oSIST prEN 673:2023
(Main)Glass in building - Determination of thermal transmittance (U value) - Calculation method
Glass in building - Determination of thermal transmittance (U value) - Calculation method
This European Standard specifies a calculation method to determine the thermal transmittance of glazing with flat and parallel surfaces.
This European Standard applies to uncoated glass (including glass with structured surfaces, e.g. patterned glass), coated glass and materials not transparent in the far infrared which is the case for soda lime glass products, borosilicate glass and glass ceramic. It applies also to multiple glazing comprising such glasses and/or materials. It does not apply to multiple glazing which include in the gas space sheets or foils that are far infrared transparent. The procedure specified in this European Standard determines the U value ) (thermal transmittance) in the central area of glazing.
The edge effects due to the thermal bridge through the spacer of a sealed glazing unit or through the window frame are not included. Furthermore, energy transfer due to solar radiation is not taken into account. The effects of Georgian and other bars are excluded from the scope of this European Standard.
The Standard for the calculation of the overall U value of windows, doors and shutters (see A.1) gives normative reference to the U value calculated for the glazing components according to this standard.
For the purpose of product comparison, a vertical position of the glazing is specified. In addition, U values are calculated using the same procedure for other purposes, in particular for predicting:
- heat loss through glazing;
- conduction heat gains in summer;
- condensation on glazing surfaces;
- the effect of the absorbed solar radiation in determining the solar factor (see Clause 2).
Reference should be made to [3], [4] and [5] or other European Standards dealing with heat loss calculations for the application of glazing U values determined by this standard.
A procedure for the determination of emissivity is given in EN 12898.
The rules have been made as simple as possible consistent with accuracy.
Glas im Bauwesen - Bestimmung des Wärmedurchgangskoeffizienten (U-Wert) - Berechnungsverfahren
Dieses Dokument legt ein Berechnungsverfahren zur Bestimmung des Wärmedurchgangskoeffizienten von Verglasungen mit ebenen und parallelen Oberflächen fest.
Dieses Dokument gilt für unbeschichtetes Glas (einschließlich Glas mit strukturierter Oberfläche, z. B. Ornamentglas), beschichtetes Glas und für Materialien, die im fernen Infrarotbereich undurchlässig sind, z. B. Produkte aus Kalknatronglas, Borosilicatglas, Glaskeramik, Erdalkali-Silicatglas und Alumo-Silicatglas. Es gilt ebenfalls für Mehrfachverglasungen aus derartigen Gläsern und/oder Materialien. Für Mehrfachverglasungen mit Schichten oder Folien im Gaszwischenraum, die im fernen Infrarotbereich durchlässig sind, gilt dieses Dokument nicht.
Mit dem in dieser Europäischen Norm festgelegten Verfahren wird der U-Wert (Wärmedurchgangs-koeffizient) im mittleren Bereich einer Verglasung bestimmt.
Die Randwirkungen infolge der Wärmebrücke durch den Abstandhalter einer hermetisch abgeschlossenen Verglasung oder durch den Fensterrahmen sind nicht berücksichtigt. Die Wärmeübertragung durch Sonneneinstrahlung wurde ebenfalls nicht berücksichtigt. Die von Sprossen und anderen Leisten/Riegeln ausgehenden Einwirkungen fallen nicht in den Anwendungsbereich dieser Norm.
Der nach der vorliegenden Norm berechnete U-Wert für Verglasungselemente ist bei der Berechnung des Gesamt-U-Werts von Fernster, Türen und anderen Abschlüssen [1] zu verwenden.
Zum Zweck des Vergleichs von Produkten ist eine senkrechte Lage der Verglasung festgelegt. Zusätzlich werden nach demselben Verfahren U-Werte für weitere Zwecke berechnet, besonders für die Voraussage von:
- Wärmeverlusten durch Verglasungen;
- Erhöhungen der Wärmeleitung im Sommer;
- Tauwasserbildung auf Glasoberflächen;
- Auswirkungen der absorbierten Sonnenstrahlung auf die Bestimmung des Sonnenfaktors [2].
Bei der Anwendung von nach dieser Norm bestimmten U-Werten sollte auf [3], [4] und [5] oder weitere Europäische Normen, die sich mit Berechnungen von Wärmeverlusten befassen, Bezug genommen werden.
