ISO 9806-1:1994

IS0
INTERNATIONAL
9806-I
STANDARD
First edition
1994-12-01
Test methods for solar collectors -
Part 1:
Thermal performance of glazed liquid heating
collectors including pressure drop
Mkthodes d’essai des capteurs so/air-es -
Partie 7: Performance thermique des capteurs vitrks P liquide, chute de
pression incluse
Reference number
IS0 9806-I :1994(E)
IS0 9806-I :1994(E)
Contents
Page
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 Symbols and units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Collector mounting and location
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Instrumentation
. . . . . . . . . . . . . . . a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Test installation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8 Outdoor steady-state efficiency test
9 Steady-state efficiency test using a solar irradiance simulator
10 Determination of the effective thermal capacity and the time
. . . . . . . . . . . 22
constant of a collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11 Collector incident angle modifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 26
12 Determination of the pressure drop across a collector
Annexes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
A Format sheets for test data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
B Collector characteristics
C Solar spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D Properties of water . .
E Measurement of effective thermal capacity . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Biaxial incident angle modifiers . . 56
F
............................... ............................................ 58
G Bibliography
0 IS0 1994
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronrc or mechanrcal, Including photocopyrng and
microfilm, without permrssion rn writing from the publrsher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
II
0 IS0
IS0 9806-1:1994(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-I was prepared by Technical Committee
lSO/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
Annex A forms an integral part of this part of IS0 9806. Annexes B, C,
D, E, F and G are for information only.
. . .
III
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INTERNATIONAL STANDARD 0 IS0
IS0 9806-l :1994(E)
Test methods for solar collectors -
Part 1:
Thermal performance of glazed liquid heating collectors
including pressure drop
1 Scope
1.1 This part of IS0 9806 establishes methods for determining the thermal performance of glazed liquid heating
solar collectors. These tests are intended for use as part of the sequence of tests specified in IS0 9806-2.
1.2 This part of IS0 9806 provides test methods and calculation procedures for determining the steady-state and
quasi-steady-state thermal performance of solar collectors. It contains methods for conducting tests outdoors un-
der natural solar irradiance and for conducting tests indoors under simulated solar irradiance.
1.3 This part of IS0 9806 is not applicable to those collectors in which the 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 unglazed solar collectors nor is it applicable to tracking concen-
trating solar collectors. (See IS0 9806-3 for a test method for unglazed collectors.)
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.
Domestic water heating systems -
IS0 9459-l :I 993, Solar heating - Part 7: Performance rating procedure using
indoor test methods.
IS0 9806-2: -1) , Test methods for solar collectors - Part 2: Qualification test procedures.
I) To be published.
0 IS0
IS0 9806-I : 1994(E)
IS0 9806-3: -I), Test methods for solar collectors - Part 3: Thermal performance of unglazed liquid heating col-
lectors (sensible heat transfer only) including pressure drop.
Reference solar spectral iradiance 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.
IS0 9846: 1993, Solar energy - Calibration of a pyranometer using a pyrheliometer.
Calibration of field pyranometers by comparison to a reference pyranometer.
IS0 9847:1992, Solar energy -
ISOfTR 9901: 1990, Solar energy - Field pyranometers - Recommended practice for use.
WMO, Guide to Meteorological instruments and Methods of Observation, 5th edn., WMO-8, Secretariat to the
World Meteorological Organization, Geneva, 1983, Chapter 9.
3 Definitions
For the purposes of this part of IS0 9806, the following definitions apply.
3.1 absorber: Device within a solar collector for absorbing radiant energy and transferring this energy as heat into
a fluid.
3.2 absorber area (of a nonconcentrating solar collector): Maximum projected area of an absorber.
(of a concentrating solar collector): Surface area of the absor ,ber which is designed to absorb
33 . absorber
solar radiation.
3.4 angle of incidence (of direct solar radiation): Angle between the line joining the centre of the solar disc to
a point on an irradiated surface and the outward-drawn normal to the irradiated surface.
3.5 aperture: Opening of a solar collector, through which the unconcentrated solar radiation is admitted.
3.6 aperture area: Maximum projected area through which the unconcentrated solar radiation enters a collector.
collector area, gross: Maximum projected area of a complete solar collector, excluding any integral means
3.7
of mounting and connecting fluid pipework.
For an array or assembly of flat plate collectors, evacuated tubes or concentrating collectors, the gross collector
area includes the entire area of the array, i.e. also borders and frame.
