ISO 9869-2:2018

INTERNATIONAL ISO
STANDARD 9869-2
First edition
2018-08
Thermal insulation — Building
elements — In-situ measurement of
thermal resistance and thermal
transmittance —
Part 2:
Infrared method for frame structure
dwelling
Isolation thermique — Éléments de construction — Mesurage in
situ de la résistance thermique et du coefficient de transmission
thermique —
Reference number
©
ISO 2018
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 2
5 Principle . 3
6 Requirements for apparatus . 4
6.1 General . 4
6.2 Infrared camera . 5
6.3 Heat transfer coefficient sensor . 6
6.4 ET sensor . 6
6.5 Thermocouple . 6
6.6 Data logger . . 6
7 Measurement method . 6
7.1 Building . 6
7.2 Location of the measured area . 6
7.3 Measurement conditions . . 7
7.4 Measurement of heat transfer coefficient . . 7
7.5 Measurement of environmental temperature . 7
7.6 Surface temperature distribution of building elements . 8
7.7 Measurement time and measurement interval . 8
7.8 Measurement terms. 8
7.9 Measurement period. 9
8 Calculations. 9
8.1 Heat transfer area . 9
8.2 Calculation of heat flow rate. 9
8.3 Calculation of thermal transmittance.10
9 Measurement accuracy .10
10 Test reports .10
Annex A (informative) Measurement principle .12
Annex B (informative) Calculation of environmental temperature, structure of ET sensor .16
Annex C (informative) Structure and calibration of heat transfer coefficient sensor .19
Annex D (informative) Uncertainty analysis .24
Annex E (informative) The calculation example of uncertainty analysis .27
Bibliography .31
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by ISO/TC 163, Thermal performance and energy use in the built
environment, SC 1, Test and measurement methods.
A list of all parts in the ISO 9869 series can be found on the ISO website.
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 © ISO 2018 – All rights reserved

Introduction
The ISO 9869 series describes the in-situ measurement of the thermal transmission properties of plane
building components, primarily consisting of opaque layers perpendicular to the heat flow and having
no significant lateral heat flow. The thermal transmittance of a building element (U-value) is defined in
ISO 7345 as the “Heat flow rate in the steady state condition divided by area and by the temperature
difference between the surroundings on each side of a system”. Since steady state conditions are never
encountered on a site in practice, such a simple measurement is not possible and thereby some statistical
methods are introduced. One of the simplest methods is using the mean values over a sufficiently long
period of time. The required time for observation for reliable measurements depends on the thermal
properties of the building components and the natures of the temperature difference between the
surroundings on each side of them.
ISO 9869-1 describes the method which is used to estimate the thermal steady-state properties of a
building element from heat flow meter (HFM) measurements through plane building components.
Annex B describes the statistical methods of simple mean and the sophisticated method of dynamic
analysis method for steady state properties. This document, describes the calculation method for the
density of heat flow rate through both the evaluation of the internal surface thermal resistance and
the measuring of the temperature difference between the indoor surface temperature of the building
element and the indoor environmental temperature using an infrared camera (thermo-viewer). It
also describes the statistical methods of simple mean with less observing duration considering night
observation and building components with light heat capacity.
This document provides a preliminary and handy measuring method for the in-situ measurement of the
thermal transmission properties of plane building components and thereby the further simplifications
are applied compared with the method described in ISO 9869-1. The method described in this document
is expected as a method of a handy diagnostic method of the thermal transmission properties of plane
building components with light heat capacity such as those in frame structure dwelling.
The thermal performance of a part of the building element is evaluated by obtaining the heat absorption
(heat penetration) at the part of the indoor surface by multiplying the indoor total heat transfer
coefficient of the part surface by the difference between the part indoor surface temperature and the
indoor environmental temperature. The thermal transmittance (U-value) of the building components
for steady state condition can be obtained with the averages of the observed values over the certain
period of time.
The indoor surface temperature distribution of the building component is measured using an IR camera.
