Interim Test Method for Measurement of Air Leakage Through Windows

Publisher’s version / Version de l'éditeur:

Technical Note (National Research Council of Canada. Division of Building Research), 1962-05-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la

première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected].

Questions? Contact the NRC Publications Archive team at

[email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information.

Archives des publications du CNRC

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/20359122

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Interim Test Method for Measurement of Air Leakage Through Windows

Sasaki, J. R.; Wilson, A. G.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=0cfa699a-70a1-4155-989e-05126efd485a https://publications-cnrc.canada.ca/fra/voir/objet/?id=0cfa699a-70a1-4155-989e-05126efd485a

DIVISION OF BUILDING RESEARCH

TEClHlNJICAlL

NOTE

375

NOT FOR PUBLICATION

J.

R. Sasaki and

PREPARED BY A_{• •}G Wil_son CHECKED BY HBD

FOR INTERNAL USE

APPROVED BY NBH

DATE May 1962

PREPARED FOR General Information

SUBJECT

INTERIM TEST METHOD FOR MEASUIm4ENT

OF AIR LEAKAGE THROUGH WINDOWS

The specifications for aluminum windows issued by the canadian Government Specifications Board late in 1960 and early 1961 (No. 63-GP-1, 2 and 3) were the first performance

type window specifications in Canada. These were based in

part on the specifications of the AWMA and in view of the

urgency with which they were required they were put to use without waiting for the development of new standard test

methods. It was thought that adequate interim testing

procedures could be maintained by exchange of information between testing agencies and a special meeting of those

concerned was called to promote this. Since then other

Canadian window specifications which also require proper test methods have been prepared or are in preparation.

In the meantime the A.S.T.M. had undertaken to develop window test methods through its committee E6, and representatives of the Pivislon of Building Research on this committee were assigned the task of preparing suggested methods of test for the air leakage and thermal aspects of window·

performance.

The draft of a test method for air leakage prepared by the Division of BUilding Research of the National Research Council for consideration of ASTM Committee E6 is the subject

of this note. The method is compatible With the brief

des-cription of test given in the appropriate CGSB specifications

and is proposed for use as the basis for the necessary air leakage testing of windows until official Canadian or U.S. test methods are issued.

INTERIM TEST METHOD FOR MEASUREMENT OF AIR LEAKAGE THROUGH WINDOWS

SCOPE·

1. (a) This method of test is intended for the determination

of the rate of air flow through cracks and openings in and around closed windows resulting from air pressure differences

across the windows. The air pressure differences are those

which may be due to wind action on a building, stack e'ffect in

a bUilding or the operation of mechanical ventilation and ･ｾｵｳｴ

systems. The method as outlined is intended to deal with air

leakage associated with the window alone, and not that through cracks between the Window and construction into which it may be fixed, although the method can be adapted for this latter purpose.

(b) This method of test describes general principles of

pressure and flow measurement to be followed in window air

leakage testing. The apparatus as described is intended for

testing with isothermal and constant humidity conditions across

the window. Provided the general principles are satisfied,

however, the details of the apparatus may be varied to suit the needs and convenience of the individual operator, for instanoe, the apparatus may be arranged to prOVide temperature differences

across the window. It should be understood that those applYing

the method shall possess a knOWledge of the principles of air

flow ｾｮ､ pressure measurement and shall understand the general

requirements of good testing practice.

SIGNIFICANCE

2. (a) Window air leakage is an important element in the

heating or cooling reqUirements of buildings and in the

main-tenance of relative humidity. A knOWledge of window air

leakage characteristics is necessary in the calculation of heating and cooling loads for purposes of equipment selection and in the calculation of seasonal energy requirements of

buildings. Window air leakage- may also be a factor in dust

transfer into bUildings. In double windows the relative air

leakage characteristics of Qracks and openings around inner and outer panes may largely determine the extent of inter-pane condensation under specified conditions and also relates to the resistance of: such windows to rain penetration.

Note 1:

(b)

In applring the results of tests br this method it

should be borne in mind that the air leakage charaoteristio of

a window is a funotion of workmanship, adjustment and in some

destgns, of the direction of air flow or of the temperature

and humiditr conditions across the window.

In service, it will

depend on the resistance of the oomponents to

､･ｴｾｲｩｯｲ｡ｴｩｯｮＮ

DEFINITIONS

3.

(a)

Window air leakage rate is, the volume rate of air flow

through oraoks

ｾ､

openings in a closed window under speoified

oonditions of air pressure differenoe aoross the Window.