3.8 collector, concentrating: Solar collector that uses reflectors, lenses or other optical elements to redirect and
concentrate the solar radiation passing through the aperture onto an absorber, the surface area of which is smaller
than the aperture area.
3.9 collector efficiency (of a solar thermal collector): Ratio of the energy removed from a specified reference
collector area (gross or absorber) by the heat transfer fluid over a specified time period, to the solar energy incident
on the collector for the same period, under steady-state conditions.
3.10 collector, evacuated tube [tubular]: Solar collector employing transparent tubing (usually glass), with an
between the tube wall and the absorber.
evacuated space
The absorber may consist of an inner tube of another shape, with means for removal of thermal energy. The
pressure in the evacuated space is usually less than 1 Pa.
3.11 collector, flat plate: Nonconcentrating solar collector in which the absorbing surface is essentially planar.
3.12 heat transfer fluid: Fluid that is used to transfer thermal energy between components in a system.
0 IS0
IS0 9806-I :1994(E)
3.13 irradiance: At a point on a surface, the radiant energy flux incident on an element of the surface, divided
by the area of that element.
lrradiance is normally expressed in watts per square metre.
3.14 irradiance, direct solar: Radiant energy flux, incident on a given plane receiving surface from a small solid
angle centred on the sun’s disc, divided by the area of that surface.
It is expressed in watts per square metre.
NOTE 1 The inclination of the surface should be specified, e.g. horizontal. If the plane is perpendicular to the axis of the solid
angle, then direct normal solar irradiance is received. For appropriate radiometers of modern design, the small solid angle
(field-of-view angle) is less than 6”.
given plane receiver surface, from a solid angle
3.15 irradiance, global solar: Radiant energy flux, incident on a
of 2X sr, divided by the area of that surface.
It is expressed in watts per square metre.
of the surface should be specified, e.g. horizontal. Solar irradiance is often termed “incident solar
NOTE 2 The inclination
intensity”, “instantaneous insolation “, “insolation” or “incident radiant flux density”. The use of these terms is deprecated.
3.16 optical air mass: Measure of the length of the path traversed by light rays from the sun through the at-
mosphere to sea-level, expressed with reference to the normal (vertical) path length.
3.17 pyranometer: Radiometer designed for measuring the irradiance on a plane receiving surface which results
from the radiant fluxes incident from the hemisphere above within the wavelength range of 0,3 pm to 3 pm.
3.18 pyrgeometer: Instrument for determining the irradiance on a plane receiving surface which results from the
radiant flux incident from the hemisphere above within the wavelength range of approximately 3 pm to 50 pm.
atmospheric longwave rad iation and is only nomi nal. The spectral re sponse
NOTE 3 This spectral range is similar to that of
used for the domes which protect each receiving surface.
of a pyrgeometer depends largely on the material
3.19 pyrheliometer: Instrument using a collimated detector for measuring the direct (beam) radiation received
from a solid angle centred on the sun’s disc, on a plane perpendicular to the axis of the solid angle.
The output of the instrument can be read as either irradiance or irradiation.
NOTE 4 pyrheliomete r sho uld be approximately constant in the wavelength range of 0,3 pm to
The spectral response of a
be less than 6”. It is synonymous with
and its a cceptance angle should the deprecated term “actinometer”.
3 pm,
3.20 radiant energy: Energy emitted, transferred or received as radiation.
3.21 radiant energy flux: Power emitted, transferred or received as radiation.
3.22 radiation: Phenomenon of energy transfer in the form of electromagnetic waves.
3.23 radiometer: Instrument used for measuring radiation.
The output of the instrument can be read as either irradiance or irradiation.
nt energy simulating solar radiation, usually an electric
3.24 solar irradiance simulator: Artificial source of radia
lamp or an a rray of such lamps.
3.25 solar thermal collector: Device designed to absorb solar radiation and to transfer the thermal energy so
gained to a fluid passing through it.
NOTE 5 Sometimes called “panel”, the use of which is deprecated to avoid potential confusion with photovoltaic panels.
@a IS0
IS0 9806=1:1994(E)
3.26 time constant: Time required for a system whose performance can be approximated by a first-order dif-
ferential equation, to have its output changed by 63,22 % of its final change in output following a step change in
input.
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
The way in which a collector is mounted will influence the results of thermal performance tests. Collectors tested
in accordance with this part of IS0 9806 shall therefore be mounted in accordance with 5.2 to 5.8.
Full-size collector modules shall be tested, because the edge losses of small collectors may significantly reduce
their overall performance.
