Specification for
Heating and
Ventilating
Contractors’
Association
Sheet
Metal
Ductwork
DW/144
DW/l44
Specification for
Sheet Metal Ductwork
Low, medium and high
pressure/velocity air systems
1998
Copyright © 1998 by the
Heating and Ventilating
Contractors’ Association
All rights reserved
ISBN 0-903783-27-4
Further copies of this publication are available from:
Publications Unit
Heating and Ventilating Contractors Association
Old Mansion House Eamont Bridge
Penrith Cumbria CA10 2BX
Tel: 01768 864771 Fax 01768 867138
e-mail: hvcapublications@hvwelfare.co.uk
THE INDUSTRY
STANDARD
Ken Parslow
Chairman
Executive Committee
Ductwork Group
1996-98
or more than a decade-and-a-half, the DW/142 Specification for Sheet Metal
Ductwork published by the Heating and Ventilating Contractors’ Association
has gained national and international recognition as the industry standard
against which the quality of ductwork manufacture and installation can be judged.
In recent years, however, it has become increasingly evident to the members of
the HVCA Ductwork Group that the developments in technology and working
practices which have taken place since the drafting of DW/142 have rendered
obsolete significant parts of the document.
It was an acknowledgement of this state of affairs which led the Technical SubCommittee of the Ductwork Group, ably chaired by Edgar Poppleton, to undertake
the task of producing a radically revised specification which would promote best
practice and quality standards well into the next Millennium.
This new publication — designated DW/144 — represents the direct result of
that initiative.
The new specification recognises the computer age — with special reference to
CAD/CAM procedures and techniques — and the international performance standards established by the Committee for European Normalisation (CEN), as well as
the need to update and consolidate much of the information contained in the original DW/142 publication and its Addendum A companion volume.
During the drafting process, the Technical Sub-Committee has consulted widely
with individuals and organisations throughout the building services and construction sectors in order to ensure that the new specification fully reflected the current
the “state-of-the-art” in terms both of technical expertise and industry best practice.
I firmly believe that this process has resulted in a publication which clearly
demonstrates the high level of professionalism which exists within the ductwork
community — and I take this opportunity of thanking all those who have contributed to its production.
In particular, my thanks go to Edgar Poppleton and his colleagues on the
Technical Sub-Committee, to Keith Elphick for the provision of invaluable technical consultancy, and to Ductwork Group secretary Gareth Keller for overseeing the
project as a whole.
F
3
MAINTAINING QUALITY
L
ike most industries, the ductwork sector
Class A, B and C air leakage characteristics,
must be prepared continually to innovate in
mandatory testing Class C only;
•
order to survive and prosper.
A key element in that innovation process is the
updated
appendices
on
galvanising
after
manufacture, stainless steel, pre-coated steel,
timely review and updating of quality standards to
aluminium, Eurovent and galvanised material,
ensure that they continue to offer realistic bench-
plus a bibliography;
•
marks to which all professional individuals and
organisations can perform.
The development of this new Specification for
Sheet Metal Ductwork — designated DW/144 —
has been carried out with that objective in mind.
In the 16 years since the publication of its
predecessor, DW/142 — and in the ten years since
the supplementary volume Addendum A appeared
Edgar Poppleton
Chairman
•
•
Technical
Sub-Committee
Ductwork Group
— many technical advances, changes in working
practices and regulatory introductions and amend-
•
transport, handling, storage and interface with
DW/TM2 Guide to Good Practice — Internal
Cleanliness of New Ductwork Installations;
an overview of fire-rated ductwork;
a new appendix on inspection, servicing and
cleaning access openings (the default inclusion
of Level 1 should be noted);
a new section on standard component drawings
— incorporating a framework of nomenclature,
and a description of drawing symbols, abbreviations and rules — which is intended to reduce
ments have taken place.
The common performance standards for duct-
•
work being developed by the Committee for
European Normalisation (CEN), for example, had
ambiguity and promote common understanding;
a rewritten description of all forms of dampers,
for which I am indebted to Bill Clark and John
Mawdsley of the HEVAC Association.
to be taken fully into account during the drafting
process. Similarly, notice had to be given to the
I take this opportunity to acknowledge the per-
provisions of the Control of Substances Hazardous
mission granted by the Sheet Metal and Air
to Health (COSHH) and Construction (Design and
Conditioning
Management) Regulations, neither of which had
(SMACNA) of the USA for the use of its tie rod
been issued when DW/142 was published.
specification (designer approval required).
Contractors’
National
Association
It is not possible — nor, I think, desirable — to
And I also include a plea on behalf of ductwork
include in this foreword an exhaustive catalogue of
constructors to be allowed to make the final choice
the points of difference between this specification
and its predecessor. These will clearly emerge
of components and techniques within the parame-
from a detailed reading of the text.
specification to satisfy performance characteristics.
ters set by the designer, and allowed within this
I should, however, like to take the opportunity
It will, of course, be clear to anyone who has
to highlight a few topics which I believe to be of
ever taken on such a task that the production of this
particular significance. They are:
specification has involved a colossal input in terms
•
•
•
•
•
•
•
•
•
the omission of high-pressure Class D (in order
to conform to European practice);
of industry consultation and from a wide variety of
the highlighting of information to be provided
by the designer;
identify for special mention.
the end-sealing of ducts and explosion risks;
members Keith Waldron and the late Keith Angood;
the removal of standard sizes of rectangular
current members Chris Collins, Stuart Howard,
ducts;
Brian James and — last but by no means least —
the omission of cleated joints;
Jim Murray; technical consultant Keith Elphick; and
the acceptance of proprietary flanges certificated
to DW/TM1 no longer illustrated in detail;
Ductwork Group secretary Gareth Keller.
the consolidation into the document of coverage
of hangers and supports;
importance of ensuring that all ductwork is manu-
the addition of a note on linings, along with their
cleaning considerations;
efficient, effective and free of risk.
the consolidated graphical representation of
significantly in the achievement of this objective.
individuals, a number of whom I should like to
They
are:
former
Technical
Sub-Committee
Finally, may I remind readers of the crucial
factured and installed in a manner which is safe,
The publication of DW/144 is intended to assist
5
Acknowledgements
The HVCA wishes to record its sincere thanks to the following
members — past and present — of the Technical Sub-Committee
of the Ductwork Group, who contributed their time, knowledge
and experience to the production of this document
Edgar Poppleton (chairman)
Keith Angood
Chris Collins
Stuart Howard
Brian James
Jim Murray
Keith Waldron
Technical Consultant:
Keith Elphick
Ductwork Group Secretary:
Gareth Keller
6
Other Ductwork-Related Publications
DW/143
DW/151
DW/171
DW/191
DW/TM1
DW/TM2
DW/TM3
TR/17
A Practical Guide to Ductwork Leakage Testing
Specification for Plastic Ductwork
Guide to Good Practice for Kitchen Ventilation Systems
Guide to Good Practice: Glass Fibre Ductwork
Acceptance Scheme for New Products: Rectangular Cross Joint Classification
Guide to Good Practice: Internal Cleanliness of New Ductwork Installations
Guide to Good Practice for the Design for the Installation of Fire and Smoke Dampers
Guide to Good Practice: Cleanliness of Ventilation Systems
Copies of the above publications are available from:
Publications Unit
Heating and Ventilating Contractors Association
Old Mansion House Eamont Bridge
Penrith Cumbria CA10 2BX
Tel: 01768 864771 Fax 01768 867138
e-mail: hvcapublications@hvwelfare.co.uk
–
–
DW/131
DW/121
DW/122B
DW/112
DW/132
DW/141
DW/142
DW/l42
Previous Sheet Metal Ductwork Specifications
Ductwork Specification for High-Velocity Air Systems (Circular)
Standard Range of Rectangular Ducting
Sheet Metal Ductwork Specification for High-Velocity Air
Systems (Rectangular)
Specification for Sheet Metal Ductwork (Low-Velocity
Low-Pressure Air Systems) (Rectangular and Circular) — Metric
Specification for Sheet Metal Ductwork (Low-Velocity
Low-Pressure Air Systems (Rectangular and Circular) — British
Standard Range of Rectangular Ducts and Fittings — Metric and
British Units
Specification for Sheet Metal Ductwork (High-Velocity
High-Pressure Air Systems) (Rectangular, Circular and Flat
Oval) — Metric
Specification for Sheet Metal Ductwork (Low and High-Velocity/
Pressure Air Systems) (Rectangular, Circular and Flat Oval)
— Metric
Specification for Sheet Metal Ductwork (Low, Medium and High
Pressure/Velocity Air Systems)
Specification for Sheet Metal Ductwork Addendum A (Low,
Medium and High Pressure/Velocity Air Systems)
7
1963
1967
1968
1969
1969
1970
1970
1977
1982
1988
Contents
Page
Notes
10
Part One - Technical Information to be
provided by the designer
1. Introduction
2. Standards
3. Components
4. Particular Requirements
11
11
11
11
Part Two - Standards
5. Application
6. Ductwork Classification and Air Leakage
7. Materials
8. Ductwork Construction and Joint Sealing
13
13
13
14
Part Three - Rectangular Ducts
9. Rectangular Duct Sizes
10. Construction
10.1 General
10.2 Steel Thicknesses
10.3 Longitudinal Seams
10.4 Cross Joints
10.5 Stiffeners
10.6 Ductwork Galvanised After
Manufacture
10.7 Fastenings
11. Fittings
11.1 Standardisation of Fittings
11.2 Stiffeners
11.3 Splitters
11.4 Turning Vanes
11.5 Branches
11.6 Change Shapes
11.7 Expansions and Contractions
11.8 Sealant
16
16
16
16
16
16
16
16
16
17
17
27
27
27
27
27
29
29
29
29
29
Part Five - Flat Oval Ducts
15. Standard Sizes and Sheet Thicknesses
16. Construction (Spirally wound)
16.1 General
16.2 Longitudinal Seams
16.3 Cross Joints
35
35
35
35
35
35
35
35
35
35
35
Part Six - Hangers and Supports
19. General
43
Part Seven - General
20. Access/Inspection Openings
21. Regulating Dampers
22. Fire Dampers
23. Smoke Dampers
24. Combination Smoke and Fire Dampers
25. Flexible Ducts
26. Flexible Joint/Connections
27. Protective Finishes
28. Connections to Building Openings
29. Internal Duct Linings
30. Thermal Insulation
31. Kitchen Ventilation
32. Fire Rated Ductwork
33. Standard Component Drawings
and Abbreviations
15
15
15
15
15
15
15
Part Four - Circular Ducts
12. Standard Sizes
13. Construction
13.1 Longitudinal Seams
13.2 Cross Joints
13.3 Fastenings
14. Fittings
14.1 Standardisation of Fittings
14.2 Nominal Diameters
14.3 Sheet Thickness
14.4 Sealing of Joints
16.4 Fastenings
16.5 Stiffening
17. Construction (Straight Seamed)
18. Fittings
18.1 General Construction Requirements
18.2 Standardisation of fittings
Part Eight - Appendices
Appendix A.
Air Leakage from
Ductwork
Appendix B.
Identification of
Ductwork
Appendix C.
Guidance Notes for the
Transport, Handling and
Storage of Ductwork
Appendix D.
Ductwork Systems and
Fire Hazards
Appendix E.
Hot Dip Galvanizing after
Manufacture
Appendix F.
Stainless Steel for Ductwork
Appendix G.
Pre-Coated Steel
Appendix H.
Aluminium Ductwork
Appendix J.
Eurovent
Appendix K.
Summary of BS.EN10142:
1991 Continuously Hot-Dip
Zinc Coated Mild Steel Strip
and Sheet for Cold Forming
Appendix L.
‘Design Notes for Ductwork’
(CIBSE Technical
Memorandum No. 8)
Appendix M. Guidance Notes For Inspection,
Servicing and Cleaning Access
Openings
Appendix N.
Bibliography
Appendix P.
Conversion Tables
8
47
48
49
50
51
51
52
53
53
54
54
54
54
54
75
80
82
83
85
86
89
90
91
92
93
94
95
97
List of Tables
Table
Page
Part Two - Standards
1. Ductwork Classification and Air
Leakage Limits
2.
3.
4.
5.
6.
7.
8.
9.
10.
Part Three - Rectangular Ducts
Constructional Requirements
Low Pressure up to 500Pa
Constructional Requirements
Medium Pressure up to 1000Pa
Constructional Requirements
High Pressure up to 2000Pa
Fastening Centres
Part Four - Circular Ducts
Standard Sizes
Spirally-Wound Ducts
Straight-Seamed Ducts
Permitted fastenings and maximum
spacings
Fittings Sheet Thicknesses
Part Five - Flat Oval Ducts
11. Standard sizes and sheet thicknesses
12. Stiffening requirements
low and medium pressures
13. Stiffening requirements
high pressure
14. Permitted fastenings and maximum
spacings
Part Six - Hangers and Supports
15. Supports for horizontal ducts - rectangular,
flat oval and circular
Part Seven - General
16. Standard Abbreviations
17.
18.
19.
20.
21.
22.
23.
24.
25.
Part Eight - Appendices
Air Leakage Rates
Recommended duct identification colours
Examples of further identification symbols
Ductwork galvanized after manufacture rectangular
Compositions of the commonly used
Stainless Steel grades
Rectangular aluminium ducts low pressure constructional requirements
Circular aluminium ducts low pressure constructional requirements
Zinc coating mass (weight)
Access requirements for inspection,
servicing and cleaning
13
18
1-8
9
10-12
19
24
31
32-38
39-45
Part Four - Circular Ducts
Spiral and straight seams
Cross joints spirally wound ducts
Cross joints straight seamed ducts
29
30-31
32-33
53-58
59-63
Part Five - Flat Oval Ducts
Cross joints spirally wound ducts
Cross joints straight seamed ducts
39-40
41-42
Part Six - Hangers and Supports
Horizontal ducts
bearers and hangers
Vertical ducts supports
45-46
46
64-75
27
28
28
76-77
Part Seven - General
Fire barrier/fire damper expansion
Flexible joint connections
Standard component drawings Rectangular
125-152 Standard component drawings Circular
153-167 Standard component drawings Flat Oval
168-177 Plant/equipment/miscellaneous
78-79
80
81-124
29
29
36
37
38
40
178
179
44
72-73
76
80
81
85
88
90
91
93
94
Pages
Part Three - Rectangular Ducts
Longitudinal Seams
Illustrations of panel stiffening
Flanged cross joints
Socket and spigot cross joints
Stiffeners
Tie rod assembly
Hard and Easy bends
Turning Vanes
19
List of Illustrations
Figs
13-17
18-24
25-28
29
30
20
20
21
9
Part Eight - Appendices
Permitted leakage at various
pressures
Example of duct identification symbol
22
23
24
25
25
50
52
55-61
62-67
68-70
71
78
81
Notes
In this document:
(1) Even where a ductwork job specification calls for the system to be
wholly in accordance with DW/144, it will still be necessary for the
designer, in addition to providing drawings showing details and
dimensions of the ductwork, to identify specific requirements, particular to his or her design.
The technical information to be provided by the designer is therefore set out in detail on page 11.
(2) All dimensions quoted in this specification refer to the nominal
sizes, which are subject to the normal relevant commercial and
published tolerances.
(3) Manufacturing techniques are continually subject to change and
improvements and in respect of proprietary methods and devices
this specification does not preclude their use if they can be demonstrated to the designer to be equally satisfactory. Where there is
divergence between the requirements of DW/144 and the
manufacturer’s recommendations for proprietary methods and
devices, the latter shall take precedence.
(4) The expressions ‘low-pressure,’ ‘medium-pressure’ and ‘highpressure’ relate to the pressure/velocity classes set out in Table 1.
(5) ‘Mean air velocity’ means the design volume flow rate related to
the cross-sectional area.
(6) Reference to the air distribution system pressure relate to the static pressure of the relevant part of the ductwork system and not to
the fan static pressure.
(7) The symbol for litres is ‘L’: 1000 litres per second is equivalent to
1 cubic metre per second.
(8) The Pascal (Pa) is the internationally agreed unit of pressure. The
relationship of the Pascal to other units of pressure is: 500 pascals
= 500 Newtons per square metre = 5 millibars = approximately 2
inches water gauge.
(9)
Duct pressure classification
As the static pressure in a duct system progressively changes from the fan,
economic advantage can be obtained by changing the duct pressure
classification to match more closely the duct distribution static pressure.
For example, some large systems could well be classified for leakage
limits as follows:
Plant rooms and risers
Class C
Main floor distribution
Class B
Low-pressure outlets
Class A
10
Part One – Technical information to be
provided by the designer to the ductwork contractor
1 INTRODUCTION
The selection of constructional methods is the
decision of the Manufacturer to conform with the
performance
requirements
of
the
specified
ductwork classification. Sections 2-4 below
define the information that is to be provided by
the Designer.
4.2 Protective finishes (Section 27)
Details and specification of any
finishes.
2 STANDARDS
4.4 Internal thermal/acoustic lining
(Section 29)
The extent of any ductwork requiring internal
acoustic/thermal lining is to be clearly identified.
A detailed specification of materials and method
of application is required. The practical aspects
of cleaning or maintenance must be addressed by
the designer before deciding to internally line
ductwork.
2.1
2.2
2.3
2.4
2.5
4.3 Fire rated and smoke extract ductwork
(Appendix D)
The extent and limits of protection for any fire
resisting ductwork.
Pressure classification (Table 1)
Leakage classification (Table 1)
Positive and Negative pressures (Table 1)
Materials (Section 7)
Any special system requirements
3 COMPONENTS
3.1 Inspection/servicing access openings
(Section 20 and Appendix M)
Number and location of all panels and covers
for inspection and/or servicing access other than
those covered in Section 20 and summarised as
Level 1 requirements in table 25 of Appendix
M. Number and location of test holes,
instrument connections and hinged doors as
defined in Section 20.
4.5
External
thermal/acoustic
insulation
(Section 30)
The extent and thickness of insulation to be
provided by others should be stated.
4.6 Special supports (Section 19)
Details of any spanning steel or special support
requirements not covered by Section 19
4.7 Attachment to building structure (Section 28)
Specific requirements for the junction of
ductwork
and
associated
components
to
openings should be detailed and specified and
the limits of responsibility defined.
3.2 Cleaning access
(Section 20.8 and Appendix M)
Designers shall stipulate their requirements for
periodic internal cleaning of ductwork and for
the consequent need for adequate access for
specialist cleaning equipment.
The provision of penetrations and associated
framings are outside the scope of this
specification.
3.3 Regulating dampers (Section 21)
Specification, location and mode of operation of
all regulating dampers.
4.8 Air terminal units
Detail and specifications of all Air Terminal
Units. It is expected that all Air Terminal Units
and their Plenums (See Figures 120 to 124) will
be supported by the Ceiling Grids unless the
designer indicates an independent method of
support.
3.4 Fire dampers (Section 22)
Specification and location of all fire dampers to
meet the requirements of the Authority directly
concerned with fire protection.
3.5 Smoke dampers (Section 23)/Combination
smoke and fire dampers (Section 24)
Specification and location of all smoke dampers
to meet the requirements of the Authority
directly concerned with fire protection.
3.6 Flexible ducts (Section 25)
Specification and location of
ductwork.
any
protective
4.9 Ductwork layout drawings
Details of any special requirements relating to
CAD, scales, etc. It is common practice and cost
effective for ductwork manufacturers to utilise
their approved ductwork layout drawings as a
basis
of
their
manufacturing/installation
information by adding the necessary details to
the same drawing. Scales of 1:50 or smaller may
preclude this practice, therefore, larger scales
might be more appropriate. The final choice of
manufacturing/installation scales shall be left to
the ductwork contractor.
flexible
3.7 Flexible joint connections (Section 26)
Specification and location of any flexible connections eg. plant or building expansion joints.
4. PARTICULAR REQUIREMENTS
4.1 Air leakage testing (Section 6 and Appendix A)
The extent of any air leakage testing. While it
shall be mandatory for high-pressure ductwork
(as defined in this specification) to be tested for
air leakage in accordance with the procedure set
out in DW/143, A practical guide to Ductwork
Leakage Testing, no such testing of low- or
medium-pressure ductwork is required.
4.10 Other requirements
Details of any requirements for the ductwork
not in accordance with the provisions of this
specification, including any modified construction required to conform with any
requirements
concerning
external
ductwork
(See 5.3) or to meet the regulations of a local
authority or other controlling body.
11
4.11 Reference to the designer
In consideration of the foregoing, reference is also
made to the designer in the following clauses:Clause
5.3
7.4, 7.5, 7.6
10.5.2
11.1
14.1
16.3.1
19.1, 19.4
19.6, 19.7
20.1, 20.1.1.1, 20.6, 20.8
20.9
21.1, 21.3.1
21.3.4
22.3, 22.7
24.3
25.1
26.1
27, 27.3.4
29.1, 29.4, 30.2, 30.3, 33.2
Fig. 176
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix L
Appendix M
Page
13
14
16
16
29
35
43
44
47
48
48
49
50
51
51
52
53
54
71
75-79
80, 81
82
83, 84
85
86-88
93
94
12
Part Two - Standards
6.3 Leakage at various pressures; and other
relationships
Applying the limits specified in Table 1, 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.
5 APPLICATION
5.1 This specification sets out minimum requirements for the manufacture and installation of ductwork for commercial and industrial air distribution systems, made from any of the materials listed
in Section 7 and being within the limits of size
and/or metal thicknesses specified in the relevant
tables.
Normal
operating
temperatures
are
assumed within the pressure/velocity limits and
the limits of air leakage for the various pressure
classes prescribed in Table 1.
DW/143 A practical guide to Ductwork Leakage
Testing, also gives details of the basis for the
leakage limits specified in Table 1.
6.4 Air leakage testing
5.2 This specification is not intended to apply to
ductwork handling air which is polluted or is otherwise exceptional in respect of temperature or
humidity (including saturated air); nor is it suitable
for ductwork exposed to a hostile environment,
e.g. contaminated air, off-shore oil rigs, etc. The
design, construction, installation, supports and
finishes in such cases should be given special consideration in relation to the circumstances of each
case.
Air leakage testing of low and medium pressure
ductwork is not mandatory under this specification.
Air leakage testing of high pressure ductwork is
mandatory under the specification and for details
of testing procedure refer to DW/143 A practical
guide to Ductwork Leakage Testing.
5.3 This specification is not suitable for ductwork
exposed to external atmosphere and the Designer
will need to give specific details of any special
finishes/construction (See Section 27).
7 MATERIALS
7.1 Application
This specification applies to ductwork constructed
from materials as defined below, or equal.
Minimum steel thickness is to be taken as a nominal
thickness
within
the
tolerances
to
BS.EN10143:1993. (See Appendix K)
6 DUCTWORK CLASSIFICATION AND
AIR LEAKAGE
6.1 Classification and air leakage limits
Ductwork classification and air leakage limits are
set out in Table 1.
7.2 Zinc-coated steel
Ductwork will normally be constructed from
hot-dip galvanized steel to BS.EN10142:1991,
Grade DX51D+Z, coating type Z275.
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 EN12237/Pr EN1507.
Table 1 Ductwork Classification and Air Leakage Limits
Static pressure limit
Duct pressure class
Positive
Negative
Maximum air
velocity
Air leakage limits
litres per second per square
metre of duct surface area
2
3
4
5
Pa
500
Pa
500
m/s
10
0.027 x p0.65
Medium-pressure – Class B
1000
750
20
0.009 x p0.65
High-pressure – Class C
2000
750
40
0.003 x p0.65
1
Low-pressure – Class A
Where p is the differential, pressure in pascals.
13
8.2.2 Liquid and mastic sealants
These are typically applied to a longitudinal
seam formed between two sheets of metal, a
socket and spigot, cleated or flanged cross joints.
Particular care is needed when sealing of “corner
pieces” on the proprietary ‘slide-on’ type flange
and reference should be made to the manufacturer’s assembly and sealing instructions.
7.3 Mild steel
Where mild steel is specified, it shall be coldreduced steel to BS.EN10130:1991, Grade FEP
01A.
7.4 Stainless steel
Where stainless steel is specified. it will be the
responsibility of the designer to indicate the type
most suitable for the conditions to which the ductwork will be exposed. In doing so, it is recommended that the factors set out in Appendix F
should be taken into account. In this connection,
reference must be made to BS 1449: Part 2, which
includes stainless steel.
8.2.3 Gaskets
These can be of various materials in the form of
a preformed roll, sheet or strip, applied between
opposing faces of flanged cross joints. In the
case of proprietary ‘slide-on’ type flanges, it is
advisable to use the gasket strip recommended
by the manufacturer.
7.5 Pre-coated steel
Pre-coated steel may be specified for aesthetic or
other reasons. The designer must then consider
the availability of suitable materials and the
restriction on fabrication methods. Guidance
notes are available in Appendix G.
Factory-fitted proprietary synthetic rubber ‘O’ring type gaskets are also acceptable for socket
and spigot joints on circular duct systems.
8.2.4 Tapes
8.2.4.1 The application of tapes – Best
suited, but not limited, to cross joints on
circular or flat oval ductwork. Where chemical reaction tape, heat shrinkable tape or other
approved material is used on flat oval ductwork care should be taken to maintain close
contact between the material and the flat sides
of the duct until the joint is completed.