Weiterhin wird ein Verfahren für die Ermittlung des Emissionsvermögens in EN 12898:2019 angegeben.
Die Regeln wurden entsprechend der Genauigkeit so einfach wie möglich gestaltet.
Verre dans la construction - Détermination du coefficient de transmission thermique, U - Méthode de calcul
Le présent document spécifie une méthode de calcul du coefficient de transmission thermique des vitrages à surfaces planes et parallèles.
Le présent document est applicable au verre sans couche (y compris le verre avec surfaces structurées, par exemple le verre imprimé), au verre recouvert d’une couche et aux matériaux opaques au rayonnement infrarouge lointain, ce qui est le cas pour les produits verriers sodo-calciques, le verre borosilicate, les vitrocéramiques, le verre de silicate alcalino-terreux et le verre aluminosilicate. Il est également applicable aux vitrages multiples qui comportent de tels verres et/ou matériaux. Il n’est pas applicable aux vitrages multiples qui comportent dans la lame de gaz des panneaux ou feuilles transparents au rayonnement infrarouge de grande longueur d’onde.
La procédure spécifiée dans la présente Norme européenne permet de déterminer la valeur U (coefficient de transmission thermique) dans la zone centrale du vitrage.
Les effets de bord dus au pont thermique de l’intercalaire d’un vitrage isolant ou du châssis de fenêtre ne sont pas inclus. Par ailleurs, il n’est pas tenu compte du transfert d’énergie dû au rayonnement solaire. Les effets des croisillons insérés et autres barres sont exclus du domaine d’application de la présente norme.
La présente norme, qui permet de calculer la valeur U pour les composants verriers, est citée comme référence normative dans la norme relative au calcul du U global de fenêtres, portes et autres fermetures [1].
Pour faciliter la comparaison entre vitrages, ceux-ci sont spécifiés comme étant en position verticale. En outre, les valeurs U sont calculées à d’autres fins en utilisant la même procédure, en particulier pour la détermination des caractéristiques suivantes :
- perte de chaleur au travers des vitrages ;
- gains de chaleur par conduction en été ;
- condensation sur les surfaces des vitrages ;
- appréciation du rayonnement solaire absorbé dans la détermination du facteur solaire [2].
Il convient de se reporter à [3], [4] et [5] ou à d’autres Normes européennes concernant les calculs de déperditions thermiques pour l’application des valeurs U obtenues selon la présente norme.
Une procédure de détermination de l’émissivité est donnée dans l’EN 12898:2019.
Les règles ont été établies de manière à être les plus simples possible sans pour autant nuire à l’exactitude.
Steklo v gradbeništvu - Določanje toplotne prehodnosti (vrednost U) - Računska metoda
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN 673:2023
01-februar-2023
Steklo v gradbeništvu - Določanje toplotne prehodnosti (vrednost U) - Računska
metoda
Glass in building - Determination of thermal transmittance (U value) - Calculation method
Glas im Bauwesen - Bestimmung des Wärmedurchgangskoeffizienten (U-Wert) -
Berechnungsverfahren
Verre dans la construction - Détermination du coefficient de transmission thermique, U -
Méthode de calcul
Ta slovenski standard je istoveten z: prEN 673
ICS:
81.040.20 Steklo v gradbeništvu Glass in building
oSIST prEN 673:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 673:2023
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oSIST prEN 673:2023
DRAFT
EUROPEAN STANDARD
prEN 673
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2022
ICS Will supersede EN 673:2011
English Version
Glass in building - Determination of thermal transmittance
(U value) - Calculation method
Verre dans la construction - Détermination du Glas im Bauwesen - Bestimmung des
coefficient de transmission thermique, U - Méthode de Wärmedurchgangskoeffizienten (U-Wert) -
calcul Berechnungsverfahren
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 129.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 673:2022 E
worldwide for CEN national Members.
