ISO 9806-3:1995
(Main)Test methods for solar collectors — Part 3: Thermal performance of unglazed liquid heating collectors (sensible heat transfer only) including pressure drop
Test methods for solar collectors — Part 3: Thermal performance of unglazed liquid heating collectors (sensible heat transfer only) including pressure drop
Establishes methods for determining the thermal performance of unglazed liquid heating solar collectors. Contains methods for conducting tests outdoors under natural solar irradiation and simulated wind and for conducting tests indoors under simulated solar irradiation and wind. Not applicable to those collectors in which the heat transfer fluid can change phase.
Méthodes d'essai des capteurs solaires — Partie 3: Performance thermique des capteurs non vitrés à liquide (transfert de chaleur appréciable seulement), chute de pression incluse
Metode za preskus sprejemnikov sončne energije - 3. del: Termični učinki nezastekljenih sprejemnikov sončne energije s kapljevino kot prenosnikom toplote (samo z zaznavnim prenosom toplote), vključno z določitvijo padca tlaka v sprejemniku
General Information
Relations
Standards Content (Sample)
IS0 9806-3: 1995(E)
Contents
Page
1
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
4 Symbols and units .
............................................... 2
5 Collector mounting and location
4
6 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
7 Test installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8 Outdoor steady-state efficiency test
15
9 Steady-state efficiency test using a solar irradiance simulator
10 Determination of the effective thermal capacity and time constant
16
of a collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 18
11 Determination of the pressure drop across a collector
Annexes
Format sheets for test data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A
B Collector incident angle modifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Unglazed solar collector characteristics . 33
C
................................................................ 35
D Properties of water
............................................................................ 36
E Bibliography
0 IS0 1995
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 Cl-i-1 211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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0 IS0
IS0 9806=3:1995(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
(IEC) 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 9806-3 was prepared by Technical Committee
ISO/TC 180, Solar energy, Subcommittee SC 5, Collectors and other
components.
IS0 9806 consists of the following parts, under the general title Test
methods for solar collectors:
- Part 7: Thermal performance of glazed liquid heating collectors in-
cluding pressure drop
- Part 2: Qualification test procedures
- Part 3: Thermal performance of unglazed liquid heating collectors
(sensible heat transfer only) including pressure drop
- Part 4: Thermal performance of air or gas heating collectors
Annex A forms an integral part of this part of IS0 9806. Annexes B, C, D
and E are for information only.
. . .
III
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INTERNATIONAL STANDARD 0 Iso IS0 9806-3: 1995(E)
Test methods for solar collectors -
Part 3:
Thermal performance of unglazed liquid heating collectors
(sensible heat transfer only) including pressure drop
1 Scope
1.1 This part of IS0 9806 establishes methods for determining the thermal performance of unglazed liquid
heating solar collectors.
1.2 This part of IS0 9806 contains methods for conducting tests outdoors under natural solar irradiance and
simulated wind and for conducting tests indoors under simulated solar irradiance and wind.
1.3 This part of IS0 9806 is not applicable to those collectors in which a thermal storage unit is an integral part
of the collector to such an extent that the collection process cannot be separated for the purpose of making
measurements of these two processes.
1.4 This part of IS0 9806 is not applicable to collectors in which the heat transfer fluid can change phase, nor
is it applicable to collectors affected by condensation of water vapour from the ambient air.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part
of IS0 9806. 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 9806 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 9060:1990, Solar energy - Specification and classification of instruments for measuring hemispherical solar
and direct solar radiation.
IS0 9806-I :I 994, Test methods for solar collectors - Part 7: Thermal performance of glazed liquid heating col-
lectors including pressure drop.
Reference solar spectral irradiance at the ground at different receiving conditions
IS0 9845-l : 1992, Solar energy -
- Part 7 : Direct normal and hemispherical solar irradiance for air mass ?,5.
Calibration of a pyranometer using a pyrheliometer.
IS0 9846: 1993, Solar energy -
Calibration of field pyranometers by comparison to a reference pyranometer.
IS0 9847: 1992, Solar energy -
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0 IS0
IS0 9806-3: 1995(E)
- Recommended practice for use.
ISO/TR 9901 :I 990, Solar energy - Field pyranometers
WMO, Guide to Meteorological Instruments and Methods of Observation, 5th ed., WMO-8, Secretariat to the
World Meteorological Organization, Geneva, 1983, Chapter 9.
3 Definitions
For the purposes of this part of IS0 9806, the definitions given in IS0 9806-I and the following definitions apply.
3.1 irradiation: Incident energy per unit area of a surface, found by integration of irradiance over a specified time
interval, often an hour or a day.
NOTES
Irradiation is normally expressed in megajoules per square metre (MJ/m’) over a specified time interval.
2 Solar irradiation is often termed “radiant exposure” or “insolation”. The use of these terms is deprecated.
3.2 longwave radiation; thermal radiation: Radiation at wavelengths greater than 3 pm, typically originating
from sources at terrestrial temperatures (e.g. ground and other terrestrial objects).
33 . turbulence level: Root mean square velocity fluctuation divided by the mean velocity.
34 . unglazed solar collector: Collector without a cover over the absorber.
4 Symbols and units
The symbols and their units used in this part of IS0 9806 are given in annex A.
5 Collector mounting and location
5.1 General
Collectors tested in accordance with this part of IS0 9806 shall be mounted in accordance with 5.2 to 5.9. The
mounting arrangement shall be reported with the results in the format sheets.
Full-size collector modules or collector arrays typical of full-size installations shall be tested, because the edge
losses of small collectors may significantly reduce their overall performance. A minimum collector gross area of
3 m* is recommended.
