Bsi bs en 12664 2001 (2002)

NORME EUROPÉENNEICS 91.100.01; 91.120.10 English version Thermal performance of building materials and products — Determination of thermal resistance by means of guarded hot plate and he

Incorporating Corrigendum No 1

means of guarded hot

plate and heat flow

meter methods — Dry

and moist products of

medium and low

thermal resistance

The European Standard EN 12664:2001 has the status of a

British Standard

ICS 91.100.01; 91.120.10

This British Standard, having

been prepared under the

direction of the Engineering

Sector Committee, was

published under the authority

of the Standards Committee

and comes into effect on

15 March 2001

© BSI 20 December 2002

ISBN 0 580 36513 1

National foreword

This British Standard is the official English language version of

EN 12664:2001 This British Standard together with BS EN 12667:2001 and

BS EN 12939:2001 supersedes BS 874-2.1:1986 and BS 874-2.2:1988 which are withdrawn.

The UK participation in its preparation was entrusted by Technical Committee RHE/9, Thermal insulating materials, to Subcommittee RHE/9/2, Thermal properties of insulating materials, which has the responsibility to:

A list of organizations represented on this subcommittee can be obtained on request to its secretary.

Cross-references

The British Standards which implement international or European

publications referred to in this document may be found in the BSI Catalogue

under the section entitled “International Standards Correspondence Index”, or

by using the “Search” facility of the BSI Electronic Catalogue or of British

— aid enquirers to understand the text;

— present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;

— monitor related international and European developments and promulgate them in the UK.

Amendments issued since publication

14031 Corrigendum No 1 20 December 2002 Addition of supersession details to national foreword

NORME EUROPÉENNE

ICS 91.100.01; 91.120.10

English version

Thermal performance of building materials and products —

Determination of thermal resistance by means of guarded hot

plate and heat flow meter methods — Dry and moist products of

medium and low thermal resistance

Performance thermique des matériaux et produits pour le

bâtiment — Détermination de la résistance thermique par la

méthode de la plaque chaude gardée et la méthode

fluxmétrique — Produits secs et humides de moyenne et

basse résistance thermique

Wärmetechnisches Verhalten von Baustoffen und Bauprodukten — Bestimmung des Wärmedurchlasswiderstandes nach dem Verfahren mit dem Plattengerät und dem Wärmestrommessplatten-Gerät

— Trockene und feuchte Produkte mit mittlerem und niedrigem Wärmedurchlasswiderstand

This European Standard was approved by CEN on 25 June 2000.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E FÜ R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2001 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members. Ref No EN 12664:2001 E

Contents Page

Foreword 3

Introduction 4

1 Scope 5

2 Normative references 6

3 Definitions, symbols and units 7

4 Principle 9

5 Apparatus 10

6 Test specimens 16

7 Testing procedure 20

8 Calculations 28

9 Test report 32

Annex A (normative) Limitations to the implementation of the measurement principle and on measurable properties 34

Annex B (normative) Limits for equipment performance and test conditions — Guarded hot plate 49

Annex C (normative) Limits for equipment performance and test conditions — Heat flow meter 54

Annex D (normative) Equipment design 59

Annex E (normative) Procedures related to measurements at moisture equilibrium 66

Annex F (informative) Conditioning to a specified moisture content in a specified atmosphere 69

Annex G (informative) Estimation of effects of condensation 71

Bibliography 72

be withdrawn at the latest by December 2001.

This document is one of a series of standards on thermal test methods that support product standardsfor building materials

The annexes A, B, C, D and E are normative The annexes F and G are informative

According to the CEN/CENELEC Internal Regulations, the national standards organizations of thefollowing countries are bound to implement this European Standard: Austria, Belgium, CzechRepublic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom

Steady state heat transfer properties may be measured by a number of standardized test methods:the choice of the most appropriate method depends on specimen characteristics This standardcovers the guarded hot plate and the heat flow meter methods only

For routine testing, the operator of these two methods needs only this standard and the relevantproduct standard, which may impose additional requirements related to specimen preparation ortesting conditions

Detailed requirements for measurements in any testing condition of thermal resistance of anycompatible plane specimen are given:

— for the guarded hot plate method, in ISO 8302:1991 and EN 1946-2:1999;

— for the heat flow meter method, in ISO 8301:1991 and EN 1946-3:1999

This standard provides general information on the apparatus, all mandatory limits for the equipmentdesign and operation, and the specification of testing procedure, for dry and moist specimens, withmedium and low thermal resistance, described in relevant technical specifications (e.g a Europeanproduct standard or a European technical approval) The information given is technically equivalent

to that in ISO 8301:1991 and ISO 8302:1991, for both these methods It is only intended for theroutine testing of specimens (within the limitations of thickness and inhomogeneity, etc given inannex A) using equipment which has been constructed according to 5.1 and which has already beenvalidated according to EN 1946-3:1999 or EN 1946-2:1999

It also includes examples of equipment designs that meet the requirements of 5.1, so that theassessment of the accuracy of an equipment designed accordingly does not need an error analysisbut only the equipment performance check

Although this standard can be used for testing dry specimens of high and medium thermalresistance, i.e on products having a thermal resistance of not less than 0,5 m2·K/W, the simplerprocedures of EN 12667:2001 are recommended for such specimens Measurements on thickproducts of high and medium thermal resistance are covered in EN 12939, see the Bibliography

It applies in principle to any mean test temperature, but the equipment design in annex D isessentially intended to operate between a minimum cooling unit temperature of -100 °C andmaximum heating unit temperature of +100 °C.

NOTE 2 Limits to the mean test temperature are only imposed by the materials used in theapparatus construction and by ancillary equipment

It supplies additional limits for equipment performance and test conditions

It does not supply general equipment design procedures, equipment error analysis, equipmentperformance check or the assessment of equipment accuracy

It supplies example designs of equipment complying with the requirements set down in thisstandard

This standard does not supply general guidance and background information (e.g the heat transferproperty to be reported, product-dependent specimen preparations, suggested materials for vapour-tight envelopes when testing moist specimens, procedures requiring multiple measurements, such asthose to assess the effect of specimen non-homogeneities, those to test specimens whose thicknessexceeds the apparatus capabilities, and those to assess the relevance of the thickness effect) Due tothese limitations, this standard shall only be used in conjunction with the product standard relevant

to the product to be tested

Although intended primarily for building materials, it may also be used for specimens of anymaterial that conforms to the requirements specified

It may be used for specimens made from the core material of hollow masonry units but formedvoids are not permitted in the specimen

This standard does not cover measurements on thick products of high and medium thermalresistance

