PUBLIC REVIEW DRAFT, SEPTEMBER 2008KENYA STANDARD  KS 1851-2:2008  
ICS 27.160 
  
 
 
  
 
  
 
  
 
 
 
  
 
 
 
Thermal solar systems and components — 
Solar collectors — Part 2: Test methods 
 
 
  
 
  
 
  
Public Review Draft, September 2008  
 
 
  
 
  
 
  
 
© KEBS 2008 Edition 1.0 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
ICS 27.160 
© KEBS 2008 — All rights reserved iii TECHNICAL COMMITTEE REPRESENTATION 
 
The following organizations were represented on the Technical Committee 
 
Kenital Solar (K) Ltd  
ASP Solar (Kenya) Ltd  
Sollatek Ltd  
Department of Electrical & Electronic Engineering, JKUAT  
Renewable Energy Department, Ministry of Energy  
Chloride Exide Kenya Limited  
Energy Alternatives Africa Ltd  
Solarnet  
Automotive and Industrial Battery Manufacturers (AIBM) (K) Ltd 
RENCON Associates  
Telesales Solar Ltd 
Kenya Industrial Research and Development Institute, KIRDI 
Kenya Bureau of Standards — Secretariat   
  
 
  
  
 
  
 
 
 
 
  
  
 
  
 
 
 
  
  
 
  
 
 
 
 
  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
iv © KEBS 2008 — All rights reserved  
 
 
 
 
 
 
 
  
 
  
 
 
  
 
 
 
 
 
 
 
  
 
 
REVISION OF KENYA STANDARDS 
 
In order to keep abreast of progress in industry, Kenya standards shall be regularly reviewed. Suggestions for 
improvement to published standards, addressed to the Managing Director, Kenya Bureau of Standards, are 
welcome. 
 
© Kenya Bureau of Standards, 2008 
 
Copyright. Users are reminded that by virtue of Section 25 of th e Copyright Act, Cap. 12 of 2001  of the Laws of Kenya, copyrig ht 
subsists in all Kenya Standards and except as provided under Section 26 of this Act, no Kenya Standard produced by Kenya Bureau  of 
Standards may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in w riting 
from the Managing Director. 
 
 
 
 
  
 
 
 
 
 
 
 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008  
© KEBS 2008 — All rights reserved v  
 
 
 
 
 
 
 
 
 
 
 
 
 
Thermal solar systems and components 
— Solar collectors — Pa rt 2: Test methods 
 
 
 
 
 
   
 
  
 
 
KENYA BUREAU OF ST ANDARDS (KEBS) 
 
Head  Office:  P.O. Box 54974, Nairobi-00200, Tel.: (+254  020) 605490, 602350, Fax: (+254 020) 609660, 604031 
E-Mail: info@kebs.org,  Web:http://www.kebs.org   
 
KEBS Coast Region 
P.O. Box 99376, Mombasa 80100 
Tel: (+254 041) 229563, 230939/40 
Fax: (+254 041) 229448 
E-mail: kebs-msa@swiftmombasa.com  KEBS Lake Region 
P.O. Box 2949, Kisumu 40100 
Tel: (+254 057) 23549,22396 
Fax: (+254 057) 21814 
E-mail: kebs-ksm@swiftkisumu.com  KEBS North Rift Region 
P.O. Box 2138, Nakuru 20100 
Tel: (+254 051) 210553, 210555PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
vi © KEBS 2008 — All rights reserved Foreword 
 
This Kenya standard was developed by the Renewable Energy Resources Technical Committee under the supervision of the Electrical Industry Standards Committee and is in accordance with the procedures of the 
Bureau. 
 
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 calculatio n procedures for determining the steady-state and quasi-
dynamic thermal performance of glazed liquid heating sola r 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 th e thermal performance of unglazed liquid heating solar 
collectors. Unglazed collectors are in most cases us ed 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. Theref ore, 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 whol e days and under stationary inlet temperature conditions 
and natural solar irradiance and natural and/or simulated wi nd 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. De pendence on flowrate is not included in this standard. 
 
Some of the advantages of the proposed extension of th e present steady-state test methods of all-day testing are: 
 
⎯ shorter and less expensive outdoor test. 
 
⎯ much wider range of collectors can be tested with the same method. 
 
⎯ at the same time, a much more complete char acterization 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 ca n 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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008  
© KEBS 2008 — All rights reserved vii  
Contents 
 
1 Scope ....................................................................................................................... ............................................................. 1 
2 Normative references ........................................................................................................ ................................................ 1 
3 Terms and definitions ....................................................................................................... ................................................ 1 
4 Symbols and units ........................................................................................................... .................................................. 1 
5 Reliability testing of liqui d heating colle ctors ................... ......................................................... .................................... 4 
5.1 General ................................................................................................................... ............................................................. 4 
5.2 Internal pressure tests for absorbers ..................................................................................... .......................................... 5 
5.2.1 Inorganic absorbers ..................................................................................................... ...................................................... 5 
5.2.2 Absorbers made of organic materials (plastics or elastomers) ............................................................ ........................ 6 
5.3 High-temperature resistance test .......................................................................................... ........................................... 8 
5.3.1 Objective ............................................................................................................... .............................................................. 8 
5.3.2 Apparatus and procedure.................................................................................................. ............................................... 8 
5.3.3 Test conditions ......................................................................................................... .......................................................... 8 
5.3.4 Results ................................................................................................................. ................................................................ 8 
5.4 Exposure test ............................................................................................................. ......................................................... 9 
5.4.1 Objective ............................................................................................................... .............................................................. 9 
5.4.2 Apparatus and procedure.................................................................................................. ............................................... 9 
5.4.3 Test conditions ......................................................................................................... .......................................................... 9 
5.4.4 Results ................................................................................................................. ................................................................ 9 
5.5 External thermal shock test ............................................................................................... ............................................. 10 
5.5.1 Objective ............................................................................................................... ............................................................ 10 
5.5.2 Apparatus and procedure.................................................................................................. ............................................. 10 
5.5.3 Test conditions ......................................................................................................... ........................................................ 10 
5.5.4 Results ................................................................................................................. .............................................................. 10 
5.6 Internal thermal shock test ............................................................................................... .............................................. 11 
5.6.1 Objective ............................................................................................................... ............................................................ 11 
5.6.2 Apparatus and procedure.................................................................................................. ............................................. 11 
5.6.3 Test conditions ......................................................................................................... ........................................................ 11 
5.6.4 Results ................................................................................................................. .............................................................. 11 
5.7 Rain penetration test ..................................................................................................... .................................................. 12 
5.7.1 Objective ............................................................................................................... ............................................................ 12 
5.7.2 Apparatus and procedure.................................................................................................. ............................................. 12 
5.7.3 Test conditions ......................................................................................................... ........................................................ 12 
5.7.4 Results ................................................................................................................. .............................................................. 13 
5.8 Freeze resistance test .................................................................................................... ................................................... 13 
5.8.1 Objective ............................................................................................................... ............................................................ 13 
5.8.2 Apparatus and procedure.................................................................................................. ............................................. 13 
5.8.3 Test conditions ......................................................................................................... ........................................................ 14 
5.8.4 Results ................................................................................................................. .............................................................. 14 
5.9 Mechanical load test ...................................................................................................... .................................................. 14 
5.9.1 Positive pressure test of the collector ................................................................................. ........................................... 14 
5.9.2 Negative pressure test of the collector ................................................................................. ......................................... 15 
5.10 Impact resistance test (optional) ........................................................................................ ............................................ 16 
5.10.1 Objective .............................................................................................................. ............................................................. 16 
5.10.2 Apparatus and procedure................................................................................................. .............................................. 16 
5.10.3 Test conditions ........................................................................................................ ......................................................... 17 
5.10.4 Results ................................................................................................................ ............................................................... 18 
5.11 Final inspection ......................................................................................................... ....................................................... 18 
5.12 Test report .............................................................................................................. ........................................................... 18 
6 Thermal performance testing of liquid heating collectors .................................................................... ...................... 18 
6.1 Glazed solar collectors under steady state conditions (including pressure drop) ........................................... ....... 18 
6.1.1 Collector mounting and location ......................................................................................... .......................................... 18 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
viii © KEBS 2008 — All rights reserved 6.1.2 Instrumentation ......................................................................................................... ...................................................... 19 
6.1.3 Test installation ....................................................................................................... ......................................................... 24 
6.1.4 Outdoor steady-state performance test ................................................................................... ...................................... 27 
6.1.5 Steady-state efficiency test using a solar irradiance simulator ......................................................... ......................... 31 
6.1.6 Determination of the effective thermal capacity and the time constant of a collector .................................... ........ 34 
6.1.7 Collector incidence angle modifier ...................................................................................... .......................................... 35 
6.1.8 Determination of the pressure drop across a collector ................................................................... ............................ 38 
6.2 Unglazed solar collectors under steady state conditions (including pressure drop) ......................................... ..... 38 
6.2.1 Collector mounting and location ......................................................................................... .......................................... 38 
6.2.2 Instrumentation ......................................................................................................... ...................................................... 40 
6.2.3 Test installation ....................................................................................................... ......................................................... 42 
6.2.4 Outdoor steady state efficiency test .................................................................................... .......................................... 42 
6.2.5 Steady-state efficiency test using a solar irradiance simulator ......................................................... ......................... 46 
6.2.6 Determination of the effective thermal capacity and the time constant of a collector .................................... ........ 46 
6.2.7 Incidence angle modifier (optional) ..................................................................................... ......................................... 47 
6.2.8 Determination of the pressure drop across a collector ................................................................... ............................ 49 
6.3 Glazed and unglazed solar collectors under quasi-dynamic conditions ....................................................... ........... 49 
6.3.1 Collector mounting and location ......................................................................................... .......................................... 49 
6.3.2 Instrumentation ......................................................................................................... ...................................................... 50 
6.3.3 Test installation ....................................................................................................... ......................................................... 51 
6.3.4 Outdoor efficiency test ................................................................................................. ................................................... 51 
6.3.5 Determination of the effective thermal capacity ......................................................................... ................................. 58 
6.3.6 Collector incidence angle modifier ...................................................................................... .......................................... 58 
Annex A (normative)  Schematics for durability and reliabi lity test s .......................................................... ................................ 60 
Annex B (normative)  Durability and re liability test report sheets ............................................................ ................................... 68 
Annex C (normative)  Stagnation temperat ure of liquid heating collectors ...................................................... .......................... 88 
Annex D (normative)  Performance test report for glazed solar collectors ...................................................... ........................... 89 
Annex E (normative)  Performance test re port for unglazed solar collectors .................................................... ......................... 94 
Annex F (normative)  Modelling of the coefficients c 1 to c 6 of the collector model of 6.3. ......................................................... 98 
Annex G (normative)  Measurement of effective thermal capacity ................................................................ .............................. 99 
Annex H (informative)  Comparison of the collector model of 6.1 to the collector model of 6.3 ................................. ........... 102 
Annex I (informative)  Properties of water .................................................................................... ................................................ 103 
Annex J (informative)  Performance test report summary for quasi dynamic test method .......................................... .......... 104 
Annex K (informative)  General guidelines for the assessment of uncertainty in solar collector efficiency testing ............ 106 
Annex L (informative)  Determination of the pressure drop across a collector .................................................. ...................... 110 
Bibliography .................................................................................................................. ..................................................................... 112 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KENYA STANDARD KS 1851-2:2008  
© KEBS 2008 — All rights reserved 1  
Thermal solar systems and component s — Solar collectors — Part 2: 
Test methods 
 
1 Scope 
 
This Kenya Standard specifies test methods for validat ing the durability, reliability and safety requirements for 
liquid heating collectors as specified in KS 1851-1. This standard also includes three test methods for the 
thermal performance characterization 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 perfo rmance 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
2. The test is 
valid only for larger collect ors than the tested module. 
 
2 Normative references 
 
The following referenced documents are indispensable for the application of this Kenya Standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced 
document (including any amendments) applies. 
 ISO 6612, Windows and door height windows — Wind resistance tests  
 ISO 15928-1, Houses — Description of performance — Part 1: Structural safety  
 
ISO 15928-2, Houses — Description of performance — Part 2: Structural serviceability  
 
KS 1851-1, Thermal solar systems and components ―Solar collectors ― Part 1: General requirements  
 
KS ISO 9488, Solar energy ― Vocabulary  
 
KS 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 Kenya Standard, the terms and definitions given in KS ISO 9488 apply. 
 
4 Symbols and units 
 
a1 heat loss coefficient at ( Tm - T a) = 0 W m2K-1 
 
a2 temperature dependence of the heat loss coefficient W m-2K-2 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
2 © KEBS 2008 — All rights reserved AA absorber area of collector m2 
 
Aa aperture area of collector m2 
 
AG gross area of collector m2 
 
AM optical air mass m2 
 b
u collector efficiency coefficient (wind dependence) m-1 s 
 
b0 constant for the calculation of the incident angle modifier  
 
b1 heat loss coefficient at (Tm – T a) = 0 W m-2K-1 
 b
2 collector efficiency coefficient W sm-3K-1 
 
c1 heat loss coefficient at ( Tm – T a) = 0 Wm-2K-1 
 c
2 temperature dependence of the heat loss coefficient W m-2K-2 
 
c3 wind speed dependence of the heat loss coefficient Jm-3K-1 
 
c4 sky temperature dependence of the heat loss coefficient Wm-2K-1 
 c
5 effective thermal capacity Jm-2K-1 
 
c6 wind dependence in the zero loss efficiency sm-1 
 
cf specific heat capacity of heat transfer fluid Jkg-1K-1 
 
C effective thermal capacity of collector JK-1 
 
D date YYMMDD 
 
EL longwave irradiance ( λ > 3μm) Wm-2 
 
Eβ longwave irradiance on an inclined surface outdoors Wm-2 
 
Es longwave irradiance Wm-2 
 
F radiation view factor  
 
F' collector efficiency factor  
 
G hemispherical solar irradiance Wm-2 
 
G* global hemispherical solar irradiance Wm-2 
 
G" net irradiance Wm-2 
 
Gb direct solar irradiance (beam irradiance) Wm-2 
 G
d diffuse solar irradiance Wm-2 
 LT local time h 
 
K
θ incidence angle modifier  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 3  
Kθb incidence angle modifier for direct radiation 
 
Kθd incidence angle modifier for diffuse radiation 
 
m thermally active mass of the collector kg 
 
m mass flowrate of heat transfer fluid kgs-1 
 
Q& useful power extracted from collector W 
 
Q&L power loss of collector W 
 
SF safety factor  
 
t time s 
 t
a ambient or surrounding air temperature °C 
 
tdp atmospheric dew point temperature °C 
 
te collector outlet (exit) temperature °C 
 
tin collector inlet temperature °C 
 
tm mean temperature of heat transfer fluid °C 
 
ts atmospheric or sky temperature °C  
 
tstg stagnation temperature °C 
 
T absolute temperature K 
 
Ta ambient or surrounding air temperature °C 
 
T*
m reduced temperature difference ( = (tm–ta)IG*)  m2KW1 
 
Ts atmospheric or equivalent sky radiation temperature K 
 
U measured overall heat loss coefficient of collector,with reference to T*m Wm-2K"1 
 U
L  overall heat loss coefficient of a collector with uniform absorber temperature Wm K 
 
u surrounding air speed ms-1 
 V
f fluid capacity of the collector m3 
 
pΔ pressure difference between fluid inlet and outlet Pa 
 
tΔ time interval  s 
 
TΔ temperature difference between fluid outlet and inlet (te– tin) K 
 
α solar absorptance 
 
β tilt angle of a plane with respect to horizontal degrees PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
4 © KEBS 2008 — All rights reserved  
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 
 
ηo zero-loss collector efficiency ( η at T*m = 0), reference to T*m 
 
σ Stefan-Boltzmann constant W m-2K-4 
 
ρ density of heat transfer fluid kgm-3 
 
cτ collector time constant s 
 
τ transmittance 
 
()τα e effective transmittance-absorptance product  
 
()τα ed effective transmittance-absorptance product for diffuse solar irradiance  
 
(τα)en effective transmittance–absorptance product for direct solar radiation at normal incidence 
 
(τα)eθ effective transmittance-absorptance product for 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 irrad iance. 
 NOTE 2 C is often denoted ( mC)e in basic literature (see also Annex F) 
 
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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 5  
Table 1 — Test list 
 
Subclause   Test
5.2  Internal pressure 
5.3  High-temperature resistance a,b 
5.4  Exposure b 
5.5  External thermal shock c 
5.6  Internal thermal shock 
5.7  Rain penetration d 
5.8  Freeze resistance e 
5.9  Mechanical load 
5.10  Impact resistance (optional test) 
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 stagna tion 
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 KS ISO 9808 and KS 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 pressurization. The inorganic absorber shall be 
filled with water at room temperature and pressurized 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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
6 © KEBS 2008 — All rights reserved  
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 sha ll 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 maintain ed 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 pressurized 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 pressurized. 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: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 7 a) connecting a heater in the oil circuit (see Figure A.3); 
 
b) heating the whole collector in a sola r 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 sola r 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 shall be used. 
 
The calculations employed to determine the test temperature are included in Annex C and shall either:  
⎯ use measured collector performance characteristics, or 
 
⎯ extrapolate from average values, measured in the high-temperature resistance test (see 5.3.3), of the 
global solar irradiance (natural or simulated) on the collector plane, the surrounding air temperature and 
the absorber temperature. 
 
Table 2 — Climate reference conditions to determine test temperatures for internal pressure test of 
organic absorbers 
 
Climate parameter  Value for all climate classes  
Global solar irradiance on collector plane, G in W/m2 1000 
Surroundin g air temperature, ta in °C 30
 
5.2.2.3.2 Pressure 
 
The test pressure shall be 1.5 times the maximum collector operating pressure specified by the manufacturer. 
 
For absorbers made of organic materials, the pressure shall be raised to the test pressure in equal stages of 
20 kPa (approximately) and maintained at each intermediate pressure for 5 min. The test pressure shall then 
be maintained for a least 1 h. 
 5.2.2.4 Results  
 The collector shall be inspected for leakage, swelling and distortion. The results of the inspection shall be reported. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
8 © KEBS 2008 — All rights reserved Full details of the test procedure used, including the temperature, intermediate pressures and test periods 
used, shall be reported with the test results. 
 
5.3 High-temperature resistance test 
 
5.3.1 Objective 
 
This test is intended to assess rapidly whether a coll ector can withstand high irradiance levels without failures 
such as glass breakage, collapse of plastic cover, melting of plastic absorber, or significant deposits on the 
collector cover from outgassing of collector material.  
5.3.2 Apparatus and procedure 
 
The collector shall be tested outdoors , or in a solar irradiance simulator. A schema for testing is shown in 
Figure A.6.  
The characteristics of the solar irradiance simulator to be used for the high-temperature resistance test shall 
be those of the solar irradiance simu lator used for efficiency testing of liquid heating solar collectors. 
 
The collector shall be mounted outdoors or in a solar simulator, and shall not be filled with fluid. All of the fluid pipes except for one shall be sealed to prevent cooling by natural circulation of air. 
 
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. 
 
NOTE 1 When testing collectors, such as evacuated tubular collectors, for which it is not appropriate to measure the stagnation  
temperature at the absorber, the temperature sensor should be placed at a suitable location in the collector, and this location  should be 
clearly described with the test results. 
 
NOTE 2 In some cases, such as evacuated collectors, it may be difficult to attach a thermocouple to the absorber. In such cases , 
instead of attaching a thermocouple to the absorber, the testing laboratory may partially fill the absorber with a special flui d, seal the 
absorber and measure the temperature of the fluid directly or measure the pressure in the absorber. The relationship between th e 
internal pressure in the absorber and its temperature should be known from the standard vapour pressure/temperature relationshi p for 
the fluid. 
 
NOTE 3 It is recommended to perform the determination of the stagnation temperature together with the high-temperature resistan ce 
test. 
 
The test shall be performed for a minimum of 1 h after steady-state conditions have been established, and the collector shall be subsequently inspected for signs of damage as specified in 5.3.4. 
 
5.3.3 Test conditions 
 
The set of reference conditions given in Table 3 or conditions resulting in the same collector temperature 
according to Equation C.1, shall be used for all climate classes. 
 
Table 3 — Climate reference conditions for high-temperature resistance test 
 
Climate parameter  Value for all climate classes 
 
Global solar irradiance on collector plane, G in W/m2 >1000 
Surrounding air temperature, ta in °C 20 – 40 
Surrounding air speed in m/s <1 
 
5.3.4 Results 
 
The collector shall be inspected for degradation, shrinkage, outgassing and distortion. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 9 The results of the inspection shall be recorded together with the average values of solar irradiance (natural or 
simulated) on the collector plane, surrounding air temperature and speed, and absorber temperature (and the 
pressure of the special fluid in the absorber, if that method is used) recorded during the test. 
 
5.4 Exposure test 
 
5.4.1 Objective  
The exposure test provides a low-cost  reliability test sequence , indicating (or simulati ng) operating conditions 
which are likely to occur during real service and also allows the collector to "settle", such that subsequent 
qualification tests are more likel y to give repeatable results. 
 
5.4.2 Apparatus and procedure 
 
The collector shall be mounted outdoors (see Figure A.7), but not filled with fluid. All except one of the fluid 
pipes shall be sealed to prevent cooling by natural circulation of air. One shall be left open to permit free 
expansion of air in the absorber. 
 The air temperature shall be recorded to a standard uncertainty of 1 K and the global irradiance on the plane 
of the collector recorded using a pyranometer of class I or better in accordance with KS ISO 9060. Irradiation 
and mean air temperature values shall be recorded at least every 5 min and rainfall shall be recorded daily. 
The collector shall be exposed until the test conditions have been met. 
 
At the end of the exposure, a visual inspection shall be made for signs of damage as specified in 5.4.4. 
 5.4.3 Test conditions 
 
The set of reference conditions given in Table 4 shall be used. 
 
The collector shall be exposed until at least 30 days (which need not be consecutive) have passed with the 
minimum irradiation H shown in Table 4. The irradiation is determined by recording irradiance measurements 
using a pyranometer. 
 
The collector shall also be exposed for at least 30 h to the minimum irradiance level G given in Table 4, as recorded by a pyranometer, when the surrounding air temperature is greater than the value shown in Table 4 
or conditions resulting in the same collector temperature according to Equation C.1. These hours shall be 
made up of periods of at least 30 min. 
 
NOTE In regions where these conditions cannot be met during ce rtain periods of the year, the 30-h exposure to high irradiance l evels 
(Table 4) can be conducted in a solar irradiance simulator hav ing characteristics identical to those of a simulator used for ef ficiency 
testing of liquid heating solar collectors. The 30-h exposure test should be conducted after the collector has completed at lea st 10 days, 
but no more than 15 days, of the exposure to the minimum irradiation level (Table 4). 
 
If the external and internal thermal shock tests are combined with the exposure test, the first external and internal shocks sh all be 
caused during the first 10 of the 30 h defined above, and the second during the last 10 of the 30 h. 
 
Table 4 — Climate reference conditions for exposure test as well as for external and internal thermal 
shock tests 
 
Climate parameter Value for all climate classes 
Global solar irradiance on collector plane, G in W/m2 850 
Global daily irradiation on collector plane, H in MJ/m2 14 
Surrounding air temperature, ta in °C 10 
NOTE Values given are minimum values for testing. 
 