5.2 Collector mounting frame
The collector shall be mounted in the manner specified by the manufacturer. The collector mounting frame shall
in no way obstruct the aperture of the collector, and shall not significantly affect the back or side insulation, unless
otherwise specified (for example, when the collector is part of an integrated roof array). The collector shall be
mounted such that the lower edge is not less than 0,5 m above the local ground surface.
If mounting instructions are not specified, the collector shall be mounted on an insulated backing of conductance
(2 + 0,5) W/(m* K) and the upper surface painted matt white and ventilated at the back. Collectors designed to
be-mounted directly on standard roofing material may be mounted over a simulated roof section.
Collector arrays constructed from pipe or strip components shall be mounted with the pipes (or strips) spaced
IO mm or one diameter (width of strip) apart, whichever is smaller. If a different pipe or strip spacing is specified
in the manufacturer’s installation instructions, then the recommended spacing shall be used. If the collector is
delivered with mounting spacers or any device fixing the spacing of the pipes (or strips), then the collector shall
be tested as delivered and its geometry shall be reported in the test report.
2
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0 IS0
IS0 9806=3:1995(E)
Currents of warm air, such as those which rise up the walls of a building, shall not be allowed to pass over the
collector. Where collectors are tested on the roof of a building, they shall be located at least 2 m away from the
roof edge.
5.3 Collector test module size
The performance of some forms of unglazed solar collectors is a function of module size. If the collector is supplied
then sufficient of the modules shall be linked together (in series or in
in fixed units of area greater than 1 m*,
If the collector is supplied in the form of strips,
parallel) to give a test system absorber surface of at least 3 m*.
the minimum built-up module area shall be 3 m* (gross area).
5.4 Tilt angle
The collector shall be tested at tilt angles such that, during the test period, the angle of incidence with direct solar
radiation, 6, is less than 30” or at angles of tilt such that the incident angle modifier for the collector varies by less
than + 2 % from its value at normal incidence. Before deciding on a tilt angle, it may be necessary to check the
incident angle modifier at two angles prior to commencing the tests (see annex B).
NOTE 3 For most unglazed collectors the influence of tilt angle and radiation angle of incidence on collector efficiency is
small, and unglazed collectors are commonly installed at low inclinations. However, care must be taken to avoid air locks. Ab-
sorbers made of separate parallel tubes may have an angle of incidence response that increases with angle of incidence.
5.5 Collector orientation outdoors
The collector may be mounted outdoors in a fixed position facing the equator, but this will result in the time
available for testing being restricted by the acceptable range of incidence angles (see 8.6). A more versatile ap-
proach is to move the collector to follow the sun in azimuth, using manual or automatic tracking.
5.6 Shading from direct solar irradiance
The location of the test stand shall be such that no shadow is cast on the collector during the test.
5.7 Diffuse and reflected solar irradiance
5.7.1 Outdoors
For the purposes of analysis of outdoor test results, solar irradiance not coming directly from the sun’s disc is
assumed to come isotropically from the hemispherical field of view of the collector. In order to minimize the errors
resulting from this approximation, the collector shall be located where there will be no significant solar radiation
reflected onto it from surrounding buildings or surfaces during the tests, and where there will be no significant
obstructions in the field of view. Not more than 5 % of the collector’s field of view 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 surface such as grass, weathered concrete or chippings is not usually high enough
to cause problems during collector testing. Surfaces to be avoided in the collector’s field of view include large
expanses of glass, metal or water.
5.7.2 Solar irradiance simulator
In most solar simulators the simulated beam approximates direct solar irradiance only. In order to simplify the
measurement of simulated irradiance, it is necessary to minimize reflected irradiance. This can be achieved by
painting all surfaces in the test chamber with a dark (low reflectance) paint.
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IS0 9806-3:1995(E)
5.8 Longwave irradiance
5.8.1 Outdoors
The temperature of surfaces adjacent to the collector shall be as close as possible to that of the ambient air in
order to minimize the influence of longwave radiation from surrounding surfaces. For example, the outdoor field
of view of the collector should not include chimneys, cooling towers hot roof surfaces or hot exhausts.
5.8.2 Solar irradiance simulator
For indoor testing, the collector shall be shielded from hot surfaces such as radiators, air-conditioning ducts and
machinery, and from cold surfaces such as windows and external walls. Shielding is important both in front of and
behind the collector. For unglazed collectors the major difference between outdoor and indoor conditions is the
longwave thermal irradiance. The longwave irradiance in a simulator shall not exceed the limits specified in 9.2.
5.9 Surrounding air speed
The performance of unglazed collectors is sensitive to air speed adjacent to the collector. In order to maximize the
reproducibility of results, collectors shall be mounted such that air can freely pass over the aperture, exposed back
and sides of the collector. Collectors designed for integration into a roof may have their backs protected from the
wind; if so, this shall be reported with the test results.
The average surrounding air speed at a distance of 100 mm above and parallel to the collector aperture shall be
within the range I15 m/s to 4 m/s, subject to the tolerance specified in table 2 (see 8.5). An artificial wind generator
shall be used to provide a turbulence level in the range 20 % to 40 % to simulate natural wind conditions. The
turbulence level shall be checked at the leading edge of the collector 100 mm above the collector surface. The
turbulence level shall be monitored using a linearized hot wire anemometer with a frequency response of at least
100 Hz. If the absorber is not mounted directly on a roof or a sheet of backing material, the surrounding air speed
must be controlled and monitored at the front and back of the absorber.
6 Instrumentation
6.1 Solar radiation measurement
6.1 .I Pyranometer
A class I (in accordance with IS0 9060) pyranometer shall be used to measure the global shortwave radiation from
both the sun and the sky. The recommended practice for use given in lSO/TR 9901 shall be observed.