The indoor environmental temperature is measured by installing the environmental temperature
sensor (ET sensor) on the surface of the building component, and the indoor total heat transfer
coefficient of the surface of the building component is measured using a heat transfer coefficient sensor.
Even the indoor measurement is intended to be carried on with less influence of solar radiation so the
standard can be used on building elements on which indoor sides are not exposed to direct sunlight
through adjacent windows.
INTERNATIONAL STANDARD ISO 9869-2:2018(E)
Thermal insulation — Building elements — In-situ
measurement of thermal resistance and thermal
transmittance —
Part 2:
Infrared method for frame structure dwelling
1 Scope
This document describes the infrared method for measuring the thermal resistance and thermal
transmittance of opaque building elements on existing buildings when observing high emissivity diffuse
surface using an infrared (IR) camera. This document demonstrates a screening test by quantitative
evaluation to identify the thermal performance defect area of building elements.
This document aims to measure the thermal transmittance (U-value) of a frame structure dwelling
with light thermal mass, typically with a daily thermal capacity calculated according to ISO 13786
below 30 kJ/(m K).
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 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 8302, Thermal insulation — Determination of steady-state thermal resistance and related properties —
Guarded hot plate apparatus
ISO 9869-1, Thermal insulation — Building elements — In-situ measurement of thermal resistance and
thermal transmittance — Part 1: Heat flow meter method
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7345 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https:/ /www.e lectropedia. org/
— ISO Online browsing platform: available at https:/ /www. iso. org/obp
3.1
thermography
image of a specific band of surface radiance detected with an infrared camera (3.2)
Note 1 to entry: On known and uniform high emissivity surfaces, with known and controlled irradiance from the
background, and with the proper instrument calibration and operator compensation, the radiance image can be
converted to a temperature distribution.
3.2
infrared camera
instrument that collects the infrared radiant energy from a target surface and produces an image in
monochrome (black and white) or colour, where the grey shades or colour hues are related to target
surface apparent temperature distribution
3.3
total heat transfer coefficient
sum of the convective heat transfer coefficient and the radiative heat transfer coefficient of the surface
of a building element
Note 1 to entry: It is assumed to be measurable using the heat transfer coefficient sensor.
3.4
heat transfer coefficient sensor
sensor to approximately measure the total heat transfer coefficient (3.3) of the surface of a building
element which can measure the total heat transfer coefficient in the neighbourhood of a section of the
building element
3.5
environmental temperature
conceptual temperature taking account of the indoor and outdoor air temperatures and radiant heat
of a building element used for calculating the thermal transmittance (thermal resistance) of the
building element
Note 1 to entry: A temperature measured by an environmental temperature sensor (3.6) is treated as the
environmental temperature.
3.6
environmental temperature sensor
ET sensor
sensor that takes an approximate measure of the indoor and outdoor environmental temperatures of a
building element to be measured
4 Symbols and units
Symbol Quantity Units
A heat transfer area of the region m
region area of the region with surface tempera-
A m
j
ture θ
sj
h total heat transfer coefficient W/(m K)
θ environmental temperature °C
n
θ surface temperature °C
s
θ inside air temperature °C
a
inside environmental temperature of the region to
θ °C
ni
be measured
outside environmental temperature of the region to
θ °C
ne
be measured
θ surface temperature of section j °C
sj
θ surface temperature of heat transfer coefficient sensor °C
hs
θ plane radiant temperature of section j °C
rj
Q heat flow rate W
q heat flow of the heat transfer coefficient sensor W/m
2 © ISO 2018 – All rights reserved

Symbol Quantity Units
r area ratio of the heat transfer area of section j —
j
R total thermal resistance (m K)/W
T
U thermal transmittance W/(m K)
5 Principle
This method (illustrated in Figure 1) measures the amount of irradiance of regions in contact with
the outside air from the surface temperature, total heat transfer coefficient and environmental
temperature. The difference between the inside and outside temperature is then used to determine
thermal transmittance/thermal resistance of the regions that are in a steady-state.
