Tiêu chuẩn ống gió DW 143

A practical guide to Heating and Ventilating Contractors' Association Ductwork Leakage Testing DW/143 DW/1 43 Ductwork Leakage Testing A practical guide A practical guide to — Ductwork Leakage Testing Based on the requirements of DW/144 specification for sheet metal ductwork First published Second edition (reprinted) Third edition (reprinted) Fourth edition (reprinted) Fifth edition (revised) 1983 1986 1991 1994 2000 HEATING AND VENTILATING CONTRACTORS' ASSOCIATION Esca House, 34 Palace Court, London W2 4JG Telephone: (020) 7313 4900 Fax: (020) 7727 9268 e-mail: contact@hvca.org.uk web: www.hvca.org DJ/ 43 COPYRIGHT © 2000 by the Heating and Ventilating Contractors Association All rights reserved ISBN: 0-903783-30-4 DW/1 43 Ductwork Leakage Testing A practical guide CONTENTS Page 2 Acknowledgements Cautions Preface PART ONE Practical guide to leakage testing Example of complete test sheet Hints on leakage testing 4-6 8-9 PART TWO Ductwork classification and air leakage Appendix A: Air leakage from ductwork Appendix B: Air leakage testing procedure 10 11-13 13-16 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 Original DW/143 Drafting Panel 1983 J H G Gardner (Chairman) K Angood H Brierley H Brocklehurst P Doyle K Waldron K Wheatley Ductwork Group Technical Sub-Committee 2000 E Poppleton (Chairman) C Collins S V Howard B James J E Murray C Robertson G P Keller (Secretary, Ductwork Group) J M Paynton (Former Secretary, Ductwork Group) R J Miller (Former Secretary, Ductwork Group) Front cover photograph by kind permission of Commtech Limited FINANCIAL CAUTION It is essential to realise that except where it is mandatory in Class C ductwork in DW/l44 this document is not an endorsement of the routine testing of ducts but purely a guide to outline the procedures, necessary for testing ducts for conformity with air leakage limits When proper methods of assembly and sealing of ducts are used a visual inspection will suffice for the verification of a well engineered construction WHERE NOT MANDAT0R} DUCT LEAKAGE TESTING IS GENERALLY AN UNJUSTIFIED SUBSTANTIAL EXPENSE DW/1 43 Ductwork Leakage Testing A practical guide PREFACE Edgar Poppleton Chairman, Technical Sub-Committee Ductwork Group, 2000 Specification DW/142, published by the HVCA in 1982, provided for the first time in a long series of such publications for leakage limits over the whole 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 still mandatory in DW/144 (as was the case in previous ductwork specifications issued by HVCA) the leakage testing of ductwork designed to operate at low and medium pressures is required only where so specified in individual job specifications Ductwork With the retention of three pressure classifications in DW/144 it is hoped that the designer, having control over performance standards, will find leakage testing an unnecessary contract expense with regard to low and medium pressure ductwork see note Financial Caution (page 2) Ductwork contractors faced with a job calling for leakage testing should take this requirement very seriously and satisfy themselves as the job progresses that the required leakage rate or rates are within the limits set by the designer or the client The cost of making good an installation that has been found on completion to have failed in this respect can be very expensive DW/144 specifies leakage limits for the ductwork alone, because the ductwork contractor has no control over the leakage characteristics of the various components which go to make up the whole of the air distribution system Where a job specification calls for a leakage limit for the whole system, it will be for the designer or client to ensure that the leakage rates of the components are also within the required limits Edgar Poppleton Chairman, Technical Sub-Committee Ductwork Group, 2000 DW/1 43 Ductwork Leakage Testing A practical guide Part One A practical guide to ductwork leakage testing I tion is related to the highest test class of the duct installation it is important that each duct test zone should only be tested to a pressure to cover the mean working pressure of that particular section of ducting — see A.9(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 pressures called for, the allowable air losses, the work sequence on site and the capacity of the test equipment General With regard to air leakage, the responsibilities for ensuring the achievement of a satisfactory job is divided between the drawing office, the factory and the ductwork installers 2.5 Arrange for the supply of suitable blanking medium, e.g heavy-duty polythene sheet on site It is essential that there is full cooperation between them 2.6 Make sure that all