AAON VCCX2 User Manual

46VCCX2 Controller Technical Guide
SEQUENCE OF OPERATIONS
Modes of Operation
Sump Drain Enable Operation
If the sump temperature is below the Sump Drain Enable Setpoint
for one minute, the sump pump drain relay will enable. The sump
drain enable relay can be disabled in one of two ways:
1. Cycle power to the VCCX2 when the sump temp is above
the Sump Drain Enable Setpoint or
2. Use BACnet point AV:94 Sump Drain Override. The
building management system (BMS) needs to set AV:94
to a value of 1 and back to 0 when the sump temp is above
the Sump Drain Enable Setpoint.
Chemical Mixing Mode
If the VCCX2 is congured to allow chemical mixing, a Chemical
Mixing Mode can occur if the evaporative condenser pump hasn’t
ran for 23 hours. If 23 hours has elapsed the Chemical Mixing
Mode will occur the next time the controller’s clock time equals the
Chemical Mixing Force Time setpoint. When this mode occurs the
unit will shutdown and enable the condenser pump for the Chemical
Mixing Run Time setpoint duration. Once the chemical mixing
time is nished the unit will stay o for the Chemical Mixing Dry
Time setpoint duration. When the dry time is nished the unit will
turn back on.
Waterside Economizer Operation
If the unit is equipped with a waterside economizer, the following
describes the operation of the waterside economizer valve, the
waterside economizer bypass valve, and the condenser valve
operation during the dierent modes.
Unit O󰀨 Mode and Unit Vent Mode
The waterside economizer, bypass, and condenser valves will be
closed.
Unit Cooling Mode
If in Cooling Mode, the entering water temperature is below the
entering air temperature (measured by the sensor connected to the
outdoor temperature sensor input), by the entering water control
deadband amount, the waterside economizer valve will modulate to
maintain the Cooling Supply Air Setpoint. The bypass and condenser
valves will remain closed.
If the waterside economizer valve opens to 100% and cannot
maintain the Cooling Supply Air Setpoint, then the unit will enable
and stage/modulate compressors to maintain the Cooling Supply Air
Setpoint, while the waterside economizer valve is locked at 100%.
The bypass valve will remain closed, while the condenser valve will
modulate to maintain the Head Pressure Setpoint.
If the outdoor air temperature is cooler than the entering water
temperature, the waterside economizer valve will remain closed,
and compressor cooling will stage/modulate to maintain the Cooling
Supply Air Setpoint. The bypass valve will modulate to maintain
the Head Pressure Setpoint, and the condenser valve will be open.
Unit Heating Mode
The waterside economizer valve is closed, while the bypass valve
and condenser valves are open.
NOTE: For waterside economizer bypass wiring, please see
the RSMD Technical Guide.
Waterside Economizer Flush Cycle
If the economizer has been closed for 72 hours, a ush cycle will
be initiated the next time the compressor is activated or at the next
6:00 AM time slot, whichever happens rst. During the ush cycle,
the economizer valve will open for ve minutes and then close again
before the compressor activates. The 72-hour timer will restart once
the ush cycle is completed or the economizer has been activated
and has closed again.
Temperature Protection
Temperature protection is activated when the supply air temperature
rises above the high cuto temperature (immediate) or drops below
the low cuto temperature (for 10 minutes). Both cuto setpoints
are user-adjustable. This mode shuts o the unit.
This mode is canceled when the supply air temperature drops 5ºF
below the High Cuto Temperature Setpoint or rises 5ºF above the
Low Temp Cuto Temperature Setpoint or when the unit changes
back into Occupied Mode.
Outdoor Air Lockouts
The compressors are disabled during Cooling Mode when the
outdoor air temperature is below the Compressor Cooling Lockout
Setpoint. Mechanical heating is disabled when the outdoor air
temperature is above the Heating Lockout Setpoint.
For air to air heat pumps, the compressors are disabled during
Heating Mode when the outdoor air temperature is below the
Compressor Heating Lockout Setpoint.
NOTE: Compressors can also be forced to be locked out
using BACnet point AV: 98 Emergency Compressor
Lockout.
System Broadcasts
The VCCX2 Controller can be congured to broadcast building
pressure, outdoor air temperature, outdoor air humidity, space
temperature, space humidity, and CO
2
to any VCCX2 Controller
that does not have one or more of these sensor(s). A CommLink 5
or MiniLink PD 5 is required to broadcast these values.

AAON VCCX2 Specifications

General

Brand	AAON
Model	VCCX2
Category	Controller
Language	English