The amount of irradiance of regions in contact with the outside air when being heated is derived from
Formula (1) in relation to the inside temperature (Annex A).
Qh=−θθ A (1)
()
ns
The amount of irradiance of the region can be determined using Formula (1) and the measurement of
the temperature of the inside surface temperature of the region made with an infrared camera, together
with the readings of the total heat transfer coefficient and environmental temperature obtained from
the heat transfer coefficient sensor and ET sensor mounted near the region. If the surface temperature
of the region being measured varies, the average temperature is used by taking the temperature of
each area of the region. This method defines the environmental temperature as a value approximately
measured by an ET sensor. The method to obtain the environmental temperature is shown in Annex B.
The amount of irradiance of the region is measured when it is in a constant state away from direct
sunlight at night for at least three hours, and calculated using Formula (2) and the difference between
the inside and outside environmental temperature.
Q
U = (2)
θθ− ⋅A
()
ni ne
Key
1 measurement area
2 outside
3 inside
Figure 1 — Outline of measurement principle
6 Requirements for apparatus
6.1 General
The necessary apparatus for in-situ measuring thermal resistance and thermal transmittance are as
following:
6.1.1 Infrared camera.
6.1.2 Heat transfer coefficient sensor.
6.1.3 ET sensor.
6.1.4 Thermocouple thermometer.
6.1.5 Data logger.
Configuration of the apparatus is shown in Figure 2.
4 © ISO 2018 – All rights reserved

Key
1 measurement area
2 ET sensor
3 heat transfer coefficient sensor
4 IR camera
5 thermocouple
6 data logger
7 outside
8 inside
Figure 2 — Measurement outline (cross-section)
6.2 Infrared camera
Infrared cameras detect infrared radiation on the surface of the object being measured, with the
intensity distribution being displayed as a thermal image. The range of wavelength that can be
measured is the same as normal thermal radiation at 8 μm to 13 μm. The camera shall be capable of
detecting temperatures between the overall blackbody temperature range of at least −20 °C to 100 °C.
Thermal sensitivity shall not be worse than 80 mK on a 30° blackbody object temperature.
Measurements can be made at regular intervals for automatic logging of temperature. Infrared cameras
that come with software that processes and displays the measured temperature data as an image are
preferable.
6.3 Heat transfer coefficient sensor
The heat transfer coefficient sensor is used to estimate the total heat transfer coefficient of the surface
of the region of the object being measured. It has an insulating plastic foam backing and has a heating
sheet connected to a heat flow meter. The surface of the heating sheet is copper sheet, with the heat
flow meter attached to the front of the copper sheet. A sheet type electrical heater is used to heat the
copper sheet in a uniform fashion. The surface of the cooper sheet is finished with a matte black coating
(with an emittance greater than 0,9), and a thermocouple (with a diameter of less than 0,2 mm or a
thermocouple for surface measurements) is attached to the surface. The sensor shall have a size of
200 × 200 mm with a thickness of 25 mm as a standard.
Using the heat flow meter stretched on the heating sheet before building it into the heat transfer
coefficient sensor, calibrate the relation of the heat flow density to the output, following the procedure
specified in ISO 8301 or in ISO 8302. The structure and calibration of heat transfer coefficient sensor is
shown in Annex C.
6.4 ET sensor
The ET sensor is used to measure the environmental temperature of the regions of the object to be
measured. The size of the meter is approximately 200 × 200 mm with a thickness of 50 mm, consisting
of an insulating plastic foam and attached on the surface of copper sheet finished with a matte black
coating (with an emittance greater than 0,9). A thermocouple (with a diameter of less than 0,2 mm or a
thermocouple for surface measurements) is attached to the surface. The construction of the ET sensor
is shown in Annex B.
6.5 Thermocouple
The recommended temperature sensor is the type T thermocouple (copper/constantan) according to
IEC 60584-1 made from wire with diameter not greater than 0,25 mm. The temperature range available
consists of a standard temperature gauge and corrected for use with a data logger. If alternative sensors
are used, they should be at least as accurate as the above-mentioned, not subject to drift or hysteresis.
