is applicable to solar-only systems and solar-preheat systems.
The performance 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.
IS0 9459-3 applies to solar plus supplementary systems. The performance
test is a “black box” system test procedure which produces coefficients in
a correlation equation that can 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
IS0 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
IS0 9459. Procedures for characterizing the performance of collectors are
given in IS0 9806-1, IS0 9806-2 and IS0 9806-3.
IS0 9459-5 presents a procedure for dynamic testing of complete systems
to determine system parameters for use in a computer model. This model
may be used with hourly values of local solar irradiation, ambient air
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@ IS0 IS0 9459=3:1997(E)
temperature and cold water temperature data to predict annual system
The procedures defined in IS0 9459-2, IS0 9459-3, IS0 9459-4 and
IS0 9459-5 for predicting yearly performance allow the output of a system
to be determined for a range of climatic conditions.
The results of tests performed in acco rdance with IS0 9459-l provide a
ratin g for a standard
The results of tests performed in accordance with IS0 9459-2 permit
performance predictions for a range of system loads and operating
conditions, but only for an evening draw-off.
The results of tests performed in accordance with IS0 9459-4 or 9459-5
are directly comparable. These procedures permit performance predictions
for a range of system loads and operating conditions.
System reliability and safety will be dealt with in IS0 11924.
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IS0 9459=3:1997(E)
- Domestic water heating systems -
Solar heating
Part 3:
Performance test for solar plus supplementary systems
1 Scope

This part of IS0 9459 establishes test procedures for characterizing the performance of solar domestic water heating

systems with in-tank auxiliary boosting, and for predicting annual performance in any given climatic conditions. A “black

box” approach is adopted which involves no assumptions about the type of system under test, and 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 IS0 9459 applies to solar domestic water heating systems designed to heat potable water to be supplied

solely for domestic water usage and is not intended to be applied to other systems. It is not generally applicable to

concentrating systems.

The solar-plus-auxiliary test procedures in clause 7 are carried out in typical operational conditions, the only restriction on

the nature of systems that can be tested is that there shall be no long-term energy storage, and the storage capacity in

the solar preheat section of the tank shall be less than twice the specified daily total load (7.2.4).

The test procedures in this part of IS0 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 will

not be determined.

This part of IS0 9459 is limited to systems in which the solar collector and the storage tank are exposed to the same

ambient conditions, and to systems in which the auxiliary energy (thermal or electric) can be monitored separately from

the solar energy input.

It is not intended to be used for testing the individual components of the system, nor is it intended to abridge any safety

or health requirements.
2 Normative references

The following standards contain provisions which, through reference in this text, constitute provisions of this part

of IS0 9459. At the time of publication, the editions indicated were valid. All standards are subject to revision, and

parties to agreements based on this part of IS0 9459 are encouraged to investigate the possibility of applying the

most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently

valid International Standards.

IS0 9459-l :I 993, Solar heating - Domestic water heating systems - Part 1: Performance rating procedure using

indoor test methods.

IS0 9059: 1996, Solar energy - Calibration of field pyrheliometers by comparison to a reference pyrheliometer.

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0 IS0
IS0 9459=3:1997(E)

Specification and ciassifica tion of instruments for measuring hemispherical solar

IS0 9060:1990, Solar energy -
and direct solar radiation.
IS0 9846: 1993, Solar energy - Calibration of pyranometer using pyrheliometer.

IS0 9806-I :I 994, Test methods for solar collectors - Part 7: Thermal performance of glazed liquid heating

collectors including pressure drop.

IS0 9845-l : 1992, Solar energy - Reference solar spectral irradiance at the ground at different receiving conditions

- Part 7: Direct normal and hemispherical solar irradiance for air mass ?,5.
IS0 9488:- 1), Solar energy - Vocabulary.

Guide to Meteorological instruments and Methods of Observation*), 5th edition, WMO-8, World Meteorological

Organization, Geneva, 1983, Chapter 9.
3 Definitions

For the purposes of this part of IS0 9459, the definitions given in IS0 9488 apply.

