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Marley
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Sigma 1000/1200 Cooling Tower
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Specifications: Options
23
Specification Value
Basin Heater:
10.2 Add the following paragraph in the
Cold Water Basin section: Provide
a system of electric immersion heat-
ers and controls for each cell of the
tower to prevent freezing of water in
the collection basin during periods of
shutdown. The system shall consist
of one or more stainless steel elec-
tric immersion heaters installed in a
galvanized steel heat shield provided
in the floor of the basin. A NEMA
4 enclosure shall house a magnetic
contactor to energize heaters; a trans-
former to provide 24 volt control circuit
power; and a solid state circuit board
for temperature and low water cutoff.
A control probe shall be located in the
basin to monitor water level and tem-
perature. The system shall be capable
of maintaining 40°F water temperature
at an ambient air temperature of __ °F.
Wiring of the heaters and controls shall
be the responsibility of the purchaser.
Fan Motor Variable Speed Drive:
Marley All Weather ACH550 System
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 NEMA 1 indoor, 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 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 discon-
nect with short circuit protection and
external operating handle, lockable in the
off position for safety. The VFD system
shall receive a speed reference signal
from the Building Management System
monitoring the tower fluid temperature.
As an option to receiving the speed
reference signal from a building manage-
ment system, the drive must have the
capability to receive a 4-20 ma tempera-
ture signal from an RTD transmitter. The
VFD shall have an internal PI regulator
■ The basin heater components described at left represent our rec-
ommendation for a reliable automatic system for the prevention
of basin freezing. They are shipped separately for installation at
the jobsite.
If aggressive operating conditions are anticipated, change “galva-
nized” in paragraph 10.2 to “Series 300 SS”.
The ambient air temperature that you fill in should be the lowest
1% level of winter temperature prevalent at site.
Ask for Marley drawing 92-3627.
■ Marley VFD drive systems are designed to combine absolute
temperature control with ideal energy management. The cool-
ing 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 components. The improved energy
management provides fast payback. Indeed, many utilities offer
generous rebates for users having installed VFD drives.
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