Glass in building - Determination of the emissivity

This draft European Standard specifies a procedure for determining the emissivity at room temperature of the surfaces of glass, coated glass and other glazing components not transparent in the far infrared. The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the standard temperature of 283 K in the determination of the U value and of the total solar transmittance of glazing according to B.1 to B.5.

Glas im Bauwesen - Bestimmung des Emissionsgrades

Dieses Dokument legt ein Verfahren zur Bestimmung des Emissionsgrades der Oberfläche von Glas und beschichtetem Glas bei Raumtemperatur fest.
Der Emissionsgrad wird zur Bestimmung des Wärmeübergangs durch Strahlung von Oberflächen bei der Normaltemperatur von 283 K bei Ermittlung des U Wertes und des solaren Gesamtdurchlassgrades von Verglasungen nach [1] bis [4] benötigt.
Das Verfahren, das auf spektralphotometrischen Messungen des gerichteten Anteils der Reflexion bei einem fast senkrechten Einfall auf im Infrarotbereich undurchlässige Werkstoffe beruht, ist nicht auf Verglasungs¬elemente anwendbar, die mindestens eine der folgenden Eigenschaften besitzen:
a)   raue oder strukturierte Oberflächen, bei denen die einfallende Strahlung streuend reflektiert wird;
b)   gekrümmte Oberflächen, bei denen die einfallende Strahlung gerichtet in Winkeln reflektiert wird, die ungeeignet sind, den Detektor bei Verwendung von üblichen Zusatzteilen zur Bestimmung des Reflexionsgrades zu erreichen;
c)   im Infrarotbereich durchlässige Werkstoffe.
Es kann jedoch unter gewissen Bedingungen auf alle Verglasungselemente angewendet werden, voraus-gesetzt ihre Oberflächen sind eben, nicht streuend (siehe 3.1.6) und im Infrarotbereich undurchlässig (siehe 3.1.7).
Obwohl Messungen des Durchlassgrades in diesem Dokument erfasst sind, sind sie im Rahmen dieses Dokuments lediglich zur Prüfung, ob die Probe im Infrarotbereich undurchlässig ist, erforderlich (siehe 3.1.7). Ist die Probe im Infrarotbereich durchlässig, ist dieses Dokument nicht anwendbar.
Die Vorgängerausgabe dieses Dokuments beruhte auf der Durchführung von Messungen des Reflexions-grades mit dispersiven Zweistrahl-Infrarot-Spektralphotometern, mit denen die Messung über fast den gesamten Spektralbereich eines schwarzen Körpers bei der Standard-Referenztemperatur und die Ermittlung des Emissionsgrades mit dem 30 Ordinaten-Verfahren möglich ist [6]. Diese Ausgabe berück-sichtigt Fourier-Transformations-Infrarotspektrometer (FTIR), wenn der Spektralbereich begrenzt ist. Sie beschreibt ein Verfahren, bei dem Spektralphotometer zur Bestimmung des Emissionsgrades genutzt werden können, wenn sie in der Lage sind, bis zum 24. Ordinatenpunkt zu messen und ein Kriterium des Rauschens für diesen Spektralbereich erfüllen. Sie ermöglicht die Einbeziehung von Daten vom 25. bis zum 30. Ordinatenpunkt. Ein neuer informativer Anhang (Anhang D), der die Grundsätze für Zusatzteile zur Messung des absoluten Reflexionsgrades beschreibt, wurde in dieser Ausgabe ergänzt. Diese Zusatzteile sind dafür vorgesehen, durch qualifiziertes Personal verwendet zu werden.
Da es sich bei FTIR-Spektralphotometern im Gegensatz zu dispersiven Spektralphotometern, die Zweistrahl¬geräte sind (und die daher in der Lage sind, Messgerätedrift zu korrigieren), um Einstrahlgeräte handelt, wurde von dem auf europäischer Ebene finanzierten Projekt THERMES ein Verfahren zur Korrektur der Drift entwickelt. Dieses Verfahren ist in [10] und [16] beschrieben. In [14] werden andere Kategorien von Ordinatenabweichungen durch FTIR-Spektralphotometer behandelt.

