ISO 9459-5:2007
(Main)Solar heating — Domestic water heating systems — Part 5: System performance characterization by means of whole-system tests and computer simulation
Solar heating — Domestic water heating systems — Part 5: System performance characterization by means of whole-system tests and computer simulation
ISO 9459-5:2007 specifies a method for outdoor laboratory testing of solar domestic hot-water (SDHW) systems. The method may also be applied for in-situ tests, and also for indoor tests by specifying appropriate draw-off profiles and irradiance profiles for indoor measurements. The system performance is characterized by means of whole-system tests using a 'black-box' approach, i.e. no measurements on the system components or inside the system are necessary. Detailed instructions are given on the measurement procedure, on processing and analysis of the measurement data, and on presentation of the test report.
Chauffage solaire — Systèmes de chauffage de l'eau sanitaire — Partie 5: Caractérisation de la performance des systèmes au moyen d'essais effectués sur l'ensemble du système et par simulation sur ordinateur
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 9459-5
First edition
2007-05-15
Solar heating — Domestic water heating
systems —
Part 5:
System performance characterization by
means of whole-system tests and
computer simulation
Chauffage solaire — Systèmes de chauffage de l'eau sanitaire —
Partie 5: Caractérisation de la performance des systèmes au moyen
d'essais effectués sur l'ensemble du système et par simulation sur
ordinateur
Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions. 2
4 Symbols, units and nomenclature . 4
5 Apparatus . 5
5.1 Mounting and location of the SDHW system . 5
5.2 Test facility . 8
5.3 Instrumentation. 10
5.4 Location of sensors. 10
6 Test method. 12
6.1 General. 12
6.2 Test conditions . 12
6.3 Test sequences . 14
6.4 Data acquisition and processing . 17
7 Identification of system parameters . 19
7.1 Dynamic fitting algorithm . 19
7.2 Options . 19
7.3 Constants . 19
7.4 Skip time . 20
7.5 Parameters . 20
8 Performance prediction. 20
8.1 Yearly performance prediction and reporting . 20
8.2 Reference conditions . 20
Annex A (normative) Basis of dynamic SDHW system testing. 21
Annex B (normative) Validation of the test method . 24
Annex C (normative) Test report . 25
Annex D (informative) Hardware and software recommendations . 30
Bibliography . 35
Foreword
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. 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. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 9459-5 was prepared by Technical Committee ISO/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 heating — Domestic water heating
systems:
⎯ Part 1: Performance rating procedure using indoor test methods
⎯ Part 2: Outdoor test methods for system performance characterization and yearly performance prediction
of solar-only systems
⎯ Part 3: Performance test for solar plus supplementary systems (withdrawn)
⎯ Part 4: System performance characterization by means of component tests and computer simulation
⎯ Part 5: System performance characterization by means of whole-system tests and computer simulation
iv © ISO 2007 – All rights reserved
Introduction
International Standard ISO 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 test 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.
ISO 9459 is divided into five parts within three broad categories, as described below.
Rating test
ISO 9459-1:1993, Solar heating — Domestic water heating systems — Part 1: Performance rating procedure
using indoor test methods, involves testing for periods of 1 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 procedures
ISO 9459-2:1995, Solar heating — Domestic water heating systems — Part 2: Outdoor test methods for
system performance characterization and yearly performance prediction of solar-only systems, 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.
ISO 9459-3:1997, Solar heating — Domestic water heating systems — Part 3: Performance test for solar plus
supplementary systems (now withdrawn), applied to solar plus supplementary systems. The performance test
was a ‘black-box’ procedure which produced coefficients in a correlation equation that could 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 was limited to predicting annual performance for one load pattern.
Testing and computer simulation
ISO/AWI 9459-4, Solar heating — Domestic water heating systems — Part 4: System performance
characterization by means of component tests and computer simulation, 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.
This part of ISO 9459 (i.e. ISO 9459-5) presents a procedure for dynamic testing of complete systems to
determine system parameters for use in the “Dynamic System Testing Program” (reference [2]). This software
has been validated on a range of systems; however, it is a proprietary product and cannot be modified by the
user. Implementation of the software requires training from a test facility experienced with the application of
the product. This model may be used with hourly values of local solar irradiation, ambient air temperature and
cold-water temperature data to predict annual system performance.
