Specifications

Specifications
Specification Value
MH Fluid Cooler — Specifications: Options
22
cold-water temperature. As an option
to receiving the speed reference signal
from a building management system, the
drive must have the capability to receive
a 4-20 mA temperature signal from an
RTD transmitter. When using an RTD for
temperature monitoring and speed control
the VFD shall have an internal PI regula-
tor to modulate fan speed maintaining set
point temperature. The drive’s panel shall
display the set-point temperature and
cold-water temperature on two separate
lines. The bypass shall include a complete
electromechanical magnetic bypass cir-
cuit with the 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 trans-
ferred to the bypass circuit the fan motor
will run at constant full speed. Operator
controls shall be mounted on the front of
the enclosure and shall consist of Start
and Stop control, Bypass/VFD selec-
tion, Auto/Manual selections and manual
speed control. To prevent heating prob-
lems in the fan motor the VFD system
shall de energize the motor once 25%
motor speed is reached and cooling is no
longer required. The manufacturer shall
supply VFD start-up assistance by a certi-
fied technician.
Marley Premium VFD System:
6.4 Add the following paragraph in the
Mechanical Equipment section when
VFD is used as a stand alone system
and not controlled by a BMS: For fan
control 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 tech-
nology with IGBT switching. VFD output
switching signal shall be programmed
as not to cause mechanical vibration
issues with back lash in gearbox teeth
or vibration issues associated with long
drive shafts. VFD shall be programmed
for variable torque application. The VFD
shall catch a fan spinning in the forward
or reverse direction without tripping. VFD
panel construction shall include a main
disconnect with short circuit and thermal
overload protection with external operat-
ing handle, lockable in the off position
for lock-out tag-out safety procedures. A
service switch directly ahead of the VFD