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VCCX2 Controller Technical Guide
For Bypass Damper operation, the VCCX2 will reverse the logic
of the Output Signal. The Output Signal decreases (closes the
Zoning Bypass Damper) if the Duct Static Pressure is below the
Duct Static Pressure Setpoint by the Deadband amount, and the
Output Signal increases (opens the Zoning Bypass Damper) if the
Duct Static Pressure is above the Duct Static Pressure Setpoint
by the Deadband amount.
If the Static Pressure ever rises 0.5” W.C. above the Duct Static
Pressure Setpoint, the Duct Static Pressure Control Output
Signal value will be cut by .15” W.C. every control period until
the Static Pressure is brought under control. This is to prevent
damage to the ductwork if all the VAV boxes are closed or some
other blockage occurs in the ductwork.
WARNING:
The manufacturer does not assume
responsibility for protecting the equipment
from over-pressurization. You should
always install mechanical high static
protection cutoffs to protect your system.
Any time the Supply Fan is off, the Duct Static Pressure Control
Output Signal will remain at 0 V. If Duct Static Pressure Control
is not configured, the Static Pressure can still be monitored if a
Static Sensor is installed, however, no control will occur.
Duct Static Setpoint Reset
If the VCCX2 Controller is being used with AAON VAV box
controllers in a VAV system, the Duct Static Pressure Setpoint
can be dynamically reset based on the most-open VAV box
associated with that unit. As long as the most-open box is less
than 80% open, the Duct Static Setpoint will be decrease at a
user-adjustable Reset Rate from the Max Static Pressure Reset
Limit Setpoint down to the Minimum Static Pressure Reset Limit.
Once the most-open box exceeds 80%, the setpoint will increase
toward the Maximum Static Pressure Reset Limit Setpoint. A
MiniLink PD 5 is required in order to poll the VAV boxes for
their damper position.
Duct Static Pressure Control for Filter
Loading
In order to maintain a constant CFM through the supply air
ducts on a mixed air CAV unit, the VCCX2 can utilize a Duct
Static Pressure Sensor (used to monitor the discharge pressure)
in conjunction with a Supply Fan VFD. If the filters are getting
dirty, the VCCX2 will ramp up the VFD to compensate for
the decrease in airflow. To utilize this feature, the unit must be
configured to use VFD Fan Control. This feature cannot be used
if this is a VAV or Zoning application with typical Duct Static
Pressure Control, or if this unit has been configured for Single
Zone VAV operation.
SEQUENCE OF OPERATIONS
Duct Static Setpoint Reset and Duct Static Pressure Control
