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DW/143Apreactical guide to -

DUCTWORK LEAKAGE TESTINGBased on the requirements of DW/142specification for sheetmetal ductwork. 1983

COPYRIGHT 1983 by theⓒHeating and VentilatingContractors' Association

All rights reserved

HEATING AND VENTILATINGCONTRACTORS' ASSOCIATIONEsca House, 34 Palace Court,

London W2 4JG

Obtainable from HVCA Publications,OLD Mansion House, Eamont Bridge, Penrith,Cumbria, CA10 2BXTelephone : Penrith (0768)64771 Telex : 64326

H V C A

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Contents

Part One Page

Acknowledgements 4

Preface 5

Financial Caution 6

Practical Guide to leakage testing 7~8

Example of complete test sheet 9

Hints on leakage testing 10~11

Part Two

Air leakage from-ductwork 13~15

Nomogram converting area basis to percentage of airflow 16

Air leakage testing procedure 17~18

ACKNOWLEDGEMENTS

The HVCA records its appreciation and thanks to the persons and organisations

who have freely contributed to this work, and in particular to the members

of the Drafting Panel.

DW/143 Drafting Panel

J.H.G Gardner (Chairman)

K, Angood

P. Doyle

K, Wheatley

K, Waldron

H. Brockiehurst

H. Brierley

J.M Paynton (Former Secretary, Duct Work Group)

R,J,Miller (Secretary, Duct Work Group)

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PREFACE

Ductwork Specification DW/142, published by the HVCA in 1982, provides for thefirst time in a long series of such publications for leakage limits over thewhole range of air pressures covered by the specification and (where required)a test procedure to establish conformity. Although leakage testing of high-pressure ductwork is mandatory in DW/142(as was the case in previous ductwork specifications issued by HVCA) the leakagetesting of ductwork designed to operate at low and medium pressure is requiredonly where so specified in individual job specifications. With the introduction of four pressure classifications in DW/142 it is hopedthat the designer,having selectional control of constructional srandards,willfind leakage testing an unnecessary contract expense with fegard to low andmedium pressure ductwork. However,it is possible that initially the advent ofmore stringent constructional requirements may be followed by an increaseddemand by clients and specifiers for the testing of low-and medium-pressureductwork and this booklet has been prepared in order to assist ductworkcontractors to minimise the cost of this unfamiliar operation. It will be noted that the leakage limits speccified in Appendix A of DW/142are expressed in litres per second per square metre of duct area.It is however possible that some ductwork specifications will still quoteleakage limits as a percentage of air flow.In order that the area basis can be converted to a percentage equivalent anomogram from DW/142 has been reproduced in this booklet on Page 16. Ductwork contractors faced with a job calling for leakage testing shouldtake this requirement very seriously and satisfy themseleves as the jobprogresses that the required leakage rate or rates are within the limits set bythe designer or the client. The cost of making good an installation that hasbeen found on completion to have failed in this respect can be very exprensiveindeed. DW/142 specifies leakage limits for the ductwork alone, not for the completeair distribution system. This is because the ductwork contractor has no controlover the leakage characteristics of the various components which go to make upthe whole of the air distribution system. Where a job specification calls fora leakage limits for the whole system. It will be for the designer or clientto ensure that the leakage rates of the components are also within therequired limits.

J.H.G. Gardner,Chairman, Executive Committee,Duct Work Grop, 1982/83

Part One - A Practical guide to

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ductwork leakage testing

1. GENERALWith regard to air leakage, the responsibility for ensuring the achievementof a satisfactory job is divided between the Drawing Office, the Factory andthe Site Erection Operatives. It is essential that there is full co-operationbetween them.

2. THE DRAWING OFFICETHE DRAWING OFFICE must :

2.1 Establish with the client or his representatives the class of ductwork calledfor in the job specification, i.e.:

Class A : up to 500 Pa positiveClass B : up to 1000 Pa positiveClass C : up to 2000 Pa positiveClass D : up to 2500 Pa positive

2.2 Establish with the client or his representative that the required leakagerate or rates are for the ductwork alone .i.e. excluding dampers,fire dampers,air handling units, fans, heater batteries, silencers, terminal boxes, etc. Additionally, establish the type of gasket material required in relationto the pressure class/velocity of the system.

Note : - Specific gasket material may be required in locations such as cleanrooms, hospitals etc.

If a leakage limits is laid down for the whole system, it will be for theclient or the designer to ensure that leakage characteristics of the components are acceptable.

2.3 Agree with the client of designer the test pressure for eath section of theinstallation. (Note that whilst duct construction) Specification is related to the highest test class of the duct installationit is important that each duct test zone should only be tested to a pressureto cover the mean working pressure of that particular section of ducting- see A.2.5(b)

2.4 Decide on the best way to isolate the installation into test zones.When doing so, the drawing office should bear in mind the test pressurecalled for, the allowable air losses, the work sequence on site and the capacity of the test equipment.

