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Sequence of Operations
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Pass-Through – this accepts a signal from another
source, likely the BMS, and sends this value directly to
the pump.
The following is the sequence of operations for pumping.
1. Pumping Enable.
2. Enable Pump.
a. VFD control with PID for flow, DP, and DT.
b. 2-Speed – 1 barrel, Low Speed- 2 barrels, or free
cooling – high speed.
c. Pass-through – send value.
3. Monitor flow – No Flow:
a. Mark pump unavailable.
b. Annunciate alarm to HMI.
c. Switch to alternate pump.
d. If no pumps available, annunciate No Pump
Available alarm.
4. Monitor Pump Fault – Pump in Fault:
a. Annunciate Pump Fault.
b. Mark pump unavailable.
c. Switch to alternate pump.
d. If no pumps available, annunciate No Pump
Available alarm.
Fluid and Refrigerant isolation
The chiller is configured in circuits and each compressor is
assigned to a circuit. When a compressor starts, this
system confirms that the valve for that circuit is open.
Chiller Operational States
Figure 32. Chiller operational states flow chart
68
Idle State
The chiller is standing idle (zero capacity) but is ready for
start of the first compressor.
Start State
The pressure ratio must be kept low while one or more
compressors are in the process of starting. The start state
maintains the low-pressure ratio until all running
compressors have reached sufficient speed to operate
without risk of surging. At that point, the state is changed
into the operational state.
Operational State
The chiller is in normal operation.
Stage-In State
Starting a compressor when other compressors are already
running requires some care because the pressure ratio has
to be low enough to start a compressor.
This is the purpose of the stage-in state. The system is
instructed to lower the pressure ratio and the rack controller
contributes by instructing all running compressors to
reduce their capacity. As soon as the pressure ratio has
reached the threshold, the new compressor is instructed to
start and the state changes into start state.
Restart State
It is assumed in the stage-in state that the pressure ratio
will come down below the threshold where another
compressor can be started. However, it must also be
assumed that this is not always the case (although this
should not happen in a well-designed system unless it is
malfunctioning). In that case, all compressors will be
stopped and restarted together with one additional
compressor. In the restart state, all compressors are
signaled to stop. As soon as they have all reached full stop,
the controller signals start to all compressors that need to
be started and switches into the start state.
Stage-out State
In the stage-out state, one compressor is instructed to stop
in order to reduce capacity. When it has reached full stop,
the state switches automatically back to the operational
state.
Shutdown State
The shutdown state is similar to the stage-out state with the
sole exception that in this case the last running compressor
is being stopped. The shutdown state therefore switches
into the idle stage when this compressor reaches full stop.
ARTC-SVX014A-EN
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