The procedures defined in ISO 9459-2, ISO 9459-3, ISO 9459-4 and ISO 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 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 conditions, but only for an evening draw-off.
The results of tests performed in accordance with ISO 9459-3 permitted annual system 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 performance 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 assessment of protection from extreme temperatures and pressures.
Introduction to ISO 9459-5
The expanding market for Solar Domestic Hot-water (SDHW) systems demands a standardized test method
for SDHW systems, which makes possible accurate long-term performance prediction for arbitrary conditions
from a test as short, simple and cheap as possible.
Two facts make this goal difficult to reach.
a) The SDHW system gain depends on many different conditions (e.g., irradiance, ambient temperature,
draw-off profile and cold-water temperature). Therefore, a sufficient number of parameters are needed to
predict the yearly system gain sufficiently accurately for arbitrary conditions.
b) The system state, that is, the temperature profile inside the store, needs a long time to 'forget' initial
conditions; a typical time constant may be one day or more. Since several parameters need to be
determined, several system states must occur during the test. If a test method did not take into account
the system state dependence on the past, and thus the dynamic behaviour of the system, the minimum
testing times would be quite long (up to several months).
The objective of the method described in this part of ISO 9459 is to minimize experimental effort by keeping
the test duration short and avoiding extensive measurements. To compensate for the relatively small amount
of experimental data, mathematical tools are used to extract as much information as possible from the test
data, while being robust enough to avoid being misled by unimportant transient effects.
There are no requirements for steady-state conditions in the tests, and, due to the 'black-box' approach, no
measurements inside the store or inside the collector loop are required.
Experience has shown that the variability of system states encompassed by the test sequence is the most
important precondition for the correct determination of all system parameters with minimum errors and cross
correlation between parameters. Only if the system is driven into many different states, is the influence of
each parameter of the model shown on the performance of the system. Therefore, the overall design criterion
of a draw-off test sequence is that the system shall be driven into as many different states as possible in a
minimum time. Here, system state means a combination of the store temperature distribution and weather
conditions. The system states should include all states that may occur in actual operation. For testing
purposes, it is much more important to have a large variability of system states than to perform draw-offs
according to 'normal user behaviour'. Accurate parameter identification will be achieved only if the range of
system states in actual operation is covered by the range of system states set up during the tests. The method
is applicable to in-situ monitoring, but difficulties arise during in-situ testing, as the operator cannot control the
operating conditions. Monitoring of 'normal user behaviour' needs to be carried out over a long time to ensure
that all relevant system states are covered, i.e. testing times can be much longer to achieve the same
performance prediction accuracy.
This part of ISO 9459 may be applicable to a wide range of systems, including systems with relatively large
collectors which have to be cooled by large, frequent draw-offs to prevent overheating, and systems with
relatively large storage tanks which need to be operated with low loads for days, in order to reach the high
store and collector temperatures needed for accurate parameter identification. No single draw-off profile can
meet these demands for all systems, since the ratio of storage volume and collector aperture area (V /A )
S C
may vary up to a factor of 20 for the systems considered in this this part of ISO 9459. Therefore, the draw-off
volumes have been made dependent on V and V /A .
S S C
vi © ISO 2007 – All rights reserved
Experience has shown that the system state variability is especially important for the determination of the
* *
effective collector area A , the effective collector loss coefficient u and the store-loss coefficient U .
C C
S
To discern between optical and thermal collector properties, the store (and thus the collector inlet
temperature) must be kept cold for some intervals with substantial irradiance (Test A) and then be allowed to
become hot while irradiance is sufficient to keep the collector loop operational (Test B).
To discern between store losses (which happen all the time) and collector losses (which happen only when
there is sufficient irradiance), the store must be operated at high temperatures during some periods with low
irradiance.
INTERNATIONAL STANDARD ISO 9459-5:2007(E)
Solar heating — Domestic water heating systems —
Part 5:
System performance characterization by means of
whole-system tests and computer simulation
1 Scope
This part of ISO 9459 specifies a method for outdoor laboratory testing of solar domestic hot-water (SDHW)
systems. The method may also be applied for in-situ tests, and also for indoor tests by specifying appropriate
draw-off profiles and irradiance profiles for indoor measurements. The system performance is characterized
by means of whole-system tests using a 'black-box' approach, i.e. no measurements on the system
components or inside the system are necessary. Detailed instructions are given on the measurement
procedure, on processing and analysis of the measurement data, and on presentation of the test report.
