Optional Low Ambient Fan Vfd - Daikin AGZ030E Installation, Operation And Maintenance Manual

The optional VFD fan control is used for unit operation below
32°F (0°C) down to a minimum of -10°F (-23°C). The control
looks at the saturated discharge temperature and varies the
fan speed to hold the temperature (pressure) at the "target"
temperature.
Low ambient air temperature control is accomplished by using
the Optional Low Ambient VFD to control the speed of the
first fan on each circuit. This VFD control uses a proportional
integral function to drive the saturated condenser temperature
to a target value by changing the fan speed. The target value
is normally the same as the saturated condenser temperature
target setpoint.
The fan VFD always starts when the saturated condenser
temperature rises higher than the target.
What is an Inverter?
The term inverter and variable-frequency drive are related and
somewhat interchangeable. An electronic motor drive, for an
AC motor, controls the motor's speed by varying the frequency
of the power sent to the motor.
In general, an inverter is a device that converts DC power to
AC power. The figure below shows how the variable-frequency
drive employs an internal inverter. The drive first converts
incoming AC power to DC through a rectifier bridge, creating
an internal DC bus voltage. Then the inverter circuit converts
the DC back to AC again to power the motor. The special
inverter can vary its output frequency and voltage according to
the desired motor speed.
IOM 1206-7 • TRAILBLAZER MODEL AGZ CHILLERS
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Inverter Output to the Motor
Avoid swapping any 2 of the 3 motor lead connections which
will cause reversal of the motor direction. In applications
where reversed rotation could cause equipment damage or
personnel injury, be sure to verify direction of rotation before
attempting full-speed operation. For safety to personnel,
the motor chassis ground must be connected to the ground
connection at the bottom of the inverter housing.
The AC motor must be connected only to the inverter's
output terminals. The output terminals are uniquely labeled
(to differentiate them from the input terminals) with the
designations U/T1, V/T2, and W/T3.
This corresponds to typical motor lead connection designations
T1, T2, and T3. The consequence of swapping any two of the
three connections is the reversal of the motor direction. This
must not be done. In applications where reversed rotation
could cause equipment damage or personnel injury, be sure
to verify direction of rotation before attempting full-speed
operation. For safety to personnel, the motor chassis ground
must be connected to the ground connection at the bottom of
the inverter housing.
Notice the three connections to the motor do not include
one marked "Neutral" or "Return." The motor represents a
balanced "Y" impedance to the inverter, so there is no need
for a separate return. In other words, each of the three "Hot"
connections serves also as a return for the other connections
because of their phase relationship.
Do not to switch off power to the inverter while the motor is
running (unless it is an emergency stop) to avoid equipment
damage. Also, do not install or use disconnect switches
in the wiring from the inverter to the motor (except thermal
disconnect).
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