SIST EN 673:2011
(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 U-Wertes (Wärmedurchgangskoeffizient) - Berechnungsverfahren
Diese Europäische Norm enthält ein Berechnungsverfahren zur Bestimmung des Wärmedurchgangs-koeffizienten von Verglasungen mit ebenen und parallelen Oberflächen.
Die vorliegenden Europäische Norm 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 und Glaskeramik. Sie 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 diese Norm nicht. Mit dem in dieser Europäischen Norm festgelegten Verfahren wird der U Wert ) (Wärme¬durchgangs¬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 Europäischen 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 (siehe EN ISO 10077 [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 (siehe Literaturhinweis [2]).
(...)
Verre dans la construction - Détermination du coefficient de transmission thermique, U - Méthode de calcul
La présente Norme européenne spécifie une méthode de calcul du coefficient de transmission thermique des vitrages à surfaces planes et parallèles.
Cette Norme européenne 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 et les vitrocéramiques. Elle est également applicable aux vitrages multiples qui comportent de tels verres et/ou matériaux. Elle 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 présentée dans
cette Norme européenne détermine la valeur de U1) (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 provenant du rayonnement solaire. Les effets des croisillons insérés et autres barres sont exclus du domaine d'application de la présente Norme européenne.
La norme qui permet le calcul du U global de fenêtres, portes et autres fermetures (voir A.1) fait référence normative à la valeur de U obtenue selon cette norme pour les composants verriers.
Pour faciliter la comparaison entre vitrages, ceux-ci sont considérés en position verticale. En outre, les valeurs de U sont calculées dans d'autres buts 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 (voir Article 2).
- convient de se reporter aux réfé
Steklo v gradbeništvu - Določevanje toplotne prehodnosti (vrednost U) - Računska metoda
Ta evropski standard določa metodo izračuna za določevanje toplotne prehodnosti stekla s ploskimi in vzporednimi površinami.
Ta evropski standard velja za nepremazano steklo (vključno s steklom s strukturirano površino, npr. vzorčastim steklom), prevlečeno steklo in materiale, ki pri skrajni infrardeči svetlobi niso prozorni, kot velja za steklene proizvode iz mešanice natrijevega hidroksida in kalcijevega hidroksida, borosilikatno steklo in stekleno keramiko. Velja tudi za večkratno zasteklitev, ki zajema taka stekla in/ali materiale. Ne velja za večkratne zasteklitve, ki v plinskem prostoru vključujejo plošče ali folije, ki so prozorne v skrajni infrardeči svetlobi. S postopkom, ki ga opredeljuje ta evropski standard, se določa vrednost U (toplotno prehodnost) v osrednjem delu stekla.
Robni učinki zaradi toplotnega mostu med vmesnikom zatesnjene steklene enote ali skozi okvir okna niso vključeni. Tudi prenos energije zaradi sončnega sevanja ni upoštevan. Učinki georgijanskih in drugih prečk so izvzeti iz obsega tega evropskega standarda.
Standard za izračune skupne vrednosti U oken, vrat in rolet (glej točko A.1) podaja normativno referenco za vrednost U, izračunano za steklene komponente v skladu s tem standardom.
Za namen primerjave proizvodov je določen navpični položaj stekla. Poleg tega se vrednosti U izračunajo z istim postopkom tudi za druge namene, predvsem za napovedovanje:
- toplotne izgube prek stekla;
- prevodnega segrevanja poleti;
- kondenza na steklenih površinah;
- učinka absorbiranega sončnega sevanja pri določevanju sončnega dejavnika (glej klavzulo 2).
Za uporabo vrednosti U-stekla, določene s tem standardom, se je treba sklicevati na [3], [4] in [5] ali druge evropske standarde, ki obravnavajo izračune toplotnih izgub.
Postopek za določevanje oddajnosti je naveden v EN 12898.
Pravila so čim bolj poenostavljena, a še vedno natančna.
General Information
Relations
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.PHWRGDGlas im Bauwesen - Bestimmung des U-Wertes (Wärmedurchgangskoeffizient) - BerechnungsverfahrenVerre dans la construction - Détermination du coefficient de transmission thermique, U - Méthode de calculGlass in building - Determination of thermal transmittance (U value) - Calculation method81.040.20Steklo v gradbeništvuGlass in buildingICS:Ta slovenski standard je istoveten z:EN 673:2011SIST EN 673:2011en,fr,de01-maj-2011SIST EN 673:2011SLOVENSKI
STANDARDSIST EN 673:1999/A2:2004SIST EN 673:1999/A1:2001SIST EN 673:19991DGRPHãþD
SIST EN 673:2011
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 673
February 2011 ICS 81.040.20 Supersedes EN 673:1997English Version
Glass in building - Determination of thermal transmittance (U value) - Calculation method
Verre dans la construction - Détermination du coefficient de transmission thermique, U - Méthode de calcul
Glas im Bauwesen - Bestimmung des U-Werts (Wärmedurchgangskoeffizient) - Berechnungsverfahren This European Standard was approved by CEN on 2 January 2011.
