SIST EN ISO 12572:2002
(Main)Hygrothermal performance of building materials and products - Determination of water vapour transmission properties (ISO 12572:2001)
Hygrothermal performance of building materials and products - Determination of water vapour transmission properties (ISO 12572:2001)
This standard specifies a method based on cup tests for determining the water vapour permeance of building products and the water vapour permeability of building materials under isothermal conditions. Different sets of test conditions are specified.
The general principles are applicable to all hygroscopic and non hygroscopic building materials and products, including those with facings and integral skins. Annexes give details of test methods suitable for different material types. This standard is not applicable in the case of test specimens with water vapour diffusion-equivalent air layer thickness values less than 0,1 m, as a result of increasing uncertainty in the measurement results. If the measured water vapour diffusion-equivalent air layer thickness is greater than 1500 m the material can be considered impermeable.
The results obtained by this method are suitable for design purposes, production control and for inclusion in product specifications.
Wärme- und feuchtetechnisches Verhalten von Baustoffen und Bauprodukten - Bestimmung der Wasserdampfdurchlässigkeit (ISO 12572:2001)
Diese Norm legt ein Verfahren zur Bestimmung des Wasserdampfdiffusions-Durchlasskoeffizienten von Bauprodukten und des Wasserdampfdiffusionsleitkoeffizienten von Baustoffen unter isothermischen Bedingungen fest, das auf Prüfungen mit Prüfgefäßen basiert. Verschiedene Prüfbedingungen werden festgelegt.
Die allgemeinen Prinzipien gelten für alle hygroskopischen und nicht hygroskopischen Baustoffe und -produkte einschließlich solcher Stoffe und Produkte mit Beschichtungen oder Häuten. Einzelheiten zu Prüfverfahren, die für einzelne Stoffarten geeignet sind, sind in den Anhängen angegeben. Aufgrund der zunehmenden Messunsicherheit gilt diese Norm nicht für Probekörper mit einer wasserdampfdiffusionsäquivalenten Luftschichtdicke geringer als 0,1 m. Übersteigt die gemessene wasserdampfdiffusionsäquivalente Luftschichtdicke 1500 m, gilt der Stoff als wasserdampfundurchlässig.
Die Ergebnisse, die man nach diesem Verfahren erhält, sind geeignet für die Bemessung, zur Produktionskontrolle und zur Aufnahme in Produktspezifikationen.
Performance hygrothermique des matériaux et produits pour le bâtiment - Détermination des propriétés de transmission de la vapeur d'eau (ISO 12572:2001)
La présente norme spécifie une méthode basée sur des essais en coupelle pour déterminer la perméance a la vapeur d'eau des produits pour le bâtiment ainsi que la perméabilité a la vapeur d'eau des matériaux pour le bâtiment dans des conditions isothermes. Différentes séries de conditions d'essai sont spécifiées.
Les principes généraux sont applicables a tous les matériaux et produits de bâtiment hygroscopiques et non hygroscopiques, y compris ceux qui possedent des parements et des revetements intégrés. Les annexes fournissent des détails sur des méthodes d'essai convenant pour différents types de matériaux. La présente norme ne s'applique pas dans le cas d'éprouvettes dont l'épaisseur d'air équivalente pour la diffusion de la vapeur d'eau est inférieure a 0,1 m, du fait de l'incertitude croissante sur les résultats de mesure. Si l'épaisseur d'air équivalente mesurée est supérieure a 1500 m, le matériau peut etre considéré comme imperméable.
Les résultats obtenus par cette méthode peuvent etre utilisés pour la conception, pour le contrôle de la production et pour insertion dans les spécifications de produits.