Sometimes the pressure differenoe is expressed as

ｴｨ･ｾｵｩｶ｡ｬ･ｮｴ

of a given wind speed.

The relationship between statio head and

wind velooitr with air at standard oonditions (note 1) is:

'bw •

4.82

x

10-

4

V

2

(1)

where

hw •

statio ,head, inohes water oolumn

V • wind ve1oottr, miles per hour

In English units the overall air leakage rate of a

ｷｩｮ､ｯｾ

is usuallr expressed as oubio feet per

ｾｩｮｵｴ･

or oubio

feet per hour.

In speoif1ing the air leakage requiroments of

windows, it is oommon praotioe to refer to the air leakage rate

per lineal foot of sash oraok under speoified oonditions.

For

this purpose it is neoess&rr to speoifr the method of measuring

the length of oraok involved.

Caution must be used in

extrapo-lating the re ult

of air leakage tests to windows having greater

or smaller oraok lengths than the window tested, sinoe the rate

of air leakage per lineal foot of sash

ｯｲｾｯｫ

mar v&rr depending

on the size of the Window.

For oomparative purposes it is best

to obtain overall air leakage rates for windows of a standard

size.

Air at standard oonditions has a speoifio weight of

0.07$ lb. per ou. -ft.

(b)

Window air

ｬ･｡ｫ｡ｾ･

oharaoteristio is the oorrelation

of statio pressure aorosshe window and the resulting window

air leakage rate.

The window air leakage rate oan be expressed

as an exponential funotion of the statio pressure aoross the'

window:

Qw •

0

hw

n

where

ｾ

•

ｷｩｮ､ｯｾ

air leakage rate

o

=

a window geometrr faotor

n

• an exponent of flow whioh talls between 1/2

and 1 depending on the nature of the

ｴｬｯｾ

APPARA'rus

4.

(a) General principles

The principle of the test is to exert a pressure difference across the window and to measure the resulting air

flow through it. The pressure difference can be induced by

either a supply or exhaust air system. The following describes

the major components of an air leakage apparatus utilizing a

supply air system. The requirements with an exhaust air system

will be similar.

The major components of the window air leakage apparatus are:

1. An airtight mounting panel in which the window

is installed and sealed

2. A pressure chamber or box

3.

An air supply

4.

A means of measuring the pressure difference

across the window

5.

A means of measuring the rate of air flow

through the window.

The general concept of the test is to seal the panel containing the test window into one face of the pressure chamber, to supply air to the chamber at the rate required to maints,in the desired pressure difference across the window and to measure

the resulting air flow through the window. When an exhaust air

system is used air is withdrat-Tn from the pr0ssure chamber at the required rate.

The air leakage apparatus can be constructed either

as a single or double chamber device. These are illustrated in

F'ip,. 1. In the single chamber arrangement the air enters the

preSSU1'e chamber and passes through the te st Hindow to atmosphere. The flow meter is placed upstream of the pressure chamber and

the extraneous ｬ･｡ｫ｡ｾ･ｦｲｯｭ the pressure chamber (note 2) must

be small to ensure tl1at the metered flow is essentially that pas sing through the windO\v.

In the double chamber arrangement a second chamber is added as part of the flow metertng system and the window in the mOlmting panel is placed between the pressure and metering

chambers. Air enters the pressure chamber, passes through the

window to the metering chamber and then through a flow meter to

atmosphere. The measurement of air flow ｴｨｲｯｵｾｨ the window in

the two-chamber apparHtus is unaffected by leakage from the

pressure chamber but the extraneous ｬ･｡ｫ｡ｾ･ from the metering

chamber (note 2) must be small in order to limit the error.

Extraneous ｬ･｡ｫ｡ｾ･ from either the pressure chamber or the

metering chamber is a function of the pressure difference between the chambers and the surrounding atmosphere and the

error due to extraneous leakafe will in general be least in the

arrangement in which this. pressure difference is least. Whether

this error is likely to be greater or less with the single chamber arrangement than with the double chamber arrangement will depend on whether the maximum pressure difference "across the window at which flow measurements are to be made is greater or less than the pressure head required by the metering chamber

flow meter. For most purposes it is not necessary to measure

air leakage rates at static pressure differences across the

specimen in excess of

0.5

inches of water column. Pressure

differences of similar magnitude are often developed between the metering chamber and surrounding atmosphere in the measurement

of flow, and the problem of extrR.neous leakage is then comparable to that with the single chamber arrangement.