6.6 Data logger
The data logger automatically records the measured data of the temperature and heat flow from this
experiment with the required accuracy at regular intervals.
7 Measurement method
7.1 Building
The measurement object shall be a frame structure dwelling with a relatively small heat capacity [a
heat capacity per unit area of about 30 kJ/(m K) or less]. It is preferable if the details of the buildings
are researched thoroughly in advance using floorplans. Visual observations are made in-situ before the
measurements are made in order to select the appropriate regions for measurement.
7.2 Location of the measured area
The measurement position shall be selected according to the purpose of the test. The measured area
shall not be under the direct influence of either a heating or a cooling device or under the draught of a
fan. And the measurement area should be free of all visual interference from curtains, wall hangings,
furnishings, plants, light fixtures and anything that impedes the field of view for the IR imager.
6 © ISO 2018 – All rights reserved

7.3 Measurement conditions
The conditions of the measurement state that there must be a difference greater than 10 °C between the
inside and outside temperature when the heater is on. When the temperature differences is small, the
accuracy required for measuring this quantity may be lowered. The heating is achieved with the heater
that is used normally to keep the inside at a constant temperature. If there is no heating equipment, an
electrical heater with a fan can be used to heat the inside of the building. When stirring the air in the
room, take caution so that the airflow moving around the building element is not greatly different from
that under normal room conditions. The inside of the region to be measured must be completely sealed
by closing the building doors. If the room where the measurement takes place has openings such as a
sash window, block the window with curtains, shades, etc. to eliminate any temperature variation. In
the case of measurement conditions that are affected, such as infiltration, liquid water, moisture, air
leakage and other uncontrolled climatic conditions, this situation should be described in the report.
7.4 Measurement of heat transfer coefficient
The heat transfer coefficient sensor is mounted near the centre of the surface of the region to be
measured. Next, the power to the heat transfer coefficient sensor electrical heater is turned on and the
power adjusted so that the temperature of the surface of the sensor is between 2 and 4 °C higher than
the inside air temperature of the region to be measured.
The use of the heat transfer coefficient sensor is assumed that the measured values would correspond
to the plane averaged local total heat transfer coefficient over the testing building element. If there
are some reasons that this assumption cannot be stood, for examples, the testing building element
is vertically long enough and the local convective heat transfer coefficient will vary a lot from the
bottom to the top, a number of heat transfer coefficient number sensors may be arranged including
the centre. The variation of the measured values from the sensors might be recorded for the reference
purpose of the measurement reliability. The surface temperature of the heat transfer sensor shall be
preset to be the same as the difference (absolute value) between air temperature in the room where
the measurement takes place and a typical surface temperature of the section to be measured. The
temperature difference shall be higher than 2 °C.
Under the condition that the surface temperature of the heat transfer coefficient sensor is stable,
measure the following:
— Surface temperature of the heat transfer coefficient sensor measured by an infrared camera: θ
hs
— Surface temperature of the ET sensor measured by an infrared camera (environmental
temperature: θ )
ni
— Heat flow meter output on the surface of the heat transfer coefficient sensor (heat flow density: q)
The total heat transfer coefficient is calculated with Formula (3).
q
h= (3)
θθ−
hs ni
In addition, when the thermal performance of the building elements is low (e.g. in case of the differences
temperature between surface and air temperature are more than 2 K as an aim), the heat flow meter
(HFM) can be attached directly to the inside surface, and surface temperature of HFM is measured by
an infrared camera, and the total heat transfer coefficient can be calculated with Formula (3). Avoid
attaching the heat flow meter to any areas where a heat bridge may be formed. The surface should be
finished with a matte black coating (with an emittance greater than 0,9). When using a heat flow meter,
refer to ISO 9869-1.