6.1.2 Precautions for effects of temperature gradient
placed in a typical test position and allowed to equilibrate for at
The pyra nometer used during the tests shall be
least 30 min before measurements commence.
6.1.3 Precautions for effects of humidity and moisture
The pyranometer shall be provided with a means of preventing accumulation of moisture that may condense on
surfaces within the instrument and affect its reading. An instrument with a desiccator that can be inspected is
required. The condition of the desiccator shall be observed prior to and following each collector test.
Precautions for infrared radiation effects on pyranometer accuracy in simulator tests
6.1.4
Pyranometers used to measure the irradiance of a solar irradiance simulator shall be mounted in such a way as
to minimize the effects on its readings of the infrared radiation of wavelength above 3 pm from the simulator light
source.
4
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IS0 9806-3: 1995(E)
6.1.5 Mounting of pyranometer
The pyranometer shall be mounted such that its sensor is coplanar, within a tolerance of + I”, with the plane of
-
the collector aperture. It shall not cast a shadow onto the collector aperture at any time during the test period. The
pyranometer shall be mounted so as to receive the same levels of direct, diffuse and reflected solar radiation as
are received by the collector.
For outdoor testing, the pyranometer shall be mounted at the midheight of the collector. The body of the
pyranometer and the emerging leads or the connector shall be shielded to minimize solar heating of the electrical
connections. Care shall also be taken to minimize energy reflected and reradiated from the solar collector onto the
pyranometer. Poles that can cast a shadow on the pyranometer shall be avoided.
For indoor testing, pyranometers may be used to measure the distribution of simulated solar irradiance over the
collector aperture, using a grid of maximum spacing 150 mm. The pyranometers shall be mounted and protected
as for outdoors testing. Alternatively, other types of radiation detector may be used, provided that they have been
calibrated for simulated solar radiation.
6.1.6 Pyranometer calibration interval
Pyranometers shall be calibrated for solar response within 12 months preceding the collector tests. Any change
of more than 1 % over a 12-month period shall warrant the use of more frequent calibration or replacement of the
instrument. If the instrument is damaged in any significant manner, it shall be recalibrated or replaced.
6.2 Longwave radiation measurement
6.2.1 Pyrgeometer
A pyrgeometer mounted in the plane of the collector shall be used to measure longwave irradiance.
6.2.2 Precautions for effects of temperature gradient
The pyrgeometer used during the tests shall be placed in the same plane as the collector absorber and allowed
to equilibrate for at least 30 min before measurements commence.
6.2.3 Precautions for effects of humidity and moisture
The pyrgeometer shall be provided with a means of preventing accumulation of moisture that may condense on
surfaces within the instrument and affect its reading. An instrument with a desiccator that can be inspected is
required. The condition of the desiccator shall be observed prior to and following each collector test.
6.2.4 Precautions for effects of solar heating
The dome of the pyrgeometer used to measure longwave irradiance shall be ventilated to minimize the influence
of solar heating effects.
6.2.5 Pyrgeometer calibration interval
The pyrgeometer shall be calibrated within 12 months preceding the tests. Any change of more than 5 y0 over a
12-month period shall warrant the use of more frequent calibration or replacement of the instrument. If the in-
strument is damaged in any significant manner, it shall be recalibrated or replaced.
6.3 Temperature measurements
The temperature measurements required for solar collector testing are the fluid temperature at the collector inlet,
the fluid temperature difference between the outlet and inlet of the collector, and the ambient air temperature.
The required accuracy and the environment for these measurements differ, and hence the transducer and
associated equipment may be different.
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IS0 9806-3: 1995(E)
6.3.1 Measurement of heat transfer fluid inlet temperature (tin)
6.3.1 .I Required accuracy
The temperature (fin) of the heat transfer fluid at the collector inlet shall be measured to an accuracy of + 0,l “C,
-
but in order to verify that the temperature is not drifting with time, a very much better resolution of the tempera-
ture signal to + 0,02 “C is required.
-
6.3.1.2 Mounting of sensors
The transducer for temperature measurement shall be mounted at no more than 200 mm from the collector inlet
and insulation shall be placed both upstream and downstream of the transducer. If it is necessary to position the
transducer more than 200 mm from the collector, then a test shall be made to verify that the measurement of fluid
temperature is not affected.
To ensure mixing of the fluid at the position of temperature measurement, a bend in the pipework, an orifice or
a fluid-mixing device shall be placed upstream of the transducer, and the transducer probe shall point upstream in
a pipe where the flow is rising (to prevent air from being trapped near the sensor), as shown in figure 1.
6.3.2 Determination of heat transfer fluid temperature difference (AT)
6.3.2.1 Required accuracy
The difference between the collector outlet and inlet temperatures (AT) shall be determined to an accuracy of
+ 0,l K. Accuracies approaching + 0,02 K can be achieved with modern well-matched and calibrated transducers,
hence it is possible to measure temperature differences down to 1 K with a reasonable accuracy. However tem-
perature differences less than 2 K should be avoided in order to minimize errors.
Dimensions in
millimetres
Temperature transducer
VP, AT)
Pipework bend
or mixing device
Temperature tra
(tin, AT)
Solar collector
or mixing device
Recommended transducer positions for measuring the heat transfer fluid inlet and outlet
Figure 1 -
temperatures
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0 IS0 IS0 9806=3:1995(E)
6.3.3 Measurement of surrounding air temperature (t,)
6.3.3.1 Required accuracy
The ambient air temperature (t,) shall be measured to an accuracy of + 0,l “C. The dew point temperature tdP shall
-
be determined to an accuracy of + - 0,5 “C.
