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Specification Value
Marley
/
MCW Cooling Tower
/
Specifications: Options
31
lockable in the off position for safety.
The system shall include a solid state, PI
temperature controller to adjust frequen-
cy output of the drive in response to the
tower fluid temperature. The temperature
of the fluid and set point shall be dis-
played 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 operating in bypass, to maintain
the set-point temperature of the cold
water. The drive design shall be oper-
ated as a stand-alone system without
the need for a BMS system. Operator
controls shall be mounted on the front of
the enclosure and shall consist of start
and stop control, bypass/VFD selector
switch, Auto/Manual selector switch,
manual speed control, and solid-state
temperature controller. An emergency
bypass selector switch internal to the
panel allowing the fluid cooler fan motor
to be run at full speed shall be furnished.
To prevent heating problems in the fluid
cooler fan motor and to assure proper
gear box lubrication the VFD system
shall de energize the motor once 25%
motor speed is reached and cooling is
no longer required. The VFD shall include
de-icing logic with auto canceling and
adjustable time. Speed in De-Ice mode
shall not exceed 50% motor speed. 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.