Specifications
Marley
/
MD
Cooling Tower
/
Specifications: Options
37
Specification Value
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 enclo-
sure and shall consist of start and stop
control, bypass/VFD selector switch, Auto/
Manual selector switch, manual speed con-
trol, and solid-state temperature controller.
An emergency bypass selector switch inter-
nal to the panel allowing the cooling tower
fan motor to be run at full speed shall be
furnished. To prevent heating problems in
the cooling tower 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 adjust-
able time. Speed in De-Ice mode shall not
exceed 50 % motor speed. The cooling
tower manufacturer shall supply VFD start-
up assistance. Tower vibration testing
throughout the speed range is required to
identify and lockout any natural frequency
vibration levels which may exceed CTI
guidelines.
6.4
Add the following paragraph in the
Mechanical Equipment section when
VFD is used with customers Building
Management System:
A complete UL
listed Variable Speed Drive system in a
IP10 indoor, IP52 indoor or IP14 outdoor
enclosure shall be provided. The VFD shall
use PWM technology with IGBT switching
and integrated bypass design. VFD out put
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 position for safety. The
VFD system shall receive a speed refer-
ence signal from the Building Management
System monitoring the tower cold-water
temperature. The bypass shall include a
complete magnetic 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.
Operator controls shall be mounted on the
front of the enclosure and shall consist of
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