AAON VCCX2 User Manual

42VCCX2 Controller Technical Guide
SEQUENCE OF OPERATIONS
Modes of Operation
Building Pressure Control
The VCCX2 can maintain building static pressure anytime the
supply fan is operating. A building pressure transducer must be
connected to the VCCX2 Controller. The following are the available
control options.
Direct Acting Building Pressure Control
On/O󰀨 Exhaust Fan
If an on/o exhaust fan is being used, a relay output must be
congured for “Exhaust Fan”. This relay will energize whenever
the building pressure rises above the Building Pressure Setpoint
by the deadband amount. The relay will de-energize when the
building pressure falls below the Building Pressure Setpoint by
the deadband amount.
Exhaust Fan VFD or Modulating Exhaust Damper
If congured for modulating exhaust, a user-adjustable voltage
output (AO4 – Building Pressure Output) will be used to control
this fan or damper. An exhaust relay can be congured if necessary
to enable the fan or damper. Whenever the building pressure rises
above the Building Pressure Setpoint by the deadband amount,
the exhaust fan relay will energize and the modulating signal will
activate to control to the Building Pressure Setpoint. If the building
pressure falls below the Building Pressure Setpoint by the deadband
amount, the modulating signal will modulate towards 0% as it
attempts to maintain the Building Pressure Setpoint. The exhaust
fan relay is energized whenever the modulating signal is above 0%.
Return Fan Tracking of Supply Fan Control
As the supply fan operates, the return fan will follow the supply
fan speed signal and operate at 100% (adj.) of its signal. The return
fan will operate and modulate down toward its minimum speed
percentage 0% (adj.).
Return Fan Tracking of Supply Fan Control with
Motorized Exhaust Damper
As the supply fan operates, the return fan will follow the supply
fan speed signal and operate at 100% (adj.) of its signal. The return
fan will operate and modulate down toward its minimum speed
percentage 0% (adj.). The exhaust damper will modulate to control
the return plenum pressure .01” WG (adj.) plus the return plenum
pressure deadband of .01” while the return exhaust fan is enabled.
As the plenum pressure rises above .01” WG., the control signal
will modulate open to achieve setpoint. As the plenum pressure falls
below .01” WG., the modulating exhaust damper will decrease to
build pressure.
Reverse Acting Building Pressure Control
Outdoor Air Damper
If this option is congured, the VCCX2 will use the user-adjustable
economizer/outdoor air damper output signal (AO2 – Economizer
Control Signal) to maintain the Building Pressure Setpoint.
Whenever the building pressure falls below the Building Pressure
Setpoint by the deadband amount, the modulating economizer
output signal will modulate the damper open to control to the
Building Pressure Setpoint. If the building pressure rises above the
Building Pressure Setpoint by the deadband amount, the damper
will modulate towards closed as it attempts to maintain the Building
Pressure Setpoint. When this option is selected, no economizer free
cooling or CO
2
indoor air quality operation will be available.
Supply Fan VFD
Careful consideration should be made regarding the eects of
potential reduced airow when using this option. If this option
is selected, the supply fan VFD output (AO1 - Main Supply Fan
VFD) will be used to control the supply fan VFD to maintain the
Building Pressure Setpoint in similar fashion to the outdoor air
damper control described above.
NOTE: If reverse acting building pressure control using the
outdoor air damper is congured, the hood on input
is ignored and will not drive the outdoor air damper
open.
Return Plenum Pressure Control
The VCCX2 Controller can control the return plenum pressure using
a motorized exhaust damper. This is used on certain RNZ units that
have a return fan that will be used to control building static pressure.
This sequence will require the use of the VCC-X EM1 Expansion
Module which has an input for a return plenum pressure transducer
(the same transducer used for the building pressure control) and
an analog output that is wired to the actuator used to control the
motorized exhaust damper. When the return fan is active (based
on building pressure) the motorized exhaust damper will modulate
to control the Return Plenum Pressure Setpoint. If the pressure is
above the setpoint the modulating signal will move towards 100%.
If the pressure is below setpoint the modulating signal will move
towards 0%.
If the return fan shuts o and the building pressure drops below
the Building Pressure Setpoint by more than three times the Build
Pressure Deadband, the economizer will modulate to meet the
Building Pressure Setpoint. The Economizer will modulate between
the Economizer Minimum Position setpoint and the Maximum
Economizer in Heating Mode setpoint.
If for any reason the economizer is equal to or greater than 90%
open and the building pressure rises above the Building Pressure
Setpoint plus the Building Pressure Deadband, the return fans will
be enabled. Before the fans are turned on, the motorized exhaust
damper will open to 30% and wait 30 seconds to turn on the return
fans. This is done to prevent any damage to either the return or
exhaust damper assemblies.

AAON VCCX2 Specifications

General

Brand	AAON
Model	VCCX2
Category	Controller
Language	English