Verre dans la construction - Détermination de l'émissivité

Le présent document définit la procédure pour déterminer l’émissivité à température ambiante des surfaces de verre ou de verre à couche.
L’émissivité est nécessaire pour prendre en compte le transfert thermique par rayonnement des surfaces à la température normale de 283 K dans la détermination de la valeur de U et du facteur de transmission solaire totale des vitrages selon [1] à[4].
Le mode opératoire, qui se base sur des mesurages spectrophotométriques du facteur de réflexion régulière à incidence proche de la normale sur des matériaux non transparents dans le domaine infrarouge, n’est pas applicable à des composants de vitrage ayant au moins l’une des caractéristiques suivantes :
a)   surfaces rugueuses ou structurées où le rayonnement incident est reflété de manière diffuse ;
b)   surfaces courbes où le rayonnement incident est reflété de manière régulière à des angles ne permettant pas d’atteindre le détecteur en utilisant des dispositifs de réflexion régulière ;
c)   transparence à l’infrarouge.
Le mode opératoire peut néanmoins être appliqué avec précaution à n’importe quel composant de vitrage si ses surfaces sont plates et non diffusantes (voir 3.1.6) et si elles sont non transparentes dans le domaine infrarouge (voir 3.1.7).
Bien que les mesurages du facteur de transmission soient couverts par la présente norme, ils ne sont nécessaires que pour vérifier si l’échantillon est non transparent dans le domaine infrarouge dans le cadre de la présente norme (voir 3.1.7). Si l’échantillon est transparent dans le domaine infrarouge, la présente norme ne s’applique pas.
La version précédente de la présente norme était basée sur le recours à des mesurages du facteur de réflexion à l’aide de spectrophotomètres infrarouges dispersifs à double faisceau capables de mesurer sur presque tout le domaine spectral d’un corps noir à la température de référence normale et de déterminer l’émissivité par la méthode des 30 ordonnées [6]. La présente version tient compte des spectrophotomètres infrarouges à transformée de Fourier (IRTF) lorsque le domaine spectral est limité. Elle décrit une méthode dans laquelle des spectrophotomètres peuvent être utilisés pour déterminer l’émissivité si ceux-ci sont capables de mesurer jusqu’au 24e point d’ordonnée et s’ils satisfont à un critère de bruit pour ce domaine spectral. Cela permet l’intégration de données du 25e point d’ordonnée au 30e point d’ordonnée. Une nouvelle annexe informative (Annexe D) décrivant les principes des dispositifs de réflexion absolue a été ajoutée à cette version. Il convient que l’utilisation de ces dispositifs soit réservée à un personnel qualifié.
Comme les spectrophotomètres IRTF sont des instruments à simple faisceau, au contraire des spectrophotomètres dispersifs qui sont des instruments à double faisceau (et sont ainsi capables corriger la dérive instrumentale), un mode opératoire a été développé par le projet THERMES, financé par l’UE, pour corriger cette dérive. Ce mode opératoire est décrit en [10 et [16]. D’autres catégories d’erreurs d’ordonnée survenant lors de l’utilisation de spectrophotomètres IRTF sont abordées en [14].

Steklo v gradbeništvu - Določanje emisivnosti

Ta osnutek evropskega standarda določa postopek za določanje emisivnosti steklenih površin, stekla z nanosom in drugih komponent zasteklitve pri sobni temperaturi, ki niso prosojni v dolgovalovnem spektru infrardeče svetlobe. Emisivnost je potrebna za upoštevanje prenosa toplote s površin zaradi sevanja pri standardni temperaturi 283 K pri postopku določanja vrednosti U in skupne sončne prepustnosti zasteklitve v skladu s točkami od B.1 do B.5.

