AAON VCCX2 User Manual

41VCCX2 Controller Technical Guide
SEQUENCE OF OPERATIONS
Modes of Operation
Duct Static Pressure Control
If the VCCX2 Controller has been congured for duct static pressure
control, then anytime the supply fan is operating, the unit will be
controlling to a Duct Static Pressure Setpoint. The static pressure
control output signal can be used to control a supply fan VFD (direct
acting operation), or a zoning or bypass damper actuator (reverse
acting operation).
The Duct Static Pressure Setpoint, the setpoint deadband, the static
pressure control signal, and the static control rate are all user-
adjustable. The static control rate is the amount of time that elapses
between each adjustment to the duct static pressure control output
signal. The default period is 10 seconds and should not be changed
unless close observation reveals that the supply fan or bypass damper
is hunting and not maintaining a stable pressure reading.
For supply fan VFD operation, the output signal increases (increases
the VFD speed) if the duct static pressure is below the Duct Static
Pressure Setpoint by the deadband amount, and the output signal
decreases (decreases VFD Speed) if the static pressure is above the
Setpoint by the deadband amount.
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 higher than 0.5” water column above
the Duct Static Pressure Setpoint, the duct static pressure control
output signal value will be reduced by a maximum adjustment of
15% every control period until the static pressure is brought under
control or the VFD fan minimum has been met. This is to prevent
damage to the ductwork if all the VAV boxes are closed or some
other blockage occurs in the ductwork.
Any time the supply fan is o, the duct static pressure control
output signal will remain at 0 V. If duct static pressure control is
not congured, the static pressure can still be monitored if a Static
Sensor is installed, however, no control will occur.
WARNING: The manufacturer does not assume
responsibility for protecting the equipment
from over-pressurization. Always install
mechanical high static protection cutos to
protect the system.
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 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
to poll the VAV boxes for their damper position.
Duct Static Pressure Control for Filter Loading
In order to maintain a constant cubic feet per minute through the
supply air ducts on a mixed air constant air 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 lters are
getting dirty, the VCCX2 will ramp up the VFD to compensate
for the decrease in airow. To utilize this feature, the unit must be
congured 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 congured for single zone VAV
operation.
Exhaust Duct Static Pressure Control of Exhaust Fan
The VCCX2 Controller can control an exhaust fan based o of
exhaust duct static pressure. This sequence will require the use of
the VCC-X EM1 Expansion Module which has a modular jack that
the Duct Static Pressure Sensor will plug into. The building pressure
output will be used to control the exhaust fan for this operation.
A standard pull-through exhaust fan creates negative duct static
pressure. Since a Duct Static Pressure Sensor reads positive pressure,
this sequence requires the tubing for the sensor to be reversed so
that the low side is in the exhaust ductwork. So, although the user
is actually controlling to a negative pressure, the VCCX2 will be
congured to use (and will display) an equivalent positive Exhaust
Duct Static Pressure Value and Setpoint. So, if the duct static
pressure is below setpoint, the control signal will ramp up.
See the VCCX2 Controller Operator Interfaces SD Technical Guide
for the setpoint and deadband ranges associated with this control.
The control rate is the same as the control rate congured for the
supply duct static pressure control.
.

AAON VCCX2 Specifications

General

Brand	AAON
Model	VCCX2
Category	Controller
Language	English