20
OM
AGSB-5
Table 7, Staging with VFD
Stage Fans
On
1 1,2,3
2 1,2,3,4
3 1,2,4,5,6
4 1,2,3,4,5,6
5 1,2,3,5,6,7,8
6 1,2,3,4,5,6,7,8
Staging Up
There are four stage-up deadbands that apply to the FanTrol stages. Stages one through
three use their respective deadbands. Stage four to eight share the fourth stage-up
deadband.
When the saturated condenser temperature is above the the active deadband, a
Stage Up error is accumulated.
The saturated condenser temperature must not be falling for a Stage Up accumulation to
occur.
Stage Up Error Step = Saturated Condenser Refrigerant temperature – ( Stage
Up Deadband)
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 added.
When a stage up occurs, or the saturated condenser temperature falls back within the Stage
Up deadband, the Stage Up Accumulator is reset to zero.
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 8, Forced Staging
Outside Air
Temperature
FanTrol Stage At Start
> 75
o
F
Forced FanTrol 1 SP
> 90
o
F
Forced FanTrol 2 SP
> 105
o
F
Forced FanTrol 3 SP
Staging Down
There are four Stage Down deadbands. Stages one through three use their respective
deadbands. Stages four to eight share the fourth Stage Down deadband.
When the condenser saturated refrigerant temperature is below the Target – the active
deadband, a Stage Down error is accumulated.
Stage Down Error Step = (Target - Stage Down deadband) - 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 turned off.
When a stage down occurs, or the saturated temperature rises back within the Stage Down
deadband, the Stage Down Error Accumulator is reset to zero. The accumulator is also held
at zero after startup until either the outside ambient temperature is less than or equal to 75
°
F,
or the saturated condenser temperature is greater than the condenser target less the active
stage down deadband.
Summary of Contents for AGS 206A
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