7.6 Aluminium
Where aluminium is specified, it will be the
responsibility of the designer to define the type
most suitable for the conditions to which the ductwork will be exposed. Reference must be made to
BS.EN485,
BS.EN515
and
BS.EN573
for
aluminium sheet and BS.EN755 Parts 3-6 for
aluminium section. (Constructional requirements
for ductwork made from aluminium sheet and
general notes on the material are set out in
Appendix H.)
8.2.4.2 Chemical reaction tape – An
impregnated woven fibre tape and a resin type
activator/adhesive. On application of the
activator/adhesive the tape becomes pliable
and can then be applied to any surface shape.
The liquid reacts with the tape, causing the 2part system to ‘set’.
8 DUCTWORK CONSTRUCTION AND
JOINT SEALING
8.2.4.3 Heat shrinkable band/tape – A thermoplastic material, coated on the inside with
hot metal adhesive. The band (or an appropriate length of tape) is cut from the roll and
wrapped around the joint. When heated the
tape shrinks tightly around the joint thus providing a seal.
8.1 Ductwork construction
The selection of longitudinal, cross joint and stiffener types within the criteria laid down in the
tables should be the responsibility of the manufacturer.
8.2 Joint sealing and sealants
8.2.1 General
The integrity of the ductwork depends on the
successful application of the correct sealant,
gaskets or tape. The materials used should be
suitable for the purpose intended and satisfy the
specified pressure classification.
8.2.4.4 Self adhesive tape – Manufactured
from various materials including cloth based,
PVC and aluminium foil. Typically applied
externally to socket and spigot cross joints.
However, it is difficult to provide the dry, dust
and grease free surface that is required for a
successful application and this method is
therefore not recommended as a primary
source of sealant.
Illustrations indicating sealant locations will be
found in the following sections dealing with the
construction of rectangular, circular and flat
oval duct sections.
NB! Risk of explosions
Where ductwork is blanked off prior to leakage
testing or to prevent the ingress of contamination,
care should be taken to ensure that all joint sealing
solvent vapours are dispersed from the ductwork
systems.
IN ALL CASES, SEALANT MATERIALS
MUST
BE
APPLIED
STRICTLY
IN
ACCORDANCE
WITH
THE
MANUFACTURER’S
INSTRUCTIONS
AND
COSHH
ASSESSMENT.
14
Part Three - Rectangular Ducts
duct size longer side and maximum spacing, are
given in Tables 2 to 4. Other limits on use are
given with the individual drawings.
9 RECTANGULAR DUCT SIZES
This specification covers duct sizes up to a maximum longer side of 3,000 mm. Duct sizes with an
aspect ratio greater than 4:1 are not recommended. Although they offer no problems of construction, they increase frictional resistance and the
possibility of noise.
Note: Proprietary products used in the construction of cross joints should be approved by an
independent test house following tests defined
in DW/TM1 “Acceptance scheme for new products – Rectangular cross joint classification.”
Figures Nos 10 and 13 to 17 illustrate non proprietary joints that have an established rating.
10 CONSTRUCTION
10.1 General
The minimum constructional requirements for
rectangular ductwork depend upon the pressure
classification as set out in Tables 2 to 4. The ductwork construction and joint sealing standards are
set out in section 8.
10.4.2 Sealant in cross joints
Sealant shall be used between sheet and section
in all cross joint assemblies. (see section 8)
With socket and spigot joints made on site,
sealant shall be applied during or after assembly
of the joint. It is permissible to use chemicalreaction tape or heat-shrink strip as alternative
methods of sealing, provided that close contact
is maintained over the whole perimeter of the
joint until the joint is completed.
10.2 Steel thicknesses
Minimum steel thicknesses related to duct longer
side to pressure classification are given in
Tables 2 to 4.
10.3 Longitudinal Seams
Longitudinal seams are illustrated in Figs. 1 to 8.
The limits of use, if any, are given with the individual illustrations.
With all flanged joints, the sealant between
sheet and section should preferably be incorporated during construction at works, but site
applied sealant is acceptable. The joint between
sections of ductwork is then made, using
approved type of sealant or gasket. With
proprietary flanging systems particular attention
should be paid to the sealing of corner pieces
and flanges, reference should be made to the
manufacturer’s assembly and sealing instructions.
10.3.1 Sealing of Longitudinal Seams
Sealant will be applied using one of the following methods:
a) As an edge sealant on the external seam surface.
b) As an edge sealant on the internal seam surface.
c) Internal to the joint seam itself.
The most appropriate method will be determined by the manufacturer relative to their
product and will be associated with either traditional fabrication/assembly methods, factory or
site based, and/or proprietary methods. The ultimate proof of a seal is that the ductwork system
meets the pressure classification specified. For
details of sealant see section 8.
10.4.3 Adjustable/slip joints
In order to accommodate manufacturing/building tolerances, site modifications etc, it is
accepted practice to use an adjustable joint as
illustrated in Fig. 14.
10.5 Stiffeners
10.5.1 External stiffeners
The sections (including proprietary flanges)
suitable for use as single stiffeners have been
given a rating from S1 to S6 in terms of duct
size longer side and maximum spacing. The ratings are specified with the illustrations of the
stiffeners, Figs. 18 to 23, and the limits of use
are given in Tables 2 to 4. The stiffeners for
socket and spigot joints covered in Figs. 15, 16
and 17 are also applicable to stiffeners in general.
10.3.2 Welded seams
A welded seam is acceptable without sealant,
provided that the welding is continuous.
10.4 Cross joints
10.4.1 Cross joint ratings
For cross joints, a system of rating has been
used to define the limits of use. The rating for
each cross joint is given with its drawing, and
the limits applying to that rating, in terms of
15
a minimum.
10.52 Internal stiffeners
Tie bars connecting the flanges of cross joints
illustrated in Figs 11 and 12, are the only form
of internal stiffening for rectangular ductwork
recognised by this specification and reference
should
be
made
to
HVCA
publication
DW/TM1.
Areas where the galvanizing has been damaged or
destroyed by welding or brazing shall be suitably
prepared and painted internally and externally with
zinc-rich or aluminium paint as defined in Section
27.3.2.
Alternative methods for the attachment of tie
bars are shown in Figs. 25 to 28.
11 FITTINGS
11.1 Standardisation of fittings
The terminology and descriptions of rectangular
duct fittings as set out in Section 33 are recommended for adoption as standard practice to provide common terms of reference for designers,
quantity surveyors and ductwork contractors, and
of those using computers in ductwork design and
fabrication.
The use of tie bars or other forms of internal
stiffening or bracing shall be acceptable if
proved to the designer to be equally satisfactory.
SMACNA (Sheet Metal and Air Conditioning
Contractors’ National Association), which is the
American equivalent to the HVCA Ductwork
Group, have produced an Addendum No.1
(November 1997) to their publication “HVAC
Duct Construction Standards, Second Edition 1995”. The addendum contains the extensive
technical information and data on the subject of
mid panel tie rods and SMACNA have given
their kind permission for this specification to
make reference to this fact. Designers and manufacturers who wish to incorporate this form of
internal stiffening into a ductwork system
should contact SMACNA direct to obtain copies
of their publications (See Appendix N,
Bibliography).
Bends are designated as ‘hard’ or ‘easy’, and these
terms as used herein have the following meanings:
‘Hard’ signifies rotation in the plane of the
longer side of the cross section.
‘Easy’ signifies rotation in the plane of the
shorter side of the cross section.
An example illustrating these terms is given in
Fig. 29.
11.2 Stiffeners
The flat sides of fittings shall be stiffened in accordance with the construction Tables 2 to 4. On the
flat sides of bends, stiffeners shall be arranged in
a radial pattern, with the spacing measured along
the centre of the bend.
10.6 Ductwork galvanized after manufacture
Appendix E sets out the recommended sheet
thicknesses and stiffening for ductwork galvanized after manufacture.
10.7.1 Permitted types and maximum centres
Table 5 sets out the permitted fastenings and the
maximum spacings for all ductwork classifications. All duct penetrations shall be sealed.
11.3 Splitters
If the leading edge of the splitters exceeds 1250
mm fit central tie bars at both ends to support the
splitters. Leading and trailing edges of splitters
must be edge folded and flattened and be parallel
to the duct axis.
10.7.2 Rivets
Manufacturers’ recommendations as to use,
size and drill size are to be followed. Rivets resulting in an unsealed aperture shall not be used.
Splitters shall be attached to the duct by bolts or
mechanically-closed rivets at 100 mm maximum
spacing (or by such other fixing as can be shown
to be equally satisfactory e.g proprietary sealed
splitter pins).
10.7.3 Set screws, nuts and lock bolts
Materials shall be of mild steel, protected by
electro-galvanizing, sherardizing, zinc-plating,
or other equal and approved corrosion resistant
finish.
11.4 Turning vanes
Where specified, or shown on drawings, square
throat bends with either duct dimension greater
than 200 mm shall be fitted with turning vanes
which are illustrated in Figures 30a and 30b.
10.7.4 Self tapping and piercing screws
Providing an adequate seal can be achieved, and
the protrusions into the ductwork are unlikely to
cause injury, then self-tapping or piercing
screws may be used.
Turning vanes at 60 mm maximum centres shall
be fixed at both ends either to the duct or compatible mounting tracks in accordance with manufacturer’s instructions, the whole bank being fixed
inside the duct with bolts or mechanically closed
rivets at 150 mm maximum spacing.
10.7 Fastenings
The maximum length of turning vane between
duct walls or intermediate support shall be 615
mm for single skin vanes and 1250 mm for double
skin vanes.
10.7.5 Welding of sheet
The suitability of welding for sheet-to-sheet
fastening will be governed by the sheet thickness, the size and shape of the duct or fitting and
the need to ensure airtighteness. Welded joints
shall provide a smooth internal surface and shall
be free from porosity. Distortion shall be kept to
Typical examples of fitting turning vanes when
the maximum permitted vane lengths are
exceeded are shown in Fig. 30c.
16
11.7 Expansions and contractions
11.5 Branches
When fitting branch ducts to a main duct, care
should be taken to ensure that the rigidity of the
duct panel is maintained in terms of the stiffening
criteria.
Where these are required, an expansion shall be
made upstream of a branch connection and a contraction downstream of a branch connection. The
slope of either an expansion or a contraction
should not exceed 22½° on any side. Where this
angle is not practicable, the slope may be increased, providing that splitters are positioned to bisect
the angle between any side and the centre line of
the duct (See Figs 99 to 101).
11.6 Change shapes
Where a change shape is necessary to accommodate the duct and the cross-sectional area is to be
maintained, the slope shall not exceed 22½° on
any side (See Figs 99 to 103). Where a change in
shape includes a local reduction in duct crosssectional area, the slope should not exceed 15° on
any side and the reduction in area should not
exceed 20 per cent.
11.8 Sealant
Sealant shall be used in all longitudinal seams and
cross joints of fittings. Sealant shall be to the
options listed in Section 8.
17
Constructional Requirements – Rectangular Ducts
Table 2 LOW PRESSURE (limited to 500 Pa positive and 500 Pa negative)
Dimensions in mm
Maximum duct size
(longer slide)
400
Minimum sheet
thickness
0.6
Type Rating
Socket & Spigot Joints
1
2
A1
A2
A3
Flanged Joints & Stiffeners
J1/S1
J2/S2
J3/S3
J4/S4
J5/S5
J6/S6
sheet
3
600
800
1000
1250
0.8
1600
2000
2500
1.0
3000
1.2
Maximum spacing between joints and stiffeners
4
5
6
7
8
9
10
11
12
PS
3000
SS
3000
PS
3000
2000
1600
1250
SS
3000
3000
1600
1250
PS
3000
2000
1600
1250
1000
800
SS
3000
3000
2000
1600
1250
800
PS
3000
1600
1250
625
SS
3000
3000
1250
625
PS
3000
2000
1600
1250
625
SS
3000
3000
1600
1250
625
PS
3000
2000
1600
1250
1000
800
SS
3000
3000
2000
1600
1250
800
PS
3000
2000
1600
1250
1000
800
800
SS
3000
3000
2000
1600
1250
1000
800
PS
3000
2000
1600
1250
1000
800
800
800
625
SS
3000
3000
2000
1600
1250
1000
800
800
800
PS
3000
2000
1600
1250
1000
800
800
800
800
SS
3000
3000
2000
1600
1250
1000
800
800
800
Notes (applicable to Tables 2 to 4)
(1) The joints and stiffeners have been rated in terms of duct longer side and maximum spacing – see 10.4
for joints and 10.5 for stiffeners.
(2) In Col. 3:
‘PS’ = plain sheet
‘SS’ = stiffened sheet, by means of
(a) beading at 400 mm maximum centres: or (b) cross-breaking within the frame formed by joints and/or
stiffeners: or (c) pleating at 150 mm maximum centres.
(3) Stiffened panels may limit the choice of insulation materials.
(4) For ductwork galvanized after manufacture, see 10.6 and Appendix E.
(5) For aluminium ductwork, see Appendix H.
(6) For constructional constraints of stainless steel ductwork see Appendix F.
(7) Although not covered in this specification, due to their relatively infrequent use, cleated cross joints are
an accepted constructional practice and the HVCA Ductwork Group should be contacted if details of
their ratings and limitations are required.
(8) Intermediate stiffeners using rolled sheet angle profiles, illustrated in Figs. 19 to 23 of the appropriate
rating may also be utilised ensuring that rigid corners are achieved.
18
Constructional Requirements – Rectangular Ducts
Table 3 MEDIUM PRESSURE (limited to 1000 Pa positive and 750 Pa negative
Dimensions in mm
Maximum duct size
(longer slide)
400
Minimum sheet
thickness
0.6
Type Rating
A2
A3
Flanged Joints & Stiffeners
J1/S1
J2/S2
J3/S3
J4/S4
J5/S5
J6/S6
1000
1250
1600
2000
2500
3000
1.0
1.2
Maximum spacing between joints and stiffeners
3
A1
800
0.8
sheet
2
Socket & Spigot Joints
1
600
4
5
6
7
8
PS
3000
SS
3000
PS
3000
SS
3000
PS
3000
1600
1250
1000
800
1250
800
SS
3000
3000
1600
PS
3000
1250
625
SS
3000
1250
625
PS
3000
1250
1250
9
10
11
12
625
SS
3000
1600
1250
625
PS
3000
1600
1250
1000
800
SS
3000
3000
1600
1250
800
PS
3000
1600
1250
1000
800
800
SS
3000
3000
1600
1250
1000
800
PS
3000
1600
1250
1000
800
800
800
625
SS
3000
3000
1600
1250
1000
800
800
800
PS
3000
1600
1250
1000
800
800
800
800
625
SS
3000
3000
1600
1250
1000
800
800
800
625
Constructional Requirements – Rectangular Ducts
Table 4 HIGH PRESSURE (limited to 2000 Pa positive and 750 Pa negative)
Dimensions in mm
Maximum duct size
(longer side)
400
600
Minimum sheet
thickness
800
1250
0.8
1600
2000
Rating
Sheet
1
2
3
4
Socket &
Spigot Joint s
A1
PS/SS
3000
A2
PS/SS
3000
A3
PS/SS
3000
J1/S1
PS/SS
3000
625
J2/S2
PS/SS
3000
1250
800
2500
1.2
1.0
Type
Flanged Joints & Stiffeners
1000
Maximum space between joints and stiffeners
5
6
7
8
9
10
J3/S3
PS/SS
3000
1250
1250
800
J4/S4
PS/SS
3000
1250
1250
1000
800
J5/S5
PS/SS
3000
1250
1250
1000
800
800
625
J6/S6
PS/SS
3000
1250
1250
1000
800
800
800
Notes on page 18 also apply to Tables 3 and 4
19
11
625
Longitudinal seams
For permitted fastenings (types and spacing), see Table 5
Fig. 1 Grooved seam
Fig. 5 Returned standing seam (internal or
external)
Alternative sealant locations
alternative
sealant
locations
Fastening
Fig. 6 Capped standing seam (internal or
external)
Fig. 2 Grooved corner seam
Fastening
Alternative
sealant
locations
Alternative sealant
locations
Fig. 3 Pittsburgh lock seam
Fig. 7 Tray standing seam (internal or
external)
Fastening
Alternative
sealant
locations
Alternative
sealant locations
Fig. 8 Lap seam
Fig. 4 Button punch snap lock seam
Alternative
sealant locations
Note. – This
seam is acceptable for use
on low and
medium-pressure
ducts only
Fastening
Alternative
sealant locations
Fig. 9 Illustrations of panel stiffening
Cross breaking between
joints or stiffeners
Pleating (may also
be along the duct)
Beading (may also
be along the
duct)
Examples of Cross sections
20
Flanged cross joints
Minimum
Dimen- Rating
sions
Type
Fig. 10 Rolled steel angleflanged joint, with welded
corners
Fixing
Bolt
Gasket or
sealant
Fastening
Sealant if
turn up not
used
Fastening
mm
25 x
30 x
40 x
50 x
Pressure
classes
Duct ends turned up 8 mm
minimum
3
4
4
5
J3
J4
J5
J6
Low
Medium
High
Fixing Bolts
25
30
40
50
x
x
x
x
Notes/corner treatments
3
4
4
5
6 mm
8 mm
8 mm
10 mm
Fixing bolts required at
each corner and at 300 mm
centres.
Angle flanged joint does NOT
require DW/TM1 certification
A turn up as illustrated is NOT
mandatory. If not used, the toe
of the angle is to be sealed.
Fig. 11 Examples of typical rollformed sheet metal profiles
Sealant, clamps/cleats and fixings omitted for clarity
Fig. 12 Examples of typical cross joint flanges formed from the duct wall
NOTE: The above illustrations are typical examples of cross joint profiles that are in common use for connecting
rectangular sheet metal ducts.
There are no set dimensions for these profiles shown in Figs. 11 and 12 provided they are certified under the HVCA
testing scheme DW/TM1 “Acceptance Scheme for new products – Rectangular cross joint classification” and are
appropriate to the duct application. The manufacturer’s technical data should be followed with respect to:
Connections to duct wall
Corner treatment
Addition of cleats
Application of sealants
Strength ratings
Application of tie bars
A list of manufacturers and profiles that are covered by current DW/TM1 certificate is available from the Ductwork
Group Secretary at HVCA.
21
Socket and spigot cross joints
Note – Particular care must be taken in the sealing of these joints. The ratings stated for cross joints
in Figs. 13 to 17 inclusive do not require DW/TM1 certification
For permitted fastenings (types and spacing), see Table 5
Angle
size mm
Type
Rating
Pressure
classes
A1
Low
Medium
High
A1
Low
Medium
High
This joint can be used
on any ducts subject to
the addition of an
adjacent stiffener with a
rating appropriate to the
duct size
A2
Low
Locate stiffener back
from end of spigot
joint to allow access
for sealing joint
Notes
Fig. 13 Plain
Alternative sealant locations
Fastening
–
Fig. 14 Adjustable
Alternative sealant locations
Fastening
Fig. 15 Angle reinforced (Ducts with
shorter side 400 mm and less)
25 x 3
Corners can be mitred
30 x 4
Fig. 16 Back to back stiffeners (Ducts with
both sides greater than 400 mm)
25 x 3
30 x 4
Fig. 17 Full girth welded stiffeners
(Ducts with both sides greater
than 400 mm)
25 x 3
30 x 4
22
A2
Low
Medium
A2
Low
A3
A2
A3
Low
Medium
Low
Low
Medium
Locate stiffener back
from end of spigot joint
to allow access for
sealing joint.
Stiffeners shown in Figs.
19 to 23 are permissible
if provided with rigid
corners.
Corners can be mitred
Locate stiffener back
from end of spigot joint
to allow access for
sealing joint.
Stiffeners shown in Figs.
19 to 23 are permissible
if provided with rigid
corners.
Corners can be
mitred
Single stiffeners
Dimensions and ratings
For permitted fastenings (types and spacings), see Table 5
Section
H
mm
Thickness
mm
Rating
25
30
40
50
60
3
4
4
5
5
S2
S3
S4
S5
S6
H
25
30
40
50
1.6
1.6
1.6
2.0
S1
S2
S3
S4
H
20
25
1.6
1.6
35
40
1.6
2.0
S1
S2
S3
Fig. 18
H
H
Fig. 19
H
2
Fig. 20
40
Fig. 21
H
25
25
25
S4
15
1.2
20
25
40
1.2
1.6
1.6
S1
S2
S3
S4
50
2.0
S5
20
30
0.8
1.0
S1
S2
40
1.2
S3
25
0.8
S1
Fig. 22
H
Fig. 23
H
Note – Other profiles may be used providing the duct deflection is limited to a maximum of 1/250 of the duct
side under operating pressure.
Intermediate
Stiffeners
Fig. 24
For permitted fastenings (types and
spacings) see Table 5
Full girth stiffener with
welded corners
Illustrations show rolled steel angle
stiffeners. Stiffeners shown in Figs. 19 to
23 are permitted. If used as full girth
stiffeners rigid corners are required.
Back to back stiffener with
bolted corners
Longest side stiffener
Ductwork with short side 400 mm and less
23
Tie rod assembly – alternative arrangement
Fig. 26 With tubing or
conduit and
threaded inserts
Fig. 25 With internal and
external nuts
Fig. 27 With spacers
Fig. 28 With shouldered rod
Table 5 Fastening Centres
Dimensions in mm
Sheet to sheet
Type
of
fastening
Longitudinal
seams
Sheet to section (1)
Cross
joints
Stiffeners
Cross joints
Lap
Standing
& Capped
standing
Socket
&
spigot
RSA
Slide
on
flanges (4)
Mechanically
closed rivets
60
300
60
150
300
150
Self piercing screws
60
–
60
–
300
150
Lock bolts
60
300
–
150
300
300
Set screws & nuts
–
300
–
150
300
300
Spot welds
30
150
–
75
300
150
Dimpling
–
150
–
–
1.50
(2)
(1) A minimum of 2 fixings per side, with a maximum distance from
(2) Except when pierced dimpling is used, one of the other types of
addition to dimpling
(3) In addition to dimpling, one of the other types of fastening must
cases not less than 1 per side
(4) Where manufacturers have specific recommendations, then these
in the Table above
(3)
(5)
–
the corner to the first fixing of 50 mm
fastening must be used at each end in
be used at 450 mm centres, and in all
shall take precedence over the centres
(5) Mechanically closed rivets are not recommended for fixing external stiffeners to ductwork exceeding
500pa negative.
24
Fig. 29 Bends - examples of ‘hard’
and ‘easy’
Hard
Easy
Fig. 30 Turning Vanes
Example of bracing when vane length
exceeds max. permitted.
Alternatively use two banks of vanes
fixing the centre rails together at
150 mm centres.
Fig. 30c
Fig. 30a Single skin
vane
Max. vane length
Single skin – 615 mm
Double skin – 1250 mm
50 mm
90°
ELEVATION
Fig. 30b Double skin
vane
50 mm
25 mm
60
m
m
pi
tc
h
25 x 50 x 1 mm
Channel or angle
fixed to duct
wall both ends
90°
10
Fig. 30a and 30b
Maximum distance between
centres of turning vanes should
not exceed 60 mm pitch.
00
M.10 clamping bolt
at 1000 mm centres
SECTIONAL PLAN SHOWING TYPICAL EXAMPLE OF FIXING
25
26
Part Four – Circular Ducts
ers and contractors in the meantime are invited to
evaluate them based on information currently
available.
12 STANDARD SIZES
The duct sizes in Table 6 have been selected from
the ISO and CEN Standard Ranges.
13.1 Longitudinal seams
Table 6 Circular Ducts – Standard
Sizes
13.1.1 Spirally-wound ducts
The seam used in spirally-wound circular ducts,
provided it is tightly formed to produce a rigid
duct, is accepted as airtight to the requirements
of all the pressure classifications covered in this
specification, without sealant in the seam.
ISO standard sizes (nominal diameter)
mm
Duct Surface
Area
m 2 /m
mm
Duct Surface
Area
m 2 /m
63
0.198
* 400
1.257
80
0.251
* 450
1.413
100
0.314
* 500
1.571
125
0.393
* 560
1.760
* 150
0.470
* 630
1.979
160
0.502
* 710
2.229
† 180
0.566
* 800
2.512
200
0.628
* 900
2.826
† 224
0.704
*1000
3.142
250
0.785
*1120
3.517
† 280
0.880
*1250
3.927
* 300
0.943
315
0.990
†1500
4.713
* 355
1.115
13.1.2 Straight-seamed ducts
The longitudinal seam for straight-seamed circular ducts shall be either the grooved seam
continued to the extreme end of the duct and
sealed, or a continuous butt lap weld or
spot/stitch weld and sealed lap joint (at 30 mm
centres) provided this gives a smooth internal
finish (see Fig. 31).
13.2 Cross joints
13.2.1 General
Cross joints for circular ducts, both spirallywound and straight-seamed, are illustrated in
Figs.32 to 45. They include several proprietary
types and the limits of use in terms of diameter
and pressure classes are noted against each.
