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Independent fan control is standard on all Vertex™ Condensers that are equipped with BALTIDRIVE® Power Train. In an
operating forced draft unit with independent fan capabilities and no partitions, idle fans tend to windmill in the reverse direction.
A windmilling fan poses no threat to the system while turning freely but can create a large shock load when the fan motor is
suddenly powered up. Proper staging of fans when starting from a windmilling condition will prevent excessive stresses on the
drive system. There are two control strategy options:
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VFD: The recommended control option is to use a variable frequency drive to control all of the motors. VFDs regulate
motor speed electronically and start motors with reduced voltage and frequency. The result is a gentle motor start, and
therefore reduced stress.
•
No VFD
Staging Up: Turn all motors off for 15 seconds. Following the 15 second delay, bring all required fans online.
o
Allow for a 1 second time delay between fan stages to reduce staging current.
Staging Down: Turn off the fan motor. No need for delays.
o
Variable Frequency Drive Operation
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Applications utilizing variable frequency drives (VFDs) for fan motor control must use inverter duty motors built in
compliance with NEMA standard MG-1, Part 31.
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Operation of the unit at a speed which resonates with components of the drive system or support structure may result in
vibrations which could damage the components or structure, and/or create objectionable noise. Therefore, these resonant
speed ranges should be identified at start-up and locked out to prevent operation of the motor at these resonant speeds.
The Resonant Speed Identification Procedure on Page 55 must be conducted.
•
Please refer to the manufacturer's variable frequency drive recommended start-up procedure for further information or
consult with your local BAC Representative for any VFD applications. For projects with BAC controls, visit
www.BaltimoreAircoil.com.
NOTICE: For fan motors controlled with VFDs, when reversing the direction of fan rotation, allow
the fan to come to a complete stop before restarting the motor.
NOTE: The minimum turndown ratio for units with a belt drive is 10:1 (or 6 hz). Units with the oil
pump do not have a minimum speed.
Vertex™ Evaporative Condenser Operation & Maintenance Manual – Fan Control
Page | 54
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