7.5 Measurement of environmental temperature
The environmental temperature is measured with the ET sensor on both the inside and outside of
the building. The ET sensor on the inside of the building is mounted near the centre (but not attached
directly to the surface of the region) of the region to be measured. Measure the surface temperature
of the indoor ET sensor, first using a thermocouple, and then using an infrared camera. When the
resultant temperatures are different, adjust the emissivity to set the surface temperature measured
by the infrared camera to that measured by the thermocouple. Use the environmental temperature
measured by the infrared camera for calculating the total heat transfer coefficient and the heat flow
rate, and use the temperature measured by the thermocouple for calculating the difference between
the indoor and outdoor environmental temperatures.
The use of the ET sensor is assumed that the air temperature distribution close to the testing building
element is not significant or almost uniform and there is no distinct imbalance of radiative temperature.
If there is a large air temperature gradient or imbalance of the inner surface temperature distribution,
a number of ET sensors may be arranged including the centre. The variation of the measured values
from the ET sensors might have some relationship with the measured internal surface temperature of
corresponding position and might give the same interpretation of the measured U-value of the testing
building element.
Place the outdoor ET sensor, as well as the indoor sensor, around the centre of the section to be measured.
Use a surface temperature of the ET sensor measured by the thermocouple as the environmental
temperature.
7.6 Surface temperature distribution of building elements
The thermal image of the surface temperature (distributed temperature) of the region to be measured
is measured with an infrared camera. Place the infrared camera in front of the section to be measured.
Adjust the position of the infrared camera to be able to measure the surface temperature of the section
as wide as possible. When the measurement covering the whole section is inevitably impossible, divide
the section into subsections, measure all, observe the surface temperature distribution, and select a
subsection representing the whole section. Since surface temperature cannot be measured properly,
avoid selecting openings such as a sash window and the neighbourhood of local heat sources.
The surface temperature of a typical subsection shall be measured using thermocouples or other
thermometers which enable measuring surface temperature with the same or more precise accuracy
than thermocouples as well as an infrared camera. The measured values shall be used for emissivity
correction for an infrared camera in order for the infrared camera to indicate the identical temperature
at the place where thermocouple measurement is done.
7.7 Measurement time and measurement interval
The measurement time period is at night when there is no sunshine (from one hour after sunset to
sunrise). When measuring a frame structure dwelling with a relatively small heat capacity [a heat
capacity per unit area of about 30 kJ/(m K) or less], select three to six hours between 0 am and 6 am as
a measurement time period.
The standard measurement intervals shall be 30 min or less. The periodically measured data both with
an infrared camera and thermocouples should be synchronically recorded.
7.8 Measurement terms
The following parameters should be measured by the infrared camera:
a) Surface temperature of the section to be measured;
b) Surface temperature of the heat transfer coefficient sensor;
c) Surface temperature of the indoor ET sensor (indoor environmental temperature).
The following parameters should be measured by the thermocouple:
a) Surface temperature of the heat transfer coefficient sensor;
8 © ISO 2018 – All rights reserved

b) Surface temperature of the indoor ET sensor (indoor environmental temperature);
c) Surface temperature of the outdoor ET sensor (outdoor environmental temperature);
d) Typical surface temperature of the section to be measured;
e) If necessary, indoor surface temperatures of sections other than the one to be measured;
f) As a reference, indoor and outdoor air temperatures.
Measure the heat flow rate using a heat transfer coefficient sensor.
Use both an infrared camera and a thermocouple when measuring the surface temperature of the
indoor ET sensor and that of the heat transfer coefficient sensor.
7.9 Measurement period
The recommended time period for measuring should be for three consecutive days. Finish the
measurement after making sure that the results of the three-day measurement of all tests fall within a
range of ±10 %. The measurement result is calculated by the procedure in Clause 8. If they do not all fall
within the range, continue the measurement until the results of consecutive three-day measurement of
all fall within a range of ±10 %.
In the cases where consecutive measurement is impossible due to time limitation, a minimum of a one-
day measurement is acceptable. In such cases, however, pay attention to weather, room temperature
variations, and other conditions before starting the measurement, and try to realize a quasi-steady
state condition as soon as possible within the measurement period. These efforts would be useful for
studying factors affecting measurement accuracy (uncertainty).
