ISO/TS 9124:2025

Technical
Specification
ISO/TS 9124
First edition
Paints and varnishes — Thermal
2025-12
performance of paint films
— Determination of solar
irradiation penetration ratio with
heat flow meter
Peintures et vernis — Performances thermiques des feuils de
peinture— Détermination du taux de pénétration de l'irradiation
solaire au moyen d'un fluxmètre thermique
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols, definitions and units. 2
5 Measurement principle . 3
6 Apparatus . 4
6.1 Composition of apparatus . .4
6.2 Solar simulator .5
6.3 Climatic chamber (external airflow path) .5
6.4 Measuring unit .6
7 Test method . 6
7.1 Sampling .6
7.2 Inspection and preparation of sample for test .6
7.3 General conditions for test .6
7.4 Setting the external surface heat transfer coefficient and adjusting the heat flux of
solar irradiation.7
7.4.1 Setting the external surface heat transfer coefficient .7
7.4.2 Adjusting heat flux of solar irradiation .7
7.5 Verification method .8
7.5.1 Verification plate .8
7.5.2 Environmental conditions .9
7.5.3 Verification .9
7.6 Measurement .9
7.6.1 Parameters to be measured .9
7.6.2 Measurement method .10
7.7 Calculation method.11
7.8 Precision . . .11
8 Test report .11
Annex A (normative) Setting of external surface heat transfer coefficient .13
Annex B (informative) Theoretical calculation of heat balance for the heat flow rate through
the test specimen. 17
Annex C (informative) Correlation between solar reflectance and solar irradiation penetration
ratio . .22
Annex D (informative) Heat flux measurements without solar irradiation .23
Bibliography .24

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The procedures used to develop this document and those intended for its further maintenance are described
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This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee SC 9,
General test methods for paints and varnishes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
An optical method called the solar reflectance of paint film has been standardized to evaluate the heat-
shielding performance of paint film. Meanwhile, various paint heat-shielding techniques other than solar
reflectance have recently been proposed.
This document evaluates the thermal barrier performance according to the solar radiation absorption
rate by measuring the amount of heat transmitted through the coating film due to solar radiation using a
heat flux meter. This measurement method allows the thermal barrier performance of a coating film to be
assessed irrespective of the thermal barrier technology of the coating film. Examples are given in Annex C
and Annex D. The measurement provides values directly in units of heat value, which are easy to understand
and can be applied to the calculation of the thermal energy balance of building structures.

v
Technical Specification ISO/TS 9124:2025(en)
Paints and varnishes — Thermal performance of paint films
— Determination of solar irradiation penetration ratio with
heat flow meter
1 Scope
This document specifies the heat flow measurement method of the solar irradiation penetration ratio of
paint films used for roofs and outer walls of buildings, structures, equipment or facilities situated outdoors
and exposed to solar irradiation.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 1513, Paints and varnishes — Examination and preparation of test samples
ISO 2808, Paints and varnishes — Determination of film thickness
ISO 2813, Paints and varnishes — Determination of gloss value at 20°, 60° and 85°
ISO 3270, Paints and varnishes and their raw materials — Temperatures and humidities for conditioning and testing
ISO 4618, Paints and varnishes — Vocabulary
ISO 7345, Thermal performance of buildings and building components — Physical quantities and definitions
ISO 8301, Thermal insulation — Determination of steady-state thermal resistance and related properties —
Heat flow meter apparatus
ISO 8894-1, Refractory materials — Determination of thermal conductivity — Part 1: Hot-wire methods (cross-
array and resistance thermometer)
ISO 9050:2003, Glass in building — Determination of light transmittance, solar direct transmittance, total solar
energy transmittance, ultraviolet transmittance and related glazing factors
ISO 10292, Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing
ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms, definitions
and surface texture parameters
ISO 22969, Paints and varnishes — Determination of solar reflectance
IEC 60584-1, Thermocouples — Part 1: EMF specifications and tolerances
IEC 60904-9, Photovoltaic devices — Part 9: Solar simulator performance requirements

