EN ISO 7345:2018

SLOVENSKI STANDARD
01-september-2018
1DGRPHãþD
SIST EN ISO 7345:1997
7RSORWQH]QDþLOQRVWLVWDYELQGHORYVWDYE)L]LNDOQHNROLþLQHLQGHILQLFLMH,62

Thermal performance of buildings and building components - Physical quantities and
definitions (ISO 7345:2018)
Wärmeschutz - Physikalische Größen und Definitionen (ISO 7345:2018)
Performance thermique des bâtiments et des matériaux pour le bâtiment - Grandeurs
physiques et définitions (ISO 7345:2018)
Ta slovenski standard je istoveten z: EN ISO 7345:2018
ICS:
01.060 9HOLþLQHLQHQRWH Quantities and units
91.120.10 Toplotna izolacija stavb Thermal insulation of
buildings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 7345
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2018
EUROPÄISCHE NORM
ICS 01.060; 27.220 Supersedes EN ISO 7345:1995
English Version
Thermal performance of buildings and building
components - Physical quantities and definitions (ISO
7345:2018)
Performance thermique des bâtiments et des Wärmeverhalten von Gebäuden und Baustoffen -
matériaux pour le bâtiment - Grandeurs physiques et Physikalische Größen und Definitionen (ISO
définitions (ISO 7345:2018) 7345:2018)
This European Standard was approved by CEN on 23 March 2018.

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 CEN-CENELEC 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 CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7345:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 7345:2018) has been prepared by Technical Committee ISO/TC 163 "Thermal
performance and energy use in the built environment" in collaboration with Technical Committee
CEN/TC 89 “Thermal performance of buildings and building components” the secretariat of which is
held by SIS.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by October 2018, and conflicting national standards shall
be withdrawn at the latest by October 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 7345:1995.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 7345:2018 has been approved by CEN as EN ISO 7345:2018 without any modification.

INTERNATIONAL ISO
STANDARD 7345
Third edition
2018-03
Thermal performance of buildings
and building components — Physical
quantities and definitions
Performance thermique des bâtiments et des matériaux pour le
bâtiment — Grandeurs physiques et définitions
Reference number
ISO 7345:2018(E)
©
ISO 2018
ISO 7345:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 7345:2018(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Annex A (informative) Concept of thermal conductivity . 8
Bibliography .12
ISO 7345:2018(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 voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 163, Thermal performance and energy use
in the built environment.
This third edition of ISO 7345 cancels and replaces the second edition (ISO 7345:1987), which has been
technically revised.
This edition includes the following significant changes with respect to the previous edition:
— title of the standard updated from ‘Thermal insulation — Physical quantities and definitions’ to
‘Thermal performance of buildings and building elements — Physical quantities and definitions’;
— title of ISO/TC 163 corrected (Foreword);
— ISO 31-4 replaced by ISO 80000-5 in the note in the Scope and added to the Bibliography;
— symbols, names and definitions (in 3.3 and 3.4) adapted to current state (Λ → L, Λ → L , U → Ψ,
l 2D l
coefficient of heat loss → heat transfer coefficient);
— “areal” used instead of “surface” in quantity names (Clause 3) where “surface” was meant to
distinguish between a length-related quantity (“linear”) and an area-related quantity (now “areal”)
with similar name;
— Formula in 3.1.4 corrected;
— subscript l added in 3.4;
— added a Note 1 to entry in 3.1.11 and a Note 3 to entry in 3.1.13;
— H’ added in 3.2.2 as an alternative name for F ;
s
— added “for homogeneous solids” to A.1 in Annex A.
iv © ISO 2018 – All rights reserved

ISO 7345:2018(E)
Introduction
This document is intended to be used in conjunction with other vocabularies related to thermal
insulation. These include:
— ISO 7945, Thermal insulation — Physical quantities and definitions
— ISO 9251, Thermal insulation — Heat transfer conditions and properties of materials — Vocabulary
— ISO 9346, Thermal insulation — Mass transfer — Physical quantities and definitions
— ISO 9229, Thermal insulation — Thermal insulating materials and products — Vocabulary
— ISO 9288, Thermal insulation — Heat transfer by radiation — Physical quantities and definitions
NOTE Annex A provides an explanation of the concept of thermal conductivity.
INTERNATIONAL STANDARD ISO 7345:2018(E)
Thermal performance of buildings and building
components — Physical quantities and definitions
1 Scope
This document defines physical quantities used in the thermal performance of buildings and building
elements, and gives the corresponding symbols and units.
NOTE Because the scope of this document is restricted to thermal performance and energy use in the built
environment, some of the definitions it contains differ from those given ISO 80000-5.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
3.1 Physical quantities and definitions
3.1.1
heat
quantity of heat
Q
Note 1 to entry: Unit: J.
3.1.2
heat flow rate
Φ
quantity of heat transferred to or from a system divided by time
dQ
Φ =
dt
Note 1 to entry: Unit: W.
3.1.3
density of heat flow rate
q
heat flow rate divided by area
dΦ
q=
dA
Note 1 to entry: The word “density” should be replaced by “areal density” when it may be confused with linear
density (3.1.4).
Note 2 to entry: Unit: W/m .
ISO 7345:2018(E)
3.1.4
linear density of heat flow rate
q
heat flow rate divided by length:
dΦ
q =
l
dl
Note 1 to entry: Unit: W/m.
3.1.5
thermal conductivity
λ
quantity defined by the following relation:
→
qT=−λgrad
Note 1 to entry: A rigorous treatment of the concept of thermal conductivity is given in the annex, which also
deals with the application of the concept of thermal conductivity to porous isotropic or anisotropic materials and
the influence of temperature and test conditions.
Note 2 to entry: Unit: W/(m·K).
3.1.6
thermal resistivity
r
quantity defined by the following relation:
→
gradTr=− q
Note 1 to entry: A rigorous treatment of the concept of thermal resistivity is given in Annex A.
Note 2 to entry: Unit: (m·K)/W.
3.1.7
thermal resistance
R
temperature difference divided by the density of heat flow rate in the steady state condition:
TT−
R=
q
Note 1 to entry: For a plane layer for which the concept of thermal conductivity applies, and when this property is
constant or linear with temperature (see Annex A):
d
R=
λ
Note 2 to entry: where d is the thickness of the layer.
Note 3 to entry: These definitions assume the definition of two reference temperatures, T and T and the area
1 2,
through which the density of heat flow rate is uniform.
Note 4 to entry: Thermal resistance can be related either to the material, structure or surface. If either T or
T is not the temperature of a solid surface, but that of a fluid, a reference temperature must be defined in each
specific case (with
...