NOTE As the quasi-steady-state condition, it is preferable that the U-value calculated every hour using
Formula (6) fall within a range of ±10 %.
8 Calculations
8.1 Heat transfer area
Set a pre-measured subsection of the section to be measured as a heat transfer area and mark its four
corners with a piece of adhesive tape so that the area fits into the thermography measured by the
infrared camera.
8.2 Calculation of heat flow rate
Using the thermography showing the surface temperature (distribution) to apply area-weighting to the
heat transfer area of the section, calculate the average surface temperature in the area. Obtain the heat
flow rate passing through the section from the calculated average surface temperature, the measured
total heat transfer coefficient, and the measured environmental temperature.
Perform image processing on the thermography of the section to be measured in 0,5 °C intervals or less,
obtain the ratio, r of the area with the temperature concerned, θ , to the area to be measured, A, and
j sj
use area-weighting to calculate the average temperature of the section from Formula (4):
θθ=⋅r (4)
sj∑ sj
Using the obtained average temperature, calculate the heat flow rate, Q, passing through the section
from Formula (5):
Qh=−()θθ A (5)
ni s
In addition, when it is considered that the indoor of a room is a natural convection state, the value of
Table 1 may be used for the value of the total heat transfer coefficient, h. If the values of Table 1 were
used, they shall be described in the report.
Table 1 — Total heat transfer coefficient without forced convection
Dimensions in W/(m K)
Surface Direction of heat flow
Upwards Horizontal Downwards
Internal 10 7,7 5,9
NOTE  The radiative heat transfer coefficient, h , is not depended in the direction of heat flow, but is set to
r
5,1 W/(m K) as fixed. This value is calculated for emissivity of the surface to 0,9, and evaluated the mean
temperature of an internal surface as 20 °C. The value of h refer to ISO 6946.
8.3 Calculation of thermal transmittance
The total heat transfer coefficient is determined from Formula (6) after calculating the average values
for irradiance and environmental temperature. The measurement results are rounded to 2 significant
figures. Calculate the average of the heat flow rates and that of the environmental temperatures
measured daily in a night-time measurement period. Using the results, obtain the thermal transmittance
of the section from Formula (6). Round the measurement results to 2 significant figures. Then calculate
the average of the thermal transmittance values consecutively measured for three days, and use it as
the thermal transmittance of the section concerned. However, the actual duration of test shall be for
circumstances. The total thermal resistance shall be calculated using Formula (7):
Q
U = (6)
θθ− ⋅A
()
ni ne
RU=1/ (7)
T
9 Measurement accuracy
The overall uncertainty of this test depends on many factors. It is desirable to conduct an analysis of
uncertainty for the U-value obtained in accordance with this document and the analysis should be
conducted with reference to Annex D and Annex E.
10 Test reports
The results of the experiment should include the following items.
a) Required details for measurement objectives:
— Location of the building where the element is measured;
— Position of the section to be measured in the building, and azimuth orientation in particular;
10 © ISO 2018 – All rights reserved

— Type of the building element (exterior wall, ceiling, floor, etc.);
— Structure, material construction, and thickness of the building element;
b) Required details for measurement conditions:
— Types, specifications, and installation of measuring instruments;
— Measurement items, measurement points;
— Measurement intervals, number of measurement;
— Measurement start date and time, measurement finish date and time;
— If In the case of measurement conditions that are affected by infiltration, liquid water, moisture,
air leakage and climatic conditions, this situation should be described in the report;
c) Measurement data:
— Graphs of measured temperatures, heat flow rates, etc.;
— Thermography;
— Inside and outside average environmental temperatures, average total heat transfer coefficient,
average heat flow rate in the measurement time period;
d) Measurement results:
— Thermal transmittance, thermal resistance;
e) Measurement organization.