test points and blanking devices can be reached with the minimum of The drawing office difficulty after the ductwork has been installed 2.1 Establish with the client or his representatives the class of ductwork called for in the job specification, i.e.: Class A: up to 500 Pa positive Class B: up to 1000 Pa positive Class C: up to 2000 Pa positive 2.2 Establish with the client or their represent- ative that the required leakage rate or rates are for the ductwork alone (eg excluding dampers, fire dampers, air handling units, 2.7 Ensure that a reading can be obtained, by planning test sections to have a permitted leakage of approximately 25 per cent less than the total volume generated by the test rig at the pressure required for each section 2.8 Provide the ductwork installers with details of the test zones, duct operating pressures and test pressures: and indicate the nature of the blanking devices, gasket material and fans, coils, attenuators, terminal boxes) unless, by prior agreement, the casings for any such items have been manufac- 2.9 Prepare test sheets giving the information turedlsealed, by the supplier, to the required standard of DW/l44 called for on the sample test sheet shown on page Additionally, establish the type of gasket This information should indicate the test material required in relation to the pressure class/velocity of the system content, the surface area of the ductwork to be tested, and the permitted leakage of each Note:- Specific gasket material may be section to be tested (this leakage is to be expressed in litres per second per square sealant to be used required in locations such as clean rooms, hospitals etc If a leakage limit is laid down for the whole system, it will be for the client or the designer to ensure that the leakage characteristics of the components are acceptable 2.3 Agree with the client or designer the test pressure for each section of the installation (Note that whilst duct construction specifica- metre of the ductwork surface area) The factory 3.1 Take care to make components with a good fit to minimise the use of sealant A poor fit cannot be remedied by the use of more sealant — it will not work DW/1 43 Ductwork Leakage Testing A practical guide 3.2 Seal all longitudinal seams, laps cross joints rivets and duct penetrations generally in 4.5 Ensure the correct gasket material has accordance with the requirements of dance with the manufacturer's instructions Check with the drawings and specifications where sealants are to be used on the cross joints, and apply the sealants as necessary (Use only as much sealant as will the job — too much sealant is as bad as too little.) been supplied and the application is in accor- DW/l44 3.3 Make sure that sealant is properly applied to the ends of all lock forms and other types of longitudinal seam, and to the corners and junctions between those seams and the cross joints 3.4 4.6 Take special care to have as small a clearance special attention to the sealing of joints that will be difficult to reach after installation of the ductwork as possible where there are penetrations of the duct, as for example damper spindles 4.7 Fix the blanking plates or other types of temporary seal in the positions shown by the drawing office (Ensure that the blanking material is accessible for subsequent removal.) 3.5 Fit and seal branch connections carefully, as required by DW/l44 3.6 To be sure of minimum leakage special care 4.8 At the earliest opportunity agree with the must be taken in the fitting and sealing of client or their representative on a progressive testing programme access doors and panels etc 3.7 To avoid the danger of breaking the seals, the ductwork when ready to despatch to site must be handled and loaded carefully Pay Site work For full details of procedure see Fig I on Pages and and Appendix B Pages 14 and 15 4.9 Before presentation to the client or their rep- resentative it is essential that a preliminary test is carried out on each section of the work at the earliest opportunity to ensure that the ductwork has been correctly manufactured and site sealant correctly applied 4.10 If these preliminary tests show that the leakage is over the limit, then: 4.1 the proper use of the test rig It is expensive precision equipment The instructions must be read carefully and the 4.10.1 Look for any obvious places where equipment handled in a responsible manner open access door or missing or Understand there may be leaks, for example, an punctured 4.2 polythene blanks Make sure that the right type of test rig is Simple methods of locating any available for the job A rig suitable for highpressure leakage testing is seldom suitable or economic for testing low- or medium- pressure