SIST EN 13947:2007
(Main)Thermal performance of curtain walling - Calculation of thermal transmittance
Thermal performance of curtain walling - Calculation of thermal transmittance
This European Standard specifies a method for calculating the thermal transmittance of curtain walls consisting of glazed and/or opaque panels fitted in, or connected to, frames.
The calculation includes:
- different types of glazing, e.g. glass or plastic; single or multiple glazing; with or without low emissivity coating; with cavities filled with air or other gases;
- frames (of any material) with or without thermal breaks;
- different types of opaque panels clad with metal, glass, ceramics or any other material.
Thermal bridge effects at the rebate or connection between the glazed area, the frame area and the panel area are included in the calculation.
The calculation does not include:
- effects of solar radiation;
- heat transfer caused by air leakage;
- calculation of condensation;
- effect of shutters;
- additional heat transfer at the corners and edges of the curtain walling;
- connections to the main building structure nor through fixing lugs;
curtain wall systems with integrated heating.
Wärmetechnisches Verhalten von Vorhangfassaden - Berechnung des Wärmedurchgangskoeffizienten
La présente Norme européenne indique une méthode de calcul du coefficient de transmission thermique des façades légeres composées de panneaux vitrés et/ou opaques montés dans, ou raccordés a des encadrements.
Le calcul prend en compte :
- les différents types de vitrage, par exemple verre ou plastique ; les vitrages simples ou multiples ; avec ou sans revetement a basse émissivité ; avec des cavités remplies d’air ou de gaz ;
- les encadrements (en tous matériaux) avec ou sans coupures thermiques ;
- les différent types de parement de panneaux opaques en métal, verre, céramique ou tout autre matériau ;
- les effets de pont thermique au niveau de la feuillure ou de la jonction entre l’aire vitrée, l’aire de l’encadrement et l’aire du panneau.
Le calcul ne tient pas compte :
- du rayonnement solaire ;
- du transfert thermique provoqué par les fuites d’air ;
- du calcul de la condensation ;
- de l’effet des fermetures ;
- du transfert thermique supplémentaire au niveau des angles et des bords de la façade légere ;
- des jonctions a la structure principale du bâtiment ou des pattes de fixation ;
- des systemes de façade légere avec chauffage intégré.
Performances thermiques des façades légeres - Calcul du coefficient de transmission thermique
La présente Norme européenne indique une méthode de calcul du coefficient de transmission thermique des façades légères composées de panneaux vitrés et/ou opaques montés dans, ou raccordés à des encadrements.
Le calcul prend en compte :
- les différents types de vitrage, par exemple, verre ou plastique ; les vitrages simples ou multiples ; avec ou sans revêtement à basse émissivité ; avec des cavités remplies d’air ou de gaz ;
- les encadrements (en tous matériaux) avec ou sans coupures thermiques ;
- les différent types de parement de panneaux opaques en métal, verre, céramique ou tout autre matériau.
Les effets de pont thermique au niveau de la feuillure ou de la jonction entre l’aire vitrée, l’aire de l’encadrement et l’aire du panneau.
Le calcul ne tient pas compte :
- du rayonnement solaire ;
- du transfert thermique provoqué par les fuites d’air ;
- du calcul de la condensation ;
- de l’effet des fermetures ;
- du transfert thermique supplémentaire au niveau des angles et des bords de la façade légère ;
- des jonctions à la structure principale du bâtiment ou des pattes de fixation ;
des systèmes de façade légère avec chauffage intégré.