Annex A
(informative)
Measurement principle
A.1 Background
Under steady state heat flow conditions, the difference between the indoor surface temperature of
a building element and the corresponding indoor environmental temperature reflects the thermal
transmittance of the building element. A large difference between the indoor and outdoor environmental
temperatures means the internal surface thermal resistance is high and the thermal resistance of the
building element is lower. Conversely, a small temperature difference means the thermal resistance
of the building element is much higher than the internal surface thermal resistance. Strictly defined,
the indoor environmental temperature cannot be measured. However, the inner surface temperature
of an adiabatic plane material placed close to but not in contact with a building element provides a
good representation of the indoor environmental temperature, since its surface temperature reaches
equilibrium with the convective heat transfer from the surrounding air and the radiation heat transfer
from the indoor building element. In this document, the surface temperature of the adiabatic plane
material is assumed to represent the indoor environmental temperature.
It is well known that the reciprocal of internal surface thermal resistance, the total heat transfer
coefficient (including both convective and radiative heat transfer) of the internal surface, does not vary
significantly and shows most of the same common values as other buildings. Therefore, the heat flow
rate through a building element can be evaluated by the difference between the temperatures of the
indoor building element surface and the indoor environment and the total heat transfer coefficient. Since
the internal surface thermal resistance with convection depends on the nature of the thermal boundary
layer on the internal surface and is usually assumed to be thin, and the density of the convective heat
transfer rate is assumed to reach equilibrium quickly, and since the internal surface resistance caused
by radiative heat transfer is very rapid and reaches equilibrium instantly, the product of the temperature
difference between the internal surface temperature and the indoor environmental temperature and
the total heat transfer coefficient can express the density of the heat transfer flow through a building
element immediately and is substituted for measurement with a heat flow meter (HFM).
An infrared (IR) camera can easily observe the internal surface temperature of the entire area of one
building element and is an effective technique for identifying thermal weak points and heat bridges.
It can also give the plane-averaged surface temperature of building elements. Thus, the IR camera is
useful for identifying thermal performance defects of building elements. A method which measures
the thermal transmittance (U-value) of building elements quantitatively is also useful, even though the
accuracy of the method may be limited.
A.2 Measurement principle
Formula (A.1) expresses the heat transfer at the indoor surface of a building element exposed to the
outdoor air (hereafter called the wall to be measured), considering both convection and radiation.
12 © ISO 2018 – All rights reserved

qh=−()θθ +−h ()θθ (A.1)
ca sr rs
where
q is the heat transfer from inside (W/m );
h is the convective heat transfer coefficient (W/(m K));
c
h is the radiative heat transfer coefficient (W/(m K));
r
θ is the indoor air temperature (°C);
a
θ is the surface temperature of wall (°C);
s
θ is the inside average surface radiative temperature excluding wall surfaces (°C).
r
Formula (A.1) is modified as
hh⋅+θθ⋅
q
ca rr
= −θ (A.2)
s
hh+ hh+
() ()
cr cr
On the assumption of Formula (A.1):
θθ=⋅hh+⋅θ / hh+ , hh=+h , (A.3)
() ()
nc ar rc r cr
Formula (A.2) is expressed as Formula (A.4).
qh=−θθ (A.4)
()
ns
where
h is the total heat transfer coefficient (W/(m K));
θ is the environmental temperature (°C).
n
The value of q can be obtained by measuring h, θ and θ . θ is measured with an IR camera, and h is
n s s
measured with a heat transfer coefficient sensor placed near the wall. The environmental temperature
θ , a conceptual quantity, is defined here as the temperature measured by an environmental
n
temperature (ET) sensor.
The temperature distribution on an actual wall surface is non-uniform and varies from area to area.
The area-weighted average surface temperature can be obtained by calculating the areas of parts of the
wall surface with equal temperatures.
Using the measured outdoor environmental temperature and assuming that a quasi-stationary state
exists, Formula (A.5) gives the thermal transmittance of the wall to be measured.
 
UQ=−/ ()θθ ⋅A (A.5)
ni ne
 
where
U is the thermal transmittance (W/(m K));
Q is the heat transfer from entire wall (W);
θ is the indoor environmental temperature (°C);
ni
...