5.2 Collector mounting frame
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), an open mounting structure shall be used which allows air to circulate freely around the front and back of
the collector. The collector shall be mounted such that the lower edge is not less than 0,5 m above the local
ground surface.
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 Tilt angle
In order to facilitate international comparisons of test results, the collector shall be mounted such that the angle
of tilt of the aperture from the horizontal is:
latitude + 5” but not less than 30”.
-
rs may be tested at other tilt angles, as reco
Collect0 mme nded by manufacturers or specified for actual instal-
lations.
NOTE 6 For many collectors, the influence of tilt angle is small, but it can be an important variable for specialized collectors
such as those incorporating heat pipes.
5.4 Collector orientation
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 acceptance range of incidence angles. A more versatile approach is to
move the collector to follow the sun in azimuth, using manual or automatic tracking.
5.5 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.

0 IS0
IS0 9806=1:1994(E)
5.6 Diffuse and reflected solar irradiance
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. With some collector types, such as evacuated tubular collectors, it may be equally
important to minimize reflections on both the back and the front fields of view. Not more than 5 % of the collec-
tor’s field of view shall be obstructed, and it is particularly important to avoid buildings or large obstructions sub-
tending an angle of greater than approximately 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 collector testing. Surfaces to be avoided in the collector’s field of view include large
expanses of glass, metal or water.
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.
5.7 Thermal irradiance
The performance of some collectors is particularly sensitive to the levels of thermal irradiance.
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 thermal radiation. For example, the outdoor field of view of the collector should
not include chimneys, cooling towers or hot exhausts.
For indoor and simulator 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.
5.8 Wind
The performance of many collectors is sensitive to air speeds. In order to maximize the reproducibility of results,
collectors shall be mounted such that air can freely pass over the aperture, back and sides of the collector. The
mean wind speed, parallel to the collector aperture, should be between the limits specified in 8.3. Where
necessary, artificial wind generators shall be used to achieve these wind speeds.
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.
6 Instrumentation
6.1 Solar radiation measurement
6.1 .I Pyranometer
A class I (according to IS0 9060) pyranometer shall be used to measure the global short-wave radiation from both
the sun and the sky. The recommended practice for use given in lSO/rR 9901 should be observed.
0 IS0
IS0 9806-I : 1994(E)
6.1.1.1 Precautions for effects of temperature gradient
The pyranometer used during the test(s) shall be placed in a typical test position and allowed to equilibrate for at
least 30 min before data-taking commences.
6.1.1.2 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 daily measurement se-
quence.
Precautions for infrared radiation effects on pyranometer accuracy
6.1 .I .3
Pyranometers used to measure the irradiance of the 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.
6.1.1.4 Mounting of pyranometers outdoors
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 of 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.
Use of pyranometers in solar irradiance simulators
6.1.1.5
Pyranometers may be used to measure both the distribution of simulated solar irradiance over the collector aper-
ture and the variation in simulated irradiance with time (see 9.6.1). The pyranometers shall be mounted and pro-
tected as for outdoor testing. Alternatively, other types of radiation detector may be used, provided that they have
been calibrated for simulated solar radiation.
6.1 .I .6 Calibration interval
Pyranometers shall be calibrated for solar response within 12 months preceding the collector test(s) in accordance
with the procedure given in IS0 9846 or IS0 9847. Any change of more than + 1 % over a year 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. All calibrations shall be performed with respect to the
world radiometric reference (WRR) scale.
6.1.2 Measurement of the angle of incidence of direct solar radiation
A simple device for measuring the angle of incidence of direct solar radiation can be produced by mounting a
pointer normal to a flat plate on which graduated concentric rings are marked. The length of the shadow cast by
the pointer may be measured using the concentric rings and used to determine the angle of incidence. The device
should be positioned in the collector plane and to one side of the collector.

0 IS0
IS0 9806-I :1994(E)
The angle of incidence of dir ect solar radiatio
NOTE 7 n (6) may be calculated fr ‘om the solar hour angle (w), the collector tilt
and the latitude
angle (J?), the collector azimuth angle of the test s te (#, using the following relat Ions:
(Y)
case = (sin6 sin+ co@) - (sin6 cOS+ sir@ COSy) + (cosd cos$ co@ cost) + (cash sin4 sin/J cosy cosw) + (cosS sir@ sin7 sina)
where the solar declination 6 for day number n of the year is given by:
6 = 23,45 sin [360(284 + n)/365]
6.2 Thermal radiation measurement
6.2.1 Measurement of thermal irradiance outdoors
The variations of thermal irradiance outdoors are not normally taken into account for collector testing. However,
a pyrgeometer may be mounted in the plane of the collector aperture and to one side at midheight, to determine
the thermal irradiance at the collector aperture.