13.2.2 Sealant
All circular cross joints shall be sealed. (see section 8)
The use of chemical-reaction tape or heatshrinkable band shall be regarded as an
effective sealant in respect of the socket and
spigot joints illustrated.
Note. The above sizes are subject to normal manufacturing tolerances.
Other sizes may be available from individual
manufacturers including larger diameters up to
2000 mm.
13.2.3 Welded joints
The limitations for welded joints are given in 13.3.5.
*May be phased out of future CEN Standards.
†Are neither ISO nor CEN Standards.
13.3 Fastenings
13.3.1 Permitted types and maximum centres
Table 9 sets out the permitted fastenings and
maximum spacings for low-, medium- and highpressure ducts. All duct penetrations shall be sealed.
13 CONSTRUCTION
Spirally-wound ducts and straight seamed
ducts
The minimum constructional requirements set out
in Table 7 and 8 are common to the full range of
pressures covered in this specification.
13.3.2 Rivets
Manufacturers’ recommendations as to use, size
and drill size are to be followed. Rivets
resulting in an unsealed aperature shall not be used.
The ductwork construction and joint sealing standards are set out in section 8.
13.3.3 Set screws, nuts and lock bolts
Materials shall be of mild steel, protected by
electro-galvanizing, sherardizing, zinc plating
or other equal and approved finish.
Spirally wound duct with thinner than traditional
wall thickness and with one or more corrugations
(ribs) formed between the lock seams are now
available. As design and installation experience
with these are gained and more functional performance criteria are identified it is anticipated that
such forms may be added to later updates. Design-
13.3.4 Self tapping and piercing screws
Providing an adequate seal can be achieved, and
the protrusions into the ductwork are unlikely to
cause injury, then self-tapping or piercing
screws may be used.
27
13.3.5 Welding of sheet
internal surface and shall be free from porosity.
Distortion shall be kept to a minimum.
The suitability of continuous welding or spot
welding for sheet to sheet fastening will be governed by the sheet thickness, the size and shape
of the duct or fitting and the need to ensure airtightness. Welded joints shall provide a smooth
Areas where the galvanizing has been damaged
or destroyed by welding or brazing shall be suitably prepared and painted internally and externally with zinc-rich or aluminium paint.
Table 7 SPIRALLY-WOUND DUCTS (ALL PRESSURE CLASSIFICATIONS)
Maximum
(nominal)
diameter
Minimum
sheet
thickness
Minimum stiffening requirements
1
2
3
mm
80
mm
0.4
None
160
0.5
None
315
0.6
None
800
0.8
None
1000
1.0
None if helically beaded. If not helically beaded use
Fig. 35 (angle reinforced) or Fig. 36, 37 or 38
(angle flanged) – all at 3000 mm maximum spacing.
1500
1.2
Figs. 36, 37 or 38 at 3000 mm maximum spacing.
Table 8 STRAIGHT-SEAMED DUCTS
Minimum sheet thickness
Maximum
(nominal)
diameter
Minimum stiffening
requirements
Low- and
mediumpressure
Highpressure
1
2
3
mm
mm
mm
200
0.6
0.8
500
0.8
0.8
Swaged at spigot end as Figs. 39 and 40
800
0.8
1.0
Swaged at socket and spigot end as Figs. 39 and 4 0
1000
1.0
1.2
Figs. 42 to 45 at 1500 mm maximum spacing
1500
1.2
1.2
Figs. 42 to 45 at 1500 mm maximum spacing
4
None
28
Table 9 Permitted fastenings and
maximum spacings –
circular ducts
14 FITTINGS
14.1 Standardisation of fittings
The terminology and descriptions of circular duct
fittings as set out in Section 33 are recommended
for adoption as standard practice, to provide common terms of reference for designers, quantity
surveyors and ductwork contractors, and those
using computers in ductwork design and fabrication.
Sheet to sheet
Type of
Fastening
Sheet to section
(jointing
flanges and
intermediate
stiffeners)
Cross Spirally Straight
Lap
Joints Joints wound seamed
The requirements for circular duct fittings apply
throughout the pressure ranges covered in this
specification.
1
14.2 Nominal diameters
The nominal diameter (see Table 6) is the size
used for design and ordering. With socket and
spigot joints, care should be taken to ensure that
the dimensions of the ducts and fittings are correctly related, so that the joint can be effectively
sealed.
14.3 Sheet thickness
Sheet thickness for circular duct fittings (determined by the largest diameter) shall be not less
than those quoted in Table 10.
14.4 Sealing of joints
Sealant shall be used in all cross joints and fittings.
Such sealant shall be in accordance with the
requirements of Section 8.
2
mm
3*
mm
4*
mm
5*
mm
Mechanically
Closed Rivets
60
150
150
150
Self piercing
screws
60
150
150
150
Set screws
and nuts
–
–
300
300
Lock Bolts
60
–
300
300
Spot Welds
30
30
150
150
* Minimum of three fixings
Fig. 31
Spirally wound duct
Table 10 Circular duct fittings –
sheet thicknesses
Straight-seamed
duct
Alternative
sealant
location
Lap seam (sealed)
Butt weld
29
Maximum
nominal diameter
Minimum sheet
thickness
1
2
mm
mm
280
0.6
500
0.7
630
0.8
1000
1.0
1500
1.2
Circular duct cross joints
Note – All duct penetrations shall be sealed
Limits of use
Spirally-wound ducts
Pressure
classes
Angle
size
mm
Maximum
diameter
mm
–
1000
Low
Medium
High
–
1000
Low
Medium
High
Fig. 32 Plain socket and spigot (duct to fitting)
Fastening
Alternative
sealant
locations
Fig. 33
Socket and spigot (duct to duct) with
connector
Fastening
Alternative
sealant
locations
Fig. 3 4
Socket and spigot with synthetic rubber
gasket
To be used strictly in
accordance with
manufacturers instructions
and size limitations.
Fastenings
Not suitable for helically beaded
spiral tube.
Gasket
Fig. 35 Angle reinforced socket and
spigot
Fastening
*25 x 3
*30 x 3
40 x 4
Alternative
sealant
locations
800
1000
1500
Low
Medium
High
*Where angle rings specified
30
Limits of use
Maximum
diameter
mm
Angle
size
mm
Spirally-wound ducts
Pressure
classes
Fig. 36 Example of typical roll formed
sheet metal profile
Fastenings and sealant
in accordance with
manufacturer’s
instructions
To be used strictly in accordance with
manufacturer’s recommendations
Fig. 37 Angle flanged (external)
Fixing Bolts
Sealant
*25 x 3
*30 x 3
40 x 4
Fastening
Fastening
Sealant
or gasket
Fig. 38 Angle flanged
(internal)
Alternative sealant locations
800
1000
1500
Low
Medium
High
Sealant
Turn up
minimum
of 8 mm
*Where flanged joints are specified.
Note: A turn up as illustrated is not
mandatory. If not used the toe of
the angle is to be sealed.
Alternative
sealant
locations
Fastening
Fastening
Sealant
or gasket
*25 x 3
*30 x 3
40 x 4
800
1500
1500
Low
Medium
High
*Where flanged joints
are specified
Note
Fixings for angle flanged joints Figs 37 & 38
Section size
Bolt size
25 x 3
30 x 3
40 x 4
6 mm
8 mm
8 mm
@ 300 mm maximum centres
minimum four per joint
31
Limits of use
Straight-seamed
ducts
Angle
size
mm
Fig. 39 Socket and spigot – plain
Maximum
diameter
mm
Pressure
classes
800
Low
Medium
high
Alternative
sealant
locations
Fastening
Socket swage not required on
ducts 500 diameter and below
Fig. 40 Socket and spigot with connector
Alternative
sealant
locations
800
Fastening
Fastening
Low
Medium
High
Socket swage not required on
ducts 500 diameter and below
Fig. 41 Socket and spigot with synthetic rubber
gasket
To be used strictly in
accordance with
manufacturer’s instructions
and size limitations.
Fastening
Gasket
Fig. 42 Socket and spigot – angle reinforced
Alternative
sealant
locations
Fastening
Fastening
*25 x 3
*30 x 3
40 x 4
Alternative angle
location, no swage
needed
Swage only
required if
alternative angle
location used
32
800
1000
1500
Low
Medium
High
*Only where angle ring
specified
Limits of use
Angle
size
mm
Straight-seamed ducts
Maximum
diameter
mm
Pressure
classes
Fig. 43 Roll formed flanged
Fastenings and sealant
in accordance with
manufacturer’s
instructions
Fig. 44 Angle
flanged
Fastening
Fastening
Sealant
or
Gasket
Sealant if
turn up
not used
To be used strictly in accordance with
manufacturer’s recommendations
*25 x 330 x 3
40 x 4
800
1000
1500
Low
Medium
High
*Only where flanged joint specified
Turn up
minimum
of 8 mm
Note: A turn up as illustrated is not
mandatory. If not used the toe of the
angle is to be sealed.
Also acceptable with flange set
internally similar to Fig. 38
Fig. 45 Flat
ring flanged
Sealant
or
Gasket
25 x 3
800
30 x 3
1000
40 x 4
1500
Low
Medium
Turn up of
8 mm
Note
Fixings for angle flanged joints Figs 44 & 45
Section size
Bolt size
25 x 3
30 x 3
40 x 4
6 mm
8 mm
8 mm
@ 300 mm maximum centres
minimum four per joint
33
34
Part Five – Flat Oval Ducts
governed by the sheet thickness, the size and
shape of the duct or fitting and the need to
ensure air-tightness. Welded joints shall provide
a smooth internal surface and shall be free
from porosity. Distortion shall be kept to a
minimum.
15 STANDARD SIZES AND SHEET
THICKNESSES
15.1 Table 11 sets out the standard sizes of spirallywound oval ducts offered by the manufacturers of
ducts of this section.
16 CONSTRUCTION (SPIRALLY-WOUND
DUCTS)
Areas where the galvanizing has been damaged
or destroyed by welding or brazing shall be
suitably prepared and painted internally and
externally with zinc-rich or aluminium paint.
16.1 General
‘Flat oval’ is the term used to describe a duct of
cross-section with flat opposed sides and semicircular ends. The duct is formed from a spirallywound circular duct, using a special former.
16.5 Stiffening
The larger sizes of flat oval duct are stiffened by
swages, as indicated in Table 11. Additionally, tie
rods (see Figs. 25 to 28) are required, positioned
as indicated in the respective tables and illustrations.
Apart from stiffening (see Tables 12 and 13), flat
oval ducts have the same constructional requirements throughout the pressure ranges covered in
this specification.
In special situations as an alternative to tie rods,
stiffening in the form of external angles may be
used to meet the requirements of the corresponding
rectangular duct sizes.
The ductwork construction and joint sealing standards are set out in Section 8.
16.2 Longitudinal seams
Spirally-wound flat oval duct is accepted as airtight
to the requirements of this specification without
sealant in the seams, provided the grooved seam is
tightly formed to produce a rigid duct.
17 CONSTRUCTION (STRAIGHT-SEAMED)
Flat oval ducts with opposed sides and
semi-circular ends may also be formed using
plain sheet and straight seams. Ducts so formed
should follow the metal thicknesses and stiffening requirements specified for the corresponding sizes of rectangular ducts, except that
stiffening is necessary on the flat sides only.
16.3 Cross joints
16.3.1 General
Cross joints shall be as Figs. 53 to 58 inclusive
or such other joint as can be demonstrated to the
designer to be equally satisfactory.
16.3.2 Sealant
All flat oval cross joints shall be sealed. (See
Standards Section 8).
Seams and cross joints (see Figs 59 to 63) shall be
sealed to ensure the necessary degree of airtightness throughout the pressure ranges covered in this
specification.
16.3.3 Welded joints
The limitations for welded joints are given in
16.4.5.
16.4 Fastenings
16.4.1 Permitted types and maximum centres
Table 14 sets out the permitted fastenings and
maximum spacings for low-, medium- and highpressure ducts. All duct penetrations shall be
sealed.
18 FITTINGS
18.1 General constructional requirements
Sheet thicknesses for flat oval fittings (determined
by the periphery of the larger end) shall be not less
than those given in Table 11 for the ducts themselves.
16.4.2 Rivets
Manufacturers’ recommendations as to use, size
and drill size are to be followed. Rivets resulting
in an unsealed aperature shall not be used.
With socket and spigot joints, care should be taken
to ensure that the dimensions of ducts and fittings
are correctly related.
All the seams and joints integral to a fitting shall be
sealed to the same standard as the duct. (See Section 8).
16.4.3 Set screws, nuts and lock bolts
Set screws and nuts shall be of mild steel,
protected by electro-galvanizing, sherardizing,
zinc plating or other equal and approved finish.
18.2 Standardisation of fittings
The terminology and descriptions of flat oval duct
fittings as set out in Section 33 are recommended
for adoption as standard practice, to provide common terms of reference for designers, quantity surveyors and ductwork contractors, and those using
computers in ductwork design and fabrication.
16.4.4 Self tapping and piercing screws
Providing an adequate seal can be achieved, and
the protrusions into the ductwork are unlikely to
cause injury, then self-tapping or piercing
screws may be used.
16.4.5 Welding of sheet
The suitability of continuous welding or spot
welding for sheet to sheet fastening will be
The requirements for flat oval duct fittings apply
throughout the pressure ranges covered in this
35
Table 11 Flat oval ducts – Standard sizes and sheet thicknesses
Nominal
sheet
thickness
length
Surface
area per
metre
length
1
2
mm
sq. metres
mm
0.718
320
0.798
100
125
150
mm
mm
360
350
330
320
0.878
400
390
370
360
0.958
440
430
410
400
1.037
480
470
450
440
520
505
490
480
545
530
520
1.197
1.277
200
250
300
350
400
450
500
mm
mm
mm
mm
mm
mm
3
mm
1.117
mm
525
635
605
580
715
690
660
630
800
770
740
710
685
655
880
845
825
790
765
735
705
680
960
930
900
875
845
815
785
755
1040
1010
985
955
925
895
865
835
1120
1090
1065
1035
1005
975
945
915
1200
1170 1145
1115
1085
1055
1025
1000
2.873
1335 1305
1275
1245
1215
1190
1160
3.192
1465
1435
1405
1375
1350
1320
3.511
1625
1595
1570
1540
1510
1480
3.830
1785
1760
1730
1700
1670
1640
1.596
1.756
1.915
2.075
2.238
2.394
2.553
Swaged
555
1.436
1.0
75
(Width of duct (minor axis — ‘W’) — nominal — mm
0.8
Depth of duct (minor axis — ‘D’) — nominal
36
Table 12 – Flat oval ducts – low- and medium-pressure – stiffening requirements
Depth of duct (minor axis — ‘D’) – nominal
Tie rods
75
100
125
150
200
1
250
300
350
400
450
500
mm
mm
mm
mm
mm
2
mm
mm
mm
mm
360
350
330
320
400
390
370
360
440
430
410
400
480
470
450
440
520
505
490
480
545
530
520
mm
mm
320
Fig. 46
1000 mm centres
Fig. 47
750 mm centres
Fig. 48
500 mm centres
Width of duct (major axis — ‘W’) — nominal — mm
Not required
555
525
635
605
580
715
690
660
630
800
770
740
710
685
655
880
845
825
790
765
735
705
680
960
930
900
875
845
815
785
755
1040
1010
985
955
925
895
865
835
1120
1090
1065
1035
1005
975
945
915
1200
1170
1145
1115
1085
1055
1025
1000
1335
1305
1275
1245
1215
1190
1160
1465
1435
1405
1375
1350
1320
1625
1595
1570
1540
1510
1480
1785
1760
1730
1700
1670
1640
37
Table 13 – Flat oval ducts – high-pressure – stiffening requirements
Depth of duct (minor axis — ‘D’) – nominal
Tie rods
75
100
125
150
200
1
250
300
350
400
450
500
mm
mm
mm
mm
mm
2
mm
mm
mm
mm
360
350
330
320
400
390
370
360
440
430
410
400
480
470
450
440
520
505
490
480
545
530
520
mm
mm
320
Width of duct (major axis — ‘W’) — nominal — mm
Not required
Fig. 49
1000 mm centres
Fig. 50
750 mm centres
Fig. 51
500 mm centres
555
525
635
605
580
715
690
660
630
800
770
740
710
685
655
880
845
825
790
765
735
705
680
960
930
900
875
845
815
785
755
1040
1010
985
955
925
895
865
835
1120
1090
1065
1035
1005
975
945
915
1200
1170
1145
1115
1085
1055
1025
1000
1335
1305
1275
1245
1215
1190
1160
1465
1435
1405
1375
1350
1320
1625
1595
1570
1540
1510
1480
1785
1760
1730
1700
1670
1640
Fig. 52
Section A-A
A
A
38
Flat oval duct cross joints
Note – All duct penetrations shall be sealed
Limits of use
Flange
size
mm
Spirally-wound ducts
Maximum
width
mm
Pressure
classes
Fig. 53 Plain socket and spigot (duct of fitting)
Fastening
–
1785
Low
Medium
High
–
1785
Low
Medium
High
Alternative
sealant
locations
Fig. 54 Socket and spigot (duct of duct) with
connector
Fastening
Alternative
sealant
locations
Fig. 55 Alternative socket and spigot (duct to
duct) with connector and tie rod
Fastening
—
Alternative
sealant
loacations
1785
Low
Medium
High
The tie rod pattern to be in accordance with Tables 12 and 13.
Fig. 56 Example of typical roll formed
sheet metal profile
Fastenings and sealant
in accordance with
manufacturer’s
instructions
39
To be used strictly in accordance with
manufacturer’s recommendations
Limits of use
Spirally-wound ducts
Angle
size
mm
Maximum
width
mm
Pressure
classes
Fig. 57 Angle flanged (external)
Fixing bolts
Fastening
Sealant
*25 x 3
*30 x 3
40 x 4
Fastening
800
1040
1785
Low
Medium
High
*Where flanged joints are specified.
Sealant
or gasket
Sealant
Angle flanged joint does not require
DW/TM1 certification.
Turn up
minimum
of 8 mm
A turn up as illustrated is not
mandatory. If not used, the toe of the
angle is to be sealed.
Fig. 58 Angle flanged
(internal)
Alternative sealant locations
Alternative
sealant
locations
*25 x 3
*30 x 3
40 x 4
Fastening
Fastening
Sealant
or gasket
Low
Medium
High
800
1040
1785
*Where flanged joints
are specified
Table 14 – Permitted fastenings and
maximum spacings – Flat oval ducts
Note
Fixings for angle flanged joints Figs. 57
& 58
Type of
Fastening
Section size
Bolt size
25 x 3
30 x 3
40 x 4
6 mm
8 mm
8 mm
Sheet to section
(jointing flanges
and intermediate
Stiffeners
Sheet to sheet
Lap
joints
Cross
joints
Flat
sides
@ 300 mm maximum
centres. minimum
four per joint
Semicircular
ends
Flat
sides
Semicircular
ends
1
2
3
4*
5
6*
Mechanically
close rivets
mm
60
mm
60
mm
150
mm
150
mm
150
Self piercing
screws
150
150
150
60
60
Set screws
and nuts
–
–
–
150
300
Lock bolts
60
–
–
150
300
Spot welds
30
30
30
75
75
*Minimum of two fixings.
Roll formed flanges shall be fitted strictly in accordance with
manufacturers instructions.
40
Limits of use
Straight-seamed ducts
Angle
size
mm
Fig. 59 Socket and spigot – plain
Maximum
width
mm
Pressure
classes
Alternative
sealant
locations
800
Fastening
Low
Medium
High
Socket swage not reqauired on
ducts 500 wide and below
Fig. 60 Socket and spigot with connector
Alternative
sealant
locations
800
Fastening
Fastening
Low
Medium
High
Socket swage not required on
ducts 500 wide and below
Fig. 61 Socket and spigot – angle reinforced
Alternative
sealant
locations
Fastening
Fastening
*25 x 3
*30 x 3
40 x 4
Alternative angle
location (No swage
needed see 13.2)
Low
Medium
High
*Only where angle ring
specified
Fig. 62 Angle
flanged
Fastening
Sealant if
turn up
not used
Fastening
800
1040
1785
Sealant
or
Gasket
Turn up
minimum
of 8 mm
*25 x 330 x 3
40 x 4
800
1040
1785
Low
Medium
High
*Only where flanged joint specified.
Angle flanged joint does not
require DW/TM1 certification.
A turn up as illustrated is not
mandatory. If not used, the toe of
the angle is to be sealed.
Also acceptable with flange set
internally similar to fig. 58
41
Limits of use
Straight-seamed
Fig. 63
Angle
size
mm
Maximum
width
mm
Sealant
25 x 3
800
or
Gasket
30 x 3
1040
40 x 4
1785
ducts
Pressure
classes
Flat
ring flanged
Turn up of
8 mm
Note
Fixings for angle flanged joints Figs. 62 & 63
Section size
Bolt size
25 x 3
30 x 3
40 x 4
6 mm
8 mm
8 mm
@ 300 mm maximum centres
minimum four per joint
42
Low
Medium
Part Six – Hangers and Supports
or studding or flat strap, pre-treated by, e.g. hotdip galvanizing, sherardizing, electro-deposited
zinc plating or by other accepted anti-corrosion
treatment. Other materials, such as stranded
wire, may also be acceptable.
19 GENERAL
19.1 Principles adopted
Supports are an essential part of the ductwork
system, and their supply and installation are normally the responsibility of the ductwork contractor. The choice between the available methods
of fixing will depend on the type of building structure and on any limitations imposed by the structural design. Further, unless the designer has
specified his requirements in detail, the load to be
carried shall be understood to be limited to the
ductwork and its associated thermal and/or
acoustic insulation.
Projection of a rod or studding hanger through
the bottom bearer should, where practicable,
not exceed twice the thickness of the securing
nut.
Provided the integrity of the ductwork is maintained, hangers may be attached to the corners
of the flanges as an alternative to the use of a
bottom bearer.
It is not practicable to deal here with the full range
of supports available, which increasingly includes
proprietary types, so in this section various
methods of support are dealt with in principle
under the three elements of:
With
proprietary
devices
manufacturers’
recommendations for use should be followed.
19.3.2 The duct bearing member
The choice of the lower support will be dictated
by the actual duct section.
(1) the attachment to the structure;
(2) the hanger itself; and
(3) the duct bearing member
19.3.3.1 Rectangular ducts
Table 15 gives
hangers and for
tions. The angle
channel sections
with illustrations of those most commonly used.
Supports for ductwork external to the building have
been excluded, as these are individually designed
to suit the circumstances, and also may be required
to meet local authority standards. For the same
reasons, floor supports have not been dealt with.
minimum dimensions for the
angle, channel and profile secis shown in Fig. 73, the profile
in Figs. 74 and 75.
Typical arrangements of bottom bearer supports for plain, and insulated ducts are shown in
Figs. 68, 69 and 70.
With a proprietary device, it will, unless the
designer has specified his requirements in detail,
be the responsibility of the ductwork installer to
ensure that it meets requirements, with a sufficient
margin of overload; and that it is installed in accordance with the manufacturer’s recommendations.
19.3.3.2 Circular ducts
Table 15 gives minimum dimensions for the
hanger and for the brackets – as illustrated in
Figs. 64 to 67.
19.3.3.3 Flat oval ducts
Table 15 gives minimum dimensions for the
hanger; and for the bearer, depending on
whether the flat side of the duct is horizontal or
vertical.
The absence of any method or device from this
specification does not preclude its use if it can be
demonstrated that it is suitable for the duty
assigned to it, with a sufficient margin of safety
against overload; and this will be the responsibility of the ductwork installer, unless the designer
has specified his requirements in detail.
Typical arrangements for flat oval duct supports
are shown in Figs. 68, 71 and 72.
19.4 Vertical ducts
The design of supports for vertical ducts is dictated
by site conditions, and they are often located to
coincide with the individual floor slabs, but if the
spacing exceeds 4 metres the designer must specify his requirements.
19.2 Fixing to building structure
The fixing to the building structure should be of a
strength and durability compatible with those of
the ductwork support attached to it. A fixing to
concrete or brickwork must be made in such a way
that it cannot loosen or pull out through normal
stressing or through normal changes in the building structure.
Vertical ducts should be supported from the stiffening angle or the angle frame, or by separate
supporting angles fixed to the duct.
19.3 Horizontal ductwork
19.3.1 The hanger itself
A typical method of supporting vertical rectangular
ducts is shown in Fig. 76 and for circular ducts in
The hanger itself is usually mild steel plain rod
43
Fig. 77. The same methods are applicable to vertical flat oval ducts.
The extent of any vapour sealing of ductwork
thermal insulation and the method to be used,
must be clearly specified in advance by the
designer.
19.5 Heavy loadings
For ducts larger than those covered by Table 15, or
where heavy equipment, mechanical services,
ceilings or other additional load is to be applied to
the ductwork, supports shall be designed to suit
the applications.
19.7 Heat transfer
It is not normally necessary to make special
arrangements for the limitation of heat transfer
via the duct supports. However, there may be
special cases where the temperature difference
justifies a heat barrier to conserve heat or to
prevent condensation and such requirements must
be specified by the designer.
