OMM TGZ-1 TGZ 040A through TGZ 190A 51
Maximum LWT Rate
The maximum rate at which the leaving water temperature can drop is limited by the
Maximum Pull Down Rate set point when the unit mode is cool. If the rate exceeds this set
point, no more compressors shall be started until the pull down rate is less than the set
point. Running compressors will not be stopped as a result of exceeding the maximum pull
down rate.
Manual Compressor Control
The operator can manually enable and disable individual compressors. When a compressor
has been disabled it is considered unavailable to start in the staging logic. With Manual
Compressor control it is possible to take a damaged compressor offline while the remaining
compressors on the circuit can still provide some cooling.
A running compressor can not be disabled until it has been shutdown. If both of the
compressors on a circuit have been disabled then the circuit is disabled. If both circuits
have all of their compressors disabled, the Unit state will remain “Off”.
Normal Circuit Shutdown
If a condition arises that requires a circuit to shut down, but it is not an emergency
situation, then the circuit will do a pump down. A normal circuit shutdown will be initiated
when any of the following occur:
• Unit State = Pump Down
• Circuit Switch = Off
• A normal stage down occurs, and only one compressor on the circuit is running
Pump Down Procedure
• If both compressors are running, shut off the appropriate compressor based on
sequencing logic
• With one compressor left running, turn off hot gas output and liquid line output
• Keep running until evaporator pressure reaches the pump down pressure, then stop
compressor
• If evaporator pressure does not reach pump down pressure within two minutes, stop
compressor and record a Failed Pumpdown event in the Event Log.
Rapid Circuit Shutdown
A situation may arise that requires a circuit to shut down immediately, without doing a
pumpdown. This rapid shutdown will be triggered by any of the following:
• Unit State = Off
• Circuit Alarm
All compressors, hot gas, and liquid line outputs should be turned off immediately for a
rapid shutdown.
Liquid Line Solenoid
The liquid line output shall be on any time a compressor on the circuit is running and the
circuit is not performing a pump down. This output should be off at all other times.
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