5.4.4 Results 
 
The collector shall be inspected for damage or degradation. The results of the inspection shall be reported together with a record of the climatic conditions during the test, including daily irradiation, surrounding air 
temperature and rain. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
10 © KEBS 2008 — All rights reserved  
5.5 External thermal shock test 
 
5.5.1 Objective 
 
Collectors may from time to time be exposed to sudden rainstorms on hot sunny days, causing a severe 
external thermal shock. This test is intended to assess the capability of a collector to withstand such thermal 
shocks without a failure.  5.5.2 Apparatus and procedure 
 The collector shall be mounted either outdoors or in a solar irradiance simu lator, but shall not be filled with 
fluid. All except one of the fluid pipes shall be sealed to  prevent cooling by natural circulation of air. One shall 
be left open to permit free expansion of air in the absorber (see Figure A.8). 
 
A temperature sensor may be optionally 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. 
 
NOTE 1 When testing collectors, such as evacuated tubular collectors, for which it is not appropriate to measure the stagnation  
temperature at the absorber, the temperature sensor should be placed at a suitable location in the collector, and this location  should be 
clearly described with the test results. 
 
NOTE 2 In some cases, such as evacuated collectors, it may be difficult to attach a thermocouple to the absorber. In such cases , 
instead of attaching a thermocouple to the absorber, the testing laboratory may partially fill the absorber with a special flui d, seal the 
absorber and measure the pressure in the absorber. The relationship between the internal pressure in the absorber and its tempe rature 
should be known from the standard vapour pressure/temperature relationship for the fluid. 
 
An array of water jets shall be arranged to provide a uniform spray of water over the collector. 
 
The collector shall be maintained under  a high level of solar irradiance for a period of 1 h before the water 
spray is turned on. It is then cooled by the water spray for 15 min before being inspected. 
 
The collector shall be subjected to two external thermal shocks. 
 5.5.3 Test conditions 
 The set of reference conditions given in Table 4 shall be used. The specified operating conditions shall be:  
⎯ solar (or simulated solar) irradiance G greater than the value shown in Table 4. 
 
⎯ surrounding air temperature ta greater than the value shown in Table 4. Or conditions resulting in the 
same collector temperature according to Equation C.1 
 
The water spray shall have a temperature of less than 25 °C and a flowrate in the range 0.03 kg/s to 0.05 
kg/s per square metre of collector aperture. 
 If the temperature of the water which first cools the collector is likely to be greater than 25 °C (for example if 
the water has been sitting in a pipe in the sun for some time), then the water shall be diverted until it has 
reached a temperature of less than 25 °C before being directed over the collector.  
5.5.4 Results 
 
The collector shall be inspected for any cracking, distortion, condensation, water penetration or loss of 
vacuum. The results of the inspection shall be reported. The measured values of solar irradiance, surrounding air temperature, absorber temperature (if measured), water temperature and water flowrate shall 
also be reported. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 11  
5.6 Internal thermal shock test 
 
5.6.1 Objective 
 
Collectors may from time to time be exposed to a sudden intake of cold heat transfer fluid on hot sunny days, 
causing a severe internal thermal shock, for example, after a period of shutdown, when the installation is 
brought back into operation while the collector is at its stagnation temperature. This test is intended to the capability of a collector to withstand such thermal shocks without failure.  
5.6.2 Apparatus and procedure  The collector shall be mounted either outdoors or in a solar irradiance simulator (see Figure A.9), but shall not be filled with fluid. One of its fluid pipes shall be connected via a shutoff valve to the heat transfer fluid 
source and the other shall be left open initially to permit the free expansion of air in the absorber and also to 
permit the heat transfer fluid to leave the absorber (and be collected). If the collector has more than two fluid 
pipes, the remaining openings shall be sealed in a way that ensures the designed flow pattern within the 
collector.  
A temperature sensor may be optionally 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. 
 
NOTE 1 When testing collectors, such as evacuated tubular collectors, for which it is not appropriate to measure the stagnation  
temperature at the absorber, the temperature sensor should be placed at a suitable location in the collector, and this location  should be 
clearly described with the test results. 
 NOTE 2 In some cases, such as evacuated collectors, it may be difficult to attach a thermocouple to the absorber. In such cases , 
instead of attaching a thermocouple to the absorber, the testing laboratory may partially fill the absorber with a special flui d, seal the 
absorber and measure the pressure in the absorber. The relationship between the internal pressure in the absorber and its tempe rature 
should be known from the standard vapour pressure/temperature relationship for the fluid.  
 
The collector shall be maintain ed under a high level of solar irradiance for a period of 1 h before it is cooled 
by supplying it with heat transfer fluid for at least 5 min or until the absorber temperature drops below 50 °C. 
 
The collector shall be subjected to two internal thermal shocks.  
5.6.3 Test conditions 
 
The set of reference conditions given in Table 4 shall be used. 
 The specified operating conditions shall be: 
 
⎯ solar (or simulated solar) irradiance G greater than the value shown in Table 4; 
 
⎯ surrounding air temperature ta greater than the value shown in Table 4. 
 
or conditions resulting in the same collector temperature according to Equation C.1 
 
The heat transfer fluid shall have a temperature of less than 25 °C. The recommended fluid flowrate is at least 0.02 kg/s per square metre of collector aperture (unless otherwise specified by the manufacturer). 
 5.6.4 Results 
 
The collector shall be inspected for any cracking, distortion, deformation, water penetration or loss of vacuum. The results of the inspection shall be reported. The measured values of solar irradiance, 
surrounding air temperature, absorber temperature (if measured), heat transfer fluid temperature and heat 
transfer fluid flowrate shall also be reported. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
12 © KEBS 2008 — All rights reserved  
5.7 Rain penetration test 
 
5.7.1 Objective  
This test is applicable only for glazed collectors and is intended to assess the extent to which glazed 
collectors are substantially resistant to rain penetration. They shall normally not permit the entry of either free-
falling rain or driving rain. Collectors may have ventila tion holes and drain holes,  but these shall not permit 
the entry of drifting rain. 
 
5.7.2 Apparatus and procedure  
5.7.2.1 General  The collector shall have its fluid inlet and outlet pi pes sealed (unless hot water is circulated through the 
absorber, see 5.7.2.2), as shown in Figure A.10, and be placed in a test rig at the shallowest angle to the 
horizontal recommended by the manufacturer. If this angle is not specified, then the collector shall be placed 
at a tilt of 30° to the horizontal. Collectors designed to be integrated into a roof structure shall be mounted in a simulated roof and have their underside protected. Other collectors shall be mounted in a conventional 
manner on an open frame or a simulated roof.  
The collector shall be sprayed on exposed sides, using spray nozzles or showers. 
 5.7.2.2 Detection of ingress of water 
 The collector shall be mounted and sprayed as explained above while the absorber in the collector is kept warm (minimum 50 °C). This can be done either by circulating hot water at about 50 °C through the absorber 
or by exposing the collector to solar radiation. The penetration of water into the collector shall be determined 
by inspection (looking for water droplets, condensation on the cover glass or other visible signs) and by one of the following methods: 
 
a) by weighing the collector (standard uncertainty better than 5 g/m2 collector area); or 
 
b) by means of humidity measurement (standard uncertainty better than 5 %) or 
 
c) by means of measuring the condensation level. 
 
The heating up of the collector should be started before the spraying of the water in order to ensure that the 
collector box is dry before testing. 
 
In cases of collectors having wood in the backs (or other special cases), the laboratory shall take all 
necessary measures during the conduction of the test so that the final result will not be influenced or altered 
by the special construction of the collector. 
 
5.7.3 Test conditions 
 
The collector shall be sprayed with water at a temperature lower than 30 °C with a flowrate of more than 0.05 
kg/s per square metre of sprayed area. The duration of the test shall be 4 h. 
 
5.7.3.1 Weighing method 
 
If the weighing method is chosen, the collector shall be put on the scale before the start of the test on three 
consecutive occasions. The weights recorded shall not vary by more than ± 5 g/m2 collector area. 
 
5.7.3.2 Humidity measurement method 
 
When measuring the penetration of water into the collector by means of humidity measurement, an absolute 
humidity sensor is placed in the air gap between absorber and glazing. Collector and sensor are connected to 
a hot fluid loop for at least five hours before the rain  is switched on in order  to stabilize. When testing 
outdoors, in order to minimize disturbances of the measurement, the collector shall be shaded during the PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 13 whole test. The humidity shall be monitored from five hour s before the raining till at least five hours after the 
raining. Ingress of water might also be detected at a later stage, during the "Final Inspection" (5.11). 
 5.7.3.3 Condensation level method 
 
If the condensation level method is chosen, the penetration of water is determined by measuring the 
condensation level on the cover glass and by measuring the water that comes out of the collector when 
tipping it. 
 The heating of the collector shall be started at least 30 min before the spraying of water and shall continue 
until it can be ensured that the collector box is dry before testing. This shall be done by circulating hot water 
(or other fluid) above 50 °C through the absorber before but also during the complete test. The water will thereafter condense on the inside of the glazing, which is being cooled by cold water on the outside. After 2 h 
an intermediate inspection of condensation on the cover glass shall be done in order to facilitate the reporting 
of the places where water penetrates.  
After finishing the spraying the inspection of condensation should be done after a short time for ventilating, in 
order to distinguish collectors with good ventilation qualifications that are without accumulation of humidity 
inside the collector. However, the inspection should be done within one minute after finishing the spraying 
before the collector will make any temperature changes.  
5.7.4 Results 
 
The collector shall be inspected for water penetration. The results of the inspection, i.e. the extension of 
water penetration and the places where water penetrated shall be reported.  
5.8 Freeze resistance test 
 
5.8.1 Objective 
 
This test is intended to assess the extent to which water heating collectors which are claimed to be freeze resistant can withstand freezing, and freeze/thaw cycling. This test is not intended for use with collectors for 
which it is clearly stated in the installation manual that they may only be used with an antifreeze fluid. Two 
test procedures are recommended: 
 
⎯ one for collectors which are claimed to be freeze-resistant when filled with water, and 
 
⎯ one for collectors which are claimed to resist freezing after being drained. 
 
5.8.2 Apparatus and procedure 
 
5.8.2.1 Freeze-resistant collectors 
 
For collectors which are claimed to be able to withstand freezing, the collector shall be mounted in a cold 
chamber (see Figure A.11). The collector shall be fitt ed correctly, shut completely and inclined at the 
shallowest angle to the horizontal recommended by the manufacturer. If no angle is specified by the 
manufacturer, then the collector shall be inclined at an angle of 30° to the horizontal. Unglazed collectors 
shall be tested in a horizontal position unless this is excluded by the manufacturer. Next, the collector shall be 
filled with water at the operating pressure. 
 
The cold-chamber temperature shall be cycled, and at the end of each cycle the collector shall be refilled with 
water at operating pressure. 
 
The temperature of the water shall be monitored throughout the test. 
 
5.8.2.2 Collectors with drain-down protection 
 
For collectors which employ a drain-down system to protect them from freezing damage, the collector shall 
be mounted in a cold chamber (see Figure A.11). The collector shall be then inclined at the shallowest angle 
to the horizontal recommended by the manufacturer. If no angle is specified by the manufacturer, then the PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
14 © KEBS 2008 — All rights reserved collector shall be inclined at an angle of 30° to the horizontal. Unglazed collectors shall be tested in a 
horizontal position unless this is exclud ed by the manufacturer. The collector  shall be next filled with water, 
kept at operating pressure for 10 min and then drained using the device installed by the manufacturer.  
If, 5 min after the start of the drain process, the amount of drained water from the collector corresponds to 
approximately 95 % of the total water which filled that colle ctor, then in that case, no test in cold chamber is 
required.  
The cold-chamber temperature shall be cycled.  
The temperature shall be measured inside the absorber close to the inlet.  
 After the last cycle the collector shall be refilled with water at operating pressure. 
 
5.8.3 Test conditions 
 
The contents of the absorber shall be maintained at (-20 ± 2) °C for at least 30 min during the freezing part of 
the cycle, and are raised to above 10 °C during the thawing part of the cycle. The duration of the thawing part 
of the cycle shall be at least 30 min. 
 The collector shall be subjected to three freeze-thaw cycles. 
 
5.8.4 Results 
 
The number of cycles carried out shall be reported. The collector shall be inspected for leakage, breakage, distortion and deformation. These shall be reported together with the absorber temperatures reached during 
the cycles and the times spent by the collector at the test temperatures. The tilt angle used for the test shall also be reported. 
 
5.9 Mechanical load test 
 
5.9.1 Positive pressure test of the collector 
 
5.9.1.1 Objective 
 
This test is intended to assess the extent to which the transparent cover of the collector and the collector box 
are able to resist the positive pressure load due to the effect of wind and snow.   
5.9.1.2 Apparatus and procedure 
 
The collector shall be placed horizontally on an even ground. On the collector a foil shall be laid and on the 
collector frame a wooden or metallic frame shall be placed, high enough to contain the required amount of 
gravel or similar material (see Figure A.12).  
The gravel, preferably type 2-32 mm, shall be weighed in portions and distributed in the frame so that everywhere the same load is created (pay attention to the bending of the glass), until the desired height is 
reached. 
 The test can also be carried out installing the collector in accordance with 5.9.2.2 and loading the cover using 
suction cups, gravel or other suitable means (e.g. water). 
 
As a further alternative, the necessary load may be created by applying an air pressure on the collector 
cover. 
 The load may also be created by applying a negative pressure on the collector cover. In this case, apparatus 
in accordance to ISO 6612 can be used. However this method cannot be applied on all collector types. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 15 5.9.1.3 Test conditions 
 
The test pressure shall be increased at maximum steps of 250 Pa until a failure occurs or up to the value 
specified by the manufacturer. The test pressure shall be at least 1000 Pa. A failure can be the destruction of 
the cover and also the permanent deformation of the collector box or the fixings. 
 
NOTE A permanent deformation should be assigned to a load value, while it is completely relieved after every load increment of 250 
Pa and the distortion is measured compared to the beginning of the test sequence. The value of an inadmissible permanent deform ation 
amounts to max. 0.5 %. (Example: 10 mm distortions at 2 m length of collector  
 
5.9.1.4 Results 
 
The pressure at which any failure of the collector cover or the box or fixings occurs shall be reported together 
with details of the failure. If no failure occurs, then the maximum pressure which the collector sustained shall 
be reported. 
 The maximum positive pressure is the pressure reache d before occurring a failure. The permissible positive 
pressure is the maximum pressure divided by the safety factor SF+ = 1.5: 
 
F
pem+  =  F max+  / SF+ with SF+ = 1.5 
 
NOTE When the test is done with an on-roof mounting system the test results are also valid for the roof integrated mounting sys tem. 
 
5.9.2 Negative pressure test of the collector 
 
5.9.2.1 Objective 
 This test is intended to assess the extent to which the fixings between the collector cover and collector box 
are able to resist uplift forces caused by the wind. 
 
For the design of the statics of the mounting system the requirements of ISO 15928 have to be applied. 
 
5.9.2.2 Apparatus and procedure 
 
The collector shall be installed horizontally on a stiff frame by means of its mounting fixtures. The frame which secures the cover to the collector box shall not be restricted in any way. 
 A lifting force which is equivalent to the specified negative pressure load shall be applied evenly over the 
cover. The load shall be increased in steps up to the final test pressure. If the cover has not been loosened at 
the final pressure, then the pressure may be stepped up until failure occurs. The time between each pressure step shall be the time needed for the pressure to stabilize. 
 Either of two alternative methods may be used to apply pressure to the cover: 
 
⎯ Method (a): The load may be applied to the collector cover by means of a uniformly distributed set of 
suction cups (see Figure A.13). 
 
⎯ Method (b): For collectors which have an almost airtight collector box, the following procedure may be 
used to create a negative pressure on the cover (see Figure A.14). Two holes are made through the 
collector box into the airgap between the collector cover and absorber, and an air source and pressure 
gauge are connected to the collector airgap through these holes. A negative pressure on the cover is 
created by pressurizing the collector box. For safety reasons the collector shall be encased in a 
transparent box to protect personnel in the event of failure during this test. 
 
During the test, the collector shall be visually inspec ted and any deformations of the cover and its fixings 
reported. The collector shall be examined at the end of the test to see if there are any permanent 
deformations. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
16 © KEBS 2008 — All rights reserved 5.9.2.3 Test conditions 
 
The test pressure shall be increased in steps of 250 Pa until a failure occurs or up the value specified by the 
manufacturer. The test pressure shall be at least 1000 Pa. A failure can be the destruction of the cover and 
also the permanent deformation of the collector box or the fixings. 
 
NOTE A permanent deformation should be assigned to a load value, while it is completely relieved after every load increment of 250 
Pa and the distortion is measured compared to the beginning of the test sequence. The value of an inadmissible permanent deform ation 
amounts to max. 0.5 %. (Example: 10 mm distortions at 2 m length of collector frame). 
 
5.9.2.4 Results 
 
The pressure at which any failure of the collector cover or the box or fixings occurs shall be reported together with details of the failure. If no failure occurs, then the maximum pressure which the collector sustained shall 
be reported.  
The maximum negative pressure is the pressure reached before occurring a failure. The permissible negative 
pressure is the maximum pressure divided by the safety factor SF- = 2:  
F
pem- = F max-  / SF- with SF- = 2 
 
5.10 Impact resistance test (optional) 
 
5.10.1 Objective 
 
This test is intended to assess the extent to which a collector can withstand the effects of heavy impacts 
caused by hailstones.  5.10.2 Apparatus and procedure 
 
5.10.2.1 General 
 
The testing of the solar collector to determine its impact resistance can be done by one of two methods, i.e. 
by using steel balls or ice balls.  
5.10.2.2 Method 1 
 
The collector shall be mounted either vertically or horizontally on a support (see Figure A.15). The support 
may be stiff enough so that there is negligible distortion or deflection at the time of impact.  
Steel balls shall be used to simulate a heavy impact. If the collector is mounted horizontally then the steel 
balls are dropped vertically, or if it is mounted vertically then the impacts are directed horizontally by means 
of a pendulum. In both cases, the height of the fall is the vertical distance between the point of release and 
the horizontal plane containing the point of impact. 
 The point of impact shall be no more than 5 cm from the edge of the collector cover, and no more than 10 cm 
from the corner of the collector cover,  but it shall be moved by several millimetres each time the steel ball is 
dropped. A steel ball shall be dropped onto the collector 10 times from the first test height, then 10 times from 
the second test height, etc. until the maximum test hei ght is reached (as specified by the manufacturer). The 
test is to be stopped when the collector sustains some damage or when the collector has survived the impact 
of steel balls at the maximum test height. 
 
NOTE This method does not correspond to the physical effect of  hailstones as the deformation energy absorbed by the ice particl es 
is not being considered. 
 
5.10.2.3 Method 2 
 
The apparatus consists of the following equipment: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 17 a) Moulds of suitable material for casting sphe rical ice balls of the required diameter (25 mm). 
 
b) A freezer, controlled at -10 °C ± 5 °C. 
 
c) A storage container for storing the ice balls at a temperature of -4 °C ± 2 °C. 
 
d) A launcher capable of propelling an ice ball at the sp ecified velocity (as specified by the manufacturer), 
within ± 5 %, so as to hit the collector within the specified impact location. The path of the ice ball from 
the launcher to the collector may be horizontal, vertical or at any intermediate angle. 
 
e) A rigid frame for supporting the collector, with the impact surface normal to the path of the projected ice 
ball; the support shall be stiff enough so that there is negligible distortion or deflection at the time of 
impact. 
 
f) A balance for determining the mass of an ice ball to a standard uncertainty of ± 2 %. 
 
g) An instrument for measuring the velocity of the ice ball to a standard uncertainty of ± 2 ms-1. The velocity 
sensor shall be no more than 1 m from the surface of the collector. 
 
As an example, Figure A.16 shows in schematic form a suitable apparatus comprising a horizontal pneumatic 
launcher, a vertical collector support and a velocity meter which measures electronically the time it takes the 
ice ball to traverse the distance between two light beams. 
 
The testing procedure shall be the following: 
 
a) Using the moulds and the freezer, make sufficient ice balls of the required size for the test, including 
some for the preliminary adjustment of the launcher. 
 
b) Examine each one for cracks, size and mass. An acceptable ball shall meet the following criteria: 
 
⎯ no cracks visible to the unaided eye; 
 
⎯ diameter within ±5 % of the ball (25 mm); 
 
⎯ mass within ±5 % of the ball (25 mm). 
 
c) Place the balls in the storage container and leave them there for at least 1 h before use. 
 
d) Ensure that all surfaces of the launcher likely to be in contact with the ice balls are near room 
temperature. 
 
e) Fire a number of trial shots at a simulated target in accordance with step g) below and adjust the 
launcher until the velocity of the ice ball, as measured with the velocity sensor in the prescribed position, 
is within ±5 % of the requ ired hailstone test velocity. 
 
f) Install the collector at room temperature in the prescribed mount, with the impact surface normal to the 
path of the ice ball. 
 
g) Take an ice ball from the storage container and place it in the launcher. Take aim at the impact location 
and fire. The time between the removal of the ice ball from the container and impact on the collector shall 
not exceed 60 s. 
 
The point of impact shall be no more than 5 cm from the edge of the collector cover, and no more than 10 cm 
from the corner of the collector cover, but it shall be moved by several millimetres each time the ice ball is 
launched. 
 
An ice ball shall be launched onto the collector 10 times; the test shall be stopped when the collector sustains 
some damage or when the collector has survived the impact of 10 ice balls.  
5.10.3 Test conditions 
 
If the test is conducted according to method 1, the steel ball shall have a mass of 150 g ± 10 g and the 
following series of test heights shall be used: 0.4 m, 0.6 m, 0.8 m, 1.0 m, 1.2 m, 1.4 m, 1.6 m, 1.8 m and 2.0 m  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
18 © KEBS 2008 — All rights reserved If the test is conducted according to method 2, the ice ball shall have a diameter of 25 mm ± 5 %, a mass of 
7.53 g ± 5 % and its velocity shall be 23 m/s ± 5 %. 
 5.10.4 Results 
 
The collector shall be inspected for damage. The results of the inspection shall be reported, together with the 
height from which the steel ball was dropped (if method 1 is used) and the number of impacts which caused 
the damage. 
 
NOTE As test method 2 is closer to reality, this method (5.10.2.3) is preferable. 
 
5.11 Final inspection 
 When the full tests have been completed, the collector shall be dismantled and inspected. All abnormalities hall be reported and accompanied by a photograph. 
 
5.12 Test report 
 
The format sheets given in Annex B shall be completed for each test, together with the introductory format 
sheet (B.1) reporting a summary of main results, including the test methods. 
 
6 Thermal performance testing of liquid heating collectors 
 
The thermal performance of glazed solar collectors shall be tested according to either 6.1 or 6.3. 
 
6.1 Glazed solar collectors under steady state conditions (including pressure drop) 
 
6.1.1 Collector mounting and location 
 
6.1.1.1 General 
 
The way in which a collector is mounted will influence the results of thermal performance tests. Collectors to 
be tested shall therefore be mounted in accordance with 6.1.1.2 to 6.1.1.8. Full-size collector modules shall 
be tested, because the edge losses of small collectors may significantly reduce their overall performance. 
 
6.1.1.2 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. 
 
6.1.1.3 Tilt angle 
 
The collector shall be tested at tilt angles such that the incidence 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 20°. 
 
NOTE 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. 
 
6.1.1.4 Collector orientation outdoors  
 
The collector may be mounted outdoors in a fixed position facing the equator, but this will result in the time 
available for testing being restricted by the 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.  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 19 6.1.1.5 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. 
 6.1.1.6 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 th e 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 collector's field of view shall be obstructed, and it is particularly important to avoid 
buildings or large obstructions subtending an angle of greater than approximately 15° to the horizontal in front 
of the collectors. The reflectance of most rough surfaces such as grass, weathered concrete or chippings is 
usually low enough so no problem is caused 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 di rect 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. 
 
