ISO 9459-1:1993

INTERNATIONAL
IS0
STANDARD 9459-1
First edition
1993-I l-01
Solar heating - Domestic water heating
systems -
Part 1:
Performance rating procedure using indoor
test methods
Chauffage solaire - Systkmes de chauffage de I’eau sanitaire -
Partie 7: Mkthodes d’essai 4 I’intbrieur pour Evaluation des performances
Reference number
IS0 9459-l :1993(E)

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IS0 9459=1:1993(E)
Contents
Page
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*. I
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .* 1
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4 Symbols and units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
5 System classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
5.1 Attribute 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*. 6
5.2 Attribute 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .*. 6
5.3 Attribute 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.4 Attribute 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*. 6
5.5 Attribute 5 . . . . . . . . . . . . .*. 6
5.6 Attribute 6 . . . . . . . . . . . . . . . . . . . . . . .*.*. 6
5.7 Attribute 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6 Requirements for indoor testing of solar domestic hot water
systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1 System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.2 Measurement requirements . 8
6.3 Test method requirements . 9
7 Indoor test procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2
7.1 Solar-only and solar-preheat systems 12
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2 Solar-plus-supplementary systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I3
7.3 Hot water - Continuous draw test - Solar energy only . . . 14
8 Recording and reporting of data I4
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annexes
A Test day specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
0 IS0 1993
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 W-1 211 Geneve 20 l Switzerland
Printed in Switzerland
ii

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0 IS0 IS0 9459-l :1993(E)
B Collector loop heater - Equations to be used in controlling thermal
20
output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
C Calculation of spectrum-weighted values of optical properties
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
D Calculation of equivalent irradiance
27
E Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.

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0 IS0
IS0 9459=1:1993(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation 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
(I 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
a vote.
International Standard IS0 9459-l 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
- Domestic water heating systems:
heating
- Part I: Performance rating using indoor test methods
- Part 2: Performance test for solar only systems
- Part 3: Performance test for solar plus supplementary systems
- Part 4: System performance characterkation by means of compo-
nent tests and computer simulation
- Part 5: System performance characterization by means of whole
system tests and computer simulation
Annexes A, B, C and D form an integral part of this part of IS0 9459. An-
nex E is for information only.

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0 IS0
IS0 9459=1:1993(E)
Introduction
International Standard IS0 9459 has been developed to help facilitate the
international comparison of solar domestic water heating systems. Be-
cause a generalized performance 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. 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 divided into five parts within three broad categories, as de-
scribed below.
Rating test
IS0 9459-1, Performance rating using indoor test methods, involves test-
ing for periods of one day for a standardized set of reference conditions.
The results, therefore, allow systems to be compared under identical so-
lar, ambient and load conditions.
Black box correlation procedures
IS0 9459-2 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” procedure which produces coefficients in a corre-
lation 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 tem-
perature and cold water temperature data to predict annual system per-
formance.

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0 IS0
IS0 9459=1:1993(E)
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 accordance with IS0 9459-l provide a
ratin g for a sta ndard .
day
The results of tests performed in accordance with IS0 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 IS0 9459-4 or IS0
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 a future standard.