2 Normative references

This standard incorporates by dated or undated reference, provisions from other publications Thesenormative references are cited at the appropriate places in the text and the publications are listedhereafter For dated references, subsequent amendments to or revisions of any of these publicationsapply to this standard only when incorporated in it by amendment or revision For undatedreferences the latest edition of the publication referred applies (including amendments)

NOTE References to ISO 8301:1991 and ISO 8302:1991 do not cover the complete testmethods, but are limited to such items as equipment design and performance check, notcovered by European Standards or parts of them; references to ISO 8301:1991 orISO 8302:1991 are not needed for routine testing according to this standard

EN 1946-2:1999 Thermal performance of building products and components — Specific criteria

for the assessment of laboratories measuring heat transfer properties — Part 2: Measurements by guarded hot plate method

EN 1946-3:1999 Thermal performance of building products and components — Specific criteria

for the assessment of laboratories measuring heat transfer properties — Part 3: Measurements by heat flow meter method

EN 12667:2001 Thermal performance of building materials and products — Determination of

thermal resistance by means of guarded hot plate and heat flow meter methods

— Products of high and medium thermal resistance

EN ISO 7345 Thermal insulation — Physical quantities and definitions (ISO 7345:1987)

EN ISO 9288 Thermal Insulation — Heat transfer by radiation — Physical quantities and

definitions (ISO 9288:1989)

EN ISO 9346 Thermal insulation — Mass transfer — Physical quantities and definitions

(ISO 9346:1987)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

3 Definitions, symbols and units

3.1 Terms and definitions

For the purposes of this standard, the terms and definitions in EN ISO 7345, EN ISO 9288,

EN ISO 9346 apply Most relevant definitions for the measurement of heat transfer properties onmedium and low thermal resistance products and the definition of hygrothermal transmissivity are

to be found in A.2

3.2 Symbols and units

A metering area measured on a selected isothermal surface m2

Am area of the metering section m2

T1 temperature of the warm surface of the specimen K

T2 temperature of the cold surface of the specimen K

Tm mean test temperature (usually (T1 + T2)/2) K

a moisture factor W·m2/(kg·K)

c specific heat capacity J/(kg·K)

d thickness; average thickness of a specimen m

-eh heat flow meter output voltage mV

erp percent error due to phase changes

-erd percent error due to non-uniform moisture distribution

-f calibration factor of the heat flow meter W/(mV·m2)

fr multiplying factor for measured thermal resistance

-g density of moisture flow rate kg/(m2·s)

he latent enthalpy of evaporation per mass J/kg

Symbol Quantity Unit

q density of heat flow rate W/m2

p deviation of the specimen surface from a true plane mm

vsat humidity by volume at saturation kg/m3

w moisture content mass by volume kg/m3

wm mean moisture content mass by volume kg/m3

DR increments of thermal resistance m2·K/W

DT temperature difference (usually T1 - T2) K

Dw change in moisture content (mass by volume) kg/m3

g conditioning time factor s/m2 (or h/cm2)

dv moisture permeability with regard to humidity by volume m2/s

l thermal conductivity W/(m·K)

lt thermal transmissivity W/(m·K)

l* hygrothermal transmissivity W/(m·K)

l0 thermal conductivity of dry material W/(m·K)

xd moisture differential capacity, dw/dz kg/m3

4 Principle

4.1 Apparatus

Both the guarded hot plate apparatus and the heat flow meter apparatus are intended to establishwithin homogeneous specimens with flat parallel faces, in the form of slabs, a unidirectionalconstant and uniform density of heat flow rate The part of the apparatus where this takes place withacceptable accuracy is around its centre; the apparatus is therefore divided in a central meteringsection in which measurements are taken, and a surrounding guard section

4.2 Measuring the density of heat flow rate

With the establishment of steady state in the metering section, the density of heat flow rate, q, is

determined from measurement of the heat flow rate, F, and the metering area, A, that the heat flow

rate crosses

4.3 Measuring the temperature difference

The temperature difference across the specimens, DT, is measured by temperature sensors fixed at

the surfaces of the apparatus in contact with the specimen and/or those of the specimens themselves,where appropriate

4.4 Deriving the thermal resistance or transfer factor

The thermal resistance, R, is calculated from a knowledge of q, A and DT if the appropriate conditions given in A.3.2 are realized From the additional knowledge of the thickness, d, of the specimen, the transfer factor, T, is computed.

4.5 Computing thermal conductivity, thermal transmissivity or hygrothermal

4.7 Specimen limits

The application of the method is also limited by the shape of the specimen(s) and the degree towhich they are identical in thickness and uniformity of structure (in the case of two specimenapparatus) and whether their surfaces are flat or parallel, see annex A

5 Apparatus

5.1 General

A guarded hot plate apparatus or a heat flow meter apparatus used for measurements according tothis standard shall comply with the limits on equipment performance and test conditions given inannex B or annex C of this standard and shall conform with the requirements concerning theassessment of equipment accuracy given in EN 1946-2:1999 or EN 1946-3:1999: this requires thatthe equipment design, error analysis and performance check be according to section 2 ofISO 8302:1991 or ISO 8301:1991 respectively

Annex D gives designs of guarded hot plate apparatus which conform with these requirements For

a heat flow meter apparatus see the annex D of EN 12667:2001 If the equipment used is designedprecisely in accordance with one of these, an error analysis need not be carried out, even though inall cases a performance check according to EN 1946-2:1999 or EN 1946-3:1999 shall be undertakenfor the initial assessment of the equipment

When it is not explicitly stated otherwise, guarded hot plate apparatus requirements are assumed asapplicable also to heat flow meter apparatus

Apparatus width or diameter shall be compatible with aggregate or pore size, see A.3.2.1

NOTE The preferred overall apparatus width, or diameter, referred to in B.3 is 0,3 m or 0,5 m

a) Two-specimen apparatus

Heating unit Heating unit Heating unit

b) Single-specimen apparatus Key

A Metering section heater G Heating unit surface thermocouples

B Metering section surface plates H Cooling unit surface thermocouples

C Guard section heater I Test specimen

D Guard section surface plates L Guard plate

E Cooling unit M Guard plate insulation

Es Cooling unit surface plate N Guard plate differential thermocouples

5.2 Guarded hot plate apparatus

5.2.1 General

In a guarded hot plate apparatus the heat flow rate is obtained from the measurement of the powerinput to the heating unit in the metering section The general features of the apparatus withspecimens installed are shown in Figure 1