2.5 Arrange for the supply of suitable blanking medium, e.g. heavy-dutypolythene sheet.

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2.6 Make sure that all test points and blanking devices can be reached withthe minimum of difficulty after the ductwork has been installed.

2.7 To ensure that a reading can be obtained, plan test sections to have apermitted loss of approximately 25 per cent less than the total volumegenerated by the test rig at the pressure required for each section.

2.8 Provide the erectors with details of the test zones, duct operating pressureand test pressure; and indicate the nature of the blanking devices, gasketmaterial and seaiant to be used.

2.9 Prepare test sheets giving the information called for on the sample testsheet shown on page 9.This information should indicate the test content, the surface area of theductwork to be tested, and permitted loss for each section to be tested (this loss is to be expressed in litres per second per square metre ofthe ductwork).

3. THE FACTORY

3.1 Ductwork specification DW/142 requires the sealing of more joints than wasthe case in previous specifications. Care must therefore be taken to makecomponents with a good fit. and to use only enough sealant to make asatisfactory joint. A poor fit cannot be remedied by the use of more sealant- it will not work.

3.2 Seal all longitudinal seams, laps, cross joint, rivets and duct penetationsgenerally, in accordance with the requirements of DW/142.

3.3 Make sure that sealant is properly applied to the ends of all lock formsnd other types of longitudinal seam, and to the corners and junctions betweenthose seams and the cross joints.

3.4 Take special care to have as small a clearance as possible where are penetrations of the duct, as for example, damper spindles.

3.5 First and seal branch connections carefully, as required by DW/142.

3.6 To be sure of minimum leakage, special care must be taken in the fitting andsealing of access doors and panels etc.

3.7 To avoid the danger of breaking the seals, the ductwork when ready for

despatch to site must be handled and loaded carefully.

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4. SITE WORKFor full details of procedure see Appendix B Pages 17 and 18 and the diagramon Page 10 and 11.

4.1 Understand the proper use of the testing. It is expensive precision equipment.The instructions must be read carefully and the equipment handled in responsible manner.

4.2 Make sure that the right type of test rig is available for the job.A rig suitable for high pressure leakage testing is seldom suitable oreconomic for testing low-or medium-pressure ductwork, and vice versa.

4.3 Note that leakage testing is always done under positive pressure even whenthe ductwork is to operate under negative pressure.

4.4 Before erectionInspect all duct sections to make sure that factory applied sealants havenot been damaged in transit. Makr good where any damage is noticed.

4.5 Ensure the correct gasket material has been supplied for your situation andthe application is in accordance with the manufacturer's instructions.Check with the drawings and specifications as to where sealants are to beused on the cross joints, and then apply the sealants as necessary.(Use only as much sealant as will do the job - too much sealant is as badas too little.)

4.6 Pay special attention to the sealing of joints that will be difficult toreach after erection of the ductwork.

4.7 Fix the blanking plates or other types of temporary seal in the positionsshown by the Drawing Office. (Again, make sure that the blanking materialcan be reached when it has to be removed.)

4.8 At the earliest opportunity agree with the client or his clerk of works on aprogressive testing programme.

4.9 To ensure that the ductwork has been correctly manufactured and site sealantcorrectly applied it is essential that a preliminary test is carried out oneach section of the work at the earliest opportunity - before presentationto the elient.

4.10 If these preliminary tests show that the leakage is over the limit, then ;

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4.10.1 Look for any obvious places where there may be leaks, for example, anopen access door or missing or punctured polythene blanks.Simple methods of locating any leakage are ;

a) by listening for them ;b) by feeling for them espencially with a wet hand ;c) by applying soapy water over the seams or joints ;d) by (with the agreement of the client) using a smoke pellet.

NOTE : When smoke pellets are used, the smoke should be introduced downstream of the test rig and not on its intake side.

4.10.2 Reseal or correct where you have found the leakage source(s).Manufacturing faults should be reported to the factory immediately.

4.10.3 Repeat the test after allowing enough thme for the sealant to set.(Remember that sealants take longer to do this in cold weather.Read the sealant manufacturer's instructions.)

4.11 When satisfied with the results of the preliminary tests then ;

4.11.1 Offer the section to the client's representative for formal acceptance : 4.11.2 On successful completion of the test obtain a signature - on the

test sheet ; 4.11.3 A permanent record of tests must be retained.

4.12 As tests are satisfactorily completed, remove all blanking off devices.

Relevant Conversion FactorsPressure

To convert Multiply byInches water gauge to milibars 2.491Inshes water gauge to pascals (Pa) 249.1

Volume Flow

To convert Multiply byLitres per second to cubic metres per hour 3.60

Example of a completed test sheetBased on ductwork shown on page 10 and 11

1 Pa = 1 Newton per square metre = 10~2 millibars

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Test No.

