RT-SVX063E-EN
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on unit type, efficiency, capacity stage and other limit
controls. The maximum speed limit applies to every
startup to maintain oil quality. When this function is
active, an indication will be made to the user interface
Evaporator Coil Surface Utilization (Two
Circuit Units Only)
All staging sequences performed by the algorithm
energize compressors on each circuit as soon as
possible to optimize cooling efficiency. If a circuit 1
compressor starts first, a circuit 2 compressor starts
second if it is available. If a circuit 2 compressor starts
first, a circuit 1 compressor starts second if it is
available.
Compressor Lockout and Inhibit
In all cases of Lockouts, Inhibits, and Limits
(Compressor Minimum OFF Time is not considered a
lockout or inhibit) Alternate Staging Sequences will be
substituted.
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Compressor lockouts are typically non-recoverable and
require user interaction at the User Interface to clear
associated diagnostics that return the compressor(s) to
operation. Other compressor lockouts will recover
automatically when the lockout command is removed.
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Inhibits of compressors are typically recoverable
without requiring user interaction. The inhibit of a
compressor will be immediate once the request is
issued. Inhibits originate from undesirable refrigeration
operating conditions and may or may not be
associated with a diagnostic event. Once the condition
has recovered, the compressor will be un-inhibited and
will be available for staging sequences.
Alternate Staging Sequence
When one or more compressors are unavailable due to
Lockouts and Inhibits, an alternate staging sequence
will be determined from a rule-based algorithm which
selects the best next stage from the available
compressors. Double Swaps will not be performed
during Alternate Staging Sequence.
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On single circuit units, two circuit units with neither
circuit active, or two circuit units with both circuits
active, the smallest available compressor will be
selected to start.
On two circuit units with one circuit active, the smallest
available compressor on the non-active circuit will be
chosen to start. If none are available on the non-active
circuit the next smallest available compressor on the
active circuit will be chosen to start.
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On single circuit units, or two circuit units with one
circuit running, the largest running compressor will be
chosen to stop.
On two circuit units with both circuits active, the largest
running compressor that will not cause a circuit to stop
will be chosen. If there is only one compressor running
per circuit the larger of the two compressors will be
chosen to stop.
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Transition to Normal Staging — When all compressors
are available on the next request to add or subtract the
current state will be evaluated against the Normal
staging table. If a match is found, the next staging
decision will be made following the Normal staging
rules. If the normal table does not contain a match for
the current state, then the Alternate Staging sequences
will be used to process the command, and the cycle
will continue until a match has been found.
Transition to Balanced Compressor Staging —
Balanced Compressor Staging is a feature setting,
when enabled balanced staging rules will be used to
process the next staging request.
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Due to Oil Management design constraints with the
20S unit, there are specific rules implemented to deal
alternate staging to prevent the unit operating in
compressor sequences that have the potential to cause
oil issues.
Compressor Staging with Variable
Speed Compressors
Units with Variable Speed Compressors will always
attempt to start the variable speed compressor first.
Subsequent stage increases start the preferred
compressor next according to the default factory
staging sequence. Special consideration during
Alternate Staging Sequences are defined as follows:
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During inhibited fixed speed compressor operation, the
VSC will be utilized over its full range of designed
speed operation prior to a stage change. Stage change
logic will be determined based on the available
compressors following alternate staging rules.
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During inhibited VSC operation, stage change logic will
be determined based on the available fixed stage
compressors. If the circuit with the inhibited VSC also
has fixed stage compressors, (FSC) these compressors
will be available for the alternate staging sequence. All
FSC must be staged OFF before the non-inhibited VSC
will become available. When the VSC becomes
available, it will be the first compressor turned ON at
the next ADD request.
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