OM AGSD-1
41
Start/Stop Timing – Cool Mode
This section defines when a compressor is to start or stop, when the chiller is operating in
cool mode.
Each circuit looks at all the required parameters independently to determine if it is time to
stage up or stage down.
Required Parameters
Startup Delta T setpoint.
Stage-Up Delta T setpoint
Stage-Down Delta T setpoint
Stop-Delta T setpoint
LWT error
Full load indicator for each compressor
Stage-Up Delay setpoint
Light Load Stage-Down setpoint
Full Load Indicator
A circuit is considered to be at full load in the compressor staging logic when any of the
following occur:
•
Slide control = manual
•
A low or high pressure limit event has been active for 10 seconds
•
Slide target >= 75% AND max slide target > 75%
•
Slide target >= max slide target AND max slide target <= 75%
Stage-Up Delay
There is a stage-up delay after starting the first compressor. After the first compressor
starts, a time equal to the stage-up delay setpoint must pass before the next compressor is
allowed to start.
The delay only applies when a compressor is already running. If the first compressor starts
and very quickly fails on alarm or some other event shuts it off, then the other compressor
may start without the delay.
Light Load Stage-Down
When multiple compressors are running and they are all at a low capacity, more efficient
operation can be achieved by shutting down a compressor and allowing the remaining
compressor to increase in capacity to handle the load.
If all running compressors have slide targets less than the Light-Load Stage-Down setpoint
and the LWT is less than the active LWT setpoint plus the Stage-Up Delta T setpoint, then
the stage down should occur.
Multiple Compressor Start/Stop Timing – Ice Mode
This section defines when a compressor is to start or stop when the chiller is operating in ice
mode.
Required Parameters
Startup Delta T setpoint.
Stage Up Delta T setpoint
LWT error (See definition under Compressor Capacity Control section.)
Summary of Contents for AGS 225D
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