Note 2: In the single chamber apparatus extraneous leakage is

the flow from the pressure chamber to atmosphere

which does not pass throur,h the window. This includes

air leakage through the mounting panel. In the

double chamber apparatus extraneous ｬ･｡ｫ｡ｾ･ is the

flow from the metering chamber to atmosphere which

does not pass through the flow meter. This does not

include air leakage through the mounting panel which

must be accounted for separately. In both types of

apparatus extraneous leakage occurs mainly at the seal between the mounting panel and chamber.

(b) Pressure chamber

The size of the pressure chamber depends on the maximum

size of specimen to be tested. Due consideration must be given

to structural strength and rigidity, since the forces due to pressure differences between chamber and atmosphere may be

substantial. The degree of air tightness required in constructing

the chamber will depend on whether the apparatus is a single or

double chamber arranGement. In the single chamber apparatus

provision must be made to admit air to the chamber for determining the &xtraneous leakage with the mounting panel sealed into

position and with the window specimen sealed. The normal air

supp.ly openinf, may be adapted for this purpose. At least one

ｳｴ｡ｾｩ｣ pressure tap shall be provided to measure the chamber

pressure. It shall be located so that the reading is unaffected

by the velocity of the air supply to the chamber.- The air supply opening into the chamber shall be arranged so that air d0es not impinge directly on the window specimen with any significant

velocity. It is convenient to have a means of access into the

chamber after the mounting panel has been sealed into position to permit sealing, unsealing and other alterations to the window

specimen without removing it. Sealing of the chamber to the

mounting panel may also be facilitated by such access.

(c) Metering chamber

The metering chamber, when used, will normally be the same size as the pressure chamber and similar considera.tions of

structural strength and rigidity are required in its design. It is particularly desirable to incorporate a means of access into the metering cha.mber to permit adjustments to the windoli\T specimen, since it covers the operating side of the window.

Such means of access may also facilitate ｳ･｡ｬｩｮｾ of the mounting

panel to the metering chamber. Provision must be made to admit

air to the chamber for determining the extraneous leakage with the mounting panel sealed into position and with the window

specimen sealed. At least one static pressure tap shall be

provided to measure the metering chamber pressure. The metering'

chamber shall incorporate a suitable air metering device. (d) ｾｴｩｮｧ :eenel

The entire side of the mounting panel facing the

pressure chamber, extending from the window specimen opening to

the outside edges, shall be made air tight. In the double

chamber apparatus it is desirable to extend the airtight surface of the mounting panel around the edges of the panel and over

the opposite side into the metering chamber for a short distance. The mounting panel must have sufficient strength and rigidity to support the windo'H specimen adequately and to ll1ithstand the

pressure differences to be imposed. The test opening should be

framed to facilitate mounting of the window specimen. (e) ｓ･｟｡ｬｾｉｬｧ and clamping

Provision must be made to hold the mounting panel against the pressure chamber opening, and in the case of the double chamber arrangement, to hold the metering chamber against

the mounting panel. The method of holding must provide sufficient

force so that no separation of the mounting panel and chamber

occurs during test. Sealing between the mounting panel and

chambers to control extraneous leakage can be achieved by several means, for example rubber gaskets and clamping, mastic compounds

or pressure sensitive ｴ｡ｰ･ｾ It should be recognized that in

using gaskets relatively large forces applied at a large number

of points may be required to overcome small ｩｾｲ･ｧｵｬ｡ｲｩｴｩ･ｳ in

meeting surfaces and to provide the required sealing pressure

at the gasket. Gaskets having flexibility and small contact area

are to be preferred. Adequate sealing can be obtained through

the use'of ｮｯｮＭｨ｡ｲ､･ｮｩｮｾ mastic compounds or strong pressure

sensitive tapes. In general, sealing is more readily achieved

with these materials when they are applied to the crack between the chambers and mounting panel on the high pressure side.

These same materials can be used advantageously in sealing the window specimen into the mounting panel, the access door into the chamber and in achieving air tightness in the construction of the chamber and mounting panel.

(f) Air supplI.system

Any blower or compressed air supply that will provide the required maximum air flow rate at the required maximum

static pressure in the pressure chamber will be acceptable. The air source should provide essentially constant air flow at a fixed pressure head for the period required to obtain records

of air flow rate and pressure difference. The same requirements

shall be met where an exhaust system is used.