Higrotermalno obnašanje gradbenih materialov in proizvodov - Ugotavljanje lastnosti za prehod vodne pare (ISO 12572:2001)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 12572:2002
01-marec-2002
Higrotermalno obnašanje gradbenih materialov in proizvodov - Ugotavljanje
lastnosti za prehod vodne pare (ISO 12572:2001)
Hygrothermal performance of building materials and products - Determination of water
vapour transmission properties (ISO 12572:2001)
Wärme- und feuchtetechnisches Verhalten von Baustoffen und Bauprodukten -
Bestimmung der Wasserdampfdurchlässigkeit (ISO 12572:2001)
Performance hygrothermique des matériaux et produits pour le bâtiment - Détermination
des propriétés de transmission de la vapeur d'eau (ISO 12572:2001)
Ta slovenski standard je istoveten z: EN ISO 12572:2001
ICS:
91.100.01 Gradbeni materiali na Construction materials in
splošno general
91.120.30 =DãþLWDSUHGYODJR Waterproofing
SIST EN ISO 12572:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 12572:2002
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SIST EN ISO 12572:2002
EUROPEAN STANDARD
EN ISO 12572
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2001
ICS 91.120.10
English version
Hygrothermal performance of building materials and products -
Determination of water vapour transmission properties (ISO
12572:2001)
Performance hygrothermique des matériaux et produits Wärme- und feuchtetechnisches Verhalten von Baustoffen
pour le bâtiment - Détermination des propriétés de und Bauprodukten - Bestimmung der
transmission de la vapeur d'eau (ISO 12572:2001) Wasserdampfdurchlässigkeit (ISO 12572:2001)
This European Standard was approved by CEN on 18 October 2000.
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 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 Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 12572:2001 E
worldwide for CEN national Members.
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EN ISO 12572:2001
Contents
Page
Foreword 3
1 Scope 4
2 Normative references 4
3 Definitions, symbols and units 5
4 Principle 7
5 Apparatus 7
6 Test specimens 8
7 Procedure 10
8 Calculation and expression of results 13
9 Accuracy of measurement 15
10 Test report 17
Annex A (normative) Methods suitable for self supporting materials 19
Annex B (normative) Methods suitable for loose fills 21
Annex C (normative) Methods suitable for membranes and foils 23
Annex D (normative) Methods suitable for mastics and sealants 24
Annex E (normative) Methods suitable for paint, varnishes, etc. 26
Annex F (normative) Correction for the effect of a masked edge of a specimen 27
Annex G (normative) Correction for resistance of air layers 28
Annex H (informative) Weighing repeatability, weighing interval and specimen size needed
to achieve desired accuracy 29
Annex J (informative) Conversion table for water vapour transmission units 30
ANNEX ZA (normative) Normative references to international publications with their
relevant European publications 31
ANNEX ZB (informative) Informative references to international publications with their
relevant European publications 31
Bibliography 32
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EN ISO 12572:2001
Foreword
The text of EN ISO 12572:2001 has been prepared by Technical Committee CEN/TC 89
"Thermal performance of buildings and building components", the secretariat of which is held
by SIS, in collaboration with Technical Committee ISO/TC 163 "Thermal insulation".
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 2001, and conflicting
national standards shall be withdrawn at the latest by December 2001.
This standard is one of a series of standards which specify test methods for the thermal and
moisture related properties of building materials and products.
The European publications to be used instead of the International Standards listed in clause 2
are given in normative annex ZA, which is an integral part of this European Standard.
The annexes A, B, C, D, E, F, G and ZA are normative.
The annexes H, J and ZB are informative.
According to the CEN/CENELEC Internal Regulations, the national standards organizations
of the following countries are bound to implement this European Standard: Austria, Belgium,
Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,
Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United
Kingdom.
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EN ISO 12572:2001
1 Scope
This standard specifies a method based on cup tests for determining the water vapour
permeance of building products and the water vapour permeability of building materials under
isothermal conditions. Different sets of test conditions are specified.