6.2.2 Determination of thermal irradiance indoors and in solar simulators
6.2.2.1 Measurement
The thermal irradiance may be measured using a pyrgeometer as indicated in 6.2.1 for outdoor measurements.
Pyrgeometers should be well ventilated in order to minimize the influence of solar or simulated solar irradiance.
For indoor testing, the thermal irradiance shall be determined with an accuracy of + IO W/m’.
6.2.2.2 Calculation
Provided that all sources and sinks of thermal radiation in the field of view of the collector can be identified, the
thermal irradiance at the collector aperture may be calculated using temperature measurements, surface emittance
measurements and radiation view factors.
The thermal irradiance incident on a collector surface (designated I), from a hotter surface (designated 2) is given
bY O&2 4, g.
(compared with that which would be present if surface 2 had
Or, more usefully, the additional thermal irradiance
is given by:
been a perfect black body at ambient temperature)
. . .
(1)
~W%7sT3
See annex A, clause A.1 for explanation of symbols. Radiation view factors are given in textbooks on radiation heat
transfer.
The thermal irradiance at the collector aperture may also be calculated from a series of measurements made for
small solid angles in the field of view. Such measurements can be made using a pyrheliometer with and without
a glass filter to identify the thermal component of the total irradiance.
6.3 Temperature measurements
Three temperature measurements are required for solar collector testing. These are the fluid temperature at the
collector inlet, the fluid temperature at the collector outlet, 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.
IS0 9806-I : 1994(E)
6.3.1 Measurement of heat transfer fluid inlet temperature (fin)
6.3.1 .I Required accuracy
The temperature of the heat transfer fluid at the collector inlet shall be measured to an accuracy of + 0,l “C, but
-
in order to check that the temperature is not drifting with time, a very much better resolution of the temperature
signal to + 0,02 “C is required.
NOTE 8 This resolution is needed for all temperatures used for collector testing (i.e. over the range 0 “C to 100 “C) which
is a particularly demanding accuracy for recording by data logger, as it requires a resolution of one part in 4 000 or a 12-bit digital
system.
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 around the pipework both upstream and downstream of the transducer. If it is
necessary to position the transducer more than 200 mm away 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
and 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)
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,
-
-
and hence it is possible to measure heat transfer fluid temperature differences of 1 K or 2 K with a reasonable
accuracy.
Dimensions in millimetres
Temperature transducer
( te, AT)
Pipework bend
or mixing device
Temperature trans
(tin, AT)
Solar collector
or mixing device
Recommended transducer positions for measuring the heat transfer fluid inlet and outlet
Figure 1 -
temperatures
0 IS0 IS0 9806-1:1994(E)
6.3.3 Measurement of surrounding air temperature (la)
6.3.3.1 Required accuracy
The ambient or surrounding air temperature shall be measured to an accuracy of + - 0,50 “C.
6.3.3.2 Mounting of sensors
For outdoor measurements the transducer shall be shaded 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 tem-
perature by more than + 1 “C.
-
6.4 Measurement of collector liquid flowrate
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 within rfr I,0 % of the measured value, in mass per unit
time.
The flowmeter shall be calibrated over the range of fluid flowrates and temperatures to be used during collector
testing.
in volumetric flowme ters should be known with sufficient accuracy to ensure that mass
NOTE 9 The temperature of the fluid
the limits specified.
flowrates can be determined to within
6.5 Wind velocity
The heat losses from a collector increase with increasing air speed over the collector, but the influence of wind
direction is not well understood. Measurements of wind direction are therefore not used for collector testing. The
relationship between the meteorological wind speed and the air speed over the collector depends on the location
of the test facility, so meteorological wind speed is not a useful parameter for collector testing. By using the wind
speed measured over the collector, it is possible to define clearly the conditions in which the tests were per-
formed.
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
& 0,5 m/s for both indoor and outdoor testing.
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.

0 IS0
IS0 9806=1:1994(E)
6.52 Mounting of sensors
During indoor testing, the air speed may vary from one end of the collector to the other. A series of air speed
measurements shall therefore be taken, at a distance of 100 mm in front of the collector aperture, at equally
spaced positions over the collector area. An average value shall then be determined. Air speed measurements
indoors in stable conditions shall be made before and after performance test points to avoid obscuring the collector
aperture.