ductwork, and vice versa leakage are: a) by listening for them; b) by feeling for them especially with a wet hand; c) by applying soapy water over 4.3 Note that leakage testing is always done under positive pressure even when the ductwork is to operate under negative pressure the seams or joints; d) by (with the agreement of the client) using a smoke pellet NOTE When smoke pellets are 4.4 Before installation, inspect all duct sections to make sure that factory applied sealants have not been damaged in transit Make good where any damage is noticed used, the smoke should he introduced downstream of the test rig and not on its intake side DW/1 43 Ductwork Leakage Testing A practical guide 4.10.2 Reseal or correct where you have found the leakage source(s) Manufacturing faults be reported to the should factory immediately 4.10.3 Repeat the test after allowing enough time for the sealant to cure (Remember that sealants take longer to cure in cold weather Read the sealant manufacturer's instructions.) 4.1 When satisfied with the results of the preliminary tests then:- 4.1 1.1 On successful completion of the test, offer the section to the client or their representative for formal acceptance and signature on the test sheet; 4.1 1.2 A permanent record of tests must be retained 4.12 As tests are satisfactorily completed, remove all blanking-off devices DW/1 43 Ductwork Leakage Testing A practical guide Example of a completed test sheet Based on ductwork shown on pages and Test No (;eneral Name of job !' Building Ref Part — Physical details a Section of ductwork to be tested b Drawing Number c Pressure Classification ' RO.uI)ESiG.VERSi d Test static pressure ?.cq e Leakage factor f Surface area of duct under test g Maximum permitted leakage k Part — Test particulars Q!19? a Duct static pressure reading b Manufacturer and type of flow measuring device c Range of measurement of flow measuring device d Reading of flow measuring device e Interpreted air flow leakage rate !' f Duration of test (normally 15 minutes) Carried out S:naturej by ?"' Date of test Printed Name Y'9(N and Company fROM RIG MANLF4cTURERS DERIVED FROM CHART SLPPUED WITH RIG LSIVG Witnessed by di SgnuIure) Printed Name and Company Width and depth or diameter Periphery Length Area millimetres millimetres metres square metres 800x750 3100 17.55 54.40 600x650 2500 5.57 13.93 300x300 1200 1.20 1.44 - 305 dia 958 7.04) 6.70 250 dia 785 4.50 3.53 TOTAL 80.00 I 300 x ru 3050 TEST RIG To be connectedand operatedin accordanceWith the apparatus instructions In general, site on firm level base and ensure gauges are tc!ppedup with correct fluid and zemed prior to commencing test Inclined manometerto read leakage rate or pressure drop which can be converted to leakage rate by referenceto graph Tab car notto ov.r pr surls system undsrtest WARNING device Fit correct flow SEQUENCE OF TEST Ptepare test sheet Connect and adjusttest rig to correct pressure Read off leakage rate Reseal ifnecessary(allow time to cure) Mintthn test for 15 mins Switch off and allow to Reapply test pressure and check reading Record details on test sheet and obtain signature dfrectlytothe ductwork uider test should be couuected of duct pressure the tube fre the luordertoavold 600 x 650 Takespecialcare with inaccessible joints Hints on Ductwork Leakage Testing Testing A practical guide FLEX Keep length to a minimum and make sure that both end connectionsare correctly sealed and that the flexible duct itselfhas no leaks Fig DW/1 43 Ductwork Leakage to read pleasure m test Vermaixjsneter test 700 800 x 750 Blank at convenient Placeweli access for ease of removal 800 x - A practical guide D1W No 20433/12 HOW TO FIND LEAKS — I.I eok perlicularlyatblanks,accesaopeninp and difficukjoints Listen Withtestngnmningleaks shonidbeaudible — running yourhand (particularlyifwet) Feel over joints can help to locate leakL Soap and Water — paint overjoints and look kr bubbles Smoke Pellet — placed inkIn ductwork (obtainpermission kr use) er Rneinherto blaM inum and Blank offall open Ductwork Leakage Testing The dimensions on this ductwork are used in an example on page DW/1 43 Page blank in original DW/1 43 Ductwork Leakage Testing A practicalguide Part Two 6.4 Air leakage testing Air leakage testing of low and medium pres- sure ductwork is not mandatory under the This section, apart from Appendix 'B', is specification DW/l44 Air leakage testing of high pressure ductwork is mandatory under the specification DW/l44 and for details of testing procedure refer to Part of this guide extracted from DW/144 — Specification for Sheet Metal Ductwork, and for ease of reference the numbering as in DW/144 has been retained The leakage limits for EUROVENT