The general principles are applicable to all hygroscopic and non hygroscopic building
materials and products, including those with facings and integral skins. Annexes give details
of test methods suitable for different material types. This standard is not applicable in the
case of test specimens with water vapour diffusion-equivalent air layer thickness values less
than 0,1 m, as a result of increasing uncertainty in the measurement results. If the measured
water vapour diffusion-equivalent air layer thickness is greater than 1500 m the material can
be considered impermeable.
The results obtained by this method are suitable for design purposes, production control and
for inclusion in product specifications.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions
of any of these publications apply to this European standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).
ISO 9346 Thermal insulation - Mass transfer - Physical quantities and definitions
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EN ISO 12572:2001
3 Definitions, symbols and units
3.1 Terms and definitions
For the purposes of this standard, the terms and definitions given in ISO 9346 and the
following apply.
3.1.1
density of water vapour flow rate
mass of water vapour transferred through the specimen per area and per time
3.1.2
homogeneous material
material with properties likely to affect the transmission of water vapour which do not vary
on a macroscopic scale
3.1.3
water vapour permeance
density of water vapour flow rate divided by the water vapour pressure difference between the
two specimen faces
3.1.4
water vapour resistance
reciprocal of water vapour permeance
3.1.5
water vapour permeability
product of the water vapour permeance and the thickness of a homogeneous specimen
NOTE Water vapour permeability can only be calculated for specimens of a
homogeneous material.
3.1.6
water vapour resistance factor
water vapour permeability of air divided by that of the material concerned
NOTE The water vapour resistance factor indicates how much greater the resistance
of the material is compared to an equally thick layer of stationary air at the same
temperature.
3.1.7
water vapour diffusion-equivalent air layer thickness
thickness of a motionless air layer which has the same water vapour resistance as the
specimen
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EN ISO 12572:2001
3.2 Symbols and units
Symbol Quantity Unit
2
A area of specimen m
G water vapour flow rate through specimen kg/s
R gas constant for water vapour = 462
Nm/(kgK)
v
S hydraulic diameter of specimen m
T thermodynamic temperature K
2
W water vapour permeance with respect to partial
kg/(m sPa)
p
vapour pressure
2
Z water vapour resistance with respect to partial m sPa/kg
p
vapour pressure
D mean thickness of specimen m
2
g density of water vapour flow rate
kg/(m s)
l diameter of circle or side of square specimen m
m mass of specimen and cup assembly kg
p barometric pressure hPa
p standard barometric pressure = 1013,25 hPa
0
s water vapour diffusion-equivalent air layer m
d
thickness
t time s
water vapour pressure difference across specimen Pa
p
v
water vapour permeability with respect to partial
kg/(msPa)
p
vapour pressure
water vapour permeability of air with respect to
kg/(msPa)
a
partial vapour pressure
water vapour resistance factor -
Celsius temperature
C
relative humidity -
NOTE The above units comply with ISO 9346; a conversion table to other units
commonly used in permeability measurements is given in annex J.
3.3 Subscripts
Subscript Denoting
I interval
r repeatability
aair
c corrected for air layer
f film
j joint
m membrane
me masked edge
s specimen
ttotal
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EN ISO 12572:2001
4 Principle
The test specimen is sealed to the open side of a test cup containing either a desiccant (dry
cup) or an aqueous saturated solution (wet cup). The assembly is then placed in a temperature
and humidity controlled test chamber. Because of the different partial vapour pressure
between the test cup and the chamber, a vapour flow occurs through permeable specimens.
Periodic weighings of the assembly are made to determine the rate of water vapour
transmission in the steady state.
5 Apparatus
a) Test cups resistant to corrosion from the desiccant or salt solutions they contain; typically
cups are made of glass or metal.
The design of cups suitable for testing various different types of materials is described in
annexes A to E.