The theoretical model described in reference [1] is used to characterize SDHW system performance under
transient operation. The identification of the parameters in the theoretical model is carried out by a parameter-
identification software program (see Annex A). The program finds the set of parameters that gives the best fit
between the theoretical model and the measured data.
A wide range of operating conditions shall be covered to ensure accurate determination of the system
parameters. Measured data shall be pre-processed before being used for identification of system parameters.
The identified parameters are used for the prediction of the long-term system performance for the climatic and
load conditions of the desired location, using the same model as for parameter identification. The system
prediction part of the theoretical model requires hourly values of meteorological data (e.g. test reference
years) and specific load data, as described in Annex C.
This part of ISO 9459 can be applied to the following SDHW systems including:
a) systems with forced circulation of fluid in the collector loop;
b) thermosiphon systems;
c) integral collector storage (ICS) systems;.
provided that for b) and c) the validation requirements described in Clause B.2 of Annex B are satisfied.
1)
Systems are limited to the following dimensions .
⎯ The collector aperture area of the SDHW system is between 1 and 10 m .
⎯ The storage capacity of the SDHW system is between 50 and 1 000 litres.
⎯ The specific storage-tank volume is between 10 and 200 litres per square metre of collector aperture area.
1) In general there are no restrictions on the size of a system being tested however validation tests of the method for
systems with more than 10 m collector area are not available. The system size may affect details of the procedure, hence
application to systems outside of the specified range requires validation tests (see Annex B).
Limits to the application of this International Standard.
1) This part of ISO 9459 is not intended to establish any safety or health requirements.
2) This part of ISO 9459 is not intended to be used for testing the individual components of the system.
However, it is permitted to obtain test data of components in combination with a test according to the
procedure described here.
3) The test procedure cannot be applied to SDHW systems containing more than one storage tank. This
does not exclude preheat systems with a second tank in series. However, only the first tank is
considered as part of the system being tested.
4) Systems with collectors having non-flat plate-type incident-angle characteristics can be tested if the
irradiance in the data file(s) is multiplied by the measured incident-angle modifier prior to parameter
identification. The same irradiance correction should, in this case, also be used during any
performance predictions based on the identified parameters.
5) The test procedure cannot be applied to SDHW systems with overheating protection devices that
2)
significantly influence the system behaviour under normal operation .
6) The test procedure cannot be applied to integrated auxiliary solar systems, with a high proportion of
the store heated concurrently by the auxiliary heater. The results of the tests are only valid when the
resulting parameter f < 0,75.
aux
7) The test procedure cannot be applied to SDHW systems with an external load-side heat exchanger
in combination with a temperature-dependent pump.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 9060, Solar energy — Specification and classification of instruments for measuring hemispherical solar
and direct solar radiation
ISO 9459-1, Solar heating — Domestic water heating systems — Part 1: Performance rating procedure using
indoor test methods
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
ISO 9488:1999, Solar energy — Vocabulary
ISO 9846, Solar energy — Calibration of a pyranometer using a pyrheliometer
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9488 and the following apply.
3.1
capacitance rate
product of volume draw-off rate, density and mass specific heat of the heat transfer fluid, i.e. the potential of a
fluid flow to carry thermal power per unit temperature increase between inlet and outlet
2) These systems can be tested if the predicted performance is corrected for the influence of the overheating device. A
validation test would be required to extend the procedure to such systems.
2 © ISO 2007 – All rights reserved
3.2
cold-water mixer
device providing potable water of constant temperature to the user by mixing draw-off water and mains water
3.3
collector azimuth angle
azimuth angle of the collector defined similarly to the solar azimuth angle
See 1.4 in ISO 9488:1999.
3.4
components
parts of the solar hot-water system
EXAMPLES Collectors, store, pumps, heat exchanger, controls.