There exist two types of guarded hot plate apparatus, which conform to the basic principle outlined

in clause 4:

a) with two specimens (and a central heating unit);

b) with a single specimen

5.2.2 Two specimen apparatus

In the two specimen apparatus [see Figure 1a)], a central round or square flat plate assembly,consisting of a heater and metal surface plates, called the heating unit, is sandwiched between twonearly identical specimens The heat flow rate is transferred through the specimens to separateround or square isothermal flat assemblies, called the cooling units

5.2.3 Single specimen apparatus

In the single specimen apparatus [see Figure 1b)], the second specimen is replaced by acombination of a piece of insulation and a guard plate A zero temperature-difference is thenestablished across this combination Providing all other applicable requirements of this standard arefulfilled, accurate measurements and reporting according to this method may be accomplished withthis type of apparatus, but particular reference to the modification of the normal hot plate with twospecimens should be made in the test report

5.2.6 Edge insulation and auxiliary guards

Additional edge insulation and/or auxiliary guard sections are required especially when operatingabove or below room temperature, see annex B of EN 1946-2:1999

5.2.7 Cooling units

The cooling units shall have dimensions at least as large as those of the heating unit, including the guardheater(s) They shall consist of metal plates maintained at a constant and uniform temperature

5.2.8 Accuracy and repeatability

Accuracy and repeatability depend both on the equipment and on testing conditions The completeassessment of testing errors in a guarded hot plate apparatus in any specific testing condition shall

be carried out in accordance with EN 1946-2:1999 The following is rough information applicablefor tests correctly executed when the mean temperature of the test is near the room temperature

Equipment constructed and operated in accordance with this standard (see also annex B) is capable ofmeasuring thermal properties of medium and low thermal resistance products accurate to within ±2 %

The repeatability of subsequent measurements made by the equipment on a specimen maintained withinthe apparatus without changes in testing conditions is typically better than ±0,5 %

When measurements are made on the same reference specimen removed and then mounted again, therepeatability of measurements is normally better than ±1 % This larger figure is due to minor changes

in testing conditions, like the pressure of the plates on the specimen (which affects contact resistances),the relative humidity of the air around the specimen (which affects its moisture content), etc

The repeatability of measurements on a moist specimen is a combination of the repeatability of theequipment, which should be better than 1 %, and the repeatability of the testing conditions, in particularmoisture content, see annex F

5.2.9 Accuracy and repeatability when testing low thermal resistance specimens

As stated in 5.2.8, the accuracy of measurements on good quality dry specimens having a thermalresistance equal to or greater than 0,1 m2·K/W should be better than 2 % for guarded hot plateapparatus Specimens having thermal resistances between 0,1 m2·K/W and 0,02 m2·K/W can be testedaccording to ISO 8302:1991 only; the corresponding accuracy is progressively reduced to 5 %, seeA.3.6.2 When testing moist specimens, there may be additional substantial errors, see 7.2.3.4

5.3 Heat flow meter apparatus

“two-specimen symmetrical”, the specimens should be substantially identical Each configuration yieldsequivalent results if used within the limitations stated in this standard

NOTE There are distinct advantages for each method in practice; brief discussion isincluded in annex B of ISO 8301:1991

a) Single-specimen asymmetricalb) Single-specimen symmetricalc) Two-specimen symmetrical

configuration configuration configuration

d) Double apparatus e) Double apparatus

Key

U', U" Cooling and heating units

H, H', H" Heat flow meters

S, S', S" Specimens

Figure 2 — Typical layouts of heat flow meter apparatus configurations

5.3.2 Heat flow meters

The heat flow meter is an assembly that measures the density of heat flow rate through thespecimen(s) by a temperature difference generated by this density of heat flow rate crossing thespecimen(s) and the heat flow meter itself Most commonly it consists of a homogeneous core, asurface temperature difference detector (a multi-junction thermopile) and a surface temperaturedetector(s) The heat flow meter region occupied by the core, where temperature differencedetectors are placed, is called the metering area

A density of heat flow rate q, through the metering area of the device results in an output eh:

q = f eh

The calibration factor f, which correlates eh and q, is not a constant in all cases, but may depend

upon temperature and, to a more limited extent, upon the density of heat flow rate

5.3.3 Calibration principle

This is a secondary or relative method, since the ratio of the thermal resistance of the specimens(s)

to that of a standard specimen(s) is measured From the measurement of the heat flow rate Fs withthe standard specimen(s) and Fu with the unknown specimen(s) to be measured, the assumption of aconstant density of heat flow rate of the metering section and the assumption of the stability of thetemperature difference DT and the mean temperature Tm, gives the ratio between the thermal

resistance Rs of the standard specimen(s) and Ru of the unknown specimen as follows:

Ru/Rs = Fs/Fu

Calibration procedures are given in ISO 8301:1991

5.3.4 Limitations due to the calibration

The calibration factor f, is a function of the mean heat flow meter temperature If a calibration curve

has been established in a temperature range, extrapolation is not allowed

The calibration factor at a given mean heat flow meter temperature may also be a function of thedensity of heat flow rate The apparatus shall only be used for densities of heat flow rate within therange covered by the calibration

5.3.5 Accuracy and repeatability

Accuracy and repeatability depend both on the equipment and on testing conditions The completeassessment of testing errors in a heat flow meter apparatus in any specific testing condition shall becarried out in accordance with EN 1946-3 The following is rough information applicable for testscorrectly executed when the mean temperature of the test is near the room temperature

The repeatability of subsequent measurements made by the equipment on a specimen maintainedwithin the apparatus without changes in testing conditions is typically better than ±0,5 %

When measurements are made on the same reference specimen removed and then mounted againafter large time intervals, the repeatability of measurements is normally better than ±1 % Thislarger figure is due to minor changes in testing conditions, like the pressure of the plates and heatflow meter on the specimen (that affect contact resistances) and the relative humidity of the airaround the specimen (that affects its moisture content), etc

The repeatability of measurements on a moist specimen is a combination of the repeatability of theapparatus, which should be better than 1 %, and the repeatability of the testing conditions, inparticular moisture content, see annex F

The accuracy of the calibration of the heat flow meter apparatus depends on the accuracy of thereference material and is normally within ±2 %

NOTE The accuracy of the calibration is mainly due to the accuracy of the guarded hot platemethod when measuring the properties of reference specimens

When the limits specified in annex C are met, the heat flow meter method is capable of determiningthe heat transfer properties within ±3 % when the mean temperature of the test is near the roomtemperature

5.4 Error analysis and equipment performance check

The error analysis (not needed if equipment design conforms with one of the ones in annex D), theequipment performance check and the consequent assessment of the equipment accuracy in therange of testing conditions given in relevant product specifications shall be made according to 5.1

