Trane RTAF-SVX001K-EN - Unloading Unstaging

Start-Up and Shutdown
RTAF-SVX001K-EN 67
Unloading Unstaging
The figure below shows the normal transition from full
load to minimum load while the chiller is running.
Figure 45. Sequence of events: unloading unstaging
Running
(All
Compressors
&Max
Capacity)
All Compressors Running At
Less Than Max Capacity
De-Energize the
Maximum Capacity
Relay after
AdjustableFilter
Time (0to 600Sec)
Remove Maximum
Capacity Submode
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Running
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StageOff Setpoint Met***
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Running
Lag CircuitMode:Shutting Down
SubMode:Operational Pumpdown
*
Operational Pumpdown
(0 Seconds to
Max Pumpdown Timer(Default:2 min.))
Fully Close EXV
Close Condenser
RfgtTank Solenoid
Valve****
IF *
No Pumpdown Required
Pumpdown
Required
CloseEXV
(0 to 25 Seconds)
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Normal Pumpdown Termination**
Criteria is Metfor Last Circuit
Send Stop
Command To Lag
Compressor
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0
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Continue to Control Capacity
byModulating Compressor
Capacity (Speed,Port Loader,
Economizer)
*** Note:The decision to stage off another compressor is determined by the
Average Running Compressor Load Command, Water Temperature Error,
and Time since Last Stage. Compressors will stage off in the reverse order
they staged on.All fixed speed compressors will stageoff beforevariable
speed compressors stageoff.
**** If Condenser Refrigerant Tank is installed.
*Operational Pumpdown is required if the Outdoor Air Temperature is less
than 50F, or the Entering Evaporator Water Temperature is greater than
(outdoorair temperature–10F). With AFD,compressors will beatmax
speed for operational pumpdown.
Stop Lag Circuits
Condenser Fans
EnergizeLag
CircuitHeaters
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Running
Lag CircuitMode:Auto
Continue to Control
Capacity by Modulating
Lead Compressor
Running Last
Compressorat
Min Capacity
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Running
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Enforce All Running
Mode Diagnostics
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Enforce All NonOperational Pumpdown
Diagnostics
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Enforce Running Mode Diagnostics for Chiller,
LastCompressorand its Circuit
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CheckforNormal
Pumpdown Termination
CriteriaMet
**
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**Operational Pumpdown -See Satisfied SetpointOperational
Pumpdown sequence diagramfor specific criteria.
PerformOperational
Pumpdown forLast
Circuit if Required
*