4 Symbols
The symbols given in IS0 9459-l and the following symbols apply.
coefficients used in performance characteristic equations
al, ql a3

fraction of hot water load supplied by solar energy = (QL - QAUX)/QL, dimensionless

fractional energy savings relative to a conventional water heater
= (QAUX NS - QAUX,S)/QAUX,NS, dimensbnless

H daily solar irradiation on the collector aperture plane, in megajoules per square metre

auxiliary energy used by solar water heater, in megajoules per day

auxiliary energy used by conventional water heater = load + QLOS, in megajoules per day

gas burner capacity (primary energy input), in watts
fossil fuel primary energy consumption, in megajoules per day

useful energy extracted from the system under load cycle operation, in megajoules per day

heat loss and pilot maintenance rate for a gas storage water heater, in watts
ambient or surrounding air temperature, in degrees Celsius
cold water supply temperature, in degrees Celsius
mean water temperature of load drawn off, in degrees Celsius
effective heat sink temperature = ta + (ta - tmain)M, in degrees Celsius
U surrounding air speed, in metres per second

product of heat loss coefficient x area for a conventional water heater tank, in watts per kelvin

1) To be published.

2) The World Radiometric Reference Scale, known as the WRR Scale, is related to the International Pyrheliometric Scale 1956

(IPS 1956) by the identity WRR = 1.022 (IPS 1956).
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IS0 9459=3:1997(E)
@ IS0
volume of daily hot water consumption, in litres
density of water, in kilograms per cubic metre
efficiency of fossil fuel auxiliary source
NS no solar energy input
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.
Table 1 - Classification of solar domestic hot water systems
a b C
Solar only Solar preheat Solar plus supplementary
Direct Indirect
Vented Closed
Drainback Draindown
Thermosiphon Forced
Circulating Series-connected
Integral collector storage
Remote storage Close-coupled collector storage
. Attribute 1

system designed to provide solar heated domestic water without use of supplementary energy

a) Solar only -
other than that required for fluid transport and control purposes.

b) Solar preheat - system not incorporating any form of supplementary heating and installed to preheat cold

water 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.

5.2 Attribute 2

a) Direct - system in which the heated water that will ultimately be consumed passes through the collector.

b) Indirect (heat exchange) - system in which a heat transfer fluid other than the heated water ultimately

consumed passes through the collector.
5.3 Attribute 3

a) Open - system in which the heat transfer fluid is in extensive contact with the atmosphere.

In the USA the term “open system” encompasses both open and vented systems as herein defined.


system in which contact between the heat transfer fluid and the atmosphere is restricted either to

b) Vented -
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

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@ IS0
IS0 9459=3:1997(E)
5.4 Attribute 4

a) Filled - system in which the collector remains filled with the heat transfer fluid.

system in which, as part of the normal working cycle, the heat transfer fluid is drained from the

b) Drainback -
collector into a storage vessel for subsequent reuse.

system in which the heat transfer fluid can be drained from the collector and run to waste.

c) Draindown -
5.5 Attribute 5
heat transfer fluid to achieve circulation
a) Thermosiphon - system which utilizes only density changes of the
between collector and storage.

system in which heat transfer fluid is forced through the co lector either by mechanical means or by

b) Forced -
externally generated pressure.
5.6 Attribute 6

a) Circulating - system in which heat transfer fluid circulates between the collector and a storage vessel or

heat exchanger during operating periods.

b) Series-connected - system in which the water to be heated passes directly from a supply point through the

collector to a storage vessel or to a point of use.
5.7 Attribute 7

system in which the storage vessel is separate from the collector and is located at some

a) Remote storage -
distance from it.

b) Close-coupled collector storage - system in which storage vessel abuts the collector, and is mounted on a

common support frame.

c) Integral collector storage - system in which the functions of collection and storage of solar energy are

performed within the same device.
6 Requirements
6.1 System requirements
6.1 .I System type

Before applying the test procedure to a system with an auxiliary heater the following must be considered.

6.1.1 .I Systems with separate auxiliary heating

The solar performance of systems which have the auxiliary heater separated from the solar-heated storage tank

will not be influenced by the auxiliary heater. However the maximum load size will be influenced by the presence of

the auxiliary heater. Therefore these types of systems shall be tested with both the solar preheater and separate

auxiliary heater considered as part of the same system. Systems with manual auxiliary heater control

Systems which have the 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 not be tested using the

procedure given in this part of IS0 9459. In order to achieve reproducible test results, such systems should be

tested with the auxiliary heater switched off using the test procedure given in IS0 9459-Z.

6.1 .I .3 Systems with integrated auxiliary boosting
ich ha

Systems wh ve a continuous or nighttime- use auxiliary heater integrated in the solar-heated storage tank shall

beassessed using the test procedure specified in this part of IS0 9459.
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0 IS0
IS0 9459-3:1997(E)
6.1.2 Test system installation

Tests shall be performed with the system components installed in accordance with 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 effects of

wind gusts.

