EN 12975-2:2006

SLOVENSKI STANDARD
01-maj-2006
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SIST EN 12975-2:2002
SIST EN 12975-2:2002/AC:2002
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Thermal solar systems and components - Solar collectors - Part 2: Test methods
Thermische Solaranlangen und ihre Bauteile - Kollektoren - Teil 2: Prüfverfahren
Installations solaires thermiques et leurs composants - Capteurs solaires - Partie 2 :
Méthode d'essai
Ta slovenski standard je istoveten z: EN 12975-2:2006
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 12975-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2006
ICS 27.160 Supersedes EN 12975-2:2001
English Version
Thermal solar systems and components - Solar collectors - Part
2: Test methods
Installations solaires thermiques et leurs composants - Thermische Solaranlangen und ihre Bauteile - Kollektoren -
Capteurs solaires - Partie 2 : Méthode d'essai Teil 2: Prüfverfahren
This European Standard was approved by CEN on 6 February 2006.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12975-2:2006: E
worldwide for CEN national Members.

Contents Page
Foreword .6
Introduction.7
1 Scope.8
2 Normative references.8
3 Terms and definitions.8
4 Symbols and units .9
5 Reliability testing of liquid heating collectors .12
5.1 General.12
5.2 Internal pressure tests for absorbers.13
5.2.1 Inorganic absorbers.13
5.2.2 Absorbers made of organic materials (plastics or elastomers) .14
5.3 High-temperature resistance test .16
5.3.1 Objective.16
5.3.2 Apparatus and procedure.16
5.3.3 Test conditions.17
5.3.4 Results.17
5.4 Exposure test.17
5.4.1 Objective.17
5.4.2 Apparatus and procedure.17
5.4.3 Test conditions.18
5.4.4 Results.18
5.5 External thermal shock test .19
5.5.1 Objective.19
5.5.2 Apparatus and procedure.19
5.5.3 Test conditions.19
5.5.4 Results.20
5.6 Internal thermal shock test.20

5.6.1 Objective.20
5.6.2 Apparatus and procedure.20
5.6.3 Test conditions.20
5.6.4 Results.21
5.7 Rain penetration test.21
5.7.1 Objective.21
5.7.2 Apparatus and procedure.21
5.7.3 Test conditions.22
5.7.4 Results.22
5.8 Freeze resistance test.22
5.8.1 Objective.22

5.8.2 Apparatus and procedure.23
5.8.3 Test conditions.23
5.8.4 Results.23
5.9 Mechanical load test.24
5.9.1 Positive pressure test of the collector .24
5.9.2 Negative pressure test of the collector .25
5.10 Impact resistance test (optional) .26
5.10.1 Objective.26
5.10.2 Apparatus and procedure.26
5.10.3 Test conditions.28
5.10.4 Results.28
5.11 Final inspection.28
5.12 Test report.28
6 Thermal performance testing of liquid heating collectors.28
6.1 Glazed solar collectors under steady state conditions (including pressure drop).28
6.1.1 Collector mounting and location .28
6.1.2 Instrumentation.30
6.1.3 Test installation.35
6.1.4 Outdoor steady-state performance test .39
6.1.5 Steady-state efficiency test using a solar irradiance simulator .43

6.1.6 Determination of the effective thermal capacity and the time constant of a collector .46
6.1.7 Collector incidence angle modifier.48
6.1.8 Determination of the pressure drop across a collector .52
6.2 Unglazed solar collectors under steady state conditions (including pressure drop) .52
6.2.1 Collector mounting and location .52
6.2.2 Instrumentation.53
6.2.3 Test installation.55
6.2.4 Outdoor steady state efficiency test.55
6.2.5 Steady-state efficiency test using a solar irradiance simulator .60
6.2.6 Determination of the effective thermal capacity and the time constant of a collector .61
6.2.7 Incidence angle modifier (optional).62
6.2.8 Determination of the pressure drop across a collector .64
6.3 Glazed and unglazed solar collectors under quasi-dynamic conditions.64
6.3.1 Collector mounting and location .64
6.3.2 Instrumentation.65
6.3.3 Test installation.66
6.3.4 Outdoor efficiency test.67
6.3.5 Determination of the effective thermal capacity.74
6.3.6 Collector incidence angle modifier.75
Annex A (normative) Schematics for durability and reliability tests.76
Annex B (normative) Durability and reliability test report sheets .87
B.1 Record of test sequence and summary of main results .87
B.2 Internal pressure test for inorganic absorbers.88
B.2.1 Technical details of collector.88

B.2.2 Test conditions.88
B.2.3 Test results.88
