SIST ISO 9806-1:1997
(Main)Test methods for solar collectors -- Part 1: Thermal performance of glazed liquid heating collectors including pressure drop
Test methods for solar collectors -- Part 1: Thermal performance of glazed liquid heating collectors including pressure drop
Establishes methods for determining the thermal performance of glazed liquid heating solar collectors; provides test methods and calculation procedures for determining the steady-state and quasi-steady-state thermal performance of solar collectors. Contains methods for conducting tests outdoors under natural solar irradiance and indoors under simulated solar irradiance. 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. Also not applicable to unglazed solar collectors nor is it applicable to tracking concentrating solar collectors.
Méthodes d'essai des capteurs solaires -- Partie 1: Performance thermique des capteurs vitrés à liquide, chute de pression incluse
Metode za preskus sprejemnikov sončne energije - 1. del: Termični učinek zasteklenih sprejemnikov s kapljevino kot prenosnikom toplote, vključno z določitvijo padca tlaka v sprejemniku
General Information
Standards Content (Sample)
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)
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IS0 9806-I :1994(E)
Contents
Page
1
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
4 Symbols and units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Collector mounting and location
5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Instrumentation
11
. . . . . . . . . . . . . . . a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Test installation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8 Outdoor steady-state efficiency test
19
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
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
51
C Solar spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
52
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
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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.
1
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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.
2
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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.
3
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@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.
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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.
5
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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.
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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.
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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
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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
relat
...
SLOVENSKI STANDARD
SIST ISO 9806-1:1997
01-marec-1997
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Test methods for solar collectors -- Part 1: Thermal performance of glazed liquid heating
collectors including pressure drop
Méthodes d'essai des capteurs solaires -- Partie 1: Performance thermique des capteurs
vitrés à liquide, chute de pression incluse
Ta slovenski standard je istoveten z: ISO 9806-1:1994
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
SIST ISO 9806-1:1997 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 9806-1:1997
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SIST ISO 9806-1:1997
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)
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SIST ISO 9806-1:1997
IS0 9806-I :1994(E)
Contents
Page
1
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
4 Symbols and units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Collector mounting and location
5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Instrumentation
11
. . . . . . . . . . . . . . . a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Test installation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8 Outdoor steady-state efficiency test
19
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
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
51
C Solar spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
52
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
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SIST ISO 9806-1:1997
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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SIST ISO 9806-1:1997
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.
1
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SIST ISO 9806-1:1997
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.
2
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SIST ISO 9806-1:1997
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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.
3
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SIST ISO 9806-1:1997
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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.
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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.
5
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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.
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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.
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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
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SIST ISO 9806-1:1997
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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 co
...
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