Toplotne značilnosti obešenih fasad - Izračun toplotne prehodnosti
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Thermal performance of curtain walling - Calculation of thermal transmittanceLPerformances thermiques des façades légeres - Calcul du coefficient de transmission thermiqueWärmetechnisches Verhalten von Vorhangfassaden - Berechnung des WärmedurchgangskoeffizientenTa slovenski standard je istoveten z:EN 13947:2006SIST EN 13947:2007en91.120.10Toplotna izolacija stavbThermal insulation91.060.10Stene. Predelne stene. FasadeWalls. Partitions. FacadesICS:SLOVENSKI
STANDARDSIST EN 13947:200701-februar-2007
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13947December 2006ICS 91.060.10; 91.120.10 English VersionThermal performance of curtain walling - Calculation of thermaltransmittancePerformances thermiques des façades légères - Calcul ducoefficient de transmission thermiqueWärmetechnisches Verhalten von Vorhangfassaden -Berechnung des WärmedurchgangskoeffizientenThis European Standard was approved by CEN on 9 November 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, 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 STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13947:2006: E
EN 13947:2006 (E) 2 Contents Page 1 Scope.6 2 Normative references.6 3 Terms and definitions, symbols and units.7 3.1 Terms and definitions.7 3.2 Symbols and units.7 3.3 Subscripts.7 3.4 Superscripts.8 4 Geometrical characteristics.8 4.1 Main principles.8 4.2 Developed areas and internal depth.11 4.3 Boundaries of curtain wall structures.11 4.3.1 General.11 4.3.2 Boundaries of a representative reference element.12 4.3.3 Curtain wall areas.13 5 Cut-off planes and partitioning of thermal zones.14 5.1 Rules for thermal modelling.14 5.2 Cut-off planes of the geometrical model.14 6 Calculation of curtain wall transmittance.14 6.1 Methodologies.14 6.2 Single assessment method.15 6.2.1 Thermal transmittance of glazing units and panels (filling elements).15 6.2.2 Determination of the heat flow through filling element / mullion or transom / filling element connection.16 6.2.3 Determination of the overall thermal transmittance of a curtain wall (Ucw).20 6.3 Component assessment method.21 6.3.1 General.21 6.3.2 Definition of areas.21 6.3.3 Thermal transmittance of glazing units and panels (filling elements).24 6.3.4 Thermal transmittance of frames, mullions and transoms.24 6.3.5 Linear thermal transmittance.25 6.4 Thermal transmittance of a curtain wall built of different elements.27 7 Input data.28 8 Report.29 8.1 Section drawings.29 8.2 Overview drawing of the whole curtain wall element.29 8.3 Values used for calculation.29 8.4 Presentation of results.29 Annex A (informative)
Guidance for calculating the thermal transmittance Ucw of curtain walling using the two methods.30 Annex B (informative)
Linear thermal transmittance of junctions.31 Annex C (normative)
A method for calculating the thermal effect of screws using a 2D numerical method and the procedures specified in EN ISO 10077-2.39 C.1 General.39 C.2 Calculation of the equivalent thermal conductivity of the screw λλλλs,eq.40 C.3 Consideration of screw heads and washers.40 Annex D (normative)
Ventilated and unventilated air spaces.41 Unventilated air layer.41
EN 13947:2006 (E) 3 Annex E (informative)
Component method: Calculation example.44 E.1 Data for examples.44 E.2 Frames.46 E.2.1 Definition and evaluation of areas.46 E.2.2 Evaluation of Uf values.47 E.3 Glazing units.48 E.3.1 Definition and evaluation of areas.48 E.3.2 Evaluation of Ug values.48 E.3.3 Definition of lg and evaluation of g, m,f and t,f.48 E.4 Panels.49 E.4.1 Definition and evaluation of areas.49 E.4.2 Evaluation of Up values.49 E.4.3 Definition of lp and evaluation of the p values.50 E.4.4 Calculation of a complete element.50 Annex F (informative)
Single assessment method: Calculation example.51 F.1 General description of examples.51 F.2 Centre U-value of the glazing unit.52 F.3 Centre U-value of the spandrel panel.52 F.4 U-values of thermal joints.52 F.5 Overall U-value of the curtain wall.53
EN 13947:2006 (E) 4 Foreword This document (EN 13947:2006) has been prepared by 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 June 2007, and conflicting national standards shall be withdrawn at the latest by June 2007. This European Standard is one of a series of standards on calculation methods for the design and evaluation of the thermal performance of buildings and building components. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, 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.
EN 13947:2006 (E) 5 Introduction The design and construction of curtain wall systems is complex. This European Standard specifies a procedure for calculating the thermal transmittance of curtain wall structures. Curtain walls often contain different kinds of materials, joined in different ways, and can exhibit numerous variations of geometrical shape. With such a complex structure, the likelihood of producing thermal bridges across the curtain wall envelope is quite high. The results of calculations, carried out following the procedures specified in this European Standard, can be used for comparison of the thermal transmittance of different types of curtain wall or as part of the input data for calculating the heat used in a building. This European Standard is not suitable for determining whether or not condensation will occur on the structure surfaces nor within the structure itself. Two different methods are given in this European Standard: - single assessment method (see 6.2); - component assessment method (see 6.3). Guidance on the use of these two methods is given in Annex A. Calculation examples for these two methods are given in Annex E and Annex F. Testing according to EN ISO 12567-1 is an alternative to this calculation method. The thermal effects of connections to the main building structure as well as fixing lugs can be calculated according to prEN ISO 10211. The thermal transmittance of the frame, Uf, is defined according to EN ISO 10077-2 or EN 12412-2 together with Annex A. The thermal transmittance of glazing units, Ug, is defined according to EN 673, EN 674 or EN 675 which do not include the edge effects. The thermal interaction of the frame and the filling element is included in the linear thermal transmittance Ψ
which is derived using the procedures specified in EN ISO 10077-2.
