Functional Control ESIE10-01
2–46 Part 2 – Functional Description
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2.3.4 Condenser Fan Control
Saturated
condenser
temperature target
The condenser fan control logic will attempt to control the saturated condenser temperature to a
calculated target. A base condenser target is calculated based on evaporator saturated temperature.
The equation is:
Base saturated condenser target = 5/6 (saturated evaporator temperature) + 3.5°C.
This value is then limited to a maximum and minimum determined by the Condenser Target Maximum
and Minimum set points. If these set points are both set to the same value, then the saturated
condenser temperature target will be locked at that value.
Fan staging The fan stage shall be adjusted in steps of 1 fan.
Fan staging shall accommodate anywhere from 5 to 12 fans according to the table below:
Staging up Six stage up dead bands shall be used. Stages one through five should use their respective dead
bands. Stages six through twelve should all use the sixth stage up dead band.
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 5 seconds, only if the
Saturated Condenser Refrigerant Temperature is not falling. When Stage Up Error Accumulator is
greater than 20 another stage is added.
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.
Staging down Five stage down dead bands shall be used. Stages two through five should use their respective dead
bands. Stages six through twelve should all use the stage six dead band.
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.
Output Number
123456# of fans# of DO
* * * * *
54
* * * * * * 6
* * * * * * *
75
* * * * * * * * 8
* * * * * * * * * 9
* * * * * * * * * * 10 6
* * * * * * * * * * *
11
* * * * * * * * * * * * 12
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