Thermal insulation -- Building elements -- In-situ measurement of thermal resistance and thermal transmittance

ISO 9869-1:2014 describes the heat flow meter method for the 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 properties which can be measured are: a) the thermal resistance, R, and thermal conductance, Λ, from surface to surface; b) the total thermal resistance, RT, and transmittance from environment to environment, U, if the environmental temperatures of both environments are well defined. The heat flow meter measurement method is also suitable for components consisting of quasi homogeneous layers perpendicular to the heat flow, provided that the dimensions of any inhomogeneity in close proximity to the heat flow meter (HFM) is much smaller than its lateral dimensions and are not thermal bridges which can be detected by infrared thermography. ISO 9869-1:2014 describes the apparatus to be used, the calibration procedure for the apparatus, the installation and the measurement procedures, the analysis of the data, including the correction of systematic errors and the reporting format.

Isolation thermique -- Éléments de construction -- Mesurage in situ de la résistance thermique et du coefficient de transmission thermique

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Published
Publication Date
28-Jul-2014
Current Stage
6060 - International Standard published
Start Date
04-Jun-2014
Completion Date
29-Jul-2014
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INTERNATIONAL ISO
STANDARD 9869-1
First edition
2014-08-01
Thermal insulation — Building
elements — In-situ measurement
of thermal resistance and thermal
transmittance —
Part 1:
Heat flow meter method
Isolation thermique — Éléments de construction — Mesurage in
situ de la résistance thermique et du coefficient de transmission
thermique —
Partie 1: Méthode du fluxmètre
Reference number
ISO 9869-1:2014(E)
ISO 2014
---------------------- Page: 1 ----------------------
ISO 9869-1:2014(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2014

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

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Published in Switzerland
ii © ISO 2014 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 9869-1:2014(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions, symbols and units ........................................................................................................................................... 2

3.1 Terms and definitions ....................................................................................................................................................................... 2

3.2 Symbols and units ................................................................................................................................................................................ 2

4 Apparatus ..................................................................................................................................................................................................................... 4

4.1 Heat flow meter (HFM) .................................................................................................................................................................... 4

4.2 Temperature sensors ......................................................................................................................................................................... 4

5 Calibration procedure ..................................................................................................................................................................................... 5

5.1 Calibration of the HFM ..................................................................................................................................................................... 5

5.2 Temperature sensors ......................................................................................................................................................................... 6

5.3 Measuring equipment ....................................................................................................................................................................... 7

6 Measurements ......................................................................................................................................................................................................... 7

6.1 Installation of the apparatus ....................................................................................................................................................... 7

6.2 Data acquisition ..................................................................................................................................................................................... 8

7 Analysis of the data ............................................................................................................................................................................................ 8

7.1 Average method ..................................................................................................................................................................................... 8

7.2 Storage effects .......................................................................................................................................................................................10

7.3 Comparison of calculated and measured values .....................................................................................................12

8 Corrections for the thermal resistance and the finite dimension of the HFM ...................................12

9 Accuracy .....................................................................................................................................................................................................................12

10 Test report ................................................................................................................................................................................................................13

Annex A (normative) Heat transfer at surfaces and U-value measurement .............................................................15

Annex B (normative) Dynamic analysis method ...................................................................................................................................18

Annex C (normative) Examination of the structure of the element ..................................................................................23

Annex D (informative) Perturbations caused by the heat flow meter ............................................................................25

Annex E (informative) Checking the accuracy of the measurement system of heat flow rate ...............31

Annex F (informative) Heat storage effects ...............................................................................................................................................34

Bibliography .............................................................................................................................................................................................................................36

© ISO 2014 – All rights reserved iii
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ISO 9869-1:2014(E)
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 meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers

to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 163, Thermal performance and energy use in the

built environment, Subcommittee SC 1, Test and measurement methods.

This first edition cancels and replaces ISO 9869:1994, which has been technically revised.