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IS0 9459=1:1993(E)
INTERNATIONAL STANDARD 0 IS0
Solar heating - Domestic water heating systems -
Part I:
Performance rating procedure using indoor test methods
It is not intended to be used for testing the individual
1 Scope
components of the system, nor is it intended to
abridge any safety or health requirements.
This part of IS0 9459 establishes a uniform indoor
test method for rating solar domestic water heating
systems for thermal performance, under benchmark
2 Normative references
conditions.
The following standards contain provisions which,
It applies only to solar water heating systems de-
through reference in this text, constitute provisions
signed solely to heat potable water to be supplied for
of this part of IS0 9459. At the time of publication, the
domestic water usage.
editions indicated were valid. All standards are subject
to revision, and parties to agreements based on this
The test procedures described in this part of IS0 9459
part of IS0 9459 are encouraged to investigate the
are applicable to systems of solar storage capacity of
possibility of applying the most recent editions of the
0,6 m3 or less. It includes procedures for testing solar
standards indicated below. Members of IEC and IS0
domestic hot water systems either with solar
maintain registers of currently valid International
irradiance simulators or thermal simulation (non-
Standards.
irradiated) methods.
IS0 9059:1990, Solar energy - Calibration of field
The test procedures in this part of IS0 9459 which
by comparison to a reference
pyrheliome ters
employ a non-irradiated solar collector array in series
pyrheliome ter.
with a conventional heat source do not apply to inte-
gral collector storage systems, nor to systems in
IS0 9060: 1990, Solar energy - Specification and
which thermosiphon flow occurs, nor to any system
classifica tion 0 f instruments for measuring
employing a collector/heat transfer fluid combination hemispherical solar and direct solar radiation.
which cannot be tested in accordance with the col-
lector test. IS0 9806-I :- l) , Test methods for solar collectors -
Part 1: Thermal performance of glazed liquid heating
The test procedures in this part of IS0 9459 do not collectors including pressure drop.
require the solar water heating system to be sub-
IS0 9845-l : 1992, Solar energy - Reference solar
jected to freezing conditions. Consequently, the en-
spectral irradiance at the ground at different receiving
ergy consumed or lost by a system while operating in
- Part 1: Direct normal and hemispherical
the freeze-protection mode is not determined. conditions
solar irradiance for air mass 1,5.
This part of IS0 9459 is not generally applicable to
IS0 9846:-J, Solar energy - Calibration of a
concentrating or evacuated tube systems, unless the
pyranometer using a reference pyrheliometer.
collimation requirements of 6.3.1.3 are met.
1) To be published.

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0 IS0
IS0 9459=1:1993(E)
World Meteorological Organization, Guide to the thermal energy so gained to a fluid passing
Meteorological lnstrumen ts and Methods of Obser- through it.
vation, No. 8, 5th edition, WMO, Geneva, 1983,
Chapter 9 - World radiometric reference, known as
3.11 collector, concentrating: Solar collector that
the WRR.
uses reflectors, lenses or other optical elements to
redirect and concentrate the solar radiation passing
through the aperture onto an absorber of which the
3 Definitions
surface area may be smaller than the aperture area.
For the purposes of this part of IS0 9459, the follow-
3.12 collector,, flat-plate: Non-concentrating solar
ing definitions apply.
collector in which the absorbing surface is essentially
planar.
3.1 absorber: That part of a collector that receives
radiant energy and transforms it into thermal energy.
3.13 collector loop: Continuous path followed by
3.2 accuracy: Ability of an instrument to indicate the
the primary heat transfer fluid in a solar energy sys-
true value of the measured physical quantity.
tem.
3.3 ambient air: Air in the space (either indoors or
3.14 collector loop heater: Heater installed within
outdoors) surrounding the thermal energy storage
the collector loop when testing the solar domestic
device or solar collectors, whichever is applicable.
water heating system with a non-irradiated array.
3.4 angle of incidence (of direct solar radiation):
3.45 collector tilt angle: Lower angle between the
Angle between the solar radiation beam and the
aperture plane of a solar collector and the horizontal
outward-drawn normal from the plane considered.
plane.
3.5 aperture area: Of a solar thermal collector,
3.16 control: Device for regulation of the solar
maximum projected area through which the uncon-
thermal system or component in normal operation;
centrated solar radiation is admitted.
can be manual or automatic.
NOTE 1 For concentrating collectors, the gross aperture
area includes any area of the reflector or refractor shaded
3.17 direct irradiance: lrradiance produced by direct
by the receiver and its supports and including gaps between
radiation on a given plane.
reflector segments within a collector module. Net aperture
area, sometimes called effective aperture area, excludes
3.18 direct solar radiation: Radiation received from
any shaded area or gaps between reflector segments.
a small solid angle centred on the sun’s disc, on a
given plane.
3.6 aperture plane: Plane at or above the solar col-
lector through which the unconcentrated solar radi-
NOTE 2 In general direct solar radiation is measured by
ation is admitted.
instruments with field-of-view angles of up to 15”. Therefore
a part of the scattered radiation around the sun’s disc
3.7 area, gross collector: Maximum projected area
(circumsolar radiation) is included. More than 99 % of the
of a completed solar collector module, exclusive of
direct solar radiation on the earth’s surface is contained
integral means of mounting and connecting fluid
within the wavelength range from 0,3 pm to 3,0 pm.
conduits. For an array of collectors, including devices
such as evacuated tube or concentrating collectors,
3.19 domestic: For use in residential and small
gross area includes the entire area of the array.
commercial buildings.
. auxiliary energy: Energy
38 provided by an auxili-
3.20 draw rate; water draw rate: Rate at which hot
ary thermal (heat) source.
water is withdrawn from a system at a specified time.
3.9 auxiliary thermal (heat) source: Source of
3.21 equivalent length: Length of a straight section
thermal energy, other than solar, used to supplement
of pipe or duct causing the same pressure drop as
the output provided by the solar energy system; usu-
that which actually occurs within the system at the
ally in the form of electrical resistance heat or thermal
same flowrate.
energy derived from combustion of fossil fuels.
3.10 collector, solar; solar thermal collector: De- 3.22 fluid transport: Transfer of air, water or other
vice designed to absorb radiant energy and to transfer fluid between components of the system.
2