classifications A, B and C, as set out in their document 2/2 (Air Leakage in Ductwork) have been adopted for the low pressure, medium pressure and high pressure Class C classifications Ductwork classification and air leakage 6.1 Classification and air leakage limits Ductwork classification and air leakage limits are set out in Table I 6.2 Compatibility with CEN The leakage factors used in Table for Classes A, B and C are the same as those for the classes similarly designated in the CEN Document Pr EN 12237/Pr EN 1507 6.3 Leakage at various pressures; and other relationships Applying the limits specified in Table I, Appendix A (Table 17) sets out the permitted leakage at each of a series of pressures up to a maximum for each class Included in that appendix is a graphical presentation of the pressure/leakage relationship (see fig 178) Appendix A, also gives details of the basis for the leakage limits specified in Table Table Ductwork Classification and Air Leakage Limits Static pressure limit Ductpressureclass Low-pressure — Class A Medium-pressure — Class B I High-pressure — Class C Positive Negative velocity Air leakage limits litres per second per square metre of duct surface area Pa Pa 500 rn/s 10 0.027 x p01 750 750 20 0.009 x p°'65 -40 0.003 x p°-65 500 1000 2000 Where p is the differential, pressure in pascals 10 Maximum air' DW/1 43 Ductwork Leakage Testing A practical guide APPENDIX A Air leakage from ductwork —750 Pascals Class C High pressure ducts suitable for a maximum positive operating pressure of 2000 Pascals and a maximum negative pressure of —750 Pascals A.1 Introduction A.3 Leakage from ductwork Leakage from ducted air distribution systems is an important consideration in the design and operation of ventilation and air conditioning systems A ductwork system that has limited air leakage, within defined limits, will ensure that the design characteristics of the system can be maintained It will also ensure that energy and operational costs are maintained at optimum levels Ductwork constructed and installed in accordance with DW/144 should minimise a level of air leakage that is appropriate to the oper- Leakage from sheet metal air ducts occurs at the seams and joints and is therefore proportional to the total surface area of the ductwork in the system The level of leakage is similarly related to the air pressure in the duct system and whilst there is no precise formula for calculating the level of air loss it is generally accepted that leakage will increase in proportion to pressure to the power of 0.65 The effect of air leakage from high pressure/velocity ductwork is critical in terms of ating static air pressure in the system system performance energy consumption However, it is recognised that the environment in which systems are installed is not always conducive to achieving a predictable and the risk of high frequency noise associated with leakage These problems are less critical with medium level of quality in terms of system air leakage pressure/velocity systems but should be and it is therefore accepted that designers considered may sometimes require the systems to be tested in part or in total It should be recognised that the testing of duct systems adds a significant cost to the installation and incurs some extra time within the programme (See 4.1 and 6.4 of DW/144 re mandatory testing) Low pressure/velocity ducts present the lowest risk in terms of the effect of leakage on the effective operation of the system A.4 System leakage loss As there is no direct relationship between the A.2 Duct pressure Ductwork constructed to DW/144 will be manufactured to a structural standard that is compatible with the system operating pressure There are three classes of duct construction to correspond with the three pressure classifications: Class A Low pressure ducts suitable for a maximum positive operating pressure of 500 Pascals and a maximum negative pressure of —500 Pascals Class B Medium pressure ducts suitable for a maxi- mum positive operating pressure of 1000 Pascals and a maximum negative pressure of volume of air conveyed and the surface area of the ductwork system required to match the building configuration it is difficult to express air leakage as a percentage of total air volume Similarly, the operating pressure will vary throughout the system and as leakage is related to pressure the calculations are complex However, it is generally accepted that in typical good quality systems the leakage from each class of duct under operating conditions will be in the region of: 6% Class A low pressure Class B medium pressure 3% 2% Class C high pressure DW/1 43 Ductwork Leakage Testing A practicalguide A.5 Specifying air leakage testing