6 Test specimens

6.1 General

Testing may be split into specimen handling, see below, and actual testing procedure, see clause 7.Some decisions about measurable heat transfer properties, specimen handling and testing conditionsshall be taken when starting testing, see A.5 Directions on these decisions shall only be sought inthis standard and/or in the relevant product standard applicable to the specimen to be tested

6.2 Selection and size

One or two specimens shall be selected (from each sample) according to the type of apparatus(see 5.2.2 or 5.2.3 for guarded hot plate apparatus and 5.3.1 for heat flow meter apparatus) Thespecimen or specimens shall meet the general requirements outlined in A.3 and A.4 When twospecimens are required they shall be as identical as possible with thicknesses differing by less than

2 % The specimen or specimens shall be of such size as to cover the heating unit surfacescompletely (including the guard section), without exceeding the overall linear dimension of theheating unit or heat flow meter by more than 3 % They shall have a thickness according to therelevant product standard and additionally the relationship between the thickness of the testspecimen used and the dimensions of the heating unit shall be restricted so as to limit the sum of theimbalance error (guarded hot plate apparatus only) and edge heat loss errors to 0,5 %, see thicknesslimits of Table A.1 in A.3 For the minimum specimen thickness see A.3.4 and Tables A.1 and A.2

6.3 Specimen preparation and instrumentation

6.3.1 Conformity with product standards

The preparation of the specimens shall be in accordance with the appropriate product standard;unless otherwise specified in product standards, the general criteria in 6.3.2 and 6.3.3 should befulfilled

6.3.2 All specimens except loose-fills

When edge-to-edge joining or joint gluing is necessary, make the joints between machined surfacesperpendicular to the main specimen surfaces and preferably symmetrical with respect to the linepassing through the centre of the specimen and perpendicular to its main surfaces Keep the number

of pieces used to the minimum dictated by the module size of the product, especially in the metering

area Ensure that, within the metering area, the total joint cross-section does not exceed 0,1 % of themetering area Use a cold setting adhesive, such as an epoxy or polyester resin for bonding;adhesives approaching the specimen conductivity are preferred Apply the adhesive to the matingsurfaces avoiding impregnation as far as possible After bonding, either grind flat the faces of eachspecimen using a surface grinder or milling machine, or hand finish the faces by rubbing withabrasive paper fixed to an engineer’s surface plate.

Cure cement and masonry materials from which specimens are to be prepared for 28 days prior totesting and record the date of manufacture Specimens may initially contain a large amount of water

as a consequence of manufacture and preparation Great care shall be taken in selecting testingconditions with reference to moisture content in order to eliminate mass transfer during the test, orestablish conditions for which mass transfer effects are repeatable and well understood, see 7.2.2and 7.2.3

The surface of the test specimens shall be made plane by appropriate means (sandpapering,face-cutting in a lathe, and grinding are often used), so that close contact between the specimensand apparatus or interposed sheets can be effected

For rigid materials, the faces of the specimens shall be made as flat as the apparatus surfaces(see A.3.6.2) and shall be parallel over the total surface area within 2 % of the specimen thickness

The planeness of the surfaces can be checked with, for example, a good quality engineer'sstraightedge (straight to 0,01 mm) held against the surface and viewing at grazing incidence with alight behind the straightedge Departures as small as 25 mm are readily visible Large departures can

be measured using feeler gauges and the straightedge as follows The straightedge should besupported on a gauge block of known thickness, say 1 mm, at each end of the surface to be checked.Positive and negative deviations can be measured using feeler gauges along a straight line Eightstraight lines should be investigated as follows: the four edges of the surface, the two diagonals and

a central cross (two lines parallel to the edges of the surface) When this procedure, applicable toboth apparatus and specimen surfaces, is applied to specimen checking, it should be repeated foreach face of the specimen

Scratches, chips or similar defects over and above the naturally occurring surface irregularities inthe finished surfaces of cellular or aggregate materials are accepted provided that the total of theirsurface areas is an acceptable fraction of the metering area and that their maximum depth is anacceptable fraction of the specimen thickness, so as to keep the added thermal resistance due to thecorresponding air pockets low For the purpose of this standard:

— if (Ad/Am)(Ra/R) < 0,000 5 the effect may be ignored;

— if 0,000 5 £ (Ad/Am)(Ra/R) £ 0,005 the test may be undertaken, but the presence of the defectshall be mentioned in the test report;

where:

Ad is the overall cross-sectional area of the defects;

Am is the area of the metering section;

Ra is the thermal resistance of an air layer of thickness equal to the maximum depth of anydefect;

R is the thermal resistance of the specimen

6.3.2.2 Selection and installation of contact sheets

Imperfect apparatus and/or specimen flatness produces contact thermal resistances, see in A.3.6.2the maximum allowed limit when testing rigid specimens without contact sheets

When the specimens’ thermal resistance is less than 0,3 m2·K/W, or if their flatness does not meetthe requirements of A.3.6.2, thin sheets of an adequately compressible material shall be insertedbetween the specimen surfaces and the plates of the apparatus to establish good thermal contactbetween them The thin sheets shall also insulate electrically the thermocouples which are then to beplaced on the specimen surfaces to determine the temperature difference across the specimen(see 6.3.2.3)

If all other requirements are met (homogeneity, compressibility, etc.), sheets of the highest thermalconductivity material available should be chosen When using contact sheets, the thermal resistance

of the sheets should be the smallest compatible with the elimination of air pockets

NOTE 1 Foamed silicone rubber of density about 600 kg/m3 and thickness about0,5 % to 1 % of the overall apparatus size (typically 2 to 3 mm for medium size apparatus)have been found to meet the requirements satisfactorily

Sufficient clamping pressure, in excess of 10 kPa, is required to produce uniform thermal contactbetween apparatus surfaces, thermocouples, thermal contact sheets and specimens

NOTE 2 These high pressures can damage the heat flow transducer of the heat flow meterapparatus, and thus the guarded hot plate apparatus is preferred for tests on specimens having

a thermal resistance less than 0,3 m2·K/W

The use of contact sheets introduces the errors described in A.3.6.3 When the contact resistance isdeemed to be too high, an alternative solution to the use of contact sheets is to improve the surfacefinish of the specimen and/or that of the plates of the apparatus

NOTE 3 The lowest measurable thermal resistance according to B.5, is 0,02 m2·K/W(e.g 0,04 m of structural concrete), but the overall accuracy of 2 % around room temperaturemay be achieved only when the specimen thermal resistance is equal to or greater than0,1 m2·K/W