6.1.1.7 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 
shall 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. 
 6.1.1.8 Airspeed 
 
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 air speed, parallel to the collector aperture, shall be between the limits specified in 
6.1.4.3. Where necessary, artificial wind generators shall be used to achieve these air 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. 
 
6.1.2 Instrumentation  
6.1.2.1 Solar radiation measurement 
 
6.1.2.1.1 Pyranometer  
6.1.2.1.1.1 General 
 
A class I or better, as specified in KS ISO 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 KS ISO/TR 9901 should be observed. Before ea ch test the pyranometer should be checke d for dust, soiling etc. on the outer dome 
and it should be cleaned if necessary.  
A class I or better pyranometer equipped with a shading ring or alternatively a pyrheliometer together with a 
pyranometer shall be used to measure the diffuse short-wave radiation.  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
20 © KEBS 2008 — All rights reserved 6.1.2.1.1.2 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. 
 6.1.2.1.1.3 Precautions for effects of humidity and moisture 
 
The pyranometer shall be provided with a means of preventing accumulation of moisture that may condense 
on surfaces within the instrument and affect its reading. An instrument with a desiccator that can be inspected is required. The condition of the desiccator shall be observed on a regular basis. 
 6.1.2.1.1.5 Precautions for infrared radiation effects on pyranometer accuracy  
 
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 µm from the 
simulator light source. 
 
6.1.2.1.1.5 Mounting of pyranometers outdoors  The pyranometer shall be mounted such that its sensor is coplanar, within a tolerance of ±1° 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. 
 
NOTE For angles of incidence of 50°, a deviation of ±1° leads to an error of 2 % when measuring the solar irradiance. 
 
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.  
6.1.2.1.1.6 Use of pyranometers in solar irradiance simulators 
 
Pyranometers may be used to measure the distribution of simulated solar irradiance over the collector 
aperture, and the variation in simulated irradiance with  time (see 6.1.5.6). Alternatively, other types of 
radiation detector may be used, provided that they have been evaluated and calibrated for simulated solar 
radiation in question. 
 The pyranometer(s) shall be mounted such that its sensor (s) is (are) coplanar, with a tolerance of ±1 ° with 
the plane of the collector aperture. The pyranometer(s) shall not cast a shadow onto the collector aperture at 
any time during the test period. The pyranometer(s) shall be mounted so as to receive the same levels of 
indirect, diffuse and reflected solar radiation as are received by the collector. 
 The method and equipment used to measure any variation in simulated irradiance with time during the test period, shall be well proven to give the required accuracy. 
 
NOTE E.g. for the most commonly used type of solar simulator, usin g an electrical arc in a sealed beam parabolic reflector as t he 
light source, the mounting of a pyranometer in a typical test position at the midheight of the collector as described for outdo or testing, will 
not be adequate. Especially, when the lamp array is powered from unstabilized mains power supply and from 3 different phases. F or 
solar simulators of this kind not equipped with stabilized power supply, integration of power supply voltage during each test p eriod is 
recommended. Solar simulators equipped with stabilized power supply, capable of stabilizing the power supply voltage within ±0. 5 %, 
normally will need no integration of simulated irradiance during (each) test period. For most types of solar simulators, the re lationship 
between the spatially integrated value of the simulated solar irradiance and the integrated power supply voltage during each te st period, 
can be found. In all cases, sufficient knowledge of burn in and life time characteristics of the lamp type used, is assumed. 
 
6.1.2.1.2 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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 21 by the pointer may be measured using the concentric rings and used to determine the angle of incidence. 
The device shall be positioned in the collector plane and to one side of the collector. 
 
6.1.2.2 Thermal radiation measurement 
 
6.1.2.2.1 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. 
 
6.1.2.2.2 Determination of thermal irradiance indoors and in solar simulators   
6.1.2.2.2.1 Measurement 
 
The thermal irradiance may be meas ured using a pyrgeometer as indi cated in 6.1.2.2.1 for outdoor 
measurements. Pyrgeometer shall be well ventilated in order to minimize the influence of solar or simulated 
solar irradiance. For indoor testing, the thermal irradiance shall be determined to a standard uncertainty of 
10Wm
-2 
 
6 A.2.2.2.2 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 1), from a hotter surface (designated 2) is given by 
 
4
2 122TFσε  (1) 
 
Or, more usefully, the additional thermal irradiance (compared with that which would be present if surface 2 
had been a perfect black body at ambient temperature) is given by  
σF124
a4
22 T T−ε ) (2) 
 
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 global irradiance.  
 
6.1.2.3 Temperature measurements 
 
6.1.2.3.1 General 
 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 sensor for temperature 
measurement and associated equipment may be different. 
 
6.1.2.3.2 Measurement of heat transfer fluid inlet temperature (t
in) 
 
6.1.2.3.2.1 Required accuracy 
 
The temperature of the heat transfer fluid at the collector inlet shall be measured to a standard uncertainty of 
0.1 K, 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 K is required  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
22 © KEBS 2008 — All rights reserved 6.1.2.3.2.2 Mounting of sensors 
 The sensor 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 sensor. If it is 
necessary to position the sensor 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 sensor, and the sensor 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.  
Dimensions in millimeters 
 
 
Figure 1 — Recommended transducer positions for measuring the heat transfer fluid inlet and outlet 
temperatures 
 
6.1.2.3.3 Determination of heat transfer fluid temperature difference ( ΔT) 
 
The difference between the collector outlet and inlet temperatures ( ΔT) shall be determined to a standard 
uncertainty of <0.05 K. Standard uncertainties 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. Delta-T sensors shall be calibrated in the relevant 
temperature range. 
 
6.1.2.3.4 Measurement of surrounding air temperature ( ta) 
 
6.1.2.3.4.1 Required accuracy 
 
The ambient or surrounding air temperature shall be measured to a standard uncertainty of 0.5 K. 
 6.1.2 .3.4.2 Mounting of sensors 
 
For outdoor measurements the sensor 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 mid height 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. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 23  
The shelter shall be positioned to one side of the collector and not more than 10 m from it. If air is forced over 
the collector by a wind generator, the air temperature shall be measured in the outlet of the wind generator 
and checks made to ensure that this temperature does not deviate from the ambient air temperature by more 
than ±1 K. 
 6.1.2.4 Measurement of collector liquid flowrate  
Mass flowrates may be measured directly or, alternatively, if the density is known, they may be determined 
from measurements of volumetric flowrate and temperature. The standard uncertainty of the liquid flowrate 
measurement shall be within ±1 % 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.  
 
NOTE The temperature of the fluid in volumetric flowmeters should be known with sufficient accuracy to ensure that mass flowrat es 
can be determined to within the limits specified by the manufacturer. 
 
6.1.2.5 Measurement of air speed  
6.1.2.5.1 General 
 
The heat losses from a collector increase with increasing air speed over the collector, but the influence of air 
speed direction is not well understood. Measurements of air speed 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 sp eed is not a useful parameter for collector testing. By 
using the air speed measured over the collector, it is possible to define clearly the conditions in which the 
tests were performed. 
 
6.1.2.5.2 Required accuracy 
 
The speed of the surrounding air over the front surface of the collector shall be measured to a standard uncertainty of 0.5 ms
-1 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. 
 
6.1.2.5.3 Mounting of sensors for the measurement of air velocity over the collector 
 
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 10 mm to 50 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 is below 2 ms
-1, an artificial wind generator 
shall be used, and anemometer measurements shall be fitted for the continuous measurement of air velocity. 
This anemometer shall be mounted on a board so that there is continuous surface pointing towards the wind 
generator from the collector edge to 0.3 m behind the anemometer. The uniformity of air speed in the field of 
collector aperture shall be checked. The wind speed shall be measured while adjusting the wind generator, 
using a hand held anemometer in a height of 10 mm to 50 mm above the collector aperture plane. 
 In windy locations, 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 the test periods.  
NOTE The recorded value of the wind speed is different to the air speed above the collector aperture. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
24 © KEBS 2008 — All rights reserved  
6.1.2.6 Elapsed time 
 Elapsed time shall be measured to a standard uncertainty of 0.2 %. 
 
6.1.2.7 Instrumentation/data recorders 
 
In no case shall the smallest scale division of the instrument or instrument system exceed twice the specified 
standard uncertainty. For example, if the specified standard uncertainty is 0.1 K, the smallest scale division shall not exceed 0.2 °C. Digital techniques and electronic integrators shall have a standard uncertainty equal 
to or better than 1.0 % of the measured value. 
 Analog and digital recorders shall have an error equal to or better than 0.5 % of the full-scale reading and 
have a time constant of 1s or less. The peak signal indication shall be between 50 % and 100 % of full scale. 
The input impedance of recorders shall be greater than 1000 times the impedance of the sensors or 10 M Ω 
whichever is higher. 
 6.1.2.8 Collector area 
 The collector area (absorber, gross or aperture) shall be measured to a standard uncertainty of 0.3 %. Area measurements shall take place at a collector temperature of (20 ± 10) °C and under operating pressure if the 
absorber is made of organic material. 
 
6.1.2.9 Collector fluid capacity 
 
The fluid capacity of the collector shall be measured to a standard uncertainty of no more than 10 %. 
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 shall be kept within ±2 K of the ambient temperature. As an alternative, a determination by calculation, which is based on the geometrical circumstances, can be given.  
6.1.3 Test installation 
 6.1.3.1 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. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 25 
 
 
Figure 2 — Example of a closed test loop 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
26 © KEBS 2008 — All rights reserved 
 
 
Figure 3 — Example of an open test loop 
 
6.1.3.2 Heat transfer fluid 
 
The heat transfer fluid used for collector testing may be water or a fluid recommended by the collector 
manufacturer. The specific heat capacity and density of the fluid used shall be known to within ±1% over the 
range of fluid temperatures used during the tests. These values are given for water in Annex I.  
 
Some fluids may need to be changed periodically to ensure that their properties remain well defined. 
 
The mass or volume 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.  
 
6.1.3.3 Pipework and fittings 
 
The piping used in the collector loop shall be resistant to corrosion and (for testing of glazed collectors) suitable for operation at temperatures up to 95 °C. If nonaqueous fluids are used, then compatibility with PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 27 system materials shall be confirmed. Pipe lengths shall generally be kept short. In particular, the length of 
piping between the outlet of the fluid temperature 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 WK-1, 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 insulation and reflective (for outdoor measurements also 
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 ±0.01 K under test conditions. Flow-mixing devices such as pipe bends are required immediately upstream of temperature sensors (see 6.1.2.3). 
 
NOTE 1 A short length of transparent tube should be installed in the fluid loop so that air bubbles and any other contaminants will be 
observed if present. The transparent tube should be placed close to the collector inlet but should not influence the fluid inle t temperature 
control or temperature measurements. 
 
A variable area flowmeter is convenient for this purpos e, as it simultaneously gives an independent visual 
indication of the flowrate. An air separator and air vent should be placed at the outlet of the collector, and 
other points in the system where air can accumulate. 
 
NOTE 2 Filters should be placed upstream of the flow measuring device and the pump, in accordance with normal practice (a nomin al 
filter size of 200 µm is usually adequate). 
 
6.1.3.4 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. With some types of pump, a simple bypass loop and 
manually controlled needle valve may provide adequate flow control. Where necessary, an appropriate flow 
control device may be added to stabilize the mass flowrate.   
The pump and flow controller shall be capable of maintaining the mass or volume flowrate through the collector stable to within 1 % despite temperature variations, at any inlet temperature chosen within the 
operating range. 
 
6.1.3.5 Temperature regulation of the heat transfer fluid 
 The collector test loop shall 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. 
 
NOTE 1 Test loops may contain two stages of fluid inlet temperature control, as shown in Figures 2 and 3. The primary temperatu re 
controller should be placed upstream of the flowmeter and flow controller. A secondary temperature regulator should be used to adjust 
the fluid temperature just before the collector inlet. This secondary regulator should normally not be used to adjust the fluid  temperature 
by more than ±2 K. 
 
NOTE 2 A secondary temperature controller close to the collector inlet is useful, provided that it does not introduce problems with 
measuring the “mean cup" inlet temperature. On the other hand, bypasses should also remain allowed as a means to reduce the 
influence of heat loss and to improve the control characteristics of the heating circuits. A constant and high flowrate through  the heaters 
will allow PID controlling with fast I and D action, while any flowrate through the collector can be chosen. 
 
6.1.4 Outdoor steady-state performance test 
 
6.1.4.1 Test installation 
 The collector shall be mounted in accordance with the specifications given in 6.1.1, and coupled to a test loop 
as described in 6.1.3. The heat transfer fluid shall flow from the bottom to the top of the collector, or as 
recommended by the manufacturer. 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
28 © KEBS 2008 — All rights reserved 6.1.4.2 Preconditioning of the collector 
 
The collector shall be visually inspected and any dama ge recorded. The collector aperture cover shall be 
thoroughly cleaned. If moisture is formed on the collector components, then the heat transfer fluid shall be 
circulated at approximately 80 °C for as long as is necessary to dry out the insulation and collector enclosure. 
 
If this form of preconditioning 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. The empty collector shall be exposed to 
irradiation for 5 h at the level of more than 700 Wm
-2. 
 
6.1.4.3 Test conditions 
 
At the time of the test, the hemispherical solar irradiance at the plane of the collector aperture shall be greater 
than 700 Wm-2. 
 
NOTE1 lf the manufacturer has limitations on operation with respect to maximum irradiance but not less than 800 Wm-2, this can be 
requested with the test. That maximum value should be clearly reported. 
 
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 usua lly be satisfied if the angle of  incidence of direct solar 
radiation at the collector aperture is less than 20°. 
 
However, much lower angles may be required for particular designs. In order to characterize collector performance at other angles, an incident angle modifier may be determined (see 6.1.7). 
 
Where diffuse solar irradiance is less than 30 %, its influence may be neglected. The collector shall not be 
tested at diffuse irradiance levels of greater than 30 %. 
 The average value of air speed parallel to the collector aperture, taking into account spatial variations over the collector and temporal variations during the test period, shall be 3 ms ± 1 ms
-1. 
 
Unless otherwise specified, the fluid flowrate shall be set at approximately 0.02 kgs-1 per square metre of 
collector aperture area. It shall be held stable to within ±1 % of the set value during each test period, and 
shall not vary by more than ±10 % of the set value from one test period to another. 
 
The testing at other flowrates may be accommodated by adhering to manufacturer's specification. 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 
measurements 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. 
 
NOTE 2 In the transition regime, the flowrate should first be set high (turbulent) and then reduced to the setpoint value. This  will prevent 
transition from laminar to turbulent during the measurements. Measurements of fluid temperature difference of less than 1 K sha ll not be 
included in the test results because of the associated problems of instrument error. 
 
6.1.4.4 Test procedure 
 
The collector shall be tested over its operating temperature range under clear sky conditions in order to 
determine its performance 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. If possible, one inlet temperature shall be selected such that the mean fluid temperature in the 
collector lies within ±3 K of the ambient air temperatur e, in order to obtain an accurate determination of 
.oηif 
water is the heat transfer fluid, the maximum temperature shall be at least around 80 °C. A maximum value of 
Tm* of at least 0.09 is recommended if test conditions permit. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 29 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 altitude using automatic tracking. 
 
During a test, measurements shall be made as specified in 6.1.4.5. These may then be used to identify test 
periods from which satisfactory data points can be derived. 
 6.1.4.5 Measurements 
 
The following data shall be measured: 
 
⎯ gross collector area  AG, the absorber area AA and the aperture area Aa; 
 
⎯ fluid capacity 
 
⎯ hemispherical solar irradiance at the collector aperture 
 
⎯ diffuse solar irradiance at the collector aperture (only outdoors) 
 
⎯ angle of incidence of direct solar radiation (alternatively, this angle may be determined by calculation)  
 
⎯ air speed parallel to the collector aperture 
 
⎯ surrounding air temperature 
 
⎯ temperature of the heat transfer fluid at the collector inlet  
 
⎯ temperature of the heat transfer fluid at the collector outlet flowrate of the heat transfer fluid 
 
6.1.4.6 Test period (steady-state) 
 
The test period for a steady state data point shall include a pre-conditioning period of at least 4 times the time 
constant of the collector (if known), or not less than 15 min (if time constant is not known), with the correct fluid temperature at the inlet, followed by a steady state measurement period of at least 4 times the time 
constant of the collector (if known), or not less than 10 min (if time constant is not known). 
 
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 5. 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  
 
Table 5 — Permitted deviation of measured parameters during a measurement period 
 
Parameter Permitted deviation from the mean value 
(Global)Test solar irradiance ±50 Wm-2 
Surrounding air temperature (indoor) ±1 K 
Surrounding air temperature (outdoor) ±1.5K 
Fluid mass flowrate ±1 % 
Fluid temperature at the collector inlet ±0.1 K 
 
 
6.1.4.7 Presentation of results 
 
The measurements shall be collated to produce a set of data points which meet the required test conditions (see 6.1.4.3), including those for steady-state operation. These shall be presented using the data format sheets given in Annex D. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
30 © KEBS 2008 — All rights reserved  
6.1.4.8 Computation of collector output  
6.1.4.8.1 General 
 
The actual useful power extracted,
Q&, is calculated from: 
 
ΔΤ=fcmQ&& (3) 
 
A value of cf corresponding to the mean fluid temperature shall be used. If m& is obtained from volumetric 
flowrate measurement, then the density shall be determined for the temperature of the fluid in the flowmeter. 
 6.1.4.8.2 Solar energy intercepted by the collector 
 
Provided that the angle of incidence is less than 20°, the use of an incident angle modifier, as described in 
6.1.7, is not required for single glazed flat plate collectors. 
 
The solar energy intercepted is A.G where the area is A
A when referred to the absorber area of the collector 
and Aa when referred to the aperture area of the collector. Introducing the collector efficiency, the actual 
useful power extracted, Q&, can also be written as 
 
ηG QΛ=& (4) 
 
6.1.4.8.3 Reduced temperature difference 
 
When the mean temperature of the heat transfer fluid fm is used, where 
 
tm = t in+2ΤΔ (5) 
 
the reduced temperature difference is calculated as:  
Gt tΤma m *−=  (6) 
 
6.1.4.8.4 Modeling of instantaneous efficiency 
 6.1.4.8.4.1 General 
 
The instantaneous efficiency 
η shall be calculated by statistical curv e fitting, using the least squares method, 
to obtain an instantaneous efficiency curve of the form 
 
()2*
2*
1 0 m m Ga a Τ−Τ−=ηη  (7) 
 Normally a second-order curve shall be used which can be achieved by least squares regression. A second-
order fit shall not be used if the value deduced for a
2 is negative. The test conditions shall be recorded on the 
data format sheets given in Annex D. 
 
Where necessary, tables of measurements of the collector performance are admitted. 
 
6.1.4.8.4.2 Instantaneous efficiency based on absorber area / aperture area  
With reference to the reduced temperature difference 
*
mΤthe equations for instantaneous efficiency are: PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 31  
2
a m
2a m
1 0 ⎟
⎠⎞⎜
⎝⎛−−−−=Gt tGaGt taηη  (8) 
 
6.1.4.8.4.3 Conversion of thermal performance test characteristics 
 
To convert the thermal performance test characteristics the following basic conversions shall be used: 
 
ΑΑΑΑ=a
a0 0ηη  (9) 
 
ΑΑΑΑ=a
aa a1 1  10) 
 
ΑΑΑΑ=a
aa a2 2  (11) 
 6.1.4.8.5 Collector output 
 
Using Equation 4 and 8 the collector output per module can be written as: 
 
()()⎟
⎠⎞⎜
⎝⎛ −−−−⋅⋅Α=Gt taGt ta G Qa a m
2m
1 0η& (4.1) 
 
Where the area is AA when referred to the absorber area of the collector and Aa when referred to the aperture 
area of the collector. 
 
The collector output per module shall be presented graphically as a function of the temperature difference 
between mean fluid and ambient temperature ( tm – ta) using G = 1000W/m2. The product AG0ηshall be 
referred to as Wpeak. 
 
6.1.5 Steady-state efficiency test using a solar irradiance simulator 
 6.1.5.1 General  
The performance of most collectors is better in direct solar radiation than in diffuse and at present there is 
little experience with diffuse solar simulation. This test method is therefore designed for use only in simulators 
where a near-normal incidence beam of simulated solar radiation can be directed at the collector.  
In practice it is difficult to produce a uniform beam of simulated solar radiation and a mean irradiance level has therefore to be measured over the collector aperture 
 6.1.5.2 The solar irradiance simulator for steady-state efficiency testing 
 
A simulator for steady-state efficiency testing shall have the following characteristics: 
 The lamps shall be capable of producing a mean irradiance over the collector aperture of at least 700 Wm
-2. 
Values in the range 300 Wm to 1000 Wm-2 may also be used for specialized tests, provided that the accuracy 
requirements given in Table 5 can be achieved and the irradiance values are noted in the test report. 
 
At any time the irradiance at a point on the collector aperture shall not differ from the mean irradiance over 
the aperture by more than ±15 %. The spectral distribution of the simulated solar radiation shall be 
approximately equivalent to that of the solar spectrum at optical air mass 1.5. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
32 © KEBS 2008 — All rights reserved Where collectors contain spectrally selective absorbers or covers, a check shall be made to establish the 
effect of the difference in spectrum on the ( τα) product for the collector. If the effective values of ( τα) under 
the simulator and under the optical air mass 1.5 solar radiation spectrum differ by more than ±1 %, then a; 
correction shall be applied to the test results. 
 
Effective ( τα) = 
∫∫
m3
m0.3m3
m3.0
)dG(dλ)()()(
μ
μμ
μ
λλλλαλτ G
 (12) 
 
Measurement of the solar simulator's spectral qualities shall be in the plane of the collector over the wavelength range of 0.3 µm to 3 µm and shall be determined in band widths of 0.1 µm or smaller. 
 For certain lamp types, i.e. metal halide designs, it is recommended that the initial spectral determination be 
performed after the lamps have completed their burn-in period. The amount of infrared thermal energy at the 
collector plane shall be suitably measured (measurements in the wavelength range above about 2.5 µm if possible, but starting not beyond 4 µm) and reported (see 6.1.2.2).  
The thermal irradiance at the collector shall not exceed that of a blackbody cavity at ambient air temperature by more than 5 % of global irradiance. 
 
The collimation of the simulator shall be such that the angles of incidence of at least 80 % of the simulated solar irradiance lie in the range in which the incident angle modifier of the collector varies by no more than ±2 
% from its value at normal incidence. For typical flat plate collectors, this condition usually will be satisfied if at least 80 % of the simulated solar radiation received at any point on the collector under test shall have 
emanated from a region of the solar irradiance simulator contained within a subtended angle of 60° or less 
when viewed from any point.  
 
NOTE 1 Additional requirements concerning collimation ap ply to measurement of the incident angle modifier (see 6.1.7.2).  
 
The method used for measuring the irradiance during the test period shall produce values of mean irradiance 
which agree with those determined by spatial integration to within ±1%. 
 
NOTE 2 The spectral distribution of the lamps (indoors) and of the sky (outdoors) can and do lead to very wide discrepancies in  
spectrally selective absorbers or covers. 
 
6.1.5.3 Test installation  
Collector mounting and location requirements outlined in 6.1.1 shall be followed. 
 
A wind generator shall be used with a solar simulator to produce an air flow in accordance with 6.1.1.8. 
 
6.1.5.4 Preconditioning of the collector 
 
The procedure outlined in 6.1.4.2 shall be followed. 
 
6.1.5.5 Test procedure 
 
The collector shall be tested over its operating temperature range in approximately the same way as 
specified for outdoor testing (see 6.1.4.4). 
 