6.3.3.2 Mounting of sensors
The transducer for measuring the ambient air temperature shall be mounted in the outlet of the artificial wind
generator. The transducer shall be shielded from direct and reflected solar radiation. One additional sensor should
be used to measure the ambient air temperature in the back of the collector, in order to ensure that the ambient
air temperature is uniform around the collector and to determine a representative average reading.
The temperature of the air flow out of the wind generator shall not deviate from the ambient air temperature more
than + 1 “C.
-
6.4 Collector fluid flowrate measurements
Mass flowrates may be measured directly or, alternatively, they may be determined from measurements of
volumetric flowrate and temperature.
The accuracy of the liquid flowrate measurement shall be equal to or better than + 1 % of the measured value,
in mass units per unit time.
The flowmeter shall be calibrated over the range of fluid flowrates and temperatures to be used during collector
testing.
temperature of the fluid in volumetric flowmete rs must be known with sufficient accuracy to ensure that mass
NOTE 4 The
e determined within the limits specified above.
flowrates can b
The direction of flow through the meter should be horizontal or rising, in order to avoid air accumulation.
6.5 Surrounding air speed
The heat loss from a collector increases with increasing air speed (u) over the collector. By controlling the wind
speed over the collector with an artificial wind generator as specified in 5.9, it is possible to define clearly the
conditions under which the tests are performed.
6.5.1 Required accuracy
The speed of the surrounding air over the front surface of the collector shall be measured to an accuracy of
+ 10 %.
-
Under outdoor conditions the surrounding air speed is seldom constant and gusting frequently occurs. The
measurement of an average air speed is therefore required during the test period. This may be obtained either by
an arithmetic average of sampled values or by a time integration over the test period.
6.5.2 Mounting of sensors
To account for air speed variations from one end of the collector to the other, a series of measurements shall be
taken at a distance of 100 mm in front of the collector aperture, at nine positions equally spaced over the collector
area. An average value shall then be determined. For a collector that does not have back insulation or is not
mounted on a simulated roof surface, the air speed shall be measured over the front and back surfaces. The av-
erage air speed over the front and back surfaces shall be used in the data correlation.
During a test, the air speed shall be monitored at a convenient point that has been calibrated relative to the mean
air speed over the collector. The anemometer shall not cast a shadow on the collector during the tests.
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I '
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IS0 9806-3:1995(E)
66 . Pressure measurements
The heat transfer fluid pressure at the collector inlet and the pressure drop across the collector shall be measured
with a device having an accuracy of + 3,5 kPa. If the collector is supplied in modules, the pressure drop shall be
specified per module. For strip absorbers, the pressure shall be specified per running metre of strip.
6.7 Elapsed time
Elapsed time shall be measured to an accuracy of + 0,2 %.
6.8 Instrumentation/data recorders
In no case shall the smallest scale division of the instrument or instrument system exceed twice the specified
accuracy. For example, if the specified accuracy is + 0,l “C, the smallest scale division shall not exceed
+ 0,2 “C.
-
Analog and digital recorders shall have an accuracy equal to or better than + 0,5 % of the full-scale reading and
have a time constant of 1 s or less. The peak signal indication shall be between 50 % and 100 % of full scale.
Digital techniques and electronic integrators shall have an accuracy equal to or better than + I,0 % of the meas-
-
ured value.
The input impedance of recorders shall be greater than 1000 times the impedance of the sensors or IO Ma,
whichever is higher.
The sampling interval shall be at most 30 s.
6.9 Collector area
The collector area (gross or absorber) shall be measured to an accuracy of + O,l%.
6.10 Collector fluid capacity
The fluid capacity of the collector, expressed as an equivalent mass of the heat transfer fluid used for the test,
shall be measured to an accuracy of at least --t 10 %.
Measurements shall be made by weighing the collector when empty and again when filled with fluid.
7 Test installation
7.1 General consideration
Examples of test configurations for testing solar collectors employing liquid as the heat transfer fluid are shown
in figures 2 and 3. These are schematic only, and are not drawn to scale.
7.2 Heat transfer fluid
The heat transfer fluid used for collector testing may be water or a fluid recommended by the collector manufac-
turer. The specific heat capacity and density of the fluid used shall be known to within + 1 % over the range of
fluid temperatures used during the tests. These values are given for water in annex D.
The mass flowrate of the heat transfer fluid shall be the same throughout the test sequence used to determine
the thermal efficiency curve, time constant and, if any, incident angle modifiers.
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IS0 9806-3: 1995(E)
/A\
Temperature
In1
Qrrounding air
Air vent
sensor (t,)
------ature sensor
F Insulated 1
pipe
Temperature
Artificial wind
1 Heater/cooler for
primary t emperature
control
Secondary
temperature
regulator
Bypass valve
Flowmeter
Sight glass
Safety
Flow control
Pump
4
valve
F
Filter
(200 pm)
Expansi on
tank
~
Example of a closed test loop
Figure 2 -
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IS0 9806-3: 1995(E)
Constant
ir vent
head tank
Artificial wind
Flow control
0
Balance
Figure 3 - Example of an open test loop
7.3 Pipework and fittings
The piping used in the loop shall be resistant to corrosion. If nonaqueous fluids are used, then compatibility with
system materials shall be confirmed before the tests commence.
Pipe lengths shall generally be kept short. In particular, the length of piping between the outlet of the fluid tem-
perature regulator and the inlet to the collector shall be minimized, to reduce the effects of the environment on
the inlet temperature of the fluid. 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 cover.
Pipework between the temperature-sensing points and the collector (inlet and outlet) shall be protected with in-
sulation and reflective weatherproof covers extending beyond the positions of the temperature sensors, such that
the calculated temperature gain or loss along either pipe portion does not exceed 0,Ol K under test conditions.
