AAON OE338-26B-VCCX2 User Manual

87
VCCX2 Controller Technical Guide
Evaporative Condenser Operation
If the unit has been congured for Evaporative Condenser Control
and the Outdoor Air Temperature is above the Evaporative/
Modulating Condenser Low Ambient Setpoint, the Evaporative
Condenser Pump relay will energize to be used as the 1st stage
of head pressure control when the compressors are active.
Modulating condenser fan control will be the 2nd stage.
If the Outdoor Air Temperature is below the Evaporative/
Modulating Condenser Low Ambient Setpoint, the modulating
condenser fan will be used as the 1st stage of head pressure
control, and the Evaporative Condenser Pump relay will energize
as the 2nd stage.
If the head pressure is above the Cooling Head Pressure Setpoint
by the Evaporative Head Pressure Deadband Setpoint, the 2nd
stage of head pressure control will be enabled. At this level below
the cooling head pressure setpoint, the 2nd stage of head pressure
control will be disabled.
Sump Heater Operation
The Sump Heater relay activates if the sump temperature is below
the Sump Heater Enable Temperature Setpoint. The Sump Heater
relay deactivates once the sump temperature rises 10 degrees
above the Sump Heater Enable Temperature Setpoint or if the
Sump Drain relay is active.
Sump Drain Enable Operation
If the Sump Temperature is below the Sump Drain Enable
Setpoint for 1 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 BMS needs to set AV:
94’s value to 1 and back to 0 when the Sump Temp is above the
Sump Drain Enable Setpoint.
Waterside Economizer (WSE)
Operation
If the unit is equipped with a Waterside Economizer (WSE), the
following describes the operation of the WSE Valve, the WSE
Bypass Valve, and the Condenser Valve operation during the
dierent modes.
Unit Off Mode and Unit Vent Mode
The WSE, Bypass, and Condenser Valves will be closed.
Unit Cooling Mode
If in the 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 WSE Valve will modulate
to maintain the Cooling Supply Air Setpoint. The Bypass and
Condenser Valves will remain closed.
If the WSE 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 WSE Valve in 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 WSE 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 WSE Valve is closed, while the Bypass Valve and Condenser
Valves are open.
NOTE: For WSE Bypass Wiring, please see the Refrigerant
System Module for Digital Compressors (RSMD)
Technical Guide.
Waterside Economizer Flush Cycle
If the Economizer has been closed for 72 hours, a Flush 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
Flush Cycle, the Economizer Valve will open for 5 minutes and
then close again. The 72 hour timer will restart once the Flush
Cycle is completed or the Economizer has been activated and
has closed again.
Temperature Protection
Temperature Protection is activated when the Supply Air
Temperature (SAT) 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 cancelled when the SAT drops 5º below the High
Cuto Temperature Setpoint or rises 5º above the Low Temp
Cuto Temperature Setpoint or when the unit changes back into
Occupied Operation.
SEQUENCE OF OPERATIONS
Evaporative Condenser, WSE, OA Lockouts and Temp Protection

AAON OE338-26B-VCCX2 Specifications

General

Brand	AAON
Model	OE338-26B-VCCX2
Category	Controller
Language	English