3.5
differential temperature controller
device that is able to detect a small temperature difference, and to control pumps and other electrical devices
according to this temperature difference
3.6
draw-off temperature
temperature of hot water withdrawn from the system
3.7
dynamic system testing
procedure which uses the same analytical basis to account for time-varying processes in parameter
identification and performance prediction
3.8
external auxiliary heating
auxiliary heater located outside of the storage tank and having no impact on the operation of the solar heating
system
3.9
integrated auxiliary heating
auxiliary heater that can influence the operation of the solar heating system
3.10
load-side heat exchanger
device to transfer the heat from a solar store containing non-potable water to potable mains water drawn off
3.11
test duration
total elapsed time for a particular test sequence
3.12
transient conditions
meteorological and system operation conditions varying in time
3.13
parameters
coefficients of the mathematical model characterizing the system as identified by the test procedure
3.14
heat capacity of the store
amount of sensible heat that can be stored per kelvin of temperature increase
3.15
test sequence
continuous measurement including compulsory conditioning at the beginning
3.16
threshold temperature
temperature below which the water is considered to be unsuitable for use
4 Symbols, units and nomenclature
Symbols marked by (P) denote model parameters to be determined by the parameter identification.
Symbol Units Meaning
A [m] Collector aperture area
C
* **
A [m ] Effective collector loop area, A =FAατ (P)
( )
C CR C
c (T , T ) [kJ/kgK] Specific heat of water, averaged over the temperature interval [T ; T ] (see
w cw S cw S
Annex D)
−1
C [MJK ] Filter constant with regard to the load draw-off
F
−1
C [MJK ] Heat capacity of the store (P)
S
D [-] Draw-off mixing parameter (P)
L
−1
C [WK ] Load-side heat capacitance rate through the store
S
f [-] Fraction of the store heated by the auxiliary heater (P)
aux
*
F [-] Heat removal factor of the collector loop
R
−2
G [Wm ] Solar irradiance in the collector plane
t
h [rad] Solar elevation
−2
I [Wm] Solar constant
P [W] Auxiliary power entering store
aux
P [W] Collector loop pumping power
cp
P [W] Load power, PC=−T T
( )
LS S cw
L
P [W] Net system power, PP=−P
net net L aux
Q [MJ] Load energy
L
Q [MJ] Energy from auxiliary heating
aux
Q [W] Net system gain QP==ddt CT−T−P t
( ( ) )
net net net S S cw aux
∫ ∫
R [K/W] Thermal resistance of load-side heat exchanger (P)
L
S [-] Collector loop stratification parameter (P)
C
t [h:min:s] Time
t [h:min:s] Actual start time of the first draw-off of the day
T [°C] Ambient air temperature in vicinity of collectors
ca
4 © ISO 2007 – All rights reserved
T [°C] Cold (mains) water temperature
cw
T [°C] Temperature demanded by the user
D
T [°C] Outlet temperature of the store
S
T [°C] Minimum outlet temperature of the store
minS
T [°C] Ambient air temperature in vicinity of the store
sa
−2 −1
u [Wm K ] Heat-loss coefficient of the collector loop
C
* *
−2 −1
u [Wm K ] uu= ατ (P)
( )
C CC
−1
U [WK ] Heat-loss rate of the store per unit temperature difference (P)
S
−3 −1
u [Jm K] Dependence of u on surrounding air velocity (P)
v C
−1
v [ms] Surrounding air velocity
V [l] Storage-tank volume
S
V [l/min] Volumetric flow through the store
S
−1
v [ms ] Wind velocity over the collector as used in the in situ software (reference
ignore
[2]) (not used but is recorded)
−1
v [ms ] Wind velocity over the collector as used in the in situ software (reference
force
[2]) (forced to a certain range and not taken into account in the parameter
identification)
−1
v [ms ] Wind velocity over the collector as used in the in situ software (reference
fit
[2]) (varied, and the wind dependence of the collector losses is determined)
(ατ) [-] Effective transmittance-absorptance product of the collector
∆T [K] Temperature difference for deactivating the collector loop pump
off
∆T [K] Temperature difference for activating the collector loop pump
on
β [rad] Collector tilt angle
γ [rad] Collector azimuth angle
ρ T [kg/l] Density of water at temperature T
()
wS S
θ [rad] Angle of incidence
τ [s] Filter time constant
F
5 Apparatus
5.1 Mounting and location of the SDHW system
5.1.1 System mounting
The requirements for mounting and location are consistent with ISO 9459-2. The complete system shall be
mounted in accordance with the manufacturer's guidelines. Whenever possible, the system shall be mounted
on the mounting structure provided by the manufacturer. If no mounting is provided, then, unless otherwise
specified (e.g., when the system is part of an integrated roof array), an open mounting system shall be used.