NOTE Circular cups can be easier to seal and transparent cups allow better control of
salt solutions.
b) For certain cups and sealing methods (see annex A), a template, with shape and size
corresponding to that of the test cup, is used when applying the sealant to give a sharply
defined, reproducible test area. The template shall have an area of at least 90 % of the
specimen to limit non-linear vapour flow.
c) Measuring instruments capable of determining specimen thickness with accuracy required
in 7.2.
d) Analytical balance, capable of weighing the test assembly with the repeatability needed
for the required accuracy. Wherever possible a balance of 0,001 g resolution shall be
used. For heavy test assemblies a balance resolution of 0,01 g may be sufficient. See
annex H for information linking the balance resolution to the duration of test.
NOTE The factors that affect the necessary accuracy of measurement are discussed in
annex H.
e) Constant temperature, constant humidity chamber, capable of being maintained within
3 % relative humidity around the set point relative humidity and 0,5 K around the set
point temperature. In order to ensure uniform conditions throughout the chamber, the air
shall be stirred so as to obtain velocities between 0,02 m/s and 0,3 m/s. If highly
permeable materials are being tested, means should be provided to measure the air speed
directly over the upper surface of the specimen - see annex G.
f) Suitable sensors and a logging system to continuously record the temperature, relative
humidity and, if necessary, the barometric pressure within the test chamber. The sensors
shall be calibrated at regular intervals.
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EN ISO 12572:2001
g) Sealant, which is impermeable to water vapour, does not undergo physical or chemical
changes during the test and does not cause physical or chemical changes to the specimen.
NOTE Examples of sealants suitable for specific materials, if necessary, are listed in
the appropriate annex.
6 Test specimens
6.1 General principles for preparation of test specimens
The test specimens shall be representative of the product. If the product has natural skins or
integral facings, these may be included in the test specimen, but they shall be removed if it is
intended to measure the permeability of the core material. If the skins or facings are different
on the two sides, specimens shall be tested with vapour flow in the direction of the intended
use. If the direction of flow is not known, duplicate specimens shall be prepared and tests
carried out for each direction of flow. Unless the product to be tested in isotropic, the test
specimens shall be cut so that the parallel faces are normal to the direction of vapour flow of
the product in use.
Specimen preparation shall not involve methods which damage the surface in ways which
affect the flow of water vapour.
6.2 Dimensions of test specimens
6.2.1 Shape and fit
Test specimens shall be cut to correspond with the dimensions of the chosen test assembly -
see annexes A to E.
6.2.2 Exposed area
The diameter of a circular specimen or the side of a square specimen shall be at least twice the
specimen thickness. The exposed area (the arithmetic mean of the upper and lower free
2
surface areas) shall be at least 0,005 m . The upper and lower free surface areas shall not
differ by more than 3 % of the mean in the case of homogeneous materials, and by no more
than 10 % in the case of other materials.
6.2.3 Thickness of test specimens.
Whenever possible, the thickness of the specimen shall be that of the product in use. In the
case of homogeneous materials, if the thickness exceeds 100 mm, this may be reduced by
cutting. In the case of non homogeneous materials, such as concrete containing aggregates, the
thickness should be at least three times (and preferably five times) the largest particle size.
If a material contains macroscopic formed voids, the solid material should be tested and the
resistance of the whole material calculated from the proportions of solid to air space assuming
one dimensional vapour flow.
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EN ISO 12572:2001
If it is necessary to test a product so thick that the available test cups do not have an area large
enough to comply with 6.2.2, the product may, only as a last resort, be sliced. In this case, all
slices shall be tested and the results reported.
NOTE This procedure may lead to significant inaccuracies, especially when wet cup
tests are carried out on hygroscopic materials.
6.3 Number of test specimens
2
If the specimen area is less than 0,02 m , a minimum of five specimens shall be tested,
otherwise a minimum of three specimens shall be tested.
6.4 Conditioning of test specimens
Before testing, the test specimens shall be stored at (23 5) C, (50 5) % relative humidity
for a period long enough for their weight to stabilise so that three successive daily
determinations of their weight agree to within 5 %.