However, eight test points shall be a dequate for testing in solar simulators provided that at least four different 
inlet temperatures are used, and adequate time is  allowed for temperatures to stabilize. One inlet 
temperature should lie within ±3 K of the ambient air temperature, if possible. During a test, measurements shall be made as specified in 6.1.5.6. These may then be used to identify test periods from which satisfactory data points can be derived. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 33  
6.1.5.6 Measurements during tests in solar irradiance simulators  
6.1.5.6.1 General 
 Measurements shall be made as specified in 6.1.4.  
6.1.5.6.2 Measurement of simulated solar irradiance 
 
NOTE Simulated solar irradiance usually varies spatially over the  collector aperture as well as varying with time during a test . It is 
therefore essential to employ a procedure for integrating the irradiance over the collector aperture. Time variations in irradi ance are 
usually caused by fluctuations in the electricity supply and changes in lamp output with temperature and running time. Some lam ps take 
more than 30 min to reach a stable working condition when warming up from cold. 
 
Pyranometers may be used to measure the irradiance of simulated solar radiation in accordance with 6.1.2.1. 
Alternatively, other types of radiation detector may be used, provided they have been calibrated for simulated 
solar radiation. Details of the instruments and the methods used to calibrate them shall be reported with the 
test results. The distribution of irradiance over the collector aperture shall be measured using a grid of 
maximum spacing 150 mm, and the spatial mean deduced by simple averaging.  
6.1.5.6.3 Measurement of thermal irradiance in simulators 
 
The thermal irradiance in a solar simulator is likely to be higher than that which typically occurs outdoors. It 
shall therefore be measured to ensure that it does not exceed the limit given in 6.1.5.8. 
 
The mean thermal irradiance in the collector test plane  shall be determined whenever changes are made in 
the simulator which could affect the thermal irradiance, and at least annually. The mean thermal irradiance in 
the collector test plane and the date when it was last measured shall be reported with collector test results. 
 
6.1.5.6.4 Ambient air temperature in simulators 
 
The ambient air temperature t
a in simulators shall be measured, taking the mean of several values if 
necessary sensors shall be shielded in order to minimize radiation exchange. The air temperature in the 
outlet of the wind generator shall be used for the calculations of collector performance. 
 
6.1.5.7 Test period 
 
The test period may be determined in the same way as for outdoor steady-state testing. 
 
The more stable environment of an indoor test facility may allow steady-state cond itions to be maintained 
more easily than outdoors, but adequate time shall still be allowed to ensure proper steady-state operation of 
the collector as specified in 6.1.4.6. 
 
6.1.5.8 Test conditions 
 
The test conditions described in 6.1.4.3 for outdoor testing shall be observed with the following additions:  
⎯ thermal irradiance in the plane of the collector apertu re shall not exceed that from a blackbody cavity at 
ambient air temperature by more than 5 % of the global irradiance. 
 
⎯ air issuing from the wind generator shall not differ in  temperature from ambient air by more than ±1 K.  
 
 
6.1.5.9 Computation and presentation of results 
 
The analysis presented in 6.1.4.8 for outdoor testing is also applicable to solar simulator tests, and the results shall be presented on the format sheets shown in Annex D. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
34 © KEBS 2008 — All rights reserved 6.1.6 Determination of the effective thermal capacity and the time constant of a collector 
 
6.1.6.1 General 
 
The effective thermal capacity and the time constant of a collector are important parameters, which determine 
its transient performance. 
 
A collector can usually be considered as a combination of masses, each at a different temperature. When a 
collector is operating, each collector component responds differently to a change in operating conditions, so it is useful to consider an effective thermal capacity for the whole collector. 
 
Unfortunately, the effective thermal capacity depends on the operating conditions and is not a collector parameter with a unique value. Several different test methods have been used to measure or calculate the 
effective thermal capacity of collectors and it has been shown that similar results can be obtained by using 
quite different methods. Just as there is no unique value of effective thermal capacity, there is no unique overall time constant for a collector. For most collectors, the dominant influence on the response time is the 
fluid transit time, and hence the first-order response varies with the fluid flowrate. Other collector components 
respond with different times to give an effective overall time constant, which depends on the operating 
conditions.  
6.1.6.2 Determination of effective thermal capacity  
The effective thermal capacity of the collector C (expressed as Joules per Kelvin) is calculated as the sum, 
for each constituent element of the collector (glass, absorber, liquid contained, insulation), of the product of its mass m: (expressed in kilograms), its specific heat c
i (expressed as joules per kilogram Kelvin) and a 
weighting factor pi; 
 
C = ii
iicmp∑ (13) 
 
The weighting factor pi (between 0 and 1) allows for the fact that certain elements are only partially involved 
in collector thermal inertia. The values of pi are given in Table 6. 
 
Table 6 — Values of weighting factors 
 
Elements pi 
Absorber Insulation 1 
Heat transfer liquid 0.5 
External glazing 0.01×a1 
Second glazing 0.2×a1 
Third glazing 0.35×a1 
 
For drain-back and drain-down systems, the capacity should be reported for the collector while it is filled with 
water and while it is empty. 
 Effective thermal capacity may also be measured by applying the procedures described in Annex G. 
 
6.1.6.3 Test procedure for collector time constant (optional) 
 Testing shall be performed either outdoors or in a solar irradiance simulator. In either case, the solar 
irradiance on the plane of the collector aperture shall be greater than 700 Wm
-2. The heat transfer fluid shall 
be circulated through the collector at the same flowrate as that used during collector thermal efficiency tests. 
The aperture of the collector shall be shielded from the solar radiation by means of a solar-reflecting cover, 
and the temperature of the heat transfer fluid at the collector inlet shall be set approximately equal to the 
ambient air temperature. When a steady state has been reached, the cover shall be removed and measurements continued until steady-state conditions have been achieved again. For the purpose of this PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 35 test, a steady-state condition is assumed to exist when the outlet temperature of the fluid varies by less than 
*0.05 K per minute. The following quantities shall be measured in accordance with 6.1.2: 
 
⎯ Collector fluid inlet temperature ( tin); 
 
⎯ Collector fluid outlet temperature ( te); 
 
⎯ Surrounding air temperature ( ta); 
 
6.1.6.4 Calculation of collector time constant (optional) 
 
The difference between the temperature of the fluid at the collector outlet and that of the surrounding air (te -
te) shall be plotted against time, beginning with the initial steady-state condition ( te - ta)0 and continuing until 
the second steady state has been achieved at a higher temperature ( te - ta)2 (see Figure 4). 
 
 
 
Figure 4 — Collector time constant 
 
The time constant τc of the collector is defined as the elapsed time between the removal of the cover and the 
point where the collector outlet temperature rises to 63.2 % of the total increase from ( te - ta)0 to (te - ta)2. If the 
response time of the temperature sensors is significant when compared with that measured for the collector, 
then it shall be taken into accoun t in calculating the test results. 
 
6.1.7 Collector incidence angle modifier 
 
6.1.7.1 General 
 
The effective transmittance-absorbance product ( τα)e can be replaced by the value at normal incidence 
provided that another factor called the incidence angle modifier, Kθ, is introduced in Equation (14). 
 
()ταθΚFη,= en-a12
a m
2α m
G⎟
⎠⎞⎜
⎝⎛−−−
Gt tGat t
 (14) 
Hence: PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
36 © KEBS 2008 — All rights reserved  
(τα)e = Kθ(τα)en (15) 
 
Figure 5 shows the variation of Kθ with angle of incidence for two solar collectors. 
 
For those collectors (e.g. evacuated tube collectors and CPC collectors) for which the incidence angle effects 
are not symmetrical with direction of incidence, it is necessary to measure the incident angle effects from 
more than one direction to fully characterize the incident angle modifier.  
The complex individual incident angle modifier can be estimated by considering it to be the product of the 
separate incident angle modifiers, 
θLΚ and θΤΚfor two perpendicular symmetry planes (Equation 15.1). 
 
Kθ=θLΚθTΚ•  (15.1) 
 
The longitudinal plane (index L) runs parallel to the optical axis of the collector, and the transversal plane 
(index T) is perpendicular to the optical axis. The angles θL and θT are the projections of the incidence angle 
θ onto the longitudinal and transversal planes, respectively. 
 
For the correlation between θ, θL and θT, the following equation holds: 
 
tan2θ = tan2θL + tan2θT (15.2) 
 
 
 
Figure 5 — Typical incidence angle modifiers Kθ PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 37  
The significance of the incidence angle modifier to the test procedures outlined in this standard is that the 
thermal efficiency values are determined for the collector at or near normal incidence conditions. Therefore, the y intercept 
η of the efficiency curve is equal to F’(τα)en, for a flat plate collector. A separate 
measurement shall be conducted to determine the value of Kθ so that the performance of the collector can be 
predicted under a wide range of conditions and/or time of day using Equation (14). 
 
6.1.7.2 Solar irradiance simulator for the measurement of incidence angle modifiers 
 For the measurement of the incidence angle modifier, only solar irradiance simulators with the following 
collimation specification shall be used. 
 
The collimation shall be such that at least 90 % of the simulated solar irradiance at any point on the collector 
under test has emanated from a region of the solar irradiance simulator contained within a subtended angle of 20° or less when viewed from the point.  6.1.7.3 Test procedures 
 
6.1.7.3.1 General 
 
The testing of the solar collector to determine it s incidence angle modifier may be done by one of two 
methods. However, during each test period, the orientation of the collector shall be such that the collector is 
maintained within ±2.5° of the angle of incidence for which the test is being conducted. The solar irradiance 
on the plane of the aperture shall be greater than 300 W/m
2. 
 
While measuring the incident angle modifier in one plane of an optical unsymmetrical collector the incident angle within the other plane should be kept to a value where the incident angle modifier does not differ more 
than 2 % from the one at normal incidence.  
NOTE 1 Care should be taken that the measurement of the inci dent angle modifier is not affected by inappropriate tilt angles. 
 
NOTE 2 For angles of incidence of 50°, a deviation of ±1° leads to an error of 2 % when measuring the solar irradiance. 
 
6.1.7.3.2 Method 1 
 This method is applicable for testing indoors using a solar simulator with the characteristics specified in 
6.1.5.2, or outdoors using a movable test rack (altazimuth collector mount) so that the orientation of the 
collector can be arbitrarily adjusted with respect to the direction of the incident solar radiation. 
 
The collector shall be orientated so that the test angle of incidence between it and the direct solar radiation 
for the test condition is 50°. For conventional flat plate collectors, this angle will be sufficient. For some 
collectors with unusual optical performance characteristics, or if it is required for system simulation, angles of 
20°, 40°, 60° and others may be necessary. 
 The mean temperature of the heat transfer fluid shall be controlled as closely as possible (preferably within 
±1 K) to the ambient air temperature. The efficiency value shall be determined in accordance with 6.1.4.4.  
6.1.7.3.3 Method 2  This method is applicable for testing outdoors using a stationary test rack on which the collector orientation 
cannot be arbitrarily adjusted with respect to direction for incident sola r radiation (except for adjustments in 
tilt). 
 
The mean temperature of the heat transfer fluid shall be controlled, if possible, to within ±1 K of the ambient 
air temperature. The efficiency value shall be determined in such a way that one value of efficiency is taken before solar noon and a second value after solar noon. The average incidence angle between the collector 
and the solar beam for both data points is the same. The efficiency of the collector for the specific incidence angle shall be considered equal to the average of the two values. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
38 © KEBS 2008 — All rights reserved  
The efficiency value shall be determined in general in accordance with the method described in 6.1.4.4. As 
with Method 1, data shall be collected for angle of incidence of 50°. For some collectors with unusual optical 
performance characteristics or if it is required for system simulation, angles of 20°, 40°, 60° and others may 
be necessary. 
 
NOTE More experience is required to confirm whether this method is applicable to special geometries, such as tubular collectors . 
 
6.1.7.4 Calculation of collector incidence angle modifier  
Regardless of which experimental method in 6.1.7.3. is used, values for the thermal efficiency of the collector 
shall be determined for each value of angle of incidence. For conventional flat plate collectors, only one angle 
of incidence is needed which is 50° (It is noted that a rating standard using this test method may require that 
K
θ be measured for a different set of angles of incidence). The mean fluid temperature is held very close to 
the ambient air temperature so that 
 
(tm– ta) ≈ 0.  The relationship between Kθ and the efficiency is: 
 
()enθ'ταη
F=Κ  16 
 
Since F’(τα)en will have already been obtained as the y-axis intercept of the efficiency curve, values of kb can 
be computed for the different angles of incidence (see 6.1.7.3.). If the mean fluid temperature cannot be 
controlled to equal the ambient air temperature within ±1 K, each value of Kθ shall be computed as: 
 
ena m
2a m
1
)(ταη
θFGt tGaGt ta
K′⎟
⎠⎞⎜
⎝⎛−+−+
=  (17) 
 
Due to more exact results Equation (17) should be used generally. 
 
Alternatively, each data point may be plotted on the same graph with the efficiency curve determined in accordance with 6.1.4 or 6.1.5, and a curve drawn through each point parallel to the efficiency curve and 
made to intersect the y-axis. The values of the y intercept are the efficiency values that would have resulted 
had the mean fluid temperature been controlled to equal ambient air temperature. Therefore, these values 
may be used in conjunction with Equation (17) to compute the different values of K
θ. 
 
6.1.8 Determination of the pressure drop across a collector 
 
If determination of pressure drop across a collector is required, this should be done according to Annex L. 
 
6.2 Unglazed solar collectors under steady st ate conditions (including pressure drop) 
 
6.2.1 Collector mounting and location 
 
6.2.1.1 General 
 
Specification given in 6.1.1.1 applies. 
 
6.2.1.2 Mounting 
 
The collector shall be mounted in the manner specified by the manufacturer. 
 
The collector mounting frame shall in no way obstruct the aperture of the collector, and shall not significantly affect the back or side insulation, unless otherwise specified (for example, when the collector is part of an 
integrated roof array). PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 39  
Collectors designed to be mounted directly on standard roofing material may be mounted over a simulated 
roof section. In case of roof integrated collectors, a model consisting of a small scale collector placed on an 
artificial roof should be prepared for the purpose of the tests. 
 
If mounting instructions are not specified, the collector shall be mounted on an insulated backing with a 
quotient of the materials thermal conductivity to its thickness of 1 Wm-2 K-1 ± 0.3 Wm-2 K-1 and the upper 
surface painted matt white and ventilated at the back. 
 
NOTE Example material suited for the insulated backing is 30 mm of polystyrene foam. 
 
The collector shall be mounted such that the lower edge is not less than 0.5 m above the local ground 
surface. 
 
Collector arrays constructed from pipe or strip components shall be mounted with the pipes (or strips) spaced 
10 mm or one diameter (width of strip) apart, whichever is the smaller. If a different pipe or strip spacing is 
specified in the manufacturers' installation instructions then the recommended spacing shall be used. If the 
collector is delivered with mounting spacers or any device fixing the spacing of the pipes (or strips) then the 
collector shall be tested as delivered and its geometry shall be reported in the test report. 
 
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.  
The performance of some forms of unglazed solar collectors is a function of module size. If the collector is supplied in fixed units of area greater than 1 m
2 then a sufficient number of modules shall be linked together 
to give a test system aperture of at least 3 m2. If the collector is supplied in the form of strips the minimum 
built-up module area shall be 3 m2 (gross area). 
 
6.2.1.3 Tilt angle 
 
The collector shall be tested at tilt angles so that the incidence angle with direct solar radiation θ is less than 
30°, or at angles of tilt so that the incidence angle modifier varies by less than ±2 % from normal incidence. 
Before deciding on a tilt angle it may be necessary to check the incidence angle modifier at two angles prior 
to commencing the tests. 
 
NOTE For most unglazed collectors, the influence of tilt angle and radiation incidence angle on collector efficiency is small a nd 
unglazed collectors are commonly installed at low inclinations. However care should be taken to avoid air locks at low inclinat ions. 
 
6.2.1.4 Collector orientation outdoors 
 
The collector orientation shall conform to 6.1.1.4. 
 6.2.1.5 Shading from direct solar irradiance 
 The collector shall be shaded from direct so lar irradiance in accordance with 6.1.1.5. 
 
6.2.1.6 Diffuse and reflected solar irradiance 
 
The collector shall diffuse and reflect sola r radiation in accordance with 6.1.1.6. 
 6.2.1.7 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. Fo r example, the outdoor field of view of the collector 
shall not include chimneys, cooling towers or hot exhausts. For indoor and simulator testing, the collector PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
40 © KEBS 2008 — All rights reserved 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. 
 
The major difference between indoor and outdoor testing of unglazed collectors is the long wave thermal 
irradiance. The relative long wave radiation in a simulator shall not be higher than ±50 Wm-2 (typically — 100 
Wm-2 for outdoor conditions). 
 
6.2.1.8 Airspeed 
 
The performance of unglazed collectors is sensitive to air speed adjacent to the collector. 
 
In order to maximize the reproducibility of results, unglaz ed collectors shall be mounted so that air can freely 
pass over the front side of the collector, and exposed back and sides of the collector. Collectors designed for 
integration into a roof may have their backs protected from the wind, but this shall be reported with the test 
results.  
The average surrounding air speed at a distance of 100 mm above and parallel to the collector aperture shall 
cover the range 0 ms
-1 to 3.5ms-1 subject to the tolerance specified in Table 7. If these conditions cannot be 
achieved under natural conditions then an artificial wind generator shall be used. If a wind generator is used 
the turbulence level shall be in the range of 20 % to 40  % to simulate natural wind conditions. The turbulence 
level shall be checked at the leading edge of the collector 100 mm above the collector surface. The 
turbulence level shall be monitored using a linearized hot wire anemometer with a frequency response of at least 100 Hz. If the absorber is not mounted directly on a roof or a sheet of backing material, the air speed 
shall be controlled and monitored on the front and back of the absorber. 
 
6.2.2 Instrumentation 
 
6.2.2.1 Solar radiation measurement 
 Specification given in 6.1.2.1 applies.  
6.2.2.2 Thermal radiation measurement  6.2.2.2.1 Measurement of long wave irradiance 
 
A pyrgeometer mounted in the plane of the collector shall be used to measure global hemispherical long wave radiation. 
 
6.2.2.2.2 Precaution for effects of temperature gradient 
 The pyrgeometer used during the tests shall be placed in the same plane as the collector absorber and allowed to equilibrate for at le ast 30 min before measuring. 
 
6.2.2.2.3 Precautions for effects of humidity and moisture  
The pyrgeometer shall be provided with a means of preventing accumulation of moisture that may condense 
on surfaces within the instrument and affect its reading. An instrument with a desiccator that can be inspected 
is required. The condition of the desiccator shall be observed prior to and following each daily measurement sequence. 
 
6.2.2.2.4 Precautions for effect of short wave heating 
 
The influence of short wave solar heating effects should be minimized. 
 6.2.2.3 Temperature measurements 
 Temperatures shall be measured in accordance with 6.1.2.3. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 41  
6.2.2.4 Measurement of collector liquid flowrate 
 Liquid flowrates shall be measured in accordance with 6.1.2.4. 
 
6.2.2.5 Measurement of air speed 
 
6.2.2.5.1 General 
 
Air speed shall be measured in accordance with 6.1.2.5.1. 
 6.2.2.5.2 Required accuracy of air speed 
 The speed of the surrounding air over the front surface of the collector shall be measured to a standard uncertainty of 0.25 ms
-1. 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. 
 
NOTE It should be taken into consideration that anemometers have starting limits which lie between 0.5 ms-1 and 1 ms-1. Therefore, 
considerable errors may occur for air velocities less than 1 ms-1. 
 
6.2.2.5.3 Mounting of sensors 
 
The wind speed shall be measured while adjusting the wind generator, using a hand held anemometer at a 
height of 10 mm to 50 mm above the collector aperture plane. A permanently installed anemometer shall be placed at one edge of the collector in order to supervise the operation of the wind generator. This 
anemometer shall be mounted on a board so that there is a continuous surface pointing towards the wind 
generator from the collector edge to 0.3 m behind the anemometer. 
 
NOTE The recorded value of the wind speed is not the air speed above the collector aperture. 
 
A series of measurements shall be taken at nine equally spaced positions over the collector area. An average 
value shall then be determined. For a collector that does not have back insulation or is not mounted on a 
simulated roof surface, the air speed shall be measured over the front and back surfaces. The average air 
speed on the front and back surface shall be used in the data correlation. 
 
During the test the air speed shall be monitored at a convenient point that has been calibrated relative to the mean air speed over the collector. The anemometer shall not cast a shadow on the collector during the tests. 
 6.2.2.6 Pressure measurements 
 The inlet pressure to the collector and the pressure drop across the collector shall be measured with a device having an error of 5 % of the measured value or ±10 Pa. If the collector is supplied in modules the pressure 
drop shall be specified per module. Fo r strip absorbers the pressure shall be specified per metre run of strip. 
 
6.2.2.7 Elapsed time  
Elapsed time shall be measured in accordance with 6.1.2.6. 
 
6.2.2.8 Instrumentation/data recorders 
 Instrumentation and data recorders shall conform to 6.1.2.7.  
6.2.2.9 Collector area 
 
The collector area shall conform to 6.1.2.8. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
42 © KEBS 2008 — All rights reserved 6.2.2.10 Collector fluid capacity 
 
The collector fluid capacity shall conform to 6.1.2.9. 
 
6.2.3 Test installation  
The test installation shall be in accordance with 6.1.3. 
 6.2.4 Outdoor steady state efficiency test 
 
6.2.4.1 Test installation 
 
The test installation shall conform to 6.1.4.1. 
 6.2.4.2 Preconditioning of the collector 
 
The collector shall be preconditioned in accordance with 6.1.4.2. 
 
6.2.4.3 Test conditions 
 
At the time of the test, the net irradiance at the plane of the collector aperture shall be greater than 650 Wm
-2. 
 
NOTE If the manufacturer has limitations on operation with respect to maximum irradiance but not less than 800 Wm, this can be 
requested with the test. That maximum value should be clearly stated in the report. 
 
The angle of incidence of direct solar radiation at the collector aperture shall be in the range in which the 
incidence angle modifier for the collector varies by no more than ±2 % from its value at normal incidence. An 
angle of incidence modifier shall be calculated so that collector performance can be characterized at other 
angles. 
 
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 in the range defined in 6.1.5.5. 
 
Unless otherwise specified, the fluid flowrate shall be set at approximately 0.04 kg/s per square metre 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 ±10 % of the set value from one test period to another. 
 The testing at a lower flowrate may be accommodated by adhering to manufacturers specification.  
 
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 
measurements 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 1 K shall not be included in the test results because of the associated problems of instrument accuracy. 
 
6.2.4.4 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 according to Table 7. 
 
One inlet temperature shall be selected so that the mean fluid temperature in the collector lies within ± 3 K of 
the ambient air temperature, in order to obtain an accurate determination of 
.0η 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 43 NOTE 1 Under consideration of the condition that the fluid inlet temperature shall be higher than the dew point temperature of the 
surrounding air, the inlet temperature should be chosen such that Tm = Ta ± 3 K applies. However, the inlet temperature should in no 
case be lower than the dew point temperature. 
 
Table 7 — Range of thermal performance test conditions 
 
Test point Net irradiance 
 
Wm-2 Tm (mean temperature) 
 
K Air Speed parallel to Collector 
 
ms-1 
1 >650 Tm = Ta ± 3 K < 1 
2 >650 Tm= Ta.± 3K 1.5 ± 0.5 
3 >650 Tm= Ta± 3K 3 ± 0.5 
4 >650 Tm= Ta+0.5 (Δtmax) ± 3 K <1 
5 >650 Tm= Ta+0.5 (Δtmax) ± 3 K 1.5 ± 0.5 
6 >650 Tm= Ta+0.5 (Δtmax) ± 3 K 3 ± 0.5 
7 >650 Tm= Ta+0.5 Δtmax ±3K <1 
8 >650 Tm= Ta +0.5 Δtmax±3K 1.5 ± 0.5 
9 >650 Tm= Ta+Δtmax±3K 3 ± 0.5 
 
Δtmax is the expected maximum temperature difference between absorber mean temperature and ambient 
temperature in real operation. 
 