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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2011 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 673:2011: ESIST EN 673:2011
EN 673:2011 (E) 2 Contents Page Foreword .3Introduction .41 Scope .42 Normative references .53 Terms and definitions .54 Symbols, dimensionless numbers and subscripts .54.1 Symbols .54.2 Dimensionless Numbers .64.3 Subscripts .65 Basic formulae .75.1 General .75.2 U value .75.3 Radiation conductance hr .85.4 Gas conductance hg .85.4.1 General .85.4.2 Vertical glazing .95.4.3 Horizontal and angled glazing .96 Basic material properties .96.1 Emissivity .96.2 Gas properties . 106.3 Infrared absorption of the gas . 127 External and internal heat transfer coefficients . 127.1 External heat transfer coefficient he . 127.2 Internal heat transfer coefficient hi . 127.3 Design values . 138 Declared values: standardized boundary conditions . 139 Expression of the results . 149.1 U values . 149.2 Intermediate values . 1410 Test report . 1410.1 Information included in the test report . 1410.2 Identification of the glazing . 1410.3 Cross section of the glazing . 1510.4 Results . 15Annex A (normative)
Iteration procedure for glazing with more than one gas space . 16Bibliography . 18 SIST EN 673:2011
EN 673:2011 (E) 3 Foreword This document (EN 673:2011) has been prepared by Technical Committee CEN/TC 129 “Glass in building”, the secretariat of which is held by NBN. 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 August 2011, and conflicting national standards shall be withdrawn at the latest by August 2011. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document supersedes EN 673:1997. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s). 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
SIST EN 673:2011
EN 673:2011 (E) 4 Introduction CEN/TC 129/WG9 "Light and energy transmission, thermal insulation" prepared a working draft based on the document ISO/DIS 10292, "Thermal insulation of glazing: Calculation rules for determining the steady state U value of double or multiple glazing", document that was prepared by ISO/TC 160, "Glass in building". This was published in 1997 as EN 673. This edition is a revision of EN 673:1997. The main change in this edition is that the internal and external heat transfer coefficients have been amended slightly to avoid any ambiguities. The original annex on the determination of emissivity has been removed and reference is made to EN 12898. Other changes include the incorporation of amendments A1 and A2 to EN 673:1997 and general improvements to the text to aid understanding. 1 Scope
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 value1) (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 EN ISO 10077-1 [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 Bibliography, [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.
1) In some countries the symbol k has been used hitherto.
SIST EN 673:2011
EN 673:2011 (E) 5 The rules have been made as simple as possible consistent with accuracy. 2 Normative references The following referenced documents are indispensable for the application 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, Glass in building — Determination of thermal transmittance (U value) — Guarded hot plate method EN 675, Glass in building — Determination of thermal transmittance (U value) — Heat flow meter method EN 12898, Glass in building — Determination of the emissivity 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 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 NOTE The U value is given in watts per square metre Kelvin [W/(m2⋅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)
d
thickness of material layer (glass
or alternative glazing material)
m
F
volume fraction
-
h
- heat transfer coefficient
W/(m2⋅K)
- also thermal conductance
W/(m2⋅K)
M
number of material layers
-
n
exponent
-
N
number of spaces
- SIST EN 673:2011
EN 673:2011 (E) 6
r
thermal resistivity of glass (glazing material)
m⋅K/W
P
gas property
-
s
width of gas space
m
T
absolute temperature
K
U
thermal transmittance
W/(m2⋅K)
∆Τ temperature difference
K
ε
corrected emissivity
-
εn
normal emissivity (perpendicular to the surface)
-
ρ
gas density
kg/m3
σ
Stefan-Boltzmann's constant 5,67 x 10-8
W/(m2⋅K4)
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
j
jth material layer
k
kth space
g
gas
m
mean
n
normal
r
radiation
s
space SIST EN 673:2011
EN 673:2011 (E) 7
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: 1U=1he+1ht+1hi (1) where
he and hi are the external and internal heat transfer coefficients;
ht is the total thermal conductance of the glazing. 1ht=1hs1N∑+dj1M∑⋅rj (2) where
hs is the thermal conductance of each gas space;
N is the number of spaces;
dj is the thickness of each material layer;
rj is the thermal res
...