6.3.2.3 Thermocouples mounted on the specimen

When contact sheets are used, thermocouples mounted on the specimen surfaces, or cemented inshallow grooves accurately machined to a known depth in the specimen surfaces, shall be used tomeasure the temperature difference through the specimens The number of uniformly distributedthermocouples on each side of the specimen in the area corresponding to the metering section of the

apparatus should be not less than N A , or 2, whichever is greater, where N = 10 m-1 and A is the

area in square metres of one side of the metering section For the error in the temperature differencewhen using contact sheets and thermocouples mounted on the specimen, see A.3.6.3

It is recommended that at least two more thermocouples are added on each side of the specimen inthe area corresponding to the metering section of the apparatus

Thermocouples mounted directly into the surfaces shall either be:

a) flattened fine wire, or

b) thin foil types which may be bought ready-made, or

c) prepared by rolling or pressing the junctions together with about 20 mm of the adjoiningwire of conventional thermocouples

The thermocouples shall be fabricated from a stock of calibrated thermocouple wire, or from wirethat has been certified by the manufacturer to comply with Table B.1 of ISO 8302:1991, or theyshall be individually calibrated

NOTE 1 It is important to establish good contact between the junctions and the specimensurfaces In some circumstances it will be necessary to improve the mounting area locally toachieve this This can be done effectively and with minimal loss of accuracy by smoothing thesurface locally using a machinable, quick-drying filling compound using a thickness of lessthan 0,5 mm

The thermocouples shall be taped in position on these prepared surface areas (approximately 15 mm

to 20 mm in diameter) using narrow strips of adhesive tape about 2 mm to 4 mm wide placed some

5 mm from the junction itself

NOTE 2 Wider strips of tape can be used in the guard area to insulate and protect the wirearound the edges of the apparatus

NOTE 3 The clamping pressure exerted on the thermal contact sheets ensures that thethermocouples are firmly in contact with the specimen surfaces during the test However,when practicable (i.e if the prepared surface is non-absorbent), a smear of thermoconductivecompound loaded with zinc oxide can be introduced between the thermocouple junctions andthe surfaces to further improve thermal contact

6.3.3 Loose-fill materials

When testing loose-fill materials, the thickness of the specimen shall be at least 10 times the meandimension of the beads, grains, flakes, etc of the loose-fill material To prepare the specimen(s) it isrecommended that a representative portion, slightly greater than the amount needed for the test, betaken from the sample and weighed before and after it has been conditioned as in 7.2, whereapplicable From these masses the percentage mass loss is calculated An amount of the conditionedmaterial is weighed out such that it will produce one (two) specimen(s) of the desired density usingthe procedure described in the relevant product standard As the ultimate volume of the specimen isknown, the required mass can be determined The specimens are then quickly mounted in theapparatus or left to reach equilibrium with the standard laboratory atmosphere (23 °C, 50 % relativehumidity), in accordance with the guidelines given in the relevant product standard or in 7.2

7 Testing procedure

7.1 General

A testing procedure is the complete set of operations to determine the desired heat transfer propertyperformed on the specimen prepared as indicated in 6.3 These may be split into the conditioning,described in 7.2, and the remaining operations to run a test with the guarded hot plate or heat flowmeter apparatus, as described in 7.3

7.2 Conditioning

7.2.1 General

There are basically two measurement procedures for masonry materials: on dry and moist specimens.NOTE 1 The theoretical background for measurements on moist or dried materials is given in[1] and [2], see also Bibliography

Conditioning shall be according to relevant product standards

NOTE 2 Drying requires the definition of the conventional dry state, see 7.2.2 Aconventional dry state is produced by heating in a well ventilated oven at 105 °C or asspecified in the relevant product standards The drying process should not alter the chemicaland physical nature of the material If the value of the thermal conductivity is required atdifferent moisture contents, or at the equilibrium moisture content of the material in thelaboratory environment, then condition the specimen without oven drying to constant mass byexposure to the air of a conditioning chamber held at (23 ± 2) °C and appropriate relativehumidity within ±5 %, see 7.2.3.2

7.2.2 Conditioning for measurements on dry materials

Routine measurements should, as far as possible, be carried out on dry materials

Dry the specimen to constant mass in a ventilated oven at 105 °C to 110 °C that takes the air from anenvironment at (23 ± 2) °C and (50 ± 5) % relative humidity Constant mass is considered to have beenestablished when the change in the mass of the test specimen over a 24 h period is random and less thanthe equivalent of 0,1 kg/m3 (or 0,01 % by volume)

After drying, the test specimen shall be enclosed in a vapour-tight envelope The envelope shall besufficiently impermeable to prevent a change in moisture content greater than 0,01 kg/(m3·h), see annex G

NOTE 1 An envelope with a moisture (diffusion) resistance Zv > 105 s/m is sufficient

The mass of the specimen shall be measured before and after the test, to determine the relative masschange according to 8.1.2

A vapour-tight envelope may be omitted if the rate of moisture accumulation in the test specimen duringthe test is lower than 0,01 kg/(m3·h) and no visible condensation occurs on the cold plate

NOTE 2 A vapour-tight envelope can change the contact resistances and special precautions mayhave to be taken to measure surface temperatures correctly

7.2.3 Conditioning for measurements on moist materials

7.2.3.1 General

Measurements on moist materials are necessary to establish the thermal transmissivity of the moistmaterial, l*, at a moisture content in equilibrium with 50 % relative humidity, 23 °C or to establishthe general relationship between l* and the moisture content These measurements should normally,however, not be routine measurements but performed at special occasions to establish the necessaryrelationships for each material, product or building component If routine measurements are planned

on moist materials, testing accuracy and testing times shall be carefully assessed, see 7.2.3.4

7.2.3.2 Conditioning in a specified atmosphere

Condition the test specimens to the required moisture content before the test This standard isrestricted to moisture contents in the hygroscopic range, that is moisture contents in equilibriumwith 98 % relative humidity or lower

NOTE 1 Information on testing at higher moisture contents, is given in [1] in the Bibliography.NOTE 2 Preferred moisture contents are:

1) in equilibrium with 50 % relative humidity (due to the requirements in the product standards);2) in equilibrium with 80 % relative humidity (because, above this level, the estimation of errors,

as given in 7.2.3.4, is no longer valid)

The conditioning procedure to a nearly uniform distribution is carried out in two steps

Step 1 Place the test specimen in an atmosphere 23/xx or in a ventilated oven at 40 °C, 70 °C or

105 °C Periodically remove and weigh the specimen to determine mass changes until:

Dw < Dwl

where:

23/xx signifies a controlled atmosphere with a temperature of (23 ± 2) °C and a relative

humidity of (xx ± 5) %, xx being any relative humidity between 0 % and 98 %;

Dw is the change in moisture content, in kg/m3, during a period of d2 hours, d being the

specimen thickness expressed in centimetres;

Dwl is the appropriate limiting value of moisture content change, in kg/m3

NOTE 3 Annex F gives guidance on the determination of Dwl

In many cases, the moisture content is already in the hygroscopic range when the product isdelivered to the testing laboratory In this case, step 1 may be omitted and only step 2 is needed

Step 2 Place the test specimen in an atmosphere of 23/xx for at least gd2 hours, where g is the

conditioning time factor and d is the specimen thickness expressed in centimetres.