NOTE 2 For typical swimming pool applications this Δtmax will usually be limited to about 10 K or less. 
 At least two independent data points shall be obtained for each fluid inlet temperature. 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 collector s are moved to follow the sun in azimuth and altitude 
using automatic tracking. 
 
During a test, measurements shall be made as specified in 6.2.4.5. These may then be used to identify test periods from which satisfactory data points can be derived. 
 
6.2.4.5 Measurements 
 The following data shall be measured:  
⎯ collector gross area AG and absorber area AA, measured at operating pressure conditions; 
 
⎯ fluid capacity; 
 
⎯ global solar irradiance at the collector area; 
 
⎯ diffuse solar irradiance at the collector area (only outdoors); 
 
⎯ long wave thermal irradiance in the collector plane (or dew point temperature tdp); 
 
⎯ surrounding air speed; 
 
⎯ surrounding air temperature; 
 
⎯ temperature of the heat transfer fluid at the collector inlet; 
 
⎯ temperature of the heat transfer fluid at the collector outlet; 
 
⎯ flowrate of the heat transfer fluid.  
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
44 © KEBS 2008 — All rights reserved 6.2.4.6 Test period (steady state) 
 
Specification given in 6.1.4.6 applies, taking into account Table 8. 
 
Table 8 — Permitted deviation of measured parameters during a measurement period 
 
Parameter  Symbol Deviation from the mean value  
Total short wave solar irradiance G ±50 Wm-2 
Long wave thermal irradiance EL ±20 Wm-2 
Surrounding air temperature ta ±1 K 
Fluid mass rate m& ±1 % 
Collector fluid inlet temperature tin ±0.1 K 
Surrounding air speed u ±0.5 ms-1 
 
6.2.4.7 Presentation of results 
 
Specification given in 6.1.4.7 applies. 
 6.2.4.8 Computation of collector output. 
 
6.2.4.8.1 General 
 
Specification given in 6.1.4.8.1 apply, with the following additions: 
 
The test results shall be used to compute efficiency 
η from the following equation: 
 
"GQ
Λ=η  (18) 
 
G” is the net irradiance determined by the equation 
 
G” = G + (ε/α)(EL - )4
aσΤ  (19) 
 
the value ( ε/σ) shall be taken 0.85 unless the manufacturer can supply a measured value. 
 
EL is the measured longwave irradiance in the collector plane. 
 
Q& is the useful power output, calculated from:  ) (in ef ttcmQ −=&& (20) 
 A value of c
f appropriate to the mean fluid temperature shall be used. 
 
If the fluid mass flowrate m is obtained from volumetric flowrate measurements, then the density shall be 
determined for the fluid at the temperature in the flowmeter.  
The test data shall be correlated by curve fitting using the least squares method to obtain an efficiency function of the form 
 
()
") () 1(a m
2 1 u 0Gt tubb ub−+−−=ηη  (21) 
 
1,u,  
o,bbη and b2 are coefficients to be determined by curve fitting. 
 
If instrumentation is not available for measuring long wave irradiance EL, the following clear sky long wave 
model may be used to determine sky emittance sεfrom measured dew point temperature tdp. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 45  
2
dp dp
s1000.731000.56 0.711ε⎟⎟
⎠⎞
⎜⎜
⎝⎛+ +=t t
 (22) 
 
where the dew point temperature tdp shall be measured to a standard uncertainty of 0.5 K. 
 
The long wave irradiance is calculated by the expression: 
 
Es = 4
s aσΤε  (23) 
 
If the collector is inclined there will be thermal radiation exchange with both the sky and ground. 
 
The relative long wave irradiance Eβ on a collector inclined at an angle β is given by: 
 
E2cosβ 1σΤ2cosβ 1σa g sβ−++=4 4ε Τεa  (24) 
 
The ground temperature will have little influence on long wave radiation on a collector inclined at less than 
since the view factor between a collector and the ground is only 0.15 for β = 45° 
 
In this case, Equation (24) can be written as: 
 
2cosβ 1σΤε4
a s+=βE  (25) 
 
Thus, in Equation (19) the longwave irradiance EL in the collector plane is equal to Eβ when the collector is 
located outdoors 
 
NOTE 1 Positive EL values are a downward oriented irradiance onto a surface with a temperature of 0 K. 
 
NOTE 2 When calculating Es Equation 23 should be used. 
 
6.2.4.8.2 Solar energy intercepted by the collector  
 
The solar energy intercepted is AG" and so in this case 
 
"AGQη&
=  (26) 
 
6.2.4.8.3 Reduced temperature difference 
 Specification given in 6.1.4.8.3 applies, by replacing G by G". 
 
6.2.4.8.4 Modeling of instantaneous efficiency 
 
6.2.4.8.4.1 General 
 
Specification given in 6.1.4.8.4.1 applies, by replacing G  by G". 
 
6.2.4.8.4.2 Instantaneous efficiency 
 
Specification given in 6.1.4.8.4.2 applies, by replacing G by G". 
 
6.2.4.8.5 Graphical presentation of the collector output 
 
Specification given in 6.1.4.8.5 applies, by replacing G by G" PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
46 © KEBS 2008 — All rights reserved  
6.2.5 Steady-state efficiency test using a solar irradiance simulator 
 
6.2.5.1 General 
 
Specification given in 6.1.5.1 applies. 
 
6.2.5.2 The solar irradiance simulator for steady-state efficiency testing 
 
Specification given in 6.1.5.2 applies. 
 6.2.5.3 Test installation 
 
Specification given in 6.1.5.3 applies.  
6.2.5.4  Preconditioning of the collector 
 
Specification given in 6.1.5.4 applies. 
 6.2.5.5 Test procedure 
 The collector shall be tested over its operating temperature range in order to determine its efficiency 
characteristic. 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 an accurate determination of 
0η 
 
The range of thermal performance test conditions is specified in Table 7. 
 
At least two independent data points shall be obtained for each fluid inlet temperature. During a test, measurements shall be made as specified in 6.2.4.5. 
 
6.2.5.6 Measurements during tests in solar irradiance simulators. 
 
Measurements shall be in accordance with 6.1.5.6. 
 
6.2.5.7 Test period 
 
The test period shall conform to 6.1.5.7.  
6.2.5.8 Test conditions 
 
Test conditions shall be in accordance with 6.1.5.8. 
 
6.2.5.9 Computation and presentation of results 
 
Results shall conform to 6.1.5.9. 
 6.2.6 Determination of the effective thermal capacity and the time constant of a collector 
 
6.2.6.1 General 
 
The effective thermal capacity and the time constant of a collector are important parameters which determine 
its transient performance. 
 
A collector can usually be considered as a combination of masses, each at a different temperature. When a collector is operating, each collector component responds differently to a change in operating conditions, so it is useful to consider an effective thermal capacity for the whole collector. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 47 Unfortunately, the effective thermal capacity depends on the operating conditions and is not a collector 
parameter with a unique value. Several different test methods have been used to measure the effective 
thermal capacity of collectors and it has been shown that similar results can be obtained by using quite 
different methods. 
 
Just as there is no unique value of effective thermal capacity, there is no unique overall time constant for a 
collector. For most collectors, the dominant influence on the response time is the fluid flowrate. Other 
collector components respond with different times to give an effective overall time constant which depends on 
the operating conditions.  
6.2.6.2 Determination of effective thermal capacity 
 
The effective thermal capacity of the collector C (expressed as joules per kelvin) shall be calculated as the 
sum, for each constituent element of the collector (absorber, heat removal fluid), of the product of its mass m
i 
of collector (expressed in kilograms), times its specific heat ci (expressed as joules per kilogram kelvin) 
 
C = i
iicm∑ (27) 
 
Effective thermal capacity may also be measured by applying the procedures described in Annex G. 
 
6.2.6.3 Test procedure for collector time constant  
The test procedure shall be in accordance with 6.1.6.3. 
 6.2.6.4 Calculation of collector time constant 
 The time constant shall be calculated in accordance with 6.1.6.4. 
 
6.2.7 Incidence angle modifier (optional) 
 6.2.7.1 General 
 
For solar beam incidence which is not near normal, the efficiency 
0ηin Equation (21) may be replaced by 
 
0ηθΚ where Kθ is the incidence angle modifier. 
 
()()"θGttubbub Κa m
u−+−−=2 1 01ηη  (28) 
 
Figure 6 shows the typical variation of Kθ with incidence angle for an unglazed solar collector. 
 
For those collectors for which the incidence angle effects are not symmetrical with direction of incidence 
specifications given in 6.1.7.1 apply. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
48 © KEBS 2008 — All rights reserved 
 
 
Figure 6 — Typical incidence angle modifier 
 
The significance of the incidence angle modifier to the test procedures outlined in this clause is that the 
thermal efficiency values are determined for the collector at or near normal incidence conditions. Therefore, 
the y intercept η of the efficiency curve is equal to 0η. 
 
A separate measurement shall be conducted to determine the value of Kθ so that the performance of the 
collector can be predicted under a wide range of conditions and/or time of day using Equation (28). 
 
6.2.7.2 Solar irradiance simulator for the measurement of incidence angle modifiers 
 Specification given in 6.1.7.2 applies.  
6.2.7.3 Test procedures 
 
Specification given in 6.1.7.3 applies. 
 
6.2.7.4 Calculation of collector incidence angle modifier 
 
Regardless of which experimental method in 6.2.7.3 is used, values for the thermal efficiency of the collector shall be determined for each value of angle of incidence. 
 For unglazed collectors, only one angle of incidence is needed which is 50°. 
 
NOTE A rating standard using this test method may require that Kθ be measured for a different set of angles of incidence. 
 
The mean temperature of the fluid shall be held very close to the ambient air temperature so that ( tm - ta) ≈ 0 
 
The relationship between Kθ and the efficiency is: 
 
()
0θθ
ηηΚ=  (29) 
Since 0η will have already been obtained as the y-axis intercept of the efficiency curve, values of Kθ can be 
computed for the different angles of incidence (see  6.2.7.3). If the mean fluid temperature cannot be 
controlled to equal the ambient air temperature within ±1 K, the value of Kθ shall be computed as: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 49 ()()
() ubGttubb
Κ
ua m
−⎟
⎠⎞⎜
⎝⎛−++
=102 1
ηθη"
θ  (30) 
 
Due to more exact results Equation (17) should be used generally. Alternatively, each data point may be 
plotted on the same graph with the efficiency curve determined in accordance with 6.2.4 or 6.2.5, and a curve drawn through each point parallel to the efficiency curve and made to intersect the y-axis. 
 
The values of the y intercept are the efficiency values that would have resulted had the mean fluid 
temperature been controlled to equal ambient air temperature. Therefore, these values may be used in 
conjunction with Equation (28) to compute the different values of K
θ. 
 
6.2.8 Determination of the pressure drop across a collector 
 
If determination of pressure drop across a collector is required, this should be done according to Annex L. 
 
6.3 Glazed and unglazed solar collect ors under quasi-dynamic conditions 
 
6.3.1 Collector mounting and location 
 
6.3.1.1 General 
 Collectors shall be located and mounted in accordance with 6.1.1.1.  
6.3.1.2 Collector mounting 
 
Glazed collectors shall conform to 6.1.1.2 and unglazed collectors shall conform to 6.2.1.2. 
 
6.3.1.3 Tilt angle 
 
Glazed collectors shall conform to 6.1.1.3 and unglazed collectors shall conform to 6.2.1.3.  
6.3.1.4 Collector orientation outdoors 
 
The collector shall be mounted outdoors in a fixed position facing the equator, within ± 5°. 
 
NOTE The azimuthal deviation of collector (or pyranometer) from  due south, should be taken into account when calculating the an gle 
of incidence of solar radiation onto the collector aperture. Larger deviations from south may be acceptable, but will lead to a  non-
symmetrical angular distribution of beam radiation in Figure 8 (see 6.3.4.6.2). This may lead to slightly biased incidence angl e 
dependence of the collector. The actual incidence angle should be calculated with a standard uncertainty better than ±1°. 
 
In case of concentrating collectors, the tracking device of the manufacturer should be used if possible. In 
case of non imaging stationary collectors as CPCs, they should be mounted so that the beam radiation from 
the sun falls within the angular acceptance range of the design. 
 
6.3.1.5 Shading from direct solar irradiance 
 
Shading shall be in accordance with 6.1.1.5. 
 
6.3.1.6 Diffuse and reflected solar irradiance 
 
Specification given in 6.1.1.6 applies. Last section of 6.1.1.6, text about solar simulator tests is not applicable. 
 
6.3.1.7 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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
50 © KEBS 2008 — All rights reserved order to minimize the influence of thermal radiation. For example, the outdoor field of view of the collector 
shall not include chimneys, cooling towers or hot exhausts. Shielding is important both in front of and behind 
the collector. 
 
6.3.1.8 Surrounding air speed 
 Glazed collectors shall conform to 6.1.1.8 and unglazed collectors shall conform to 6.2.1.8.  
 6.3.2 Instrumentation 
 
6.3.2.1 Solar radiation measurement 
 
Measurements shall conform to 6.1.2.1. 
 6.3.2.1.1 Pyranometer 
 
Pyranometers shall conform to 6.1.2.1.1 with the following exception: Subclause 6.1.2.1.1.5 is not applicable. 
 
6.3.2.2 Thermal radiation measurement  
 
Measurements shall be in accordance with 6.2.2.2. 
 
6.3.2.3 Temperature measurements 
 
Measurements shall conform to 6.1.2.3.  
6.3.2.4 Measurement of collector liquid flowrate  
Measurements shall be in accordance with 6.1.2.4.  
6.3.2.5 Measurement of air speed  
6.3.2.5.1 General  
Measurements shall be in accordance with 6.1.2.5.1 
 
6.3.2.5.2 Required accuracy 
 
The speed of the surrounding air over the front surface of the collector shall be measured to a standard 
uncertainty of 0.5 ms
-1 (glazed collectors) and 0.25 ms-1 (unglazed collectors). 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 by a time integration over the test 
period. 
 
6.3.2.5.3 Mounting of sensors 
 
When testing outdoors in locations where the mean air speed lies below 2 ms-1 an artificial wind generator 
shall be used, and anemometer measurements shall be fitted for continuous measurement of air velocity. 
This anemometer shall be mounted on a board so that there is continuous surface pointing towards the wind 
generator from the collector edge to 0.3 m behind the anemometer. The uniformity of air speed in the field of 
collector aperture shall be checked as the air speed may vary from one end of the collector to the other. A 
series of air speed measurement shall therefore be taken, at a distance of 100 mm in front of the collector 
aperture and equally spaced positions over the collector area. An average value shall then be determined 
and related to the continuous measurement. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 51 In windy locations, the wind speed measurement shall be made near to the collector at the mid height 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. 
 
6.3.2.6 Pressure measurements 
 Measurements shall be in accordance with 6.2.2.6. 
 6.3.2.7 Elapsed time 
 
Time shall be measured in accordance with 6.1.2.6. 
 
6.3.2.8 Instrumentation/data recorders 
 Instruments shall conform to 6.1.2.7.  
6.3.2.9 Collector area 
 
The collector area shall conform to 6.1.2.8. 
 
6.3.2.10 Collector fluid capacity 
 
Fluid capacity shall conform to 6.1.2.9. 
 
6.3.3 Test installation 
 The installation shall be tested in accordance with 6.1.3.  
6.3.4 Outdoor efficiency test 
 
6.3.4.1 Test installation 
 
The installation shall be tested in accordance with 6.1.4.1. 
 6.3.4.2 Preconditioning of the collector 
 
The collector shall be preconditioned in accordance with 6.1.4.2. 
 
6.3.4.3 Test conditions  
In the following, test requirements are given for what can be called a quasi-dynamic test method (QDT). To 
facilitate the understanding and acceptance of this kind of approach, the recommended test sequence and other test requirements given here are closely connected to those widely accepted for steady-state testing of 
solar thermal collectors, as outlined in 6.1 and 6.2. Basically the demand on suitable test data are the same 
for both types of approaches, and hence the recommended test sequence will allow also for conventional steady-state parameter identification, by obtaining and cutting out those measurement data sequences 
corresponding to steady-state requirements. The test method and recommended test sequence, will combine 
and allow for the evaluation of the effective thermal capacitance, incidence angle modifier — (IAM), wind 
speed — as well as sky temperature — dependence of the collector efficiency. In the collector parameter 
identification phase the collector model of actual useful power is used.  
The average value of the surrounding air speed, taking into account spatial variations over the collector and 
temporal variations during the test period, shall be greater than 1 ms
-1 and less than 4 ms-1. Wind generators 
may be used if necessary to achieve sufficient wind speeds. 
 
Unless otherwise specified, the fluid flowrate shall be set at approximately 0.02 kgs-1 per square metre of 
collector reference area (A). It shall be held stable to within ±1 % of the set value during each test period, and PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
52 © KEBS 2008 — All rights reserved shall not vary by more than ±10 % of the set value from one test period to another. Testing at other flowrates 
can be accommodated by adhering to manufacturer's specification. 
 
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 
measurements 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 1.0 K shall not be included in the test results, because of the associated problems of instrument accuracy. 
 
NOTE As the quasi-dynamic method is based on the minimization of the error in the power output of the collector (not efficiency  as in 
stationary testing described in 6.1 and 6.2) the relative error of low fluid temperature differences will no longer cause a pro blem. 
Therefore the limitation to 1.0 K temperature difference can be removed in a later revision of the standard and more data from each test 
day can be used. 
 
6.3.4.4 Test proce dure 
 
The collector shall be tested over its operating temperature range under outdoor conditions in order to 
determine its efficiency characteristics. Data points which satisfy the requirements given below shall be obtained for at least 4 fluid inlet temperatures spaced evenly over the operating temperature range of the 
collector.  
If possible, one inlet temperature shall be selected such that the mean fluid temperature in the collector lies 
within ±3 K of the ambient air temperature at around solar noon, in order to obtain an accurate determination The inlet temperature shall be kept above the dew point, so that condensation of water on the absorber is 
avoided, which otherwise would result in erroneous test results. Weather conditions shall be as described in 
6.3.4.6, sequence type 1 and 2.  
The second and third inlet temperature shall be selected so that the mean fluid temperature in the collector is 
evenly spaced between the lowest and highest operating range of the collector, as measured at about solar noon. For unglazed collectors only 3 fluid inlet temperatures are requested. The second shall then be chosen 
in to be close to the middle of the operating range of the collector. Weather conditions shall be as described in 6.3.4.6, sequence type 3. 
 
Depending on type of collector, the highest fluid inlet temperature shall be chosen as specified in 6.1.4.4 and 
6.2.4.4. 
 The change in inlet temperature should be done after each test sequence has been completed. Data 
recorded during this "step-change" period shall not be included in the test data. The inlet temperature shall be 
kept stable within ±1 K during each test sequence. 
 
NOTE 1 If comparison with steady-state parameters is to be done, at least 4 data points with the required duration, should be o btained 
for each fluid inlet temperature. If test conditions permit, an equal number of data points should be taken before and after so lar noon for 
each fluid inlet temperature. 
 
NOTE 2 As the collector model used here, more accurately describes the collector performance, the importance of 4 measuring poi nts 
as well as independent data points within these is reduced or eliminated. In a later revision of this method, only 3 measuring points 
should be considered. The more complete characterization of the colle ctor also leads to fewer restrictions on the collector des igns and a 
wider range of collectors will be covered by this test method. 
 
During a test, measurements shall be made as specified in 6.3.4.5. These may then be used to identify test 
periods from which satisfactory test data can be derived.  
6.3.4.5 Measurements and data acquisition 
 
6.3.4.5.1 Measurements 
 
The following measurements shall be carried out: 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 53 ⎯ aperture area Aa, the absorber area AA and the gross collector area AG; 
 
⎯ fluid capacity; 
 
⎯ global solar irradiance at the collector aperture; 
 
⎯ diffuse solar irradiance at the collector aperture; 
 
⎯ incident longwave radiation at the collector aperture; 
 
⎯ angle of incidence of direct solar radiation or may be determined by calculation; 
 
⎯ azimuth and tilt angle of the collector aperture (standard uncertainty better than ±1°); 
 
⎯ surrounding air speed; 
 
⎯ surrounding air temperature; 
 
⎯ temperature of the heat transfer fluid at the collector inlet; 
 
⎯ temperature of the heat transfer fluid at the collector outlet; 
 
⎯ flowrate of the heat transfer fluid. 
 
6.3.4.5.2 Data acquisition requirements 
 
Sampling rate: 1s to 6 s 
 
Averaging interval: 5 min to 10 min 
 
Each data line (record) shall contain a unique time label (standard uncertainty better than ±1 min), giving the 
possibility to calculate the angle of incidence of solar radiation onto the collector for each such data line (time 
period). See also under 6.3.1.4.  
The following on line calculations should be performed and included in the measurement database:  
⎯ useful output power of the collector or Q 
 
⎯ time derivative of t m in the collector, i.e. dtm/dt as (tm new - tm old) / (sampling interval for tjn and te) 
 
The calculation of time derivative dtm/dt should be performed on-line as it has a big impact on the final results. 
 
Sampling rate and averaging interval as for measured values. 
 
NOTE If the measurement system allows for on line calculation of collector model output with expected collector parameters, thi s will 
be a very useful tool to detect any measurement error or problem. If not and in general, it is recommended to plot a diagram of  measured 
output versus modelled output after each test day. 
 
6.3.4.6 Test period 
 
6.3.4.6.1 General  The recommended test sequence consis ts of 4-5 days. The number of actual days will, as for all outdoor 
collector testing, be dependent on the actual weather conditions on the test site. The data record shall contain data equivalent to all important normal operat ing conditions (enough variability and dynamic range), 
to give decoupled collector parameters. This is done similar to the stationary method (see 6.1 and 6.2), by PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
54 © KEBS 2008 — All rights reserved varying the inlet temperature to the collector within its design range. If sufficient data has been recorded after 
4-5 days, this data shall be evaluated for each test day, following the guidelines outlined below in 6.3.4.6.2. 
 6.3.4.6.2 Description of test sequences 
 
The minimum length of a test sequences according to the requirements of 6.3.4.3 shall be 3 h. The test 
sequence under 
0η-conditions as specified in 6.3.4.4 should be conducted under mostly clear sky conditions. 
It shall include values of the incident angle from larger than 60° down to values where the difference of the 
incident angle modifier of the beam irradiance differs not more than 2 % from the value at normal incidence. 
 
One test sequence shall be conducted under partly cloudy conditions, including broken cloud as well as clear 
sky conditions. This can be a test sequence under elevated operating temperature or under 0η–conditions 
specified in 6.3.4.4. 
 
The relative order of the different test sequences is not critical, but may be adjusted to the actual weather on 
the test site. 
 6.3.4.6.3 Optional test: Dependence of tilt angle 
 
If dependence of tilt angle shall be evaluated, one extra test day shall be added. 
 During this day, the collector shall be tested at the other requested tilt angle and at the high operating 
temperature (Day type 4). This additional test database may be evaluated with extended MLR, together with 
and at the same time as all other collector parameters.  
NOTE Extended MLR, see note 2 under 6.3.4.8.1. 
 
