1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN 674:2011Glass in building Determination of thermal transmittance (U value) Guarded hot plate methodBS EN 674:2011 BRITISH STANDARDNational forewordThis British Standard is
2、the UK implementation of EN 674:2011. It supersedes BS EN 674:1998 which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee B/520/4, Properties and glazing methods.A list of organizations represented on this committee can be obtained on request to its secretary
3、.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. BSI 2011 ISBN 978 0 580 71595 2 ICS 81.040.20 Compliance with a British Standard cannot confer immunity from legal obligations.This British Standard was publis
4、hed under the authority of the Standards Policy and Strategy Committee on 31 July 2011.Amendments issued since publicationDate T e x t a f f e c t e dBS EN 674:2011EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 674 June 2011 ICS 81.040.20 Supersedes EN 674:1997English Version Glass in building
5、 - Determination of thermal transmittance (U value) - Guarded hot plate method Verre dans la construction - Dtermination du coefficient de transmission thermique, U - Mthode de lanneau de gardeGlas im Bauwesen - Bestimmung des Wrmedurchgangskoeffizienten (U-Wert) - Verfahren mit dem Plattengert This
6、 European Standard was approved by CEN on 29 April 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 reference
7、s 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 mem
8、ber 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
9、, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Ma
10、rnix 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 674:2011: EBS EN 674:2011EN 674:2011 (E) 2 Contents Page Foreword 31 Scope 42 Normative references 43 Terms and definitions .54 Basic formula .55 Brief o
11、utline of the measuring procedure .56 Test apparatus .57 Dimensions of the specimens 68 Preparation of the specimens 69 Performance of the measurements710 Evaluation of the results .710.1 Thermal resistance of the multiple glazing .710.2 Declared U Value710.3 Design U value .811 Expression of the re
12、sults 811.1 U values 811.2 Thermal resistance 811.3 Intermediate values .812 Test report 912.1 Information included in the test report 912.2 Identification of each glazing specimen 912.3 Cross section of the specimen .912.4 Results 9Bibliography . 11BS EN 674:2011EN 674:2011 (E) 3 Foreword This docu
13、ment (EN 674:2011) 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 December 2011,
14、and conflicting national standards shall be withdrawn at the latest by December 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.
15、This document supersedes EN 674:1997. 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, Germ
16、any, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 674:2011EN 674:2011 (E) 4 1 Scope This European Standard specifies a measurement method to
17、 determine the thermal transmittance of glazing with flat and parallel surfaces. Structured surfaces, e.g. patterned glass, can be considered to be flat. This European Standard applies to multiple glazing with outer panes which are not transparent to far infrared radiation, which is the case for sod
18、a lime silicate glass products, borosilicate glass and glass ceramics. Internal elements may be 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 thro
19、ugh the spacer of an insulating glass unit or through the window frame are not included. Furthermore energy transfer due to solar radiation is not taken into account. The procedure specified in this European Standard should generally only be considered when the calculation method detailed in EN 673
20、is inappropriate or unsuitable. The document for the calculation of the overall U value of windows, doors and shutters (see 3) gives normative reference to the U value evaluated for the glazing components according to this standard. A vertical position of the glazing is specified. U values evaluated
21、 according to the present standard are used for product comparison as well as for other purposes, in particular for predicting: heat loss through glazing; conduction heat gains in summer; condensation on glazing surfaces; the effects of the absorbed solar radiation in determining the solar factor (s
22、ee 1). Reference should be made to 4, 5, or other European Standards dealing with heat loss calculations for the application of glazing U values determined by this standard. The determination of the thermal transmittance is performed for conditions which correspond to the average situation for glazi
23、ng in practice. 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 12898,
24、Glass in building Determination of the emissivity ISO 8302:1991, Thermal insulation Determination of steady-state thermal resistance and related properties Guarded hot plate apparatus 1) In some countries the symbol k has been used hitherto. BS EN 674:2011EN 674:2011 (E) 5 3 Terms and definitions Fo
25、r the purposes of this standard, 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, which states the steady-state density of heat transfer rate per temperature differen
26、ce between the environmental temperatures on each side, and which is given in watts per square metre Kelvin W/(m2K) 3.2 declared value U value obtained under standardized boundary conditions NOTE See 10.2. 4 Basic formula The U value depends on the thermal resistance of the multiple glazing and on t
27、he external and internal surface heat transfer coefficients according to the relation: iehhRU111+=(1) where R is the thermal resistance of the multiple glazing in square metres Kelvins per Watt WKm /)(2; he is the external surface heat transfer coefficient in Watts per square metre Kelvin WKm /)(2;
28、hiis the internal surface heat transfer coefficient in Watts per square metre Kelvin WKm /)(2. According to this standard, the surface to surface thermal resistance is determined by measurements taken using the guarded hot plate method. Thereupon the declared value is determined according to Equatio
29、n (1) with the values for the internal and external heat transfer coefficients specified in 10.2. 5 Brief outline of the measuring procedure The surface to surface thermal resistance of the multiple glazing is determined by means of the guarded hot plate method laid down in ISO 8302. The recommendat
30、ions of that standard shall be complied with except for variations contained in this standard and for variations resulting from the special structure of the glazing. Within the present context further requirements are necessary, viz. the size of the test specimens and the performance of the measurem
31、ents are laid down to meet special requirements for measuring multiple glazing (see Clause 6 to Clause 12). 6 Test apparatus For the measurement of the thermal resistance of the specimen, the two specimen apparatus is used. Figure 1 gives a general outline of this apparatus including special require
32、ments for the measurement of multiple glazing. BS EN 674:2011EN 674:2011 (E) 6 A square flat plate assembly consisting of a heater and metal surface plates and called the heating unit is sandwiched between two nearly identical specimens. The thermal flux is transferred through the specimens to separ
33、ate square isothermal flat assemblies called the cooling units. The heating unit consists of a separate central metering section, where the unidirectional constant heat flux can be established, surrounded by a guard section separated by a narrow gap. The metering section has dimensions of 500 mm x 5
34、00 mm. The cooling units have surface dimensions as large as those of the heating unit, including the guard heater. To ensure sufficient contact between the specimens and the adjacent surface plates, rubber sponge sheets in the quality of natural rubber with a thickness of about 3 mm shall be used.