Annexes A, B and C form an integral part of this part of ISO 9869. Annexes D, E and F are for information

only.
iv © ISO 2014 – All rights reserved
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ISO 9869-1:2014(E)
Introduction

The thermal transmittance of a building element (U-value) is defined in ISO 7345 as the “Heat flow rate

in the steady state divided by area and by the temperature difference between the surroundings on each

side of a system”.

In principle, the U-value can be obtained by measuring the heat flow rate through an element with a heat

flow meter or a calorimeter, together with the temperatures on both sides of the element under steady-

state conditions.

However, since steady-state conditions are never encountered on a site in practice, such a simple

measurement is not possible. But there are several ways of overcoming this difficulty:

a) Imposing steady-state conditions by the use of a hot and a cold box. This method is commonly used

in the laboratory (ISO 8990) but is cumbersome in the field;

b) Assuming that the mean values of the heat flow rate and temperatures over a sufficiently long period

of time give a good estimate of the steady-state. This method is valid if:

1) the thermal properties of the materials and the heat transfer coefficients are constant over the

range of temperature fluctuations occurring during the test;

2) the change of amount of heat stored in the element is negligible when compared to the amount

of heat going through the element. This method is widely used but may lead to long periods of

measurement and may give erroneous results in certain cases.

c) Using a dynamic theory to take into account the fluctuations of the heat flow rate and temperatures

in the analysis of the recorded data.

NOTE The temperatures of the surroundings, used in the definition of the U-value, are not precisely defined

in ISO 7345. Their exact definition depends on the subsequent use of the U-value and may be different in different

countries (see Annex A).
© ISO 2014 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 9869-1:2014(E)
Thermal insulation — Building elements — In-situ
measurement of thermal resistance and thermal
transmittance —
Part 1:
Heat flow meter method
1 Scope

This part of ISO 9869 describes the heat flow meter method for the 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 properties which can be measured are:

a) the thermal resistance, R, and thermal conductance, Λ, from surface to surface;

b) the total thermal resistance, R , and transmittance from environment to environment, U, if the

environmental temperatures of both environments are well defined.

The heat flow meter measurement method is also suitable for components consisting of quasi

homogeneous layers perpendicular to the heat flow, provided that the dimensions of any inhomogeneity

in close proximity to the heat flow meter (HFM) is much smaller than its lateral dimensions and are not

thermal bridges which can be detected by infrared thermography (see 6.1.1).

This part of ISO 9869 describes the apparatus to be used, the calibration procedure for the apparatus,

the installation and the measurement procedures, the analysis of the data, including the correction of

systematic errors and the reporting format.

NOTE 1 It is not intended as a high precision method replacing the laboratory instruments such as hot boxes

that are specified in ISO 8990:1994.

NOTE 2 For other components, an average thermal transmittance may be obtained using a calorimeter or by

averaging the results of several heat flow meter measurements.

NOTE 3 In building with large heat capacities, the average thermal transmittance of a component can be

obtained by measurement over an extended period, or the apparent transmittance of the part can be estimated

by a dynamic analysis of its thermal absorption response (see Annex B).
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 6781:1983, Thermal insulation — Qualitative detection of thermal irregularities in building envelopes —

Infrared method

ISO 6946:2007, Building components and building elements — Thermal resistance and thermal

transmittance — Calculation method
ISO 7345:1987, Thermal insulation — Physical quantities and definitions
© ISO 2014 – All rights reserved 1
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ISO 9869-1:2014(E)

ISO 8301:1991, Thermal insulation — Determination of steady-state thermal resistance and related

properties — Heat flow meter apparatus

ISO 8302:1991, Thermal insulation — Determination of steady-state thermal resistance and related

properties — Guarded hot plate apparatus

ISO 8990:1994, Thermal insulation — Determination of steady-state thermal transmission properties —

Calibrated and guarded hot box
3 Terms, definitions, symbols and units
3.1 Terms and definitions

For the purpose of this document, the terms and definitions given in ISO 7345:1987 apply.