19.6 Insulated ducts with vapour sealing
Where the temperature of the air within the
duct is at any time low enough to promote condensation on the exterior surface of the duct and
cause moisture penetration through the thermal
insulation, vapour sealing may be called for, and
in this case the most important requirement is to
limit penetration of the seal.
Table 15
19.8 Fire rated ductwork
DW/144 supports cannot be used on fire rated
ductwork systems. See Appendix D and in
particular notes in D.2.1 Method 3 and D.2.3.
Supports for horizontal ducts – rectangular, flat oval and circular
HANGERS
DUCT SIZES
FLAT STRAPS
DROP
ROD
DIAM
RECT
F’OVAL CIRC
BEARERS
STIRRUPS
SPACINGS
RECT
F’OVAL
CIRC
Fig
70
Fig
72
Figs 64,
65, 67
Fig
69
Fig
71
Fig
66
Fig
68
Fig
68
4
5
6
7
8
9
10
11
12
13
14
mm
mm
mm
mm
mm
mm
mm
mm
longer
side
major
axis
diam
1
2
3
mm
mm
mm
mm
mm
mm
400
400
315
6
25 × 0.8
plain
or
25 × 0.8
plain
or
perf
perf
perf
R E C T F’OVAL
ANGLES
Roll formed
channel
section
profile
W
H
25 × 0.8 2.5 × 3
plain
or
CIRC
RECT & F’OVAL
RECT
F’OVAL
CIRC
25 × 3
25 × 3 25 × 25 × 1.6 W
H
40 × 20 × 1.5
3000
3000
600
605
457
8
30 x 3
25 x 3
25 x 3
30 x 3
30 x 3
30 x 3
25 x 25 x 3 40 x 20 x 1.5
3000
3000
1000
1040
813
8
N/A
30 x 3
30 x 3
N/A
30 x 3
30 x 3 30 x 30 x 3 40 x 20 x 1.5
3000
3000
1500
15
1510
1120
10
N/A
N/A
40 x 5
N/A
N/A
40 x 5 40 x 40 x 3 40 x 40 x 1.5
2500
3000
2000
1785
1525
10
N/A
N/A
40 x 5
N/A
N/A
40 x 5 50 x 50 x 5 40 x 40 x 2.5
2500
3000
1000
N/A
2000
12
N/A
N/A
50 x 6
N/A
N/A
50 x 6 60 x 60 x 6
2500
N/A
N/A
Notes to Table 15
(1) The dimensions included in Table 15 are to be regarded as minima.
(2) The maximum spacings set out in Table 15 are related solely to duct weight considerations. Closer spacings may be required by reason of the limitations of the building structure or to achieve the necessary
duct rigidity.
(3) Rolled steel channels may be used as bearing members provided they meet the design characteristics of
the bearing members tabled above.
(4) As an alternative to drop rod or studding, wire rope may be utilised to suit individual manufacturer’s
fixing methods and loading limitations.
44
Arrangement of Bearers and Hangers
(to be read in conjunction with Table 15
which lists material sizes relative to duct sizes)
KEY
Limits refer to actual duct sizes – insulation is additional
– Attachment
to structure
– Typical
attachment
to structure
Rectangular
or flat oval
– Flat Bar
– Drop rod,
studding
or
wire rope
– Outline of
Insulation (if
applicable)
Fig. 68 Rolled or Profiled Bearer
Limit: NONE
Alternative
Drop rod,
studding or
wire rope.
Fig. 69 Stirrup
Limit: 600 wide
Fig. 65 Flat Strap Hanger & Split Clips
Fig. 70 Flat Strap Hanger
Limit: 600 wide
Fig. 66 Stirrup
Limit: 2000 DIA
Fig. 71 Stirrup
Limit: 1040 wide
Fig. 67 Flat Strap Hanger
Limit: 2000 DIA
Fig. 72 Flat Strap Hanger
Limit: 1040 wide
Fig. 64 Wrap-Round Hanger
Limit: 315 DIA
Alternative
Drop rod,
studding or
wire rope.
Limit: 315 DIA
45
SUPPORT BEARERS
Fig. 73
Rolled steel
angle
Fig. 75 Inverted profile
channel (alternatives)
Fig. 74
Profile
channel
(alternatives)
VERTICAL DUCTS
Stiffening frame
or flanged joint
Flat bar clips,
stiffening frame
or flanged joint
Outline of insulation
(if applicable)
Support bearer
(see notes below)
Drop rod
or studding
Stiffening frame
or flanged joint
Fig. 76
Vertical rectangular ducts
Fig. 77
Vertical circular ducts
The support bearer, which, depending on duct/structural opening size, could be either channel or angle
section, may be utilised in any of the following arrangements:a)
Fixed directly to duct skin with sealed fixings (flat face only of either rectangular or flat
oval)
b)
To support the underside of a flat bar clip in halves (circular or flat oval)
c)
To support the underside of either the stiffening frame of the flanged joint of any duct
section
d)
To support either a stiffening frame or a flanged joint below using drop rods/studding.
46
Part Seven – General
duct dimensions, openings for access shall
satisfy the maintenance needs of the designated
equipment with consideration being given, if
more practicable, to the use of removable duct
sections or flexible ducts/connections.
20 ACCESS/INSPECTION OPENINGS
20.1 General
This section covers inspection/servicing access
only. Appendix M sets out guidance notes, in summary form, of the access considerations that
should be made by the designer in terms of
inspection, servicing and cleaning access.
All openings shall be made safe and have sealed
panels/covers designed so that they can be speedily removed and refixed. Multiple set screws are
not recommended, and self-piercing screws are
not acceptable as a method of fixing.
The services co-ordinator should ensure that there
is an area free of services and other obstructions to
enable a panel/cover to be removed.
20.3 Inspection covers
It shall be standard practice to provide inspection
covers adjacent to regulating dampers where
either the control linkage is mounted internally
within the airstream or if a multi-bladed unit is an
integral part of the ductwork run. It is not necessary to provide inspection covers adjacent to
either single blade regulating dampers or flanged
damper units.
20.4 Hand holes
Hand holes to permit proper jointing of duct
sections shall be provided at the manufacturer’s
discretion, but should be kept to a minimum and
made as small as practicable. The hand hole cover
shall be sealed and securely fastened.
20.1.1 Function
20.1.1.1 An access panel is to be provided
adjacent to items of in-line equipment that
require either regular servicing or intermittent
access. The opening will be sized to provide
hand and/or arm access only and the designer
shall specify the size and location of panels
where larger dimensions are required and in
these cases the panels should not exceed 450
× 450 mm.
20.1.1.2 An inspection cover is to be provided adjacent to items of in-line equipment that
need visual inspection only of internal elements from outside of the ductwork. The
inspection opening should have a minimum
size of 100 mm sq/dia.
20.5 Openings in insulated ducts
It will be the responsibility of the insulation
contractor to ‘dress’ their insulation to the edge of
the access opening without impeding the functionality of the panel, cover or door.
20.6 Test holes for plant system commissioning
It shall be standard practice to provide test holes,
normally 13 mm diameter and fitted with an effective removable seal, at the following locations: at
fans (in the straightest section of duct near to the
fan outlet); at cooling coils and heating coils (both
before and after the coil). The actual location of
the test holes shall be confirmed by the Designer
and/or Commissioning Engineer either at the
drawing approval stage (to be works drilled) or
during the commissioning activity (to be site
drilled). For practical access reasons the latter
method is usually preferred.
20.2 Access panels
20.2.1 It shall be standard practice to provide
access panels for the inspection and servicing of
plant and equipment as follows:
20.2.1.1 Fire/Smoke dampers
Panels to be located so as to give access both
to the blades and fusible links. On multiple
assembly units it may be necessary to provide
more than one panel and this may be determined by both external access conditions and
the internal reach to the blades and the fusible
links.
20.2.1.2 Filters
Panel to be located on the air entry side
ie. upstream (Note: Dimensions of access may
need to be changed to suit filter elements of
the front withdrawal type.)
20.2.1.3 Heating/cooling coils and in-duct
fans/devices
Panel to be located on the air entry side
ie. upstream
20.7 Instrument connections
Instrument connections shall be provided where
shown on the contract drawings, suitably drilled
or bossed and screwed as sizes specified.
20.8 Cleaning/maintenance
Designers shall take specialist advice and then
stipulate their requirements for the periodic
internal cleaning/maintenance of ductwork and of
the consequent need for adequate access for specialist cleaning equipment including the size, type
and location/frequency of the actual access openings required.
Appendix M sets out guidance notes for the
consideration of cleaning access and also makes
reference to the HVCA publication TR17 “Guide
to Good Practice, Cleanliness of Ventilation Systems” which covers the subject in greater detail.
20.2.2 It shall be standard practice to connect
safety restraints to access panels located in riser
ducts.
20.2.3 Subject to the restrictions imposed by
47
20.9 Openings required for other purposes
It shall be the designers responsibility to specify
the location and size of any openings required
other than those covered in this section. In the
case of hinged access doors it shall be the designer’s responsibility to indicate on the drawings the
location and size of any hinged access doors
required, ensuring that there is an area free of services and other obstructions to enable the door to
be satisfactorily opened. Unless otherwise specified by the designer, openings should not be larger than 1350 mm high by 500 mm wide. Doors
could open against the air pressure. Both the
opening in the duct and the access door itself shall
be adequately reinforced to prevent distortion. A
suitable sealing gasket shall be provided, together
with sufficient clamping type latches to ensure an
airtight seal between the door and the duct.
Single-blade dampers (single-skin section) shall
have a maximum duct width of 300 mm and a
maximum duct height of 300 mm for rectangular ducts; and for circular ducts a maximum
diameter of 315 mm.
Single-blade dampers (double-skin section) are
suitable for use in rectangular ducts, and shall
have a maximum duct width of 1250 mm and a
maximum height of 300 mm.
21.2.2 Multi-blade dampers (single or
double skin) parallel or opposed blade
Multi-blade dampers shall consist of a number
of pivoted blades contained within a casing. The
blades shall be adjustable through a nominal 90°
angle simultaneously by interconnected linkage
or gears, connected to a quadrant or similar
operating mechanism. Where automatic control
of the damper is required a spindle shall be
extended to enable a powered actuator to be
mounted.
For safety reasons, the manufacturer shall incorporate means to prevent personnel being trapped
inside the duct e.g. man access with operating
handles both inside and outside the duct.
There is no restriction on the size of duct in
which multi-blade dampers or damper assemblies may be used. Where dampers are required
for blade lengths in excess of 1250 mm, the
blades should be suitably re-inforced or supported. No individual damper blade should
exceed 200 mm in width.
21 REGULATING DAMPERS
21.1 General
Balancing dampers and control dampers are elements inserted into an air distribution system, or
elements of an air distribution system. Balancing
dampers permit modification of the air resistance
of the system and consequently changing of the
airflow rate. Control dampers control the airflow
rate and in addition provide low leakage closure
of the airflow.
21.2.3 Iris dampers
Iris dampers shall consist of a number of radially inter-connected blades which open or close
within a casing with duct connection spigots.
The blades shall be simultaneously adjusted by
a quadrant or similar operating mechanism.
The designer shall specify damper locations and
select the damper type as defined in 21.2 appropriate to the airflow, pressure and acoustic
characteristics.
Iris dampers should be installed as specified by
the manufacturer’s operating and installation
instructions, w h e r e t h e p r o d u c t i s u n i directional with regard to airflow.
21.1.1 Balancing damper
To achieve the required distribution of air in the
ductwork system at inlets and/or outlets. For
this purpose, the damper blades are set and
locked manually in any required position
between fully open and fully closed.
21.1.2 Control damper
To secure dynamic control of the air flow in the
ductwork system. In this function, the damper
will always be power – actuated and may
require to be modulated between fully open and
fully closed, and to be capable of taking up any
position between these extremes. In the fully open
position, the damper should have a minimum
pressure drop. In the fully closed position, it
will not necessarily achieve a complete shut off.
Iris dampers are available for circular ducts
only, in diameters up to 800 mm (It should be
noted that the damper casing is approximately
twice the diameter of the duct).
21.2.4 Backdraft dampers
Air pressure operated uni-directional rectangular (single or multi-blade) with adaptors if fitted
to circular or oval ducts.
21.2.5 Hit and miss dampers
Two parallel adjacent plates each with multiple
openings sliding against each other. The openings are designed to provide 50% air volume
flow rates when they fully coincide. Used for
simple operations up to 400 mm longest side.
21.2.6 Slide and blast gate dampers
A damper used as a shut off facility, normally
for use in circular ductwork with an external
slide housing allowing a blade to be fully inserted to fully extended for maximum air flow.
21.2 Types of airflow control damper
Air flow dampers of various types are available
for specific purposes as follows.
21.2.1 Single-blade dampers (Single or double skin)
Single-blade dampers shall consist of a single
pivoted blade contained within a casing or section of ductwork. The blade shall be adjustable
through a nominal 90° angle by means of a
quadrant or similar operating mechanism.
Where automatic control of the damper is
required the spindle shall be extended to enable
a powered actuator to be mounted.
Generally available in cast/pressed formats up
to 355 mm diameter and normally used in
industrial exhaust applications.
21.3 Construction
21.3.1 Materials
Dampers shall be constructed from steel, stainless steel, aluminium or synthetic materials.
48
22 FIRE DAMPERS
All products shall be protected against corrosion
as necessary and supplied in a fully finished
condition as specified by the designer.
22.1 General
Dampers are required in air distribution systems
for fire containment. Generally they are called for
where ducts penetrate walls or floors which form
fire compartmentation. The damper assembly
should have a fire resistance rating equal to that of
the fire barrier it penetrates and shall be fire tested and rated to the time/temperature curve of
BS476 part 20 and 22.
21.3.2 Dampers used in low and medium
pressure systems
The following recommendations apply to
dampers forming an integral part of ductwork
with pressure classification A and B air leakage
limits.
The dampers shall be constructed to prevent
distortion and jamming in operation. The blades
shall be sufficiently rigid to minimise movement when in the locked position.
22.1 Types of fire dampers
Fire dampers of various types are available for
specific purposes, as follows:
The blades shall be securely fixed to the operating mechanism. Spindles shall be carried in
either non-ferrous, synthetic or roller bearings.
All balancing dampers shall have a locking
device located on the outside of the case and
shall give clear indication of the actual blade
position. All penetrations of the duct shall be
fitted with suitable seals where necessary.
22.2.1 Folding curtain
Folding curtain fire dampers shall be constructed of a series of interlocking blades which
fold to the top of the assembly permitting the
maximum free area in the airway. The blades
shall be held in the open position by means of a
thermal release mechanism rated at 72°C ± 4°C.
21.3.3 Dampers used in high pressure
systems
Regulating dampers used in ductwork systems to
pressure classification C shall meet the construction requirements specified in 21.3.1 and 21.3.2
with operating mechanisms out of the airstream.
The fire damper must be able to close against
static air conditions when mounted in either the
vertical or horizontal planes.
In the event of a signal from a remote sensor the
fire damper blades shall be released and close
the airway. A local excess temperature in the
area of the fire damper shall, independent of any
remote sensors, automatically release the blades
and close the airway by means of the thermal
release mechanism, electric solenoid or electromagnet.
21.3.4 Proprietary types of damper
The use of any specific type of proprietary
damper shall be confirmed by the designer. In
all cases, proprietary dampers shall meet the
relevant requirements of this specification.
21.3.5 Damper casings
Duct damper casings shall be constructed to
meet the minimum leakage limits specified for
the ductwork system to which they are installed.
22.2.2 Single blade
Single blade fire dampers shall consist of a
single pivoted blade within a fire resistant case.
In order to apply the square metreage leakage
calculation as detailed in DW/143 A practical
guide to Ductwork Leakage Testing, the reference casing area shall be taken as the perimeter
size of the damper multiplied by the equivalent
length of one metre eg. an 800 mm x 400 mm
duct damper shall have a surface area for casing
leakage performance calculated as follows;
[(2 x 0.8) + (2 x 0.4)] x 1 = 2.4m2 casing area.
The blade shall be released from its open position by means of a thermal release mechanism
rated at 72°C ± 4°C, electric solenoid, electromagnet(s) or other device.
The blade shall close the airway by means of
any one, or combination of, an eccentric pivot,
balance weight(s) and/or spring(s), the spring
element being incorporated within the damper
or actuator mechanism.
Other performance and rating test methods for
dampers and valves are specified in ISO5129
and BS/EN1751, and are referenced below:
a) Leakage past a closed
damper or valve
b) Flow rate/pressure
requirement characteristics
c) Operational torque testing
d) Thermal transfer testing
e) Regenerated sound power
levels
The fire damper shall be able to operate in either
or both the vertical and horizontal planes.
BS/EN 1751
22.2.3 Multi-blade
BS/EN 1751
BS/EN 1751
BS/EN 1751
Multi-blade fire dampers shall consist of a
number of linked blades contained within a fire
resistant case.
ISO 5129
The blades shall be released from their open
position by means of either a thermal release
mechanism rated at 72°C ± 4°C, or by the force
applied from electrical solenoid(s), electromagnet(s), electrical/pneumatic actuator or
other device.
21.4 Installation
Dampers shall be installed in accordance with any
relevant ISO, EN or British Standard, local building regulations and national codes of practice as
well as the manufacturer’s recommendations.
49
ALTERNATIVE PROVISION FOR EXPANSION
Fig. 79
Fig. 78
This design was developed
in collaboration by HVCA
and the HEVAC Association.
Space for
expansion
Close contact
between damper
and frame
This method is also normally used for a
multiple assembly of shutter-type dampers
Damper fixed on
centre of fire
barrier or 50 mm
minimum on
access side of wall
Damper
Damper
Split frame assembled
around damper by
manufacturer/installer
and built into fire
barrier by builder.
Expansion space
filled with
compressible
fire resistant
packing
Angle frames
secured after
fire barrier
is built
The blades shall close the airway by means of a
spring(s), the spring element being incorporated
within the damper or actuator mechanism.
22.5 Location
The effective formed barrier of the damper assembly shall be located within the structural opening.
Where this is not possible the section of the casing outside a fire barrier must have a fire resistance not less than that of the fire barrier and be
adequately supported/protected against the possibility of displacement/damage by impact.
The fire damper shall be able to operate in either
or both the vertical and horizontal planes.
22.2.4 Intumescent
Intumescent fire dampers shall be constructed
from strips of intumescent material formed into
a lattice or from honeycomb material covered
with intumescent paint. The damper shall fully
seal when heat or flame is applied from either
side. Note: these devices are generally used in
door/partition low velocity applications.
22.6 Provision for expansion
Damper assemblies generally include built-in
clearance frames to meet the requirement that the
casing be free to expand in the event of fire. The
integrity of the fire barrier is maintained either by
metal to metal contact or by fire resistant packing.
Acceptable arrangements are shown in Figs. 78
and 79.
22.3 Materials and construction
The damper shall be constructed from steel or
stainless steel or other approved material. Steel
products shall be protected against corrosion and
supplied in a fully assembled condition as specified by the designer.
22.7 Installation
Damper installation shall be in accordance with
the manufacturer’s recommendations and the
impending HVCA Publication DW/TM3 – Guide
to Good Practice, for the design for the installation of Fire and Smoke Dampers and any conflict
between the two should be resolved and authorised by the designer responsible for the fire
damper selection.
22.4 Air leakage
Fire damper casings shall meet the equivalent
leakage performance standard specified for the
ductwork system to which they are installed.
Classes A, B and C are used to signify the leakage
performance of the damper casing with the
respective testing method illustrated and specified
in BS/EN1751.
23 SMOKE DAMPERS
23.1 General
Smoke dampers shall be constructed in such a
manner as to restrict the spread of smoke and
other products of combustion from one occupied
space to another. The blade(s) shall overlap each
other and/or include edge seals. The blade(s) shall
be arranged to minimise the leakage of smoke. If
degradable seals are fitted, care should be taken to
establish the temperature range of the material
used to ensure performance compatibility.
In order to apply the square metreage leakage calculation as detailed in the standard, the reference
casing area shall be taken as the perimeter size of
the damper multiplied by an equivalent length of
one metre eg. an 800 mm x 400 mm duct damper
shall have a surface area for casing leakage performance calculated as follows: [(2 x 0.8) + (2 x
0.4)] x 1 = 2.4m2 casing area.
50
dampers shall consist of a single pivoted blade
contained within a fire resistant case.
The smoke damper shall be able to operate in
either or both the vertical and horizontal planes
and close against dynamic air conditions.
The blade shall be released from its open position by means of either a thermal release mechanism rated at 72°C ± 4°C, or in addition operated by the force applied from electrical solenoid(s), electro-magnet(s), electrical/pneumatic
actuator or other device.
23.2 Types of smoke damper
Smoke dampers of various types are available for
specific purposes, as follows:
23.2.1 Single blade
Single blade dampers shall consist of a blade of
smoke tight material held in either the open or
closed position by a mechanical linkage releasing to close or open and seal against the damper
case. The blade shall be mechanically connected
to the actuator (electric or pneumatic) and shall
be triggered by interfacing with a smoke
detector or fire control panel.
The combination smoke and fire damper shall
be able to operate in either or both the vertical
and horizontal planes and close against dynamic
air conditions.
24.2.2 Multi-blade
Multi-blade combination smoke and fire
dampers shall consist of a series of blades
mechanically linked and connected to a damper
actuator with manual, electric or pneumatic
opening and spring loaded closure contained
within a fire resistant case.
23.2.2 Multi blade
Multi blade dampers shall consist of blades of
smoke tight material including the blade to
blade seals, where fitted. The blades shall be
mechanically linked to an actuator (electrical or
pneumatic) to hold the blades in either the open
or closed position. The actuator shall interface
with a smoke detector or fire control panel and
shall be so designed as to hold the blades close
against the smoke seals, where fitted.
The blades shall be released from their open
position by means of either a thermal release
mechanism rated at 72°C ± 4°C, or in addition
operated by the force applied from electrical
solenoid(s), electro-magnet(s), electrical/ pneumatic actuator or other device.
23.3 Materials and construction
The damper shall be constructed from steel, stainless steel, other material or composite material
with blades fitted to reduce the leakage of smoke
and hot gases when the blades are in the closed
position. Steel products shall be protected against
corrosion and assembled in a fully finished condition as specified by the designer, in some circumstances controls may be supplied separately.
The combination smoke and fire damper shall
be able to operate in either or both the vertical
and horizontal planes and close against
dynamic air conditions.
23.4 Air leakage
Smoke damper casings shall be as Clause 22.4
24.3 Materials and construction
The combination smoke and fire damper case
shall be constructed from steel, stainless steel,
other material or composite material with compressible side seals fitted between the blade ends
and the casing to reduce the leakage of hot gases
when the blades are in the closed position.
23.5 Installation
Damper installation shall be as Clauses 22.6 and
22.7.
Steel products shall be protected against corrosion
and supplied in a fully finished condition as
specified by the designer.
24 COMBINATION SMOKE AND FIRE
DAMPERS
24.1 General
Combination smoke and fire dampers are required
in air distribution systems to prevent the spread of
smoke and hot gases from the fire zone and to
maintain the integrity of a fire rated structure for a
period compatible with that of the separating
structure. They shall be tested and rated to BS476
Part 20 and 22. Reference maybe made to BS5588
Part 4 for specific smoke rating requirements.
24.4 Air leakage
Damper casings shall be as Clause 22.4.
24.5 Installation
Damper installation shall be as Clauses 22.6 and
22.7.
25 FLEXIBLE DUCTS
25.1 General
Flexible duct connections shall be used in the following applications:• Terminal units
• Fan coil units
• Constant Volume/Variable Air Volume units
• Grilles and Diffusers
• Plenum boxes
• Distribution ducts between the above items.
The closure of the fire damper under action of the
thermal release element shall override all other
subsequent signals.
24.2 Types of combination smoke and fire
damper
Combination smoke and fire dampers of various
types are available for specific purposes, as
follows:
They are available in a range of materials including metal, P.V.C, fabric and with or without thermal insulation.
24.2.1 Single blade
Single blade combination smoke and fire
The designer/contractor shall consider the
51
Flexible joint connections
Fig. 80 Rectangular, circular, flat oval alternative flanged, roll formed flange and spigot
connections
Effective length of the unsupported
material shall be
50 mm minimum – 250 mm maximum
Effective length of the unsupported
material shall be
50 mm minimum – 250 mm maximum
5.
1.
Flexible
material
Metal
2.
6.
3.
7.
4.
8.
Note The ends of the flexible material must be lapped then stitched, glued or stapled using manufacturers
recommended glue and industrial staples to form an airtight joint.
25.2.2 Flexible ducts – Fabric
Flexible ducts made from materials including
P.V.C/Polyester laminate, Aluminium/Polyester
laminate encapsulating high tensile steel wire
helix are a very flexible form of construction.
The length of flexible duct used should therefore be kept to a minimum, consistent with the
particular application.
following when selecting a particular type of
flexible duct including:
• Temperature range
• Fire rating
• Resistance to air flow
• Airtightness characteristics
• Length restrictions if applicable
• Support requirements
• Flexibility
• Insulation values
• System pressure.
Flexible ducts shall be fastened at each end
using a propriety band. Care should be taken not
to damage the flexible duct and to ensure that
the required airtightness of the system is
maintained.