NOTE 4 Annex F gives guidance on the determination of g.

After conditioning, the test specimen shall be enclosed in a vapour-tight envelope The envelope shall

be impermeable enough to prevent a change in moisture content larger than 0,01 kg/m3 per hour.NOTE 5 This criterion is explained in annex G In practice, an envelope with a moisture

(diffusion) resistance Zv > 105 s/m is sufficient

The mass of the specimen shall be measured before and after the test, to determine the relative masschanges according to 8.1.2.

7.2.3.3 Effects of moisture on the determination of the hygrothermal transmissivity

7.2.3.3.1Preliminary considerations

To determine l* correctly, it is necessary either to avoid mass transfer during the test, or to establishconditions for which the effect of mass transfer on the measured result can be estimated

Tests may be carried out according to either 7.2.3.3.2 or 7.2.3.3.3

7.2.3.3.2 Tests when moisture movements are sufficiently small that effects of phase changes during the test can be neglected

NOTE This is the most straightforward option provided that the error given below is acceptable.Errors occur due to phase changes and non-uniform moisture distribution

The error, erp, due to phase changes, expressed in %, is:

erp = 0,25 ´ 106dvj/l*

where:

j is the relative humidity in the material, in %;

dv is the moisture permeability with regard to humidity by volume, in m2/s

Moisture redistribution will cause the thermal resistance to increase during the test The error in

thermal conductivity due to this redistribution (erd) is limited to 0,5 %, provided that the Fourier

number Fo does not exceed 0,25, i.e.

Fo = 4 Dwt/d2 = (4 dv vsat t)/(d2xd) £ 0,25

where:

vsat is the humidity by volume at saturation, in kg/m3;

xd is the moisture differential capacity, in kg/m3

Typical values of dv, l*, xd and vsat for different materials are given in Table 1 and Table 2

The errors due to phase changes and non-uniform moisture distribution have opposite signs and sothe maximum error from the combination of these two effects is consequently:

max(erp, erd)

where:

erp is the error due to phase changes, in %;

erd is the error due to non-uniform moisture distribution, in %

Table 1 — Typical values of dv, l* and x for different materials

Table 2 — Values of vsat for different temperatures

7.2.3.3.3Measurement at moisture equilibrium

If it is not possible to accept the inaccuracies from phase changes and non-uniform moisturedistribution, the measurement may be carried out in moisture equilibrium

There are different options depending on whether it is possible to measure or calculate thetemperature and moisture distribution at equilibrium, see the flow chart of Figure 3

NOTE 1 The mean moisture content in the specimen, wm, is always assumed to be known.There are two preferred paths, marked A and B in the flow chart

Path A The moisture distribution is deemed uniform and l* is determined at the mean

moisture content, wm

NOTE 2 This only gives one point on the curve for the relationship between l* and w.

To achieve a moisture distribution which may be considered uniform, the test shall be carried outwith a temperature difference not exceeding 10 K and a moisture content not exceeding equilibriumwith 80 % relative humidity Provided these requirements are fulfilled, the error due to non-uniformmoisture distribution is less than 2 %

Temperature

0 5 10 15 20

Figure 3 — Flow chart showing how to measure or calculate the temperature and moisture

distribution Path B Moisture distribution calculated or measured and the relationship between l* and

w assumed linear

The moisture distribution may be determined by either

— parallel tests with the same material and the same boundary conditions, see annex E, or

— calculations as described in annex E

l* may be obtained from:

l* = l0 + a w

where the constant a is calculated according to annex E.

7.3.2 Thickness and density

The specimen thickness is either the thickness imposed by positioning the heating and the coolingunit or the thickness of the specimen(s) as measured at the beginning of the test, as stated byrelevant product standards

Specimen(s) thickness can be measured either in the apparatus at the existing test temperature andcompression conditions or outside the apparatus with instrumentation that will reproduce thepressure on the specimen during the test, see the relevant product standard

For thickness measurements in the apparatus, gauging points, or measuring studs mounted onpurpose at the outer four corners of the cooling unit (or the heating and cooling units for a singlespecimen apparatus) or along the axes perpendicular to the units, at their centres, shall be used Thespecimen thickness is determined from the average difference in the distance between the gaugingpoints when the specimen(s) is (are) in place in the apparatus and when it is not in place, and thesame force is used to press the apparatus units towards each other

From the specimen dimensions, the thickness measured as above and the mass of the conditionedspecimen determined as in 7.3.1 the as-tested density can be computed

7.3.3 Temperature difference selection

Select the temperature difference to be in accordance with A.3.8 and the relevant product standard

7.3.4 Ambient conditions

When heat transfer properties are desired for the situation in which the specimen is surrounded byair (or some other gas), adjust the humidity of the atmosphere surrounding the apparatus unitsduring a test to a dew-point temperature at least 5 K below the cooling unit temperature

When enclosing the specimen in a vapour-tight envelope to prevent moisture migration to or fromthe specimen, the testing conditions shall be such that no water condensation will take place on theportion of the envelope in contact with the cold side of the specimen

7.3.5 Heat flow rate measurements

7.3.5.1 Heat flow rate in the guarded hot plate apparatus

Measure the average electrical power supplied to the metering area to within ±0,1 %

Fluctuations or changes in the temperatures of the heating unit surfaces during the test period, due

to random fluctuations or changes in their input power, shall not exceed 0,3 % of the temperaturedifference between the heating and cooling units

Adjust and maintain the power input to the guard section, preferably by automatic control, to obtainthe degree of temperature balance between the metering and guard section that is required to keepthe sum of the imbalance and edge heat loss errors within 0,5 % (see 6.2)

7.3.5.2 Heat flow rate in the heat flow meter apparatus

Observe the mean temperature and the electromotive force output of the heat flow meter, the meantemperature and the temperature drop across the specimen(s) to check when they are stabilized

Ensure that the temperature fluctuations (as a function of time) at the surface of the heat flow meter

do not cause fluctuations in its electrical output greater than 2 % during the test period

Ensure that the density of heat flow rate is in a range such that the accuracy of the calibration factor,

f, and of the electrical instrumentation to read the heat flow meter output are in accordance with