both the cost and programme In the case where a random test is selected for medium pressure ducts the following clause is suggested for inclusion by the designer implications associated with testing ducts for leakage, the designer may, for example indi- mum of 10% of the duct system to be tested for Respecting The designer shall select at random a inaxi- cate that a particular system is tested as air leakage The duct shall be tested at the follows: a) High pressure ducts — all tested pressure recommended in Table 17 of DW/144 b) Medium pressure ducts — 10% for the classification for the section of the of the ductwork shall be selected at random and tested c) Low pressure — untested Table 17 Air leakage rates Maximum leakage of ductork Static Low-pressure Class A pressure Medium-pressure Class B High-pressure Class C differential ductwork that is to be tested The tests shall be carried out as the t'ork proceeds and prior to the application of thermal insulation In the event of test failure of the randomly selected section, the designer shall have the right to select two further sections at random for testing Where successive failures are identified there shall be a right to require the contractor to apply remedial attention to the complete ductwork system Lit:es per second per square metre of su:ce area Pa 100 0.54 0.18 200 0.84 0.28 300 1.10 0.37 400 1.32 0.44 500 1.53 0.51 There may be situations on a project where 0.58 0.19 700 0.64 0.21 800 0.69 0.23 900 0.75 0.25 1000 0.80 - 0.27 1100 0.29 1200 0.30 1300 0.32 1400 0.33 1500 0.35 1600 0.36 1700 0.38 1800 0.39 1900 0.40 2000 0.42 Note: Recommended 'mean' test pressures are highlighted in bold type with the actual selection being left to the test 12 evidence of the calculations used to arrive at the allowable loss for the section to be tested and the client, or his agent, shall witness and sign the results of the test A.6 Special cases 600 operator The contractor shall provide documented circumstances dictate that special consideration be given to containing air losses, e.g a long run of ductwork may incur a disproportionate level of air loss In cases such as this example the designer can specify an improved standard of airtightness, i.e 80% of allowable loss for Class 'B' ducts The designer should not specify a Class 'C' test at Class 'C' pressure for a Class 'B' duct A.7 Suggested range of testing cautionary note on page of this guide) 100% test • High pressure ducts • Medium pressure ducts see A5 • Low pressure ducts Untested Untested • Exposed extract systems • Ceiling void extract Untested systems • Secondary ducts from VAV or fan coil units Untested • Flexible ducts Untested (see — • Final connections and branches to grilles and diffusers DW/1 43 Ductwork Leakage Testing A practical guide Appendix B Untested A.8 Testing of plant items Air leakage testing Procedure Items of inline plant (eg Figs 168 to 175) will not normally be included in the air leakage test The ductwork contractor may include such items in the test if the equipment has a certificate of conformity for the pressure class and air leakage classification for the system under test A.9 Designer's calculations B.1 General Section (page 10) of this specification deals with the performance requirements of ductwork in respect of air leakage, and Table 17 (Appendix A) tabulates the limits of leakage applicable to each class of ductwork Appendix B is solely concerned with recommendations for the testing procedure The designer can calculate with reasonable accuracy the predicted total loss from a system by: a) Calculating the operating pressure in each section of the system b) Calculating the surface area of the B.2 Extent of ductwork to be tested B.2.1 The procedure set out in this section ductwork in each corresponding pressure section is limited to the ductwork and those items of in-line plant equipment that are manufacturedlsealed to the crite- c) Calculating the allowable loss at the ria set out in Table (also see operating pressure for each section of the system (see Table 17 for allowable leakage figures) A.1O Variable pressures in systems Designers can achieve significant cost savings by matching operating pressures throughout the system to constructional standards and appropriate air leakage testing e.g the practice of specifying construction standards for whole duct systems based on fan discharge pressures may incur unnecessary costs on a project For example, some large systems could well be classified for leakage limits as follows: Plant room risers Class C Main floor distribution Class B Low pressure outlets Class A Appendix A.8) B.2.2 The extent of the ductwork to be tested and the method of selection (where not included