Flexible ducts are also available in twin wall format where the inner liner is perforated to provide
acoustic properties or plain for thermal insulation.
25.3 Supports
Flexible ducts have a higher resistance factor than
conventional ductwork and should be supported
in such a way that excessive sagging and consequently kinking of the duct is avoided.
25.2 Flexible ducts – Metal
2 5 . 2 . 1 Flexible ducts made of coated steel,
stainless steel or aluminium are normally helically wound with a lock seam to form a corrugated duct capable of being bent without
deforming the circular section. Bending is done
by closing the corrugations in the throat and
slightly opening the corrugations at the back of
the bend. Some re-adjustment is possible but
small radius bends cannot be straightened without leaving some distortion of the corrugations.
Repeated bending is not recommended.
25.4 Test Holes
It is not practicable to make test holes or take test
readings in metal or fabric flexible ducts. Where
readings are required, the test holes should be
made in rigid ductwork.
26 FLEXIBLE JOINT CONNECTIONS
26.1 General properties
The material used for flexible joints must meet the
designers requirement for temperature, air pressure, fire resistance, vibration, noise breakout
when incorporated into a joint/connection and
shall comply with the standard of airtightness
specified for the ductwork system of which it
forms part (See Fig. 80 for typical connection
details).
The ducts shall be mechanically fastened at
each end and particular care shall be taken to
ensure that the required airtightness of the
system is maintained.
Fastenings should be as for rigid circular ducts
Section 13.3 and Table 9. Sealing should be as
Section 8.
26.2 Location
Flexible joints are typically used at building
52
expansion joints and fan inlet/outlets. Any others
required should be indicated on the design drawings. Care should be taken to maintain alignment
across joints/connections.
27.2 Metal spraying
Zinc or aluminium spraying shall be to BS EN
22063 (1994), Part 1.
27.3 Paints
2 7 . 3 . 1 Surface
preparation
and
paint
application
Surface preparation of the metal and paint
application shall be in accordance with the paint
manufacturer’s recommendations.
Joints/connections shall not be installed taught,
but under a reasonable amount of compression.
26.3 Length
Flexible joints shall be kept as short as practicable
above a minimum effective length of 50 mm. In no
case shall a flexible joint exceed 250 mm in length.
27.3.2 Making good welding damage
Galvanizing or other metallic zinc finish
damaged by welding shall be suitably cleaned
and painted with one coat of zinc-rich or
aluminium paint.
26.4 Connections to rectangular ducts
With flanged rectangular connections, the flexible
material shall be held in place with flat bar strips
of not less than 2 mm thick attached to the flanges
using suitable fixings. Where a proprietary brand
of lightweight material is used with sheet metal
fitted to either side consideration should be given
to the size of connection it is used on and how it
is fitted. The more heavy weight type of flexible
material may also be obtained formed into a channel section with corners fitted and stitched to give
a neat airtight joint. For spigot connections the
flexible material shall be held in place with flat
bar strips of not less than 2 mm thick.
27.3.3 Ducts made from pre-galvanized sheet
or coil
Ducts and profile sections made from pregalvanized sheet or coil will have no need for
paint or further protection where located inside
a building. This also applies to exposed cut
edges in accordance with criteria laid down by
British Steel PLC. See Appendix N Bibliography.
27.3.4 Ducts made from other types of mild
steel sheet
Where circumstances require ducts to be made
from mild steel sheet or coil other than the
foregoing, protective requirements shall be
specified by the designer.
26.5 Connections to circular ducts
With flanged circular connections the flexible
material shall be held in place with alternative flat
bar rings, flat bar clip rings or proprietary clip
bands with screw or toggle fittings. Where a proprietary brand of light weight flexible with metal
to either side is used, careful consideration must
be given to sealing when fitting to spirally-wound
ducts.
27.3.5 Untreated steelwork profiles
Any plain mill finish unprotected
such as rolled steel sections and/or
for flanging, stiffeners, supports and
must be treated.
26.6 Connections to oval ducts
Special consideration should be given to the construction but the type of joint applies as for
circular ducts except proprietary clip band with
screw or toggle fastening is not suitable on oval
ducts.
and sheet
mild steel
sheet used
duct walls
Treatment would be an appropriate primer such
as zinc rich, zinc chromate, red oxide or aluminium paint.
28 CONNECTIONS TO BUILDING
OPENINGS
28.1 Forming and finishing building openings are
not the responsibility of the ductwork contractor
and the notes that follow are for guidance purposes only.
27 PROTECTIVE FINISHES
Unless otherwise stated all ductwork will be
manufactured in pre-galvanised sheet steel,
aluminium or stainless steel as specified, with
prime coating where applicable (see 27.3.5). Any
additions to this would normally be the responsibility of others. Any special coating/paint finishes
to be provided by the ductwork contractor must be
advised by the designer.
2 8 . 1 . 1 Openings in brick, block or concrete
walls shall have inset frames to provide a suitable means of fixing grilles, louvres, masking
flanges or the flanged ends of ductwork.
The inset frames shall be constructed to maintain the structural integrity of the wall and
where applicable cavities shall be suitably lined.
27.1 Galvanizing after manufacture
Galvanizing after manufacture is not recommended for general use, as distortion of the duct or
fitting is probable, thus making if difficult to
achieve an airtight joint. Galvanizing after manufacture is, however, an acceptable protective finish
for circular pressed fittings and external ductwork
exposed to atmosphere.
28.1.2 Openings in dry lining partitions shall
have inset frames as in 28.1.1.
28.1.3 Openings in cladding walls and roofs
shall have flanged sleeves/frames to provide a
suitable means of fixing as in 28.1.1.
28.1.4 Horizontal and vertical openings that are
exposed to outside atmosphere shall be provided
with a suitable weathering finish at the external
face especially if profiled cladding is involved.
Where galvanizing after manufacture is specified,
it shall be to BS 729, see Appendix E. No paint
protection is required.
53
30 THERMAL INSULATION
2 8 . 1 . 5 Timber framed openings are not permitted in fire compartment walls.
30.1 The provision and application of thermal
insulation to ductwork is not normally the responsibility of the ductwork contractor.
28.2 Ductwork connections to building openings
shall have a flange of suitable profile to permit
practical fixing to the opening frame. In selecting
the profile, consideration shall be given to Table 2
in this specification relating to duct size and
rating. Gasket strip or sealer shall be applied
between the flange and building opening frame.
3 0 . 2 Where ductwork is required to be preinsulated, the specification should be agreed with
the designer.
30.3 Where the temperature of the air within the
duct is at any time low enough to promote condensation on the exterior surface of the duct and
cause moisture penetration through the thermal
insulation, vapour sealing may be called for, and
in this case the most important requirement is to
limit penetration of the seal.
29 INTERNAL DUCT LININGS
29.1 General
Where an acoustic or thermal lining to ductwork
is specified it should preferably be fitted at works.
Before duct manufacture it should be clarified that
specified external duct dimensions allow for the
lining thickness. Any form of lining should have
fire characteristics having minimum Class O rating and must be specified by the Designer for
material type, thickness, and application method.
The extent of any vapour sealing of ductwork
thermal insullation and the support method to be
used must be clearly specified in advance by the
designer.
29.2 Lining Application Considerations
Prior to the application of any lining the internal
duct surface must be thoroughly cleaned to
provide a dust free dry surface which may additionally be degreased.
3 0 . 4 For detailed information on the thermal
insulation of ductwork, reference should be made
to BS 5422:1990 which covers the specification
for thermal insulation materials on pipes, ductwork and equipment (in the temperature range
–40°C to +700°C) and BS 5970:1992 which is a
Code of practice for thermal insulation of
pipework and equipment (in the temperature
range –100°C to +870°C).
Securing the lining to the internal duct surface can
be achieved in several ways including applied
adhesive, self adhesive and physical methods such
as fasteners in conjunction with surface washers at
a specified square pitch.
Adjacent sections of lining should abut with minimal gap and integral or separate surface finish lap
to such joints and or gap filling proprietary
products being applied. This procedure is to obviate any particle migration.
31 KITCHEN VENTILATION
31.1 For detailed information reference should be
made to HVCA Publication, Guide to good
Practice
for
Kitchen
Ventilation
Systems
DW/171.
During application and any curing, consideration
should be given to ambient temperature and
humidity requirements.
32 FIRE RATED DUCTWORK
In all circumstances linings should be fitted to
material manufacturer’s recommended methods.
3 2 . 1 For information see Appendix D of this
specification.
29.3 Circular ducts
Lining circular ducts is impractical and is not recommended.
33 STANDARD COMPONENT
AND ABBREVIATIONS
29.4 Cleaning and maintenance
Designers should be aware of the possible porous/
fibrous surface nature of linings as they may present practical/hazardous problems in cleaning and
maintenance. Reference in this respect should be
made to the following HVCA Publications
DRAWINGS
3 3 . 1 The illustrations in this section not only
highlight, where applicable, geometric limitations
for the design and manufacture of ductwork components but also recommend standard drawing
representation, terminology and abbreviations for
both ductwork components and some of the more
commonly used ancillary/plant items.
i) DW/TM2 Guide to Good Practice, Internal
Cleanliness of New Ductwork Installations.
33.2 Designers and surveyors should note that
bills of quantities should provide a full description
ii) TR17 Guide to Good Practice, Cleanliness
of Ventilation Systems.
54
STANDARD COMPONENT DRAWINGS — RECTANGULAR
DRAWING
FIG
DETAILS
81
Straight Duct with slip joints for ducts up to
400 mm longest size
82
Straight Duct with stiffened slip joints
N.B. Depending upon duct size additional stiffeners
may be required
83
Straight Duct with integral or slide-on flanges
N.B. Additional stiffeners may be required
84
Straight Duct with RSA flanges
N.B. Additional stiffeners may be required
W
Mitred Throat Bend
For ducts up to 400 mm wide
85
Short Radius Bend
Applies to any angle and for ducts up to 400 mm
wide
W
86
Minimum throat radius = 100 mm
W
Medium Radius Bend (as illustrated)
Applies to any angle
87
Long Radius Bend
Similar but radius = W
Applies to any angle
Throat radius = W/2
A
B
C
Short Radius Bend with splitters
88
W
Minimum throat radius = 100 mm
Splitter Position
C
A
B
‘W’ - mm
Splitters
400–800
1
W/3
–
–
801–1600
2
W/4
W/2
–
1601–2000
3
W/8
W/3
W/2
Splitters not required in bend angles less than 45°
55
STANDARD COMPONENT DRAWINGS — RECTANGULAR
FIG
DRAWING
DETAILS
89
Square Bend with turning vanes
90
Radius Tee with internal splitters
91
Radiussed Twin Bend
92
93
94
Swept Branch
Square Tee with Turning Vanes
Breeches Piece
56
STANDARD COMPONENT DRAWINGS — RECTANGULAR
FIG
DRAWING
95
96
97
DETAILS
‘Y’ Piece
15° MAX.
Angled Offset
30° MAX.
Mitred Offset
98
Radiussed Offset
Minimum throat radius = 100 mm
22.5° MAX.
99
22.5° MAX.
100
22.5° MAX.
101
22.5° MAX.
Concentric Taper
22.5° max in either plane
Splitters are required for angles greater than 22.5°
and should bisect the angle between any side and
duct centreline
Eccentric Taper
22.5° max in either plane
Splitters are required for angles greater than 22.5°
and should bisect the angle between any side and
duct centreline
Offset Taper
Splitters are required for angles greater than 22.5°
and should bisect the angle between any side and
duct centreline
57
STANDARD COMPONENT DRAWINGS — RECTANGULAR
FIG
DRAWING
DETAILS
22.5° MAX
102
Rectangular – Round Transformation
22.5° MAX
103
Rectangular – Flat Oval Transformation
104
Square Branch
105
Angled Branch
W
106
Shoe Branch
A
45° MAX
45° MAX
A
W
107
108
A
Bell Mouth Branch
Bell Mouth
45° MAX
W
58
Branch duct
width (W)
Dimensions
(A)
mm
Up to 200
300
„
400
„
600
„
Over 600
mm
75
100
125
150
200
Branch duct
width (W)
Dimensions
(A)
mm
Up to 200
300
„
400
„
600
„
Over 600
mm
75
100
125
150
200
Branch duct
width (W)
Dimensions
(A)
mm
Up to 200
300
„
400
„
600
„
Over 600
mm
75
100
125
150
200
STANDARD COMPONENT DRAWINGS — RECTANGULAR
FIG
DETAILS
DRAWING
TJ
SMF
Telescopic Joint
Illustrated with SMF – self metal flange
109
110
111
SBD
Single Bladed Damper
NRD
Non-Return Damper
Multi-Leaf Damper
Can be spiggoted or flanged,
opposed or parallel blade
Alternative controls are:-
112
113
HD
Hand
MD
Motorised
PD
Pneumatic
BG
Blast Gate Damper
Fire/Smoke Dampers
2hr
2hr. Rating
With installation frame
114
4hr
4hr. Rating
SD
Smoke damper
59
STANDARD COMPONENT DRAWINGS — RECTANGULAR
FIG
DRAWING
DETAILS
Access Openings
AP
AP
Access Panel – Removable
AD
AD
Access Door – Hinged
IC
IC
115
Inspection Cover
IC
116
IC
Flexible Connection
117
Drop Cheeked Radiussed Twin Bend
118
119
Drop Cheek Bend
Air Flow Symbol
60
STANDARD COMPONENT DRAWINGS — RECTANGULAR
FIG
DRAWING
DETAILS
Air Terminal Plenums
120
Plenum with side connection
121
Plenum with top connection
122
Cover plate with connection
123
Special plenum with connection
124
Telescopic connection
in direction of air flow
THE ABOVE DETAILS ARE TYPICAL
PLENUMS
61
STANDARD COMPONENT DRAWINGS — CIRCULAR
FIG
DRAWING
DETAILS
Straight Duct
With male and female connectors
125
(MALE)
(FEMALE)
126
Straight Duct
With flange joint and slip joint
127
Pressed Bend
Applies to any angle, eg. 30°, 45°, 60°
Medium radius bend as illustrated.
Long radius similar but throat radius = D
D
THROAT RADIUS = D/2 AS STANDARD
Segmented Bend
90° four section minimum as illustrated
128
D
Other
60° =
45° =
30° =
Angles
3 sections
3 sections
2 sections
THROAT RADIUS = D/2 AS STANDARD
62
STANDARD COMPONENT DRAWINGS — CIRCULAR
FIG
DRAWING
DETAILS
Segmented Twin Bend
Radius = D/2 max
129
R
May also be fabricated from pressed bends
D
130
Pressed Equal Tee
131
Pressed Twin Bend
15° MAX.
Taper
Concentric 15° in either plane as illustrated.
Eccentric 30° included angle.
132
133
45° MAX.
Short Taper
63
STANDARD COMPONENT DRAWINGS — CIRCULAR
FIG
DRAWING
DETAILS
30° max
Offset
134
Square Branch
Off rectangular
135
D
Branch duct
dia (D)
136
Shoe Branch
Off rectangular
A
45°
A
45°
138
139
140
Conical Branch
Also acceptable with
full conical surface
D
137
END VIEW
Angle Branch
Square Branch
Shoe Branch
64
mm
Up to 200
300
„
400
„
600
„
Over 600
Dimensions
(A)
mm
75
100
125
150
200
Branch duct
dia (D)
Dimensions
(A)
mm
Up to 200
300
„
400
„
600
„
Over
600
mm
75
100
125
150
200
STANDARD COMPONENT DRAWINGS — CIRCULAR
FIG
DRAWING
DETAILS
141
Pressed Branch
142
Bell Mouth Branch
A
45°
END VIEW
143
Mitred Branch
144
Blank End
Multi-Leaf Damper
Can be spiggoted or flanged,
opposed or parallel blade.
Alternative controls are:-
145
HD
Hand
MD
Motorised
PD
Pneumatic
65
Branch duct
dia (D)
Dimensions
(A)
mm
Up to 200
300
„
400
„
600
„
Over 600
mm
75
100
125
150
200
STANDARD COMPONENT DRAWINGS — CIRCULAR
FIG
DRAWING
146
DETAILS
Single Bladed Damper
SBD
147
NRD
148
Non-Return Damper
Vertical application only
Iris Damper
ID
Fire/Smoke Dampers
2hr
149
2hr Rating
With installation frame
4hr
4hr Rating
SD
Smoke damper
150
Breeches Piece
30° TO 90°
66
STANDARD COMPONENT DRAWINGS — CIRCULAR
DRAWING
FIG
DETAILS
Access Openings
AP
Access panel – removable
AD
Access door – hinged
IC
Inspection cover
151
IC
2D
D/3
D/2
152
D/2
1.5D
Discharge Cowl
Inner cone optional
D
67
STANDARD COMPONENT DRAWINGS — FLAT OVAL
DRAWING
FIG
DETAILS
General Note:
In describing flat oval ductwork, the major axis is
referred to as the width (W) & the minor axis is
referred to as the depth (D).
For tie rod requirements see Tables 12 and 13
D
Straight Duct with connectors
W
153
WITH TIE ROD
D
Straight Duct with flange joint and slipjoint
W
154
155
D
W
Segmented bend (easy)
90° four section minimum as illustrated
Other
60° =
45° =
30° =
angles
3 sections
3 sections
2 sections
THROAT RADIUS = D/2
AS STANDARD
Segmented bend (hard)
90° four section minimum as illustrated
156
W
D
Other
60° =
45° =
30° =
angles
3 sections
3 sections
2 sections
THROAT RADIUS = W/2
30° MAX
Mitred Bend – Easy
D
157
W
68
STANDARD COMPONENT DRAWINGS — FLAT OVAL
DETAILS
DRAWING
FIG
30° MAX
Mitred Bend – Hard
W
158
D
159
W
22.5° MAX
Taper – Concentric
D
160
W
22.5° MAX
Taper – Eccentric
D
22.5° MAX
Flat Oval – Circular
Transformation piece
Can be concentric, eccentric or offset
W
161
DIA
D
22.5° MAX
22.5° MAX
W
162
Flat Oval – Rectangular
Transformation piece
Can be concentric, eccentric or offset
D
22.5° MAX
69
STANDARD COMPONENT DRAWINGS — FLAT OVAL
DRAWING
FIG
DETAILS
163
D
30° MAX
Offset - Easy
W
164
W
30° MAX
Offset - Hard
D
166
Square Branch as illustrated
NB! Shoe branch similar to Fig. 136 also acceptable
W
165
Branches
Note: For rectangular or circular branches off the flat
or circular part of the flat oval, see the appropriate
rectangular or circular Fig Nos pages 58, 64 and 65
D
BRANCH
DUCT
WIDTH
45°
A
Conical Branch
W
167
D
70
Branch duct
width
Dimensions
(A)
mm
Up to 200
„
300
„
400
„
600
Over 600
mm
75
100
125
150
200
STANDARD COMPONENT DRAWINGS — PLANT/EQUIPMENT/MISCELLANEOUS
FIG
DRAWING
DETAILS
168
Rectangular Attenuator
169
Circular Attenuator
170
Bend Attenuator
171
Heating Coil
172
Cooling Coil
173
Electric Heating Coil
174
Humidifier
175
Axial Fan
176
Non-standard Ductwork
Cross hatching (of any separate type) indicates by reference to
a key, any non DW/144 ductwork system. eg. internally lined,
fire rated, stainless steel, aluminium, pre-coated or other.
177
Flexible Ductwork
71
TABLE 16 — STANDARD ABBREVIATIONS
ABBREVIATION
FULL
AD
Access Door
AFF
Axial Flow Fan
AHU
Air Handling Unit
ALI
Aluminium
AP
Access Panel
ATT
Attenuator
ATU
Air Terminal Unit
BE
Blank End
BG
Blast Gate Damper
CC
Cooling Coil
CF
Centrifugal Fan
CTA
Cross Talk Attenuator
CVU
Constant Volume Unit
DP
Drain Point
EHC
Electric Heating Coil
FAI
Fresh Air Inlet
FA
From Above
FB
From Below
Flex/C
Flexible Connection
Flex/D
Flexible Duct
FC
False Ceiling
FCU
Fan Coil Unit
FD
Fire Damper
FFL
Finished Floor Level
FJ
Flanged Joint
FOB
Flat on Bottom
FOT
Flat on Top
FRP
Fire Retardent Polypropylene
GAM
Galvanised after Manufacture
GRP
Glass Reinforced Plastic
GSS
Galvanised Sheet Steel
HC
Heating Coil
HD
Hand controlled Damper
HH
Hand Hole
HL
High Level
IC
Inspection Cover
ID
Iris Damper
IU
Induction Unit
LL
Low Level
MD
Motor controlled Damper
MS
Mild Steel
NRD
Non Return Damper
72
TABLE 16 — STANDARD ABBREVIATIONS — CONTINUED
FULL
ABBREVIATION
NTS
Not to Scale
OBD
Opposed Blade Damper
OE
Open End
PBD
Parallel Blade Damper
PD
Pneumatic controlled Damper
PP
Polypropylene
PRD
Pressure Relief Damper
PVC
Polyvinyl Chloride
RFC
Rolled Form Channel
RSC
Rolled Steel Channel
RU
Roof Unit
SBD
Single Blade Damper
SD
Smoke Damper
SJ
Slip Joint
ST/ST
Stainless Steel
SSL
Structural Slab Level
TA
To Above
TB
To Below
TD
Top Down (In Direction of Flow)
TJ
Telescopic Joint
TP
Test Point
TV
Turning Vane
TU
Top Up (In Direction of Flow)
UOS
Unless Otherwise Stated
UPVC
Unplasticised Polyvinyl Chloride
US
Underside
VAV
Variable Air Volume
40 SMF
Self Metal Flange (With Size)
50 RSA
Rolled Steel Angle (With Size)
73
74
Part Eight—Appendices
APPENDIX A — AIR LEAKAGE FROM DUCTWORK
To
be
read
in
conjunction
with
DW/143
A
practical
guide
to
Ductwork
Leakage
Testing
CAUTION
As highlighted in both this document and DW/143, not enough emphasis can be placed on the fact that, except for high
pressure class C, the much tighter ductwork constructional standards brought about by the general acceptance of DW/142
have virtually negated the requirement for leakage-testing. It is essential to realise that except where it is mandatory this
document is not an endorsement of the routine testing of ducts but purely a guide to outline the procedures for conformity
with the air leakage limits in Table 1. When proper methods of assembly and sealing of ducts are used, a visual inspection
will ordinarily suffice for verification of a well engineered and acceptably airtight construction.
WHERE NOT MANDATORY, DUCT LEAKAGE TESTING IS GENERALLY AN UNJUSTIFIED AND
SUBSTANTIAL EXPENSE.
A.3 LEAKAGE FROM DUCTWORK
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.
A.1 INTRODUCTION
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 operating static air
pressure in the system. However, it is recognised
that the environment in which systems are
installed is not always conducive to achieving a
predictable level of quality in terms of system airleakage and it is therefore accepted that designers
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 re mandatory
testing).
The
effect
of
air
leakage
from
high
pressure/velocity ductwork is critical in terms of
system performance, energy consumption and the
risk of high frequency noise associated 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.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 maximum
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.
A.4 SYSTEM LEAKAGE LOSS
As there 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 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:
Class A
Class B
Class C
75
low pressure
medium pressure
high pressure
6%
3%
2%
A.5 SPECIFYING AIR LEAKAGE TESTING
for the classification for the section of the ductwork that is to be tested.
Respecting both the cost and programme implications associated with testing ducts for leakage, the
designer may, for example indicate that a particular system is tested as follows:
The tests shall be carried out as the work proceeds and prior to the application of thermal
insulation.
a)
b)
High pressure ducts – all tested.
Medium pressure ducts – 10% of the
ductwork shall be selected at random and
tested.
c) Low pressure – untested.
In the case where a random test is selected for
medium pressure ducts the following clause is
suggested for inclusion by the designer.
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.
The contractor shall provide
dence of the calculations used
allowable loss for the section
the client, or his agent, shall
the results of the test.
The designer shall select at random a maximum of 10% of the duct system to be tested for
air leakage. The duct shall be tested at the
pressure recommended in Table 17 of DW/144
documented evito arrive at the
to be tested and
witness and sign
Table 17 Air leakage rates
Maximum leakage of ductwork
Static
pressure
differential
1
Pa
Low-pressure
Class A
Medium-pressure
Class B
High-pressure
Class C
2
3
4
Litres per second per square metre of surface area
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
600
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: R e c o m m e n d e d ‘mean’ test pressures are highlighted in bold type with the
actual selection being left to the test operator.
76
conformity for the pressure class and air leakage
classification for the system under test.
A.6 SPECIAL CASES
There may be situations on a project where 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.
A.9 DESIGNER’S CALCULATIONS
The designer can calculate with reasonable
accuracy the predicted total loss from a system
by:
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
•
•
•
•
•
•
•
•
High pressure ducts
Medium pressure ducts
Low pressure ducts
Exposed extract systems
Ceiling void extract
systems
Secondary ducts from
VAV or fan coil units
Flexible ducts
Final connections and
branches to grilles and
diffusers
100% test
See A5
Untested
Untested
a)
Calculating the operating pressure in each
section of the system.
b)
Calculating the surface area of the ductwork in each corresponding pressure
section.
c)
Calculating the allowable loss at the operating pressure for each section of the system (see table 17 for allowable leakage
figures).