6.3.4.6.4 Evaluation of test data 
 
In the following, guide lines for evaluating the suitability of the data  recorded are outlined. It is reminded that 
when evaluating the suitability of test data the following criteria should be satisfied: 
 
⎯ Tout – Tin > 1 K 
 
⎯ Tin stable within ± 1K 
 
⎯ flowrate stable within ± 1% of the set value during test day or test sequence and 10 % from one 
sequence to another 
 During evaluation of the test data a pre-conditioning period of at least 4 times the time constant of the 
collector (if known), or not less than 15 min (if time constant is not known), with the correct fluid temperature at the inlet shall be skipped to ensure that the initial state of the collectors fades away and does not influence 
the result of the parameter identification. 
 
It is also noted that outliners that cannot be explained shall not be excluded from the data set. 
 For clearness reasons, most requirements are given in the form of idealized diagrams, showing important 
relationships between different test conditions, including the dynamic ranges that shall be in the data to§; 
achieve reliable and de-coupled collector parameters. These diagrams shall be plotted for the evaluation of the goodness of the test data used for parameter identification and shall be included in the test report. 
 
Figure 7 shows t
m – t a versus G*to check if sufficient data has been taken under η0-conditions and at higher 
inlet temperatures. This data will give all nec essary information for the identification of F'(τα)en and the 
collector heat losses. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 55 
 
Figure 7 — tm – ta versus G* 
 
Figure 8 and 9 show if the data includes enough data at high and low incident angle of the beam irradiance to 
identify Kθb(θ) and if enough data at high diffuse radiation levels was taken to identify Kθd. 
 
 
 
Figure 8 — Gb versus iθ 
 
NOTE Measurement data with higher Gb-values (upper curve), will give Kθb(θ). The lower values will give Kθd.  
 
 
Figure 9 — Gd versus G* 
 
If wind speed dependence of the collector was considered Figure 10 shall be included. Figure 10 shows the 
ideal distribution of the relati onship of wind speed versus G* 
 
The wind speeds as described in 6.3.4.3 should be considered. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
56 © KEBS 2008 — All rights reserved 
 
 
Figure 10 — Wind speed versus G* 
 
6.3.4.7 Presentation of test results 
 
The test results shall be presented in a report using the data format sheets, given in Annex D and Annex E 
and with the text and content adjusted in accordance with what is given by 6.3 (see also under 6.3.4.8.4). The 
measurements shall be collated to produce a set of data points, which meet the requirements of the test 
conditions and provide sufficient information in the test data. In addition to what is given by Annex D and E, 
the measurement data used for collector parameter identification shall be presented in four diagrams, 1 to 4 
as described under 6.3.4.6.4, Figure 7 to Figure 10. A diagram 5, showing measured collector output versus modelled output, shall also be included in the test report. Diagram 5 shall include all test data used for 
collector parameter identification in one diagram (see also 6.3.4.5.2, note). The incidence angle modifier 
(IAM), 
Kθb(θ)shall be presented in a diagram 6 as indicated in Figure 5 or 6. 
 
In addition to the collector performance coefficients as requested by Annex D or E, the full set of quasi-
dynamic performance coefficients as identified by Equation (32), should be included in the test report. 
 6.3.4.8 Parameter identification and computation of useful collector output  
 
6.3.4.8.1 Collector parameter identification tool 
 
Multiple Linear Regression (MLR), is a non iterative very fast matrix method, that is available in most 
standard programme packages with statistical functions, such as spreadsheets or more specialized statistical programmes like MINITAB or SISS. Linear, in this instance means that the model has to be written as a sum 
of terms with the parameters p
n as a multiplier in front of the terms. 
 
For example: Yout = p0 + p 1f(x1, x2) + p 2g(x1, x3, x4) + p 3h(x2, x5) 
 
The sub models f(x..) g(x..) and h(x..)  in each term can be highly non-linear. 
 
The MLR method allows for fully free selection of data from the test database, according to any test specification before applying the MLR parameter identification. 
 
This selection can be made afterwards from measurements during a few days. 
 
NOTE 1 To give an example, this means e.g., that test data with G* > 700 Wm-2, dtm/dt < 0.002 Ks-1, u > 2 ms-1 and ta – ts > 10k could be 
selected for the MLR parameter identification, if those test requirements are considered. Even for an extensive database, the p arameter 
identification will need only a few seconds of computer time, making MLR very versatile also in development and research. 
 NOTE 2 For several years, a special case of MLR (extended MLR) has also been tested out, which makes it possible to identify th e 
same parameter in different subsets of the database. This has made it possible to identify for example the zero loss efficiency  angle by PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 57 angle without the need to have an equation and also in two axis Lθand )(i bθtθKθ is than generalized and replaced by  
θbΚ ),(t Lθθ  in Equation (32). The parameters can still be identified with standard MLR software in the same run. This is very useful 
for special collectors as ETC, CPC or unglazed collectors with round separate absorber tubes that cannot be modelled with the s tandard 
IAM equations. The derived IAM results can be used directly in simul ation programmes like TRNSYS, WATSUN or MINSUN. Recently it  
was also found, that the heat loss factor can be identified in successive ranges of ΔT. This overcomes the problem of a slight 
correlation between the ΔT and ΔT2 terms. The heat loss coefficient can also be modelled in this way for collectors with special heat 
loss effects as heat pipe collectors or other special designs. 
 
Other non linear methods, provided that th ey are minimizing the error in the output power of the collector as in the MLR 
method, can be used as parameter identi fication tool as beside the MLR method. 
 
6.3.4.8.2 The Collector Model for different collector 
 
This model is basically the same as the steady-state model used in 6.1 and 6.2, but with some extra 
correction terms. Here the dependence of direct and diffuse radiation, wind speed, sky temperature, 
incidence angle effects and effective thermal capacitance are modelled. For more information see Annex H. 
dtdtcTEcttucttcttcuGcGK FG K FAQa / ) () ( ) () (* )(' )( )(' /m L a m a m a m dθd en bθb en 54
4 32
2 1 6 −−+−−−−−−− + = σ ταθτα  (32) 
 
where the area is  AA when referred to the absorber area of the collector and Aa when referred to the aperture 
area of the collector (see Annex J). 
 
NOTE Kelvin degrees are used for convenience in the radiation term.  At all other places Celsius degrees are used, see Clause 4.  
 
6.3.4.8.3 Use of the collector model for different collector types 
 
The collector model as described in 6.3.4.8.2, should cover most collector designs available on the market, 
except ICS collectors. If the full collector model should be applied for a certain type of collector (or collector 
design) or not, will in general be given by the result of the parameter identification, but for all types of 
collectors, the use of F’(τα)en, ()θd θb  ,θΚΚ  and the coefficients c1, c2 and c5 are mandatory and they should 
be identified. 
 
NOTE 1 For sun tracking, high concentrating collectors the inclusion of θdΚ may not always be significant and should therefore be 
determined by the T-ratio of the parameter identification as given below. Then K )(θbθ= 1.0 and θdΚ  = 0 should be used in Equation 
(32) and the parameter identification should be repeated. 
 
If the coefficients c3, c4, and c6 shall be included in the collector model, will be determined by the T-ratio 
(parameter value / standard deviation of parameter value) of the parameter identification. The T-ratio should 
be greater than 2 for those parameters presented in the test results. If the T-ratio is less than 2, (enough 
variability in the input data is assumed), the coefficient  shall be set to zero and the parameter identification 
should be repeated with the adjusted collector model. 
 
For unglazed collectors, the use of the full collector model is mandatory. 
 
NOTE 2 Empirically found, the full collector model including capacitance, diffuse and incidence angle corrections is very accur ate. If the 
model does not fit to the data, in most cases the problem will be found in the collector, the test installation or the measurem ents. 
 
6.3.4.8.2 Graphical presentation of test results 
 
To conform with the presentation of test results, when testing in accordance with 6.1 and 6.2, the test results 
shall be presented in the form of a power curve as a function of the temperature difference between mean fluid and ambient temperature ( t
m – ta), which shall be calculated from the power function, Equation 32, using 
the value of G* = 1000 Wm-2 and a diffuse fraction of 15 %, i.e. Gd = 150 Wm-2. The parameter d tm/dt is set to 
zero and iθ to 15° (d tm/dt = 0 and iθ = 15) to adjust to stationary operating conditions around solar noon 
(Equation 32.1). If wind speed dependence of the heat losses and the zero loss efficiency are used in the collector model for glazed collectors (c
3>0 and c 6>0) as outlined in 6.3.4.8.3, the wind speed u = 3 ms-1 
should be used in the equation. If sky temperature dependence of the heat loss coefficient is used in the 
collector model (c 4>0), then (()4
aT Eσ−L  = -100 Wm-2 should be used in the equation. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
58 © KEBS 2008 — All rights reserved ))/ () )(/( ) () ()/( . )(' .)( )('*)((a m a m a m θd en θb en2
4 32
2 1 6 100 3 3 150 85015 mW cttsmc ttcttcsmc K F K FAGQ −− −−−−− − + = τα τα& (32.1) 
 
Graphical presentation of test results for unglazed collectors should be made accordingly, but with reference 
to Annex E. 
 
The product ). )(' .)( )('*)((θd en θb en 150 85015 K F K FAGQ τα τα + =& shall be referred to as Wpeak. 
 
NOTE ()4
aT Eσ−Lhas normally a negative value as the effective sky radiation temperature is lower than the ambient air temperature. A 
net longwave irradiance of minus 100 Wm-2 will correspond to about a clear sky condition when 
 
ta = 20 °C  and ts = 0 °C.  
 
6.3.5 Determination of the effective thermal capacity 
 6.3.5.1 General 
 
The effective thermal capacity ( C) and the time constant of a collector are important parameters which 
determine its transient performance. A collector can usually be considered as a combination of masses, each 
at a different temperature. When a collector is operating, each collector component responds differently to a 
change in operating conditions, so it is useful to consider an effective thermal capacity for the whole collector.   
The determination of c
5 (see Equation 32) requires a large enough variation in dtm/dt. In the test, this can only 
be achieved by variations in irradiation level as the inlet temperature is fixed due to the requirement for 
compatibility with testing according to 6.1 and 6.2. 
 
6.3.5.2 Procedure 
 The effective thermal capacitance, modelled as c
5 and equal to C/A, is a mandatory part of the collector 
model, Equation 32, and is identified simultaneously together with all other collector parameters. 
 
It is essential to have large enough variability in solar radiation during the test so that the thermal capacitance 
effects will be significant. In all empirical data so far, partly cloudy conditions will induce enough variability in 
dtm/dt for the determination of c 5. dtm/dt should exceed ± 0.005 K/s during the partly cloudy day. If the unlikely 
case happens that this is not met during the test period, an extra test day, type 2, as described under 
6.3.4.6.1 with partly cloudy conditions, shall be added to the data used for identification. 
 
6.3.6 Collector incidence angle modifier 
 
The Collector incidence angle modifiers (IAM), modelled as K θb(θ) for direct radiation and as Kθd for diffuse 
radiation (see also 6.3.4.8.3, Note 1), are mandatory parts of the collector model, Equation 32. These are 
identified simultaneously together wi th all other collector parameters. 
 
The basic modelling of lAM-dependence of flat plate collectors shall be done with the equation  
 
Kθb(θ) = )) cos/(( 1 1 11 0 − − θ b  (33) 
 
as described in e.g. ASHRAE 93-77. 
 
For those collectors (e.g. evacuated tube collectors and CPC collectors) for which the incidence angle effects 
are not symmetrical with direction of incidence, it is necessary to measure the incident angle effects from 
more than one direction to fully characterize the incident angle modifier.  
The complex individual incident angle modifier can be estimated by considering it to be the product of the 
separate incident angle modifiers, 
KθL and KθT for two perpendicular symmetry planes (Equation 33.1). 
 
Kθb(θ) = θT θLK K⋅  (33.1) PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 59  
The longitudinal plane (index L) runs parallel to the optical axis of the collector, and the transversal plane 
(index T) is perpendicular to the optical axis. The angles θL and θT are the projections of the incidence angle θ 
onto the longitudinal and transversal planes, respectively. 
 
For the correlation between θ, θL and θT, the following equation holds: 
 
θT tanθL tan tanθ tan2 2 2 2+== (33.2) 
 
While measuring the incident angle modifier in one plane of an optical unsymmetrical collector the incident 
angle within the other plane should be kept to a value where the incident angle modifier does not differ more than 2 % from the one at normal incidence. 
 
For collectors with special lAM-dependence, see also note under 6.3.4.8.1. 
 
K
θb shall be modelled as a collector constant.  
 
For general information, also refer to 6.1.7. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
60 © KEBS 2008 — All rights reserved  
Annex A 
(normative) 
 
Schematics for durability and reliability tests 
 
 
 
Figure A.1 — Schematic for internal pressure test of inorganic absorbers 
 
 
 
Figure A.2 — Schematic for internal pressure test of organic absorbers for use in unglazed collectors 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 61 
 
Figure A.3 — Schematic for internal pressure test of organic absorbers for use with oil-based fluids 
(hot oil source) 
 
 
Figure A.4 — Schematic for internal pressure test of organic absorbers for use with oil-based fluids 
(test under solar irradiance) PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
62 © KEBS 2008 — All rights reserved  
 
 
 
Figure A.5 — Schematic for internal pressure test of organic absorbers (pneumatic test under solar 
irradiance) 
  
  
 
 
Figure A.6 — Schematic for high-temperature resistance test (outdoor or in simulator) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 63 
 
 
 
Figure A.7 — Schematic for exposure test 
 
  
 
 
Figure A.8 — Schematic for external thermal shock test 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
64 © KEBS 2008 — All rights reserved 
 
 
 
Figure A.9 — Schematic for internal thermal shock test 
 
 
 
 
 
 
Figure A.10 — Schematic for rain penetration test 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 65 
 
 
Figure A.11 — Schematic for freeze resistance test 
 
 
Key 
1 Wooden frame for gravel 2 Collector 
 
Figure A.12 — Schematic for mechanical test (positive pressure on the collector cover) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
66 © KEBS 2008 — All rights reserved 
 
Key 
 
1 Pneumatic pressure source 
2 Collector 
3 Pressure gauge 
4 Holes into airgap between the collector cover and absorber 
 
Figure A.13 — Schematic for mechanical test (negative pressure on fixings between the cover and the 
collector box) 
 
 
Key  
1 Stiff support 2 Collector 
3 Air cushions to apply pressure 
 
Figure A.14 — Schematic for mechanical test (negative pressure on collector mounting) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 67 
 
 
Figure A.15 — Schematic for impact resistance test using steel balls 
 
 
Key 
 1 Reservoir   2 Solenoid valve large, fast opening 
3 Barrel   4 Collector 
5 Rigid frame   6 Photoelectric velocity measuring system 
7 Pneumatic pressure source 8 Safety valve 9 Pressure gauge 
 
Figure A.16 — Schematic for impact resistance test using ice balls  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
68 © KEBS 2008 — All rights reserved  
Annex B 
(normative) 
 
Durability and reliability test report sheets 
 
Collector Identification 
Manufacturer: 
Brand Name: 
Collector Type:  Unglazed/Glazed/Evacuated Year of Production: 
Serial No: Drawing Document No: 
 
Collector reference No: …………………………………………………….. 
 
B.1 Record of test sequence and summary of main results 
 
All significant damage to the collector, including rain penetration, should be summarized in Table B.1. Full 
details should be given in the individual test result sheets. 
 
Table B.1 
 
Test Date Summary of main test results
 Start End  
Internal pressure  
  
   
High-temperature resistance  
  
   
Exposure  
  
   
External thermal shock First  
  
   
 
 Second    
Internal thermal shock First  
     
 Second  
  
   
Rain penetration  
     
Freeze resistance  
  
   
Mechanical load  
     
Thermal performance  
     
Impact resistance (optional)  
  
   
Final inspection    
 
Remarks: …………………………………………………………………………………………………………………. 
    ………………………………………………………………………………………………………………….. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 69  
Collector reference No.  ……………………………………………….. 
 
B.2 Internal pressure test for inorganic absorbers 
 
NOTE See B.3 for internal pressure test for absorbers made of organic materials. 
 
B.2.1 Technical details of collector 
 
B.2.1.1 Collector type: 
 
Glazed 
 
Unglazed 
 
B.2.1.2 Maximum collector operating pressure specified by manufacturer:   kPa 
 
B.2.2 Test conditions 
 
Test temperature:  ............................................................................................................ ..... ….. °C 
 
Test pressure:  ............................................................................................................... ....... ….. kPa 
 
Test duration:  ............................................................................................................... ........ ….. min 
 
B.2.3 Test results 
 
Give details of any observed or measured leakage, swelling or distortion and any of the failures 
denoting "major failure", defined in 5.3.1 of KS 1851-1. 
 
 .............................................................................................................................. ............................. 
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 .............................................................................................................................. .............................  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
70 © KEBS 2008 — All rights reserved  
 
Collector reference No:  ……………………..  
 
B.3 Internal pressure test for absorbers made of organic materials 
 
NOTE  See B.2 for internal pressure test for absorbers made of inorganic materials. 
 
B.3.1 Technical details of collector 
 
B.3.1.1 Collector type: 
 
   Glazed 
    Unglazed 
 
B.3.1.2 Maximum collector operating pressure specified by manufacturer   kPa 
 
B.3.1.3 Calculated collector stagnation temperature:                                                               °C 
 
Provide details of calculation, showing input data used (attach separate page if necessary)  
 
B.3.2 Test conditions 
 
B.3.2.1 Fluid used to pressurize absorber: 
 
Oil 
 
Air 
  Other (specify):  
 
B.3.2.2 Method used to heat absorber: 
 
  Water bath 
 
Heater in fluid loop 
 
  Natural solar irradiance 
 
Simulated solar irradiance 
 
B.3.2.3 Measured absorber test temperature:       °C 
 
B.3.2.4 Final test pressure:         kPa 
 
B.3.2.5 Duration of test at final test pressure:       min PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 71  
 
Collector reference No.:.............................. 
 
 
 B.3.2.6 
 
Intermediate test pressures 
 
 
kPa Duration of test at each 
intermediate pressure 
 
min 
 
 
  
 
  
 
B.3.2.7  For absorber tested under irradiance 
 
Collector tilt angle (degrees from horizontal): ....................................................................... o 
 
Average irradiance during test:  ............................................................................................ W /m2 
 Average ambient temperature during test:  .......................................................................... °C  
Average wind speed during test:  .......................................................................................... m/s 
 
B.3.3 Test results 
 
Details of any observed or measured leakage, swelling or distortion and the test pressure at which it 
occurred and any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1. 
  .............................................................................................................................. .............................  
  .............................................................................................................................. .............................  
 
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 .............................................................................................................................. .............................  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
72 © KEBS 2008 — All rights reserved  
 
Collector reference No:…………………… 
 
 
B.4 High-temperature resistance test 
 
B.4.1 Method used to heat collectors 
 
Outdoor testing  
 
 In solar simulator 
 
B.4.2 Test conditions 
 B.4.2.1 General 
 
Collector tilt angle (degrees from horizontal): …………………………………………………………. ° 
 
Average irradiance during test: …………………………………………………………………….…  W/m2 
 
Average surrounding air temperature:  ................................................................................. °C  
Average surrounding air speed: ............................................................................................  m/ s 
 
Average absorber temperature: ............................................................................................ °C 
 
Duration of test:  ............................................................................................................ ........ min 
 
B.4.2.2 Additional information required if an evacuated tubular collector was tested  
 
The temperature of the collector was measured at the location shown below: 
 
B.4.2.3 Additional information required if the absorber temperature was measured using a special 
fluid (as described in 5.3.2, note 2) 
 
The absorber was partially filled with …………………… and the average pressure as..................................Pa, 
which corresponds to the average absorber temperature given in B.4.2.  
B.4.3 Test results 
 
Give details of any observed or measured degradation, distortion, shrinkage or outgassing and any of 
the failures denoting "major failure", defined in 5.3.1 of KS 1851-1. 
 
 .............................................................................................................................. .............................  
 
 .............................................................................................................................. .............................  
 
 .............................................................................................................................. .............................  
  .............................................................................................................................. .............................  
  .............................................................................................................................. .............................  
 .............................................................................................................................. .............................  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 73  
 
Collector reference No.:……………………. 
 
 
B.5 Exposure test 
 
B.5.1 Test conditions 
Collector tilt angle (degrees from horizontal): 
 
In Tables B.2 and B.3 full details should be given of the climatic conditions for all days during the test, including:  
⎯ daily global irradiation, H (MJ/m2); 
 
⎯ periods when the global irradiance G and the surrounding air temperature ta have values greater 
than those specified in Table 4; 
 
⎯ surrounding air temperature,  ta (°C); 
 
⎯ rain (mm). 
 
B.5.2 Test results 
 
Inspection should be conducted according to B.5.5. A full description and evaluation should be given 
of any problems or failures observed, including any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1, together with appropriate photographs. 
 
 .............................................................................................................................. .............................  
 
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 .............................................................................................................................. .............................  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
74 © KEBS 2008 — All rights reserved  
 
Collector reference No.:…………………. 
 
 
B.5.3 Climatic conditions for all days during the test 
 
Table B.2 
 
Date 
 H 
 
MJ/m2 
 ta 
 
°C 
 Rain 
mm 
 Date 
 H 
 
MJ/m2 Ta 
 
°C Rain 
 
mm 
 
  
  
           
 
Total: …………………………… days in which H> …………………………..MJ/m2 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 75  
 
Collector reference No.:……………………………………. 
 
 
B.5.4 Time periods in which irradiance and surrounding air temperature have values greater than 
those specified in Table 4  
 
 
Table B.3 
 
 
Date 
 G 
W/m2 ta 
°C Time periods 
min 
 
 
 
 
 
 
  
 
  
 
 
 
 
    
 
  Total:  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
76 © KEBS 2008 — All rights reserved  
 
Collector reference No.:…………………………… 
 
 
B.5.5  Inspection results 
 
Evaluate each potential problem according to the following scale: 
 
 0      –      No problem 
 1      –      Minor problem  
2      –      Severe problem 
 
• Inspection to establish the condition was not possible 
 
Collector component  Potential problem 
 
Evaluation 
 
 a)      Collector box/fasteners  Cracking/warping/corrosion/rain penetration 
 
     …………….  
b)       Mountings/structure  Strength/safety 
 
     ……………. 
 
 
c)      Seals/gaskets   Cracking/adhesion/elasticity 
      ……………. 
 
d)       Cover/reflector   Cracking/crazing/buckling/delamination/  
     …………….  
warping/outgassing  
 
e)      Absorber coating    Cracking/crazing/blistering 
 
……………. 
 Absorber tubes and headers  Deformation/corrosion/leakage/loss of bonding         …………….. 
  
Absorber mountings    Deformation/corrosion 
  
f)     Insulation    Water retention/outgassing/degradation. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 77  
 
Colllector refrence No.:……………. 
 
 
B.6 External thermal shock test: 
 
B.6.1 Test conditions 
 B.6.1.1 General 
  
Test performed 
 
 
 Outdoor In solar irradiance simulator 
  
  
Test combined with exposure test 
 
  
   Yes                                      No 
  Test combined with high-temperature resistance test: 
 
   Yes                                       No  
 Collector tilt angle (degrees from horizontal):………………………………………………………………
0 
 
 Average irradiance during test:............................................................................................... ... W/m 2 
 
Minimum irradiance during test:................................................................................................ ..... W/m2 
 
 Average surrounding air temperature:.......................................................................................... ...... °C 
 
 Minimum surrounding air temperature:.......................................................................................... ..... °C 
  Period during which the required operating conditions were 
 maintained prior to external thermal shock:................................................................................... ....min 
 
Flowrate of water spray:....................................................................................................... .....kg/(s
×m2 
 
 Temperature of water spray:................................................................................................... .............°C 
 
 Duration of water spray:...................................................................................................... .............. min 
 
 Absorber temperature immediately prior to water spray:.................................................................... °C 
 
B.6.1.2 Additional information required if an evacuated tubular collector was tested 
 
 The temperature of the collector was measured at the location shown below:  
B.6.1.3 Additional information required if the absorber temperature was measured using a special 
fluid (as described in 5.5.2, note 2) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
78 © KEBS 2008 — All rights reserved The absorber was partially filled with .............. and the average pressure was                   Pa, 
which corresponds to the absorber temperature given in B.6.1.1. 
  
