SPX Cooling Technologies Marley Sigma Steel - Manual (Page 21)

Specifications Specification Value
Marley / Sigma Steel Cooling Tower / Specifications: Options
21
Basin Heaters:
10.2 Add the following paragraph in the
Cold Water Basin section: Provide a
system of electric immersion heaters
and controls for each cell of the tower
to prevent freezing of water in the
collection basin during periods of shut-
down. The system shall consist of one
or more stainless steel electric immer-
sion heaters installed in the basin. A
NEMA 4 enclosure shall house a mag-
netic contactor to energize heaters; a
transformer 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 temperature. The system shall be
capable of maintaining 40°F water tem-
perature at an ambient air temperature
of __ °F.
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
to modulate fan speed maintaining set
point temperature. The drive's panel dis-
play shall be able to display the set-point
■ The basin heater components described at left represent our recom-
mendation for a reliable automatic system for the prevention of basin
freezing. They are shipped separately for installation at the job site.
The ambient air temperature that you fill in 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 com-
ponents. The improved energy management provides fast payback.
Indeed, many utilities offer generous rebates for users having installed
VFD drives.
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