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IS0 9459=1:1993(E)
3.23 heat exchanger: Device specifically designed fluxes incident from a well-defined solid angle whose
to transfer heat between two physically separated axis is perpendicular to the plane receiver surface.
fluids. Heat exchangers may have either single or
NOTE 6 According to this definition pyrheliometers are
double walls.
applied to the measurement of direct solar irradiance at
normal incidence. The field-of-view angle of pyrheliometers
3.24 heat transfer fluid: Fluid that is used to trans-
ranges typically from 5” to IO”.
fer thermal energy between components in a system.
3.33 solar energy: Energy emitted by the sun in the
3.25 irradiance: Power density of radiation incident
form of electromagnetic radiation (primarily in the
on a surface, i.e. the radiant flux incident on a surface
wavelength range 0,3 pm to 3 pm), or any energy
divided by the area of that surface, or the rate at
made available by the reception and conversion of
which radiant energy is incident on a surface per unit
solar radiation.
area of that surface.
3.34 solar contribution: Ratio of the energy sup-
NOTE 3
Solar irradiance is often termed “incident solar
plied by the solar part of a system to the total load of
radiation intensity”, “instantaneous insolation”, or “incident
the system.
radiant flux density”; the use of these terms is deprecated.
3.35 solar noon: Local time of day, for any given
3.26 load: Daily system hot water load defined as
location, when the sun is at its highest altitude for that
the product of the mass, specific heat and tempera-
day, i.e. the time when the sun crosses the ob-
ture increase of the water as it passes through the
server’s meridian.
solar hot water system.
3.36 solar radiation: Radiation emitted by the sun,
3.27 potable: Suitable for human consumption;
practically all of which is incident at the earth’s sur-
drinkable.
face at wavelengths less than 3 Fm; often termed
“short-wave radiation “.
3.28 precision: Measure of the closeness of agree-
ment among repeated measurements of the same
3.37 solar irradiance simulator: Artificial source of
physical quantity.
radiant energy simulating solar radiation (usually an
electric lamp or an array of such lamps).
3.29 preheating: See solar preheat system [5.1 b)].
3.38 solar storage capacity: Quantity of sensible
3.30 pyranometer: Radiometer for measuring the
heat that can be stored per unit volume of store for
irradiance on a plane receiver surface which results
every degree of temperature change.
from the radiant fluxes incident from the hemisphere
above within the wavelength range 0,3 pm to 3 pm.
3.39 solar hot water system: Complete assembly
of subsystems and components necessary to convert
NOTE 4 The spectral range given represents roughly the
solar energy into thermal energy for the heating of
spectral range of solar radiation (also called solar or short-
water; may include an auxiliary heat source.
wave range) at the ground and is only nominal. Depending
on the material used for the domes which protect the re-
3.40 standard air: Air weighing 1,204 kg/m3 which
ceiver surface of a pyranometer, the spectral limits of its
responsivity approximate to the limits mentioned above.
approximates dry air at a temperature of 20 “C and a
barometric. pressure of 101,325 kPa.
3.31 pyrgeometer: Instrument for determining the
3.41 standard barometric pressure: Barometric
irradiance on a plane receiving surface which results
pressure of 101,325 kPa at 0 “C.
from the radiant fluxes incident from the hemisphere
above within the approximate wavelength range
3.42 storage device (thermal): Container(s) plus all
4 pm to 50 pm.
contents of the container(s) used for storing thermal
NOTE 5
The given spectral range is nearly identical with energy.
that of so-called terrestrial radiation or long-wave radiation,
and is only nominal. Depending on the material used for the
NOTE 7 The transfer fluid and accessories such as heat
domes which protect the receiving surface of a
exchangers, flow switching devices, valves and baffles
pyrgeometer, the spectral limits of its responsivity approxi-
which are firmly fixed to the thermal storage container(s) are
mate to the limits mentioned above.
considered a part of the storage device.
3.32 pyrheliometer: Radiometer for measuring di- 3.43 storage tank volumetric capacity: Measured
(solar) irradiance which results from the radiant
rect volume of the fluid in the tank when full.

