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Circular aluminium ducts - low pressure constructional requirements
APPENDIX K - SUMMARY OF BS.EN10142: 1991 CONTINUOUSLY HOT DIP ZINC
COATED MILD STEEL STRIP AND SHEET FOR COLD FORMING
Note - The extracts from BS.EN 10142: 1991 have been
prepared by the HVCA and are included here by courtesy
of the British Standards Institution.
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summarised in DW/142 has been superseded by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).
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.)
The type of steel normally used for ductwork is
DX51D and Z275.
K.2 STEEL GRADES
K.2.1 BS.EN10142: 1991 and
the grades of steel set out in
Name of grade
DX51D + Z Bending and
DX52D + Z Drawing quality
DX53D + Z Deep drawing
DX54D + Z Special deep
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
NOTE. Normal spangle is the type normally supplied
for a wide variety of applications.
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.5 SURFACE PROTECTION
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
amendment A1:1995 lists
the next column, among
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.
steel suitable for
manufacture of the most
profiles and more
Forming quality steel
suitable for simple
drawing operations and
for more difficult
steel suitable for
deep drawing and
steel suitable for
deep drawing and
operations where a nonageing steel is required
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
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.6.1 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 DX51 D + Z sheet up to a thickness
of 1.5 mm and DX52D + Z sheet up to 2 mm; and
snap lock seams with DX51 D + 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
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
K.4 COATING FINISHES
K.4.1 BS.EN10142: 1991 and A1 1995 includes a
description of the various types of finish available:
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.
APPENDIX L -'DESIGN NOTES FOR DUCTWORK'
(CIBSE Technical Memorandum No. 8)
L.1 At the time of publication (1983) this technical
memorandum brought together information on the
design of ductwork systems.
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 updated 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:
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
Standard dimensions of circular, rectangular and flat
Duct sizing methods, including velocity, equalfriction and static regain methods, and pressure loss
calculations, with an example calculation.
Heat loss from and gain to air in the duct; condensation, noise control and fire.
Commissioning and testing.
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.
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
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.
APPENDIX M - GUIDANCE NOTES FOR INSPECTION, SERVICING AND
CLEANING ACCESS OPENINGS
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 levels 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
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."
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."
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
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
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
v) Specialist cleaning to the measurable standards
defined in TR17 will allow an objective definition
of cleanliness to be achieved.
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.
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
M.3 ACCESS TO IN-LINE EQUIPMENT
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 N - BIBLIOGRAPHY
RR01/95: Ventilation system hygiene - A review of published
information on the occurrence and effects of
RR02/95: Air-to-air heat recovery
RR03/95: Influence of HVAC on smoke detectors
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
NATIONAL ENGINEERING SPECIFICATION
Southgate Chambers, 37/39 Southgate Street,
Winchester S023 9EH
(Telephone: 01962 842058; Fax: 01962 868982)
BUILDING SERVICES RESEARCH AND
Old Bracknell Lane West, Bracknell, Berkshire RG12
4AH (Telephone: Bracknell (01344) 426511; Fax:
HEATING AND VENTILATING
34 Palace Court, London W2 4JG Telephone: 0171-229
2488; Fax: 0171-727 9268.
Orders to HVCA Publications, Old Mansion House,
Eamont Bridge, Penrith. Cumbria CA10 2BX
(Telephone: 01768 864771 Fax: 01768 867138) Email:
Specification for sheet metal ductwork (low-, mediumand high-pressure) (1998)
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 DWITM1
Acceptance scheme for new products -Rectangular cross
Guide to good practice - Internal cleanliness of new
Guide to good practice for the design for the Installation
of fire and smoke dampers
Designing Variable Volume Systems for Room Air
Commissioning of VAV Systems in Buildings.
Ventilation of Kitchens
The Commissioning of Air Systems in Buildings
Commissioning of Bems - A Code of Practice
Fire Dampers in Ventilating Ducts.
HEATING, VENTILATING AND AIR
Sterling House, 6 Furlong Road, Bourne End, Bucks
SL8 5DG (Telephone: 01628 531186 Fax: 01628
810423 Email: email@example.com)
H&V safety guide 5th edition
Tool box talks
Welding Safety booklet
Safety facts booklet. Fact sheets 1-24 2nd edition
COSHH manual volume I Advice on compliance with
COSHH manual volume 2 Assessment sheets
Risk management manual
Brazing and bronze welding of copper pipework and
Welding of carbon steel pipework (1980)
Guide to Good Practice for Site Pressure Testing of
Guide to good practice cleanliness of ventilation
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
CHARTERED INSTITUTION OF BUILDING
Delta House, 222 Balham High Road;
London SW12 9BS (Telephone: 0181-675 5211 Fax:
Test Procedure for Acoustic Louvres
Installation and Equipment Data
Fan Application Guide
These Codes cover the preliminary checks, setting to work and
regulation of various categories of plant. The Codes give a guide to
Air Distribution Systems
Automatic Control Systems
Water Distribution Systems
Specification of Requirements for Natural Smoke and Heat Exhaust
Specification for Floor Grilles - Types, Performance and Method of
Specification for the Determination of the Collection Efficiency of
Sand Trap Louvres
Domestic Mechanical Ventilation Systems with Heat Recovery
Fan and Ductwork Installation Guide
Guide to Fan Noise and Vibration
Specification for Powered Smoke and Heat Exhaust Ventilators
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
Application of Smoke Control Equipment and Systems: Guide to
Good Practice - Issue 1
Design Notes for the Middle East
Design Notes for Ductwork
Minimising the Risk of Legionnaires Disease