Flow-mixing devices such as pipe bends are required immediately upstream of temperature sensors (see 6.3).
A short length of transparent tube shall be installed in the fluid loop so that air bubbles and any other contaminants
will be observed if present. The transparent tube shall be placed close to the collector inlet but shall not influence
10
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0 IS0
IS0 9806=3:1995(E)
the fluid inlet temperature control or temperature measurements. A variable area flowmeter is convenient for this
purpose, as it simultaneously gives an independent visual indication of the flowrate.
of the coll
...
SLOVENSKI STANDARD
SIST ISO 9806-3:1997
01-marec-1997
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Test methods for solar collectors -- Part 3: Thermal performance of unglazed liquid
heating collectors (sensible heat transfer only) including pressure drop
Méthodes d'essai des capteurs solaires -- Partie 3: Performance thermique des capteurs
non vitrés à liquide (transfert de chaleur appréciable seulement), chute de pression
incluse
Ta slovenski standard je istoveten z: ISO 9806-3:1995
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
SIST ISO 9806-3:1997 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 9806-3:1997
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SIST ISO 9806-3:1997
INTERNATIONAL
IS0
STANDARD
9806-3
First edition
1995-12-15
Test methods for solar collectors -
Part 3:
Thermal performance of unglazed liquid
heating collectors (sensible heat transfer only)
including pressure drop
M&hodes d’essai des capteurs solaires -
Partie 3: Performance thermique des capteurs non vitrks a liquide
(transfert de chaleur apprkiable seulement), chute de pression in&se
Reference number
IS0 9806-3: 1995(E)
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SIST ISO 9806-3:1997
IS0 9806-3: 1995(E)
Contents
Page
1
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
4 Symbols and units .
............................................... 2
5 Collector mounting and location
4
6 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
7 Test installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8 Outdoor steady-state efficiency test
15
9 Steady-state efficiency test using a solar irradiance simulator
10 Determination of the effective thermal capacity and time constant
16
of a collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 18
11 Determination of the pressure drop across a collector
Annexes
Format sheets for test data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A
B Collector incident angle modifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Unglazed solar collector characteristics . 33
C
................................................................ 35
D Properties of water
............................................................................ 36
E Bibliography
0 IS0 1995
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 Cl-i-1 211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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SIST ISO 9806-3:1997
0 IS0
IS0 9806=3:1995(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
(IEC) 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 9806-3 was prepared by Technical Committee
ISO/TC 180, Solar energy, Subcommittee SC 5, Collectors and other
components.
IS0 9806 consists of the following parts, under the general title Test
methods for solar collectors:
- Part 7: Thermal performance of glazed liquid heating collectors in-
cluding pressure drop
- Part 2: Qualification test procedures
- Part 3: Thermal performance of unglazed liquid heating collectors
(sensible heat transfer only) including pressure drop
- Part 4: Thermal performance of air or gas heating collectors
Annex A forms an integral part of this part of IS0 9806. Annexes B, C, D
and E are for information only.
. . .
III
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SIST ISO 9806-3:1997
INTERNATIONAL STANDARD 0 Iso IS0 9806-3: 1995(E)
Test methods for solar collectors -
Part 3:
Thermal performance of unglazed liquid heating collectors
(sensible heat transfer only) including pressure drop
1 Scope
1.1 This part of IS0 9806 establishes methods for determining the thermal performance of unglazed liquid
heating solar collectors.
1.2 This part of IS0 9806 contains methods for conducting tests outdoors under natural solar irradiance and
simulated wind and for conducting tests indoors under simulated solar irradiance and wind.
1.3 This part of IS0 9806 is not applicable to those collectors in which a thermal storage unit is an integral part
of the collector to such an extent that the collection process cannot be separated for the purpose of making
measurements of these two processes.
1.4 This part of IS0 9806 is not applicable to collectors in which the heat transfer fluid can change phase, nor
is it applicable to collectors affected by condensation of water vapour from the ambient air.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part
of IS0 9806. 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 9806 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 9060:1990, Solar energy - Specification and classification of instruments for measuring hemispherical solar
and direct solar radiation.
IS0 9806-I :I 994, Test methods for solar collectors - Part 7: Thermal performance of glazed liquid heating col-
lectors including pressure drop.
Reference solar spectral irradiance at the ground at different receiving conditions
IS0 9845-l : 1992, Solar energy -
- Part 7 : Direct normal and hemispherical solar irradiance for air mass ?,5.
Calibration of a pyranometer using a pyrheliometer.
IS0 9846: 1993, Solar energy -
Calibration of field pyranometers by comparison to a reference pyranometer.
IS0 9847: 1992, Solar energy -
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SIST ISO 9806-3:1997
0 IS0
IS0 9806-3: 1995(E)
- Recommended practice for use.
ISO/TR 9901 :I 990, Solar energy - Field pyranometers
WMO, Guide to Meteorological Instruments and Methods of Observation, 5th ed., WMO-8, Secretariat to the
World Meteorological Organization, Geneva, 1983, Chapter 9.
3 Definitions
For the purposes of this part of IS0 9806, the definitions given in IS0 9806-I and the following definitions apply.
3.1 irradiation: Incident energy per unit area of a surface, found by integration of irradiance over a specified time
interval, often an hour or a day.
NOTES
Irradiation is normally expressed in megajoules per square metre (MJ/m’) over a specified time interval.
2 Solar irradiation is often termed “radiant exposure” or “insolation”. The use of these terms is deprecated.
3.2 longwave radiation; thermal radiation: Radiation at wavelengths greater than 3 pm, typically originating
from sources at terrestrial temperatures (e.g. ground and other terrestrial objects).
