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Operation Manual
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8.2
Circuit Control Logic
8.2.1
Circuit Availability
A circuit is available to start if the following conditions are true:
•
Circuit switch is closed
•
No circuit alarms are active
•
Circuit Mode set point is set to Enable
•
BAS Circuit Mode set point is set to Auto
•
No cycle timers are active
•
Discharge Temperature is at least 5°C higher than Oil Saturated Temperature
8.2.2
Starting
The circuit will start if all these conditions are true:
•
Adequate pressure in the evaporator and condenser (see No Pressure At Start Alarm)
•
Circuit Switch is closed
•
Circuit Mode set point is set to Enable
•
BAS Circuit Mode set point is set to Auto
•
No cycle timers are active
•
No alarms are active
•
Staging logic requires this circuit to start
•
Unit state is Auto
•
Evaporator pump state is Run
Circuit Startup Logic
Circuit startup is the time period following the starting of the compressor on a circuit. During the startup, the low evaporator
pressure alarm logic is ignored. When the compressor has been running at least 20 seconds and the evaporator pressure
rises above the low evaporator pressure unload set point, the startup is complete.
If the pressure does not rise above the unload set point and the circuit has been running longer than the Startup Time set
point, then the circuit is turned off and an alarm triggered. If the evaporator pressure drops below the absolute low pressure
limit then the circuit is turned off and the same alarm t riggered.
Stopping
Normal Shutdown
A normal shutdown requires the circuit to pumpdown before the compressor is turned off. This is done by closing the EXV,
and closing the liquid line solenoid (if present) while the compressor is running.
The circuit will do a normal shutdown (pumpdown) if any of the following are true:
•
Staging logic requires this circuit to stop
•
Unit State is Pumpdown
•
A pumpdown alarm occurs on the circuit
•
Circuit switch is open
•
Circuit Mode set point is set to Disable
•
BAS Circuit Mode set point is set to Off
The normal shutdown is complete when any of the following are true:
•
Evaporator Pressure is less than the Pumpdown Pressure set point
•
Service Pumpdown set point is set to Yes and Evaporator Pressure is less than 5 psi
•
Circuit has been pumping down for longer than the Pumpdown Time Limit setpoint
Rapid Shutdown
A rapid shutdown requires the compressor to stop and the circuit to go to the Off state immediately.
The circuit will do a rapid shutdown if either of these conditions occurs at any time:
•
Unit State is Off
•
A rapid stop alarm occurs on the circuit
