SPX Cooling Technologies SS-NC-08A - Manual (Page 16)

Specifications Specification Value
Marley / NC Class Stainless Cooling Tower / Specifications: Options
16
in quantities and locations as indicated
on the drawings. An overflow and drain
connection shall be provided in each
cell of the cooling tower. The basin
floor shall slope toward the drain to
allow complete flush out of debris and
silt which may accumulate. Towers of
more than one cell shall include stain-
less steel flumes for flow and equal-
ization between cells. The basin shall
be accessible and maintainable while
water is circulating.
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
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 reference
signal from the Building Management
System monitoring the tower cold-water
temperature. As an option to receiving
the speed reference signal from a build-
ing management system, the drive must
have the capability to receive a 4-20 ma
temperature signal from an RTD trans-
mitter. The VFD shall have an internal PI
regulator to modulate fan speed main-
taining set point temperature. The drive's
panel display shall be able to display the
set-point temperature and cold-water
temperature on two separate lines. The
bypass shall include a complete mag-
netic 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
■ Marley Variable Speed Drive systems are designed to combine absolute
temperature 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 to the
user.