A.10 VARIABLE PRESSURES IN SYSTEMS
Untested
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.
Untested
Untested
Untested
A.8 TESTING OF PLANT ITEMS
For example, some large systems could well be
classified for leakage limits as follows:
Items of inline plant (eg. Figs. 168 to 175) will
not normally be included in an air leakage test.
The ductwork contractor may include such items
in the test if the equipment has a certificate of
Plant room risers
Main floor distribution
Low pressure outlets
77
Class C
Class B
Class A
78
100
200
300
400
500
600
700
800
900
1000
1200
1300
1400
1500
1600
1700
1800
1900
2000
Pressure difference in pascals
0.25
0.25
0
0.5
1.0
1.0
0.5
1.25
1.25
0.75
1.5
1.5
0.75
1.75
1.75
Fig. 178 Permitted leakage at various pressures
Leakage in litres per second per square metre duct surface area
Specimen of air leakage test sheet
*Test No. ......................................
General
Name
of job ..................................................................................................................................................
Building reference
..................................................................................................................
Part 1 – Physical details
a
Se ction of ductwork to be tested*......................... ....................................................................................
b
Su rface area of duct under test†..............................................................................................................
c
T est static pressure....................................................................................................................................
d
Leakage factor.............................................................................................................................................
e
M aximum permitted leakage (b x d)..........................................................................................litres/sec.
Part 2 – Test particulars
a
Du ct static pressure reading......................................................................................................................
b
Ty pe of flow measuring device................................................................................................................
c
R ange of measurement of flow measuring device....................................................................................
d
R eading of flow measuringdevice ...........................................................................................................
e
Interpreted air flow leakage rate..............................................................................................................
f
Duration of test (normally 15 minutes)....................................................................................................
Date
of test.......................
Carried out by
............................
Witnessed by.....................................
Length
Width and depth
or diameter
Peripheral
Area
metres
millimitres
millimitres
square metres
†TOTAL
79
APPENDIX B – IDENTIFICATION OF DUCTWORK
Note
The information given in this Appendix is for the
guidance of mechanical services contractors, consulting engineers, etc. The identification of ductwork does not form part of the work carried out by
the ductwork contractor unless required by the
designer in the job specification.
possible, where there is adequate natural or artificial light.
B.1 GENERAL
B.1.1 Introduction
With the increasing complexity of ventilation and
air conditioning systems, it is becoming more
important to ensure ready identification of ducts
for the purposes of commissioning, operation and
maintenance of systems. The purpose of these
recommendations is to lead towards the use and
standardisation of a system of identification for
ducts for the benefit of designers, contractors and
clients.
B.2.2 Identification symbols will be needed in
plant rooms and remote areas. Symbols should
occur frequently enough to avoid the need for ducts
to be traced back. Symbols should be placed at
any service and access points to the distribution
system, including points where the distribution
system has reduced to a single duct.
B.2.3 Colour coding
The choice of colours has been based on the need
to provide:
B.1.2 Scope
B.1.2.1 These recommendations deal with the
identification of ducts for ventilation, air conditioning and simple industrial exhaust systems.
They do not include piped gas systems such as
those dealt with in BS 1710 1984, nor ductwork
systems for industrial processes, although the
general considerations and intentions could be
extended with the agreement of the client to
cover such systems.
B.2.3.1 Strong contrasting colours which are
recognisable even though covered with dust.
B . 2 . 3 . 2 Contrast between the symbol colour
and the base colour of the duct. Usually the base
colour metallic grey of galvanized or aluminium
sheet or foil sheathing, or the white, pale grey,
or buff paint on the insulation is a neutral colour
against which the recommended symbol colours
will stand out.
B.1.2.2 The method is designed to identify the
air being conveyed, the direction of flow, the
destination of the air and/or the location or
nomenclature of the plant where the air was
treated. With small or simple plants, it may not
be strictly necessary to provide identification
because the function is apparent, but it is considered advisable to do so because this will
increase familiarity with the labelling system
and also because the nature and direction of air
flow may not always be apparent.
B . 2 . 4 The recommended colours are given in
Table 18. The colour coding indicates the type of
air being conveyed.
Table 18 Recommended duct identification colours
B.2 IDENTIFICATION
B.2.1 Location
To be effective the identification must be placed
where it can be easily seen and at positions where
identification will be required. To ensure that the
symbols are seen, the following points should be
considered.
B.2.1.1 The symbols should be on the surfaces
which face the positions of normal access to the
completed installation.
B.2.1.2 The symbols should not be hidden from
view by structural members, other ducts, plant,
or other services distribution systems.
B.2.1.3 The symbols should be placed, where
80
Type
Colour
BS 4800
1
2
3
Conditioned air
Red and
Blue
04 E 53
18 E 53
Warm air
Yellow
10 E 53
Fresh air
Green
14 E 53
Exhaust/extract/
recirculated air
Grey
00 A 09
Foul air
Brown
06 C 39
Dual duct system—
hot supply air
Red
04 E 53
Dual duct system—
cold supply air
Blue
18 E 53
of the plant. The plant itself must be clearly
numbered to correspond. Letters for Supply,
Flow, Extract, etc., should not be added because
identification will be clear from the colour symbol. Thus confusion between ‘S’ for Supply and
‘S’ for South will be avoided.
B.2.5 For conditioned air, two symbols (one red,
one blue) may be used, or a single symbol coloured
part red, part blue.
B.2.6 If a finer grading than that given in Table 18
is required, as for instance in a laboratory with two
separate contaminated air exhaust systems, it is
recommended that the type colour be used with,
say, a stripe of a second colour. Where the duct
contents constitute a hazard, a symbol as given in
BS 1710 1984 should be added to the type colour.
Table 19 Examples of further identification
symbols
Code
B.2.7 Direction of flow
B-.2.7.1 The form of symbol chosen indicates
direction. It is an equilateral triangle (see Fig.
179) with one apex pointing in the direction of
air flow. Where the boundaries of the duct are
not visible, two triangles should be arranged in
line ahead to indicate direction of flow.
B.2.7.2 The size of the symbol will depend on
the size of the duct and the viewing distance.
The recommended minimum size for normal
use is 150 mm length of side.
Information given
9 SW P2
9th Floor,
South-West Zone,
Plant Two
Comp 2 P2
Computer 2,
Plant Two
3 Lab 8 P4
3rd Floor,
Laboratory 8,
Plant Four
2 Op Th 2P1
2nd Floor,
Operating Theatre 2,
Plant One
Bay 5 N P5
Bay 5, North end,
Plant Five
Fig. 179 Example of duct identification
symbol
B.2.8.3 Where identification of the space is by
room number, this must be agreed with the user
who otherwise may have numbered the rooms
differently.
Some examples of further identification systems
are given in Table 19.
B.2.8.4 The letters and numbers should be in
either black or white, whichever gives the better
contrast. They should be marked on the colour
symbol or immediately adjacent to it. The size
of the figures will depend on how easily they can
be seen, but should not be less than 25 mm high.
Direction
of flow
B.2.9 Explanatory chart
An explanatory chart shall be included in the O
(Operating) and M (Maintenance) manual and
shall also be kept in the plant room or other convenient place. The chart should show and explain
the colour symbols used on the installation and
where appropriate the figure and letter codes used
for further identification.
B.2.8 Further identification
B.2.8.1 On small or simple installations where
there is one plant and one or two zones and
therefore little chance of confusing the ducts, it
will not be necessary to provide identification
other than the colour symbol. On large complex
installations with many zones, widely branched
distribution systems or several plants, further
identification is necessary. In this connection a
plant refers to the ductwork and equipment
associated with one particular fan.
B.3
METHOD
SYMBOLS
OF
APPLICATION
OF
B.3.1 Several methods are available for applying
the symbols, the main factor being that the symbol
is permanently affixed. Suitable methods are:
B.2.8.2 The further information to be given
will normally be the space served by the duct
and in some cases the associated plant. The
information should be given as briefly as possible using commonly accepted forms such as a
number indicating which floor of a building.
The plant identification should always be preceded by the letter ‘P’ to avoid confusion between the number of the floor and the number
B.3.1.1 Painting, using stencilled letters and
figures.
B.3.1.2 Self-adhesive plastics or transfers with
water soluble backing. (It is important to ensure
that the surface is smooth and clean and that the
adhesion will not deteriorate due to the surrounding atmosphere.)
B.3.1.3 Purpose-made plastics or metal labels.
81
APPENDIX C – GUIDANCE NOTES FOR THE TRANSPORT,
HANDLING AND STORAGE OF DUCTWORK
It is recommended that before a contract is
finalised, that consideration is given to the
subject of site access, material handling and storage as they have a strong influence on the cost
efficiency of the overall activity of ductwork
installation.
until they become an integral part of a completed
ductwork system. Whilst this may temporarily
detract from its intended appearance, this
deformation will not have any affect on the
functionality of the finally assembled system.
Installation of ductwork and associated plant
items will inevitably involve manual handling.
The responsibility of employers and employees to
assess the risk of personal injury during manual
handling operations is set out in the H.S.E. publication L23, Guidance on Manual Handling Regulations 1992.
C.1 Transport
Large capacity vehicles with high-sided open or
closed-top bodies are the most suitable for the
transport of ductwork.
Careful consideration should be given to the
unloading of transport on site as not all sites
benefit from the material handling and access
facilities that exist in a manufacturing workshop
such as cranes, fork-lifts or loading bays. Site
handling facilities along with vehicular access
restrictions may influence the type and size of
transport to be utilised.
C.3 Site storage
Adequate floor space must be provided within the
building for the site storage of ductwork. Such
storage shall make due allowance for the storage
of ductwork in stacks such that access between
them is of sufficient width to permit the removal
of items without interference to adjoining stacks.
Ductwork components should be positioned so as
to avoid crushing. Ductwork of small panel size
may be stored horizontally; however care should
be exercised to ensure that stack sizes are limited
to within the structural strength of the duct sections to prevent distortion of the lower sections
within the stack.
Lengths of ductwork should be positioned so as to
avoid crushing. Lengths with projections, such as
branches and bends, flanges, girths, damper quadrants should be loaded so as to avoid damage to
adjacent duct panels. In some cases, particularly
on contracts calling for repetitive sizes, the use of
timber jigs and spacers may be justified.
Where reduced bulk and greater protection are
major factors, such as consignments for export,
transporting ductwork in ‘L’ shape sections may
justify the increased site assembly costs.
C.4 Internal cleanliness of new ductwork
The site storage of ductwork introduces the
important
consideration
of
maintaining
the
internal cleanliness of the ductwork. Reference
should be made to HVCA document:-
C.2 Handling
To minimise the risk of damage, duct sections
should be clearly identified and deliveries to site
should be closely linked to the installation programme, so as to avoid accumulation of unfixed
ductwork and minimise double handling. It is
important to recognise that ductwork panels,
joints and corners are susceptible to damage and
care must be taken when handling such material
through a site.
•
DW/TM2 Guide to Good Practice – Internal
Cleanliness of New Ductwork Installations.
If the above conditions can not be satisfied consideration should be given by the designer to
amending the specification to include for “Post
Installation Cleaning” as covered by the HVCA
document:-
• TR17
Guide to Good Practice – Cleanliness of
Ventilation Systems.
During handling, individual items of ductwork
may be liable to slight cross sectional deformation
82
APPENDIX D – DUCTWORK SYSTEMS AND FIRE HAZARDS
Method 3 – Protection using Fire Resisting
Ductwork
The ductwork itself forms a protected shaft. The
fire resistance may be achieved by the ductwork
material itself or through the application of a protective material provided that the ductwork has
been tested and/or assessed to BS476 Part 24 with
a fire resistance, when tested from either side that
should not be less than the fire resistance required
for the elements of construction in the area
through which it passes. It should also be noted
that the fire resisting ductwork must be supported
with suitably sized and designed hangers, which
reflect the reduction in tensile strength of steel in
a fire condition i.e:
D . 1 Fire and smoke containment/hazards are
factors which influence the design and installation
of ductwork systems.
Information concerning fire protection systems is
laid down in BS 5588, Fire Precautions in the
design and construction of Building Part 9 (1989)
Code of Practice for Ventilation and Air Conditioning Ductwork and tested in accordance with
BS 476 Part 20 (1987) and BS 476 Part 22 (1987)
for Fire and Smoke Dampers and British Standard
476 Part 24 (1987) – ISO 6944 – (1985) for Fire
Rated Ductwork.
D.2 Building Regulations in the United Kingdom
require that new buildings be divided into fire
compartments in order that the spread of smoke
and fire in the building is inhibited, and to stop the
spread of smoke and fire from one compartment
to another, for given periods of time as specified
by the Building Regulations 1991 (Approved
Document B).
Fire resisting ductwork rated at 60 minutes
(945°C), reduces the tensile strength from 430
N/mm2 to 15 N/mm2.
Fire resisting ductwork rated at 120 minutes
(1,049°C) tensile strength reduced to 10 N/mn 2 .
D.2.1 There are three methods of fire protection,
related to ductwork systems as given in BS 5588
Part 9 (1989).
Fire resisting ductwork rated at 240 minutes
(1,153°C) tensile strength reduced to 6 N/mm2.
Where the fire resisting ductwork passes through
a fire compartment wall or floor, a penetration
seal must be provided which has been tested
and/or assessed with the ductwork to BS476 Part
24, to the same fire rating as the compartment
wall through which the fire resisting ductwork
passes. It should also be noted that where the fire
resisting ductwork passes through the fire compartment wall or floor, the ductwork itself must be
stiffened to prevent deformation of the duct in a
fire to:
Method 1 – Protection using Fire Dampers
The fire is isolated in the compartment of origin
by the automatic or manual actuation of closures
within the system. Fire dampers should, therefore,
be sited at the point of penetration of a
compartment wall or floor, or at the point of
penetration of the enclosure of a protected escape
route.
Fire dampers should be framed in such a way as to
allow for thermal expansion in the event of fire,
and the design must provide for the protection of
any packing material included.
a)
maintain the cross-sectional area of the duct
b) ensure that the fire rated penetration seal
around the duct is not compromised.
Standard types of fire dampers and frames are
described in Section 22 of this specification.
D.2.2 – Main areas within building where
Ductwork should be fire protected
The following notes are for guidance only, and it
should be noted that authority rests with the
Building Control Officer and/or the Fire Officer
responsible for the building. Reference on the
folowing systems should also be made to the current Building Regulations.
For further information refer to the impending
HVCA publication DW/TM3, ‘Guide to Good
Practice for the Design for the Installation of Fire
and Smoke Dampers’.
Method 2 – Protection using Fire Resisting
Enclosures
Where a building services shaft is provided
through which the ventilation ductwork passes
and if the shaft is constructed to the highest standard of fire resistance of the structure which it
penetrates, it forms a compartment known as a
protected shaft. This allows a complicated multiplicity of services to be transferred together
through a shaft transversing a number of compartments and reaching remote parts of the building,
without requiring further internal divisions along
its length. The provision of fire dampers is then
required only at points where the ventilation duct
leaves the confines of the protected shaft.
However, if there is only one ventilation duct and
there are no other services within the protected
shaft, between the fire compartment and the outside of the building, no fire dampers will be
required.
a.
Smoke Extract Systems:
If the ductwork incorporated in a smoke
extract system is wholly contained within the
fire compartment, it must be capable of resisting the anticipated temperatures generated
through the development of a fire. BS 476
Part 24 also requires ductwork, which is
intended as a smoke extract, must retain at
least 75% of its cross-sectional area within the
fire compartment. If the ductwork penetrates a
fire resisting barrier, it must also be capable of
providing the same period of fire resistance.
b.
Escape Routes covering Stairways, Lobbies and Corridors
All escape routes must be designed so that the
building occupants can evacuate the building
83
safely in the case of fire. Ductwork which
passes through a protected escape route must
have a fire resistance at least equal to the fire
compartment through which the ductwork
passes, either by the use of fire dampers or
fire resisting ductwork.
c.
compartment). Basements with natural ventilation should have permanent openings, not
less than 2.5% of the floor area and
be arranged to provide a through draft with
separate fire ducts for each compartment.
f.
Non Domestic Kitchen Extract Systems
Where there is no immediate discharge to
atmosphere, i.e. the ductwork passes to
atmosphere via another fire compartment, fire
resistant ductwork must be used. Kitchen
extract ductwork presents a particular hazard
as combustible deposits such as grease ‘are
likely to accumulate on internal surfaces,
therefore, all internal surfaces of the ductwork
must be smooth. A fire in an adjacent compartment, through which the ductwork passes,
could lead to ignition of the grease deposits,
which may continue through the ductwork
system, possibly prejudicing the safety of the
kitchen occupants. For this reason consideration must be given to the stability, integrity
and insulation performance of the kitchen
extract duct which should be specifically tested
to BS 476 Part 24 for a kitchen extract rating.
• Access doors for cleaning must be provided at distances not exceeding 3 metres.
• Fire dampers must not be used.
• Use of volume control dampers and tuming vanes are not recommended.
g.
Hazardous Areas
There are other areas within the building
where the Building Control Officer or the Fire
Officer could state a requirement for fire
resisting ductwork, eg. areas of high risk,
Boiler
Houses,
Plantrooms,
Transformer
Rooms etc.
D.2.3 Cautionary note to all Ductwork
Designers/ Manufacturers:
Ductwork constructed to DW/144 Standard has
no tested fire resistance. General purpose ventilation/air conditioning ductwork and its ancillary
items do not have a fire rating and cannot be either
utilised as or converted into a fire rated ductwork
system unless the construction materials of the
whole system including supports and penetration
seals are proven by test and assessment in accordance with BS 476 Part 24.
In the case where galvanised sheet steel ductwork
is clad by the application of a protective material,
the ductwork construction must be as type tested
and comply with the protective material manufacturers recommendations, eg. gauge of ductwork,
frequency of stiffeners and non-use of low melting point fasteners or rivets. Sealants, gaskets and
flexible joints should be as tested and certificated
in accordance with BS 476 Part 24 and comply
with the manufacturers recommendations.
Careful consideration must also be given to the
maximum certificated size tested to BS 476 Part
24 and the manufacturers recommendations
should always be followed.
Further information on kitchen extract systems
will be found in the HVCA publication DW/171
Specification for Kitchen Ventilation Systems.
d.
Enclosed Car Parks – which are
mechanically ventilated
Car Parks must have separate and independent extract systems, because of the polluted
nature of the extract air. Due to the fire risk
associated with car parks, these systems
should be treated as smoke extract systems
and therefore maintain a minimum of 75%
cross-sectional area under fire conditions in
accordance with BS 476 Part 24. Fire dampers
must not be installed in extract ductwork serving car parks.
e.
Basements – Ductwork from Basements
must be Fire Rated
If basements are compartmented, each separate compartment must have a separate outlet
and have access to ventilation without having
to gain access (i.e. open a door to another
Pressurisation Systems
Pressurisation is a method of restricting the
penetration of smoke into certain critical areas
of a building by maintaining the air at higher
pressures than those in adjacent areas. It
applies particularly to protect stairways, lobbies, corridors and fire fighting shafts serving
deep basements as smoke penetration to these
areas would inhibit escape.
As the air supply creating the pressurisation
must be maintained for the duration of a fire,
fire dampers cannot be used within the ductwork to prevent the spread of fire. Any ductwork penetrating fire resisting barriers must
be capable of providing the same period of
fire resistance.
This appendix incorporates information given in the A.S.F.P publication ‘Fire Rated and Smoke Outlet
Ductwork: An Industry Guide to Design and Installation’ available from Association for Specialist Fire
Protection, Association House, 235 Ash Road, Aldershot, Hampshire GU12 4DD (Telephone: 01252 21322
Fax: 01252 333901)
84
APPENDIX E – HOT DIP GALVANIZING AFTER MANUFACTURE
E.1 General
E.1.1 For Hot Dip galvanizing after the fabrication
of any article it is necessary to appreciate the
nature of the process, including the surface preparation of the object to be treated and the precautions
to be taken in design, fabrication and handling.
Table 20 Ductwork galvanized after
manufacture – rectangular
E.1.2 Hot Dip galvanizing involves dipping the
object into a bath of molten zinc (at a temperature
of between 445° and 465° C), and it is necessary
for the zinc to cover the whole of the surface
leaving no gaps in the coating.
E.2 Design and fabrication
E.2.1 Rectangular ductwork must be fabricated
using all welded construction techniques with vented flanges and stiffening frames (see E.2.3) as
mechanical fixing and lock-forming techniques are
not compatible with the galvanising process. In the
course of dipping into the molten zinc bath,
unsightly panel distortion will occur due to the
relief of inherent stress in the steel sheet or of any
stresses that may have been built into the item during fabrication, or indeed of any stresses introduced
during the handling, loading or unloading of the
item. Table 20 indicates the minimum requirements
for the construction of rectangular ductwork.
mm
10
16
20
25
Fig.18
stiffener
rating
*
Maximum
spacing
for joints/
stiffeners
1
2
3
4
5
mm
mm
mm
mm
mm
400
1.2
J3
S2
3000
1000
1.6
J4
S3
1250
1600
1.6
J5
S4
800
2000
1.6
J6
S5
800
E.4 Handling and storage after galvanizing
E.4.1 While a galvanized surface will not develop
rust in the ordinary sense as long as the zinc coating
is undamaged, zinc is subject to what is known as
‘wet storage stain,’ which is a white powdery
deposit on the zinc surface. Wet storage stain can
arise from the stacking of articles when wet, acid
vapours, the effect of salt spray, the reaction of
rain with flux residues, etc.
The damage to the zinc coating is negligible in
most cases. When the deposits are heavy, these
should be removed by brushing with a stiff bristle
or wire brush.
E.2.4 Vent holes should be of sizes as follows:
mm
Up to 25
50 to 100
100 to 150
Over 150
Fig. 10
joint
rating
*
ever, the pickling process does not generally
remove grease, oil or oil-based paint, and such substances should be removed by the fabricator by the
use of suitable solvents before the object to be treated is delivered to the galvanizing works. Any surface rust that develops on the object between
the time of treatment by the fabricator and
delivery to the galvanizing works is not important,
as this is cleaned off by the acid pickling process.
E.2.3 Any sealed hollow section or cavity must
be adequately vented in order to obviate any possibility of explosion. Holes of sufficient size (See
E.2.4) in vertical members must be provided diagonally opposite each other, top and bottom of the
member.
Minimum
diameter of
vent end
drainage holes
Recommended
sheet
thickness
*This refers to material size only – see E.2.1
E.2.2 It is essential to have a free flow of the
molten zinc over the object to be galvanized, together with quick and complete drainage of the
molten metal. Because of the high temperature
involved, the object to be galvanized should be as
rigid as possible, either by the use of sufficiently
heavy sheet or by stiffening or bracing, or both.
Size of
hollow
section
(dia. or side)
Maximum
duct size
(longer
side)
E.4.2 Galvanized articles should therefore not be
stacked or loaded when wet; they should preferably
be transported under cover or shipped in dry, well
ventilated conditions, inserting spacers (but not
resinous wood) between the galvanized articles.
E . 4 . 3 When stored on site or elsewhere, care
should be taken to avoid resting the galvanized
article on cinders or clinker, as the acid content of
these substances will attack the zinc surface.
E.2.5
Stiffeners should desirably have their
corners cropped so as to allow a free flow of zinc.
Stiffeners should be rolled steel angle, uncoated.
E.5 Subsequent finishing
E.5.1 Paint finishing subsequent to galvanizing is
sometimes required either for additional protection or for decorative reasons. Galvanised surfaces require chemical pretreatment prior to painting. Examples of such a treatment are T-Wash and
Etch Primer Types. Advice should be sought from
the paint manufacturer.
E.3 Surface preparation before galvanizing
E.3.1 The steel surface to be galvanized must be
chemically clean before dipping to ensure a continuous coating. This is mainly achieved at the galvanizer’s works by pickling in an acid bath and fluxing before the article goes into the zinc bath. How-
This Appendix incorporates information given in publications available from the
Galvanizers’ Association, 6 Wrens Court, 56 Victoria Road, Sutton Coldfield, West Midlands B72 1SY
85
APPENDIX F – STAINLESS STEEL FOR DUCTWORK
F.1 General
F.1.1 Stainless steel is not a single specific material: There is a large family of stainless steels with
varying compositions to suit specific applications,
but all contain at least 11% of chromium as an
alloying addition.
usually adjusted by the manufacturer to balance
forming response, weldability and corrosion
resistance. It is readily welded in thin sheet form
and, since it does not form a hardened weld
HAZ, no post-weld heat treatment is required. It
is widely used for automotive exhaust system
parts and is suitable for a range of ducting and
structural applications in mildly corrosive
applications.
F.1.2 Modern stainless steels have a combination
of good formability and weldability, and can be
supplied with a variety of surface finishes (see
F.4.1 below) They have been developed to cover a
wide range of structural uses where high resistance to corrosion and low maintenance costs are
demanded.
F.2.2.2 17% chromium ferritic steel, 430S17,
New Designation 1.4016, x6Cr17.
Forming and general characteristics are similar
to the 409 grade, but the higher chromium level
confers better general corrosion resistance.