EN 13947:2006 (E) 6 1 Scope This European Standard specifies a method for calculating the thermal transmittance of curtain walls consisting of glazed and/or opaque panels fitted in, or connected to, frames. The calculation includes: different types of glazing, e.g. glass or plastic; single or multiple glazing; with or without low emissivity coating; with cavities filled with air or other gases; frames (of any material) with or without thermal breaks; different types of opaque panels clad with metal, glass, ceramics or any other material. Thermal bridge effects at the rebate or connection between the glazed area, the frame area and the panel area are included in the calculation. The calculation does not include: effects of solar radiation; heat transfer caused by air leakage; calculation of condensation; effect of shutters; additional heat transfer at the corners and edges of the curtain walling; connections to the main building structure nor through fixing lugs; curtain wall systems with integrated heating. 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 673:1997, Glass in building — Determination of thermal transmittance (U value) — Calculation method 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 12412-2, Thermal performance of windows, doors and shutters — Determination of thermal transmittance by hot box method — Part 2: Frames prEN ISO 6946:2005, Building components and building elements — Thermal resistance and thermal transmittance — Calculation method (ISO/DIS 6946:2005) EN ISO 7345:1995, Thermal insulation — Physical quantities and definitions (ISO 7345:1987) EN ISO 10077-1:2006, Thermal performance of windows, doors and shutters — Calculation of thermal transmittance — Part 1: General (ISO 10077-1:2006)
EN 13947:2006 (E) 7 EN ISO 10077-2:2003, Thermal performance of windows, doors and shutters — Calculation of thermal transmittance — Part 2: Numerical method for frames (ISO 10077-2:2003) prEN ISO 10211, Thermal bridges in building construction — Heat flows and surface temperatures — Detailed calculations (ISO/DIS 10211:2005) EN ISO 12567-1, Thermal performance of windows and doors — Determination of thermal transmittance by hot box method — Part 1: Complete windows and doors (ISO 12567-1:2000) 3 Terms and definitions, symbols and units 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in EN 673:1997, EN ISO 7345:1995, prEN ISO 6946:2005 and the following apply. NOTE Clause 4 includes descriptions of a number of geometrical characteristics of glazing units, frame sections and panels. 3.2 Symbols and units Table 1 — Symbols and units Symbol Quantity Unit A area m2 T thermodynamic temperature K U thermal transmittance W/(m2·K) l length m d depth m Φ heat flow rate W Ψ linear thermal transmittance W/(m·K) û difference
summation
ε emissivity
3.3 Subscripts cw curtain walling d developed e external eq equivalent f frame f,g frame/glazing FE filling element g glazing i internal j joint m mullion
EN 13947:2006 (E) 8 m,f mulliom/frame m,g mullion/glazing n normal p panel (opaque) s screw t transom t,f transom/frame t,g transom/glazing tot total TJ thermal joint at a connection between two filling elements W window 3.4 Superscripts * definition of areas for length-related treatment of thermal joints (see 6.2.2.3) 4 Geometrical characteristics 4.1 Main principles The main principles of curtain walling are shown in Figures 1 and 2.
EN 13947:2006 (E) 9
Key 1
structure fixing bracket A-A
vertical section Figure 1 — Principle of curtain walling construction: unitised construction
EN 13947:2006 (E) 10
Key 1
structure fixing bracket A-A
vertical section Figure 2 — Principle of curtain walling construction: stick construction
EN 13947:2006 (E) 11 4.2 Developed areas and internal depth Internal and external developed areas and internal depth are defined as shown in Figure 3.
