IOMM AGZ-5
AGZ 026B through 130B
67
Forced Fan Stage At Start
Fans may be started simultaneously with the compressor based on outdoor ambient
temperature. When the compressor starts, a Fantrol stage is forced based on the
following table.
Table 44, Forced Fan Staging
,
Fantrol Stage At Start
> 75
o
F
Forced Fan 1 SP
> 90
o
F
Forced Fan 2 SP
> 105
o
F
Forced Fan 3 SP
Up to four fans may be forced on when the compressor starts. If the unit has the Optional Low
Ambient VFD option, then only three fans can start with the compressor, and the VFD will start
normally when the saturated condenser temperature is higher than the target.
After forcing fans on, the saturated condenser temperature may temporarily stay below the
target by some amount. In order to keep these fans from staging off, no stage down error can
be accumulated until either the OAT drops below 75
o
F, or the saturated condenser temperature
goes above the target.
Optional Low Ambient VFD
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.
An inverter, in general, 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.
Summary of Contents for AGZ026BS
Page 103: ...IOMM AGZ 5 AGZ 026B through 130B 103...
Page 104: ...104 AGZ 026B through 130B IOMM AGZ 5...
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