Specifications
Marley
/
Sigma F Series
Cooling Tower
/
Specifications: Options
26
Specification Value
and cooling is no longer required. The
fluid cooler manufacturer shall supply
VFD start-up assistance. Tower vibration
testing throughout the speed range is
required to identify and lockout any natu-
ral frequency vibration levels which may
exceed CTI guidelines.
Marley Premium VFD System
6.4
Add the following paragraph in the
Mechanical Equipment section when
VFD is used as a stand alone system:
A complete UL listed Variable Speed
Drive system in a NEMA 12 indoor
or NEMA 3R outdoor enclosure shall
be provided. The VFD shall use PWM
technology with IGBT switching and
integrated bypass design. VFD output
switching shall not cause mechanical
issues with gearbox teeth or drive shafts.
The VFD shall catch a fan spinning in the
reverse direction without tripping. The
panel shall include a main disconnect
with short circuit protection and external
operating handle, lockable in the off posi-
tion for safety. The system shall include
a solid state, PI temperature controller
to adjust frequency output of the drive
in response to the tower fluid tempera-
ture. The temperature of the fluid and
set point shall be displayed on the door
of the control panel. The bypass shall
include a complete magnetic bypass
circuit with capability to isolate the VFD
when in the bypass mode. Transfer to
the bypass mode shall be automatic in
the event of VFD failure or for specific
trip conditions allowing safe transfer of
utility voltage to the motor. Automatic
bypass with an earth ground condition
is not allowed. The bypass contactor
shall be cycled on and off while operat-
ing in bypass, to maintain the set-point
temperature of the cold water. The drive
design shall be operated as a stand-alone
system without the need for a BMS sys-
tem. Operator controls shall be mounted
on the front of the enclosure and shall
