AAON VCCX2 User Manual

40VCCX2 Controller Technical Guide
SEQUENCE OF OPERATIONS
Modes of Operation
In all cases, as the reset source value moves within its range
established by the congured High and Low Reset Setpoints, the
Supply Air Setpoint will be proportionally reset within its range
established by the congured Low and High Supply Air Temperature
Setpoints.
If a remote supply air temperature reset signal is congured as
the reset source, a congurable voltage signal (between 0 and 10
VDC, direct or reverse acting) can be used to reset the Supply Air
Temperature Setpoint. The voltage that corresponds to the Low
Supply Air Temperature Setpoint and to the High Supply Air
Temperature Setpoint in both the Heating and the Cooling Modes
is user-congurable.
NOTE: This supply air temperature reset cannot be used on
a single zone VAV unit.
Airow Monitoring
Outdoor, supply, return and exhaust airow can be monitored using
the EBTRON GTC116 or HTN104 series, Paragon MicroTransEQ or
MTSE series, or GreenTrol GA-200-N Module in conjunction with
a GreenTrol GF series of airow station. Contact AAON Controls
for information on other airow station options. The VCCX2 will
control the outdoor air damper to maintain an Outdoor Air Cubic
Foot per Minute Setpoint. This operation can be overridden higher
by normal economizer control.
On an MUA unit or a unit congured for space control of high
percentage outdoor air, since the damper is typically at 100%, the
VCCX2 can be congured to modulate the supply fan VFD to
maintain an Outdoor Cubic Foot per Minute Setpoint.
Preheater Operation
A preheat relay can be congured to energize anytime the supply fan
is operating and the outdoor air temperature is below the Preheat
Setpoint. This option allows preheating of cold outside air before
it reaches the evaporator coils and is useful in hot water/chilled
water applications or during CO
2
control of the economizer in low
temperature conditions. This operation only occurs in the Occupied
Mode.
If using the PREHEAT-X, an SCR Preheater and/or stages of preheat
can be controlled. If the entering air temperature (sensor connected
to the PREHEAT-X) falls below the Preheat Setpoint, then preheat
will be controlled to either a Cooling, Heating or Vent Mode
Preheater Leaving Air Setpoint — depending on if the VCCX2 is
currently in the Cooling, Heating, or Vent Mode. These setpoints
are all set in the VCCX2 Controller.
If using the PREHEAT-X in conjunction with the VCCX2 Controller,
the entering air temperature on the PREHEAT-X (instead of
the Outdoor Air Temperature Sensor connected directly to the
VCCX2 Controller) will be used as the temperature that locks out
compressors during heat pump heating mode. See the PREHEAT-X
Module Technical Guide for more details.
Low Ambient Operation
A low ambient relay can be congured. Whenever the outdoor air
temperature falls below the Low Ambient Setpoint, this low ambient
relay will energize. This operation occurs in both the Occupied and
Unoccupied Modes of Operation.
Heat Wheel
One of the relay outputs can be congured as a heat wheel relay.
This relay will enable the heat wheel when the unit goes into the
Occupied Mode. If the unit is a recirculating unit congured to use
economizer free cooling, the relay will disable during economizer
operation.
If the unit is a 100% outdoor air unit congured to use the Outdoor
Air Sensor as the controlling sensor, then the heat wheel relay will
disable in between the outdoor air Cooling and Heating Mode
Enable Setpoints (Outdoor Air Vent Mode). Similarly, on a unit
congured for space control of high percentage outdoor air, and
the unit is in Outdoor Air Vent Mode, the wheel is disabled. The
controller can also be congured to disable the heat wheel relay
between High and Low Outdoor Air Enthalpy Setpoints.
Heat Wheel Defrost
A Defrost Mode will occur if the heat wheel relay is active, the
outdoor air temperature is below the Heat Wheel Defrost Setpoint,
and 30 minutes have elapsed since the last Defrost Mode. The
Defrost Mode will disable the heat wheel relay for two minutes.
Before the heat wheel relay disables, a two minute delay will occur
while the economizer closes to a 10% position to allow the return
air to have maximum defrost eect on the wheel. At the end of the
Defrost Mode, the heat wheel relay will enable, and the economizer
will return to its normal position. This 10% re-positioning will
not occur on units congured for MUA control (Outdoor Air is
the controlling sensor), or for units in hood-on operation, or for
units that are congured for space temperature control of a high
percentage of outdoor air.

AAON VCCX2 Specifications

General

Brand	AAON
Model	VCCX2
Category	Controller
Language	English