NOTE This period will vary from a few hours in the case of some insulating materials
to 3 - 4 weeks or more for massive hygroscopic materials and products. Wet field
specimens may be dried before conditioning using the methods specified in
ISO 12570, Hygrothermal performance of building materials and products -
Determination of moisture content by drying at elevated temperature.
A period of conditioning is not necessary in the case of plastic membranes.
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EN ISO 12572:2001
7 Procedure
7.1 Test conditions
Select the desired test environment from the sets of conditions given in Table 1.
Table 1 - Test conditions
Tolerances
Set Condition Temperature Relative humidity
C - % RH C %
Dry state Wet state
Set point Tolerance Set point Tolerance
A 23 - 0/50 0+ 3 50
23 0,5 3
B 23 - 0/85 0+ 3 85
23 0,5 3
C 23 - 50/93 50 93
23 0,5 3 3
D 38 - 0/93 38 0,5 0+ 3 93 3
NOTE 1 ‘Dry cup’ tests (condition A) give information about the performance of
materials at low humidities when moisture transfer is dominated by vapour diffusion.
‘Wet cup’ tests (condition C) give guidance about the performance of materials under
high humidity conditions. At higher humidities, the material pores start to fill with
water; this increases the transport of liquid water and reduces vapour transport. Tests
in this area therefore give some information about liquid water transport within
materials. This is discussed further in ISO 15148, Hygrothermal performance of
building materials and products - Determination of water absorption coefficient by
partial immersion.
Other sets of temperature and relative humidity may be agreed between the parties when
needed for special application conditions.
NOTE 2 The following are examples of desiccants and saturated aqueous solutions
which produce the specified air relative humidities at 23 C:
a) Desiccants
Calcium chloride, CaCl - particle size < 3 mm 0 %
2
Magnesium perchlorate, Mg(ClO ) ) 0 %
4 2
b) Aqueous solutions
Magnesium nitrate, Mg(NO ) 53 %
3 2
Potassium chloride, KCl 85 %
Ammonium dihydrogen phosphate, NH H PO 93 %
4 2 4
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EN ISO 12572:2001
Potassium nitrate, KNO 94 %
3
Further details of suitable solutions can be found in annexes A and B of ISO 12571,
Hygrothermal performance of building materials and products - Determination of
hygroscopic sorption curves.
Regular checks shall be made, especially during long tests, to ensure that saturated solutions
remain as a mixture of liquid with a large amount of undissolved substance.
All chemical substances shall be handled with care and in accordance with relevant safety
regulations.
7.2 Preparation of specimen and test assembly
Prepare test specimens to correspond to the test assembly used - see annexes A to E.
Measure the thickness of specimens to the nearest 0,1 mm, or to an accuracy of 0,5 %,
whichever is the more accurate. For rigid materials, measure the thickness of test specimens
at four positions equally spaced around the circumference. Calculate the mean thickness of
each test specimen. Record the procedure used to measure the effective thickness of
compressible and loose-fill materials and of test specimens with irregular surfaces.
Place the desiccant or aqueous solution, with a minimum depth of 15 mm in the bottom of
each cup. Seal the test specimen into the cup, using the appropriate technique specified in the
relevant annex. The air space between the desiccant or saturated solution and the specimen
shall be (15 5) mm.
Prepare a test assembly using a cup and sealant system suitable for the type of material under
test - see annexes A to E.
7.3 Test procedure
Place the test assemblies in the test chamber. Then weigh in turn each test assembly at time
intervals selected according to the specimen characteristics and to the repeatability of the
weighing procedure.
NOTE Annex H gives guidance on the ways of reaching the required accuracy.
Weighings shall be carried out in an environment with a temperature within 2 C of the test
condition, wherever possible within the test chamber. Figure 1 shows an arrangement for
small chambers.
The temperature and relative humidity within the test chamber shall be recorded continuously
with suitable sensors. The calibration of the sensors shall be checked regularly.