B.3 Internal pressure test for absorbers made of organic materials.89
B.3.1 Technical details of collector.89
B.3.2 Test conditions.89
B.3.3 Test results.90
B.4 High-temperature resistance test .91
B.4.1 Method used to heat collectors .91
B.4.2 Test conditions.91
B.4.3 Test results.91
B.5 Exposure test.92
B.5.1 Test conditions.92
B.5.2 Test results.92
B.5.3 Climatic conditions for all days during the test.93
B.5.4 Time periods in which irradiance and surrounding air temperature have values greater
than those specified in Table 4.94
B.5.5 Inspection results.95
B.6 External thermal shock test: .96
B.6.1 Test conditions.96
B.6.2 Test results.97
B.7 Internal thermal shock test: .98
B.7.1 Test conditions.98
B.7.2 Test results.99
B.8 Rain penetration test.100
B.8.1 Test conditions.100
B.8.2 Test results.100
B.9 Freeze resistance test.101
B.9.1 Collector type.101
B.9.2 Test conditions.101
B.9.3 Test results.102
B.10 Mechanical load test.103
B.10.1 Positive pressure test of the collector cover.103
B.10.2 Negative pressure test of fixings between the cover and the collector box .103
B.10.3 Negative pressure test of collector mountings .105
B.11 Impact resistance test using steel balls.106
B.11.1 Test conditions.106
B.11.2 Test procedure.106
B.11.3 Test results.106
B.12 Impact resistance test using ice balls.107
B.12.1 Test conditions.107
B.12.2 Test procedure.107
B.12.3 Test results.107
B.13 Final inspection results .108
Annex C (normative) Stagnation temperature of liquid heating collectors .109
C.1 General.109
C.2 Determination of stagnation temperature .109
Annex D (normative) Performance test report for glazed solar collectors .111
D.1 General.111
D.2 Solar collector description .111
D.3 Test results.113
Annex E (normative) Performance test report for unglazed solar collectors.116
E.1 General.116
E.2 Solar collector description .116
E.3 Test results.118
Annex F (normative) Modelling of the coefficients c to c of the collector model of 6.3. .121
1 6
Annex G (normative) Measurement of effective thermal capacity .123
G.1 Test installation.123
G.2 Indoor test procedure.123
G.2.1 General.123
G.2.2 Measurements.123
G.2.3 Calculation of the effective thermal capacity.123
G.2.4 Determination of effective thermal capacity from experimental data .124
G.3 Outdoor or solar irradiance simulator test procedure .125
Annex H (informative) Comparison of the collector model of 6.1 to the collector model of 6.3.126
Annex I (informative) Properties of water (see DIN V 4757-4:1995-11).127
I.1 Density of water (at 1 bar) in kg/m³.127
I.2 Specific heat capacity of water (at 1 bar) in kJ/(kg K).127
Annex J (informative) Performance test report summary for quasi dynamic test method.128
Annex K (informative) General guidelines for the assessment of uncertainty in solar collector
efficiency testing.130
K.1 Introduction.130
K.2 Measurement uncertainties in solar collector efficiency testing.130
Annex L (informative) Determination of the pressure drop across a collector .134
L.1 General.134
L.2 Test installation.134
L.3 Preconditioning of the collector .134
L.4 Test procedure.134
L.5 Measurements.135
L.6 Pressure drop caused by fittings.135
L.7 Test conditions.135
L.8 Calculation and presentation of results.135
Bibliography.136

Foreword
This European Standard (EN 12975-2:2006) has been prepared by Technical Committee CEN/TC 312
“Thermal solar systems and components”, the secretariat of which is held by ELOT.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by September 2006, and conflicting national standards shall be
withdrawn at the latest by September 2006.
This European Standard supersedes EN 12975-2:2001.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.
Introduction
This standard specifies test methods for determining the ability of a liquid heating solar collector to resist the
influence of degrading agents. It defines procedures for testing collectors under well-defined and repeatable
conditions.
This standard also provides test methods and calculation procedures for determining the steady-state and
quasi-dynamic thermal performance of glazed liquid heating solar collectors. It contains methods for
conducting tests outdoors under natural solar irradiance and natural and simulated wind and for conducting
tests indoors under simulated solar irradiance and wind.