GeneralName of jobBuilding Ref.

Part 1 - Physical detailsa Senction of ductwork to be testedb Drawing Numberc Pressure Classification (PROVIDED BY DESIGNERS)

d Test static pressure (FROM DESIGNERS BY REF TO TABLE 32)

e Leakage factor (FROM REF TO TABLE 31 OR 32)

f Surface area of duct under test (FROM CALCULATION BELOW)

g Maximum permitted leakage (OBTAINED BY MULTIPLYING AND f)

Part 2 - Test particularsa Duct static pressure reading (READ OFF MANOMETER ON TEST RIG)

b Type of flow measuring device (ALSO STATE MANUFACTURER & TYPE)

c Range of measurement of flow measuring device (FROM RIG MANU. LITERATURE)

d Reading of flow measuring devicee Interpreted air flow leakage rate (DERIVED FROM CHARTSUPPLIED WITH RIG USING"d")

f Duration of test (normally 15 minutes)

Date of test Carried out by Witnessed by

Width and depth Periphery Length Areaor diameter

millimetres millimetres metres square metres

800 x 750 3100 17.550 54.405

600 x 650 2500 5.570 13.925

300 x 300 1200 1.200 1.440

305 dia. 958 7.000 6.706

250 dia. 785 4.500 3.533

TOTAL 80.009

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Hints on Ductwork Leakage Testing

Take special carewith inaccessiblejoints

FLEXKeep length to a minimumand make sure that bothend connections arethe flexible dict itselfhas no leaks.

In order to avoidincorrect readingsof duct pressurethe tube from thevertical manometershould be connecteddirectly to theductwork under test.

TEST APPARATUSSite on firm level base andensure gauges are topped upwith correct fluid andzeroed prior tocommencing test.Fit correct flow measuringdevice.

Inslined manometer toread leakage rate

SEQUENCE OFF TEST1. Prepare test sheet.2. Connect and adjust test apparatus to correct pressure.3. Read off leakage rate.4. Reseal if necessary (allow time to cure).5. Maintain test for 15 mins.6. Switch off and allow to zero.7. Reapply test pressure and check reading.8. Record details on test sheet and obtain signature.

WARNINGTake care not to over pressurisesystem under test

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Part Two

The dimensions on this ductwork are used in an example on page 9

Blank off all openends with polythenecarefully taped in toposition to avoid leaks.Remember to blankinstrument tappingsand test holes.

Vertical manometer toread duct pressure

Blank at convenientplace with accessfor ease of removal 800 x 750

HOW TO FIND LEAKS1. Look - particularly at blanks, access openings and difficult joints.2. Listen - with test apparatus running, leaks should be audible.3. Feel - running your hand (particularly if wet) over joints can help to locate leaks.4. Soap and Water - Paint over joints and look for bubbles5. Smoke Pellet - placed inside ductwork (obtain permission for use)

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This section is predominantly extracted from DW/142 - Specification for Sheet Metal

Ductwork, and for ease of reference the numbering as in DW/142 has been retained.

The leakage limits for EUROVENT classifications A,B and C, as set out in their

ducument 2/2 (Air Leakage in Ductwork) have been adopted for the low pressure,

medium pressure and high pressure Class C classifications. EUROVENT document 2/2

has no standard for a leakage class equivalent to our Class D and therefore the

leakage limits for high pressure ductwork used in DW/141 (the predecessor to DW/142)

have been retained.

6 AIR LEAKAGE STANDARS

6.1 Limits for each pressure class Permitted air leakage is related to fourstandards of airtightness, as set out in Table 2.

6.2 Compatibility with EUROVENTThe leakage factors used in Table 2 for Class A, B and C are the same asthose used for the classes similarly designated in the Eurovent Document2/2 (Air leakage in Ductwork).

6.3 Leakage at various pressure : and other relationshipsApplying the limits specified in Table 2, Appendix A (Table 31) sets out thepernitted leakage at each of a series of pressures up to the maximum for eachclass. Included in that appendix is a graphical presentation of the pressure/leakage relationship ; and also charts from which may be determined leakageas a percentage of airflow for classes A,B or C.Appendix A also gives details of the basis for the leakage limits specfiedin Table 2.

6.4 Testing for air leakageAll ductwork operating at pressure classified in this specification as high pressure' shall be tested to establish conformity with the relevantleakage limits set out in Table 2.

Testing for leakage of ductwork within the low and medium ranges of pressurein this specification will not form part of the ductwork cintract unlessthis requirement is set out in the job specification - sec also Note(2)on page 1 of DW/142

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Table 2 Air Leakage Limits

Air leakage Leakage limits1 2

litres per second per squareLow-pressure - Class A metre of ducts surface area

Medium-pressure - Class BHigh-pressure - Class CHigh-pressure - Class D

APPENDIX A - AIR LEAKAGE FROM DUCTWORK

A.1 GENERAL CONSIDERATIONS

A.1.1 Leakage points in ductworkAir leakage in installed ductwork occurs almost entirely at the longitudinal seams and the cross joints, particularly at the corners,and at the intersection of the seams and cross joints.