When testing outdoors in locations where the mean wind speed lies below 3 m/s, an artificial wind generator shall
be used, and anemometer measurements made in the same way as for indoor testing. In windy locations, the
wind speed measurement shall be made near to the collector at the midheight of the collector. The sensor shall
not be shielded from the wind and it shall not cast a shadow on the collector during test periods.
6.5.3 Calibration
The anemometer shall be recalibrated at yearly intervals.
6.6 Pressure measurements
The heat transfer fluid pressure drop across the collector shall be measured with a device having an accuracy of
+ 3,5 kPa.
-
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.
Digital techniques and electronic integrators shall have an accuracy equal to or better than - + 1 ,O % of the meas-
ured value.
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.
The input impedance of recorders shall be greater than 1 000 times the impedance of the sensors or IO Ma,
whichever is higher.
6.9 Collector area
The collector area (absorber, gross or aperture) shall be measured to an accuracy of + 0,l %.
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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 + IO %.
Measurements may be made either by weighing the collector when empty and again when filled with fluid, or by
filling and emptying the collector to determine the mass of fluid which it will contain. The temperature of the fluid
should be kept within 20 “C of the ambient temperature.
d
0 IS0
IS0 9806=1:1994(E)
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.
Surrounding air
vent
temperature sensor
olar collector
Artificial wind
1 Heater/cooler for
primary temperature
control.
Pressure
JI
-. gauge
Bypass valve
+
Sight glass
Safety
Flow control
-
Pump
I valve
valve
2+
I
L
I
k
Filter
(200 pm)
Expansion
tank
Figure 2 - Example of a closed test loop
IS0 9806-I : 1994(E) CJ IS0
Constant
head tank
Ar
ge
Pump
-
Sight glass
a
I
\
I
-
Heater/cooler for
, \
primary temperature
Filter
control
(200 pm)
Figure 3 - Example of an open test loop
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
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temperatures used during the tests. These values are given for water in annex D. Some fluids may need to be
changed periodically to ensure that their properties remain well defined.
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 incident angle modifiers for a given collector.
7.3 Pipework and fittings
The piping used in the collector loop shall be resistant to corrosion and suitable for operation at temperatures up
to 95 “C. If nonaqueous fluids are used, then compatibility with system materials shall be confirmed.
0 IS0
IS0 9806=1:1994(E)
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 shall be protected by a reflective weatherproof coating.
Pipework between the temperature sensing points and the collector (inlet and outlet) shall be protected with in-
sulation and reflective weatherproof covers to 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
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.
An air separator and air vent shall be placed at the outlet of the collector, and at other points in the system where
air can accumulate.
placed upstream of the flow measuring device and the pump, in accordance with normal practice
Fil ters sha II be
nominal filte r size of 200 pm i s usua Ily adequate).
(a
7.4 Pump and flow control devices
The fluid pump shall be located in the collector test loop in such a position that the heat from it which is dissipated
in the fluid does not affect either the control of the collector inlet temperature or the measurements of the fluid
temperature rise through the collector.
may provide adequate flow
With some types of pump, a simple bypass loop and manually controlled needle valve
control. Where necessary, a proprietary flow control device may be added to stabilize
the mass flowrate.
The pump and flow controller shall be capable of maintaining the mass flowrate through the collector stable to
within k 1 % despite temperature variations, at any inlet temperature chosen within the operating range.
7.5 Temperature regulation of the heat transfer fluid
It is imperative that a collector test loop be capable of maintaining a constant collector inlet temperature at any
temperature level chosen within the operating range. Since the rate of energy collection in the collector is deduced
by measuring instantaneous values of the fluid inlet and outlet temperatures, it follows that small variations in inlet
temperature could lead to errors in the rates of energy collection deduced. It is particularly important to avoid any
drift in the collector inlet temperature.
Test loops shall therefore contain two stages of fluid inlet temperature control, as shown in figures 2 and 3. The
primary temperature controller shall be placed upstream of the flowmeter and flow controller. A secondary tem-
perature regulator shalt be used to adjust the fluid temperature just before the collector inlet. This secondary reg-
ulator should normally not be used to adjust the fluid temperature by more than + 2 K.
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8 Outdoor steady-state efficiency test
8.1 Test installation
The collector shall be mounted in accordance with the recommendations given in clause 5, and coupled to a test
loop as described in clause 7. The heat transfer fluid shall flow from the bottom to the top of the collector, or as
recommended by the manufacturer.