This standard also provides methods for determining the thermal performance of unglazed liquid heating solar
collectors. Unglazed collectors are in most cases used for heating swimming pools or other low temperature
consumers. In general the collectors are put together on-site, connecting absorber strips with manifolds. Real
absorber areas are mostly between ten to one hundred square meters. For unglazed absorbers, readily
fabricated modules with a specific size are seldom used. Therefore, during the test, it should be checked that
a realistic flow pattern and flow velocity is used.
This standard also provides test methods and calculation procedures for determining the steady-state as well
as the all-day thermal performance parameters for liquid heating solar collectors, under changing weather
conditions. It contains methods for conducting tests outdoors during whole days and under stationary inlet
temperature conditions and natural solar irradiance and natural and/or simulated wind conditions. Important
effects for the all-day performance of the collector, as the dependence on incident angle, wind speed, diffuse
fraction of solar irradiance, thermal sky radiation and thermal capacity are taken into account. Dependence on
flowrate is not included in this standard.
Some of the advantages of the proposed extension of the present steady-state test methods of all-day testing
are:
− shorter and less expensive outdoor test, suitable for European climate conditions.
− much wider range of collectors can be tested with the same method.
− at the same time, a much more complete characterisation of the collector is achieved.
− collector model is still directly compatible with that of the present basic test standards, and only correction
terms are applied in this extended approach.
− all additions are based on long agreed collector theory.
− at any time, full backwards comparability to steady-state can be established by evaluating only periods of
the test days that correspond to steady-state test requirements.
� same test equipment can be used as for stationary testing with only minor changes, which will also
improve the accuracy of steady-state testing.
� commonly available standard PC software can be used for the parameter identification, such as
spreadsheets or more advanced statistical packages that have Multiple Linear Regression (MLR) as an
option.
1 Scope
This European Standard specifies test methods for validating the durability, reliability and safety requirements
for liquid heating collectors as specified in EN 12975-1. This standard also includes three test methods for the
thermal performance characterisation for liquid heating collectors.
It 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 from the storage process for the purpose of
making measurements of these two processes.
It is basically applicable to tracking concentrating collectors, thermal performance testing as given in 6.3
(quasi dynamic testing) is also applicable to most concentrating collector designs, from stationary non-imaging
concentrators as CPCs to high concentrating tracking designs. Parts of the solar radiation measurement
should be adjusted in case of a tracking collector and in case a pyrheliometer is used to measure beam
radiation.
Collectors that are custom built (built in; e.g. roof integrated collectors that do not compose of factory made
modules and are assembled directly on the place of installation) cannot be tested in their actual form for
durability, reliability and thermal performance according to this standard. Instead, a module with the same
structure as the ready collector may be tested. The module gross area should be at least 2 m . The test is
valid only for larger collectors than the tested module.
2 Normative references
The following referenced documents are indispensable for the application of this European Standard. For
dated references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 1991 (all parts), Eurocode 1: Actions on structures
EN 12975-1:2006, Thermal solar systems and components – Solar collectors – Part 1: General requirements
EN ISO 9488, Solar energy – Vocabulary (ISO 9488:1999)
ISO 9060, Solar energy – Specification and classification of instruments for measuring hemispherical solar
and direct solar radiation
3 Terms and definitions
For the purposes of this European Standard, the terms and definitions given in EN ISO 9488 apply.
4 Symbols and units
-2 -1
a heat loss coefficient at (T - T)=0 Wm K
m a
-2 -2
a temperature dependence of the heat loss coefficient Wm K
A absorber area of collector m
A
A aperture area of collector m
a
A gross area of collector m
G
AM optical air mass
-1
b collector efficiency coefficient (wind dependence) m s
u
b constant for the calculation of the incident angle modifier
o
-2 -1
b heat loss coefficient at (T - T)=0 Wm K
m a
-3 -1
b collector efficiency coefficient Wsm K
-2 -1
c heat loss coefficient at (T - T)=0 Wm K
m a
-2 -2
c temperature dependence of the heat loss coefficient Wm K
-3 -1
c wind speed dependence of the heat loss coefficient Jm K
-2 -1
c sky temperature dependence of the heat loss coefficient Wm K
-2 -1
c effective thermal capacity J m K
-1
c wind dependence in the zero loss efficiency sm
-1 -1
c specific heat capacity of heat transfer fluid Jkg K
f
-1
C effective thermal capacity of collector JK
D date YYMMDD
-2
E longwave irradiance (λ >3µm) Wm
L
-2
E longwave irradiance on an inclined surface outdoors Wm
β
-2
E longwave irradiance Wm
s
F radiation view factor
F´ collector efficiency factor
-2
G hemispherical solar irradiance Wm
-2
G* global hemispherical solar irradiance Wm
-2
G'' net irradiance Wm
-2
G direct solar irradiance (beam irradiance) Wm
b
-2
G diffuse solar irradiance Wm
d
LT local time h
K incidence angle modifier
θ
K incidence angle modifier for direct radiation
θ
b
K incidence angle modifier for diffuse radiation
θ
d
m thermally active mass of the collector kg
.
