ISO 9251:1987

Thermal insulation - Heat transfer conditions and properties of materials - Vocabulary

Defines terms used in the field of thermal insulation to describe heat transfer conditions, such as steady state, non-steady state, periodic state, transient state and heat transfer, and properties of materials.

Isolation thermique — Conditions de transfert thermique et propriétés des matériaux — Vocabulaire

La présente Norme internationale définit des termes utilisés dans le domaine de l'isolation thermique pour décrire les conditions de transfert thermique et les propriétés des matériaux.

General Information

• Status: Published
• Publication Date: 18-Nov-1987
• ICS: 01.040.27 - Energy and heat transfer engineering (Vocabularies)
• ICS: 27.220 - Heat recovery. Thermal insulation
• Technical Committee: ISO/TC 163 - Thermal performance and energy use in the built environment
• Drafting Committee: ISO/TC 163 - Thermal performance and energy use in the built environment
• Current Stage: 9093 - International Standard confirmed
• Start Date: 22-Feb-2022
• Completion Date: 13-Dec-2025

Overview

ISO 9251:1987 - "Thermal insulation - Heat transfer conditions and properties of materials - Vocabulary" is an ISO vocabulary standard developed by ISO/TC 163 (Thermal insulation). Published as the first edition in 1987, it provides standardized definitions for terms used in the field of thermal insulation to describe heat transfer conditions (e.g., steady state, non‑steady state, periodic, transient) and the properties of materials (e.g., porosity, local porosity, porous media types, density, isotropy/anisotropy).

This vocabulary standard promotes consistent use of terminology across testing, specification, research and product documentation for thermal insulation and related engineering disciplines.

Key topics

ISO 9251 defines and clarifies essential technical terms, including:

• Heat transfer conditions
  • Steady state: parameters do not vary with time
  • Non‑steady state: parameters vary with time
  • Periodic state: non‑steady state with repeating parameter values
  • Transient state: evolution from an initial state toward steady or periodic
  • Heat transfer: energy transmission by conduction, convection, radiation or combinations
• Material properties
  • Porosity and local porosity - total void volume definitions and point‑wise averaging
  • Classification of porous media (fibrous, granular/loose‑fill, cellular, interconnected)
  • Homogeneous / heterogeneous and isotropic / anisotropic media distinctions
  • (Mass) density - bulk and material density considerations

The standard also cross‑references related vocabulary in the ISO thermal insulation series (see Related Standards).

Applications

ISO 9251 is practical for:

• Standardizing terminology in test methods, lab reports and certification for thermal insulation materials
• Supporting clear product specifications and procurement documents for manufacturers and suppliers
• Enabling consistent communication in building engineering, HVAC design, refrigeration, industrial insulation and material R&D
• Helping regulatory bodies, compliance auditors and researchers interpret measurement results and compare data across studies

By providing precise definitions, ISO 9251 improves clarity in technical documentation, reduces misinterpretation in testing and design, and assists in harmonizing international practice.

Who should use it

• Insulation manufacturers and product developers
• Test laboratories and certification bodies
• Architects, building engineers and HVAC designers
• Materials scientists and researchers
• Standards writers and regulatory authorities

Related Standards

Part of a series on thermal insulation vocabulary and quantities; related documents include:

• ISO 7345 (Physical quantities and definitions)
• ISO 9346 (Mass transfer - quantities and definitions)
• ISO 9229 (Thermal insulating materials and products - vocabulary)
• ISO 9288 (Heat transfer by radiation - quantities and definitions)

Keywords: ISO 9251, thermal insulation vocabulary, heat transfer conditions, porosity, steady state, transient state, porous medium, material properties.

Standards Content (Sample)