8.2 Preconditioning of the collector
Before being tested for performance, the collector shall have undergone the sequence of qualification tests
specified in IS0 9806-2.
IS0 9806-I : 1994(E)
The collector shall be visually inspected and any damage recorded.
The collector aperture cover shall be thoroughly cleaned.
If moisture has formed on the collector components, then the heat transfer fluid shall be circulated at approxi-
mately 80 “C for as long as is necessary to dry out the insulation and collector enclosure. If this form of precon-
ditioning is carried out, then it shall be reported with the test results.
The collector pipework shall be vented of trapped air by means of an air valve or by circulating the fluid at a high
flowrate, as necessary.
The fluid shall be inspected for entrained air or particles, by means of the transparent tube built into the fluid loop
pipework. Any contaminants shall be removed.
8.3 Test conditions
At the time of the test, the total solar irradiance at the plane of the collector aperture shall be greater than
800 W/m*.
The angle of incidence of direct solar radiation at the collector aperture shall be in the range in which the incident
angle modifier for the collector varies by no more than + 2 % from its value at normal incidence. For single glazed
flat plate collectors, this condition will usually be satisfied if the angle of incidence of direct solar radiation at the
collector aperture is less than 30 O. However, much lower angles may be required for particular designs. ln order
to characterize collector performance at other angles, an incident angle modifier may be determined (see
clause 1 I).
The average value of the surrounding air speed, taking into account spatial variations over the collector and
temporal variations during the test period, shall lie between 2 m/s and 4 m/s.
Unless otherwise recommended, the fluid flowrate shall be set at approximately 0,02 kg/s per square mare of
collector gross area. It shall be held stable to within + 1 % of the set value during each test period, and shall not
vary by more than + IO % of the set value from one test period to another.
In some collectors the recommended fluid flowrate may be close to the transition region between laminar and
turbulent flow. This may cause instability of the internal heat transfer coefficient and hence variations in meas-
urements of collector efficiency. In order to characterize such a collector in a reproducible way, it may be
necessary to use a higher flowrate, but this shall be clearly stated with the test results.
Measurements of fluid temperature difference of less than I,5 K shall not be included in the test results because
of the associated problems of instrument accuracy.
8.4 Test procedure
The collector shall be tested over its operating temperature range under clear sky conditions in order to determine
its efficiency characteristic.
Data points which satisfy the requirements given below shall be obtained for at least four fluid inlet temperatures
spaced evenly over the operating temperature range of the collector. One inlet temperature shall be selected such
that the mean fluid temperature in the collector lies within + 3 K of the ambient air temperature, in order to obtain
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an accurate determination of qo. (If water is the heat transfer fluid, 70 “C is usually adequate as a maximum tem-
perature.)
At least four independent data points shall be obtained for each fluid inlet temperature, to give a total of 16 data
points. If test conditions permit, an equal number of data points shall be taken before and after solar noon for each
fluid inlet temperature. The latter is not required if the collectors are moved to follow the sun in azimuth and alti-
tude using automatic tracking.
During a test, measurements shall be made as specified in 8.5. These may then be used to identify test periods
from which satisfactory data points can be derived.
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IS0 9806=1:1994(E)
8.5 Measurements
The following measurements shall be obtained:
the absorber area A, and the aperture area A,;
a) the gross collector area A,,
b) the fluid capacity;
c) the global solar irradiance at the collector aperture;
d) the diffuse solar irradiance at the collector aperture;
e) the angle of incidence of direct solar radiation (alternatively, this angle may be determined by calculation);
f) the surrounding air speed;
g) the surrounding air temperature;
h) the temperature of the heat transfer fluid at the collector inlet;
the temperature of the heat transfer fluid at the collector outlet;
i)
j) the flowrate of the heat transfer fluid.
8.6 Test period (steady-state)
The test period for a steady-state data point shall include a preconditioning period of at least 15 min with the
correct fluid measurement temperature at the inlet, followed by a steady-state measurement period of at least
15 min.
In all cases, the length of the steady-state measurement period shall be greater than four times the ratio of the
effective thermal capacity C of the collector to the thermal flowrate yizcr of the fluid through the collector (see
clause IO for determination of the effective thermal capacity).
A collector is considered to have been operating in steady-state conditions over a given measurement period if
none of the experimental parameters deviate from their mean values over the measurement period by more than
the limits given in table 1. To establish that a steady state exists, average values of each parameter taken over
successive periods of 30 s shall be compared with the mean value over the measurement period.
- Permitted deviation of measured parameters during a measurement period
...