5.3.5 and relevant requirements given in annex C

7.3.6 Cold surface control (for two-specimen guarded hot plate apparatus)

When a two specimen apparatus is used, adjust the cooling units or cold surface heaters so that thetemperature differences through the two specimens do not differ by more than 2 %

7.3.7 Temperature difference detection

Determine the heating and cooling unit temperatures and the centre-to-guard temperature balance(for guarded hot plate apparatus only) by methods having sufficient repeatability and accuracy tomeet all relevant requirements given in annex B for guarded hot plate apparatus, or relevantrequirements given in annex C for heat flow meter apparatus

7.3.8 Settling time and measurement interval

Make sets of observations as in 7.3.5 and 7.3.7 at measurement intervals as recommended in A.3.11until, during a period equal to or larger than four times the time interval Dt defined in A.3.11,

successive sets of observations give thermal resistance values which do not differ by more than 1 %and are not changing monotonically

When an accurate estimate of settling time is not possible or if there is no test experience on similarspecimens in the same equipment at the same testing conditions (e.g when starting routine testing

on a new product), continue these observations until at least 24 hours have elapsed since thebeginning of the steady state conditions so defined

NOTE To check, at a glance, the attainment of steady state conditions, it may be helpful torecord graphically the relevant measured quantities

7.3.9 Final mass and thickness measurements

Upon completion of the observations in 7.3.8, measure the mass of the specimen(s) immediately.Repeat the thickness measurement and report any specimen change in volume

r0 is the density of the dry material as tested;

rc is the density of the material after a more complex conditioning procedure (veryfrequently up to the equilibrium with the standard laboratory atmosphere);

m2 is the mass of the material after drying;

m3 is the mass of the material after a more complex conditioning procedure;

V is the volume occupied by the material after drying or conditioning

m1 is the mass of the material in as-received condition;

m2 and m3 are as defined in 8.1.1

When required by the product standards, or when it is considered useful to evaluate the testconditions correctly, beside Dmc, calculate the following relative mass change Dmd due to theconditioning after the drying:

m4 is the mass of material in the specimen immediately after the test;

m5 is the mass of dried or conditioned material in the specimen immediately before the test

8.2.2 Guarded hot plate apparatus measurements

Compute the thermal resistance R, using the following equation:

A T T

F is the average power supplied to the metering section of the heating unit;

T1 is the average specimen(s) hot side temperature;

T2 is the average specimen(s) cold side temperature;

A is the metering area as defined in 5.2.5 For two specimen apparatus the metering areadefined in 5.2.5 shall be multiplied by two;

d is the average specimen(s) thickness

If the conditions described in A.3.2 and A.4.3 are applicable, compute either the thermaltransmissivity, lt, or the hygrothermal transmissivity, l*, or the thermal conductivity, l, (or thermal

resistivity, r = 1/l), using the following equation:

( 1 2)

*or

or

T T A

d t

ll

l

where F, A, T1, T2 and d are as defined above.

8.2.3 Heat flow meter apparatus measurements

8.2.3.1 Single specimen configuration

8.2.3.1.1Single heat flow meter configuration

Compute the thermal resistance, R, using the following equation:

h

2 1

e f

T T

-where:

f is the calibration factor of the heat flow meter;

eh is the heat flow meter output;

T1 and T2 are as defined in 8.2.2;

or compute the transfer factor, T, using the following equation:

T

2 1

h

T T

d e

f

-=

where T1, T2 and d are as defined in 8.2.2.

If the conditions described in A.3.2 and A.4.3 are applicable, compute either the thermaltransmissivity, lt, or the hygrothermal transmissivity, l*, or the thermal conductivity, l, (or thermal

resistivity, r = 1/l), using the following equation:

2 1

* or

or

T T

d e

f h t

-=ll

l

where f, eh, T1, T2 and d are as defined above.

All the requirements of 8.2.3.1.1 are applicable to this configuration, with f eh replaced by

0,5 (f1eh1 + f2eh2) where the indexes 1 and 2 refer to the first and second heat flow meter respectively

(of which the surface temperatures are respectively T1 and T2)

T T T T

=

2 1

"

2

' 1 '

' h

m m tm

"

"

2or

or *

T T

d T

T

d e

ll

a) Test method used (guarded hot plate or heat flow meter conforming to this standard), type

of apparatus used (with one or two specimens, see 5.2.2, 5.2.3 or 5.3.1) and the identification

of the equipment Method to reduce edge heat losses Ambient temperature of theenvironment surrounding the apparatus during the test Product standard applicable to thetested specimen(s)

b) Name and any other pertinent identification of the material, including a physicaldescription supplied by the manufacturer

c) Description of the specimen and reference to the product standard according to whichsampling and specimen preparation was carried out

d) Thickness of the specimens in metres, specifying if either imposed or measured Reference

to a specific test method used, if imposed by a product standard Criteria from the relevantproduct standard to define the imposed thickness

e) Method and temperatures of conditioning

f) Densities of the conditioned material as tested

g) Relative mass changes during drying and/or conditioning (see 8.1)

h) Relative mass change during the test (see 8.1) Observed thickness (and volume) changesduring the test (see 7.3.9)

i) Average temperature difference across the specimen(s) during the test, see 7.3.7, in K

j) Mean temperature of test, in K or C.

k) Density of heat flow rate through the specimen during test (q = /A for guarded hot plate apparatus or q = f eh for heat flow meter apparatus, see 8.2)

l) Thermal resistance or transfer factor of the specimen(s) Where applicable, the thermalresistivity, thermal conductivity, thermal transmissivity, or hygrothermal transmissivity.m) Date of completion of the test; duration of the full test and of the steady state part of thetest, if such information is required by the relevant product standard

For heat flow meter apparatus only: date of last heat flow meter calibration Type or types ofthe calibration specimens used, their thermal resistance, date of specimen certification, source

of certification, expiration date of calibration, and the certification test number

n) Orientation of the apparatus; vertical, horizontal, or any other orientation In the case ofsingle specimen apparatus, the position of the hot side of the specimen when not vertical: top,bottom or any other position

o) For tests made using water-vapour tight envelopes, information shall be given on thenature and thickness of the envelope

p) A graphical representation of the results in the report shall be given when required by therelevant product standard This shall consist of a plot of each value of the thermal propertiesobtained versus the corresponding mean temperature of the test, plotted as ordinates andabscissae respectively Plots of thermal resistance or transfer factor as a function of specimenthickness shall be given when required by the relevant product standard

q) The report shall contain information on estimated surface thermal resistance or on errorsassociated with the use of contact sheets, see A.3.6

A statement providing the maximum expected error in a measured property as indicated in5.2.8 and 5.2.9 for guarded hot plate apparatus or in 5.3.5 for heat flow meter apparatus shall

be included in the test report

When one or more of the requirements stated in this standard or in EN 1946-2:1999 or