3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618, ISO 7345, ISO 22969,
IEC 60584-1, IEC 60904-9 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
heat flow rate of solar irradiation penetration
Φ
η
heat flow rate that passes through the test specimen due to the solar radiation that is perpendicularly
incident on the test piece, when the amount of heat that passes through the test specimen (transmitting
heat) that is generated by the difference between the exterior air temperature and the interior temperature
is adjusted to zero in advance
Note 1 to entry: It is expressed in watts (W).
3.2
paint film solar irradiation penetration ratio
η
p
ratio of the heat flux, which absorbs the solar radiation perpendicularly incident on the test piece and
conducts heat to the internal surface, to the heat flux of solar irradiation
3.3
primary standard plate
specified plate used to calibrate apparatus
3.4
verification plate
specified plate used to verify a measuring apparatus
3.5
incident angle
vertical angle between the line from the detected element to the sensor and the local surface normal (tangent
plane normal)
[SOURCE: ISO 19130-1:2018, 3.13]
4 Symbols, definitions and units
For the purpose of this document, the symbols, definitions and units given in Table 1 apply.
Table 1 — Symbols, definitions and units
Symbol Definition Unit
A area of test specimen m
W
h external convective surface heat transfer coefficient W/(m ·K)
CV
h external radiative surface heat transfer coefficient W/(m ·K)
r
h external surface heat transfer coefficient W/(m ·K)
se
I Φ /A heat flux of solar irradiation W/m
Solar, solar W
T external air absolute temperature K
ex
T surface absolute temperature of baffle plate K
g
T internal absolute temperature K
in
T paint film surface absolute temperature K
p
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Definition Unit
W width of test specimen m
w
ε corrected emissivity of baffle plate -
g
ε corrected emissivity of paint film -
p
η paint film solar irradiation penetration ratio -
p
θ external air temperature °C
ex
θ external air temperature near the airflow generator °C
ex,A
θ external air temperature away from the airflow generator °C
ex,A’
θ internal temperature °C
in
v external airflow velocity near the airflow generator m/s
ex,A
−8 2 4
σ Stefan-Boltzmann constant, 5,67 × 10 W/(m ·K )
Φ heat flow rate transferred by convection from the test specimen W
CV
Φ heat flow rate transferred by radiation from the test specimen W
r
Φ heat flow rate of solar irradiation W
Solar
Φ heat flow rate through the test specimen W
W
Φ /A , q heat flux through the test specimen W/m
W W W
Φ heat flow rate of solar irradiation penetration W
η
Φ /A heat flux of solar irradiation penetration W/m
η W
Φ the absorbed heat flow rate of solar irradiation in the test specimen W
α
5 Measurement principle
A paint film surface is irradiated with radiation from artificial sunlight (solar simulator) to simulate heat
transfer that occurs in the outer and inner structures of buildings. The heat flux of the paint film is calculated
from the parameters set and measured based on the phenomena observed. The solar irradiation penetration
ratio (η ), a parameter used for parallel evaluation of various types of paint films, is determined.
p
The heat flow rate of solar irradiation (Φ ) is obtained according to Formula (1) by measuring the heat
Solar
flux of solar irradiation (I ) taken with a radiometer considering the area of test specimen (A ).
Solar W
Φ = I × Α (1)
Solar Solar W
When the heat flow rate transferred through the test specimen due to the difference between external air
temperature and internal temperature is zero, the heat flow rate through the test specimen (Φ ) is equal to
W
the heat flow rate of solar irradiation penetration (Φ ) as shown in Formula (2):
η
Φ = Φ (2)
η W
The paint film solar irradiation penetration ratio (η ) is obtained from above (Φ ) and (Φ ) according to
p Solar η
Formula (3).
Φ
η
η = (3)
P
Φ
Solar
See Figure 1 for an illustration of heat transfers that occur in a test specimen with solar radiation.