in the job specification) should be determined in collaboration between the designer and the ductwork contractor with consideration having been given to the recommendations outlined in Appendix A B.2.3 Fit blanking devices in accordance with the drawing office guidance notes (Part I, Section 2) To enable a blank to be cut out after the testing is completed, access may be required adjacent to each blank B.2.4 Alternatively, rigid removable blanking plates can be used, although this involves remaking joints 13 DW/1 43 Ductwork Leakage Testing A practical guide Fig 178 Permitted leakage at various pressures Leakage in litres per second per square metre duct surface area ** * * *-t — 'I * * *-t * * Cl DW/1 43 Ductwork Leakage Testing A practical guide B.3 Testing to be completed before insulation, etc B.6 Test pressures and leakage rates shall be satisfactorily completed before insulation or enclosure of the ductwork and before terminal units (if any) are The maximum permissible leakage rates for fitted various classes of ductwork are set out in Testing the full range of pressures are given in Table 17 The recommended test pressures for the Table 2, and unless otherwise specified, the choice of test pressure shall be at the discretion of the test operator B.4 Re-testing procedure where necessary B.4.1 The air leakage rate for any section B.7 Test rig shall not be in excess of the permitted rate for that section If a first test B.7.1 The accuracy of the test rig shall be produces leakage in excess of the permitted maximum, the section within: ± 10 per cent of the indicated flow shall be resealed and retested until a leakage not greater than the permit- rate, or 0.4 litres per second whichever is the greater and ± per cent at the indicated static pressure in the duct under test ted maximum for that section is achieved B.4.2 If at the time of witnessing the test it B.7.2 The test rig shall be inspected by the user before use on site, and is apparent that excessive additional sealing of seams or joints has been shall have a calibration certificate, chart or graph dated not earlier than one year before the test for which it is used done in order to meet the required leakage level, the section of ductwork under test shall not be counted as part of the tested ductwork, B.7.3 except where the whole of the ductwork is required to be tested A schematic arrangement of an air leakage test is given in Fig B.8 Procedure B.5 Minimum area to be tested The section of ductwork to be tested shall B.8.1 The section of ductwork to be test- have an area large enough to enable the test rig to register a measurable leakage ed for air leakage shall be sealed Main ducts should be provided Table Recommended maximum test pressures (with leakage rates) Maximum leakage of ductwork Static pressure differential Low-pressure Class A Medium-pressure Class B High-pressure I Pa 200 400 800 1200 1500 Class C Litres per secnd per square metre 'of surface area 0.84 1.32 0.44 0.69 0.30 0.35 - DW/1 43 Ductwork Leakage Testing A practical guide with flanged joints to enable B.9.1 Complete Part of the Test Sheet blanking plates to be fitted, while B.9.2 small open ends may be sealed with polythene or inflatable bags, which should be left in position until final connections are made Connect test rig to section of duct- work to be tested B.9.3 Adjust test rig until the static pressure differential is obtained B.8.2 On low-pressure systems, final B.9.4 grille spigots made as a second fix within the permitted rate (No addition shall be made to the permissible leakage rate for access doors, access panels or dampers where these are included in the ductwork.) operation shall be excluded from the test The joint shall, where practica- ble, be checked by external visual examination B.8.3 Sufficient time shall be allowed between installation and leakage B.9.5 Maintain the test for fifteen minutes and check that the leakage rate has not increased testing for sealants to cure B.8.4 B.8.5 Special Check that the measured leakage is care must be exercised in making all joints which fall outside the scope of the testing procedure i.e., joints between tested sections of ductwork and between ductwork and items of in-line equipment not included in the test B.9.6 Due notice of tests shall be given, so B.9.7 Reduce pressure in section to zero by switching off the fan; then imme- diately re-apply test pressure to establish that the air leakage rate is not greater than the previous reading Record details on Part of the Test Sheet and complete, including witnessing that arrangements for witnessing the tests can be made B.9 Testing sequence B.1O Air leakage test sheet A example of a suitable Test Sheet is give on