A.1.2 Leakage related to duct areaIn practice, leakage can be taken as proportional to the surface areaof the ductwork, whether rectangular or circular, even though there maybe considerable variation in different sections of a complete systembecause of the changing sizes of the ducts and the number and varietyof the fittings. The surface area is easily calculable as part of thedesign procedure.

A.1.3 Pressure/leakage relationshipFor a given pressure, the leakage through an orifice of a given areawill vary according to its shape. With installed ductwork, the leakageorifices are of differing shapes, so a precise value cannot be givento the pressure/leakage relation shop. However, Swedish tests on avariety of constructions have shown that for ductwork operating withinthe range conered in this specification, leakage can be taken asproportional to pressure to the power of 0.65. (This value has beenadopted by EUROVENT in preparing their Document 2/2 - Air Leakage inDuctwork - see Appendix L - and has also been adopted in thisspecification (see Table 2) and has been applied in Table 31.

0.027 xp0.65

0.009 xp0.65

0.003 xp0.65

0.001 xp0.65

where p is the differential pressure in pascals

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A.2 LEAKAGE LIMITS - RELATIONSHIPS

A.2.1 Limits for each pressure classApplying the values given in Table 2 (page 13), the permitted leakageat each of a series of pressures up to the maximum for each class isset out in Table 31.

A.2.2 Graphical presentationsThe pressure/leakage relationships given in Table 31 are expressedgraphically in Fig. 169.

A.2.3 Leakage as a percentage of airflowAs air leakage is related to surface area of the ductwork, it cannotin advance of the detailed calculations be expressed as a percentageof total airflow, nor will a percentage loss be acceptable as a standardof performance. However, application of the leakage limits to a varietyof ductwork systems indicates that under iparating conditions air losseswill usually be within 6 per cent of total airflow for the low-pressureclass and 3 per cent for the medium-pressure class. For the high-pressureclass . Air loss is likely to be between 2 ans 0.5 per cent, according towhich leakage limit is applied.

A.2.4 Special casesThe percentages mentioned in A.2.3 apply to normal rations of duct areato normal ratios of duct area to airflow ; but where the ratio is high(e.g long runs of small ducts), it may be necessary for the designerto specify a higher standard of airtightness in order to keep the actualleakage within an acceptable limit.

A.2.5 Designer's required calculationsDesigners will be concerned with the total loss of air through leakagewhich must be allowed for the ductwork, and will need to ;

a) calculate the pressure class ;

b) calculate the surface area and estimate the mean system pressure difference for the ductwork system (or part of system) ;

Definition of mean pressurePm = P1 + P2, where ;

2Pm = mean or average pressure.P 1 = operating pressure at the beginning of the ductwork system or part of system.P 2 = operating pressure at the end of the ductwork system or part of system.IT IS RECOMMENDED THAT MAXIMUM TEST PRESSURES AND LEAKAGE RATESSHOWN IN TABLE 32, PAGE 17, BE ADOPTED.

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c) Calculate the total leakage using the appropriate rate from Table 31.

Alternatively, the designer may ;d) decide on the maximum total leakage that he can accept ;

e) calculate the wurface area and estimate the mean system pressure difference for the ductwork system (or part of system) and from thesedetermine the required pressure class.

A.2.6 Leakage of complete systemDW/142 deals only with the ductwork. The leakage characteristics of plantitems and accessories are not within the control of the ductwork contractor,and therefore any leakage limits and leakage testing called for underDW/142 shall be understood to apply only to the ductwork itself.

Table 31 Air Leakage ratesStatic Maximum leakage of ductworkpressure Low-pressureMed-pressure High-pressure

differential Class A Class B Class C Class D1 2 3 4 5Pa Litres per second per square metre of surface area

100 0.54 0.18200 0.84 0.28300 1.10 0.37400 1.32 0.44500 1.53 0.51600 0.58 0.19700 0.64 0.21800 0.69 0.23900 0.75 0.251000 0.80 0.271100 0.29 0.101200 0.30 0.101300 0.32 0.111400 0.33 0.111500 0.35 0.121600 0.36 0.121700 0.38 0.131800 0.39 0.131900 0.40 0.142000 0.42 0.142100 0.142200 0.152300 0.152400 0.162500 0.16

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Fig. 169 Permitted leakage at various pressures

(a) LOW & MEDIUM PRESSURE CLASSES-LEAKAGE LIMITS

(b) HIGH PRESSURE CLASSES-LEAKAGE LIMITS

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APPENDIX B - AIR LEAKAGE TESTING PROCEDURE

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B.1 GENERALSection 6 (page 13) of this specification deals with the performancerequirements of ductwork in respect or air leakage ; and Table 31 (Appendix A)tabulates the limits of leakage applicable to each class of ductwork. Appendix Bis solely concerned with recommendations for the testing procedure.