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0 IS0
IS0 9459=1:1993(E)
3.44 temperature, ambient air: Temperature of the total (global) irradiance incident upon the
Gt
air surrounding the thermal energy storage device or aperture plane of the collector, in
solar collectors being tested.
kilojoules per square metre hour
wJ/(m*ql;
3.45 time constant: Time required for a first-order
system to change output by 63,2 % of its final change
incident angle modifier, dimen sionles
s;
Kclz
in output following a step change in input.
M number of rows of collector modules in
3.46 thermopile: Set of thermocouples wired con-
parallel in the collector array,
sistently in series or parallel to measure small or av-
dimensionless;
erage temperature differences.
.
mass flowrate of the transfer fluid
mc
4 Symbols and units
through the collector during the collector
tests, in kilograms per second;
collector module aperture area, in
square metres;
mass of the jth withdrawal of water, in
mj
kilograms;
A,FR b) e n
intercept of the collector efficiency
A, ’
curve determined in accordance with mass flowrate of the transfer fluid
collector tests, dimensionless; through the collector array during the
solar hot water system test, in kilograms
per second;
A,FRuL
slope of the collector efficiency curve
A,
determined in accordance with collector
N number of collector modules in series in
tests, in kilojoules per hour square me-
each parallel row in the collector array,
tre degree Celsius [kJ/ (h~m*~“C)];
dimensionless;
gross collector area, in square metres;
A,
daily consumed for auxiliary
energy
QAUX
specific heat of the transfer fluid used in
cP,c
heating in the solar hot water system, in
the collector during the collector tests,
kilojoules;
in kilojoules per kilogram degree Celsius
[kJ/(b"C)l;
daily system hot water load defined as
QL,NS
the product of the mass, specific heat,
specific heat of the transfer fluid used in
cPs
and temperature increase of the water
the collector during the solar hot water
as it passes through the solar hot water
system test, in kilojoules per kilogram
system for the case of no solar energy
degree Celsius [kJ/(kg-OC)];
input, in kilojoules;
specific heat of water, in kilojoules per
cP,w
kilogram degree Celsius [kJ/(kg-“C)];
thermal losses from solar system during
QLOS
the test day, in kilojoules;
D nozzle throat diameter, in metres;
daily system hot water load defined as
F collector absorber plate efficiency factor,
QL,S
the product of the mass, specific heat,
dimensionless;
and temperature increase of the water
collector heat removal factor,
as it passes through the solar hot water
dimensionless;
system for the case of solar energy in-
put, in kilojoules;
beam irradiance from solar irradiance
GbP
measured in a plane parallel to the col-
rate of energy output from the collector
ci,,
lector aperture, in kilojoules per square
loop heater in series with the non-
metre hour [kJ/(m*=h)];
irradiated solar collector array (if used),
in kilojoules per hour;
diffuse irradiance from solar irradiance
Gd
measured in a plane parallel to the col-
lector aperture, in kilojoules per square
daily energy consumed for parasitic
QPAR
metre hour [kJ/(m*gh)];
power by pumps, controls, solenoid