INTERNATIONAL STANDARD
IS0
NORME INTERNATIONALE
First edition
Premiere kdition
1987-12-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXAYHAPOJJHAH OPTAHM3A~M~ fl0 CTAHflAPTM3A~MM
Thermal in”sulation - Heat transfer conditions and
properties of materials - Vocabulary
Isolation thermique - Conditions de transfert
thermique et propriMs des materiaux - Vocabulaire
Reference number
Numkro de rkfh-ence
IS0 925 1 : 1987 (E/F)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work of preparing International
Standards is normally carried out through IS0 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, govern-
mental and non-governmental, in liaison with ISO, also take part in the work.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the IS0 Coun’cil. They are approved in accordance with IS0 procedures requiring at
least 75 % approval by the member bodies voting.
International Standard IS0 9251 was prepared by Technical Committee ISO/TC 163,
Thermal insulation.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
Avant-propos
L’ISO (Organisation internationale de normalisation) est une federation mondiale
d’organismes nationaux de normalisation (cornit& membres de I’ISO). LAaboration
des Normes internationales est normalement confide aux cornit& techniques de I’ISO.
Chaque cornit membre intAres& par une &ude a le droit de faire partie du cornit
technique cr& a cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec I’ISO participent egalement aux. travaux.
Les projets de Normes internationales adopt& par les comit6s techniques sont soumis
aux cornit& membres pour approbation, avant leur acceptation comme Normes inter-
nationales par le Conseil de I’ISO. Les Normes internationales sont approuv6es confor-
m6ment aux proc6dures de I’ISO qui requierent I’approbation de 75 % au moins des
cornit& membres votants.
La Norme internationale IS0 9251 a et6 6labor6e par le cornit technique ISO/TC 163,
lsola tion thermique.
L’attention des utilisateurs est attir6e sur le fait que toutes les Normes internationales
sont de temps en temps soumises 3 Gvision et que toute reference faite B une autre
Norme internationale dans le present document implique qu’il s’agit, sauf indication
contraire, de la derni&e 6dition.
0 International Organization for Standardization, 1987 l
@ Organisation internationale de normalisation, 1987 l
Printed in Switzerland/lmprimb en Suisse

INTERNATIONAL STANDARD
IS0 9251 : 1987 (E/F)
NORME INTERNATIONALE
Isolation thermique -
Thermal insulation - Heat
Conditions de transfert
transfer conditions and
thermique et propriMs des
properties of materials -
materiaux - Vocabulaire
Vocabulary
0 Introduction 0 Introduction
This International Standard forms part of a series of La presente Norme internationale fait partie d’une serie de
vocabularies related to thermal insulation. vocabulaires de I’isolation thermique.
La serie comportera
The series will include
IS0 7345, Isolation thermique - Grandeurs physiques et defi-
I SO 7345, Thermal insulation - Physical quantities and defini-
nitions.
tions.
I SO 9251, Isolation thermique - Conditions de transfert ther-
IS0 9251, Thermal insulation - Heat transfer conditions and
propertl’es of materials - Vocabulary. mique et proprietes des materiaux - Vocabulaire.
IS0 9346, Thermal insulation - Mass transfer - Physical IS0 9346, Isolation thermique - Transfer-t de masse - Gran-
deurs physiques et definitions.
quantities and definitions.
IS0 9229, Isolation thermique - Materiaux et produits iso-
IS0 9229, Thermal insulation - Thermal insulating materials
and products - Vocabulary. 1 ) lants - Vocabulaire. 1 )
I SO 9288, Thermal insulation - Heat transfer by radiation - IS 0 9208, lsola tion thermique - Jransfert de chaleur par radia-
Physical quantities and dehnitions. 1 ) tion - Grandeurs physiques et definitions. ’ )
1 Objet et domaine d’ap’plication
1 Scope and field of application
La presente Norme internationale definit des termes utilises
This International Standard defines terms used in the field of
thermal insulation to describe heat transfer conditions and dans le domaine de I’isolation thermique pour decrire les condi-
tions de transfert thermique et les proprietes des materiaux.
properties of materials.
2 Conditions de transfert thermique
2 Heat transfer conditions
Condition for which all relevant 2.1 &at stationnaire : &at dans lequel tous les parametres
2.1 steady state :
parameters do not vary with time. utiles sont independants du temps.
Condition for which relevant 2.2 &at non stationnaire : kat dans lequel les parametres
2.2 non-steady state :
utiles varient avec le temps.
parameters vary with time.
2.3 periodic state : Non-steady state in which values of the 2.3 &at pbriodique : &at non stationnaire dans lequel les
valeurs des parametres utiles se rep&tent a intervalles de temps
relevant parameters repeat themselves at regular time intervals
independent of initial conditions. reguliers independants des conditions initiales.
1) In preparation. 1) En prkparation.

IS0 9251 : 1987 (E/F)
2.4 &at transitoire : itat non stationnaire dans lequel les
2.4 transient state : Non-steady state in which values of the
relevant parameters evolve from an initial state asymptotically valeurs des parametres utiles evoluent asymptotiquement d’un
&at initial vers un 6tat stationnaire ou pkriodique.
to either steady or periodic state.
transfert de chaleur : Transmission d’energie par con-
2.5 heat-transfer : Transmission of energy by thermal 2.5
duction thermique, convection therm
...