Such mounting shall not obstruct the aperture of collectors and shall not significantly affect the back or side
insulation of the collectors or the storage tank. Mounting shall be able to withstand the effects of wind gusts.
5.1.2 Collectors
5.1.2.1 Collector location
If collectors designed for integration into a roof have their underside protected from the wind, this shall be
reported with the test results. In this case, the underside heat-loss coefficient of the collector test-rig shall be
−2 −1
set in accordance with the manufacturer's guidelines, or shall have a value of 0,35 ± 0,05 Wm K if not
prescribed by the manufacturer.
The height between the lower edge of the collectors and the ground of the test-rig shall be a minimum of
50 cm, unless specified otherwise by the manufacturer. Natural ventilation of the collector surface shall not be
restricted by the mounting.
The temperature of surfaces adjacent to the system shall be as close as possible to that of the ambient air, in
order to minimize the influence of thermal radiation. For example, the field of view of the system shall not
include chimneys, cooling towers or hot exhausts. Warm currents of air, such as those that rise up the walls of
buildings, shall not be allowed to pass over the system. Collectors mounted on the roof of a building should be
located at least 2 m away from the edge of the roof.
5.1.2.2 Collector azimuth orientation
The collectors shall be mounted in a fixed position facing the equator to within ± 10°.
5.1.2.3 Collector tilt angle
The tilt angle shall remain constant throughout the test. The system shall be tested with the collector at a tilt
angle within ± 5° of the latitude of the test site, unless otherwise specified by the manufacturer. This shall be
reported with the test results.
5.1.2.4 Shading of collectors from direct solar irradiance
The collector shall be positioned in such a manner that no significant shadows of any object, other than the
collector itself, will be cast into the collector aperture at any time during the test period.
5.1.2.5 Diffuse and reflected solar irradiance on collector plane
The collector shall be located where there will be no significant direct solar radiation reflected into it from
surrounding buildings or surfaces during the tests, and where there will be no significant obstructions in the
field of view.
With some collectors, such as evacuated tubular collectors, reflections onto both the back and the front of the
collector shall be minimized. Not more than 5 % of the collector’s field of view of the sky shall be obstructed,
and it is particularly important to avoid buildings or large obstructions subtending an angle of greater than 15°
with the horizontal in front of the collectors.
The reflectance of most rough surfaces, such as grass, weathered concrete or chippings, is not usually high
enough to cause problems during testing. It is recommended that surfaces in the collector’s field of view, that
include large expanses of glass, metal, snow or water, be avoided.
5.1.2.6 Heat transfer fluid
The heat transfer fluid used in the system during testing shall be the fluid recommended by the manufacturer.
The fluid used shall be reported. For all systems, the fluid flow rate resulting from system operation, as
recommended by the manufacturer, shall be used.
6 © ISO 2007 – All rights reserved
5.1.2.7 Controller
Any controller included in the collector loop shall be set in accordance with the manufacturer's instructions. If
no instructions are given, ∆T shall be set to 7 K. ∆T , if adjustable, should be set to 2 K. The controller
on off
setting shall be stated clearly in the test report.
5.1.3 Storage
5.1.3.1 Storage-tank location
The store shall be installed as specified in the manufacturer's installation instructions.
5.1.3.2 Storage ambient conditions
The store shall be mounted in a way that there is a uniform ambient air temperature in its vicinity.
Storage tanks separated from the collector array shall be situated in a closed room, taking into account the
requirements regarding pipe length as stated in 5.1.4 and the manufacturer's instructions. The ambient
temperature of the store shall be in accordance with 6.2.3.
5.1.4 Piping and insulation
The total length of the connecting pipes between the collector and the store shall be the longest length
allowed by the published installation instructions for the systems. In the absence of such instructions, the total
pipe length shall be 15 m ± 0,1 m. This piping shall be placed in such a way that the environment of the piping
will be the same as for the store, as far as possible, in order to increase the reproducibility of the test results.