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IS0 9459=1:1993(E)
valves, etc. in the solar hot water sys- mixed temperature of the jth withdrawal
t
sj
tem, in kilojoules; of water from the solar tank, in degrees
Celsius;
energy output from the collector loop
QOUTPUT
heater (if used) during the test, in
t temperature of the incoming cold water
main
kilojoules;
supply to the solar hot water system, in
degrees Celsius;
daily net energy supplied by solar energy
Qs
for the system during the test day, in
collector heat transfer loss coefficient, in
UL
kilojoules; kilojoules per hour square metre degree
Celsius [kJ/ (h-m**“C)];
.
rate of useful heat output from the col-
Q
U
V total volume draw as determined from
lector, in kilojoules per hour;
no-solar-input test, in litres;
R rating number which is the ratio of the
Subscripts
auxiliary plus parasitic energies to the
daily system load during the solar day
NS no solar energy input;
[ (QAUX + QpAR) /QL], dimensionless;
S solar energy input;
fraction of hot water load supplied by
4lf
solar energy, dimensionless;
Greek symbols
absorptance of the collector absorber
ambient air temperature, in degrees
%
ta
coating to the solar spectrum at normal
Celsius;
incidence, dimensionless;
t ambient air temperature in the labora-
a,1
8 angle of incidence between the direct
tory during the system test, in degrees
solar beam and the normal to the col-
Celsius;
lector aperture, in degrees;
t ambient air temperature specified for
a,t
angle of incidence between the beam
0
m
the test solar day, in degrees Celsius;
irradiance from the solar irradiance
simulator and the normal to the collector
temperature of the transfer fluid enter-
tf,i
aperture, in degrees;
ing the collector, in degrees Celsius;
specular reflectance of the cover plate
temperature of the transfer fluid leaving
tr,e
assembly at an incident angle of 60”,
the collector, in degrees Celsius;
dimensionless;
mixed temperature of the water with-
transmittance of the cover plate as-
4
57
drawn from the solar hot water system,
sembly to the solar spectrum at normal
in degrees Celsius;
incidence, dimensionless;
effective transmittance-absorptance
mean plate temperature of the collector
( za > e,n
bm
product for the collector at normal inci-
absorber, in degrees Celsius;
dence, dimensionless;
mean plate temperature of the collector
tp,m,non
n
summation over all water withdrawal
absorber under non-irradiated con-
periods during a test day.
c
ditions, in degrees Celsius;
j=l
t ultimate desired hot water delivery tem- 5 System classifications
set
perature after the addition of sup-
Solar domestic hot water systems are classified by
plemental energy, in degrees Celsius;
seven attributes, each divided into two or three cat-
egories. The categories of each attributed are defined
t mixed temperature of the jth withdrawal
wj
as shown in table 1.
of water to the load, in degrees Celsius;

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IS0 9459=1:1993(E) 0 IS0
b) Vented - system in which contact between the
heat transfer fluid and the atmosphere is re-
Table 1 - Classification of solar domestic hot
stricted either to the free surface of a feed and
water systems
expansion cistern or to an open vent pipe only.
Category
Attri- -
C Closed (sealed or unvented) - system in which
bute ‘1
a b C
the heat transfer fluid is completely sealed from
the atmosphere.
Solar only 1 Solar preheat 1 Solar plus
supplemen-
tary
5.4 Attribute 4
2 Direct Indirect
3 Open Vented Closed
Filled - system in which the collector remains
4 Filled Drainback Draindown filled with the heat transfer fluid.
5 Thermosiphon Forced
Drainback - system in which, as part of the
6 Circulating Series-
normal working cycle, the heat transfer fluid is
connected
drained from the collector into a storage vessel for
7 Remote stor- Close-coupled Integral stor-
subsequent reuse.
storage
age we
system in which the heat transfer
c) Draindown -
fluid can be drained from the collector and run to
5.1 Attribute 1
waste.
Solar only - system designed to provide solar
heated domestic water without use of sup-
plementary energy other than that required for 5.5 Attribute 5
fluid transport and control purposes.
a) Thermosiphon - system which utilizes only
Solar preheat - system not incorporating any density changes of the heat transfer fluid to
achieve circulation between collector and storage.
form of supplementary heating and installed to
preheat cold water prior to its entry into any other
b) Forced - system in which heat transfer fluid is
type of household water heater.
forced through the collector either by mechanical
c) Solar plus supplementary - system which util- means or by externally generated pres
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