General Information

Status
Published
Public Enquiry End Date
19-Dec-2017
Publication Date
07-May-2019
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
21-Mar-2019
Due Date
26-May-2019
Completion Date
08-May-2019

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SLOVENSKI STANDARD
SIST EN 12898:2019
01-junij-2019
Nadomešča:
SIST EN 12898:2001
Steklo v gradbeništvu - Določanje emisivnosti
Glass in building - Determination of the emissivity
Glas im Bauwesen - Bestimmung des Emissionsgrades
Verre dans la construction - Détermination de l'émissivité
Ta slovenski standard je istoveten z: EN 12898:2019
ICS:
81.040.20 Steklo v gradbeništvu Glass in building
SIST EN 12898:2019 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 12898:2019
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SIST EN 12898:2019
EN 12898
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2019
EUROPÄISCHE NORM
ICS 81.040.20 Supersedes EN 12898:2001
English Version
Glass in building - Determination of the emissivity

Verre dans la construction - Détermination de Glas im Bauwesen - Bestimmung des Emissionsgrades

l'émissivité
This European Standard was approved by CEN on 14 December 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12898:2019 E

worldwide for CEN national Members.
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EN 12898:2019 (E)
Contents Page

European foreword ....................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 5

2 Normative references .................................................................................................................................... 5

3 Terms, definitions and abbreviations ..................................................................................................... 5

3.1 Terms and definitions ................................................................................................................................... 5

3.2 Abbreviations ................................................................................................................................................... 7

4 Brief outline of the procedure to determine corrected emissivity ............................................... 7

5 Spectral normal reflectance measurements and calculations ........................................................ 8

5.1 Sample preparation ........................................................................................................................................ 8

5.2 Spectral normal reflectance measurements ......................................................................................... 8

5.2.1 General ................................................................................................................................................................ 8

5.2.2 Test apparatus.................................................................................................................................................. 8

5.2.3 Measurement .................................................................................................................................................... 9

5.2.4 Accuracy ............................................................................................................................................................. 9

5.3 Interpolation ..................................................................................................................................................... 9

5.4 Determination of normal reflectance ...................................................................................................... 9

5.4.1 General ................................................................................................................................................................ 9

5.4.2 Calculation method ...................................................................................................................................... 10

5.4.3 Noise criterion ............................................................................................................................................... 10

6 Calculation of total normal emissivity and corrected emissivity ............................................... 11

6.1 Total normal emissivity ............................................................................................................................. 11

6.2 Corrected emissivity ................................................................................................................................... 11

7 Test report ...................................................................................................................................................... 11

Annex A (normative) Table for determining total normal reflectance ................................................... 13

Annex B (informative) Procedures to improve the accuracy of spectral normal reflectance

measurements ............................................................................................................................................... 14

B.1 General ............................................................................................................................................................. 14

B.2 Spectrophotometer ..................................................................................................................................... 14

B.3 Reference mirror .......................................................................................................................................... 14

B.4 Reflectance accessory ................................................................................................................................. 14

Annex C (informative) Transmittance and diffuse reflectance measurements and calculation

of total normal transmittance ................................................................................................................. 15

C.1 Transmittance measurements ................................................................................................................ 15

C.2 Calculation of total normal transmittance .......................................................................................... 15

C.3 Diffuse reflectance measurements ........................................................................................................ 15

Annex D (informative) Determination of absolute reflectance by comparing the energy of

the beam reflected from the sample to that of the incident beam ............................................. 16

D.1 General ............................................................................................................................................................. 16

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D.2 VW absolute reflectance accessory (also known as a “Strong-type” accessory) ................... 16

D.3 IV absolute reflection accessories .......................................................................................................... 19

D.4 Uncertainty ..................................................................................................................................................... 20

Bibliography ................................................................................................................................................................. 21

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SIST EN 12898:2019
EN 12898:2019 (E)
European foreword

This document (EN 12898:2019) 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 September 2019, and conflicting national standards

shall be withdrawn at the latest by September 2019.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN 12898:2001.
The main changes compared to the previous edition are the following:

— introduction of a method to determine the emissivity using Fourier Transform Infrared (FTIR)

spectrophotometers where the spectral range is limited;
— provision of a new method for the calculation of corrected emissivity; and
— clarification of rounding rules for normal emissivity.

In this version, the procedures covering transmittance and diffuse reflectance measurements and

calculation of total normal transmittance have been moved to an informative annex (Annex C).

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
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EN 12898:2019 (E)
1 Scope

This document specifies a procedure for determining the emissivity at room temperature of the

surfaces of glass and coated glass.

The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the

standard temperature of 283 K in the determination of the U value and of the total solar transmittance

of glazing according to [1] to [4].