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oSIST prEN 673:2023
prEN 673:2022 (E)
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 5
4 Symbols, dimensionless numbers and subscripts . 5
4.1 Symbols . 5
4.2 Dimensionless Numbers . 6
4.3 Subscripts . 6
5 Basic formulae . 6
5.1 General. 6
5.2 U value . 6
5.3 Internal radiative heat transfer coefficient h . 7
r
5.4 Gas conductance h . 8
g
5.4.1 General. 8
5.4.2 Vertical glazing . 8
5.4.3 Horizontal and angled glazing. 9
6 Basic material properties . 9
6.1 Emissivity . 9
6.2 Gas properties . 10
6.3 Infrared absorption of the gas . 11
7 External and internal heat transfer coefficients . 11
7.1 External heat transfer coefficient h . 11
e
7.2 Internal heat transfer coefficient hi . 12
7.3 Design values . 13
8 Declared values: standardized boundary conditions . 13
9 Expression of the results . 14
9.1 U values . 14
9.2 Intermediate values . 14
10 Report . 14
10.1 Information included in the report . 14
10.2 Identification of the glazing . 14
10.3 Cross section of the glazing . 14
Annex A (normative) Iteration procedure for glazing with more than one gas space . 16
Annex B (informative) Determination of gas properties at different temperatures. 18
Bibliography . 19
2
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prEN 673:2022 (E)
European foreword
This document (prEN 673:2022) has been prepared by Technical Committee CEN/TC 129 “Glass in
building”, the secretariat of which is held by NBN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 673:2011.
This edition is a combined revision of EN 673: 2011 and ISO 10292: 1994
In comparison with the previous edition, the following technical modifications have been made:
— update of references to normal and corrected emissivity for consistency with EN 12898: 2019;
— changes to some of the gas properties;
— introduction of a linear approximation for determining gas properties at different temperatures;
— provision of more details on heat transfer coefficients for glazing at angles other than vertical;
— additional clarification provided on the iteration procedure for glazing with more than one gas space.
3
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oSIST prEN 673:2023
prEN 673:2022 (E)
1 Scope
This document specifies a calculation method to determine the thermal transmittance of glazing with flat
and parallel surfaces.
This document applies to uncoated glass (including glass with structured surfaces, e.g. patterned glass),
coated glass and materials not transparent in the far infrared which is the case for soda lime glass
products, borosilicate glass, glass ceramic, alkaline earth silicate glass and alumino silicate glass. It
applies also to multiple glazing comprising such glasses and/or materials. It does not apply to multiple
glazing which include in the gas space sheets or foils that are far infrared transparent.
The procedure specified in this European Standard determines the U value (thermal transmittance) in
the central area of glazing.
The edge effects due to the thermal bridge through the spacer of a sealed glazing unit or through the
window frame are not included. Furthermore, energy transfer due to solar radiation is not taken into
account. The effects of Georgian and other bars are excluded from the scope of this Standard.
The Standard for the calculation of the overall U value of windows, doors and shutters [1] gives normative
reference to the U value calculated for the glazing components according to this standard.
For the purpose of product comparison, a vertical position of the glazing is specified. In addition, U values
are calculated using the same procedure for other purposes, in particular for predicting:
— heat loss through glazing;
— conduction heat gains in summer;
— condensation on glazing surfaces;
— the effect of the absorbed solar radiation in determining the solar factor [2].
Reference should be made to [3], [4] and [5] or other European Standards dealing with heat loss
calculations for the application of glazing U values determined by this standard.
A procedure for the determination of emissivity is given in EN 12898:2019.
The rules have been made as simple as possible consistent with accuracy.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 674:2011, Glass in building - Determination of thermal transmittance (U value) - Guarded hot plate
method
EN 675:2011, Glass in building - Determination of thermal transmittance (U value) - Heat flow meter
method
EN 12898:2019, Glass in building - Determination of the emissivity
1
EN ISO 10456:2007, Building materials and products - Hygrothermal properties - Tabulated design values
and procedures for determining declared and design thermal values - Technical Corrigendum 1 (ISO
10456:2007/Cor 1:2009)
1
Impacted by EN ISO 10456:2007/AC:2009.
