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Balanced Compressor Staging
The Balanced Staging function is a user-defined option
for fixed-speed compressor units. To perform Wear
Balancing, the Symbio 800 controller will keep track of
each installed compressor’ number of starts, and run-
time. The controller will use this information to
equalize wear across all compressors installed in the
unit. Double Swaps will not be performed during
Balanced Compressor Staging The Balanced
Compressor Staging function can be Enabled or
Disabled at the user interface. When disabled,
compressor staging follows the Normal Staging
Sequence.
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The wear balancing formula for compressor operation
is the number of compressor starts multiplied by a
factory determined wear factor, plus all of the normal
run time. Starting accounts for a significant amount of
normal run time wear and adds quickly to the wear
calculation sum.
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The lowest wear compressor starts first. Subsequent
stage increases start the next lowest wear compressor.
The final stage increase starts the last compressor.
Each stage decrease de-energizes the highest wear
compressor first.
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The lowest wear compressor from either circuit starts
first. The second stage increase starts the next lowest
wear compressor from the “Off” circuit. Subsequent
stage increase requests will start the lowest wear
compressor available. Stage decreases with both
circuits active, the highest wear running compressor
that will not cause a circuit to stop will be chosen. If
there is only one compressor running per circuit the
compressor with a higher wear calculation will be
chosen to stop.
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If multiple compressors with equal wear are available
for the next stage, the smallest compressor will start.
The largest compressor will stop.
If Balanced Starts is Disabled from the Front Panel,
compressor staging follows the factory staging
sequence. The nominal unit size configuration setting
maps to the factory staging sequence selection.
Compressor Protections
There are a number of functions which provide
protection of the refrigerant systems during
compressor operation. These protections typically
involve reducing, if not completely removing, one or
more compressors from operation on a given
refrigeration circuit. There are basically two types. The
first are Lockouts which are those associated with
diagnostics and are persisted until human intervention
or significant unit mode change occurs, The second are
Inhibits which are typically temporary, self-correcting,
and may not involve a diagnostic.
Working in concert with compressor protection are the
general algorithms of compressor staging (timing) as
well as refrigeration and electrical capacity control.
Low Ambient Lockout
Low Ambient Lockout prevents compressor operation
when Outdoor Air Temperature Active falls below an
adjustable setpoint. The low ambient lockout setpoint
range and default value is dependent on unit
configuration. When the outdoor air temperature rises
above the Low Ambient Lockout Se 5˚F, inhibit
will be removed and the compressors will be available.
Low Compressor Suction Pressure
Protection
The Low Compressor Suction Pressure diagnostic, Low
Compressor Suction Pressure Start Inhibit, and Low
Compressor Suction Pressure Limit work together to
prevent damage to compressors and suction cooled
compressor motors operating with little or no
refrigerant charge.
The Low Compressor Suction Pressure diagnostic
protects against an inadvertent compressor start when
the system is in a vacuum (such as can be produced
during service procedures). It also avoids compressor
failures and extremely inefficient operation due to total
charge loss. The Low Compressor Suction Pressure
diagnostic will shut down the affected circuit, if already
running, when the circuit’s Compressor Suction
Refrigerant Pressure measurement drops below a
factory determined pressure threshold value for
normal operation (normal threshold value). When the
circuit is not running, and for a period of time (in
seconds) immediately after the circuit starts running,
the effective start-up pressure threshold is lower than
the normal threshold value. These values are
dependent on unit model.
The Low Compressor Suction Pressure Start Inhibit and
Low Compressor Suction Pressure Limit work together
to reduce the likelihood of Low Compressor Suction
Pressure diagnostic, which will lock out the circuit and
force a manual diagnostic reset. When either functions
are active, an indication will be made to the user
interface.
The Low Compressor Suction Pressure Start Inhibit is
designed to prevent a circuit from starting when low
compressor suction pressure exists, but will not shut
down a circuit that is already running. When the
function is in the Active state, the circuit will be
prevented from operating (locked out). The threshold
value for this function is 1.2 times the normal threshold
value.
Low Compressor Suction Pressure Limit only applies to
circuits which have more than 1 compressor installed.
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