3.2 Symbols and units
Symbol Quantity Unit
thermal resistance m ·K/W
R
total thermal resistance m ·K/W
R
internal surface thermal resistance m ·K/W
R
external surface thermal resistance m ·K/W
R
thermal conductance W/(m ·K)
Λ
thermal transmittance W/(m ·K)
U
heat flow rate W
Φ
area m
A
density of heat flow rate =Φ/A W/m
q
interior environmental (ambient) temperature °C or K
T
2 © ISO 2014 – All rights reserved
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ISO 9869-1:2014(E)
Symbol Quantity Unit
exterior environmental (ambient) temperature °C or K
T
interior surface temperature of the building ele-
°C or K
T
ment
exterior surface temperature °C or K
T
density of a material kg/m
ρ
thickness of a layer m
d
specific heat capacity J/(kg·K)
c
thermal capacity of a layer: C=ρcd J/(m ·K))
C
correction factors calculated with Formula (8) to
[J/(m ·K)]
F , F
i e
take into account the storage effects
operational error (of an installed HFM) which is
the relative error between the measured and the -
E
actual heat flow

NOTE The environmental (ambient) temperatures shall correspond with those used in the definition adopted

for the U-value (see Annex A).

In the steady-state, the thermal properties of the elements have the following definitions:

R is the thermal resistance of an element, surface to surface and is given by
TT− 1
si se
R= = (1)
q Λ
where Λ is the thermal conductance of the building element, surface to surface.

U is the thermal transmittance of the element, environment to environment and is given by

q 1
U = = (2)
TT− R
ie T
where R is the total thermal resistance which is given by
RR=+ RR+ (3)
Tsise

where R and R are the internal and external surface thermal resistances, respectively.

si se

R and R have units of square metres kelvin per watt (m ·K/W); U and Λ have units of watts per square

metre kelvin [W/(m ·K)].
© ISO 2014 – All rights reserved 3
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ISO 9869-1:2014(E)
4 Apparatus
4.1 Heat flow meter (HFM)

The HFM is a transducer giving an electrical signal which is a direct function of the heat flow transmitted

through it.

Most HFMs are thin, thermally resistive plates with temperature sensors arranged in such a way that the

electrical signal given by the sensors is directly related to the heat flow through the plate (see Figure 1).

The essential properties of an HFM are that it should have a low thermal resistance in order to minimize

the perturbation caused by the HFM, and a high enough sensitivity to give a sufficiently large signal for

the lowest heat flow rates measured. Recent HFMs are very thin, with low thermal resistance, and highly

sensitive. If the thermal resistance of the HFM is low enough, the effects of perturbation of the surface

heat flow by positioning the HFM is negligible. The heat flow rate is influenced by building elements

and the difference between indoor and outdoor temperature. Therefore, HFM with an appropriate

sensitivity shall be selected in consideration of these influences (see Annex E).

NOTE More detailed information on the structure and calibration of HFMs can be found in ISO 8301:1991.

4.2 Temperature sensors

Temperature sensors are transducers giving an electrical signal which is a monotonic function of its

temperature.

The effects of the heat flow going through the sensor and on other physical quantities, such as stresses,

electromagnetic radiation on the signal have to be taken into account (see Clause 5).

Suitable surface temperature sensors (for R- or Λ-value measurements) are thin thermocouples and flat

resistance thermometers. It is possible, for the conductance measurements, for one or several sensors

to be incorporated within one side of the HFM, the side which will be in contact with the surface of the

element being measured.

Environmental (ambient) temperature sensors (for U-value measurements) shall be chosen according

to the temperature to be measured. For example, if the U-value is defined by the ratio of density of heat

flow rate to the air temperature difference, air temperature sensors are to be used. These sensors are

shielded against solar and thermal radiation and are ventilated. Other sensors may measure the so-

called sol-air temperature, the comfort temperature etc. (see Annex A).
4 © ISO 2014 – All rights reserved
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ISO 9869-1:2014(E)
Dimensions in millimetres
Key
1 base material 5 upper surface
2 metal A 6 cross-section
3 metal B 7 under surface
4 coating
Figure 1 — A typical heat flow meter showing the various parts
(the vertical scale is enlarged)
5 Calibration procedure
5.1 Calibration of the HFM

The HFM calibration factors (e.g. the density of heat flow rate for a signal equal to one unit) may change

with the temperature, the thermal conductivity of the material on which the HFM is installed, and the heat

flow itself. Therefore, the calibration factor of a new type of heat flow meter shall be evaluated on various

materials through an absolute test method such as the guarded hot plate apparatus (ISO 8302:1991) or a

heat flow meter apparatus (ISO 8301) on various materials, at various temperatures, and heat flow rates.

