installed in the air handling unit. Mount fans on steel shafts, accurately
ground and finished. Fan bearings shall be sealed against dust and dirt
and shall be precision self-aligning ball or roller type. Bearing life
shall be L50 rated at not less than 200,000 hours as defined by ABMA 9 and
ABMA 11. Bearings shall be permanently lubricated or lubricated type with
lubrication fittings readily accessible at the drive side of the unit.
Bearings shall be supported by structural shapes, or die formed sheet
structural members, or support plates securely attached to the unit casing.
Bearings may not be fastened directly to the unit sheet metal casing.
Furnish fans and scrolls with coating indicated. Fans shall be driven by a
unit-mounted or a floor-mounted motor connected to fans by V-belt drive
complete with belt guard for externally mounted motors. Belt guards shall
be the three-sided enclosed type with solid or expanded metal face. Belt
drives shall be designed for not less than a 1.3 service factor based on
motor nameplate rating. [Motor sheaves shall be variable pitch for 20 kW
25 hp and below and fixed pitch above 20 kW 25 hp as defined by ARI
Guideline D.] Where fixed sheaves are required, variable pitch sheaves may
be used during air balance, but shall be replaced with an appropriate fixed
sheave after air balance is completed. Select variable pitch sheaves to
drive the fan at a speed that will produce the specified capacity when set
at the approximate midpoint of the sheave adjustment. Furnish motors for
V-belt drives with adjustable bases. Fan motors shall have [open]
[splashproof] [totally enclosed] enclosures. Motor starters shall be
[manual] [magnetic] [across-the-line] [reduced-voltage-start] type with
[general-purpose] [weather-resistant] [watertight] enclosure. Unit fan or
fans shall be selected to produce the required capacity at the fan static
pressure. Sound power level shall be as indicated. The sound power level
values shall be obtained according to AMCA 300, ASHRAE 68, or ARI 260.
2.8.2.5
Access Sections and Filter/Mixing Boxes
Provide access sections where indicated and furnish with access doors as
shown. Construct access sections and filter/mixing boxes in a manner
identical to the remainder of the unit casing and equip with access doors.
Design mixing boxes to minimize air stratification and to promote thorough
mixing of the air streams.
2.8.2.6
Diffuser Sections
Furnish diffuser sections between the discharge of all housed supply fans
[and cooling coils of blow-through single zone units] [and] [filter
sections of those units with high efficiency filters located immediately
downstream of the air handling unit fan section]. Diffuser sections shall
be fabricated by the unit manufacturer in a manner identical to the
remainder of the unit casing, designed to be airtight under positive static
pressures up to [2] [_____] kPa [8] [_____] inches water gauge and with an
access door on each side for inspection purposes. Diffuser section shall
contain a perforated diffusion plate, fabricated of galvanized steel, Type
316 stainless steel, aluminum, or steel treated for corrosion with
manufacturer's standard corrosion-resisting finish. The diffusion plate
shall be designed to accomplish uniform air flow across the down-stream
[coil] [filters] while reducing the higher fan outlet velocity to within
plus or minus 5 percent of the required face velocity of the downstream
component.
2.8.2.7
Dampers
Dampers shall be as specified in paragraph CONTROLS.
SECTION 15895
Page 41
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