Key 1 internal 2 external di internal depth of mullion or transom Ad,i
internal developed area Ad,e
external developed area
Figure 3 — Internal and external developed area, internal depth 4.3 Boundaries of curtain wall structures 4.3.1 General To evaluate the thermal transmittance of façades representative reference areas should be defined. The following subclauses define the various areas.
EN 13947:2006 (E) 12 4.3.2 Boundaries of a representative reference element The boundaries of the representative reference element shall be chosen according to the principles shown in Figure 4.
Figure 4 — Boundaries of a representative reference element of a façade
EN 13947:2006 (E) 13 4.3.3 Curtain wall areas The representative reference element is divided into areas of different thermal properties (sash, frame, mullion, transom, glazing units and panel sections) (see Figure 5).
Key 1 mullion 2 transom 3 sash and frame 4 glazing 5 panel Figure 5 — Areas with different thermal properties
EN 13947:2006 (E) 14 5 Cut-off planes and partitioning of thermal zones 5.1 Rules for thermal modelling In most cases the façade can be partitioned into several sections by using cut-off planes so that the thermal transmittance of the overall façade can be calculated as the area-weighted average of the thermal transmittance of each section. The necessary input data (thermal properties of each section) can be evaluated by measurement, two-dimensional finite element or finite difference software calculation or by tables or diagrams. In general there are two possibilities: the single assessment method (see 6.2); the component assessment method (see 6.3). The partitioning of the façade shall be performed in such a way as to avoid any significant differences in calculation results of the façade treated as a whole and the heat flow rate through the partitioned façade. Appropriate partitioning into several geometrical parts is achieved by choosing suitable cut-off planes. 5.2 Cut-off planes of the geometrical model The geometrical model includes central elements (glazing units, spandrel panels etc.) and thermal joints (mullion, transom, silicone joint etc.), which connect the different central elements. The geometrical model is delimited by cut-off planes. Curtain walling often contains highly conductive elements (glass and metals) which implies that significant lateral heat flow is possible. Cut-off planes shall represent adiabatic boundaries, which can be either: a symmetry plane, or a plane where the heat flow through that plane is perpendicular to the plane of the curtain wall, i.e. no edge effect is present (e.g. at least 190 mm away from the edge of a double glazing unit). Cut-off planes may be positioned only where there is a clear adiabatic situation (i.e. the heat flow is perpendicular to the plane). Figure 6 shows adiabatic lines (in the middle of the glass or panel far enough from the frame) where the heat flow will be perpendicular to the glass panes. Cut-off planes do not necessarily fall at the same place as the geometrical boundaries of a unitised element (i.e. through the frame). The middle of a frame might not be an adiabatic boundary. This might be due to asymmetric geometrical shape of the frame, asymmetric material properties (e.g. different conductivity of sub-components at each side of the frame), or asymmetric connection of panels in a symmetric frame (e.g. a frame that connects a spandrel panel and a glazing unit, or two glazing units with different thermal properties). 6 Calculation of curtain wall transmittance 6.1 Methodologies Two methods of calculating the thermal transmittance of curtain wall systems are specified: the single assessment method and the component assessment method. The single assessment method (see 6.2) is based on detailed computer calculations of the heat transfer through a complete construction including mullions, transoms, and filling elements (e.g. glazing unit, opaque panel). The heat flow rate (between two adiabatic lines) is calculated by modelling each thermal joint between two filling elements (opaque panel and/or glazing unit) using two-dimensional or three dimensional finite element analysis software. By area weighting the U-values of thermal joints and filling elements, the overall façade U-value can be calculated. This method can be used for any curtain walling system (i.e. unitised systems, stick systems, patent glazing, structural sealant glazing, rain screens, structural glazing).
EN 13947:2006 (E) 15 The component assessment method (see 6.3) divides the representative element into areas of different thermal properties e.g. glazing units, opaque panels and frames. By area weighting the U-values of these elements with additional correction terms describing the thermal interaction between these elements (Ψ-values), the overall façade U-value can be calculated. This method can be used for curtain walling systems such as unitised systems, stick systems and patent glazing. Structural silicone glazing, rain screens and structural glazing are excluded from the component assessment method. For the purpose of this European Standard, the term “filling element” is any façade component that has a one-dimensional heat flow in the absence of edge effects (the flat surface being perpendicular to the heat flow direction). Examples are glazing units and spandrel panels.