Whenever possible the system shall be mounted on a 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 or storage


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 lowest position

allowed in the manufacturer’s installation instructions, or with the bottom of the store located 5 m below the

bottom of the collector if no specification is supplied by the manufacturer.

For systems where the hot water store is separate from the collectors, the total length of the connecting pipes

between the collector and store shall be 15 m (i.e. 2 x 7,5 m). The diameter and insulation of the pipes shall be in

accordance with the manufacturer’s installation instructions.
6.1.3 Collector installation

Systems shall be tested at tilt angles recommended by manufacturers or specified for actual installations, provided

that the angle used is specified with the test results. The specified tilt angle shall remain constant throughout the

test. The collector shall be mounted in a fixed position facing the equator to within + IO”.

be mounted in a fixed position facing the equator to within * IO”.
The collector shal
a shadow will not be cast onto the collector
The collector sha I be located such that at any time during the test

l be located where there will be no significant solar radiation reflected onto it from surrounding

The collector sha
I *I 1. r

burrarngs or surtaces during the tests, and where there will be no significant obstructions in the field of view.

The tern perature of surfaces adjacent to the syste m shall be as cl ose as possible to that of the ambient air. For

example , the field of view of the system s hall not in elude chim cooling towers or hot exha usts.

6.1.4 Liquid flow system

A test loop of the type shown in figure 1 shall be used. The piping used in the loop shall be suitable for operation at

temperatures up to 95 OC. Pipe lengths should be kept short. In particular, the piping between the outlet of the cold

water temperature regulator and the inlet to the storage vessel shall be minimized, to reduce the effects of the

environment on the inlet temperature of the water. This section of pipe shall be insulated to ensure a rate of heat

loss of less than 0,2 W/K and be protected by a reflective weatherproof coating.

Pipework between the temperature-sensing points and the store (inlet and outlet) shall be protected with insulation

and reflective weatherproof covers extending beyond the positions of the temperature sensors, such that the

calculated temperature gain or loss along either pipe does not exceed 0,Ol K under test conditions. Flow mixing

devices such as pipe bends are required immediately upstream of temperature sensors.

The flow control device and flow meter shall be installed on the cold water inlet pipe, so that readings are not

affected by temperature changes. The flowrate during the draw-off of hot water from the store is important, as it

may influence the draw-off temperature profile. The flow controller shall maintain a constant flowrate through the

storage vessel of (600 + 50) I/h.
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@ IS0
Shaded ambient air
temperature sensor
(adjacent to collector)
pyranometer f
(if necessary)

Figure 1 - Schematic representation of experimental apparatus for system performance test

When testing systems with pumped circulation, a flow meter shall be installed to measure the fluid flowrate in the

collector loop to an accuracy of Itr 5 %.

NOTE - This measurement is excluded from the requirements of 62.3 which require flow measurements to have an

accuracy of + 1 %.

The heat transfer fluid used in the system during testing shall be the fluid recommended by the manufacturer.

When testing forced-circulation systems, the fluid flowrate recommended by the manufacturer shall be used. If the

solar collector loop is designed to be used with non-freezing fluids, the test procedures in this standard shall be

carried out with these fluids, according to the manufacturer’s requirements.
6.2 Measurement requirements
6.2.1 Solar radiation

Solar radiation measurement shall be carried out in accordance with IS0 9060 and WMO No. 8.

A pyranometer shall be used to measure the solar radiation on the collector aperture plane. The pyranometer shall

be a first class (or better) pyranometer as specified in IS0 9060. The recommended practice described in

lSO/TR 9901 should be observed.

The pyranometer shall be calibrated using a standard pyrheliometer in accordance with IS0 9846 and IS0 9059.

Any change in the responsivity of more than + 1% over a year period shall warrant the use of more frequent

calibration or replacement of the instrument if the instability is permanent. If an instrument is damaged in any

significant manner, it shall be recalibrated to check the stability of the calibration factor and the time constant. In

case of replacement of one of the domes, the cosine response should also be checked.