(g) Pressure measuring apparatus

The pressure difference across the window specimen

shall be measured with an error not greater than ±5%. At

pressure differences of 0.1 inches of water column or greater, the required accuracy can be met with commercially available

inclined manometers. At lower pressure differences more

sensitive pressure measuring devices will be required.

(h) Air flow metering system

The flow through the window specimen shall be measured

with an error not greater than

t5%.

Sources of error in-the

measurement of flow are the extraneous leakage from the chamber

and the inaccuracy of the flow meter. The extraneous leakage

from the chamber shall not introduce an error in the measurement of air flow rate through the window specimen in excess of ±l%. It is recommended that the extraneous leakage not exceed 10% of the window leakage at pressure differences across the window greater than 0.1 inches water column.

Due consideration must be given to good fluid metering

practice (note

3)

in the choice, installation and use of the air

metering device. In the single chamber apparatus the pressure

drop across the air flow meter is not a limiting factor in its

choice. Any flow meter having the required range and accuracy

will be suitable. In the double chamber apparatus it is desirable

to limit the maximum pressure drop across the air flow meter to

minimize extraneous leakage. Any flow meter with this

charac-teristic can be used. It is common for this purpose to use

several sharp-edged orifices sealed into the wall of the metering

chamber to cover the required flow range. The flow is determined

from the measured static pressure difference between the metering box and surrounding atmosphere and the known discharge coefficient

of the orifices. The reference given in note 3 does not

specifically describe the characteristics of this orifice

arrangement. If the construction of the orifices used ｩｾ this

arrangement adheres to practices referred to in note

3,

an

orifice discharge coefficient of 0.60 can be used without calibration at flow Reynolds Numbers greater than 10,000. Otherwise such orifice arrangements shall be calibrated to provide the accuracy required in this test procedure.

Note

3:

For good fluid metering practice reference shall be

made to Fluid Meters - Their Theory and Application, The American Soctety of Mechanical Engineers,

WINDOW SPECIMEN

50 (a) Selection

In selecting the window specimen it should be recognized

that the air leakage characteristic 1 s like ly to be a ｦｵｮＨｾｴｩｯｮ

of size and geometry and it is therefore desirable to select specimens covering the range of sizes in a given application. If only one specimen is to be tested and size is not specified the largest available size should be selected.

(b) Mounting

Prior to installation in the mounting panel, any sealing material or construction that is not normally a part of the

window as installed in a bUilding shall be removed. The window

specimen shall be fitted in the opening in the mounting panel in such a way that any cracks or openings in the wlndow frame

are not obstructed. The exterior of the window shall face the

high pressure (the pressure chamber when a supply air system·

is used). The airtight face of the mounting panel shall be

sealed directly to the exterior trim of the window frame and there shall be sealing between the specimen and the mounting panel at no other point.

PROCEDURE

6. (a) The mounting panel incorporating the window specimen

shall be sealed to the pressure chamber, and in the two-chamber apparatus, the metering box shall be sealed to the mounting panel.

(b) Prior to measurements of window air leakage, two factors

which affect the accuracy of the air leakage determination shall

be eliminated or accounted for. These are the extraneous box

leakage and the mounting panel leakage. In the single chamber

apparatus, the mounting panel leakage ts included in the extraneous

leakage and need not be ､･ｴ･ｲｭｾｮ･､ separately; the extraneous

leakage from the pressure chamber shall be measured, with the window specimen sealed, at pressure dtfferences that will be

exerted across the window specimen in the window air leakage test. The air metering equtpment for the measurement of the window air leakage may be used for measuring the extraneous leakage from the pressure chamber provided the requirements of paragraph 4(h)

are met. However, it may be necessary to provide additional

air metering equipment in order to meet these requirements. In the two-chamber apparatus, the mounting panel

leakage and extraneous metering box leakage must be accounted for

separately. The extraneous leakage from the metering chamber

shall be measured, with the window specimen sealed, at pressure differences between the metering chamber and surrounding

metering equipment attached to the wall of the metering chamber shall be sealed and air supplied to the chamber through a

separate air flow meter. One method for determining the

extraneous air leakage is to supply air to both the pressure and metering chambers and to measure the flow to the metering chamber while maintaining zero pressure difference across the

mounting panel. The mounting panel leakage shall be measured

at pressure differences across the panel that will be exerted across the window specimen in the window air leakage test. One method for determining the mounting panel leakage is to supply air to the pressure chamber following the measurement of

extraneous leakage from the metering chamber. With the window

specimen and metering box sealed the panel leakage can be

determined from measurements of air flow from the'metering box and its known leakage characteristics.