Figure 6 — Thermal section representing the full curtain wall
6.2 Single assessment method 6.2.1 Thermal transmittance of glazing units and panels (filling elements) The thermal transmittance of opaque panels Up shall be evaluated according to prEN ISO 6946. The thermal transmittance of glazing units Ug shall be evaluated according to EN 673, EN 674 or EN 675. In some cases, there is a different filling element at each side of the thermal joint (mullion, transom), so that two thermal transmittances have to be determined.
EN 13947:2006 (E) 16 6.2.2 Determination of the heat flow through filling element / mullion or transom / filling element connection 6.2.2.1 General The total heat flow rate Φtot of the complete connection shall be calculated using computer software that conforms to prEN ISO 10211 and EN ISO 10077-2 or measured according to EN ISO 12567-1 with the filling elements positioned between the adiabatic lines. The modelling of screws (if present) in the two dimensional calculation shall be performed according to Annex C. Since the heat flow rate is determined between the two adiabatic boundaries, it represents the heat flow through the filling elements, the thermal joint (e.g. mullion/transom) and also the lateral heat flow (edge effects) of the interaction between the two filling elements. Therefore Φtot represents the total heat flow rate that results from making a thermal joint between two filling elements and includes: heat flow rate straight through filling element 1 and filling element 2 (one dimensional heat flow perpendicular to the surface of the filling element); heat flow rate through the thermal joint that is used to connect the two filling elements together (e.g. a frame in a framed curtain wall, a silicone joint in case of structural glazing); lateral and edge heat-flows due to the thermal interaction between the filling elements and the thermal joint and due to the edge constructions of the two individual filling elements (e.g. glass spacer). As in most cases these different heat flows are difficult to separate, and to assign to a specific sub-component of the thermal joint, it is appropriate to split the overall heat flow through a thermal joint into only three parts (see Figure 7a): the heat flow rate ΦFE1 through filling element 1 without the presence of the thermal joint (i.e. the heat flow derived from the centre U-value of filling element 1); the heat flow rate ΦFE2 through filling element 2 without the presence of the thermal joint (i.e. the heat flow derived from the centre U-value of filling element 2); the heat flow rate ΦTJ which is the additional heat flow rate due to making a thermal joint (which includes direct and lateral heat flows of all joint edges and the thermal joint itself excluding the one dimensional heat flow through the filling elements). There are two ways of allowing for the additional heat flow rate ΦTJ, which are equivalent and either approach will yield the same result for the thermal transmittance of the curtain wall. The possibilities are: - consider the heat flow rate ΦTJ in terms of an area-related joint thermal transmittance UTJ; - consider the heat flow rate ΦTJ in terms of a length-related linear joint thermal transmittance ΨTJ. NOTE The thermal transmittance of the joint UTJ or the linear thermal transmittance of the joint ΨTJ includes, in one single parameter, all thermal bridging effects resulting from making a thermal joint between the filling elements. This definition should not be compared with the frame thermal transmittance Uf (e.g. as defined in EN ISO 10077-2 or in the alternative method described in 6.3), which is solely the heat flow rate through the frame excluding the lateral heat flow effects of panels and interaction with the frame. UTJ should not be used to assess condensation risk.
EN 13947:2006 (E) 17 6.2.2.2 Determination of the area-related joint thermal transmittance UTJ
Figure 7a — Definition of the areas when using UTJ (example: glazing, mullion, panel) The heat flow rate ΦTJ, which represents the additional heat flow rate due to making a thermal joint between two filling elements, can be calculated as: ΦTJ = Φtot – (UFE1 AFE1 + UFE2 AFE2) ∆T (1a) where ∆T is the temperature difference between internal and external environments used to simulate the heat transfer. The thermal transmittance of the joint UTJ is calculated as: UTJ = ΦTJ / (A TJ ∆T) (2a) where ATJ is the projected area of the thermal joint; ∆T is the temperature difference between the internal and external environment used for the simulation. 6.2.2.3 Determination of the linear joint thermal transmittance ΨΨΨΨTJ
The definition of the filling element areas is different from the definition in Figure 7a and is as specified in Figure 7b. The calculation of ΦTJ
is according to Equation (1b). The heat flow rate ΦTJ can be calculated as: ΦTJ
= Φtot – (UFE1 A*FE1 + UFE2 A*FE2) ∆T (1b) where ∆T is the temperature difference between inside and outside air used to simulate the heat transfer.
EN 13947:2006 (E) 18
Figure 7b — Definition of the areas when using
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