F.1.3 Ductwork applications for which stainless
steels are particularly suited include those where a
high integrity inert material is essential; where a
high degree of hygiene is required; in the chemical industries where toxic or hazardous materials
may be contained; in nuclear and marine applications (e.g. on offshore platforms). Stainless steels
also find application in exposed ductwork where
their finish can be used to aesthetic advantage.
F.2.2.3 18% chromium, 9% nickel austenitic
stainless steels.
A widely used grade is 304S15, New Designation 1.4301, x5CrNi18-10. There are compositional variants within this family, designed to
give specific formability and welding characteristics. All are weldable and have good general
corrosion resistance to normal and mildly corrosive atmospheres. They are ductile and
formable, but forming loads are higher than for
mild steels and suitable, robust equipment is
required.
F.2 Grades of stainless steel
F.2.1 The grades of stainless steel most commonly used for ductwork applications are among those
covered currently by BS 1449, Part 2. However, a
European Standard, will supersede this British
Standard. New designations of the most common
steel grades are given in Table 21.
F.2.2.4
17% chromium, 11% nickel, 2%
molybdenum austenitic steel, a widely used
grade of this type is 316S31, New Designation
1.4401, x5CrNiMo17-11-2.
In some cases there are minor differences in
chemical composition between the BS and EN
grades.
This steel has a significantly higher corrosion
resistance than the standard 18% chromium, 9%
nickel steels and is suitable for use in more
aggressive environments such as are met in
ductwork in process plants. However, more
highly alloyed stainless steels with better corrosion resistance are also available and the advice
concerning
aggressive
environments
given
under section F.2.1 above should be noted.
Before a grade is specified, the nature of the
interior and exterior environments of the ductwork system should be taken into account. The
steels described below cover most normal applications. However, advice on specific corrosion
risks should be taken if the ductwork is to be
installed in a chemically contaminated atmosphere, or is to be used to transport contaminated
air, particularly if there is a risk of internal condensation. More highly alloyed grades of stainless
steel with enhanced corrosion resistance are available if required.
F.3 Availability
Stainless steel is supplied in a wide range of thicknesses, from 0.4 mm for cold-rolled sheet and
coil, and from 0.075 mm for precision rolled strip.
It is supplied in slit widths as specified by the customer, up to a maximum width of 2030 mm,
depending on thickness.
The commonly used steels divide into two main
families; the lower alloy ferritic 11-18% chromium stainless steels are magnetic. The austenitic,
18% chromium, 9% nickel steels have generally
better corrosion resistance and are non- or only
slightly magnetic.
Material compatability of sheet, section and fixings is not always assured in practice due to commercial availability.
F.2.2 The more commonly used stainless steels
and their characteristics are described below.
F.4 Surface finishes
F.4.1 Stainless steel is available in a wide selection of finishes, varying from fine matt to mirror
polished, as defined in BS 1449: Part 2: and in
EN10088: Part 2.
F.2.2.1 11.5% chromium ferritic steel with a
titanium addition, 409S19, New designation
1.4512, X2CrTi12.
This, and related grades, are among the leanest
alloyed of the stainless steels. Forming characteristics are similar to those of mild steel, so it
can be worked using conventional practices.
The composition and processing of the steel is
Mill finishes
Type 2D
Cold finished softened and
descaled. A uniform matt finish.
86
Type 2B
Type 2A/2R
essary, however, depending on the type of stainless steel being used.
Cold rolled, softened, descaled
and lightly worked with polished
rolls. A smooth finish brighter
than 2D.
F.6.3 As a general rule, the 400 series of stainless
steels can be formed using normal mild steel settings. The 300 series, however, because of the
higher yield point and the greater rate of work
hardening, will require higher working pressures.
Bright annealed. A cold finished
reflective appearance retained
through annealing.
F.6.4 Ductwork contractors who have experience
of the use of stainless steel report difficulty in
forming Pittsburgh and button punch snap lock
seams. As regards cross joints, socket and spigot
joints are recommended, and one or two of the
slide-on flanges are suitable. In view of the foregoing, it is recommended that trials be carried out
before starting on production.
Polished finishes
Type 4/2J
Dull polished. A lustrous unidirectional finish produced by
fine grinding, generally with
abrasives of 150 grit size. It has
little
specular
reflectivity.
Further dull polishing after fabrication will diminish the effects
on appearance of welds or accidental damage by blending them
into the surrounding metal.
Type 5/2K
Type 8/2P
F.7 Rectangular ducts
The constructional requirements for rectangular
stainless steel ducts are the same as for galvanized
mild steel.
Dull
polished
with
specific
requirements, to achieve a fine,
clean cut surface finish with
good corrosion resistance.
F.8 Circular ducts
The constructional requirements for circular stainless steel ducts are the same as for galvanized
mild steel.
Mirror polished. A bright, nondirectional reflective finish with
a high degree of image clarity.
F.9 Stiffening
Wherever possible, the material used for stiffening should be of the same grade of stainless steel
as used for the construction of the ducts, or should
be made equally corrosion resistant to suit the
environment in which the ductwork is situated.
F.4.2 Where other finishes are required, such as
for aesthetic purposes, a range of patterned or textured (2F,2M) finishes is available. Colour may be
applied in the form of paint or lacquer, or the
material may be supplied pre-coloured as by the
‘INCO’ process or by mill application of polymer
coatings.
F.10 Fixings and fastenings
The types of fastening and the maximum spacings
specified in Table 5 (rectangular) and Table 9 (circular) also apply to stainless steel ductwork.
F.5 Surface protection
F.5.1 No surface protection is required for stainless ductwork used indoors or outdoors, provided
the correct quality is specified. This is because the
naturally occurring chromium-rich oxide film
which is present on the surface of the metal, if
damaged, reforms immediately by reaction
between the steel and the atmospheric or other
source of oxygen.
Fixings and fastenings should be of the appropriate grade of stainless steel as used in the construction of the ductwork, or should be made
equally resistant to corrosion in relation to the
environment in which the ductwork is situated.
The type of stainless steel fastening used should
conform to the appropriate specification BS 6105:
1981.
F.11 Welding
All the modern welding processes may be used to
weld stainless steel but carburising operations
such as oxy-acetylene and carbon arc welding are
not suitable. The Tungsten inert gas (TIG) and resistance welding techniques are most likely to be
used for thin gauge materials. Attention is drawn to
BS 4872: Part 1 1982, (welder qualification) and
BS 7475: 1991 (welding processes).
F.5.2 If a mixture of metals is used, such as mild
steel supports for stainless steel ductwork, the surface of the mild steel must be adequately protected
from the galvanic corrosion that might result from
the intimate contact between the two types of
metal. (The appropriate protective finish should
be employed. See 27.3.5)
F.6 Construction
F.6.1 Sheet thicknesses for stainless steel ductwork should be the same as for galvanized steel
(see Tables 2, 3 and 4). Provided the correct grade
of stainless steel has been selected, there is no
requirement for a corrosion allowance with stainless steels and the gauge can be selected on structural considerations only.
Selection of the correct welding electrodes and
filler rods is important, particularly when
w e l d i n g d i s s i m i l a r m e t a l s , such as stainless
steels to non-stainless structural steels. Reference
for guidance should be made to BS 2901: Part 2:
1990 for rods and wires for gas shielded welding
and BS 2926:1984 for electrodes for Manual
Metal Arc. (MMA) welding.
F.6.2 The forming of rectangular and circular
ducts can be carried out by the use of conventional
press working and sheet metal forming machines.
Some alteration in working practices may be nec-
F.12 Avoidance of contamination
Attention is drawn to the risks of rust staining of
stainless steel surfaces resulting from contamination by non-stainless steel or iron debris.
87
F.13 Fire dampers
Stainless steel is an ideal material for use in the
construction of fire dampers, because of its high
resistance both to heat and corrosion. It is therefore most applicable where a fire authority specifies a requirement for corrosion resistance.
If particles such as filings of a non-stainless steel
or iron are expressed into contact with a stainless
steel, subsequent exposure to moisture will lead to
staining of the surface as these particles rust.
Whilst this staining often can be removed without
harm to the stainless steel surface, in aggressive
environments corrosion products around the rust
centre can create a risk of pitting of the stainless
steel. As a general rule, stainless steels should be
kept free from iron dust and debris contamination.
In particular, wire brushes must be made of stainless steel and shot, beads and abrasive media used
to clean surfaces must be ‘iron free’.
F.14 Sealants, gaskets and tapes
The sealing materials and methods set out in this
publication are also applicable to stainless steel
ductwork. However, any chloride-based material,
such as polyvinyl chloride (PVC), should be
avoided, as breakdown of such material at certain
elevated temperatures could lead to corrosion of
the stainless steel.
Contamination can arise from tools which have
been used previously for cutting non-stainless
steels without adequate cleaning and from abrasion on stillages and racks. It is good practice to
dedicate storage and bench areas for stainless
steels, with soft surfaces, e.g. wooden battens, to
mininise scratching of the surface and if practicable designate stainless only working areas.
F.15 General design considerations
It is the designer’s responsibility to indicate the
type of stainless steel most suitable for the conditions to which the ductwork is to be exposed. If
users and designers are in doubt as to which material is appropriate to a particular application, technical advice may be obtained from the source
noted below.
Table 21, showing the approximate correspondence between the chemical compositions of the commonly used stainless steel grades in BS 1449, Part 2: 1983, and the European Standard EN 10088-1,
List of Stainless Steels. (Part 1 gives the chemical compositions and identifications of the stainless
steels, it is for information. Part 2 of this standard describes the technical delivery conditions for
sheet/plate and strip for general purposes.)
Grade Designation,
Grade Name and
Fit on chemical composition
BS 1449 pt 2: 1983
Number in EN10088-1
between standards
409S19
x2CrTi12
1.4512
430S17
x6Cr17
1.4016
304S15,
x5CrNi18-10
1.4301
wider
close fit
wider
close fit
304S16
304S31
x2CrNi18-09
1.4307
wider
x2CrNi19-11
1.4306
wider
316S11
x2CrNiMo17-12-2
1.4404
close fit
316S31
x5CrNiMo17-12-2
1.4401
close fit
304S11
This appendix is based largely on information kindly
supplied by the
Avesta Sheffield Technical Advisory Centre, ASTAC,
P.O. Box 161,
Shepcote Lane,
Sheffield S9 1TR
Telephone: 0114 244 0060 Fax: 0114-242 0162
88
APPENDIX G - PRE-COATED STEEL
G.5 Ductwork construction from pre-coated steel
G.5.1 The type of pre-coated steel most suitable
for ductwork should be carefully considered,
mainly from the point of view of the fabrication
properties of the coating type. It is probable that a
plastisol coating will be found to be most suitable
for ductwork, as this type of coating will withstand
forming at normal ambient temperatures. It also
tolerates rougher handling during forming and
erection than the much thinner paint coating types.
G.1 Nature of the material
G.1.1 ‘Pre-coated’ steel is sheet, coil or strip to
which has been applied at the steel mills a coating
having a decorative or protective function, or both.
G.1.2 The basis metal to which the coatings are
applied are hot-dip galvanized or aluminium-zinc
coated sheet or coil, uncoated steel or electrogalvanized steel (e.g., Zintec).
G.2 Range of coatings available
G.2.1 A number of different types of coating, in
various thicknesses, are available – PVC
(‘Plastisol’ and ‘Organosol’); paint coatings of
several types, silicone enamels, etc.
G.5.2 Careful consideration should be given to
the constructional methods to be used for ductwork to be made from pre-coated steel. The
principle to be followed should be to make seams
and joints as unobtrusive as possible. Some of the
conventional methods of seaming may be used,
but a number of others are not suitable. Welding
with conventional equipment should not be
attempted. Mechanical fastenings should be
chosen with care having regard to appearance as
well as efficiency; and sealant should be applied
with these factors in mind. Stiffening should be
carefully considered in relation to appearance.
G.2.2 A wide range of colours and surface finishes are available, but there are minimum quantity requirements for some types of coating, finish
and colour. The characteristics of the particular
type of coating contemplated for a particular use
should be investigated in respect of formability,
fastness to light, chemical resistance and other
relevant properties.
G.2.3 The material can be supplied with one or
both sides treated, with the specified coating.
Standard ‘backing coat’ finishes are usually
applied to the reverse side unless otherwise
stated.
G.6 Handling, storage, transport and erection
G.6.1 Much more care than usual is required in
these respects, as the coatings are all to a greater
or lesser degree susceptible to mechanical damage.
For example, sheet should not be dragged off
the top of a pile but removed by ‘turning’ off the
stack.
G.3 Sizes available
G.3.1 Pre-coated steel is available in sheet or coil
form. The maximum available width can vary
according to the steel thickness required.
Availability varies according to type of substrate
and coating, so prospective purchasers should
query the sizes available for the specific type
required.
G.6.2 With sheet pre-coated on one side only, it
may be found desirable to stack face to face.
G.6.3 The flexibility of coatings of the types used
on pre-coated steel depends on temperature.
Therefore, manipulation should be carried out at
temperatures above 16°C (60°F) in order to minimise
the risk of the film cracking on roll forming, etc.
If the material has been stored outside at low
temperature, a warm-up period should be allowed
before manipulation of the sheet is undertaken.
G.4 Sources of supply
G.4.1 Pre-coated steel is widely available but it
should be noted that minimum order quantities
may apply.
The information on which this appendix is based
has been kindly supplied mainly by British Steel
plc. More detailed information may be obtained
from:
British Steel plc,
Product Development Centre,
Shotton Works,
Deeside,
Flints CH5 2NH
Telephone: Chester (01244) 812345
Fax: 01244 836134
89
APPENDIX H – ALUMINIUM DUCTWORK
H.5 Fastenings
H.5.1 The types of fastening and the maximum
spacings specified in Table 5 (rectangular) and
Table 9 (circular) apply to aluminium ductwork,
except that such fastenings shall be of aluminium,
stainless steel or monel metal.
H.1 Scope
This section applies only to rectangular and circular aluminium ductwork operating at low pressure, as defined in Tables 22 and 23.
If consideration is being given to either higher
pressures or flat oval ductwork then it would be
prudent to seek advice from manufacturers who
have the experience and capacity to manufacture
aluminium ductwork.
H.6 Welding
H.6.1 All the aluminium alloys can be welded by
MIG (Metal and Inert Gas) or TIG (Tungsten and
Inert Gas) methods, with argon as the shielding
gas. Helium or a mixture of helium and argon can
be used, but not C0 2 . Alloys in a work-hardened
temper are reduced to the annealed condition in
the heat affected zone; 6082-T6 is reduced approximately from the T6 to the T4 temper. Alloys 1200
and 3103 are easy to braze, as is 6082, but the latter
needs to be re-heat treated to regain its strength.
H.2 Suitable grades
H.2.1 Ductwork can be constructed from all the
commonly used aluminium alloys, the choice
depending on the purpose for which the ducts will
be used and the service environment.
H.2.2 The alloys 1200, 3103 and 5251 (as specified in BS.EN485, BS.EN515, BS.EN573) are
easy to form and to join, and have excellent resistance to atmospheric corrosion, with 5251 being
rather more resistant to marine atmospheres.
H.7 Protective finishes
H.7.1 No protective finishes are required for aluminium ductwork used indoors or outdoors in
normal atmospheric conditions. In moist atmospheres, particularly if they are contaminated by
industrial effluent or by salt from the sea, surfaces
not exposed to washing by rain will become
roughened and covered with a layer of white corrosion product. However, this has the effect of
sealing the surface against further attack, and the
mechanical properties of any but the thinnest of
materials will be only slightly affected.
H.2.3 These alloys can be supplied in various
tempers produced by different degrees of cold rolling, so that a range of strengths is available. In
choosing a temper, it is necessary to consider any
forming that will be done, as with the harder
tempers the forming of tight bends might cause
cracking. Where high strength is required, alloy
6082-T6 sheet can be used.
H.2.4 Aluminium coil is available in plain form
and pre-painted finish.
H.7.2 If surface protection is specified, any of the
normal organic finishes can be used, including the
laminated PVC films, although paints with heavy
metal pigments are not suitable. The use of prepainted strip in coil form provides a reliable quality finish and often proves more economical than
painting after assembly. Anodising provides an
excellent finish for aluminium, but this process
would have to be carried out after forming and
would therefore not usually be practicable for
ductwork, except perhaps for ducts formed from
extrusions.
H.3 Construction – rectangular ducts
H.3.1 Table 22 sets out the minimum constructional
and stiffening requirements for rectangular aluminium ducts and the permitted types of cross joint.
H.3.2 Sealant
The sealant requirements set out in this specification for galvanized steel rectangular ductwork
also apply to the longitudinal seams and cross
joints in aluminium ductwork.
H.4 Construction - circular ducts
H.4.1 Table 23 sets out the minimum constructional and stiffening requirements for circular
ducts made from aluminium, and the permitted
types of cross joint.
Table 22
H . 7 . 3 Mild steel section used in supporting
aluminium ductwork shall have a protective finish
(See 27.3.5).
Rectangular aluminium ducts – low pressure constructional requirements
Maximum
duct size
(longer side)
Minimum
sheet
thickness
Maximum spacing
between joints/stiffeners
Suitable
cross-joints
Plain
sheet
With cross
breaking or
pleating
5
mm
–
Minimum
aluminium
angle section
for cross-joints
and stiffeners
1
2
3
4
mm
400
mm
0.8
Figs
13, 14
mm
–
600
0.8
10 - 12, 15 - 17
1500
–
25 x 25 x 3
800
1.0
10 - 12, 15 - 17
1200
1500
30 x 30 x 4
1000
1.0
10 - 12, 15 - 17
800
1200
40 x 40 x 4
1500
1.2
10 - 12, 15 - 17
600
800
40 x 40 x 4
2250
1.2
10, 11
600
800
50 x 50 x 5
3000
1.6
10, 11
600
600
60 x 60 x 5
90
6
mm
–
Table 23 Circular aluminium ducts (spirally-wound and straight-seamed) – low
pressure constructional requirements
Straight-seamed duct
Spiral-wound duct
Normal
sheet
thickness
as for
galvanised
duct
Table
7
Cross
joints
figs
32 - 38
with LP
Limits
Minimum
stiffening
requirements
as for
galvanised
duct
Table
7
Normal
sheet
thickness
Cross
joints
figs
39 - 45
with LP
limits
as for
galvanised
duct
Table 8
Col. 2
Minimum
stiffening
requirements
Minimum aluminium
angle section for cross
joints and stiffeners
Duct
diameter
angle
mm
mm
as for
galvanised
duct
Table
8
800
25 x 25 x 3
1000
30 x 30 x 3
1500
40 x 40 x 4
Incorporates
information
provided
by
the
Aluminium Federation Ltd., Broadway House,
Calthorpe Road, Five Ways, Birmingham B15 1TN
(telephone: 0121-456 1103) from whom more
detailed information may be obtained.
APPENDIX J – EUROVENT
tate commercial exchanges between its
nations in the search for improved quality;
adoption of rules, directives and codes of
in the technical and economic spheres
member countries’.
J.1 General
Some explanation of the function, composition,
objectives and membership of EUROVENT is
given below.
member
and the
practice
in the
J.2 Membership
EUROVENT is an omnibus word standing for the
European Committee of the Construction of Air
Handling Equipment. The committee was formed
in 1959, and in 1977 its constituent members were
the relevant national associations in Austria,
Belgium, Denmark, Finland, France, German
Federal Republic, Italy, Netherlands, Norway,
Sweden, Switzerland and the United Kingdom.
J.4 EUROVENT publications
EUROVENT has published a number of documents in the air handling field, and these include
Document 2/2 covering the procedure for testing
for air leakage in ductwork, and provides for two
levels of permissible air leakage for low-pressure
air distribution systems. Document 2/3 covers the
standardisation of duct sizes.
J.3 Objectives
The objectives of EUROVENT are ‘to improve and
develop technical matters in the manufacture and
operation of air handling equipment; to improve
the professional status of its members and to facili-
J.5 Air leakage
The basis on which air leakage is calculated in
EUROVENT Document 2/2 has been adopted in
DW/143 A practical guide to Ductwork Leakage
Testing.
Information about EUROVENT may be obtained
from the HEVAC Association, Sterling House, 6
Furlong Road, Bourne End, Bucks SL8 5DG
(Telephone: 01628 531186 Fax: 01628 810423)
91
APPENDIX K – SUMMARY OF BS.EN10142: 1991 CONTINUOUSLY
HOT-DIP ZINC COATED MILD STEEL STRIP AND SHEET
FOR COLD FORMING
Normal spangle (N). This finish is obtained when
the zinc coating is left to solidify normally. Either
no spangle or zinc crystals of different sizes and
brightness appear depending on the galvanizing
conditions. The quality of the coating is not
affected by this.
NOTE. Normal spangle is the type normally supplied for a wide variety of applications.
Note – The extracts from BS.EN10142: 1991 have
been prepared by the HVCA and are included here
by courtesy of the British Standards Institution.
K.1 GENERAL
K.1.1 The BS 2989: 1975 and 1982 entitled
‘Continuously hot-dip zinc coated and iron-zinc
alloy coated steel: wide strip, sheet/plate and slit
wide strip’ summarised in DW/142 has been
superseded by BS.EN10142: 1991 entitled
‘Continuously hot-dip zinc coated mild steel strip
and sheet for cold forming’ (including amendment
A1:1995).
Minimized spangle (M). The surface has minimized spangles obtained by influencing the
solidification process in a specific way. The finish
may be specified if the normal spangle applicable
does
not
satisfy
the
surface
appearance
requirements.
K.1.2 British Standard BS.EN10142: 1991 sets
out requirements for the conventional galvanized
sheet and coil and for zinc-iron coated steel. (Both
these are included in DW/144 - see Section 7.)
K.5 SURFACE PROTECTION
K.5.1 General
Hot-dip zinc coated strip and sheet products
generally receive surface protection at the producer’s plant. The period of protection afforded
depends on the atmospheric conditions.
The type of steel normally used for ductwork is
DX51D and Z275.
K.2 STEEL GRADES
K.2.1
BS.EN10142:
1991
and
amendment
A1: 1995 lists the grades of steel set out in the next
column, among others:
Grade
DX51D + Z
DX52D + Z
DX53D + Z
DX54D + Z
K.5.2 Chemical Passivation
Chemical Passivation protects the surface against
humidity and reduces the risk of formation of
‘white rust’ during transportation and storage.
Local discolouring as a result of this treatment is
permissible and does not impair the quality.
Name of grade
Bending and
profiling
quality
Application 1
Forming quality
steel suitable for
manufacture of
the most profiles
and more difficult
bending operations
Drawing quality Forming quality
steel suitable for
simple drawing
operations and for
more difficult profiling operations
Deep drawing
Forming quality
quality
steel suitable for
deep drawing and
difficult forming
operations
Special deep
Forming quality
drawing quality steel suitable for
deep drawing and
difficult forming
operations where
a non-ageing steel
is required
K.5.3 Oiling
This treatment also reduces the risk of corrosion
of the surface. It shall be possible to remove the
oil layer with a suitable degreasing solvent which
does not adversely affect the zinc.
K.5.4 Chemical Passivation and Oiling
Agreement may be reached with the producer on
this combination of surface treatment if increased
protection against the formation of ‘white rust’ is
required.
K.5.5 Untreated
Hot-dip zinc coated strip and sheet products complying with the requirements of this standard are
only supplied without surface protection if
expressly desired by the purchaser on his own
responsibility. In this case, there is increased risk
of corrosion.
K.6 FORMING
K.6.1 The British Standard says that provided
that the profiling machine is set to avoid excessive
stretching in the product, it is possible to form
lock seams successfully with DX51D + Z sheet up
to a thickness of 1.5 mm and DX52D + Z sheet up
to 2 mm; and snap lock seams with DX51D + Z up
to 0.9 mm thick sheet and DX52D + Z sheet up to
2 mm.
K.3 COATING TYPES AND TOLERANCES
K.3.1 The types of zinc coating are set out in
Table 24. BS.EN10142: 1991 (reproduced at the
foot of this summary).
K.3.2 Whilst the coating thickness is not subject
to tolerances the substrate and consequently the
gauge thickness does have accepted tolerances
and these including sheet widths/lengths will be
found in BS.EN10143: 1991.
K.7 WELDING
K.7.1 Care should be taken to use proper
methods and procedures. The iron-zinc coating is
more suitable for resistance welding than the conventional zinc coating.
K.4 COATING FINISHES
K.4.1 BS.EN10142: 1991 and A1 1995 includes a
description of the various types of finish available:
92
Table 24 (Extract from BS.EN10142: 1991) Coating mass (weight)
Minimum coating mass
(including both sides
Suggested applications (see note 2)
Coating designation
Triple
spot test
Single
spot test
g/m2
g/m2
Z100
Z200
100
200
85
170
Light – for use where corrosion conditions are
not severe and/or where forming
operations preclude heavier coatings.
Z275
275
235
Standard
Z350
Z450
Z600
350
450
600
300
385
510
Heavy duty – for longer life relative to
Heavy duty – standard and light coatings.
100
180
85
150
Iron-zinc alloys – alloyed coatings of iron and zinc
for easy painting and particularly
resistance welding.