-1
mass flowrate of heat transfer fluid kgs
m
.
Q useful power extracted from collector W
.
Q power loss of collector W
L
SF safety factor
t time s
t ambient or surrounding air temperature °C
a
t atmospheric dew point temperature °C
dp
t collector outlet (exit) temperature °C
e
t collector inlet temperature        °C
in
t mean temperature of heat transfer fluid °C
m
t atmospheric or sky temperature °C
s
t stagnation temperature °C
stg
T absolute temperature K
T ambient or surrounding air temperature °C
a
* 2 -1
T reduced temperature difference ( = (t – t )/G*) m KW
m m a
T atmospheric or equivalent sky radiation temperature K
s
U measured overall heat loss coefficient of collector,
* -2 -1
with reference to T Wm K
m
U overall heat loss coefficient of a collector with uni-
L
-2 -1
form absorber temperature t Wm K
m
-1
u surrounding air speed ms
V fluid capacity of the collector m
f
∆p pressure difference between fluid inlet and outlet Pa
∆t time interval s
∆T temperature difference between fluid outlet and inlet (t - t) K
e in
α solar absorptance
β tilt angle of a plane with respect to horizontal degrees
γ azimuth angle degrees
ε hemispherical emittance
ω solar hour angle degrees
θ angle of incidence degrees
Φ latitude degrees
λ wavelength µm
*
η collector efficiency, with reference to T
m
* *
η zero-loss collector efficiency (η at T = 0), reference to T
o m m
-2 -4
σ Stefan-Boltzmann constant Wm K
-3
ρ density of heat transfer fluid kgm
τ collector time constant s
c
τ transmittance
(τα) effective transmittance-absorptance product
e
(τα) effective transmittance-absorptance product for
ed
diffuse solar irradiance
(τα) effective transmittance-absorptance product for
en
direct solar radiation at normal incidence
(τα) effective transmittance-absorptance product for
eθ
direct solar radiation at angle of incidence θ
NOTE 1 In the field of solar energy the symbol G is used to denote solar irradiance, rather than the generic symbol E for
irradiance.
NOTE 2 C is often denoted (mC) in basic literature (see also Annex F)
e
NOTE 3 For more information about thermal performance coefficients (parameters) c1 to c6, see Annex F.
5 Reliability testing of liquid heating collectors
5.1 General
The details regarding the number of collectors and sequences used to carry out the qualifications tests
detailed in the list below (Table 1) shall be given in the report.
For some qualification tests, a part of the collector may have to be tampered with in some way, for example a
hole may have to be drilled in the back of the collector to attach a temperature sensor to the absorber. In
these cases care should be taken to ensure that any damage caused does not affect the results of
subsequent qualification tests, for example by allowing water to enter into a previously raintight collector.
Table 1 - Test List
Subclause Test
5.2 Internal pressure
a, b
5.3
High-temperature resistance
b
5.4
Exposure
c
5.5
External thermal shock
c
5.6
Internal thermal shock
d
5.7
Rain penetration
e
5.8
Freeze resistance
5.9 Mechanical load
5.10 Impact resistance (optional test)
f
6.1-6.2-6.3
Thermal performance
a
For organic absorbers, the high-temperature resistance test shall be performed first in order to
determine the collector stagnation temperature needed for the internal pressure test.
b
The high temperature and exposure test shall be carried out on the same collector
c
The external and internal thermal shock tests may be combined with the exposure test or the
high-temperature resistance test.
d
The rain penetration test shall be carried out only for glazed collectors.
e
The freeze resistance test shall be carried out only for collectors claimed to be freeze resistant.
f
The Thermal performance test shall be carried out on a collector that had not been used for other
tests.
NOTE Regarding the durability and reliability of elastic materials it is recommended to refer to ISO 9808 and ISO 9553.
5.2 Internal pressure tests for absorbers
5.2.1 Inorganic absorbers
5.2.1.1 Objective
The absorber shall be pressure-tested to assess the extent to which it can withstand the pressures which it
might meet in service.