33 . turbulence level: Root mean square velocity fluctuation divided by the mean velocity.
34 . unglazed solar collector: Collector without a cover over the absorber.
4 Symbols and units
The symbols and their units used in this part of IS0 9806 are given in annex A.
5 Collector mounting and location
5.1 General
Collectors tested in accordance with this part of IS0 9806 shall be mounted in accordance with 5.2 to 5.9. The
mounting arrangement shall be reported with the results in the format sheets.
Full-size collector modules or collector arrays typical of full-size installations shall be tested, because the edge
losses of small collectors may significantly reduce their overall performance. A minimum collector gross area of
3 m* is recommended.
5.2 Collector mounting frame
The collector shall be mounted in the manner specified by the manufacturer. The collector mounting frame shall
in no way obstruct the aperture of the collector, and shall not significantly affect the back or side insulation, unless
otherwise specified (for example, when the collector is part of an integrated roof array). The collector shall be
mounted such that the lower edge is not less than 0,5 m above the local ground surface.
If mounting instructions are not specified, the collector shall be mounted on an insulated backing of conductance
(2 + 0,5) W/(m* K) and the upper surface painted matt white and ventilated at the back. Collectors designed to
be-mounted directly on standard roofing material may be mounted over a simulated roof section.
Collector arrays constructed from pipe or strip components shall be mounted with the pipes (or strips) spaced
IO mm or one diameter (width of strip) apart, whichever is smaller. If a different pipe or strip spacing is specified
in the manufacturer’s installation instructions, then the recommended spacing shall be used. If the collector is
delivered with mounting spacers or any device fixing the spacing of the pipes (or strips), then the collector shall
be tested as delivered and its geometry shall be reported in the test report.
2
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IS0 9806=3:1995(E)
Currents of warm air, such as those which rise up the walls of a building, shall not be allowed to pass over the
collector. Where collectors are tested on the roof of a building, they shall be located at least 2 m away from the
roof edge.
5.3 Collector test module size
The performance of some forms of unglazed solar collectors is a function of module size. If the collector is supplied
then sufficient of the modules shall be linked together (in series or in
in fixed units of area greater than 1 m*,
If the collector is supplied in the form of strips,
parallel) to give a test system absorber surface of at least 3 m*.
the minimum built-up module area shall be 3 m* (gross area).
5.4 Tilt angle
The collector shall be tested at tilt angles such that, during the test period, the angle of incidence with direct solar
radiation, 6, is less than 30” or at angles of tilt such that the incident angle modifier for the collector varies by less
than + 2 % from its value at normal incidence. Before deciding on a tilt angle, it may be necessary to check the
incident angle modifier at two angles prior to commencing the tests (see annex B).
NOTE 3 For most unglazed collectors the influence of tilt angle and radiation angle of incidence on collector efficiency is
small, and unglazed collectors are commonly installed at low inclinations. However, care must be taken to avoid air locks. Ab-
sorbers made of separate parallel tubes may have an angle of incidence response that increases with angle of incidence.
5.5 Collector orientation outdoors
The collector may be mounted outdoors in a fixed position facing the equator, but this will result in the time
available for testing being restricted by the acceptable range of incidence angles (see 8.6). A more versatile ap-
proach is to move the collector to follow the sun in azimuth, using manual or automatic tracking.
5.6 Shading from direct solar irradiance
The location of the test stand shall be such that no shadow is cast on the collector during the test.
5.7 Diffuse and reflected solar irradiance
5.7.1 Outdoors
For the purposes of analysis of outdoor test results, solar irradiance not coming directly from the sun’s disc is
assumed to come isotropically from the hemispherical field of view of the collector. In order to minimize the errors
resulting from this approximation, the collector shall be located where there will be no significant solar radiation
reflected onto it from surrounding buildings or surfaces during the tests, and where there will be no significant
obstructions in the field of view. Not more than 5 % of the collector’s field of view 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 surface such as grass, weathered concrete or chippings is not usually high enough
to cause problems during collector testing. Surfaces to be avoided in the collector’s field of view include large
expanses of glass, metal or water.
5.7.2 Solar irradiance simulator
In most solar simulators the simulated beam approximates direct solar irradiance only. In order to simplify the
measurement of simulated irradiance, it is necessary to minimize reflected irradiance. This can be achieved by
painting all surfaces in the test chamber with a dark (low reflectance) paint.
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IS0 9806-3:1995(E)
5.8 Longwave irradiance
5.8.1 Outdoors
The temperature of surfaces adjacent to the collector shall be as close as possible to that of the ambient air in
order to minimize the influence of longwave radiation from surrounding surfaces. For example, the outdoor field
of view of the collector should not include chimneys, cooling towers hot roof surfaces or hot exhausts.
5.8.2 Solar irradiance simulator
For indoor testing, the collector shall be shielded from hot surfaces such as radiators, air-conditioning ducts and
machinery, and from cold surfaces such as windows and external walls. Shielding is important both in front of and
behind the collector. For unglazed collectors the major difference between outdoor and indoor conditions is the
longwave thermal irradiance. The longwave irradiance in a simulator shall not exceed the limits specified in 9.2.
5.9 Surrounding air speed
The performance of unglazed collectors is sensitive to air speed adjacent to the collector. In order to maximize the
reproducibility of results, collectors shall be mounted such that air can freely pass over the aperture, exposed back
and sides of the collector. Collectors designed for integration into a roof may have their backs protected from the
wind; if so, this shall be reported with the test results.
