DW143 Ductwork Leakage Testing [PDF]

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143 A practical guide to



DUCTWORK LEAKAGE TESTING Based on the requirements of DW/142 specification for sheet metal ductwork



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COPYRIGHT © 1983 by the Heating and Ventilating Contractors' Association All rights reserved



HEATING AND VENTILATING CONTRACTORS' ASSOCIATION Esca House, 34 Palace Court, London W2 4JG Telephone: 071 229 2488 Fax: 071 727 9268



Obtainable from: HVCA Publications, Old Mansion House, Eamont Bridge, Penrith, Cumbria, CAIO 2BX Telephone: (0768) 64771 Fax: (0768) 67138 Price: £9 (including inland postage) Overseas: Surface mail £10.50 Air mail £11.00



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Contents Part One



Page



Acknowledgements



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4



Preface



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5



Financial Caution



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6



Practical Guide to leakage testing



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7-8



Example of complete test sheet



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9



Hints on leakage testing



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10-11



Part Two



Page



13-15



Air leakage from ductwork Nomogram converting area basis to percentage of airflow



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16



Air leakage testing procedure



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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. Brocklehurst 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 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 mandatory in DW/142 (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. With the introduction offour pressure classifications in DWI142 it is hoped that the designer, having selectional control of constructional standards, will find leakage testing an unnecessary contract expense with regard to low and medium pressure ductwork. However, it is possible that initially the advent of more stringent constructional requirements may be followed by an increased demand by clients and specifiers for the testing oflow-and medium- pressure ductwork and this booklet has been prepared in order to assist ductwork contractors to minimise the cost of this unfamiliar operation. It will be noted that the leakage limits specified in Appendix A of DW/142 are expressed in litres per second per square metre of duct area. It is however possible that some ductwork specifications will still quote leakage limits as a percentage of air flow. In order that the area basis can be converted to a percentage equivalent a nomogram from DW/142 has been reproduced in this booklet on Page 16. 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 indeed. DW/142 specifies leakage limits for the ductwork alone, not for the complete air distribution system. This is 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.



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



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FINANCIAL CAUTION



As highlighted in the Prefaces ofboth this document and DWI142 not enough emphasis can be placed on the fact that the much tighter ductwork constructional standards brought about by the general acceptance of DW/142, virtually negates the requirement for leakage testing, except for the high pressure classes C & D. It is essential to realise that except where it is mandatory this document is not an endorsement of the routine testing ofducts but purely a guide to outline the procedures, necessary for testing ducts for conformity with air leakage limits set forth in a designer's specification. When proper methods of assembly and sealing of ducts are used a visual inspection will ordinarily suffice for verification of well engineered reasonably air right construction.



WHERE NOT MANDATORY, DUCT LEAKAGE TESTING IS GENERALLY AN UNJUSTIFIED SUBSTANTIAL EXPENSE.



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Part One - A practical guide tel ductwork leakage testing I GENERAL With regard to air leakage, the responsibility for ensuring the achievement of a satisfactory job is divided between the Drawing Office, the Factory and the Site Erection Operatives. It is essential that there is full co-operation between them.



2.5 Arrange for the supply of suitable blanking medium, e.g. heavy-duty polythene sheet. 2.6 Make sure that all test points and blanking devices can be reached with the minimum of difficulty after the ductwork has been installed.



2 THE DRAWING OFFICE



2.7 To ensure that a reading can be obtained, plan test sections to have a permitted loss of approximately 25 per cent less than the total volume generated by the test rig at the pres-



The drawing office must: 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 Class D: up to 2500 Pa positive



sure required for each section.



2.8 Provide the erectors with details of the test zones, duct operating pressures and test pressures; and indicate the nature of the blanking devices, gasket material and sealant to be used. 2.9 Prepare test sheets giving the information called for on the sample test sheet shown on page 9. This information should indicate the test content, the surface area of the ductwork to be tested, and the permitted loss for each section to be tested (this loss is to be expressed in litres per second per square metre of the ductwork).



2.2 Establish with the client or his representative that the required leakage rate 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 to the pressure class/velocity of the system.



3 THE FACTORY



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



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



H 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 specification 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 ofducting - see A.2.5(b).



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



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.



junctions between those seams and the cross



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



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



carried out on each section of the work at the earliest opportunity - before presentation to the client.



3.6 To be sure of minimum leakage, special



4.10 If these preliminary tests show that the leakage is over the limit, then: 4.10.1 Look for any obvious places where there may be leaks, for example, an open 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 especially 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 time for the sealant to set. (Remember that sealants take longer to do this in cold weather. Read the sealant manufacturer's instructions.)



care must be taken in the fitting and sealing 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. 4 SITE WORK



For full details of procedure see Appendix B Pages 17 and 18 and the diagram on Pages 10 and II. 4.1 Understand the proper use of the test rig. It is expensive precision equipment. The instructions must be read carefully and the equipment handled in a responsible manner. 4.2 Make sure that the right type of test rig is 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.



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



4.4 Before erection Inspect all duct sections to make sure that factory applied sealants have not been damaged in transit. Make good where any damage is noticed.



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 ofthe test obtain a signature - on the test sheet; 4.11.3 A permanent record of tests must be retained.



4.5 Ensure the correct gasket material has been supplied for your situation and the application is in accordance with the manufacturer's instructions. Check with the drawings and specifications as to where sealants are to be used 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 as too little.)



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



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



Relevant Conversion Factors Pressure



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



To convert Multiply by Inches water gauge to millibars 2.491 Inches water gauge to pascals (Pa) 249.1 I Pa = 1 Newton per square metre = 10,2 millibars



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



Volume Flow



To convert



4.9 To ensure that the ductwork has been correctly manufactured and site sealant correctly applied it is essential that a preliminary test is



Litres per second to cubic metres



per hour



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Multiply by



3.60



a con1pleted test sheet Based on dllldwod{ shownn oun page 10 and 11 Test No



N.ew +It>



General Name of job Building Ref.



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Pt'Ciecl



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..................................................................................................................... Part 1 - Physical details a



Section of ductwork to be tested ..



b



Drawing Number



c



Pressure Classification



d



Test static pressure



e



Leakage factor



f



Surface area of duct under test



g



Maximum permitted leakage



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O\ass B.



(PROVIDED BY DESIGNERS)



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Part 2 - Test particulars a



Duct static pressure reading



b



Type of flow measuring device



c



Range of measurement of flow measuring device



d



Reading of flow measuring device



'2D 5



e



Interpreted air flow leakage rate



f



Duration of test (normally 15 miuutes)



Date of test ...



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