Key
1 paint film
2 base substrate
3 heat flow meter
4 heating and cooling plate
5 insulation board
Φ heat flow rate of solar irradiation, in W
Solar
Φ heat flow rate transferred by convection from the test specimen, in W
CV
Φ heat flow rate transferred by radiation from the test specimen, in W
r
Φ heat flow rate through the test specimen, in W
W
Figure 1 — Heat transfers that occur in a test specimen
6 Apparatus
6.1 Composition of apparatus
The measuring apparatus shall consist of a solar simulator, a climatic chamber and a measuring unit. The
light emitted from the solar simulator passes through the light guide window and the baffle plate and
irradiates the test specimen. The heat absorbed by the test specimen then transfers to and through a heat
flow meter. Figure 2 shows the overall view of apparatus composition.

Key
1 solar simulator
2 climatic chamber
3 airflow generator
4 measuring unit
5 test specimen
6 heat flow meter with auxiliary plate
7 heating and cooling plate
8 light guide window
9 baffle plate
10 external airflow path
11 insulation board
Figure 2 — Example of measurement component
6.2 Solar simulator
The light source for the solar simulator shall be a xenon lamp or a metal-halide lamp of Class BBB or superior
as specified in IEC 60904-9 and shall satisfy the following.
a) Maximum incident angle: The maximum incident angle to the test specimen shall not be greater than 10°.
b) Effective irradiated area: The width of the effective irradiated area shall be not less than 105 % of the
width and length of the test specimen.
6.3 Climatic chamber (external airflow path)
The climatic chamber which simulates the external airflow path shall consist of a light guide window, a
baffle plate, an airflow generator, etc. (see Figure 2), and shall be as follows.
a) Light guide window, through which the incident light of the solar simulator irradiates the test specimen
via the external airflow path, shall meet the following requirements.
1) The solar transmittance measured in accordance with ISO 9050 shall be not less than 88,0 %.
2) The difference between the maximum and the minimum spectral transmittance in the range of
380 nm to 2 100 nm among the wavelengths given in ISO 9050:2003, Table 2 shall be 0,05 or less.
b) Baffle plate, made of high transmittance glass in accordance with 6.3 a) 1) and 2).
c) Airflow generator, generating airflow between the baffle plate and the test specimen in order to
maintain the external surface heat transfer coefficient.