The average surrounding air speed at a distance of 100 mm above and parallel to the collector aperture shall be
within the range I15 m/s to 4 m/s, subject to the tolerance specified in table 2 (see 8.5). An artificial wind generator
shall be used to provide a turbulence level in the range 20 % to 40 % to simulate natural wind conditions. The
turbulence level shall be checked at the leading edge of the collector 100 mm above the collector surface. The
turbulence level shall be monitored using a linearized hot wire anemometer with a frequency response of at least
100 Hz. If the absorber is not mounted directly on a roof or a sheet of backing material, the surrounding air speed
must be controlled and monitored at the front and back of the absorber.
6 Instrumentation
6.1 Solar radiation measurement
6.1 .I Pyranometer
A class I (in accordance with IS0 9060) pyranometer shall be used to measure the global shortwave radiation from
both the sun and the sky. The recommended practice for use given in lSO/TR 9901 shall be observed.
6.1.2 Precautions for effects of temperature gradient
placed in a typical test position and allowed to equilibrate for at
The pyra nometer used during the tests shall be
least 30 min before measurements commence.
6.1.3 Precautions for effects of humidity and moisture
The pyranometer shall be provided with a means of preventing accumulation of moisture that may condense on
surfaces within the instrument and affect its reading. An instrument with a desiccator that can be inspected is
required. The condition of the desiccator shall be observed prior to and following each collector test.
Precautions for infrared radiation effects on pyranometer accuracy in simulator tests
6.1.4
Pyranometers used to measure the irradiance of a solar irradiance simulator shall be mounted in such a way as
to minimize the effects on its readings of the infrared radiation of wavelength above 3 pm from the simulator light
source.
4
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SIST ISO 9806-3:1997
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IS0 9806-3: 1995(E)
6.1.5 Mounting of pyranometer
The pyranometer shall be mounted such that its sensor is coplanar, within a tolerance of + I”, with the plane of
-
the collector aperture. It shall not cast a shadow onto the collector aperture at any time during the test period. The
pyranometer shall be mounted so as to receive the same levels of direct, diffuse and reflected solar radiation as
are received by the collector.
For outdoor testing, the pyranometer shall be mounted at the midheight of the collector. The body of the
pyranometer and the emerging leads or the connector shall be shielded to minimize solar heating of the electrical
connections. Care shall also be taken to minimize energy reflected and reradiated from the solar collector onto the
pyranometer. Poles that can cast a shadow on the pyranometer shall be avoided.
For indoor testing, pyranometers may be used to measure the distribution of simulated solar irradiance over the
collector aperture, using a grid of maximum spacing 150 mm. The pyranometers shall be mounted and protected
as for outdoors testing. Alternatively, other types of radiation detector may be used, provided that they have been
calibrated for simulated solar radiation.
6.1.6 Pyranometer calibration interval
Pyranometers shall be calibrated for solar response within 12 months preceding the collector tests. Any change
of more than 1 % over a 12-month period shall warrant the use of more frequent calibration or replacement of the
instrument. If the instrument is damaged in any significant manner, it shall be recalibrated or replaced.
6.2 Longwave radiation measurement
6.2.1 Pyrgeometer
A pyrgeometer mounted in the plane of the collector shall be used to measure longwave irradiance.
6.2.2 Precautions for effects of temperature gradient
The pyrgeometer used during the tests shall be placed in the same plane as the collector absorber and allowed
to equilibrate for at least 30 min before measurements commence.
6.2.3 Precautions for effects of humidity and moisture
The pyrgeometer shall be provided with a means of preventing accumulation of moisture that may condense on
surfaces within the instrument and affect its reading. An instrument with a desiccator that can be inspected is
required. The condition of the desiccator shall be observed prior to and following each collector test.
6.2.4 Precautions for effects of solar heating
The dome of the pyrgeometer used to measure longwave irradiance shall be ventilated to minimize the influence
of solar heating effects.
6.2.5 Pyrgeometer calibration interval
The pyrgeometer shall be calibrated within 12 months preceding the tests. Any change of more than 5 y0 over a
12-month period shall warrant the use of more frequent calibration or replacement of the instrument. If the in-
strument is damaged in any significant manner, it shall be recalibrated or replaced.
6.3 Temperature measurements
The temperature measurements required for solar collector testing are the fluid temperature at the collector inlet,
the fluid temperature difference between the outlet and inlet of the collector, and the ambient air temperature.
The required accuracy and the environment for these measurements differ, and hence the transducer and
associated equipment may be different.
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SIST ISO 9806-3:1997
IS0 9806-3: 1995(E)
6.3.1 Measurement of heat transfer fluid inlet temperature (tin)
6.3.1 .I Required accuracy
The temperature (fin) of the heat transfer fluid at the collector inlet shall be measured to an accuracy of + 0,l “C,
-
but in order to verify that the temperature is not drifting with time, a very much better resolution of the tempera-
ture signal to + 0,02 “C is required.
-
6.3.1.2 Mounting of sensors
The transducer for temperature measurement shall be mounted at no more than 200 mm from the collector inlet
and insulation shall be placed both upstream and downstream of the transducer. If it is necessary to position the
transducer more than 200 mm from the collector, then a test shall be made to verify that the measurement of fluid
temperature is not affected.
To ensure mixing of the fluid at the position of temperature measurement, a bend in the pipework, an orifice or
a fluid-mixing device shall be placed upstream of the transducer, and the transducer probe shall point upstream in
a pipe where the flow is rising (to prevent air from being trapped near the sensor), as shown in figure 1.
6.3.2 Determination of heat transfer fluid temperature difference (AT)
6.3.2.1 Required accuracy
The difference between the collector outlet and inlet temperatures (AT) shall be determined to an accuracy of
+ 0,l K. Accuracies approaching + 0,02 K can be achieved with modern well-matched and calibrated transducers,
hence it is possible to measure temperature differences down to 1 K with a reasonable accuracy. However tem-
perature differences less than 2 K should be avoided in order to minimize errors.