35、A minimum of three equally spaced thermocouples shall be positioned on the specimen diagonal on each side to determine the average surface temperatures. Such thermocouples shall have a thickness not exceeding 0,2 mm; the junctions shall be flattened so as not to exceed 0,2 mm and a contact material
36、(e.g. zinc oxide loaded silicon grease or metal tape) shall be used to insure a good thermal contact between the junction and the specimen. The specimens shall be of such a size as to completely cover the heating unit surface. Additional edge insulation and/or auxiliary guard sections are required a
37、s stated in ISO 8302. The glass layers of multiple glazing in contact with the apparatus make critical the correct detection of imbalance across the gap due to the high thermal conductivity of the glass. The installation of imbalance sensors as indicated in Figure 4b) of ISO 8302:1991 is most probab
38、ly the only way of detecting with acceptable accuracy the actual imbalance through the gap when testing multiple glazing, see 2.1.1.3 to 2.1.1.5 of ISO 8302:1991. When a guarded hot plate is intended for tests on multiple glazing, the imbalance error shall be evaluated according to 2.2.1 of ISO 8302
39、:1991, using the thermal conductivity of the glass, i.e. 1 W/(m K), as the specimen thermal conductivity. If the resulting calculated imbalance error is larger than 1 % (instead of the 0,5 % required by 2.1.4.1.1 of ISO 8302:1991), then the imbalance error shall be assessed using the experimental pr
40、ocedure of 2.4.4 of ISO 8302:1991. If the 1 % limit is still exceeded, the gap design and the imbalance detection system shall be reviewed before attempting any test on multiple glazing. 7 Dimensions of the specimens The specimens shall be square and have dimensions of preferably 800 mm x 800 mm wit
41、h a maximum spread ranging from 750 mm x 750 mm to 850 mm x 850 mm. The two specimens needed for the measurement shall be as identical as possible. The difference in thickness between the two specimens measured at the edges shall not be more than 2 %. The surfaces of the specimens shall be flat and
42、parallel. Specimen sizes down to 450 mm x 450 mm may be used if it can be shown that no convection occurs in the gas space and that the errors occurring are not greater than those allowed for the 800 mm x 800 mm arrangement. 8 Preparation of the specimens The sum of the bowing or dishing of the oute
43、r panes in the central area of each specimen shall not exceed 0,5 mm. The control of bowing or dishing effects is performed by cooling down the specimens to 10 C until isothermal equilibrium is reached and by measuring immediately before the specimens are positioned in the test apparatus for the mea
44、surement. BS EN 674:2011EN 674:2011 (E) 7 In the case of excessive bowing, a correction of the thickness of the specimens in the central area may be performed by a corresponding pressure change. In the case of excessive dishing such a correction for gas fillings except air is only allowed if the nee
45、ded correction (by introducing a small volume of air) does not exceed 0,5 mm. 9 Performance of the measurements The measurements shall be taken with the specimens in a vertical position. The measurements shall be performed at a mean temperature of each specimen of (10 0,5) C. The mean temperature di
46、fference between the hot and the cold surface of the specimens shall be (15 0,5) K. 10 Evaluation of the results 10.1 Thermal resistance of the multiple glazing The thermal resistance R is calculated according to the equation: =)TA(TR212m2K/W (2) where is the average power supplied to the central se
47、ction of the heating unit in watts (W); T1is the average hot side temperature of the specimens in Kelvins (K); T2is the average cold side temperature of the specimens in Kelvins (K); A is the metering area in square metres (m2). 10.2 Declared U Value The declared U value is calculated according to E
48、quation (1). For multiple glazing without a coating having an emissivity lower than 0,837 on the outer surfaces, the following standardized values for the surface heat transfer coefficients are used: internal heat transfer coefficient: hi = 7,7 W/(m2K); external heat transfer coefficient: he= 25 W/(
49、m2K). BS EN 674:2011EN 674:2011 (E) 8 For a multiple glazing with a coating having an emissivity lower than 0,837 on the surface adjacent to the inner room, the standardized value of hiis modified according to the equation: 83701463,h+=iW/(m2K) (3) where is the corrected emissivity of the surface; 0,837 is the corrected emissivity of uncoated soda lime silicate glass and borosilicate glass. The corrected emissivity shall be dete
