with each fan. Fans indicated to be mounted on exterior of building shall
be provided with weatherproof covers for the motor drive unit or other
weatherproofing as recommended by the manufacturer. Each fan shall be
selected to produce the capacity required at the fan total pressure
indicated. Weather hoods, flashing, and bird screens shall be provided
where indicated.
2.11.2
Fans
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NOTE: Refer to TM 5-805-4, Noise and Vibration
Control for Mechanical Equipment, for vibration
criteria. Vibration isolation required should be
shown and included in the appropriate schedule on
the drawings.
**************************************************************************
The sound power level shall be as indicated and values shall be obtained
according to AMCA 300. Standard AMCA arrangement, rotation, and discharge
shall be as indicated. Fans shall be tested and rated according to AMCA 210.
Each fan shall be selected to produce the capacity required at the fan
static pressure indicated. Fans may be connected to the motors either
directly or indirectly with V-belt drive. V-belt drives shall be designed
for not less than [150] [140] [120] percent of the connected driving
capacity. Motor sheaves shall be variable pitch for 11 kW 15 hp and below
and fixed pitch as defined by ARI Guideline D. Variable pitch sheaves
shall be selected to drive the fan at a speed which will produce the
specified capacity when set at the approximate midpoint of the sheave
adjustment. When fixed pitch sheaves are furnished, a replaceable sheave
shall be provided when needed to achieve system air balance.
2.11.2.1
Motors for V-belt drives shall be provided with adjustable rails or bases.
Removable metal guards shall be provided for all exposed V-belt drives, and
speed-test openings shall be provided at the center of all rotating shafts.
Fans shall be provided with personnel screens or guards on both suction
and supply ends, except that the screens need not be provided, unless
otherwise indicated, where ducts are connected to the fan. Fan and motor
assemblies shall be provided with vibration-isolation supports or mountings
as indicated. Vibration-isolation units shall be standard products with
published loading ratings.
2.11.2.2
Centrifugal Fans
Centrifugal fans shall be fully enclosed, single-width single-inlet, or
double-width double-inlet, AMCA Pressure Class I, II, or III as required or
indicated for the design system pressure. Impeller wheels shall be rigidly
constructed, accurately balanced both statically and dynamically. [Fan
blades may be forward curved, backward-inclined or airfoil design in wheel
sizes up to 750 mm 30 inches. Fan blades for wheels over 750 mm 30 inches
in diameter shall be backward-inclined or airfoil design].
These fans
shall be suitable for the temperatures encountered. The fan shaft shall be
provided with a heat slinger to dissipate heat buildup along the shaft. An
access (service) door to facilitate maintenance shall be supplied with
these fans. Fan wheels over 900 mm 36 inches in diameter shall have
overhung pulleys and a bearing on each side of the wheel. Indirect drive
fan wheels 900 mm 36 inches or less in diameter may have one or more extra
long bearings between the fan wheel and the drive. Bearings shall be
SECTION 15940A
Page 15
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