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The barometric pressure at the testing laboratory shall be measured daily during the test or
obtained from a closely adjacent meteorological station.
Key
1 Balance
2 Controlled environment test chamber with ‘glove box’ access door
3 Suspended weighing platform
4 Test assembly during weighing
Figure 1 - Example of an arrangement of balance and test assemblies for weighing
procedures in a chamber
Continue weighings until five successive determinations of change in mass per weighing
interval for each test specimen are constant within 5 % of the mean value for this specimen
(or within 10 % for low permeance materials with > 750 000) and until the change in
weight of the cup assembly exceeds 100 times the repeatability of the weighing procedure.
Plot a curve of change in mass against time to facilitate recognition of the condition of
constant mass change rate.
The test shall be terminated prematurely when:
i) in a dry cup test, the assembly has gained more that 1,5 g per 25 ml of desiccant in the cup;
ii) in a wet cup test, the weight loss is half the initial mass of the solution in the cup.
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8 Calculation and expression of results
8.1 Mass change rate
For each set of successive weighings of the specimens, calculate the mass change rate, m ,
12
using :
m - m
2 1
m = (1)
12
t - t
2 1
where
m is the change of mass per time for a single determination, in kg/s;
12
m is the mass of the test assembly at time t , in kg;
1 1
m is the mass of the test assembly at time t , in kg;
2 2
t and t are the successive times of weighings, in s.
1 2
Calculate the regression line between mass and time, excluding the earlier, non-linear, stage of
the test. The slope of this line is G, in kg/s.
NOTE If required, the standard error of the slope of the regression line (i.e. the
standard error of the flow rate) can be found by standard statistical methods.
8.2 Density of water vapour flow rate
The density of water vapour flow rate, g, is given by:
G
g= (2)
A
where
A is the exposed area (arithmetic mean of the free upper and free lower surface
2
areas) of the test specimen, in m .
If a cup and sealant system which includes a 'masked edge' (see annex A) has been used,
values shall be corrected before being used to calculate further parameters - see annex F.
8.3 Water vapour permeance
The water vapour permeance, W, is given by :
G
W (3)
A p
v
The value of p shall be calculated from the mean of the measured temperature and relative
v
humidity over the course of the test.
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NOTE For temperatures greater than 0 C, the vapour pressure on either side of the
specimen may be calculated from the temperature and relative humidity using (see
reference [11] in the Bibliography):
17,269
237,3
p 610,5 e
sat
If highly permeable materials or thin membranes, with s < 0,2 m, are being tested, the
d
resistance of the air gap between the base of the sample and the desiccant or saturated solution
shall be taken into account in the calculation of W - see annex G.
8.4 Water vapour resistance
The water vapour resistance, Z, is the reciprocal of the water vapour permeance:
1
Z= (4)
W
8.5 Water vapour permeability
The water vapour permeability, , is given by:
(5)
Wd
8.6 Water vapour resistance factor
The water vapour resistance factor, , is defined by the equation :
a
(6)
Equation (7), known as the Schirmer formula, is used to calculate , using the mean
a
barometric pressure, p, over the test.
1,81
0,083
p
0
(7)
a
R p 273
v
Values of at 23 C are shown in Figure 2.
a
The water vapour permeability of air and the material may be assumed to vary equally with
the barometric pressure. The factor can therefore be considered independent of barometric
pressure. When calculating the density of water vapour flow rate using the expression :
p
a
g (8)
d
the value of shall correspond to the actual barometric pressure.
a
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EN ISO 12572:2001
-10
Vapour permeability 10
kg/(m.s.Pa)
2,5
2,4
2.4
2,3
2,2
2,2
2,1
2
2,0
1,9
1,8
1,8
800 850 900 950 1000 1050 1100
hPa
Barometric Pressure
Figure 2 – Water vapour permeability of air as a function of barometric pressure at
23C
8.7 Water vapour diffusion-equivalent air layer thickness
The water vapour diffusion-equivalent air layer thickness, s , is given by either:
d
s = d (9a)
d
or
s = Z (9b)
d a
9 Accuracy of measurement
9.1 General
This clause and annex H discuss the factors that affect the accuracy of the result and give
guidance how to improve it, if necessary.