Zinc coatings (Z)
Zinc-Iron alloy coatings (ZF)
ZF100
ZF180
Note 1. The mass of zinc is not always equally distributed on both surfaces of the sheet. However, it can
normally be expected that not less than 40% of the specified minimum coating mass, as determined by
the single spot test, will be found on each surface.
Note 2. The suggested applications included in the right-hand column of the above table are those provided by
British Steel PLC.
APPENDIX L – ‘DESIGN NOTES FOR DUCTWORK’
(CIBSE Technical Memorandum No. 8)
Standard dimensions of circular, rectangular
and flat oval ducts.
L.1 At the time of publication (1983) this technical memorandum brought together information on
the design of ductwork systems.
Duct sizing methods, including velocity, equalfriction and static regain methods, and pressure
loss calculations, with an example calculation.
L.2 The contents had been drawn from the relevant sections of the CIBSE Guide and other
recognised references, and include additional
material on good design practice. The Notes make
frequent reference to DW/142, and an effort was
made to ensure consistency between the two publications. Whilst DW/142 has now been superceded by DW/144, the technical memorandum, has
not currently been up-dated but still contains relevant information that may be of use to a ductwork
designer/manufacturer. Whilst some of the information may now be superceded, TM8 includes
chapters on:
Heat loss from and gain to air in the duct; condensation, noise control and fire.
Commissioning and testing.
Overseas work.
Drawing symbols in current use.
L.3 The flow of heavily contaminated air in ducts
is not covered in detail in the Notes; nor are the
constructional aspects of ductwork, which are
dealt with in DW/144.
Pressure loss in ducts, including corrections for
duct surface type, air pressure, air density, temperature and altitude, and loss factors for fittings.
Equivalent diameters of rectangular and flat
oval ducts.
L.4. The Notes were completed by references, a
bibliography of over thirty titles and appendices
covering properties of air, ductwork support
loads, velocity pressure for air flow and conversion to SI units.
Technical Memorandum No. 8 was published by the Chartered Institution of Building Services Engineers,
Delta House, 222 Balham High Road, London SW12 9BS (Telephone: 0181 675 5211)
and whilst it is no longer available as a publication, it is still available in photo-copy form.
93
to be fitted as close as practically possible to the
‘obstruction’ and then at 10 metre intervals from that
point until the next internal ‘obstruction’ occurs.
APPENDIX M (Revised)
..................................................................
Guidance notes for
inspection, servicing and
cleaning access
openings
NOTE!
Kitchen extract systems, with panels at 3 metre
intervals, and vertical ductwork, with a panel at
the bottom and. top of each riser, are the only
exceptions to panels behg at 10 metre intervals.
b)
M.1
General
This appendix highhghts, in summary form, the access
considerations that should be made by the designer in
terms of inspection, servicing and cleaning. Having considered the scope and the design of the ductwork system
relative to the guidelines outlined below, the designer
should clearly indicate the access requirements that are to
be incorporated into the manufacture of a new ductwork
system.
M.2
The minimum requirements in (a) and (b), if specified by
the designer, negates the requirement for panels to be
provided at ‘changes of direction’ in the ductwork system
i.e. bends, branches, etc, and which do not constitute an
‘obstruction’ in terms of the definition referred to in (a)
previously.
Design Considerations
M.2.1 Inspection and servicing requirements are ‘set out in
Section 20 of this specification.
M.2.2 Care, protection and standards of cleanliness prior to
commissioning are set out in the HVCA publication
D W ; m 2 “Guide to Good Practice, Internal Cleanliness
of New Ductwork Installations” and the guide states
‘Where specific levels of cleanliness are required, ductwork shall be cleaned after installation by a specialist
cleaning contractor”.
M.2.3 It will be in the interests of the designer, both financially
and practically, to consider employing a specialist cleaning contractor at the outset of a contract to internally
clekn newly installed duckork prior to hand-over. This
approach would realise the following benefits:i) The actual number of cleaning access panels could
be determined to suit the method of cleaning to be
adopted.
ii) As a result of the involvement of a specialist clean.
ing contractor, clear,directionscould be given to the
ductwork contractor as to the size and location of
cleaning access panels that &e required to be fitted
during the manufacturing process.
iii) A specialist cleaning operation prior tocommissioning would enable the cleaning contra&
tor to venfy the practical access requirements for the
future cleaning operations associated with a regular
maintenance progapme.
iv) A specialist c l e e g operation prior to commissioning would allow the designer to omit from the specification the DW/TM2 requirements for factory
sealing, protection, wipe downs and capping-off.
.
.
. .
M.2.4 In the absence, at the ductwork manufacturing stage, of
any access panel size and location input from a specialist
cleaning contractor @en the designer may consider that
the following minimum requirements should be incorporated into a new ductwork system:a) -4naccess panel, of specified size, should be fitted
upstream of any internal ‘obstruction’ i.e. splitters,
airturns,blades, pods, coils, filters, etc. The panel is
The designer should identify any ‘obstruction’ or
item of equipment that requires an access panel on
both the upstream and downstream side duct connections with the upstream panel being used as the
start point measure for any subsequent panels as
referred to in (a) previously
M.2.5 Careful consideration must be given by the designer to
the practical problems associated with the manufacture
and fitting of suitably sized access panels on both small
cross section rectangular ducts and the circular faces of
. round and flat oval ducts and the ductwork manufacturer
should be instructed accordingly.
M.2.6 Cleaning requirements for both new and existing ventilation systems are set out in the HVCA publication W 1 7 ,
“Guide to Good Practice, Cleanliness of Ventilation
Systems”. The guide establishes standards for testing,
cleaning and verification and provides greater detail for
the designer’s consideration than the basic information
included in this appendix. The guide also includes the
statement; “The precise location, size and type of access
would be dependent on the type of ductwork cleaning,
inspection and testing methods to be adopted”.
I
NOTE!
In the absence of any indication by the designer
for cleaning requirements, only thc access panels
for inspection and servicing set out in Section 20
of this specification will be incorporated into a
new ductwork system.
M.2.7 Special consideration must be given by the designer to
the practical problems associated with gaining personnel
access to heavily congested ceiling areas and multi-layered ductwork systems. Such consideration would avoid
the possibility of access panels being incorporated into a
ductwork system at the manufacturing stage that were
later found to be inaccessible for either servicing or
cleaning activities.
M.3
Access to in-line equipment
M.3.1 This appendix only covers access/inspection through the
ductwork body adjacent to an item of in-line equipment
and not openings in the equipment itself.
Appendix M (Revised) June 2002
.
APPENDIX M – GUIDANCE NOTES FOR INSPECTION, SERVICING
AND CLEANING ACCESS OPENINGS
M.1 GENERAL
This appendix highlights, in summary form, the
access consideration that should be made by the
designer in terms of inspection, servicing and
cleaning. Having considered the scope and the
design of the ductwork system relative to the
guidelines outlined below the designer should
clearly indicate which level/s of access should be
incorporated into the manufacture of a new ductwork system (See Table 25 and Note 1 below it).
M.2 DESIGN CONSIDERATIONS
ii)
Clear directions could be given to the ductwork contractor as to the size and location
of cleaning access panels that are required to
be fitted during the manufacturing process.
iii)
The specialist cleaning operation prior to
commissioning would enable the cleaning
contractor to verify the practical access
requirements for the future cleaning operations associated with a regular maintenance
programme.
iv)
A specialist cleaning operation prior to commissioning would allow the designer to omit
from the specification the DW/TM2 requirements for factory sealing, protection, wipe
downs and capping-off.
v)
Specialist cleaning to the measurable standards defined in TR17 will allow an objective definition of cleanliness to be achieved.
M.2.1 Inspection and servicing requirements are
set out in Section 20 of this specification.
M.2.2 Cleaning requirements are set out in the
HVCA publication TR17 “Guide to Good
Practice, Cleanliness of Ventilation Systems” and
the guide states “The precise location, size and
type of access would be dependent on the type of
ductwork cleaning, inspection and testing methods to be adopted.”
Careful consideration must be given by the
designer to the practical problems associated with
the manufacture and fitting of suitably sized access
panels on small cross section ducts and the circular faces of round and flat oval ducts in particular.
Care, protection and standards of cleanliness prior
to commissioning are set out in the HVCA publication DW/TM2 “Guide to Good Practice,
Internal
Cleanliness
of
New
Ductwork
Installations” and the guide states “Where specific limits of cleanliness are required, ductwork
shall be cleaned after installation by a specialist
cleaning contractor.”
M.2.3 Special consideration must be given by the
designer to the practical problems associated with
gaining personnel access to heavily congested ceiling areas and multi-layered ductwork systems.
This approach would avoid the possibility of
access panels being incorporated into a ductwork
system at the manufacturing stage that were later
found in practice to be inaccessible for either servicing or cleaning activities.
It will be in the interests of the designer, both
financially and practically, to consider employing
a specialist cleaning contractor at the outset of a
contract to internally clean newly installed ductwork prior to handover. This approach would
realise the following benefits:-
M.3 ACCESS TO IN-LINE EQUIPMENT
The actual number of cleaning access panels
could be determined to suit the method of
cleaning to be adopted (This may be less
than the maximum requirements listed
under Level 3 of Table 25).
i)
This appendix only covers access/inspection
through the ductwork body adjacent to an item of
in-line equipment and not openings in the equipment itself.
Table 25 Access requirements for inspection, servicing and cleaning
HVCA PUBLICATION REFERENCE
Adjacent
in-line
items/equipment
Guide to Good Practice
Cleanliness of Ventilation Systems
DW/144
Inspection/Servicing
Section ref
20.1.1
Control Dampers
Fire Dampers
Heating/Cooling Coils
Attenuators (rectangular)
Attenuators (circular)
Filter Sections
Air Turn Vanes
Changes of Direction
In-Duct Fans/Devices
Notes
Level 2
Level 3
Cleaning Survey/Inspection Panels
(minimum size subject to duct size)
Cleaning
Access Panels
Level 1
One (inspection)
One (servicing)
One (inspection)
None required
None required
One (inspection)
None required
None required
One (inspection)
One 300mm x
One 300mm x
One 300mm x
One 300mm x
One 300mm x
None required
None required
None required
None required
20.3
20.2.1.1
20.2.1.3
20.2.1.2
20.2.1.3
200mm
200mm
200mm (upstream)
200mm (downstream)
200mm (downstream)
Both sides
One side
Both sides
Both sides
One side
Both sides
Both sides
One side
Both sides
1. In the absence of any indication by the designer only Level 1 access will be incorporated into a new ductwork system.
2. The panel sizes associated with Level/s 1 and 3 access are established by reference to Section 20 of DW/144 and Section
2 of TR17 respectively
94
APPENDIX N – BIBLIOGRAPHY
Included in this Bibliography are technical publications which
may be of interest to ductwork designers. fabricators and erectors, and to those in the heating, ventilating, air conditioning
industries generally. Enquiries should be made of the relevant
organisation, at the address quoted. Since its publication other
addresses contained within DW/144 may have changed, and
some publications may have been superseded.
Research Reports
Ventilation system hygiene — A review of
RR01/95:
published information on the occurrence and
effects of contamination
HEATING AND VENTILATING
CONTRACTORS’ ASSOCIATION
34 Palace Court, London W2 4JG Telephone:
0171-229 2488; Fax: 0171-727 9268.
NATIONAL ENGINEERING SPECIFICATION LIMITED
Southgate Chambers, 37/39 Southgate Street,
Winchester SO23 9EH
(Telephone: 01962 842058; Fax: 01962 868982)
Orders to HVCA Publications, Old Mansion
House, Eamont Bridge, Penrith. Cumbria CA10 2BX
(Telephone: 01768 864771 Fax: 01768 867138)
Email: hvcapublications@hvwelfare.co.uk
DW/144
Specification for sheet metal ductwork (low-,
medium- and high-pressure) (1998)
DW/143
A practical guide to ductwork leakage testing
(1983)
Specification for plastics ductwork
Guide to good Practice for kitchen ventilation
systems
Guide to good practice glass fibre ductwork
Acceptance scheme for new products
—
Rectangular cross joint classification
Guide to good practice — Internal cleanliness of
new ductwork installations
Guide to good practice for the design for the
Installation of fire and smoke dampers
DW/151
DW/171
DW/191
DW/TM1
DW/TM2
DW/TM3
Tool box talks
JS5
Welding Safety booklet
JS19
Safety facts
edition
JS21
COSHH manual volume 1 Advice on compliance with the regulations
JS 21A
COSHH manual volume 2 Assessment sheets
JS23
Risk management manual
TR/3
Brazing and bronze welding of copper pipework
and sheet (1976)
TR5
Welding of carbon steel pipework (1980)
TR6
Guide to Good Practice for Site Pressure Testing
of Pipework (1980)
Guide to good practice cleanliness of ventilation
systems.
TR17
booklet.
Fact
sheets
1-24
Influence of HVAC on smoke detectors
Application Guides
AG.1/74
Designing Variable Volume Systems for Room
Air Movement
AG.1/91
Commissioning of VAV Systems in Buildings.
TN.6/94
Fire Dampers
LB.65/94
Ventilation of Kitchens
AG.3/89
The Commissioning of Air Systems in Buildings
AH.2/92
Commissioning of Bems - A Code of Practice
TN.24/71
Fire Dampers in Ventilating Ducts.
HEATING, VENTILATING AND AIR
CONDITIONING MANUFACTURERS
ASSOCIATION (HEVAC)
Sterling House, 6 Furlong Road, Bourne End,
Bucks SL8 5DG (Telephone: 01628 531186 Fax:
01628 810423 Email: info@feta.co.uk)
2nd
Publications
Air Diffusion Guide
Guide to Air Handling Unit Leakage Testing
Guide to Good Practice: Air Handling Units
Real Room Acoustic Test Procedure
Specification for the Certification of Air Filters
Method of Test for Water Rejection Performance of Louvres
Subjected to Simulated Rainfall
Test Procedure for Acoustic Louvres
Specification for Floor Grilles – Types, Performance and
Method of Test
CHARTERED INSTITUTION OF BUILDING
SERVICES ENGINEERS
Delta House, 222 Balham High Road;
London SW12 9BS (Telephone: 0181-675 5211
Fax: 0181-675 5449)
CIBSE
Volume
Volume
Volume
Air-to-air heat recovery
RR03/95:
BUILDING SERVICES RESEARCH AND
INFORMATION ASSOCIATION
Old Bracknell Lane West, Bracknell, Berkshire
RG12 4AH (Telephone:
Bracknell (01344)
426511; Fax: 01344 487575)
Other publications
H&V safety guide 5th edition
JS1
JS2
RR02/95:
Specification for the Determination
Efficiency of Sand Trap Louvres
Domestic
Mechanical
Recovery
Ventilation
of
Systems
the
Collection
with
Heat
Fan Application Guide
Guide
A
Design Data
Installation and Equipment Data
B
C
Reference Data
Fan and Ductwork Installation Guide
Guide to Fan Noise and Vibration
Specification of Requirements for Natural Smoke and Heat
Exhaust Ventilators
Commissioning Codes
These Codes cover the preliminary checks, setting to work
and regulation of various categories of plant. The Codes give
a guide to design implications.
Air Distribution Systems
Series A
Boiler Plant
Series B
Automatic Control Systems
Series C
Refrigerating Systems
Series R
Water Distribution Systems
Series W
Specification
Ventilators
for
Powered
Smoke
and
Heat
Exhaust
Specification of Requirements for Smoke Curtains
Design Guide of Smoke Ventilation for Single Storey
Industrial Buildings Including those with Mezzanine Floors
and High Racked Storage Warehouses – Issue 3
Guidance for the Design of Smoke Ventilation Systems for
Covered and Underground Car Parks – Issue 1
Technical Memoranda
Design Notes for the Middle East
TM 4
Design Notes for Ductwork
TM 8
Minimising the Risk of Legionnaires Disease
TM 13
Application of Smoke Control Equipment
Guide to Good Practice – Issue 1
95
and
Systems:
BRITISH STANDARDS INSTITUTION
Sales Department, 101 Pentonville Road, London
N1 9ND (Telephone: 0171-837 8801)
BS 381C:1996
Colours (of ready-mixed paints) for specific
purposes
CP 413: 1973
Ducts for building services
BS 476:
Fire tests on building materials and structures
Part4: 1984
Non-combustibility test for materials
Part6: 1989
Fire propagation test for materials
SHEET METAL AND AIR CONDITIONING
CONTRACTORS’ NATIONAL
ASSOCIATION INC. (SMACNA)
Headquarters:
4201 Lafayette Center Drive
Chantilly
Virginia 20151-1209
Mailing Address
P.O. Box 221230
Chantilly
Virginia 20153-1230
Part7: 1993
Surface spread of flame tests for materials
Part 20: 1987
Fire resistance
struction
Part 21:1987
Fire resistance of loadbearing elements
of construction
Part 22:1987
Fire
resistance
of
non-loadbearing
elements of construction
Accepted Industry Practice for Industrial Duct Construction
Part 23:1987
Contribution of components to the fire
resistance of a structure
Architectural Sheet Metal Manual (1993)
elements
of
con-
Telephone (703) 803-2980
Fax
(703) 803-3732
(1975)
Contractors Guide for Modification to Construction Contracts
Fire resistance of ventilation ducts
Part 24:1987
BS 5588
Part 9:1980
of
(1993)
Fire Precautions in the design and construction of buildings
Ducted Electric Heat Guide for Air Handling Systems (1994)
BS 729:1971
Hot dip galvanized coatings for iron and
steel articles
Energy Recovery Equipment & Systems (1991)
BS 1449:
Steel plate, sheet and strip
Fire, Smoke & Radiation Damper Install. Guide for HVAC
Part 1:1991
Carbon steel plate, sheet and strip
Systems (1992)
Part 2:1983
Stainless steel plate, sheet and strip.
Guide to Steel Stack (1995)
Energy Conservation Guidelines (1984)
Fibrous Glass Duct Construction Standards (1992)
HVAC Air Duct Leakage Test Manual (1985)
and
BS.EN10149-2:
HVAC Commissioning Manual (1994)
1996
HVAC Duct Construction Standards-Metal & Flexible (1995)
BS.EN 10149-3: 1996
Addendum No. 1 (Nov 1997)
BS.EN 10131: 1992
BS.EN485
Parts l-4
BS.EN515 1993
HVAC Duct Systems Inspection Guide (1989)
Wrought aluminium and aluminium alloys
for general engineering purposes – plate,
sheet and strip.
HVAC Systems-Application (1986)
HVAC Systems-Duct Design (1990)
HVAC Systems-Testing, Adjusting & Balancing (1993)
BS.EN573
Parts l-4
BS 1474:1972
and
Indoor Air Quality Manual (1993)
Kitchen Equipment Fabrication Guidelines (1990)
Wrought aluminium and aluminium alloys
bars, tubes and sections
Managers’ Guide for Welding (1993)
Rectangular Industrial Duct Construction Standards (1980)
BS.EN755
Parts 3-6
BS.EN22063:
1994
Round Industrial Duct Construction Standards (1977)
Sprayed metal coatings
Protection of iron and steel by aluminium
and zinc against atmospheric corrosion
Protection of iron and
corrosion
and
oxidation
temperatures
Continuously hot-dip zinc coated mild
steel strip and sheet for cold forming technical delivery conditions
BS.EN10143:
1991
Continuously hot-dip zinc coated and
ironzinc alloy coated steel sheet and strip tolerances on dimensions and shade
BS 3533: 1981
Glossary of
insulation
BS.EN.ISO: 1479
relating
SMACNA Master Index of Technical Publications (1995)
Thermoplastic Duct (PVC) Construction Manual (1994)
steel against
at
elevated
BS.EN10142:
1991
terms
Seismic Restraint Manual (1991) (w/ Appendix E, 1993)
to
DEPARTMENT OF THE ENVIRONMENT
(Publications Centre)
H.M. Stationery Office, 51 Nine Elms Lane,
London SW8 5DR
M & E No.1 1972
Electrical installations in buildings (New
Edition)
M & E No.3 1988
Heating, hot and cold water, steam and
M & E No.4 1970
Central heating and hot and cold water
thermal
gas installations for buildings
Self-tapping screws and metallic drive screws
installations for dwellings
BS.EN.ISO: 7049:
M & E No.100 1971 Mechanical ventilation for buildings
1994
BS 4800:1989
Paint colours for building purposes
BS 4848:
Part4: 1972
Hot rolled structural steel sections
Equal and unequal angles
BS 5422:1990
Specification for the use of thermal insulating materials
BS 5720: 1979
Code of practice for mechanical ventilating
and air conditioning in buildings
BS 5970: 1992
Code of practice for thermal insulation of
pipework
BRITISH STEEL PLC
Market Communications Dept
British Steel PLC
Strip Products
P.O. Box 10 Newport
South Wales NP9 0XN
(Telephone 01633 290022)
(Fax
01633 464087)
Publication: Edge protection by zinc
96
HEALTH AND SAFETY EXECUTIVE
Rose Court
2 Southwark Bridge
London SE1 9HS
ASSOCIATION FOR SPECIALIST FIRE
PROTECTION
Association House
235 Ash Road
Aldershot
Hampshire GU12 4DD
Telephone 0171-717 6000
Telephone 01252 21322
01252 333901
Fax
Publications.
Fire Rated and Smoke Outlet Ductwork: An
Industry Guide to Design and Installation.
APPENDIX P – CONVERSION TABLES
Sheet thicknesses
Aluminium
Galvanized steel *
Standard
thickness
inch
.0197
.0236
.0276
.0315
.0354
.0394
.0472
.0630
.0787
.0984
mm
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.6
2.0
2.5
Birmingham
Gauge
inch
BG
26
.0196
24
.0248
22
.0312
20
.0394
18
16
14
12
.0495
.0625
.0785
.0991
Standard
Wire Gauge
Standard
thickness
0.5 mm is a standard thickness for galvanized
sheet only
2.5 mm is a standard thickness for hot-rolled
sheet only
* See Appendix K (Section K.3) which contains
information on gauge and sheet width/length
tolerances
97
inch
mm
.0197
0.5
.0236
.0276
.0315
.0354
.0394
.0472
.0630
.0787
.0984
0.6
0.7
0.8
0.9
1.0
1.2
1.6
2.0
2.5
.1181
3.0
swg
26
inch
.018
24
.022
22
.028
20
.036
18
16
14
.048
.064
.080
12
.104
10
.128
Some miscellaneous conversion factors
Multiply by
To convert
To convert
Multiply by
Length
Inches to millimetres
Feet to metres
25.40
0.3048
Millimetres to inches
Metres to feet
0.03937
3.281
Area
Square inches to square millimetres
Square feet to square metres
645.2
0.0929
Square millimetres to square inches
Square metres to square feet
0.00155
10.764
Volume
Cubic feet to cubic metres
Cubic feet to litres
Gallons (UK) to litres
0.02832
28.31
4.546
Mass
Ounces to grams
Pounds to kilograms
Tons to tonnes
Cubic metres to cubic feet
Litres to cubic feet
Litres to gallons (UK)
28.35
0.4536
1.016
Volume flow
Cubic feet per minute to cubic
metres per second
Cubic feet per minute to litres
per second
Grams to ounces
Kilograms to pounds
Tonnes to tons
Cubic
feet
Litres
per
0.000472
0.4719
Motion
Feet per minute to metres per second
35.315
0.0353
0.22
0.00508
0.03527
2.205
0.9842
metres per second to cubic
per minute
per second to cubic feet
minute
Metres per second to feet per minute
Pressure
Inches water gauge to millibars
2.491
Inches water gauge to pascals (Pa)
249.1
1 Pa = 1 Newton per square metre = 10–2 millibars
Standard dimensions of steel
and aluminium sheet
Steel
(mild and galvanized)
Metric
mm
2000 ×
2500 ×
3000 ×
3000 ×
1000
1250
1350
1500
Equivalent
6'
8'
9'
9'
ft/in
6 3 / 4 " × 3' 3 3 / 8 "
2 7 / 16 " × 4' 1 1 / 4 "
10 1 / 8 " × 4' 5 1 / 8 "
10 1 / 8 " × 4' 11 1 / 16 "
Weight of galvanized steel sheet
Aluminium
(commercially pure and alloy)
Metric
mm
2000 × 1000
2500 × 1250
3750 × 1250
Equivalent
ft/in
6 ' 6 3/ 4 " × 3 ' 3 3/8 "
8' 2 7/16 " × 4' 11/4 "
12' 3 5/ 8 " × 4' 11/ 4 "
98
Thickness
Weight per
square metre
mm
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.6
2.0
2.5
kg
3.9213
4.7056
5.4898
6.2741
7.0584
7.8426
9.4111
12.5481
15.6852
19.6064
2119
2.119
197
Details of how to obtain
further copies of this
guide and other
publications are
available from:
HVCA Publications
Old Mansion House
Eamont Bridge
Penrith
Cumbria
CA10 2BX
Tel: 01768 864771
Fax: 01768 867138
e-mail hvcapublications@hvwelfare.co.uk
Heating and Ventilating Contractors’ Association
Esca House 34 Palace Court London W2 4JG
Tel: 0171-229 2488 Fax: 0171-727 9268