5.2.1.2 Apparatus and procedure
The apparatus, shown in Figure A.1, consists of a hydraulic pressure source (electrical pump or hand pump),
a safety valve, an air-bleed valve and a pressure gauge with a standard uncertainty better than 5 %. The air-
bleed valve shall be used to empty the absorber of air before pressurisation. The inorganic absorber shall be
filled with water at room temperature and pressurised to the test pressure for the test period (see 5.2.1.3.2).
This pressure shall be maintained while the absorber is inspected for swelling, distortion or ruptures.
5.2.1.3 Test conditions
5.2.1.3.1 Temperature
Inorganic absorbers shall be pressure-tested (see 5.2.1.3.2) at ambient temperature within the range 5 °C to
30 °C.
5.2.1.3.2 Pressure
The test pressure shall be 1,5 times the maximum collector operating pressure specified by the manufacturer.
The test pressure shall be maintained for 15 min.
5.2.1.4 Results
The collector shall be inspected for leakage, swelling and distortion. The results of this inspection shall be
reported together with the values of pressure and temperature used and the duration of the test.
5.2.2 Absorbers made of organic materials (plastics or elastomers)
5.2.2.1 Objective
The absorber shall be pressure-tested (see 5.2.1.3.2) to assess the extent to which it can withstand the
pressures which it might meet in service while operating at elevated temperature. The tests shall be carried
out at elevated temperatures, because the pressure resistance of an organic absorber may be adversely
affected as its temperature is increased. One of the methods described in 5.2.2.2.2 through 5.2.2.2.4 may be
chosen.
5.2.2.2 Apparatus and procedure
5.2.2.2.1 General
The apparatus consists of either a hydraulic or a pneumatic pressure source, and a means of heating the
absorber to the required test temperature.
The characteristics of a solar irradiance simulator shall be the same as those of the simulator used for
efficiency testing of liquid heating solar collectors.
A temperature sensor shall be attached to the absorber to monitor its temperature during the test. The sensor
shall be positioned at two-thirds of the absorber height and half the absorber width. It shall be fixed firmly in a
position to ensure good thermal contact with the absorber. The sensor shall be shielded from solar radiation.
The test conditions specified in 5.2.2.3 shall be maintained for at least 30 min prior to test and for the full
duration of the test.
The pressure in the absorber shall be raised in stages as specified in 5.2.2.3, and the absorber shall be
inspected for swelling, distortion or rupture after each increase in pressure. The pressure shall be maintained
while the absorber is being inspected.
For safety reasons, the collector shall be encased in a transparent box to protect personnel in the event of
explosive failure during this test.
One of the methods described in 5.2.2.2.2 through 5.2.2.2.4 may be chosen.
5.2.2.2.2 Organic absorbers for use in unglazed collectors (test temperature < 90 °C)
Where the maximum test temperature is below 90 °C, absorbers may be submerged in a heated water bath
and pressure-tested. The pressurised fluid supply to the absorber shall be fitted with a safety valve, air-bleed
valve (if required) and pressure gauge having a standard uncertainty better than 5 %. The apparatus is shown
in Figure A.2.
5.2.2.2.3 Organic absorbers for use with oil-based fluids (test temperature > 90 °C)
When the test temperature exceeds 90 °C, the absorber may be connected to a hot oil circuit. The absorber
and hot oil circuit are then pressurised. The hot oil circuit shall be fitted with a safety valve, air-bleed valve and
pressure gauge having a standard uncertainty better than 5 %.
The absorber may be heated by any of the following methods:
a) connecting a heater in the oil circuit (see Figure A.3);
b) heating the whole collector in a solar irradiance simulator (see Figure A.4);
c) heating the whole collector outdoors under natural solar irradiance (see Figure A.4).
Safety measures should be taken to protect personnel from hot oil in the event of explosive failure during this
test.
5.2.2.2.4 Organic absorbers - high temperature pneumatic pressure test
The absorber may be pressure-tested using compressed air, when heated by either of the following methods:
a) heating the whole collector in a solar irradiance simulator (see Figure A.5);
b) heating the whole collector outdoors under natural solar irradiance (see Figure A.5).
The compressed air supply to the absorber shall be fitted with a safety valve and a pressure gauge having a
standard uncertainty better than 5 %.
5.2.2.3 Test conditions
5.2.2.3.1 Temperature
For absorbers made of organic materials, the test temperature shall be the maximum temperature which the
absorber will reach under stagnation conditions.
The reference conditions given in Table 2 s
...