 
B.6.2 Test results 
 
Give details of any cracking, distortion, condensation, water penetration or loss of vacuum found and 
any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1 when examining the 
collector after the test. 
 
 .............................................................................................................................. .............................  
 
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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 79  
 
Collector reference No: ………………………… 
 
 
B.7 Internal thermal shock test: 
 
B.7.1 Test conditions 
 B.7.1.1 General 
 
Test performed: 
 
      Outdoors     In solar irradiance simulator 
 
Test combined with exposure test: 
 
 
Yes   No 
 
Test combined with high-temperature resistance test: 
 n     Yes     No 
 
Collector tilt angle (degrees from horizontal): ............................................................................... ........o 
 
Average irradiance during test:   ............................................................................................. .......W/m
2 
 
Minimum irradiance during test:  .............................................................................................. ......W/m2 
 
Average surrounding air temperature during test: ..............................................................................oC 
 
Minimum surrounding air temperature:   ........................................................................................ .... oC 
 
Period during which the required operating conditions were maintained prior to internal thermal  
 
shock: ........................................................................................................................ ........................min 
 
Flowrate of heat transfer fluid:............................................................................................... .. kg/(s-m2 ) 
 Temperature of heat transfer fluid:  .......................................................................................... ...........
oC 
 
Duration of heat transfer fluid flow: ......................................................................................... ..........min 
 
Absorber temperature immediately prior to heat transfer fluid flow: ..................................................oC 
 
B.7.1.2 Additional information required if an evacuated tubular collector was tested 
 
The temperature of the collector was measured at the location shown below: 
 
B.7.1.3 Additional information required if the absorber temperature was measured using a special 
fluid (as described in 5.6.2, note 2) 
 
The absorber was partially filled with ........................... and the average pressure was ...........Pa, which corresponds to the absorber temperature given in B.7.1.1. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
80 © KEBS 2008 — All rights reserved  
B.7.2 Test results 
 
Give details of any cracking, distortion, deformation, water penetration or loss of vacuum found and 
any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1 when examining the 
collector after the test. 
 
 .............................................................................................................................. .............................  
 
 .............................................................................................................................. .............................  
  .............................................................................................................................. .............................  
 
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  .............................................................................................................................. .............................  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 81  
 
Collector reference No.:………………………………….. 
 
 
B.8 Rain penetration test  
 
B.8.1 Test conditions 
 B.8.1.1 Collector mounting 
 
Collector mounted on:  
    Open frame 
 
    Simulated roof 
 
Collector tilt angle (degrees from horizontal): 
 
B.8.1.2    Method used to keep absorber warm: 
 
   Hot water circulation 
 
    Exposure of collector to solar radiation 
 
 
B.8.1.3 Water spray 
 
Water spray flowrate:          kg/(s-m2) 
 
D u r a t i o n  o f  w a t e r  s p r a y :           h  
 
B.8.2  Test results 
 
Area with visible sign of water penetration (expressed as a percentage of aperture area):   % 
 
Give details of water penetration, reporting the places where water penetrated and the time the sign 
of rain penetration took to vanish.  
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Give details of any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1. 
 
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82 © KEBS 2008 — All rights reserved  
 
Collector reference No,:…………………………………………………. 
 
 
B.9 Freeze resistance test 
 
B.9.1 Collector type 
 
        Freeze-resistant when filled with water 
 
   Drain-down 
 
B.9.2 Test conditions 
 
B.9.2.1 Tilt angle of collector during test ( degrees from horizontal):  
 
B.9.2.2 Details of freeze-thaw cycles 
 
No. of freeze-thaw cycles  Freeze conditions  Thaw conditions   
 Test temperature 
°C Duration 
min Test temperature  Duration min
 
1 
2 3 
     
For freeze-resistant collectors, this is the temperature of the contents of the collector, e.g. water, ice. 
For drain-down collectors, this is the temperature measured inside the absorber close to the inlet.  
 
B.9.2.3 Rate of chamber cooling: 
 
B.9.2.4 Rate of chamber heating: 
 
B.9.3 Test results 
 
Give details of leakages distortion or deformation and any of the failures denoting “major failure” 
defined in 5.3.1 of KS 1851-1.  
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© KEBS 2008 — All rights reserved 83  
Collector reference No.:……………………………………… 
 
B.10 Mechanical load test 
 
B.10.1 Positive pressure test of the collector cover 
 
B.10.1.1 Method used to apply pressure: 
 
      Loading with gravel or similar material 
     
      Loading with water 
      Suction cups  
    Pressurization of collector cover 
 
 
B.10.1.2 Test conditions 
 
Maximum pressure load: 
 
B.10.1.3 Test results 
 
Give details of any damage to the collector cover after the test, reporting the value of pressure load which caused the damage and any of the failures denoting "major failure", defined in 5.3.1 of KS 
1851-1 
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B.10.2 Negative pressure test of fixings between the cover and the collector box  
 
B. 10.2.1 Method used to apply pressure: 
 
Suction cups       Pressurization of collector box  
 
B.10.2.2 Test conditions 
 
Maximum pressure load: 
 
B.10.2.3 Test results 
 
Give details of any damage to the collector cover or cover fixings after the test, reporting the value of 
pressure load which caused the damage and any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1 
  .............................................................................................................................. .............................  
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 .............................................................................................................................. .............................  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
84 © KEBS 2008 — All rights reserved  
 
Collector reference No.:…………………………………………………………………………. 
 
 
 
B.10.3 Negative pressure test of collector mountings 
 
B.10.3.1  Method used to apply pressure:  
     Suction cups      Air bags  
 
B.10.3.2 Test conditions 
 Maximum pressure load:         Pa 
 
B.10.3.3 Test results 
 
Give details of any damage to the collector mounting fixtures or fixing points after the test, reporting 
the value of pressure load which caused the damage and any of the failures denoting "major failure", 
defined in 5.3.1 of KS 1851-1 
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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 85  
 
Collector reference No.:…………………………………………………………………….. 
 
 
 
B.11 Impact resistance test using steel balls 
 
B.11.1 Test conditions 
 
Diameter of ball: 
 
M a s s  o f  b a l l :           m m  
 
Test performed using:         g 
 
Vertical impact (dropping ball) 
 
  Horizontal impact (pendulum)  
 
B.11.2 Test procedure 
 
Drop height 
m No. of drops 
  
  
  
  
  
  
  
  
  
 
 B.11.3 Test results 
 
Give details of any damage to the collector and any of the failures denoting "major failure", defined in 
5.3.1 of KS 1851-1 
 
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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
86 © KEBS 2008 — All rights reserved  
 
Collector reference No.:………………………………………………………………….. 
 
 
 
B.12 Impact resistance test using ice balls 
 
B.12.1 Test conditions 
 
 
Diameter of ball:  ...................................................................................................... mm 
 
Mass of ball:  ............................................................................................................ g 
 Velocity of ball:  ........................................................................................................ m/s  
 
B.12.2 Test procedure 
 
No. of impacts: 
 
B.12.3 Test results 
 
Give details of any damage to the collector and any of the failures denoting "major failure", defined in 
5.3.1 of KS 1851-1  
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 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 87  
 
Collector reference No.:………………………………………………………………………. 
 
 
B.13 Final inspection results 
 
Evaluate each potential problem according to the following scale: 
 
0 – No problem 
 1 – Requirement apart from testing not fulfilled  
2 – Requirements for testing not fulfilled 
 
• – Inspection to establish the condition was not possible  
 
Collector component Potential problem Evaluation 
 
a) Collector box/fasteners Cracking/warping/corrosion/rain penetration ………..  
b) Mountings/structure Strength/safety ....................... 
 
c) Seals/gaskets Cracking/adhesion/elasticity ....................... 
 d) Cover/reflector Cracking/crazing/buckling/delamination/  ................... 
warping/outgassing 
 
e) Absorber coating  Cracking/crazing/blistering  of bonding  …………….. 
 
Absorber tubes and headers  Deformation/corrosion/leakage/loss of bonding 
…………….…………….. 
 
Absorber mountings Deformation/corrosion ……………… 
 
f) Insulation Water retention/outgassing/degradation PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
88 © KEBS 2008 — All rights reserved  
Annex C 
(normative) 
 
Stagnation temperature of liquid heating collectors 
 
 
C.1 General 
 
This annex provides a method for calculating the stagnation temperature of a collector, i.e. the temperature of 
the collector during periods of no useful heat removal from the collector with high solar radiation and ambient surrounding temperatures.  
The stagnation temperature should be determined for a selected solar irradiance 
Gs and a selected ambient 
temperature tas: 
 
The calculated stagnation temperature is used for determining the test temperature for: 
 
⎯ internal pressure testing of collectors with organic absorbers (see 5.2.2); 
 
⎯ high-temperature resistance test using a hot fluid loop (see 5.3). 
 
C.2 Determination of stagnation temperature 
 The stagnation temperature
 tstg, for the selected values of solar irradiance G s and ambient temperature tas, is 
calculated by extrapolating from measured steady-state values of: 
 
⎯ solar irradiance Gm (natural or simulated) on the collector plane; 
 
⎯ surrounding air temperature tam; 
 
⎯ absorber temperature tsm 
 
while the collector is exposed to the available solar irradiance and ambient temperature (outdoors, or in a 
solar irradiance simulator) under steady-state conditions without heat extraction from the collector (stagnation 
conditions).  
The expression for determining the stagnation temperature for the selected parameters (
Gs and tas) is: 
 
 
 
  ()am sm
ms
as stg t tGGt t − +=  
 
It is based on the approximation that the ratio ( tsm – tam)/G m remains constant under steady-state collector 
stagnation conditions. 
 
This approximation is acceptable only if the irradiance level (Gm) used during the test is within 10 % of the irradiance specified for the stagnation conditions (G
s). 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 89  
Annex D 
(normative) 
 
Performance test report for glazed solar collectors 
 
D.1 General 
 
Collector reference No: 
 
Test performed by:  
Address: 
 
Date, Tel, Fax: 
 
D.2 Solar collector description 
 
Name of manufacturer:  
Brand Name:     Serial No: 
 
Collector Type : Glazed/Evacuated  Drawing Document No: 
Year of Production: 
 
F l o w  r a n g e :            t o  k g / s   
Operating pressure:          kPa 
 Stagnation temperature at 1000 W/m
2 
 
and 30 °C ambient temperature:         °C 
 
Collector mounting: 
 
Collector: 
 
Type name: 
 
Flat plate / evacuated / subatmospheric:Gross area:  
Aperture area: 
 
Absorber area: 
 
Dimensions of collector unit 
 
Length:   mm    Absorber area:    m2 
Width:   mm    Aperture are:    m2 
Height:   mm    Gross Area    m2 
Weight empty: 
Fluid content: 
Number of covers: 
Cover materials: 
Cover thickness: 
Cover solar transmittance: PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
90 © KEBS 2008 — All rights reserved  
Absorber: 
 
Material: 
 
Fin width: 
 
Fin thickness: 
 
Solar absorptance α: 
 
Hemispherical emittance ε: 
 
Surface treatment: 
 
Construction type:  
Number of risers: 
 
Riser diameter or dimensions: 
 Distance between risers: 
 Dimensions: 
 
Thermal insulation and casing: 
 
Thermal insulation thickness: 
 
Insulation material: 
 
Casing material:  
Sealing material: 
 
 
Limitations: 
 
Maximum operation temperature:  
Maximum operation pressure: Other limitations: 
 
Photograph of the collector 
 
Comments on collector design 
 
Schematic diagram of collector mounting 
 Schematic diagram of the test loop 
 Heat transfer medium:    water / oil / other 
 
Specifications (additives etc.):  
Alternative acceptable heat transfer fluids: 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 91 D.3 Test results 
 
Thermal performance has been tested based on test methods: 
 
16.1Outdoor – Steady   6.1 Indoor – Steady  16.3 Outdoor-Quasi-dynamic 
 State Method   State Method   Method 
 
Outdoor        indoor 
 
Latitude:       mean solar irradiance: 
 
Longitude:       type of the lamps:  
Collector azimuth:      shading of longwave radiation: yes     no 
 
Collector tilt: 
 
Orientation of absorber tubes during testing (horizontal or vertical): 
 
Peak Power (G = 1000 W/m
2) per collector unit.......................................W peak 
 
Power output per collector unit (W): 
 
Irradiance 
 
Tm-Ta in = 2 K 
 400 W/m2 
 700 W/m2 
 1000W/m2 
 
10    
30    
50    
NOTE The reported values are for normal incidence. 
 
 
 
 
 
Figure D.1 — Power output per collector unit (for G = 1000 W/m2) 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
92 © KEBS 2008 — All rights reserved Instantaneous efficiency curve based on (absorber/aperture) area and mean temperature of heat 
transfer fluid. 
 
Reference area: Absorber area AA    Reference area: Aperture area Aa 
 
absorber area  used for curve in m2 :aperture area  used for curve in m2 : 
 
The instantaneous efficiency is defined by: 
 
GΑη
ΑΛQ&
=    (D.1)  GΑQη
aa&
=     (D.2) 
 
Fluid flowrate used for the tests:         kgs-1 
 
Gross collector area:          m2 
 
Second order fit to data: 
 
2
⎟
⎠⎞⎜
⎝⎛−−⎟
⎠⎞⎜
⎝⎛−−=GttGaGttaηηa m
2Αa m
1A oΑ Α  
 
2
a m
2aa m
1a oa a ⎟
⎠⎞⎜
⎝⎛−−⎟
⎠⎞⎜
⎝⎛−−=GttGaGttaηη  
 
Based on Absorber Area  
 Std. Deviation
 Based on Aperture Area  
 Std. Deviation 
 
oAη   οaη   
a1A  
  
 a1a  
   
a2A 
  
   a
2a 
     
In case of 6.3, test results according to Annex J should be attached to this document 
 
Time constant 
 
τC = s 
 
Effective thermal capacity 
 
C = JK-1 
 
Determination: 
 
Calculation:  
Indoors: 
 
Outdoors: 
 
Incident angle modifier 
 
Angle:  
Kθ: PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 93  
Observed failures 
 
Give details of any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1 
 
Delivery of sample: 
 
Start of test: 
 End of test: 
 
Test Institute:....................................   Date: ..................... PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
94 © KEBS 2008 — All rights reserved  
Annex E 
(normative) 
 
Performance test report for unglazed solar collectors 
 
E.1 General 
 
Collector reference No: 
 
Test performed by:  
Address: 
 
Date, Tel, Fax: 
 
E.2 Solar collector description 
 
Name of manufacturer:  
Brand Name:        Serial No: 
 
Collector Type:        Drawing Document No: 
 
Year of Production: 
 Flow range:        to kg/s 
 
Operating pressure:       kPa  Stagnation temperature at 1000 W/m
2 
 
and 30 °C ambient temperature:      °C 
 
Collector mounting: 
 
Collector: 
 
Type name:  
Flat plate / evacuated / subatmospheric: 
 
Gross area: 
 
Aperture area: 
 
Absorber area: 
 Serial No: Drawing Document No: 
Dimensions of collector unit 
 
Length:    mm    Absorber area:   m2 
 
Width:    mm    Aperture area:   m2 
 
H e i g h t :     m m     G r o s s  A r e a :    m2 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 95  
Weight empty: 
 
Fluid content:  
Absorber: 
 
Material: 
 Fin Width: 
 
Fin thickness:  
Solar absorptance 
α: 
 
Hemispherical emittance ε: 
 
Surface treatment: 
 
Construction type: 
 Number of risers: 
 
Riser diameter or dimensions:  
Distance between risers:  
Dimensions: 
 
Limitations: 
 
Maximum operation temperature: 
 
Maximum operation pressure at 45 °C: 
 
Maximum operating pressure at maximum temperature of operation: 
 
Other limitations: 
 
Photograph of the collector  
Comments on collector design  
Schematic diagram of collector mounting 
 
Instantaneous efficiency 
 Heat transfer medium:     water / oil / other 
 
Specifications (additives etc.): Alternative acceptable heat transfer fluids: PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
96 © KEBS 2008 — All rights reserved  
E.3 Test results 
 
Thermal performance has been tested based on test methods: 
 
16.1Outdoor – Steady   6.1 Indoor – Steady  16.3 Outdoor-Quasi-dynamic 
 State Method   State Method   Method 
 
Outdoor :       i n d o o r  
 
Latitude:      mean solar irradiance: 
 Longitude:      type of the lamps: 
 
Collector tilt:      shading of longwave radiation: yes      no  
Collector azimuth: 
 
Peak Power (G = 1000 W/m
2) per collector unit:…………………………………………………..W Peak 
 
Power Output per collector unit (W): 
 
 Irradiance 
Tm-Ta = 2 K 
 400 W/m2 
 700 W/m2 
 1000 W/m2 
 
u < 1 m/s 
       
u= 1.5 ± 0.5 m/s 
       
u = 3 ± 0.5 m/s    
 
The power output per collector unit shall be presented graphically according to Figure E.1 for the following 
wind conditions: u < 1 ms-1, u = 1.5 ± 0.5 ms-1 and u=3 ± 0.5 ms-1 
 
 
 
Figure E.1 — Power output per collector unit PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 97  
Instantaneous efficiency curve based on collector area and mean temperature of heat transfer fluid. 
 
The instantaneous efficiency is defined by: η="GQ
Α&
      (E.1) 
 
collector area used for curve:  m2 
 Fluid flowrate used for the tests:  kgs
-1 
 
     ()() ⎟
⎠⎞⎜
⎝⎛−+−−="Gttubbuba m
u 2 1 01ηη    (E.2) 
Based on Absorber Area  
 Based on Aperture Area  
 
⋅
Αoη   
oaη  
buA  b ua  
b1A  b 1a  
b2A  b 2a  
In case of 6.3, test results according to Annex J should be attached to this document 
 
Time constant  
cτ= s 
 
Effective thermal capacity  
C = JK
-1 
 
Determination:  
Calculation: 
 
Indoors: 
 Outdoors: 
 
Incident angle modifier 
 
Angle: 
 
Kθ: 
 
Observed failures 
 
Give details of any of the failures denoting "major failure", defined in 5.3.1 of KS 1851-1 
 
Delivery of sample:  
Start of test:  
End of test: 
 
Test Institute:……………………………….     Date:………………………… PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
98 © KEBS 2008 — All rights reserved  
Annex F 
(normative) 
 
Modelling of the coefficients c 1 to c 6 of the collector model of 6.3. 
 
Coefficient c 1 is the Heat loss coefficient at ( tm - ta) = 0       [ W m-2K-1] 
 
c1 is modelled as F’U0 
 
Coefficient c 2 is the Temperature dependence of the heat loss coefficient   [Wm-2K-2 
] 
C2 is equal to F’U1 
 
Coefficient c 3 is the Wind speed dependence of the heat loss coefficient    [Jm-3K-1] 
 
c3 is equal to F’Uu 
 
Coefficient c 4 is the Long wave irradiance dependence of the heat loss coefficient    [-] 
 
c4 is equal to ε'F 
 
NOTE The modelling of the long wave irradiance dependence of the collector is made in the same principle way as described in th e 
basic ISO 9806-3, 8.8, for testing of unglazed collectors. The Net long wave irradiance, is defined as (4
a LT Eσ− ) and where EL is the 
measured long wave thermal irradiance in the collector plane. 
 
However, a purely mathematical difference exists between ISO 9806-3 and this standard that eliminates G" and the use of the ε/α-
coefficient in the equation. Physically, the long wave radiation corrections are the same. In this standard, the correction fac tor for long 
wave radiation is treated as a separate heat loss term and is not involved in an effective radiation term G" as in ISO 9806-3. The main 
reason for this is that the collector equation is simplified by doing so, as this approach also takes into account incidence an gle effects 
and diffuse radiation effects. In this case, α otherwise should be corrected for these effects. In ISO 9806-3, these factors are not taken 
into account and the equation is simplified by using G" and the ε/α-factor. 
 
Coefficient c 5 is the Effective thermal capacitance      [Jm-2K-1] 
 
c5 is equal to C/A (definition of C, see under 6.1.6.2 ). 
 
NOTE c is often denoted ( mC)e in basic literature 
 
Coefficient c 6 is the Wind speed dependence in the zero loss efficiency    [sm-1] 
 
C6 is modelled as a collector constant 
 
Kθb(θ) is the Incidence angle modifier (IAM) for direct radiation      [-] 
 
The basic modelling of lAM-dependence is made with the equation  
K
θ(θ) = 1-b 0((1/cosθ1)-1) (H.1) 
 
as described in e.g. ASHRAE 93-77 
 For collectors with special lAM-dependence, see note 2 under 6.3.4.8.1. 
θdΚis the Incidence angle modifier for diffuse radiation 
 
θdΚ is modelled as a collector constant PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 99  
Annex G 
(normative) 
 
Measurement of effective thermal capacity 
 
G.1 Test installation 
 
The collector is mounted in accordance with the recommendations of 6.1.1 and coupled to a test loop for 
thermal capacity measurement. 
 Effective thermal capacity measurements may be carried out indoors, where only heat loss is measured. 
They may also be made outdoors in steady-state clear sky conditions, or in a solar irradiance simulator. 
 
G.2 Indoor test procedure 
 
G.2.1 General 
 
The heat fluid is circulated from the top to the bottom of the collector with a constant inlet temperature, using 
a flowrate similar to that defined for collector efficiency testing, until steady-state conditions are reached. 
 The inlet temperature of the fluid is raised rapidly by about 10 K, and measurements made continuously until 
steady-state conditions are achieved again. This process is performed four times and an arithmetic mean 
value of the effective thermal capacity calculated.  
G.2.2 Measurements 
 The following quantities are measured: 
 a) heat transfer fluid mass flowrate;  
b) temperature of the heat transfer fluid at the collector inlet;  
c) temperature of the heat transfer fluid at the collector outlet; 
 
d) surrounding air temperature. 
 
NOTE When testing collectors having a low thermal capacity, the sampling frequency selected for measuring the fluid temperature s 
may need to be greater than the usually used for collector efficiency testing, in order to adequately follow the transient beha viour of the 
collector. 
 
G.2.3 Calculation of the effective thermal capacity 
 
The transient behaviour of the collector between the two indoor steady states 1 and 2 is represented by the following equation: 
 
) ( ΔΤdtd
a m fmttAU mCtC −−−=  (G.1) 
 
where 
 
ΔT = (ta – t a)(negative) (G.2) 
 
and tin and te are the heat transfer fluid temperatures at the collector inlet and outlet (exit), respectively, under 
the new flow direction of the heat transfer fluid. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
100 © KEBS 2008 — All rights reserved Integrating the equation over the period between the two steady-states gives 
 
C() ( ) tttΤcm t t d dtΔ2
12
1t
ta mt
t1 mt m2 ∫∫− −&  (G.3) 
Since 
 
in mt t=+ 2ΔΤ (G.4) 
 
we may express (tm-ta) as 
 
tm - ta=()2Τtta mΔ+−  (G.5) 
 
Combining the above equations, and rearranging, gives the following equation for the collector thermal 
capacity. 
 