B.2 Extent of ductwork to be tested

B.2.1 The procedure set out in this section is limited to the ductwork. Terminalconnections, and items such as air handling devices, terminal boxes, soundattenuators, heat exchangers, builder's work construction, are excludedfrom the tests.

B.2.2 The proportion of the ductwork to be tested and the method of selection(where not included in the job specification) should be determined incollaboration between the designer and the ductwork contractor. Where themethod is by random selection, the use of polythene sheet or similarinsertion blamks between duct cross joints and duct-mounted componentswill assist in avoiding delays in installation when tests are beingcarried out.

B.2.3 To enable the blank to be cut out after the testing is completed, accessmay be required adjacent to each blank. This procedure used on eitherside of a duct-mounted component will enable the component to be includedin a sub sequent additional test if specified.

B.2.4 Alternatively, rigid removable blanking plates can be used, although thisinvolves remaking joints.

B.3 Testing to be completed before insulation, etc.Testing shall be satisfactorily completed before insulation or enclosure of theductwork and before terminal units (if any) are fitted.

B.4 Retesting procedure where necessary

B.4.1 The air leakage rate for any section shall not be in excess of thepermitted rate for that section. If a first test produces leakage inexcess of the permitted maximum, the section shall be resealed andretested until a leakage not greater than the permitted maximum forthat section is achieved.

B.4.2 If at the time of witnessing the test it is apparent that excessiveadditional sealing of seams or joints has been done in order to meetthe required leakage level, the section of ductwork under test shall notbe counted as part of the tested ductwork, except where the whole of theductwork is required to be tested.

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B.5 Minimum area to be testedThe section of ductwork to be tested shall have an area large enough to enablethe test aparatus to register a measurable leakage.

B.6 Test pressures and leakage ratesThe maximum permissible leakage rates for the full range of pressures are givenin Table 31. The recommended test pressures for the various classes of ductworkare set out in Table 32, and unless otherwise specified, the choice of testpressure shall be at the discretion of the test operator.

Table 31 Air Leakage ratesStatic Maximum leakage of ductworkpressure Low-pressur Med-pressur High-pressure

differential Class A Class B Class C Class D1 2 3 4 5Pa Litres per second per square metre of surface area

200 0.84400 1.32 0.44800 0.691200 0.301500 0.35 0.122000 0.14

B.7 Test apparatus

B.7.1 The accuracy of the test apparatus shall be within ;± 10 per cent of the indicated flow rate, or 0.4 litres per second,whichever is the greater ; and ± 5 per cent at the indicated staticpressure in the duct under test.

B.7.2 the test apparatus shall be inspected by the user before use on site, andshall have a calibration certificate, chart or graph dated not earlier thanone year before the test for which it is used.

B.7.3 A diagram of a suitable test apparatus is given in Fig. 171.

B.8 Procedure

B.8.1 The section of ductwork to be tested for air leakage shall be sealed.Main ducts should be provided with flanged joints to enable blanking platesto be fitted, while small open ends may be sealed with polythene orinflatable bags, which should be left in position until final connectionsare made.

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B.8.2 On low-pressure systems, final grille spigots made as a second fix operationshall be excluded from the test. The joint shall, where practicable, bechecked by external visual examination.

B.8.3 Sufficient time shall be allowed between erection and leakage testing forsealants to cure.

B.8.4 Special care must be exercised in making all joints which fall outsidethe scope of the testing procedure, i.e., joints between tested sdctionsof ductwork and between ductwork and other units.

B.8.5 Due notice of testes shall be given, so that arrangements for witnessingthe tests, if required, can be made.

B.9 Testing sequenceThe recommended sequence fo testing is as follows.

B.9.1 Complete Part 1 of the Test Sheet.

B.9.2 Connect test apparatus to section of ductwork to be tested.

B.9.3 Adjust test aparatus until the static pressure differential is obtained.

B.9.4 Check that the measured leakage is with in the permitted rate. (Noassition shall be made to the permissible leakage rate for access doors,access panels or dampers where these are included in the ductwork.)

B.9.5 Maintain the test for fiften minutes and check that the leakage ratehas not increased.

B.9.6 Reduce pressure in section to zero by switching off the fan ; thenimmediately re-apply test pressure to establish that the air leakage rateis not greater than the previous reading.

B.9.7 Record details on Part 2 of the Test Sheet and complete, including witnessing.

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B.10 Air leakage test sheetA specimen of a suitable Test Sheet is given on page 9.