The pipe length (total, length indoors and length outdoors) used shall be stated in the test report.
The diameter and insulation of the pipes shall be in accordance with the manufacturer's installation
instructions. If not prescribed by the manufacturer, the pipe diameter and the insulation shall be chosen
according to common installation practice and the pipe diameter and insulation used shall be stated in the test
report. All pipes and pipe connections additional to the system under test shall be properly insulated, so that
thermal losses are minimized.
5.1.5 Auxiliary heating
5.1.5.1 Integrated auxiliary heating
Integrated auxiliary heating can be provided either by a heat exchanger or an immersed electrical or gas
heater. All parts of the integrated auxiliary heater that are located outside the store, the demand heater and all
accompanying pipes shall be properly insulated so that thermal losses are minimized, and the measured
energy corresponds to the actual auxiliary energy supply.
5.1.5.1.1 Heat exchanger
To avoid reverse thermosiphonic convection for auxiliary heating provided by a heat exchanger, the auxiliary
heater shall be below the heat exchanger, or the pipes between the auxiliary heater and the heat exchanger
shall have a downward bend of at least 300 mm deep, as close to the store as possible.
If a heat exchanger driven by a non-electrical heat source is used, a thermostatically controlled electrical
water heater can be mounted as a by-pass to the non-electrical heater and can be used as the only auxiliary
heat source during the test. The nominal power of this electrical demand heater shall be consistent with the
rating of the boiler, if specified; or 100 W ± 30 W per litre of store volume above the lowest part of the heat
exchanger. The power rating of the electrical demand heater used shall be reported.
5.1.5.1.2 Immersed heater
If an immersed heater is used, the heater delivered with the system shall be used. If no such heater is
delivered with the system, a heater with a nominal power consistent with the rating of the immersed heater, if
specified; or 25 ± 8 W per litre of store volume above the lowest part of the heater, shall be used. The actual
power used shall be reported.
5.1.5.2 External auxiliary heating
Systems with external auxiliary heating shall be tested without auxiliary heating. The hot-water temperature
sensor, and the volume flow-meter if mounted in the hot-water outlet line, shall be mounted between the
storage tank and the external auxiliary heater.
All parts of the external auxiliary heater, that are located outside the store, the demand heater and all
accompanying pipes, shall be properly insulated so that thermal losses are minimized, and the measured
energy corresponds to the actual auxiliary energy supply.
5.1.6 Mixing valve
If a thermostatic mixing valve for limiting the outlet temperature is a part of the system, it shall be removed or
disabled during the test.
5.2 Test facility
5.2.1 Measurement schematic
A typical measurement schematic for a system with forced circulation flow in the collector loop, and with an
indoor store equipped with electrical auxiliary heating is shown in Figure 1. For different systems, the
measurement points remain the same but the plumbing layout may vary as appropriate.
5.2.2 Piping
The piping used in the load loop shall be resistant to corrosion and suitable for operation at temperatures up
to 95 °C. Pipe lengths in the load loop shall be kept short. In particular, the piping between the mains source
of water with constant temperature and the inlet to the storage tank shall be minimized, in order to reduce the
effects of the environment on the water-inlet temperature. The mains-water temperature is specified in 6.2.1.
If a pipe with substantial length, which is in thermal contact with ambient air, leads from the mains-water
supply to the storage tank, it is recommended to flush this part of the piping immediately before each draw-off
in order to provide a constant mains-water temperature.
8 © ISO 2007 – All rights reserved
Key
1 collector 6 pump
2 safety valve 7 non-return valve
3 draw-off valve 8 expansion vessel
4 fan 9 rinse valve
5 safety valve
= Pyranometer = Fluid thermometer (T) or flow meter (V)
= Anemometer = Air thermometer
NOTE See 5.4.5 for an alternative location of the flow-meter
Figure 1 — Typical test facility for a system with forced circulation of fluid in the collector loop and
storage tank equipped with an immersed electrical auxiliary heater
Piping between the temperature-sensing points and the store (inlet and outlet) shall be protected with
insulation and reflective weather-proof covers extending beyond the positions of the temperature sensors,
such that the calculated temperature gain or loss along either pipe does not exceed 0,01 K under test
conditions. This is assured if the pipe heat loss does not exceed 0,15 W/K for each pipe.