C=()
1 2 m mt tΤ tt mc
−⎥⎥
⎦⎤
⎢⎢
⎣⎡
+− − −∫∫∫2
12
12
1t
tt
tt
ta m f dtΔ21dt ΑU ΔΤdt
 (G.6 
 
G.2.4 Determination of effective thermal capacity from experimental data 
 
From the test results, ( tin - ta) and ΔT are plotted as a function of time. The areas under the curves, between 
the two steady states, are 
 
()  dt2
1t
ta in∫−tt  and ∫2
1t
tdtΔΤ 
 
respectively. 
 The heat transfer coefficient 
U of the collector may already have been determined during indoor collector 
heat loss measurement. However, AU may be obtained directly from two steady states since in a steady state 
we have: 
 
0 = -mcf()a mttUΤ −Α−Δ  (G.7) 
 
and hence 
 
a mttΤ mcU−Δ=Αf (G.8) 
 
AU is evaluated for both steady states, and arithmetic mean value taken. 
 
A value of the effective thermal capacity is determined by inserting these experimental values in Equation (G.6). 
 
G.3 Outdoor or solar irradiance simulator test procedure 
 The fluid is circulated with a constant temperature, using a flowrate similar to that defined for collector efficiency testing, until steady-state conditions are reached. The aperture of the collector should be shielded 
from the solar radiation (natural or simulated) by means of a solar-reflecting cover. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 101  
The cover is removed and measurements are made continuously until steady-state conditions are achieved 
again. This process is performed four times and an arithmetic mean value of the effective thermal capacity 
deduced.  
The measurements indicated in G.2.2 are made. In addition, the solar irradiance (natural or simulated) 
G is 
measured. 
 
The transient behavior of the collector between two steady states 1 and 2 is represented by the following equation 
 
C ()a m fmttUcmGdtdt−Δ−Α=Ο&η  (G.9) 
 
at where, as in G.2.3, 
 
()in ettΤ−=Δ (positive) 
 
Integrating the Equation (G.9) over the period between the two steady states gives the following equation for 
the collector thermal capacity: 
 
C=()
m1 m2a m f
t tΤdt dtttΑUΤdt mc Gdtt
tt
tt
tt
t
−⎥⎥
⎦⎤
⎢⎢
⎣⎡
Δ+− −Δ− Α∫∫ ∫ ∫2
12
12
12
121
0η
 (G.10) 
 
From the test records, ( tm – t a), ΔT and G are plotted as a function of time. The areas under the curves, 
between the two steady states, are: 
 
() dt,2t
ta m∫−
1tt , ∫2
1t
tdtΔ  Τ and ∫2
1t
tdt  G 
 
respectively. 
 
The y intercept η0 and the slope U of the linear form of the instantaneous efficiency η are known from testing. 
 
A value for the effective thermal capacity is determined by inserting these experimental values in Equation 
(G.10).  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
102 © KEBS 2008 — All rights reserved  
Annex H 
(informative) 
 
Comparison of the collector model of 6.1 to the collector model of 6.3 
 
In a comparison, we start to describe the present stationary collector model used in 6.1. This model has been 
widely used both in testing (ISO 9806-1 and ASHRAE 93-77) and for simulation. The basic equation is a 
stationary model for near normal incidence angle operation and can be written as: 
 
Q&/A = F’(τα)enG* – c 1(tm – t a) – c 2(tm – ta)2  (H.1) 
 
The irradiance is denoted G*, but could instead be denoted Gb to point out that only high irradiance levels are 
accepted in the test sequence, and thus a low diffuse fraction. No correction for non stationary conditions is 
made, so very stable inlet and radiation conditions are needed for each test point.  
Furthermore, it is assumed that the incidence angle is near normal, so that incidence angle effects can be 
neglected.  
In 6.1, there are furthermore optional test procedures also for the determination of incidence angle 
dependence of the zero loss efficiency and the effective thermal capacitance of the collector. Therefore the 
full instantaneous equation from all the options in 6.1 can be written as: 
 
Q&/A = F’(τα)enKθb(θ)G* – c 1(tm – t a) – c 2(tm – ta)2 – c5dtm/dt (H.2) 
 
As a first step in the approach of 6.3, the first term of the equation is divided into two parts, giving the sum of 
the zero loss efficiency for beam radiation and the diffuse radiation, or F’(τα)enKθb(θ)G* is divided into 
F’(τα)enKθb(θ)Gb + F’(τα)enKθd(θ)Gd while the rest of the equation is kept unchanged. 
 
To make it possible to test a much wider range of solar collectors, but also to achieve a much more complete 
characterization of the collector from the same test and with the same method, just another correction is 
added to the collector model, namely the correction for the wind-dependence. In the 6.1-method, this is  
handled by limiting the test requirements for wind-speed to 2-4 m/s for glazed collectors during test. For 
unglazed, their sensitivity to wind-speed has resulted in the need for a test method (6.2) of their own, which 
prescribes that 3 different efficiency functions have to be measured for each collector at 3 given wind-speeds. A fact that makes testing of each collector expensive and time consuming. For test sites with varying climate, 
such tests can also be difficult to conduct outdoors.  
In this approach, wind-dependence is modeled by 2 terms added to the basic equation. One gives the effect 
on the zero loss efficiency (-
c6uG*) and the other the effect on the heat losses (-c 3u(tm-ta)). After a final 
addition of the Long-wave irradiance dependence of the heat losses (+c 4(EL–σTa4)), modeled as done for 
unglazed collectors (see Annex F), the collector model is completed and is written as in Equation 7. Equation 
7 gives the output power of the collector per square meter of the reference area used. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 103  
Annex I 
(informative) 
 
Properties of water (see DIN V 4757-4:1995-11) 
 
1.1 Density of water (at 1 bar) in kg/m3 
 
ρ(ϑ) = a0 + a1ϑ + a2ϑ2 + a3ϑ3 + a4ϑ4 
 
(0 ≤ ϑ  ≤ 99.5 °C) 
 
with  
a0 = 999.85  
 
a1= 6.187 × 10-2 
 
a2= -7.654 × 10-3 
 
a3= -3.974 × 10-5 
 
a4= -1.110 × 10-7 
 The deviation of the polynomial to the values published in tables is always smaller than 0.02 %. R
2 equals 
0.99998  
1.2 Specific heat capacity of water (at 1 bar) in kJ/(kg K) 
 
cp(ϑ) = a0 + a1ϑ + a2ϑ2 + a3ϑ3 + a4ϑ4 
 
(0 ≤ ϑ  ≤ 99.5 °C 
 
with 
 
a0= 4.217 
 
a1= -3.358 × 10-3  
 
a2= 1.089 × 10-4 
 
a3= -1.675 × 10-6 
 
a4= 1.309 × 10-8 
 
a5 =  -3.884 × 10-11 
 
The deviation of the polynomial to the values published in tables is always smaller than 0.02%. R2 equals 
0.9994 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
104 © KEBS 2008 — All rights reserved  
Annex J 
(informative) 
 
Performance test report summary for quasi dynamic test method 
 
Identification: 
 
Manufacturer: 
 
Brand Name: ................................................................................................................... ................... Serial No: 
 
Collector Type: ......................................................................................................... Drawi ng document No: 
 
Dimensions of Collector unit: 
 
Length:                          mm                                       Absorber area: ...................................... .......... m2 
 
Width:                            mm                                       Aperture area: ..................................... ........... m2 
 
Height:                           mm                                       Gross area (casing): ............................... ........ m2 
 
General Specifications: 
 
Weight: ....................................................................................................................... ........................ kg 
 Heat transfer fluid: 
 
Flow range: ................................................................................................................... ..................... to     l/h  
 
Operating pressure: ........................................................................................................... ................ bar 
 Stagnation Temperature at 1000Wm
-2, 
 
and 30 °C ambient temperature ................................................................................................. ........ °C 
  PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 105  
Thermal performance based on: 
 
Aperture Area:          Absorber Area:  
 
 
 
  
 
  Value 
 Standard deviation 
   Value 
 Standard deviation 
 
F’(τα)en 
  
   F’(τα)en 
     
Kθd 
  
   Kθd      
b0 
  
   b
0 
     
c1 
  
   c
1 
     
c2 
  
   c
2 
     
c3 
  
   c
3 
     
c4 
  
   c
4 
     
c5 
     c
5 
     
c6 
  
   c
6 
     
 
Table M.1 — Incidence angle modifier,  Kθb(θ)  
 
θ 10 
 20  30  40 50 60 70 80 
 
Kθb(θ)  
               
 This test report should be completed in conjunction with the test report according to Annex D or E. 
 
Tested by: 
 
Date: 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
106 © KEBS 2008 — All rights reserved  
Annex K 
(informative) 
 
General guidelines for the assessment of uncer tainty in solar collector efficiency 
testing 
 
 
K.1 Introduction 
 
The aim of this annex is to provide a general guidance for the assessment of uncertainty in the result of solar 
collector testing performed according to the present standard. Testing laboratories are often invited to provide 
a statement of uncertainty in test results in quantitative tests, in the framework of their accreditation or of application of product certification schemes. It is not the aim of this annex to define whether and in which 
cases the calculation of uncertainty in test results is necessary. 
 
This guidance concerns only in collector efficiency testing due to i) the great importance of the result of this 
testing for the user, and ii) the peculiarities of the calculations, since the final result of efficiency testing is not derived by a single measurement but by elaboration of a large number of primary measurements. 
 
It is noted that the proposed methodology is one of the possible approaches for the assessment of 
uncertainty, and other approaches can be implemented. It is of the responsibility of each Laboratory to 
choose and to implement a scientifically valid approach for the determination of uncertainties, following the recommendations of the accreditation bodies, where appropriate. For a more detailed review of the different 
aspects of determination of uncertainties in solar collector testing see also (Mathioulakis et al., 1999; 
Sabatelli et al., 2002; Müller-Schöll and Frei, 2000).  
K.2 Measurement uncertainties in solar collector efficiency testing 
 
The basic target of solar collector efficiency testing is the determination of the collector efficiency by 
measurements under specific conditions. More specifically, it is assumed that the behavior of the collector 
can be described by a M-parameter single node, steady state or quasi-dynamic model: 
 
M Mpc pcc +++= ....22 1η  ..................................................................................................... (K.1) 
 
where; 
 
η is the collector instantaneous efficiency. 
 
p1, p2,…., pN are quantities, the values of which are determined experimentally through testing 
 
c1, c2, ….., cM are characteristic constants of the collector that are determined through testing. 
 
In the case of the steady state model, for example, M = 3, c1= 0η, c2 = U1: c3 = U2, p1 = 1, p 2= ( Tm - Ta)/G 
and p3 = (Tm - Ta)2/G 
 
During the experimental phase, the output, solar energy and the basic climatic quantities are measured in J 
steady-state or quasi-dynamic state points, depending the model used. From these primary measurements 
the values of parameters ,η p1, p2, ..., pM are derived for each point of observation j, j = 1... J. Generally, the 
experimental procedure of the testing leads to a formation of a group of J observations which comprise, for 
each one of the J testing points, the values of ηj, p1,j, p2,j, …., pM,j. 
 
For the determination of uncertainties, it is essential to calculate the respective combined standard 
uncertainties u(ηj), u(p1,j), …..., u(pM,j) in each observations point. It should be noted that in practice the PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 107 uncertainties u(ηj), u(p1,j), …..., u(pM,j) are almost never constant and the same for all points, but that each 
testing point has its own standard deviation. 
 For the calculation of the standard deviation (squared standard uncertainty) in each point j, the following 
general rules can be applied (ISO GUM): 
 I. Standard uncertainties in experimental data are determined by taking into account Type A and Type B 
uncertainties. According to the recommendation of ISO GUM, the former are the uncertainties determined by statistical means while the latter are determined by other means. 
 
II. The uncertainty 
u(s) associated with a measurement s is the result of a combination of the Type B 
uncertainty uB(s), which is a characteristic feature of the calibration setup, and of the Type A uncertainty 
uA(s), which represents fluctuation during sampling of data. If there is more than one independent 
source of uncertainty (Type B or type A) uk, the final uncertainty is calculated according to the general 
law of uncertainties combination: 
 
U = 2/1
2
⎟⎟
⎠⎞
⎜⎜
⎝⎛∑
kku  (K.2) 
 
III. Type B uncertainty uB(s) derives from a combination of uncertainties over the whole measurement 
chain, taking into account all available data, such as sensor uncertainty, data logger uncertainty, 
uncertainty resulting from the possible differences between the measured values perceived by the 
measuring device. Relevant information should be obtained from calibration certificates or other technical data related to the devices used. 
 
IV. By nature, Type A uncertainties depend on the specific conditions of measurement and they account for 
the fluctuations in the measured quantities during the measurement. Type A uncertainty 
uA(s) derives 
from the statistical analysis of experimental data. In some cases (for example in the case of the steady-
state model), the best estimate of S is the arithmetic means s of the I repeated observations si(i = 1 … I) 
and its Type A uncertainty is the standard deviations of the mean: 
 
S = IsI
Iii∑
=, and 2/1
2
)1() (
    )( 
⎟⎟⎟⎟⎟
⎠⎞
⎜⎜⎜⎜⎜
⎝⎛
−−
=∑
=
ΑIIss
suI
lii
 (K.3) 
In some other cases (for example in the case of the quasi-dynamic model where no arithmetic mean of 
the repetitive measurements is used) uncertainty uA(s) can be equal to zero. 
 
V. The term combined standard uncertainty  means the standard uncertainty in a result when that result is 
obtained from the values of a number of other quantities. In most cases a measured Y is determined 
indirectly from P other directly measured quantities X 1, X2, ..., X P through a functional relationship Y = 
f(X1, X2,, ...X P). The standard uncertainty in the estimate y is given by the law of error propagation: 
 
U(y)= ()() ()2/1
,
11
122
cov 2⎟⎟
⎠⎞
⎜⎜
⎝⎛
∂∂
∂∂+⎟⎟
⎠⎞
⎜⎜
⎝⎛
∂∂∑∑ ∑
+=−
= =ji
j iP
ijP
ii
iP
jixxxf
xfxuxf (K.4) 
 
An example of such indirect determination in the case of solar collector efficiency testing is the 
determination of instantaneous efficiency η, which derives from the values of global solar irradiance in 
the collector level G, fluid mass flowrate m, temperate difference , ,ΤΔ collector area A and specific heat 
capacity c f. Thus, in this case the standard uncertainty u(jη) in each value jη of instantaneous PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
108 © KEBS 2008 — All rights reserved efficiency is calculated by the combination of standard uncertainties in the values of the primary 
measured quantities, taking into account their relation to the derived quantity η. 
 
K.3 Fitting and uncertainties in efficiency testing results 
 
During analyzing the data a least square fitting of the model equation is performed, in order to determine the 
values of coefficients c1, c2, ..., cM for which the model of Equation (K.1) represents the series of J 
observations with the greatest accuracy. 
 
Since in reality the typical deviation is almost never constant and the same for all observations, but each data 
point (ηj, p1,j, p2,j, ..., pM,j) has its own standard deviation σj, an interesting solution is the use of the weighted 
least square (WLS)  method, which calculates, on the base of the measured values and their uncertainties, 
not only the model parameters but also their uncertainty. In the case of WLS, the maximum likelihood 
estimate of the model parameters is obtained by minimizing the chi-square function: 
 
22
, ,22 ,11
12)) ... ( (
jjMN j j jJ
jupc pc pc ++−
=∑
=η
χ  (K.5) 
 
Where 2
juis the variance of the difference ) ... (, 22 ,11 jMN j j j pc pc pc ++−η  
 
() ( ) ()()2
,2 2
,12
12
, ,22 ,12) ( ... ) ( )( ) ... (jM M j j jMN j j I j j puc puc u pc pc pc Var u ++ + = ++−= η η  (K.6) 
 
Finding coefficients c 1, c2, ..., cM and their standard uncertainties by minimizing chi-square function is 
complicated, because of the non-linearity present in Equation (K.5). A strategy is therefore to find these 
uncertainties numerically. A method for the case of a M-parameter model is presented below (Press et al., 
1996). 
 
Let K also be a matrix whose J×M components kj,m are constructed from M basic functions evaluated at the J 
experimental values of p1,..., pM weighted by the uncertainty uj,: 
JJM,
JJ1,1M1,
1j1,
jim,
mj,
up..up. .....
..
..
..up..up
       ,= = Κupk (K.7) 
Let also L be a vector of length J whose components lj are constructed from values of jη to be fitted, 
weighted by the uncertainty uj. 
 
jj
julη
= , 
J Juu
L
/.../1 1
ηη
=  (K.8) 
 
The normal equation of the least square problem can be written:  
(K
T • K) • INV(C) = KT • L (K.9) 
 
where C is a vector whose elements are the fitted coefficients. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 109 Given the fact that for the calculation of variances 2
ju the knowledge of coefficients c1, c2,..., cM is needed, a 
possible solution is to use the values of coefficients calculated by standard least squares fitting as the initial 
values. These initial values can be used in Equation (K.6) for the calculation of 2
ju, J=1 ...J and the formation 
of matrix K and of vector L. 
 
The solution of Equation (K.9) gives the new values of coefficients c1, c2, ...., cM, which however are not 
expected to differ noticeably from those calculated by standard least squares fitting and used as initial values 
for the calculation of 2
ju. 
 
Moreover, Z=INV(KT•K) is a matrix whose diagonal elements zk,k are the squared uncertainties (variances) 
and the off-diagonal elements zk,I = zI,k, k ≠ I are the covariance between fitted coefficients: 
 
M m z cu ,...., , )(mm, m 1= =  (K.10) 
 
M k z ccCovlk lk ,...,    ) (,, , 1==  and M l,...,1=  and lk≠ (K.11) 
 
It should be noted that the knowledge of covariance between the fitted coefficients is necessary if one wishes 
to calculate, in a next stage, the uncertainty u(η) in the predicted values of η using Equations (K.1) and (K.4). 
Equation (K.9) can be solved by a standard numerical method, for example, by Gauss-Jordan elimination. It 
is also possible to use matrix manipulation functions of commonly used spreadsheet software. 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
110 © KEBS 2008 — All rights reserved  
Annex L 
(informative) 
 
Determination of the pressure drop across a collector 
 
L.1 general 
 
The pressure drop across a collector may be of importance to designers of solar collector systems. The fluid 
used in the collector for the test shall be water or a mixture water:glycol (60:40), or a mixture recommended 
by the manufacturer. 
 
The temperature of the fluid shall be (20 ± 2) °C. 
 
L.2 Test installation 
 
The collector shall be mounted in accordance with 6.1.1 and coupled to a test loop which conforms broadly 
with 6.1.3, although less instrumentation is required for pressure drop determination than for collector 
efficiency testing.  
The heat transfer fluid shall flow from the bottom to the top of the collector, and particular attention shall be paid to the selection of appropriate pipe fittings at the co llector entry and exit ports, as specified in 6.1.3.3. In 
the case of unglazed collectors the direction of the fluid flow may be recommended by the manufacturer.  
L.3 Preconditioning of the collector 
 
The fluid shall be inspected to ensure that it is clean. 
 
The collector shall be vented of air by means of an air bleed valve or other suitable means, such as 
increasing the fluid flowrate for a short period to force air from the collector. 
 
L.4 Test procedure 
 
a) Glazed solar collectors 
 
The pressure drop between the collector inlet and outlet connections shall be determined for flowrates 
which span the range likely to be used in real operation. In the absence of specific flowrate 
recommendations by the manufacturer, pressure drop measurements shall be made over the range of 
flowrates from 0.005 kgs-1 to 0.03 kgs-1 per square metre of collector area. The origin of the pressure 
drop diagram — the point (0,0) should be considered as well. 
 
At least five measurements shall be made at values equally spaced over the flowrate range. 
 
b) Unglazed solar collectors 
 
The pressure drop between the collector inlet and outlet connections shall be determined with the 
collector and its fluid close to ambient air temperature, and for flowrates, which span the range likely to be used in the application for which the collector is intended. 
 
Because the arrangement of the strips and the manifolds used in the test usually differs from typical 
installations, the pressure drop of a strip and of the manifolds shall be determined separately. This may 
be achieved by two consecutive pressure drop measurements of one short absorber strip including 
manifolds (at least 3 m) and one long absorber strip including manifolds (e.g. 15 m). 
 
The difference of both pressure drop curves may then be divided by the difference of strip lengths between both absorbers. The resulting curve is the undisturbed pressure drop per meter strip. PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
© KEBS 2008 — All rights reserved 111 The test should be carried out at a constant pressure which corresponds to the intended operating 
pressure.  
 
In the absence of specific flowrate recommendations by the manufacturer, pressure drop measurements shall 1be made over the range of flowrates from 0.02 kgs
-1 to 0.1 kgs-1 per square metre of collector area. 
 
At least five measurements shall be made at values equally spaced over the flowrate range. The zero 
level shall be checked as well. 
 
L.5 Measurements 
 
The following data shall be measured in accordance with 6.1.2: 
 
a) fluid temperature at the collector inlet; 
 
b) fluid flowrate; 
 
c) heat transfer fluid pressure drop between the collector inlet and outlet connections.  
The heat transfer fluid pressure drop across the collector shall be measured with a device having a standard uncertainty of 5 % of the measured value or ±10 Pa whichever is higher. 
 
L.6 Pressure drop caused by fittings 
 
The fittings used to measure the fluid pressure may themselves cause a drop in pressure. A zero check on 
the pressure drop shall be made by removing the collector from the fluid loop and repeating the tests with the 
pressure-measuring fittings directly connected together. The pressure drop caused by the fittings shall be used to correct the measured pressure drop of the collector. 
 
L.7 Test conditions 
 
The fluid flowrate shall be held constant to within ± 1 % of the nominal value during test measurements. 
 
The inlet temperature of the heat transfer fluid shall be held constant to within ±5 K (±1 K for unglazed 
collectors) during test measurements. The test shall be carried out with the collector at a temperature which 
lies within ±10 K of that of the surrounding air. Pressure drop tests at other temperatures may be important for oil-based heat transfer fluids. 
 
L.8 Calculation and presentation of results 
 
The pressure drop shall be presented graphically as a function of the fluid flowrate for each of the tests 
performed, using the format sheets given in Annex D (glazed collectors) or in Annex E (unglazed collectors). 
 
 PUBLIC REVIEW DRAFT, SEPTEMBER 2008KS 1851-2:2008 
112 © KEBS 2008 — All rights reserved  
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No. 4-6, pp. 163-178, 1997. 
 
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and Simulation Programmes. Journal of the Int. Solar Energy Society Vol. 50, No. 6, pp. 517-526, 
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Prediction using Standard Spreadsheet and Simulation Programmes. ISES Conference, Budapest, (1993). 
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[74] WMO, Guide to Meteorological Instruments and Methods of Observation, 5th edn., WMO-8, Secretariat 
to the World Meteorological Organization, Geneva, 1983, Chapter 9. 
 [75] ISO 9806-1, 
Test methods for solar collectors — Part 1: Thermal performance of glazed liquid heating 
collectors including pressure drop  
 
[76] ISO 9806-2, Test methods for solar collectors — Part 2: Qualification test procedures  
 
[77] ISO 9806-3:1995, Test methods for solar collectors — Part 3: Thermal performance of unglazed liquid 
heating collectors (sensible heat transfer only) including pressure drop  
 
[78] ISO 9846, Solar energy — Calibration of a pyranometer using a pyrheliometer  
 
[79] ISO 9847, Solar energy — Calibration of field pyranometers by comparison to a reference pyranometer  
 
[80] ISO/TR 9901, Solar energy ⎯ Field pyranometers ⎯ Recommended practice for use  
 
[81] ISO 9808, Solar water heaters ⎯ Elastomeric materials for absorbers, connecting pipes and fittings ⎯ 
Method of assessment  
 
[82] ISO 9553, Solar energy ⎯ Methods of testing preformed rubber seals and sealing compounds used in 
collectors