Fig. 171 Diagram of typical apparatus for air leakage tests

Bleed valve(not necessarFlow measuring device Blanking plate

if variable speed (may be located on

fan used) the suction side of

the fan)

Electrically

driven fan

Duct under test

Dust test

Inclined gauge pressure gauge

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specification for sheetmetal ductwork. 1983

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The HVCA records its appreciation and thanks to the persons and organisations

who have freely contributed to this work, and in particular to the members

page 23 of 40

Ductwork Specification DW/142, published by the HVCA in 1982, provides for thefirst time in a long series of such publications for leakage limits over thewhole range of air pressures covered by the specification and (where required)

Although leakage testing of high-pressure ductwork is mandatory in DW/142(as was the case in previous ductwork specifications issued by HVCA) the leakagetesting of ductwork designed to operate at low and medium pressure is required

With the introduction of four pressure classifications in DW/142 it is hopedthat the designer,having selectional control of constructional srandards,willfind leakage testing an unnecessary contract expense with fegard to low andmedium pressure ductwork. However,it is possible that initially the advent ofmore stringent constructional requirements may be followed by an increaseddemand by clients and specifiers for the testing of low-and medium-pressureductwork and this booklet has been prepared in order to assist ductwork

It will be noted that the leakage limits speccified in Appendix A of DW/142

It is however possible that some ductwork specifications will still quote

In order that the area basis can be converted to a percentage equivalent a

Ductwork contractors faced with a job calling for leakage testing shouldtake this requirement very seriously and satisfy themseleves as the jobprogresses that the required leakage rate or rates are within the limits set bythe designer or the client. The cost of making good an installation that hasbeen found on completion to have failed in this respect can be very exprensive

DW/142 specifies leakage limits for the ductwork alone, not for the completeair distribution system. This is because the ductwork contractor has no controlover the leakage characteristics of the various components which go to make upthe whole of the air distribution system. Where a job specification calls fora leakage limits for the whole system. It will be for the designer or clientto ensure that the leakage rates of the components are also within the

Chairman, Executive Committee,

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With regard to air leakage, the responsibility for ensuring the achievementof a satisfactory job is divided between the Drawing Office, the Factory andthe Site Erection Operatives. It is essential that there is full co-operation

Establish with the client or his representatives the class of ductwork called

Establish with the client or his representative that the required leakagerate or rates are for the ductwork alone .i.e. excluding dampers,fire dampers,air handling units, fans, heater batteries, silencers, terminal boxes, etc. Additionally, establish the type of gasket material required in relation

Note : - Specific gasket material may be required in locations such as clean

If a leakage limits is laid down for the whole system, it will be for theclient or the designer to ensure that leakage characteristics of the

Agree with the client of designer the test pressure for eath section of the

Specification is related to the highest test class of the duct installationit is important that each duct test zone should only be tested to a pressureto cover the mean working pressure of that particular section of ducting

Decide on the best way to isolate the installation into test zones.When doing so, the drawing office should bear in mind the test pressurecalled for, the allowable air losses, the work sequence on site and the

Arrange for the supply of suitable blanking medium, e.g. heavy-duty

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Make sure that all test points and blanking devices can be reached with

To ensure that a reading can be obtained, plan test sections to have apermitted loss of approximately 25 per cent less than the total volumegenerated by the test rig at the pressure required for each section.

Provide the erectors with details of the test zones, duct operating pressureand test pressure; and indicate the nature of the blanking devices, gasket

Prepare test sheets giving the information called for on the sample test

This information should indicate the test content, the surface area of theductwork to be tested, and permitted loss for each section to be tested (this loss is to be expressed in litres per second per square metre of

Ductwork specification DW/142 requires the sealing of more joints than wasthe case in previous specifications. Care must therefore be taken to makecomponents with a good fit. and to use only enough sealant to make asatisfactory joint. A poor fit cannot be remedied by the use of more sealant

Seal all longitudinal seams, laps, cross joint, rivets and duct penetations

Make sure that sealant is properly applied to the ends of all lock formsnd other types of longitudinal seam, and to the corners and junctions between

Take special care to have as small a clearance as possible where are

First and seal branch connections carefully, as required by DW/142.

To be sure of minimum leakage, special care must be taken in the fitting and

To avoid the danger of breaking the seals, the ductwork when ready for

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For full details of procedure see Appendix B Pages 17 and 18 and the diagram

Understand the proper use of the testing. It is expensive precision equipment.The instructions must be read carefully and the equipment handled in

Make sure that the right type of test rig is available for the job.A rig suitable for high pressure leakage testing is seldom suitable oreconomic for testing low-or medium-pressure ductwork, and vice versa.

Note that leakage testing is always done under positive pressure even when

Inspect all duct sections to make sure that factory applied sealants havenot been damaged in transit. Makr good where any damage is noticed.

