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Specification Value
Marley
/
MCW Cooling Tower
/
Specifications: Options
30
System monitoring the tower fluid tem-
perature. As an option to receiving the
speed reference signal from a building
management system, the drive must
have the capability to receive a 4-20 ma
temperature signal from an RTD trans-
mitter. The VFD shall have an internal PI
regulator to modulate fan speed main-
taining set point temperature. The drive's
panel display shall be able to display
the set-point temperature and cold-fluid
temperature on two separate lines. The
bypass shall include a complete mag-
netic bypass circuit and with capability
to isolate the VFD when in the bypass
mode. Transfer to the bypass mode shall
be manual in the event of VFD failure.
Once the motor is transferred to the by-
pass circuit the fan motor will run at con-
stant full speed. The bypass circuit will
not modulate ON and OFF based on fluid
temperature. The application must be
able to handle very cold fluid tempera-
tures while the VFD is in a by-pass mode.
Operator controls shall be mounted on
the front of the enclosure and shall con-
sist of start and stop control, bypass/VFD
selection, Auto/Manual selections, manu-
al speed control. To prevent heating prob-
lems in the fluid cooloer fan motor and
to assure proper gear reducer lubrication
the VFD system shall de energize the
motor once 25% motor speed is reached
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 IP52 indoor or IP14
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 pro-
tection and external operating handle,