The HFM is placed, with its facings and a guard ring of similar average resistance and same thickness, in

the guarded hot plate apparatus, the side adjacent to the element being measured on a material of known

thermal conductivity and the other side, which will be in the air, against an insulating layer [thermal

conductivity less than 0,04 W/(m·K)]. The HFM calibration with the hot box method (ISO 8990:1994)

shall be suited since the calibration condition of the method is closer to the condition of the practical

measurement.
© ISO 2014 – All rights reserved 5
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ISO 9869-1:2014(E)

The calibration procedure shall be such that the calibration factor is known with an accuracy of ± 2 % in

the conditions of use. The heat flow rates as well as the temperatures and the thermal conductivities of

the materials shall cover the range of values usually encountered in practice.
5.1.1 Calibration of a new type of HFM

A set of calibration curves or an equation shall be prepared (calibration factor versus mean temperature,

thermal conductivity of the underlying material, and eventually the density of heat flow rate) for any

new type of heat flow meter or any modified HFM (e.g. new facing or new incorporated guard ring).

2 2

The calibration shall be done at three different densities of heat flow rate (e.g. 3 W/m , 10 W/m and

20 W/m ) in order to check the linearity of the response of the HFM versus q. If the relationship is

not linear, more densities of heat flow rate shall be tested and the precise function shall be taken into

account during the measurements.

The calibration shall be done at a minimum of two temperatures (minimum and maximum limits). If there

is a significant difference between the two results, a third point shall be measured at the average of the

two temperatures to test the linearity of the relationship of the calibration factor to the temperature. If

the relationship is not linear, more temperatures shall be used in order to obtain the dependence of the

calibration factor on the temperature.

The complete calibration shall be done with the HFM placed on at least two materials (low and high

thermal conductivity). If any dependence of the calibration factor to this parameter is found, more

materials shall be used in order to get the complete relationship between the thermal conductivity of

the material and the calibration factor.

A partial calibration may be done if the HFM is used only for a specific application. In this case, it may

be calibrated only on the material on which the HFM will be installed and/or for the temperatures used.

The HFM shall be tested for the following characteristics:

a) zero offset: if there is a nonzero output for zero heat flow (HFM placed in a thermally homogeneous

medium), this can be due to a bad electrical connection, which shall be checked;

b) effect of stresses on the calibration factor. This effect shall be negligible in the range of perpendicular

and parallel stresses involved in the measurements;

c) effect of electromagnetic radiation (50 Hz to 60 Hz, radio waves). This effect shall be negligible in

the range of electromagnetic fields encountered in practice.
5.1.2 Calibration of a known type of HFM

For an HFM whose effects mentioned above are well known, the calibration factor shall be measured for

one heat flow, at a temperature close to its temperature in use and on a typical building material.

Every two years, or more frequently if required, the calibration factor shall be verified by a measurement

at one temperature on one material. A drift of the calibration factor can be caused by material ageing or

delamination. If the variation of the calibration factor is more than 2 %, a complete calibration procedure

shall be followed.

In all cases, a correction shall be applied to the measurements where a change in the calibration factor

of greater than ± 2 % occurs over the range of operation.
5.2 Temperature sensors

The calibration procedure shall be such that the temperature difference between a pair of sensors is

determined with an accuracy better than ± 2 % and that the temperature can be measured with an

accuracy better than 0,5 K. If the temperature difference is obtained by subtracting two temperatures,

the sensors shall be calibrated to an accuracy of ± 0,1 K.
6 © ISO 2014 – All rights reserved
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ISO 9869-1:2014(E)

The surface and air temperature sensors are calibrated for several temperatures in the relevant range

(generally −10 °C to 50 °C) in a well-stirred medium (e.g. water or air), in a well-insulated container, in

comparison with a reference thermometer having an accuracy better than 0,1 K. Sensors manufactured

to this accuracy may be used without calibration.

