SPX Cooling Technologies Marley Sigma Steel Ventilation Hood User Manual


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Specifications
Specification Value
Marley
/
Sigma Steel Cooling Tower
/
Specifications: Options
22
temperature and cold-fluid temperature
on two separate lines. 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.Oncethemotor
is transferred to the by-pass circuit the
fan motor will run at constant full speed.
The bypass circuit will not modulate ON
andOFFbasedonuidtemperature.The
application must be able to handle very
colduidtemperatureswhiletheVFD
is in a by-pass mode. Operator controls
shall be mounted on the front of the
enclosure and shall consist of start and
stopcontrol,bypass/VFDselection,Auto/
Manual selections, manual speed control.
To prevent heating problems 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 manu-
facturershallsupplyVFDstart-upassis-
tance. Tower vibration testing throughout
the speed range is required to identify
and lockout any natural frequency vibra-
tion levels which may exceed CTI guide-
lines.
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
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