EN 1946-3:1999 are not fulfilled by the specimen(s) (see also r)) on the statement of compliance) it is recommended that a complete estimation of the error or errors in measuredproperty be included in the report

non-Moisture content corrections shall not be included in the test report but handled in a separatereport, e.g on the definition of design values

r) Where circumstances or requirements preclude complete compliance with the procedure ofthe test described in this standard, exceptions allowed by the relevant product standard may bemade, but shall be specifically explained in the report A suggested wording is: “This test

conformed with all requirements of EN 12664:2001, Thermal performance of building

materials and products — Determination of thermal resistance by means of guarded hot plate and heat flow meter methods — Dry and moist products of medium and low thermal resistance, with the exception of (a complete list of the exceptions follows)”.

s) Name of the operator who carried out the test

Annex A

(normative)

Limitations to the implementation of the measurement principle and on

measurable properties

A.1 Considerations on heat transfer and measured properties

When testing medium and low thermal resistance products either homogeneous or with porousstructure or containing porous aggregates, thermal properties of both dry and moist material are ofinterest The thermal conductivity is an intrinsic property of an homogeneous material where heat istransferred by conduction only The actual heat transfer within most building materials can involve

a complex combination of different contributions of:

— conduction both in the solid and in the gas phase;

— mass transfer (in moist materials);

— radiation;

— convection (in some operating conditions);

plus their interactions While these heat and mass transfer phenomena are transitory in nature, some

of them have long-term contributions that must be recognized in the evaluation of thermalperformance For such materials, where heat is transferred not only by conduction, the heat transferproperty, very often improperly called “thermal conductivity”, calculated for a specimen byapplying a defined formula to the measured heat flow rate, temperature difference and dimensions,may be not an intrinsic property of the material itself, as it may depend on the testing conditions.This property should therefore be called “transfer factor” (the transfer factor is often referred toelsewhere as “apparent” or “effective thermal conductivity”) The transfer factor may have asignificant dependence on moisture distribution and testing conditions within moist specimens or onthe thickness of the specimen and/or on the temperature difference for the same mean testtemperature and on the radiative characteristics of the surfaces adjoining those of the specimenwhen testing high porosity specimens

NOTE While testing on moist specimen is covered in this standard, specific problem oftesting thick specimens exceeding apparatus capabilities and/or exhibiting the so-calledthickness effect is addressed in EN 12939, see the Bibliography

The intrinsic property of the material where combined conduction and radiation take place is called

“thermal transmissivity” For moist materials the intrinsic property, depending on the moisturecontent at moisture equilibrium and not affected by moisture movement is called “hygrothermaltransmissivity” The hygrothermal transmissivity is needed, together with the knowledge of themoisture distribution under service conditions, for the assessment of design values of thermalproperties

For all the above reasons the thermal resistance, as the transfer factor, is a property that properlydescribes the thermal behaviour of the specimen in its specific testing conditions If there is thepossibility of the onset of convection within the test specimen (e.g specimens containing coarseaggregates and having open structure), the apparatus orientation, the thickness and the temperaturedifference can influence both the transfer factor and the thermal resistance.

If a heat transfer property of many specimens of the same material is measured, this property may:1) vary due to variability of composition of the material or samples of it;

2) be affected by moisture or other factors;

3) change with time;

4) change with mean temperature;

5) depend upon the prior thermal history

It shall be recognized, therefore, that the selection of a typical value of heat transfer propertiesrepresentative of a material in a particular application, shall be based on appropriate samplingschemes, testing conditions and conversion rules, see also A.4

A.2 Definitions

A.2.1 thermal conductivity, l, at a point P: Quantity defined in each point P of a purely

conducting medium by the following relation between the vectors q and grad(T):

q = - l grad(T)

NOTE In the most general case the thermal conductivity is a nine element tensor and not aconstant

A.2.2 thermally homogeneous medium: Medium in which the thermal conductivity is not a

function of the position within the medium but may be a function of the direction, time andtemperature

A.2.3 porosity, x: Total volume of the voids within a porous medium (a porous medium is onewhich is heterogeneous due to the presence of e.g fibres, cell walls, grains) divided by the totalvolume of the medium The local porosity, xP at the point P is the porosity within a specimen whenthe volume of an elementary part of the specimen is small with respect of the specimen, but largeenough to evaluate a meaningful average

A.2.4 homogeneous porous medium: Medium in which the local porosity is independent of the

point where the value is computed (EN ISO 9251:1995)

NOTE Most medium and low thermal resistance specimens are homogeneous porous, i.e nothomogeneous (see the definition of porosity) and hence not thermally homogeneous

A.2.5 thermally isotropic medium: Medium in which the thermal conductivity is not a function of

the direction but may be a function of the position within the medium, of time and temperatureNOTE The thermal conductivity of an isotropic medium is defined through a single value ineach point, instead of a matrix of values

A.2.6 thermally stable medium: Medium in which the thermal conductivity is not a function of

time, but may be a function of the co-ordinates, of temperature and, when applicable, of direction

A.2.7 mean thermal conductivity of a specimen: Property defined in steady state conditions in a

body that has the form of a slab bounded by two parallel, flat isothermal faces and by adiabaticedges perpendicular to the faces, that is made of a material thermally homogeneous, isotropic (oranisotropic with a symmetry axis perpendicular to the faces), stable only within the precision of ameasurement and the time required to execute it, and with the thermal conductivity constant or alinear function of temperature

A.2.8 transfer factor of a specimen: Defined by:

T

R

d T

d

q

=D

=

NOTE This definition is applicable to any steady state test with a guarded hot plate or heatflow meter apparatus, including e.g measurements on specimens including air layers, whereconduction, convection, radiation and moisture migration take place together It depends onexperimental conditions, e.g temperature difference, liquid and vapour flow, moisturedistribution within the specimen, apparatus emissivity and specimen thickness, and in these

conditions characterizes a specimen in relation to moisture migration and/or the combined

conduction, convection and radiation heat transfer It is often referred to elsewhere as

measured, equivalent, apparent or effective thermal conductivity of a specimen.

A.2.9 hygrothermal transmissivity of a material, l*: Defined by the ratio of the density of heatflow rate and temperature gradient, as the thermal conductivity It applies to moist materials duringsteady state conditions when moisture distribution within the material is in equilibrium and there is

no moisture movement within the material (with the possible exception of moisture circulationlocally or within a pore) When these conditions apply, it is also:

R

d T

“thermal conductivity of a moist material” It may be used in one-dimensional steady statecalculations only