Tiêu chuẩn ống gió DW 143

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 Cl

A practical guide to

Heating and

Ventilating

Contractors'

Association

Ductwork

Leakage

Testing

DW/143

A practical guide to —

Ductwork

Leakage

Testing

DW/144 specification for

sheet metal ductwork.

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

by the Heating and Ventilating Contractors Association All rights reserved

ISBN: 0-903783-30-4

DW/1 43 Ductwork Leakage Testing A practicalguide

PART ONE

PART TWO

ACKNOWLEDGEMENTS

contributed to this work, and in particular to the members of the Drafting Panel

Original DW/143 Drafting Panel 1983 Ductwork Group Technical Sub-Committee 2000

K Wheatley

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.

2

EdgarPoppleton Chairman, Technical Sub-Committee Ductwork Group, 2000

Ductwork

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

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 Apractical guide

Part One

A practical guide to

ductwork leakage

testing

I General

With regard to air leakage, the

responsibili-ties for ensuring the achievement of a

satis-factory job is divided between the drawing

office, the factory and the ductwork installers

on site It is essential that there is full

co-operation between them

2 The drawing office

represent-atives 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,

fans, coils, attenuators, terminal boxes)

unless, by prior agreement, the casings

for any such items have been

manufac-turedlsealed, by the supplier, to the required

standard of DW/l44

Additionally, establish the type of gasket

material required in relation to the pressure

class/velocity of the system

Note:- Specific gasket material may be

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

design-er to ensure that the leakage charactdesign-eristics

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-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 —seeA.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

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

2.7 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

sealant to be used

2.9 Prepare test sheets giving the information

called for on the sample test sheet shown on page 7

This information should indicate the test

content, the surface area of the ductwork to

be tested, and the permitted leakage of each

section to be tested (this leakage is to be expressed in litres per second per square

metre of the ductwork surface area)

3 The factory

fit to minimise the use of sealant A poor fit

cannot be remedied by the use of more

sealant —it will not work

3.2 Sealall longitudinal seams, laps cross joints.

rivets and duct penetrations generally in

accordance with the requirements of

DW/l44

3.3 Makesure 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 Takespecial care to have as small a clearance

as possible where there are penetrations of

the duct, as for example damper spindles

required by DW/l44

3.6 Tobe sure of minimum leakage special care

must be taken in the fitting and sealing of

access doors and panels etc

3.7 Toavoid the danger of breaking the seals, the

ductwork when ready to despatch to site

must be handled and loaded carefully

Forfull details of procedure see Fig I on Pages

8 and 9 and Appendix B Pages 14 and 15

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

high-pressure leakage testing is seldom suitable or

economic for testing low- or medium-

pres-sure ductwork, and vice versa

4.3 Note that leakage testing is always done

under positive pressure even when the

duct-work is to operate under negative pressure

4.4 Beforeinstallation, inspect all duct sections

to make sure that factory applied sealants

have not been damaged in transit Make

good where any damage is noticed

4.5 Ensure the correct gasket material has been supplied and the application is in

accor-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 do the job

—toomuch sealant is as bad as too little.)

that will be difficult to reach after installation

of the ductwork

4.7 Fix the blanking plates or other types of

tem-porary seal in the positions shown by the draw-ing office (Ensure that the blankdraw-ing material is accessible for subsequent removal.)

client or their representative on a progressive testing programme

4.9 Beforepresentation 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 Ifthese preliminary tests show that the leak-age 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

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 he intro-duced downstream of the test rig

and not on its intake side.

5

DW/1 43 Ductwork Leakage Testing A practicalguide

found the leakage source(s).

immediately

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 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

5 Example of a completed test sheet

Based on ductwork shown on pages 8 and 9

Test No

(;eneral

Name of job !'

Building Ref. 2

Part 1 —Physicaldetails

a Section of ductwork to be tested

b Drawing Number

d Test static pressure ?.cq

e Leakage factor

f Surface area of duct under test

g Maximum permitted leakage k

Part 2 —Test particulars

b Manufacturer and type of flow measuring device

fROM RIG MANLF4cTURERS

c Range of measurement of flow measuring device

d Reading of flow measuring device

DERIVED FROM CHART SLPPUED WITH RIG LSIVG di

f Duration of test (normally 15 minutes)

Date of test Carried out by ?"'S:naturej Witnessed by SgnuIure)

and Company andCompany

Width and depth

or diameter - Periphery Length Area

DW/1

A practical

A practical

FLEX Keep

luordertoavold of

dfrectlytothe ductwork

flow device

to commencing

to graph

inum and

if necessary

to cure)

WARNING Tab

removal 800

perlicularlyatblanks,accesaopeninp and

- Withtestngnmningleaks shonid

if wet)

use) D1W

Page blank

DW/1 43 Ductwork Leakage Testing A practicalguide

Part Two

6 This section, apart from Appendix 'B', is

Sheet Metal Ductwork, and for ease of

refer-ence 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

classifica-tions

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 1 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

Table 1

6.4 Air leakage testing Air leakage testing of low and medium

pres-sure ductwork is not mandatory under the

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 1 of this guide

Table 1 Ductwork Classification and Air Leakage Limits

Static pressure limit Ductpressureclass

Positive Negative

Pa

I High-pressure— Class C 2000

Maximum air'

velocity

rn/s

10 20

-40

Where p is the differential, pressure in pascals.

Pa 500 750 750

10

Air leakage limits

litres per second per square metre of duct surface area

5

0.027 x p01

0.009 x p°'65

0.003 x p°-65

APPENDIX A

Air leakage from

ductwork

A.1 Introduction

Leakage from ducted air distribution systems

is an important consideration in the design

and operation of ventilation and air

condi-tioning 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

main-tained at optimum levels

Ductwork constructed and installed in

accor-dance with DW/144 should minimise a level

of air leakage that is appropriate to the

oper-ating static air pressure in the system.

However, it is recognised that the

environ-ment in which systems are installed is not

always conducive to achieving a predictable

level of quality in terms of system air leakage

and it is therefore accepted that designers

may sometimes require the systems to be

test-ed in part or in total It should be recognistest-ed

that the testing of duct systems adds a

signif-icant cost to the installation and incurs some

extra time within the programme (See 4.1 and

6.4 of DW/144 re mandatory testing)

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

—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

Leakagefrom sheet metal air ducts occurs at the seams and joints and is therefore

propor-tional to the total surface area of the ductwork

in the system The level of leakage is

similar-ly related to the air pressure in the duct sys-tem and whilst there is no precise formula for calculating the level of air loss it is generally accepted that leakage will increase in propor-tion to pressure to the power of 0.65

The effect of air leakage from high

pres-sure/velocity ductwork is critical in terms of

system performance energy consumption

and the risk of high frequency noise

associat-ed with leakage

These problems are less critical with medium

pressure/velocity systems but should be

considered

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

Asthere is no direct relationship between the 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

vol-ume

Similarly, the operating pressure will vary

throughout the system and as leakage is

relat-ed to pressure the calculations are complex However, it is generally accepted that in

typ-ical good quality systems the leakage from

each class of duct under operating conditions will be in the region of:

Class A low pressure 6%

Class B medium pressure 3%

Class C high pressure 2%