NOTE A number of ‘round-robin’ intercomparisons of measurements by different
laboratories have been carried out - see references [6], [7] and [8] in the Bibliography
for discussion of the results.
A number of factors affect the accuracy of the measured values.
9.2 Specimen area
The diameter of a circular test cup or the side of a square test cup shall be measured to an
accuracy of 0,5 mm, giving a possible error in the area of a specimen of the minimum size
2
specified in 6.2.2 (i.e. 0,005 m ) of 0,5 %. This error will be less with larger specimens.
For certain cup types it will be necessary to correct for the effect of a masked edge as
specified in annex F.
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9.3 Specimen thickness
If the permeance or resistance of a complete product is being measured, the accuracy is not
affected by the thickness. However if the permeability of a material is needed, the accuracy
with which the specimen thickness can be measured will directly effect the accuracy of the
result. The thickness of a rigid specimen can be measured to better than 0,5 % with a
micrometer.
NOTE The accuracy will be lower in the case of loose fill and similar materials.
9.4 Sealants
If an appropriate sealant is installed as specified in the annexes, errors caused by leakage can
be much less than those from other sources. A faulty seal will result in a much higher flow
rate through one of the test assemblies; that result shall be rejected before averages are taken
over the samples.
9.5 Weighing precision
The influence of weighing uncertainty on the accuracy of the results depends on the size of the
specimen and the time interval between successive weighings.
NOTE Information about the weighing repeatability needed to achieve a desired
accuracy in relation to the specimen size and weighing interval is given in annex H.
9.6 Control of environmental conditions
The vapour pressure difference between the test cup and the environmental chamber is the
driving potential for the whole test. The accuracy with which this difference is known
consequently determines the accuracy of the measured values.
The vapour pressure within the cup is determined by the desiccant or saturated solution used.
A suitable desiccant should give effectively zero vapour pressure. The relative humidity over
saturated solutions is quoted to the nearest 0,5 % relative humidity in tables and this can be
achieved if care is taken in their preparation.
The test conditions in Table 1 will result in a variation in vapour pressure difference across
the test specimen of 10 % of the set point value.
Conditions within the environmental chamber shall be carefully monitored with accurately
calibrated instruments to determine an accurate mean vapour pressure over the test.
NOTE Considerable care is needed in the measurement of conditions within the
environmental chamber in order to obtain accurate permeability data.
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SIST EN ISO 12572:2002
Page 17
EN ISO 12572:2001
9.7 Variations in barometric pressure during test
For products with low water vapour transmission rates, especially thin flexible membranes,
large day-to-day pressure variations may affect the results. Account shall be taken of the
buoyancy effect either by including the change of weight of a 'dummy' specimen, without an
aqueous saturated solution or desiccant, or by extending the test over several weeks and
selecting the measurements taken on the days with a similar barometric pressure for further
analysis.
9.8 High permeance specimens
The measurement uncertainties discussed in 9.1 to 9.7 are too large to allow the properties of
high permeance specimens (i.e. those with s < 0,1 m) to be measured with the methods
d
specified in this standard.
10 Test report
The test report shall include the following :
a) reference to this standard;
b) product identification:
- product name, factory, manufacturer or supplier;
- type of product ;
- production code number or similar identifier;
- the form in which the product arrived at the laboratory, including facings, if any;
- the method of preparation of the specimen, including slicing where done, and details of
any curing process, where necessary;
- other details of the product e.g. nominal thickness or nominal density;
c) test procedure:
- the mean air pressure and the temperature and relative humidity gradients across the
specimen and the range of any deviations from the mean;
- test
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