Specifications
Marley
/
MD Cooling Tower
/
Specifications: Options
36
Specification Value
Vibration Limit Switch:
6.5 Add the following paragraph in the
Mechanical Equipment section: A
single-pole, double-throw vibration limit
switch in a NEMA 4 housing shall be
installed on the mechanical equipment
support for wiring into the fan motor
shutdown circuit. The purpose of this
switch will be to interrupt power to the
motor in the event of excessive vibra-
tion. It shall be adjustable for sensitiv-
ity, and shall require manual reset.
Basin Heater:
11.2 Add the following paragraph in the
Cold Water Provide an electric immer-
sion heater for each cell of the tower
to prevent freezing of water in the
collection basin during periods of shut-
down. The rod type heater is installed
in the side of the cold water basin.
Each heater will include an integral
thermostat, set point nominally 4°C
but adjustable to suit local operating
requirements.
Fan Motor Variable Speed Drive:
6.4 Add the following paragraph in
the Mechanical Equipment section
when VFD is used as a stand alone
system:
AcompleteULlistedVariable
Speed Drive system in a IP52 indoor or
IP563Routdoorenclosureshallbepro-
vided.TheVFDshallusePWMtechnol-
ogy with IGBT switching and integrated
bypassdesign.VFDoutputswitching
shall not cause mechanical issues with
gearboxteethordriveshafts.TheVFD
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 system shall include a solid
state, PI temperature controller to adjust
frequency output of the drive in response
to the tower cold-water temperature.
The temperature of the cold water and
set point shall be displayed on the door
of the control panel. The bypass shall
include a complete magnetic bypass
circuitwithcapabilitytoisolatetheVFD
when in the bypass mode. Transfer to
the bypass mode shall be automatic in
theeventofVFDfailureorforspecic
trip conditions allowing safe transfer
■ Unless specified otherwise, a 3171 switch will
be provided. A double-pole, double-throw
model is also available. If purchased in con-
junction with the Control System, it is also
factory-wired. The requirement for manual
reset assures that the tower will be visited to
determine the cause of excess vibration.
■ The Marley basin heater components described at left represent our rec-
ommendation for a reliable automatic system for the prevention of basin
freezing. They are normally shipped separately for installation at the job-
site by the installing contractor. When purchased in conjunction with the
enhanced Control System option, however, they are customarily factory-
mounted and tested.
Submerged in basin water, in which zinc ions are present, copper
immersion heaters must not be used. Insist upon stainless steel.
The ambient air temperature that you insert in the specifications should
be the lowest 1% level of winter temperature prevalent at site.
■ Marley VFD drive systems are designed to combine absolute tempera-
ture control with ideal energy management. The cooling tower user
selects a cold water temperature and the drive system will vary the
fan speed to maintain that temperature. Precise temperature control is
accomplished with far less stress to the mechanical equipment compo-
nents. The improved energy management provides fast payback.