The facility shall allow continuous operation of the SDHW system and measuring of its performance under
natural climatic conditions over a measurement period of several weeks, and shall fulfil all the requirements
specified in Clause 6.
5.3 Instrumentation
5.3.1 Solar radiation measurement
A pyranometer shall be used to measure the solar irradiance. The pyranometer shall have characteristics in
accordance with Class II of WMO classification and ISO 9060.
The pyranometer shall be calibrated using a standard pyrheliometer, in accordance with ISO 9060 and
ISO 9846.
5.3.2 Temperature measurement
The accuracy and repeatability of the instruments, including their associated readout devices, shall be within
the limits given in Table 1. The time constant (time required for 63,2 % response to a step change) shall be
less than 3 s for sensors measuring fluid temperatures.
Table 1 — Temperature measurement accuracy
Parameter Measurement accuracy
Temperature, ambient air ± 0,5 K
Temperature, cold-water inlet
± 0,3 K
Temperature difference across system ± 0,1 K or 1 %
(cold water into hot water out) whichever is higher
NOTE For short draw-offs, the thermal inertia of temperature sensors may become the primary power-measurement
error source. The use of slowly opening valves may greatly reduce this systematic power error.
5.3.3 Volumetric draw-off rate measurements
The accuracy of the volumetric draw-off rate measurement shall be equal to or better than ± 1,0 %.
5.3.4 Electrical energy
The electrical energy used shall be measured with an accuracy of ± 1,0 % of the reading or ± 15 W⋅h,
whichever is greater.
5.3.5 Elapsed time
Elapsed time measurements shall be made to an accuracy of ± 0,2 %.
5.3.6 Surrounding air velocity
The surrounding air velocity shall be measured with an instrument and associated data acquisition system that
−1
can determine hourly mean values of the surrounding air velocity to an accuracy of ± 0,5 m⋅s . The start
−1
velocity of the instrument shall be 0,5 m⋅s or less.
5.4 Location of sensors
5.4.1 Pyranometer
The pyranometer shall be mounted and operated in accordance with ISO 9060. It shall be installed at the
same tilt and azimuth as for the collector plane. It shall be installed near the upper part of the collector array.
10 © ISO 2007 – All rights reserved
5.4.2 Ambient air temperature of the collector
The ambient air transducer shall be shielded from direct and reflected solar radiation by means of a
white-painted, well-ventilated shelter, preferably with forced ventilation. The shelter itself shall be shaded and
placed at the midheight of the collector, but at least 1 m above the local ground surface to ensure that it is
removed from the influence of ground heating. The shelter shall be positioned to one side of the collector and
not more than 10 m from it.
If air is forced over the collector by a wind generator, the air temperature shall be measured in the outlet of the
wind generator, and checks made to ensure that this temperature does not deviate from the ambient air
temperature by more than ± 1 °C.
5.4.3 Ambient air temperature of the store
The ambient air temperature shall be measured using a shaded ventilated sampling device approximately 1 m
above the ground, not closer than 1,5 m to the store and system components and not further away than 10 m
from the store.
5.4.4 Temperature sensors for fluid temperatures
The measurement points for mains water and draw-off temperature shall be located as close as possible to
the store. The piping between measurement points and the storage tank shall contain no more than 0,3 l of
water each. The hot-water sensor shall be mounted close to the store, so that the store and transducer are
thermally coupled even when there is no draw-off.
5.4.5 Volumetric flow-meter and flow control device
It is recommended to install the flow-meter directly adjacent to the draw-off temperature sensor as shown in
Figure 1. If variations of the draw-off temperature influence the flow-meter accuracy such that it does not
comply with the requirements of 5.3.3, it shall be installed in the mains-water pipe directly adjacent to the
measurement point of the mains-water temperature and the mass flow rate adjusted for the change in density
according to the formulas given in 6.3.2.
The mass flow rate at the store outlet equals the mass flow rate delivered to the user; therefore, the volume
flow rate at the outlet should be measured and multiplied by the density of water at the current draw-off
temperature to obtain the correct mass flow rate. However, if the flow-meter is not able to operate with
sufficient accuracy over the wide range of temperatures occurring at the outlet, the volume flow rate may be
measured at the store inlet. In this case, the
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