page The recommended sequence of testing is as follows Fig Schematic arrangement of an air leakage test Blanking plate Flow measunng device (may be located on the suction side of the fan( Duct under test fan Duct test pressure gauge Inclined gauge 16 Bleed valve (not necessary if variable speed fan used( Heating and Ventilating Contractors' Association Esca House 34 Palace Court London W2 4JG Tel: 020 7313 4900 Fax: 020 7727 9268 e-mail contact@hvca.org.uk web site www.hvca.org.uk Publications Department Mansion House Eamont Bridge Penrith Cumbria CA1O 2BX Old Tel: 01768 860405 Fax: 01768 860401 email: hvcapublications@hvwelfare.co.uk website: www.hvca.org.uk [...].. .DW/ 1 43 Ductwork Leakage Testing A practicalguide Part Two 6.4 Air leakage testing Air leakage testing of low and medium pres- sure ductwork is not mandatory under the 6 This section, apart from Appendix 'B', is specification DW/ l44 Air leakage testing of high pressure ductwork is mandatory under the specification DW/ l44 and for details of testing procedure... testing of high pressure ductwork is mandatory under the specification DW/ l44 and for details of testing procedure refer to Part 1 of this guide extracted from DW/ 144 — Specification for Sheet Metal Ductwork, and for ease of reference the numbering as in DW/ 144 has been retained The leakage limits for EUROVENT classifications A, B and C, as set out in their document 2/2 (Air Leakage in Ductwork) have been... and incurs some extra time within the programme (See 4.1 and 6.4 of DW/ 144 re mandatory testing) Low pressure/velocity ducts present the lowest risk in terms of the effect of leakage on the effective operation of the system A.4 System leakage loss As there is no direct relationship between the A.2 Duct pressure Ductwork constructed to DW/ 144 will be manufactured to a structural standard that is compatible... B.2.4 Alternatively, rigid removable blanking plates can be used, although this involves remaking joints 13 DW/ 1 43 Ductwork Leakage Testing A practical guide Fig 178 Permitted leakage at various pressures Leakage in litres per second per square metre duct surface area ** * * *-t — 'I * * *-t * * Cl DW/ 1 43 Ductwork Leakage Testing A practical guide B.3 Testing to be completed before insulation, etc B.6... second per square metre of duct surface area 5 2 3 Pa Pa 500 rn/s 10 0.027 x p01 750 750 20 0.009 x p°'65 -40 0.003 x p°-65 500 1000 2000 Where p is the differential, pressure in pascals 10 Maximum air' DW/ 1 43 Ductwork Leakage Testing A practical guide APPENDIX A Air leakage from ductwork —750 Pascals Class C High pressure ducts suitable for a maximum positive operating pressure of 2000 Pascals and a... that in typical good quality systems the leakage from each class of duct under operating conditions will be in the region of: 6% Class A low pressure Class B medium pressure 3% 2% Class C high pressure DW/ 1 43 Ductwork Leakage Testing A practicalguide A.5 Specifying air leakage testing both the cost and programme In the case where a random test is selected for medium pressure ducts the following clause... shall select at random a inaxi- cate that a particular system is tested as air leakage The duct shall be tested at the follows: a) High pressure ducts — all tested pressure recommended in Table 17 of DW/ 144 b) Medium pressure ducts — 10% for the classification for the section of the of the ductwork shall be selected at random and tested c) Low pressure — untested Table 17 Air leakage rates Maximum... extract systems • Ceiling void extract Untested systems • Secondary ducts from VAV or fan coil units Untested • Flexible ducts Untested (see — • Final connections and branches to grilles and diffusers DW/ 1 43 Ductwork Leakage Testing A practical guide Appendix B Untested A.8 Testing of plant items Air leakage testing Procedure Items of inline plant (eg Figs 168 to 175) will not normally be included... the design characteristics of the system can be maintained It will also ensure that energy and operational costs are maintained at optimum levels Ductwork constructed and installed in accordance with DW/ 144 should minimise a level of air leakage that is appropriate to the oper- Leakage from sheet metal air ducts occurs at the seams and joints and is therefore proportional to the total surface area... pressure differential Low-pressure Class A Medium-pressure Class B High-pressure I 2 3 4 Pa 200 400 800 1200 1500 Class C Litres per secnd per square metre 'of surface area 0.84 1.32 0.44 0.69 0.30 0.35 - DW/ 1 43 Ductwork Leakage Testing A practical guide with flanged joints to enable B.9.1 Complete Part 1 of the Test Sheet blanking plates to be fitted, while B.9.2 small open ends may be sealed with polythene