Ensure the correct gasket material has been supplied for your situation andthe application is in accordance with the manufacturer's instructions.Check with the drawings and specifications as to where sealants are to beused on the cross joints, and then apply the sealants as necessary.(Use only as much sealant as will do the job - too much sealant is as bad

Pay special attention to the sealing of joints that will be difficult to

Fix the blanking plates or other types of temporary seal in the positionsshown by the Drawing Office. (Again, make sure that the blanking material

At the earliest opportunity agree with the client or his clerk of works on a

To ensure that the ductwork has been correctly manufactured and site sealantcorrectly applied it is essential that a preliminary test is carried out oneach section of the work at the earliest opportunity - before presentation

If these preliminary tests show that the leakage is over the limit, then ;

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Look for any obvious places where there may be leaks, for example, an

NOTE : When smoke pellets are used, the smoke should be introduced downstream

Manufacturing faults should be reported to the factory immediately.

Repeat the test after allowing enough thme for the sealant to set.(Remember that sealants take longer to do this in cold weather.

Offer the section to the client's representative for formal acceptance :On successful completion of the test obtain a signature - on the

As tests are satisfactorily completed, remove all blanking off devices.

Multiply by

Multiply by

Example of a completed test sheetBased on ductwork shown on page 10 and 11

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(PROVIDED BY DESIGNERS)

(FROM DESIGNERS BY REF TO TABLE 32)

(FROM REF TO TABLE 31 OR 32)

(FROM CALCULATION BELOW)

(OBTAINED BY MULTIPLYING AND f)

(READ OFF MANOMETER ON TEST RIG)

(ALSO STATE MANUFACTURER & TYPE)

(FROM RIG MANU. LITERATURE)

(FROM RIG)

(DERIVED FROM CHARTSUPPLIED WITH RIG USING"d")

Area

square metres

54.405

13.925

1.440

6.706

3.533

80.009

page 29 of 40

TEST APPARATUSSite on firm level base andensure gauges are topped upwith correct fluid andzeroed prior tocommencing test.Fit correct flow measuringdevice.

WARNINGTake care not to over pressurisesystem under test

page 30 of 40

Part Two

The dimensions on this ductwork are used in an example on page 9

HOW TO FIND LEAKS1. Look - particularly at blanks, access openings and difficult joints.2. Listen - with test apparatus running, leaks should be audible.3. Feel - running your hand (particularly if wet) over joints can help to locate leaks.4. Soap and Water - Paint over joints and look for bubbles5. Smoke Pellet - placed inside ductwork (obtain permission for use)

page 31 of 40

This section is predominantly extracted from DW/142 - Specification for Sheet Metal

Ductwork, and for ease of reference the numbering as in DW/142 has been retained.

The leakage limits for EUROVENT classifications A,B and C, as set out in their

ducument 2/2 (Air Leakage in Ductwork) have been adopted for the low pressure,

medium pressure and high pressure Class C classifications. EUROVENT document 2/2

has no standard for a leakage class equivalent to our Class D and therefore the

leakage limits for high pressure ductwork used in DW/141 (the predecessor to DW/142)

6 AIR LEAKAGE STANDARS

Limits for each pressure class Permitted air leakage is related to four

The leakage factors used in Table 2 for Class A, B and C are the same asthose used for the classes similarly designated in the Eurovent Document

Applying the limits specified in Table 2, Appendix A (Table 31) sets out thepernitted leakage at each of a series of pressures up to the maximum for eachclass. Included in that appendix is a graphical presentation of the pressure/leakage relationship ; and also charts from which may be determined leakage

Appendix A also gives details of the basis for the leakage limits specfied

All ductwork operating at pressure classified in this specification as high pressure' shall be tested to establish conformity with the relevant

Testing for leakage of ductwork within the low and medium ranges of pressurein this specification will not form part of the ductwork cintract unlessthis requirement is set out in the job specification - sec also Note(2)

page 32 of 40

APPENDIX A - AIR LEAKAGE FROM DUCTWORK

Air leakage in installed ductwork occurs almost entirely at the longitudinal seams and the cross joints, particularly at the corners,

In practice, leakage can be taken as proportional to the surface areaof the ductwork, whether rectangular or circular, even though there maybe considerable variation in different sections of a complete systembecause of the changing sizes of the ducts and the number and varietyof the fittings. The surface area is easily calculable as part of the

For a given pressure, the leakage through an orifice of a given areawill vary according to its shape. With installed ductwork, the leakageorifices are of differing shapes, so a precise value cannot be givento the pressure/leakage relation shop. However, Swedish tests on avariety of constructions have shown that for ductwork operating withinthe range conered in this specification, leakage can be taken asproportional to pressure to the power of 0.65. (This value has beenadopted by EUROVENT in preparing their Document 2/2 - Air Leakage in

page 33 of 40

Applying the values given in Table 2 (page 13), the permitted leakageat each of a series of pressures up to the maximum for each class is