(c) The window specimen shall be adjusted for the

measure-ment of window air leakage without disturbing the seal between mounting panel and pressure chamber, or between mounting 'panel

and metering chamber in the two-chamber apparatus. The

adjust-ment of the lock may have a significant effect on the window

air leakage rate. When not otherwise specified the lock should

normally be adjusted for maximum tightness. The pressure applied

in closing the sash may also affect the window air leakage rate. It is therefore often desirable to make two or more successive measurements of air leakage rate between which the sash have

been opened and closed.

(d) At each measurement of window air leakage rate the

pressure difference across the window and corresponding flow

shall be measured. In addition the barometric pressure and the

temperature, gauge pressure and relative humidity of the air passing through the window and through the flow metering device shall be measured.

(e) Measurements of window air leakage rate shall be

obtained for at least three values of pressure difference across

the window specimen. Where a specific value of window pressure

difference is specified it should be included in the pressure differences used in the test.

(f) At the completion of the measurements of window air

leakage rate, the extraneous leakage shall be remeasured.as outlined in paragraph 6(b).

CALCULAT ION

7.

(a) The following expressions can be used to calculate

the specific weights of the air at the flow meter and at the windoll! :

e

ＮＱｩｾｴｑ

(B

o

14

m

III ｏｾＳＷｂ

Pv

+

b

m)

(3)

m Ww

=

.1.326_T

(Be ·

0.378

Pv + b_w) (4)

w

where W

m

&

Ww

=

the specific weights of air at the meter_{and window respectively, lb. per cu. ft.}

Bc

=

the barometric pressure corrected for

temperature, inches mercury column

Tm

&

_{Tw = absolute air temperature at the meter and}

window respectively, oR.

Pv

=

water vapour pressure in the air, inches

mercury column

bm

&

_{bw = gauge pressures at the meter and window}

respectively, inches mercury column (b)

shall be oalculated as:The window air leakage rate at the conditions of test

'lw

=::

ＨｾＭ

Q_{L )} (

5)

for the single chamber apparatus or

w

_ m

--

_ww (6)

for the double chamber apparatus where

=

air flow through the window at conditions

of test, cfm.

= air flow measured by flow meter, cfm. = pressure or metering chamber

extraneous leakage, cfm.

The window air leakage rate at standard conditions shall be calculated as follows:

l-n

ｾｳ

=

ｾ

(:: )

(

7 )

where

ｾｳ

=

window air leakage rate at standard

conditions, scfm.

w_s

=

specific .weip;ht of air at standard conditions,

0.075

lb. per cu. ft.

Equation (2) can be rearranged to,

(8)

Note

4:

!J.log ｾ n

=

_Alog

ｾ

The value of n expressed by equation (8) assumes a

constant value for the window geometry factor, c. In some windows, the geometry factor varies with

pressure and equation (8) may give a value of n

greater than 1. In this case, n = 1 shall be used

in equation (7).

(c) Where required, the window air leakage rate per foot

of sash crack shall be calculated as:

where

ｾｳ

-t

c

-t

c

=

length of prime sash crack, ft.

When not otherwise specified, the length of prime sash crack shall be based on the dimensions of the prime sash opening. The crack at meeting rails in sliding windows shall be included in computing crack length.

REPORT

8.

(a) The report shall include the following:

(i)

(ii)

(iii) (iv)

Identification of the window specimen tested

A description of the physical characteristics of

the specimen including the sash arrangement, weatherstripping and locking arrangement, hardware, dimensions including the prime sash opening, and any other pertinent construction

features. Where practical a detailed drawing of

the window specimen for positive identification should be included.

A description of the sash and lock configuration

for the test

A tabulation of pressure differences across the window specimen during test and the corresponding window air leakage rate at standard conditions, for each configuration tested.

ｦＧｒ･ｳｳｵｾｅ

t1

E_{ａｓｬＮｬｾ ING} 'DE"'CE ｾ 5 ....ｯｷ･ｾ Ｈｉ｜ｵｾＮ

SU."'l..y)

ｴＱｅｔ･ｾｉｎｾ CHAMBER ｐｒｾｓｓｕｾｅ

M..

"CO\.lRIN<l "ev,ce5 - - -