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.PHWRGDGlas im Bauwesen - Bestimmung des U-Wertes (Wärmedurchgangskoeffizient) - BerechnungsverfahrenVerre dans la construction - Détermination du coefficient de transmission thermique, U - Méthode de calculGlass in building - Determination of thermal transmittance (U value) - Calculation method81.040.20Steklo v gradbeništvuGlass in buildingICS:Ta slovenski standard je istoveten z:FprEN 673kSIST FprEN 673:2010en,fr,de01-september-2010kSIST FprEN 673:2010SLOVENSKI
STANDARD
kSIST FprEN 673:2010
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
FINAL DRAFT
FprEN 673
July 2010 ICS 81.040.20 Will supersede EN 673:1997English Version
Glass in building - Determination of thermal transmittance (U value) - Calculation method
Verre dans la construction - Détermination du coefficient de transmission thermique, U - Méthode de calcul
Glas im Bauwesen - Bestimmung des U-Wertes (Wärmedurchgangskoeffizient) - Berechnungsverfahren This draft European Standard is submitted to CEN members for unique acceptance procedure. 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 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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2010 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. FprEN 673:2010: EkSIST FprEN 673:2010
FprEN 673:2010 (E) 2 Contents Page Foreword .3Introduction .41 Scope .42 Normative references .53 Terms and definitions .54 Symbols, dimensionless numbers and subscripts .54.1 Symbols .54.2 Dimensionless Numbers .64.3 Subscripts .65 Basic formulae .75.1 General .75.2 U value .75.3 Radiation conductance hr .75.4 Gas conductance hg .85.4.1 General .85.4.2 Vertical glazing .95.4.3 Horizontal and angled glazing .96 Basic material properties .96.1 Emissivity .96.2 Gas properties . 106.3 Infrared absorption of the gas . 127 External and internal heat transfer coefficients . 127.1 External heat transfer coefficient he. 127.2 Internal heat transfer coefficient hi . 127.3 Design values . 138 Declared values: standardized boundary conditions . 139 Expression of the results . 149.1 U values . 149.2 Intermediate values . 1410 Test report . 1410.1 Information included in the test report . 1410.2 Identification of the glazing . 1410.3 Cross section of the glazing . 1510.4 Results . 15Annex A (normative)
Iteration procedure for glazing with more than one gas space . 16Bibliography . 18 kSIST FprEN 673:2010
FprEN 673:2010 (E) 3 Foreword This document (FprEN 673:2010) 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 Unique Acceptance Procedure. This document will supersede EN 673:1997. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s).
kSIST FprEN 673:2010
FprEN 673:2010 (E) 4 Introduction CEN/TC 129/WG9 "Light and energy transmission, thermal insulation" prepared a working draft based on the document ISO/DIS 10292, "Thermal insulation of glazing: Calculation rules for determining the steady state U value of double or multiple glazing", document that was prepared by ISO/TC 160, "Glass in building". This was published in 1997 as EN 673. This edition is a revision of EN 673:1997. The main change in this edition is that the internal and external heat transfer coefficients have been amended slightly to avoid any ambiguities regarding rounding of intermediate values. The original Annex on the determination of emissivity has been removed and reference is made to EN 12898. Other changes include the incorporation of amendments A1 and A2 to EN 673:1997 and general improvements to the text to aid understanding. 1 Scope
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 value1) (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.
1) In some countries the symbol k has been used hitherto.
kSIST FprEN 673:2010
FprEN 673:2010 (E) 5 The rules have been made as simple as possible consistent with accuracy. 2 Normative references The following referenced documents are indispensable for the application 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, Glass in building — Determination of thermal transmittance (U value) — Guarded hot plate method EN 675, Glass in building — Determination of thermal transmittance (U value) — Heat flow meter method EN 12898, Glass in building — Determination of the emissivity 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 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 NOTE The U value is given in watts per square metre Kelvin [W/(m2⋅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)
d
thickness of material layer (glass
or alternative glazing material)
m
F
volume fraction
-
h
- heat transfer coefficient
W/(m2⋅K)
- also thermal conductance
W/(m2⋅K)
M
number of material layers
-
n
exponent
-
N
number of spaces
- kSIST FprEN 673:2010
FprEN 673:2010 (E) 6
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
U
thermal transmittance
W/(m2⋅K)
∆Τ temperature difference
K
ε
corrected emissivity
-
εn
normal emissivity (perpendicular to the surface)
-
ρ
gas density
kg/m3
σ
Stefan-Boltzmann's constant 5,67 x 10-8
W/(m2⋅K4)
µ
dynamic viscosity of gas
kg/(m⋅s)
λ
- thermal conductivity of gas in space
W/(m⋅K)
- also wavelength
µm
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
j
j-th material layer
g
gas
m
mean
n
normal
r
radiation kSIST FprEN 673:2010
FprEN 673:2010 (E) 7
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: 1U=1he+1ht+1hi (1) where
he and hi are the external and internal heat transfer coefficients;
ht is the total thermal conductance of the glazing. 1ht=1hs1N∑+dj1M∑⋅rj (2) where
hs is the thermal conductance of each gas space;
N
is the number of spaces;
dj is the thickness of each material layer;
rj is the thermal resistivity of each material (thermal resistivity of soda lime glass =
1,0 m⋅K/W);
M is the number of material layers. hs
=
hr + hg (3) NOTE The thermal resistiv
...
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