AAON VCCX2 User Manual

43VCCX2 Controller Technical Guide
SEQUENCE OF OPERATIONS
Modes of Operation
Make-up Air Operation
Occupied Mode
The VCCX2 will use the normal Cooling and Heating Mode
Enable Setpoints (not the Hood On Setpoints) in conjunction with
the Outdoor Air Temperature Sensor to determine the mode of
operation. The Outdoor Air Dewpoint Setpoint will initiate the
Dehumidication Mode. The outdoor air damper will be modulated
to the economizer minimum damper position (normally set at 100%
for a MUA unit).
Unoccupied Mode
Normally, an MUA unit is off during the Unoccupied Mode.
However, if the unit has return air, it can be congured to operate
as a recirculating night setback controlled unit during unoccupied
hours. This is accomplished by simply conguring Night Setback
Temperature Setpoints (anything other than the default 30ºF) on a
unit that is also congured for outdoor temperature control (MUA).
With this conguration, when the unit goes Unoccupied, it will close
the outdoor air damper and begin to use a Space Temperature Sensor
in conjunction with the existing Heating and Cooling Setpoints,
oset by the night setbacks, to make night setback calls. If a
Space Humidity Sensor is installed, and the unit is congured for
night humidity control, the VCCX2 Controller will use the Space
Humidity Setpoint for Unoccupied Dehumidication calls.
DX-DOAS Operation
When the VCCX2 is congured for DX-DOAS operation it requires
the outdoor air damper to be 100% open and have an EBUS supply
air temperature and humidity sensor installed. Modes of operation
are determined the same way a unit congured as a Make-up Air
would calculate its modes. The main dierence is when the unit is in
dehumidication mode it will try to control to a supply air dewpoint
setpoint. To achieve the Supply Air Dewpoint setpoint, the VCCX2
will monitor the supply air dewpoint and will rest the Coil Setpoint
the RSM modules use to control the compressors.
Constant Air Volume/Make-up Air Dual Mode
(Hood On/O󰀨 Operation)
The VCCX2 can be congured as a CAV controller but switch to
MUA operation when an exhaust hood is energized. This MUA
Force Mode occurs when a 24 VAC wet contact closure is received
on the hood on binary input on the VCCX2. Under normal operation
(CAV), the unit will operate as a recirculating space temperature
(and space humidity) controlled unit. This sequence should not be
used on a VAV unit.
When the hood on contact is made, the unit will open the outdoor air
damper to its full open position. The Heating and Cooling Modes
are determined by the Outdoor Air Temperature Sensor using the
hood on Outdoor Air Heating and Cooling Setpoints which are used
only in hood on operation.
Dehumidication is initiated by an Outdoor Dewpoint Setpoint. If
using reverse building pressure control using the outdoor air damper,
the hood on input will not aect the damper position.
When the Hood On Force Mode is removed, the unit will revert to
CAV operation with the outdoor damper returning to its minimum
position (unless economizer operation is enabled) and with mode
control initiated by the Space Temperature and Humidity Sensors.
Commercial Kitchen MUA
When the VCCX2 is congured to enable Commercial Kitchen
MUA Control, the controller will control the amount of air being
brought into the building to make up for the air being exhausted.
The air being exhausted is controlled by a separate control system
that sends the VCCX2 a 0-10 VDC signal on analog input 6 based
on its exhaust demand. The VCCX2 uses the voltage signal being
sent to it to calculate its OA damper position.
Three setpoints are used for determining where the OA damper
should be positioned to bring in the correct amount of outdoor
air. The MUA Min setpoint is the amount of CFM when 0 VDC is
present on analog input 6. The MUA Max setpoint is the amount
of CFM when 10 VDC is present. The Fan Speed Factor setpoint
is used to calculate how far open the OA damper needs to be to get
the required CFM based on the current fan speed.
When the MUA CFM Priority is checked the outdoor air damper will
modulate solely based on the 0-10 VDC coming from the Exhaust
system and the supply fan speed. When the MUA CFM Priority is
unchecked it will use the higher value between the normal ECON
desired output and the exhaust calculated desired output.
CAUTION: If the ECON dampers need more air, it will
override the Exhaust and possibly over pressurize
the kitchen.
Space Temperature Control of High
Percentage Outdoor Air Units
This option allows for space temperature control of 100% outdoor
air units or units with a high percentage of outdoor air (normally
50% or greater). Congure “Space Temperature w/High Percentage
OA” for the controlling sensor option. The intent of this sequence is
to allow space temperature and humidity control of the unit while
preventing the dumping of hot or cold outside air into the space
during the Space Vent Mode of operation. If a Return Air Humidity
Sensor is available, it can be congured to initiate dehumidication.
As long as there is a space temperature call for Cooling or Heating
or if there is a Space Dehumidication call, the unit will remain
under space control.

AAON VCCX2 Specifications

General

Brand	AAON
Model	VCCX2
Category	Controller
Language	English