6.2.2 Temperature Accuracy, precision and response time

The accuracy and precision of the instruments including their associated readout devices shall be within the limits

given in table 2. The response time shall be less than 5 s.
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IS0 9459=3:1997(E)
- Accuracy and precision of instruments for temperature measurement
Table 2
Parameter 1 Instrument accuracy 1 Instrument precision 1
Temperature difference across hot water
fO,l K +O,l K
system (cold water in to hot water out)
Temperature difference across auxiliary
fO,l K kO,l K
thermal energy source
I I Ambient temperature

The ambient air temperature shall be measured using a shaded aspirated sampling device approximately 1 m above

the ground, not closer than I,5 m to the tank and system components and not further away than IO m from the

system. Input water temperature

The tests are carried out in typical domestic operational conditions hence there is no need to control the cold water

supply temperature. The data correlation function accounts for the effect of cold water temperature. However, to

avoid measurement errors due to abrupt changes in cold water temperature during a draw-off, the cold water

should be drawn from a mixed reservoir of volume greater than the load volume. The temperature of the cold

water reservoir should be typical of the location for which the tests are being performed.

6.2.3 Liquid flow

The accuracy of the liquid flowrate measurement shall be equal to or better than IfI 0,l % of the measured value, in

mass units per unit time.
6.2.4 Electrical energy

The electrical energy used shall be measured with an instrument and associated readout devices that are accurate

to within + 1 % of the reading or to 15 W-h, whichever is greater.
6.2.5 Fossil fuels

The quantity of fuel used for auxiliary energy by the solar hot water system shall be measured with an instrument

and associated readout device that is accurate within + 1 % of the reading. Where the energy is provided from gas,

the accuracy of the calorific value of the gas fuel supplied shall be given.

If the auxiliary input to the solar tank is from a fossil fuel thermal source, the energy delivered into the solar tank

shall be measured using temperature and flow transducers in accordance with 6.2.2 and 6.2.3.

6.2.6 Mass
Mass measurement shall be made with an accuracy of + 1 %.
6.2.7 Elapsed time
Elapsed time measurements shall be made with an accuracy of & 0,20 %.
6.2.8 Surrounding air speed

The surrounding air speed shall be measured with an instrument and associated readout device that can determine

the integrated average surrounding air speed for each test period to an accuracy of + 0,5 m/s.

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IS0 9459=3:1997(E)
7 Test procedure
7.1 Principle

The procedure defined in this part of IS0 9459 accounts for mixing between the auxiliary-heated and solar-heated

parts of the tank. The test is performed while the system is operating under a typical domestic load cycle. The load

cycle consists of a fixed-energy draw-off pattern over each day for a range of daily loads. As the solar contribution

is influenced by auxiliary heating, the tests are performed for a range of solar conditions ranging from a no-solar

test (auxiliary only) to solar tests that give high solar contribution.

Each test consists of a series of measurements over a period of five to 15 days, selected so that the irradiation

conditions are similar on the day before and the last day of the test period. The averaging process is necessary in

order to minimize variability of the data due to changes in storage tank internal energy.

Due to the need to establish test data for a range of operating conditions under quasi-steady state conditions, the

test period may be as long as 8 to 12 weeks. Monitoring of solar irradiation conditions shall be carried out for a

minimum of 21 stable test periods, as detailed in 7.4.2.

. The procedure requires long-term monitoring of daily performance for a period that is a function of the weather

conditions at the test size. Testing shall be continued until the specfied number of stable test periods have been

7.2 Test conditions
7.2.1 Surrounding air speed

The performance of some collectors is sensitive to air speeds over the collector in the range < 3 m/s. In order to

maximize the reproducibility of results, collectors that are sensitive to surrounding air speed shall be mounted such

that air with a mean speed of between 3 m/s and 5 m/s will freely pass over the aperture, back and sides of the

collector. Artificial wind generators shall be used as necessary to achieve these wind speeds. The average speed of

the air flowing over the collector shall lie between 3 m/s and 5 m/s when measured in the plane of the collector at a

distance of 50 mm from the surface of the cover, and at no point over the collector aperture shall the speed deviate

from the mean by more than + 25 %. The speed at any point over the collector aperture shall remain steady and

the temperature of the air leaving the wind generator shall lie within * 1 OC of the ambient air temperature.

allowed to pass ov ‘er the

Warm currents of air, such as those which rise up the walls of a buildi ng, shall n ot be

shall be located at least 2 m away from the edge of the roof
system. Systems tested on the roof of a building

Collectors designed for integration into a roof may have their backs protected from the wind, although this shall be

reported with the test results.
7.2.2 Auxiliary heater operation

The auxiliary heater may be operated on a continuously available basis or restricted by a time clock to simulate any

required tariff supply system. Thermostat settings shall be as recommended by the manufacturer. The thermostat

and time clock operation shall not be altered during the tests.
7.2.3 Draw-off schedule
The draw-off of hot water energy during the tests shall be specified in table 3.
NOTE - The draw-off schedule in table 3 is

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