shall be coated, not less than 25 mm 1 inch thick. Where acoustical
duct liner is used, liner or combination of liner and insulation
applied to the exterior of the ductwork shall be the thermal equivalent
of the insulation specified in Section 15080 THERMAL INSULATION FOR
MECHANICAL SYSTEMS. Duct sizes shown shall be increased to compensate
for the thickness of the lining used. [In lieu of sheet metal duct
with field-applied acoustical lining, acoustically equivalent lengths
of fibrous glass duct or factory fabricated double-walled internally
insulated duct with perforated liner may be provided.]
2.6.5
Diffusers, Registers, and Grilles
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NOTE: Coordinate with paragraph Sound Attenuation
Equipment.
If diffusers or registers or grilles are not
required, delete reference to the omitted items.
Delete specified performance characteristics
peculiar to the omitted items. If any one or two of
the three types of units are omitted, delete the
corresponding subparagraph.
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Units shall be factory-fabricated of [steel] [corrosion-resistant steel]
[or] [aluminum] and shall distribute the specified quantity of air evenly
over space intended without causing noticeable drafts, air movement faster
than 0.25 m/s 50 fpm in occupied zone, or dead spots anywhere in the
conditioned area. Outlets for diffusion, spread, throw, and noise level
shall be as required for specified performance. Performance shall be
certified according to ASHRAE 70. Inlets and outlets shall be sound rated
and certified according to ASHRAE 70. Sound power level shall be as
indicated. Diffusers and registers shall be provided with volume damper
with accessible operator, unless otherwise indicated; or if standard with
the manufacturer, an automatically controlled device will be acceptable.
Volume dampers shall be opposed blade type for all diffusers and registers,
except linear slot diffusers. Provide linear slot diffusers with round or
elliptical balancing dampers. Where the inlet and outlet openings are
located less than 2 m 7 feet above the floor, they shall be protected by a
grille or screen according to NFPA 90A.
2.6.5.1
Diffusers
Diffuser types shall be as indicated. Furnish ceiling mounted units with
anti-smudge devices, unless the diffuser unit minimizes ceiling smudging
through design features. Provide diffusers with air deflectors of the type
indicated. Air handling troffers or combination light and ceiling
diffusers shall conform to the requirements of UL Elec Const Dir for the
interchangeable use as cooled or heated air supply diffusers or return air
units. Install ceiling mounted units with rims tight against ceiling.
Provide sponge rubber gaskets between ceiling and surface mounted diffusers
for air leakage control. Suitable trim shall be provided for flush mounted
diffusers. Duct collar connecting the duct to diffuser shall be airtight
and shall not interfere with volume controller. Return or exhaust units
shall be similar to supply diffusers.
2.6.5.2
Perforated Plate Diffusers
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SECTION 15895
Page 23
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