4
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prEN 673:2022 (E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
thermal transmittance
U value
parameter of glazing which characterizes the heat transfer through the central part of the glazing, i.e.
without edge effects, and states the steady-state density of heat transfer rate per temperature difference
between the environmental temperatures on each side
2
Note 1 to entry: The U value is given in watts per square metre Kelvin [W/(m ·K)]
3.2
declared value
U value obtained under standardized boundary conditions (see Clause 8)
4 Symbols, dimensionless numbers and subscripts
4.1 Symbols
A constant -
c specific heat capacity of gas J/(kg·K)
nominal thickness of material layer (glass or alternative glazing
d m
material)
F volume fraction -
2
h — heat transfer coefficient W/(m ·K)
2
— also thermal conductance W/(m ·K)
M number of material layers -
n Exponent -
N number of spaces -
r thermal resistivity of glass (glazing material) m·K/W
P gas property -
Rn normal reflectance (perpendicular to the surface) -
s width of gas space m
T absolute temperature K
2
U thermal transmittance W/(m ·K)
ΔT temperature difference K
ε corrected emissivity -
5
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ε normal emissivity (perpendicular to the surface) -
n
3
ρ gas density Kg/m
2 4
σ Stefan-Boltzmann's constant 5,67 × 10-8 W/(m ·K )
μ dynamic viscosity of gas kg/(m·s)
λ thermal conductivity of gas in space W/(m·K)
ϑ temperature on the Celsius scale °C
4.2 Dimensionless Numbers
Gr Grashof number
Nu Nusselt number
Pr Prandtl number
4.3 Subscripts
c convection
e external
i internal
th
j j material layer
th
k k space
g gas
m mean
n normal
r radiation
s space
t total
1;2 first, second etc.
5 Basic formulae
5.1 General
The method of this standard is based on a calculation according to the following principles.
5.2 U value
The U value is given by:
1 1 11
= ++ (1)
U h hh
et i
where
h and h are the external and internal heat transfer coefficients;
e i
h is the total thermal conductance of the glazing.
t
6
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oSIST prEN 673:2023
prEN 673:2022 (E)
NM
11
+ dr⋅ (2)
∑∑ jj
hh
t 11s
where
h is the thermal conductance of each gas space;
s
N is the number of spaces;
d is the thickness of each material layer;
j
r is the thermal resistivity of each material (thermal resistivity of soda lime glass = 1,0 m·K/W);
j
M is the number of material layers.
hh +h (3)
sk,,r k g,k
where
th
h is the heat transfer of the k space;
s,k
h is the internal radiative heat transfer coefficient;
r,k
th
h is the U value of gas of the k space.
g,k
The thermal resistivity of components other than glass (e.g. interlayers in laminated glass) may be taken
into account in determining the U value. Data on thermal conductivity of components other than glass
should be obtained from the supplier or a default value taken from EN ISO 10456. In instances where the
effects are not considered significant or important, a simplified approach may be taken, i.e. ignoring the
effects of components other than glass.
NOTE In the absence of measured data from the manufacturer, a generic value for the thermal conductivity of
the interlayer can be taken from the document Glass in Building — Folio Interlayers for the Manufacturing of
Laminated Glass — Product standard (in preparation by CEN/TC129/WG3).
5.3 Internal radiative heat transfer coefficient h
r
The internal radiative heat transfer coefficient is given by:
−1
11
3
hT41σ +− (4)
r mk,
εε
1,k 2,k
where:
σ is the Stefan-Boltzmann's constant;
T is the mean absolute temperature of the gas space;
m,k
ε and ε are the corrected emissivities at T .
1,k 2,k m,k
7
=
=
=
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5.4 Gas conductance h
g
5.4.1 General
The gas conductance is given by:
λ
k
h = Nu (5)
gk,
S
k
where:
s is the width of the space;
k
λ is the thermal conductivity;
k
Nu is the Nusselt number.
n
Nu=A⋅⋅Gr Pr (6)
( )
where:
A is a constant
Gr is the Grashof number
Pr is the Prandtl number
n is an exponent
32
9,81⋅sT⋅∆ ⋅ρ
Gr= (7)
2
T ⋅µ
m
µ⋅c
Pr= (8)
λ
where:
ΔT is the temperature difference between glass surfaces bounding the gas space;
ρ is the density;
µ is the dynamic viscosity;
c is the specific heat capacity;
T is the mean temperature.
m
The Nusselt number is calculated from Formula (6).
If Nu is less than 1, then the value unity is used for Nu in Formula (5).
5.4.2 Vertical glazing
For vertical glazing:
A is 0,035
n is 0,38
8
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5.4.3 Horizontal and angled glazing
For horizontal or angled glazing and upward heat flow the heat transfer
...
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