Special procedures shall be used for the sensors measuring the environment (ambient) temperatures,

according to the temperature to be measured.

The effects of stresses and of electromagnetic radiation (solar and thermal radiation, 50 Hz to 60 Hz,

radio waves) at reasonable levels have to be examined and eliminated if the changes are greater than

the accuracy mentioned above.
5.3 Measuring equipment

Where direct readout equipment is provided, adequate provision shall be made for calibration of this

equipment. Calibrated voltage sources and resistances can be used in place of the HFM and temperature

sensors.
6 Measurements
6.1 Installation of the apparatus
6.1.1 Location of the measured area

The sensors (HFMs and thermometers) shall be mounted according to the purpose of the test. The

appropriate location(s) may be investigated by thermography (in accordance with ISO 6781:1983).

Sensors shall be mounted in such a way so as to ensure a result which is representative of the whole

element.

NOTE It can be appropriate to install several HFMs so as to obtain a representative average.

HFMs shall not be installed in the vicinity of thermal bridges, cracks or similar sources of error. Sensors

shall not be under the direct influence of either a heating or a cooling device or under the draught of a

fan.

The outer surface of the element should be protected from rain, snow and direct solar radiation. Artificial

screening may be used for that purpose.
6.1.2 Installation of the HFM

The dimensions of the HFM are chosen according to the structure of the element under test. For

homogeneous elements, any reasonable dimensions can be used, but some corrections may be necessary

(see Clause 8).

The HFM (with its surface temperature sensor if any) shall be mounted directly on the face of the element

adjacent to the more stable temperature. The HFM shall be in direct thermal contact with the surface of

the element over the whole area of the sensor. A thin layer of thermal contact paste can be used for this

purpose.

A guard ring, made of a material which has similar thermal properties as the HFM and of the same

thickness, may be mounted around the HFM.
6.1.3 Temperature sensors

If the thermal resistance (or the conductance) is to be measured, surface temperature sensors shall be

used. If not incorporated in the HFM, the internal surface temperature sensor shall be mounted on the

internal surface either under or in the vicinity of the HFM. The external surface temperature sensor

shall be mounted on the external surface opposite the HFM.
© ISO 2014 – All rights reserved 7
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ISO 9869-1:2014(E)

Both surface temperature sensors shall be mounted so as to achieve good thermal contact between the

surface and both the sensor and 0,1 m of lead wires.

NOTE For accurate results, it is recommended that the HFM and surface temperature sensors have the

same colour and emissivity as their respective substrates. This is particularly important for sensors exposed to

sunlight.

To measure the U-value or the total resistance, environmental (ambient) temperature sensors shall

be used. These sensors shall measure the temperature used in the definition of the U-value. They are

chosen and installed accordingly at both sides of the element being measured (see Annex A).

The duration of the test can be greatly reduced if the temperatures on both sides of the element, but

particularly on the side where the HFM is installed are stable before and during the test.

6.2 Data acquisition

The electrical data from the HFM and the temperature sensors shall be recorded continuously or at

fixed intervals over a period of complete days. The maximum time period between two records and the

minimum test duration depends on
— the nature of the element (heavy, light, inside or outside insulation);

— indoor and outdoor temperatures (average and fluctuations, before and during measurement);

— the method used for analysis.

The minimum test duration is 72 h (3 d) if the temperature is stable around the HFM. Otherwise, this

duration may be more than 7 d. However, the actual duration of test shall be determined by applying

criteria to values obtained during the course of the test. These values shall be obtained without

interrupting the data acquisition process.

It is useful to record the data so that it can be used for computer analysis. It is recommended that

recordings are made at fixed time intervals which are the average values of several measurements

sampled at shorter intervals.

The recording interval depends on the method used for analysis (see Clause 7). It is typically 0,5 h to 1 h

for the average method and may be less for the dynamic method.

The sampling interval shall be shorter than half the smallest time constant of the sensors.

...

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