d) Bottom and side surfaces of the external airflow path, whose lightness value L* is 10 or less when
measured in accordance with ISO/CIE 11664-4.
6.4 Measuring unit
The measuring unit shall consist of a heat flow meter, a heating and cooling plate simulating the internal
side, etc., and shall be as follows.
a) Heat flow meter, as specified in ISO 8301. If the heat flow meter is smaller than the test specimen, it
shall be attached to the centre back side of the test specimen and the gap formed between the test
specimen and the heating and cooling plate shall completely be filled by an auxiliary plate having the
same material and thermal resistance. To ensure the heat transfer between the heat flow meter and the
test specimen, thermal conductive materials that do not impede the thermal conductivity shall be used.
To verify that the heat flow rate shows the correct value under condition without solar irradiation, a test
specimen with a known thermal resistance value can be measured and checked.
NOTE The test specimen is uniformly attached to heat flow meter using silicone compound.
b) Heating and cooling plate, satisfying the following:
1) The variation of temperature distribution of the working surface shall be within 0,5 °C.
2) The working surface shall be made of metal with high thermal conductivity and finished to a
flatness (deviation from a true flat surface) within 0,025 %.
c) Temperature sensor, equivalent to the T-type thermocouple specified in IEC 60584-1, with an element
wire diameter of 0,2 mm or less. When used for surface temperature measurement, the thermocouples
shall be fixed using adhesives, pressure-sensitive adhesives or adhesive tape.
d) Radiometer (thermopile-type), instrument for measuring electromagnetic radiation, consisting of a
detector, any necessary filters and diffusers, and a signal-processing device.
7 Test method
7.1 Sampling
Sampling shall be in accordance with ISO 15528.
7.2 Inspection and preparation of sample for test
The inspection and preparation of the sample used for the test shall be in accordance with ISO 1513.
7.3 General conditions for test
The general conditions of the test shall be as follows.
a) Location for testing: Preparation of test specimens and testing shall be performed inside a room
protected from direct sunlight, free from gas, steam or dust that may affect curing and testing, free from
significant drafts, and maintained in a condition conforming to the standard conditions, temperature of
(23 ± 2) °C and relative humidity of (50 ± 5) %, specified in ISO 3270.
b) Preparation of test specimen: One test specimen prepared according to the following by applying and
drying paint for testing on a base substrate shall be used.
1) Base substrate: An aluminium plate painted black, of the specifications provided in Table 2.
2) Black paint: Jet black paint for automotive refinish or general industrial coating such as 2 K urethane
can be used.
3) Paint application and drying: Apply the paint on the aluminium plate
and dry in accordance with the direction provided by the manufacturer.
Table 2 — Specifications for base substrate
Component Parameter Specification
[1]
Aluminium plate with a purity not less than 99,50 % (thickness, 1,0 mm)
Substrate Aluminium plate
Sample size, 180 × 180 mm
a
Paint pigment Carbon black (CAS Registry Number® 1333–86–4)
Solar reflectance
5 % max. (ISO 22969)
(300 nm to 2 500 nm)
Corrected emissivity 0,85 ± 0,05 (ISO 10292)
Dry-film thickness (50 ± 10) μm (ISO 2808)
Black paint
Surface roughness Ra max. 2 μm (ISO 21920-2)
Surface colour (L*) 5 max. (ISO/CIE 11664-4)
Specular gloss (60°) 90 ± 5 (ISO 2813)
Thermal conductivity 0,4 ± 0,1 W/(m·K) (ISO 8894-1)
a
CAS Registry Number® is a trademark of the American Chemical Society (ACS). This information is given for the convenience
of users of this document and does not constitute an endorsement by ISO of the product named. Equivalent products may be used
if they can be shown to lead to the same results.
c) Test specimen attachment method: The test specimen is attached to the measurement unit using a
silicone compound, etc.
1) Apply silicone compound to the test specimen.
2) The test specimen applied with silicone compound is attached to the measurement unit.
3) To verify that the test specimen has been attached correctly, four measurements are taken and each
value of heat flow rate is within ± 5 %.
7.4 Setting the external surface heat transfer coefficient and adjusting the heat flux of solar
irradiation
7.4.1 Setting the external surface heat transfer coefficient
The external surface heat transfer coefficient shall be calibrated to the accuracy of ± 1 W/(m ·K) in
accordance with Annex A, and its median value shall be set according to the circumstances and climate
of each country. An example of the environmental conditions is shown in Table A.2. The external radiative
surface heat transfer coefficient (h ) and the external convective surface heat transfer coefficient (h ) that
r cv
are used for measurement shall be set in accordance with Annex A.
7.4.2 Adjusting heat flux of solar irradiation
Remove the measuring unit and install the radiometer specified in 6.4 d) in the opening for accommodating
the test specimen so that it directly faces the light source of the solar simulator. Adjust the lamp power of
the solar simulator and adjust the local environmental conditions so that they meet the values as per the
example in Table 4.
Key
1 solar simulator
2 photodetector
3 climatic chamber
4 airflow generator
5 measuring unit
6 radiometer
7 baffle plate
8 external airflow path
9 insulation board
Figure 3 — Position of radiometer and photodetector in the measuring apparatus
Measurements shall be taken at the same position as the centre of the test specimen (see Figure A.1).
A photodetector installed in a position other than on the specimen surface, since its purpose is to monitor the
heat flux of solar irradiation during measurement, shall be adjusted to match the readings of the radiometer.
...