McQuay AGZXXXBS Series - Page 62

62 AGZ 026B through 130B IOMM AGZ-5
Required Parameters
• Number of starts for all compressors
• Number of run-hours for all compressors
• Status of all compressors (Available/Unavailable)
• Compressor number
Compressor Start/Stop Timing-Cool Mode
This section defines when a compressor is to start, or stop, and the scenario for doing
so.
Required Parameters
1. Start Delta setpoint.
2. Max Pulldown Rate setpoint
3. Evap Delta T setpoint
4. Number of Compressors/Circuit setpoint
5. LWT error
6. LWT Slope
7. Number of compressors running
8. Interstage timer status
Stage Up
For 2 compressors/circuit:
Control band = Evap Delta T x .25
For 3 compressors/circuit:
Control band = Evap Delta T x .17
IF [LWT Error > Startup_Delta_T_SP + 0.5(Control band)
AND No Compressors Running
AND Stage Up Timer Expired]
THEN Stage_Up_Now = YES
ELSE IF
[LWT Error > 0.5(Control band) AND LWT Slope <= Max Pulldown setpoint
AND Stage Up Timer Expired]
THEN Stage_Up_Now = YES
Stage Down
IF [LWT Error < -0.5(Control band)
AND Stage Down Timer Expires]
THEN Stage_Down_Now = YES
Compressor Start/Stop Timing – Ice Mode
This section defines when a compressor is to start, or stop, and the scenario for doing
so.
Required Parameters
Start Delta setpoint
Evap Delta T setpoint
Number of Compressors/Circuit setpoint
LWT error
Number of compressors running
Interstage timer status
Ice timer status (12 hours between starts)