ACC-APG001A-EN
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General Support Sequences
Fan Setpoints with VFD-driven Fan Types
When a system is equipped with a VFD, the minimum and maximum VFD parameters can be
adjusted to tune the airflow to meet the application requirements.
In addition to this, the Symbio 700 supports setpoints that can adjust airflow as needed:
• Supply Fan Maximum Speed Setpoint
– Range: 67-100%
– Operation: This setpoint “trims” the maximum fan speed, based on the configured
maximum VFD speed
– Example: VFD Max = 60Hz
• Supply Fan Maximum Speed Setpoint @ 75% yields a maximum of 45Hz VFD output.
• Effective VFD Max (to be used in Supply Fan Minimum Speed Setpoint application)
will be set to 45Hz
• Supply Fan Minimum Speed Setpoint
– Range: 0-100%
– Operation: 0-100% over minimum to effective maximum VFD configured fan speed
– Example: VFD Min = 30Hz, Effective VFD Max = 60Hz
• Supply Fan Minimum Speed Setpoint @ 50% yields 45Hz VFD output.
• Minimum and Maximum Speed Setpoints interact to ensure that the minimum defined fan
speed at a given equipment operating condition is maintained.
Compressor Minimum Runtime
Under all normal running conditions, a 3–minute minimum ON and OFF timer is maintained for
each compressor. Once a compressor is turned ON, it remains on for a minimum of 3 minutes.
Once a compressor is turned OFF, it remains off for a minimum of 3 minutes. System overrides
that require immediate shutdown of the equipment, test modes, and compressor diagnostics/
protection functions can override these 3–minute timers. However for normal temperature and
thermostatic-based control, these minimum ON/OFF timers are maintained.
Refrigeration Circuit Management
There are two refrigeration configurations that the controller will use to determine proper
response to refrigeration system faults:
• When the unit is configured with a MMaanniiffoolldd refrigeration system, if any compressor
protection device or function trips for a given compressor, all compressors associated with
the circuit on which the protection device or functions trips will be commanded to OFF.
• When the unit is configured with an IInnddeeppeennddeenntt refrigeration system, if any compressor
protection device or function trips, for a given compressor, only the compressor associated
with the protection device or function that tripped will be commanded to OFF.
Compressor Proof of Operation
For each compressor. a Compressor Proving binary input is used to monitor the state of an
auxiliary switch that is used to indicate compressor motor contactor status. Under normal
operation, detected operation indicates that all safety devices within the compressor safety
circuit are in their normal state. The switch operates as OPEN when the compressor motor is OFF
and CLOSED when the compressor motor is ON.
Refer to the Diagnostics section below for specific diagnostics that are generated based on the
Compressor Proving signals.
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