Orion System VCC-X Controller - Manual (Page 62)

Zone
Zone
SEQUENCE OF OPERATIONS
VCC-X Controller Technical Guide 62
Airfl ow Monitoring
Outdoor, Supply, Return and Exhaust Airfl ow can be monitored
using the EBTRON
® GTC116 series, Paragon MicroTrans EQ series,
or GreenTrol GA-200-N Module in conjunction with a GreenTrol GF
series of airfl ow station. Contact WattMaster Controls for information
on other airflow station options. The VCC-X will control the
Outdoor Air Damper to maintain an Outdoor Air CFM Setpoint. This
operation can be overridden higher by normal Economizer control.
CO
2
override cannot be used in conjunction with airfl ow control of
the Outdoor Air Damper in this version.
Pre-Heater Operation
A Pre-Heat relay can be confi gured to energize anytime the Supply
Fan is operating and the Outdoor Air Temperature is below the
Pre-Heat Setpoint. This option allows pre-heating 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 of Operation.
If using the Preheat-X Controller, 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 Pre-Heat Setpoint, then
preheat will be controlled to either a Cooling, Heating or Vent Mode
Preheater Leaving Air Setpoint - depending on if the VCC-X is
currently in the Cooling, Heating, or Vent mode of operation. These
setpoints are all set in the VCC-X Controller. See the PREHEAT-X
Controller Technical Guide for more details.
Low Ambient Operation
A Low Ambient Relay can be confi 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 confi 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 confi gured for Economizer Operation,
this relay will disable the Heat Wheel when the unit goes into
Economizer Mode. If the Heat Wheel Relay is active, a Heat Wheel
Defrost Cycle will occur that will disable the Heat Wheel Relay for
2 minutes if the Outdoor Air Temperature is below the Heat Wheel
Defrost Setpoint and 30 minutes have elapsed since the last Heat
Wheel Defrost Cycle.
Duct Static Pressure Control
If the VCC-X Controller has been confi gured for Duct Static Pressure
Control, then anytime the Supply Fan is operating, the unit will be
controlling to a Duct Static Pressure Setpoint. The Static Pressure
Control Output Signal can be used to control a Supply Fan VFD
(Direct Acting Operation) or a Zoning Bypass Damper Actuator
(Reverse Acting Operation).
The Duct Static Pressure Setpoint, the Setpoint Deadband, the Static
Pressure Control Signal, and the Static Control Rate are all user-
adjustable. The Static Control Rate is the amount of time that elapses
between each adjustment to the Duct Static Pressure Control Output
Signal. The default period is 10 seconds and should not be changed
unless close observation reveals that the Supply Fan or Bypass
Damper is hunting and not maintaining a stable pressure reading.
For Supply Fan VFD operation, the Output Signal increases
(increases the VFD speed) if the Duct Static Pressure is below the
Duct Static Pressure Setpoint by the Deadband amount, and the
Output Signal decreases (decreases VFD Speed) if the Static Pressure
is above the Setpoint by the Deadband amount.
For Bypass Damper operation, the VCC-X will reverse the logic
of the Output Signal. The Output Signal decreases (closes the
Zoning Bypass Damper) if the Duct Static Pressure is below the
Duct Static Pressure Setpoint by the Deadband amount, and the
Output Signal increases (opens the Zoning Bypass Damper) if the
Duct Static Pressure is above the Duct Static Pressure Setpoint by
the Deadband amount.
If the Static Pressure ever rises 0.5” above the Duct Static Pressure
Setpoint, the Duct Static Pressure Control Output Signal will be cut
in half every control period until the Static Pressure is brought under
control. This is to prevent damage to the ductwork if all the VAV
boxes are closed or some other blockage occurs in the ductwork.
WARNING: The manufacturer does not assume responsibility
for protecting the equipment from over-pressurization! You
should always install mechanical high static protection cutoffs
to protect your system!
Any time the Supply Fan is off, the Duct Static Pressure Control
Output Signal will remain at zero volts. If Duct Static Pressure
Control is not confi gured, the Static Pressure can still be monitored
if a Static Sensor is installed, however, no control will occur.
Airfl ow Monitoring and Duct Static Pressure Control