66 AGZ 026B through 130B IOMM AGZ-5
Fan Stages
There are 2, 3, or 4 fans available per circuit. On 8 fan units, fans 5/7 and 6/8 are
controlled by one contactor for each pair, using virtual stages to allow a difference of
only one fan between stages. See the tables below:
4 and 6 Fan Units
Stage (3-Fan) Fans On Cir. 1 Fans On Cir. 2
1 1 2
2 1,3 2,4
3 1,3,5 2,4,6
8 Fan Units
Stage (2&4-Fan) Fans On Cir 1 Fans On Cir. 2
1 1 2
2 1,3 2,4
3 1,5,7 2,6,8
4 1,3,5,7 2,4,6,8
Normal Operation - Staging Up
At startup, the first fan will start when the saturated condenser temperature rises above
the target. After this, the stage-up deadbands apply.
When the saturated condenser temperature is above the Target + the active deadband, a
Stage Up error is accumulated.
Stage Up Error Step = Saturated Condenser Refrigerant temperature – (Target + Stage
Up dead band)
The Stage Up Error Step is added to Stage Up Accumulator once every Stage Up Error
Delay seconds. When Stage Up Error Accumulator is greater than the Stage Up Error
Setpoint another stage is started.
When a stage-up occurs or the saturated condenser temperature falls back within the
Stage Up dead band, the Stage Up Accumulator is reset to zero.
Normal Operation - Staging Down
There are four Stage Down dead bands, one for each stage.
When the saturated condenser refrigerant temperature is below the Target – the active
deadband, a Stage Down error is accumulated.
Stage Down Error Step = (Target − Stage Down dead band) − Saturated Condenser
Refrigerant temperature
The Stage Down Error Step is added to Stage Down Accumulator once every Stage
Down Error Delay seconds. When the Stage Down Error Accumulator is greater than
the Stage Down Error Setpoint, another stage of condenser fans turns off. The last
stage on will not shut off until the circuit is in an off state.
When a stage down occurs, or the saturated temperature rises back within the Stage
Down dead band, the Stage Down Error Accumulator is reset to zero.
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