The procedure, being based on spectrophotometric regular reflectance measurements at near normal

incidence on materials that are non-transparent in the infrared region, is not applicable to glazing

components with at least one of the following characteristics:

a) with rough or structured surfaces where the incident radiation is diffusely reflected;

b) with curved surfaces where the incident radiation is regularly reflected at angles unsuitable to

reach the detector while using regular reflectance accessories;
c) infrared transparent.

However, it can be applied with caution to any glazing component provided its surfaces are flat and

non-diffusing (see 3.1.6) and it is non-transparent in the infrared region (see 3.1.7).

Although transmittance measurements are included in this document, they are only necessary to check

if the sample is non-transparent in the infrared region in the context of this document (see 3.1.7). If the

sample is transparent in the infrared region, this document is not applicable.

The previous version of this document was based on the use of reflectance measurements using double

beam dispersive infrared spectrophotometers capable of measuring over almost the entire spectral

range of a black body at the standard reference temperature and determining the emissivity by the 30

ordinate method [6]. This version takes account of Fourier Transform Infrared (FTIR)

spectrophotometers where the spectral range is limited. It describes a method whereby

spectrophotometers can be used to determine emissivity if they are able to measure up to the 24th

ordinate point and if they satisfy a noise criterion for this spectral range. It allows the inclusion of data

from the 25th ordinate point up to the 30th ordinate point. A new informative annex (Annex D)

describing the principles of absolute reflection accessories has been added to this version. These

accessories are intended to be used by qualified personnel.

As FTIR spectrophotometers are single beam instruments as opposed to dispersive spectrophotometers

which are double beam instruments (and thus able to correct for instrument drift), a procedure was

developed by the European funded project, THERMES, to correct for drift. This procedure is described

in [10] and [16]. Other categories of ordinate errors using FTIR spectrophotometers are discussed in

[14].
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviations
3.1 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 http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
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EN 12898:2019 (E)
3.1.1
infrared
5 µm to 50 µm spectral range
3.1.2
emissivity

ratio of the energy emitted by a given surface at a given temperature to that of a perfect emitter (black

body with normal and corrected emissivity = 1,0) at the same temperature

Note 1 to entry: Two different definitions of emissivity should theoretically be used to describe radiation

exchange between:
a) glass surfaces facing each other in multiple glazing (effective emissivity);
b) a glass surface facing a room (hemispherical emissivity).

However, in practice numerical differences were found to be negligibly small (see [5]). Thus, corrected emissivity

is used to describe both types of heat exchange with a close approximation.
3.1.3
specular reflectance
regular reflectance

reflectance according to the laws of geometrical optics, without the diffuse component

Note 1 to entry: The measurement arrangement should be such that the instrument beam reaches the detector

after being specularly reflected on the surface of the sample (reference mirror) at an angle of incidence ≤ 10°.

3.1.4
diffuse reflectance

reflectance not containing any regular component, due to rough surfaces and/or transparent materials

containing inhomogeneous particles
3.1.5
total reflectance
sum of regular and diffuse reflectance
3.1.6
non-diffusing glazing component

glazing component with a diffuse reflectance ≤ 0,05, measured at the near infrared wavelength of 2 µm

(see Annex C)

Note 1 to entry: The purpose of this measurement is to ensure that the sample is non-diffusing in the

measurement range. Most integrating spheres sold with visible/near infrared spectrophotometers have a port

designed to measure diffuse reflectance. Diffuse reflectance measurements in the infrared range are difficult to

perform.
3.1.7
glazing component non-transparent in the infrared region

glazing component with a total normal transmittance ≤ 0,05 at 283 K, measured spectrophotometrically

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3.2 Abbreviations
For the purposes of this document, the following abbreviations apply.
ε total corrected emissivity at 283 K
ε total normal emissivity at 283 K

E reading of the spectrophotometer with the sample placed on the sample support of the

reflectance accessory
E the instrument reading without placing anything on the sample support
E the instrument reading with the reference mirror replacing the sample
R total normal reflectance at 283 K
R (λ ) spectral normal reflectance at wavelength λ
i i
R spectral normal reflectance of the reference mirror
n,st
T (λ ) spectral normal transmittance at wavelength λ
i i
T total normal transmittance at 283 K
N number of measurement points to determine total normal reflectance
4 Brief outline of the procedure to determine corrected emissivity