Dimensions in
millimetres
Temperature transducer
VP, AT)
Pipework bend
or mixing device
Temperature tra
(tin, AT)
Solar collector
or mixing device
Recommended transducer positions for measuring the heat transfer fluid inlet and outlet
Figure 1 -
temperatures
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6.3.3 Measurement of surrounding air temperature (t,)
6.3.3.1 Required accuracy
The ambient air temperature (t,) shall be measured to an accuracy of + 0,l “C. The dew point temperature tdP shall
-
be determined to an accuracy of + - 0,5 “C.
6.3.3.2 Mounting of sensors
The transducer for measuring the ambient air temperature shall be mounted in the outlet of the artificial wind
generator. The transducer shall be shielded from direct and reflected solar radiation. One additional sensor should
be used to measure the ambient air temperature in the back of the collector, in order to ensure that the ambient
air temperature is uniform around the collector and to determine a representative average reading.
The temperature of the air flow out of the wind generator shall not deviate from the ambient air temperature more
than + 1 “C.
-
6.4 Collector fluid flowrate measurements
Mass flowrates may be measured directly or, alternatively, they may be determined from measurements of
volumetric flowrate and temperature.
The accuracy of the liquid flowrate measurement shall be equal to or better than + 1 % of the measured value,
in mass units per unit time.
The flowmeter shall be calibrated over the range of fluid flowrates and temperatures to be used during collector
testing.
temperature of the fluid in volumetric flowmete rs must be known with sufficient accuracy to ensure that mass
NOTE 4 The
e determined within the limits specified above.
flowrates can b
The direction of flow through the meter should be horizontal or rising, in order to avoid air accumulation.
6.5 Surrounding air speed
The heat loss from a collector increases with increasing air speed (u) over the collector. By controlling the wind
speed over the collector with an artificial wind generator as specified in 5.9, it is possible to define clearly the
conditions under which the tests are performed.
6.5.1 Required accuracy
The speed of the surrounding air over the front surface of the collector shall be measured to an accuracy of
+ 10 %.
-
Under outdoor conditions the surrounding air speed is seldom constant and gusting frequently occurs. The
measurement of an average air speed is therefore required during the test period. This may be obtained either by
an arithmetic average of sampled values or by a time integration over the test period.
6.5.2 Mounting of sensors
To account for air speed variations from one end of the collector to the other, a series of measurements shall be
taken at a distance of 100 mm in front of the collector aperture, at nine positions equally spaced over the collector
area. An average value shall then be determined. For a collector that does not have back insulation or is not
mounted on a simulated roof surface, the air speed shall be measured over the front and back surfaces. The av-
erage air speed over the front and back surfaces shall be used in the data correlation.
During a test, the air speed shall be monitored at a convenient point that has been calibrated relative to the mean
air speed over the collector. The anemometer shall not cast a shadow on the collector during the tests.
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IS0 9806-3:1995(E)
66 . Pressure measurements
The heat transfer fluid pressure at the collector inlet and the pressure drop across the collector shall be measured
with a device having an accuracy of + 3,5 kPa. If the collector is supplied in modules, the pressure drop shall be
specified per module. For strip absorbers, the pressure shall be specified per running metre of strip.
6.7 Elapsed time
Elapsed time shall be measured to an accuracy of + 0,2 %.
6.8 Instrumentation/data recorders
In no case shall the smallest scale division of the instrument or instrument system exceed twice the specified
accuracy. For example, if the specified accuracy is + 0,l “C, the smallest scale division shall not exceed
+ 0,2 “C.
-
Analog and digital recorders shall have an accuracy equal to or better than + 0,5 % of the full-scale reading and
have a time constant of 1 s or less. The peak signal indication shall be between 50 % and 100 % of full scale.
Digital techniques and electronic integrators shall have an accuracy equal to or better than + I,0 % of the meas-
-
ured value.
The input impedance of recorders shall be greater than 1000 times the impedance of the sensors or IO Ma,
whichever is higher.
The sampling interval shall be at most 30 s.
6.9 Collector area
The collector area (gross or absorber) shall be measured to an accuracy of + O,l%.
6.10 Collector fluid capacity
The fluid capacity of the collector, expressed as an equivalent mass of the heat transfer fluid used for the test,
shall be measured to an accuracy of at least --t 10 %.
Measurements shall be made by weighing the collector when empty and again when filled with fluid.
7 Test installation
7.1 General consideration
Examples of test configurations for testing solar collectors employing liquid as the heat transfer fluid are shown
in figures 2 and 3. These are schematic only, and are not drawn to scale.
7.2 Heat transfer fluid
The heat transfer fluid used for collector testing may be water or a fluid recommended by the collector manufac-
turer. The specific heat capacity and density of the fluid used shall be known to within + 1 % over the range of
fluid temperatures used during the tests. These values are given for water in annex D.
The mass flowrate of the heat transfer fluid shall be the same throughout the test sequence used to determine
the thermal efficiency curve, time constant and, if any, incident angle modifiers.
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SIST ISO 9806-3:1997
IS0 9806-3: 1995(E)
/A\
Temperature
In1
Qrrounding air
Air vent
sensor (t,)
------ature sensor
F Insulated 1
pipe
Temperature
Artificial wind
1 Heater/cooler for
primary t emperature
control
Secondary
temperature
regulator
Bypass valve
Flowmeter
Sight glass
Safety
Flow control
Pump
4
valve
F
Filter
(200 pm)
Expansi on
tank
~
Example of a closed test loop
Figur
...
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