The pressure/leakage relationships given in Table 31 are expressed

As air leakage is related to surface area of the ductwork, it cannotin advance of the detailed calculations be expressed as a percentageof total airflow, nor will a percentage loss be acceptable as a standardof performance. However, application of the leakage limits to a varietyof ductwork systems indicates that under iparating conditions air losseswill usually be within 6 per cent of total airflow for the low-pressureclass and 3 per cent for the medium-pressure class. For the high-pressureclass . Air loss is likely to be between 2 ans 0.5 per cent, according to

The percentages mentioned in A.2.3 apply to normal rations of duct areato normal ratios of duct area to airflow ; but where the ratio is high(e.g long runs of small ducts), it may be necessary for the designerto specify a higher standard of airtightness in order to keep the actual

Designers will be concerned with the total loss of air through leakage

calculate the surface area and estimate the mean system pressure

P 1 = operating pressure at the beginning of the ductwork system

P 2 = operating pressure at the end of the ductwork system or

IT IS RECOMMENDED THAT MAXIMUM TEST PRESSURES AND LEAKAGE RATES

page 34 of 40

Calculate the total leakage using the appropriate rate from Table 31.

calculate the wurface area and estimate the mean system pressure difference for the ductwork system (or part of system) and from these

DW/142 deals only with the ductwork. The leakage characteristics of plantitems and accessories are not within the control of the ductwork contractor,and therefore any leakage limits and leakage testing called for underDW/142 shall be understood to apply only to the ductwork itself.

page 35 of 40

Fig. 169 Permitted leakage at various pressures

(a) LOW & MEDIUM PRESSURE CLASSES-LEAKAGE LIMITS

(b) HIGH PRESSURE CLASSES-LEAKAGE LIMITS

page 36 of 40

APPENDIX B - AIR LEAKAGE TESTING PROCEDURE

page 37 of 40

Section 6 (page 13) of this specification deals with the performancerequirements of ductwork in respect or air leakage ; and Table 31 (Appendix A)tabulates the limits of leakage applicable to each class of ductwork. Appendix Bis solely concerned with recommendations for the testing procedure.

The procedure set out in this section is limited to the ductwork. Terminalconnections, and items such as air handling devices, terminal boxes, soundattenuators, heat exchangers, builder's work construction, are excluded

The proportion of the ductwork to be tested and the method of selection(where not included in the job specification) should be determined incollaboration between the designer and the ductwork contractor. Where themethod is by random selection, the use of polythene sheet or similarinsertion blamks between duct cross joints and duct-mounted componentswill assist in avoiding delays in installation when tests are being

To enable the blank to be cut out after the testing is completed, accessmay be required adjacent to each blank. This procedure used on eitherside of a duct-mounted component will enable the component to be included

Alternatively, rigid removable blanking plates can be used, although this

Testing shall be satisfactorily completed before insulation or enclosure of the

The air leakage rate for any section shall not be in excess of thepermitted rate for that section. If a first test produces leakage inexcess of the permitted maximum, the section shall be resealed andretested until a leakage not greater than the permitted maximum for

If at the time of witnessing the test it is apparent that excessiveadditional sealing of seams or joints has been done in order to meetthe required leakage level, the section of ductwork under test shall notbe counted as part of the tested ductwork, except where the whole of the

page 38 of 40

The section of ductwork to be tested shall have an area large enough to enable

The maximum permissible leakage rates for the full range of pressures are givenin Table 31. The recommended test pressures for the various classes of ductworkare set out in Table 32, and unless otherwise specified, the choice of test

Litres per second per square metre of surface area

± 10 per cent of the indicated flow rate, or 0.4 litres per second,whichever is the greater ; and ± 5 per cent at the indicated static

the test apparatus shall be inspected by the user before use on site, andshall have a calibration certificate, chart or graph dated not earlier than

The section of ductwork to be tested for air leakage shall be sealed.Main ducts should be provided with flanged joints to enable blanking platesto be fitted, while small open ends may be sealed with polythene orinflatable bags, which should be left in position until final connections

page 39 of 40

On low-pressure systems, final grille spigots made as a second fix operationshall be excluded from the test. The joint shall, where practicable, be

Sufficient time shall be allowed between erection and leakage testing for

Special care must be exercised in making all joints which fall outsidethe scope of the testing procedure, i.e., joints between tested sdctions

Due notice of testes shall be given, so that arrangements for witnessing

Adjust test aparatus until the static pressure differential is obtained.

Check that the measured leakage is with in the permitted rate. (Noassition shall be made to the permissible leakage rate for access doors,access panels or dampers where these are included in the ductwork.)

Maintain the test for fiften minutes and check that the leakage rate

Reduce pressure in section to zero by switching off the fan ; thenimmediately re-apply test pressure to establish that the air leakage rate

Record details on Part 2 of the Test Sheet and complete, including witnessing.

page 40 of 40

Duct under test

pressure gauge