The procedure for determining the corrected emissivity of coated glass surfaces includes the following

steps:

a) the spectral regular reflectance of a glazing component non-transparent in the infrared region at

near normal incidence, R (λ), shall be determined with an infrared spectrophotometer in the

range (5 to 50) µm (see Clause 5);

b) total normal reflectance at 283 K, R , shall be calculated using the integration procedure specified

in 5.4 from the corresponding spectral reflectance values measured according to step a);

c) total normal emissivity, ε , shall be calculated from the total normal reflectance as specified

in Clause 6;

d) the corresponding corrected emissivity, ε, shall be determined from the normal emissivity in

accordance with Formula (6).

NOTE 1 The corrected emissivity, calculated from the normal emissivity with the help of a multiplicative

correction factor, takes into account the effect of the angular distribution of emissivity in the heat transfer

calculations of glazing according to [1] to [4].

NOTE 2 Both the normal and the corrected emissivity are total emissivities at 283 K, i.e. they are integrated

over the relevant spectral range using as a weighting function Planck's radiation function for a black body at 283 K

(see [6]).

For uncoated soda lime silicate glass surfaces or for soda lime silicate glass surfaces with coatings

which have no effects on the emissivity, the normal emissivity to be used in the calculations specified in

[1] to [4] shall be 0,89 (see [7]). For all other glazing materials or components it shall be measured.

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EN 12898:2019 (E)

NOTE 3 With reasonable confidence ε = 0,89 can be used for uncoated borosilicate glass, glass ceramics,

alkaline earth silicate glass and alumino silicate glass (see [7]).

NOTE 4 For temperatures included in the range 253 K to 313 K emissivity is not strongly dependent on the

temperature (see [7] and [8]).
5 Spectral normal reflectance measurements and calculations
5.1 Sample preparation

Samples shall be of a size suitable for being inserted into the sample compartment or placed on the

reflectance accessory. In doing so, care shall be taken to ensure that the portion of the coated surface

probed by the instrument beam is free of damage or any surface contamination. The procedures

recommended by the producer for storing the samples and cleaning their surfaces shall be followed.

The sample shall be supported in a suitable way to ensure that the measuring spot during transmittance

and reflectance measurements falls on a flat part.
5.2 Spectral normal reflectance measurements
5.2.1 General

The spectral regular reflectance curve of the sample at near normal incidence between 5 µm and 50 µm

shall be determined with an infrared spectrophotometer equipped with a specular reflectance

accessory at near normal incidence.
5.2.2 Test apparatus
The following equipment shall be used for the measurements:

— a spectrophotometer covering the spectral range 5 µm to 50 µm. Alternatively, a

spectrophotometer that covers the spectral range from 5 µm to a wavelength less than 50 µm can

be used as long as it is capable of measuring up to the 24th point (23,3 µm) and satisfying the noise

criterion (see 5.4.3) for all points up to the 24th point inclusive;

— a reference mirror (free of surface scratches and contamination, see [6], [8] and [9]) whose

spectral regular reflectance at near normal incidence Rn,st (λ) shall be traceable to a standard

material from a metrological laboratory [15];

— a specular reflectance accessory consisting of a suitable array of mirrors and a sample support.

When the accessory is placed in the sample compartment of the spectrophotometer and the sample

(or reference mirror) placed on the sample support, the instrument beam reaches the detector

after being specularly reflected on the surface of the sample (reference mirror) at an angle of

incidence ≤ 10°.

As an alternative, Annex D provides a method for determining absolute reflectance by comparing the

energy of the beam reflected from the sample to that of the incident beam. However, these accessories

can be difficult to align and should be used with caution.
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5.2.3 Measurement

The spectral regular reflectance curve of the sample at near normal incidence shall be determined with

the relative method. The following measurements are required to determine the spectral normal

reflectance of the sample Rn (λi) at each wavelength λi reported in Table A.1 of Annex A:

— E the instrument reading with the sample placed on the sample support of the reflectance

accessory;

— E the instrument reading with the standard reference mirror replacing the sample;

— E the instrument reading without placing anything on the sample support.
These wavelengths are selected at the centre of equal energy wavelength in
...

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