2.10
DUCTWORK COMPONENTS
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NOTE: The appropriate pressure classification from
SMACNA HVAC Duct Const Stds, including points of
changes in pressure classification, will be noted on
the drawings.
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2.10.1
Metal Ductwork
All aspects of metal ductwork construction, including all fittings and
components, shall comply with SMACNA HVAC Duct Const Stds unless otherwise
specified. Elbows shall be radius type with a centerline radius of 1-1/2
times the width or diameter of the duct where space permits. Otherwise,
elbows having a minimum radius equal to the width or diameter of the duct
or square elbows with factory fabricated turning vanes may be used. Static
pressure Class 125, 250, and 500 Pa 1/2, 1, and 2 inch w.g. ductwork shall
meet the requirements of Seal Class C. Class 750 through 2500 Pa 3 through
10 inch shall meet the requirements of Seal Class A. Sealants shall
conform to fire hazard classification specified in Section 15080A THERMAL
INSULATION FOR MECHANICAL SYSTEMS. Pressure sensitive tape shall not be
used as a sealant. Spiral lock seam duct, and flat oval shall be made with
duct sealant and locked with not less than 3 equally spaced drive screws or
other approved methods indicated in SMACNA HVAC Duct Const Stds. The
sealant shall be applied to the exposed male part of the fitting collar so
that the sealer will be on the inside of the joint and fully protected by
the metal of the duct fitting. One brush coat of the sealant shall be
applied over the outside of the joint to at least 50 mm 2 inch band width
covering all screw heads and joint gap. Dents in the male portion of the
slip fitting collar will not be acceptable.
2.10.1.1
Transitions
Diverging air flow transitions shall be made with each side pitched out a
maximum of 15 degrees, for an included angle of 30 degrees. Transitions
for converging air flow shall be made with each side pitched in a maximum
of 30 degrees, for an included angle of 60 degrees, or shall be as
indicated. Factory-fabricated reducing fittings for systems using round
duct sections when formed to the shape of the ASME short flow nozzle, need
not comply with the maximum angles specified.
2.10.1.2
Insulated Nonmetallic Flexible Duct Runouts
Flexible duct runouts shall be used only where indicated. Runouts length
shall be as shown on the drawings, but shall not exceed 3 m 10 feet.
Runouts shall be preinsulated, factory fabricated, and shall comply with
NFPA 90A and UL 181. Either field or factory applied vapor barrier shall
be provided. Where coil induction or high velocity units are supplied with
vertical air inlets, a streamlined and vaned and mitered elbow transition
piece shall be provided for connection to the flexible duct or hose. The
last elbow to these units, other than the vertical air inlet type, shall be
a die-stamped elbow and not a flexible connector. Insulated flexible
connectors may be used as runouts. The insulated material and vapor
barrier shall conform to the requirements of Section 15080A THERMAL
INSULATION FOR MECHANICAL SYSTEMS. The insulation material surface shall
not be exposed to the air stream.
SECTION 15566A
Page 15
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