AAON Orion VCCX2 Technical Manual

Also see for Orion VCCX2: Technical guide Technical guide Technical guide

Contents

AAON Orion VCCX2 Technical Manual Manual pdf 72 page image

ZoneZoneSEQUENCE OF OPERATIONSVCCX2 Controller Technical Guide72Duct Static Pressure Control & Building Pressure ControlDuct Static Pressure Control for FilterLoadingIn order to maintain a constant CFM through the supply air ducts ona mixed air CAV unit, the VCCX2 can utilize a Duct Static PressureSensor (used to monitor the discharge pressure) in conjunction witha Supply Fan VFD. If the filters are getting dirty, the VCCX2 willramp up the VFD to compensate for the decrease in airflow. To utilizethis feature, the unit must be configured to use VFD Fan Control.This feature cannot be used if this is a VAV or Zoning applicationwith typical Duct Static Pressure Control, or if this unit has beenconfi gured for Single Zone VAV operation.Building Pressure ControlThe VCCX2 can maintain Building Static Pressure anytime theSupply Fan is operating. A Building Pressure Transducer must beconnected to the VCCX2 Controller. The following are the availablecontrol options.Direct Acting Building Pressure Control• On/Off Exhaust Fan—If an On/Off Exhaust Fan isbeing used, a relay output must be configured for“Exhaust Fan”. This relay will energize whenever theBuilding Pressure rises above the Building PressureSetpoint by the Deadband amount. The relay will de-energize when the Building Pressure falls below theBuilding Pressure Setpoint by the Deadband amount.• Exhaust Fan VFD or Modulating Exhaust Damper—If configured for Modulating Exhaust, a user-adjustable voltage output (AOUT4 – Building PressureOutput on the VCCX2 Controller) will be used tocontrol this fan or damper. An Exhaust Relay can beconfigured if necessary to enable the fan or damper.Whenever the Building Pressure rises above theBuilding Pressure Setpoint by the Deadband amount,the Exhaust Fan Relay will energize and the ModulatingSignal will activate to control to the Building PressureSetpoint. If the Building Pressure falls below the Build-ing Pressure Setpoint by the Deadband amount, theModulating Signal will modulate towards 0% as itattempts to maintain the Building Pressure Setpoint.The Exhaust Fan Relay is energized whenever theModulating Signal is above 0%.Reverse Acting Building Pressure Control• Outdoor Air Damper—If this option is configured,the VCCX2 will use the user-adjustable Economizer/Outdoor Air Damper output signal (AOUT2 –Economizer Control Signal) to maintain the BuildingPressure Setpoint. Whenever the Building Pressurefalls below the Building Pressure Setpoint by theDeadband amount, the modulating Economizer OutputSignal will modulate the damper open to control tothe Building Pressure Setpoint. If the Building PressureDuct Static Pressure ControlIf the VCCX2 Controller has been configured for Duct Static PressureControl, then anytime the Supply Fan is operating, the unit will becontrolling to a Duct Static Pressure Setpoint. The Static PressureControl 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 StaticPressure Control Signal, and the Static Control Rate are all user-adjustable. The Static Control Rate is the amount of time that elapsesbetween each adjustment to the Duct Static Pressure Control OutputSignal. The default period is 10 seconds and should not be changedunless close observation reveals that the Supply Fan or BypassDamper 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 theDuct Static Pressure Setpoint by the Deadband amount, and theOutput Signal decreases (decreases VFD Speed) if the Static Pressureis above the Setpoint by the Deadband amount.For Bypass Damper operation, the VCCX2 will reverse the logicof the Output Signal. The Output Signal decreases (closes theZoning Bypass Damper) if the Duct Static Pressure is below theDuct Static Pressure Setpoint by the Deadband amount, and theOutput Signal increases (opens the Zoning Bypass Damper) if theDuct Static Pressure is above the Duct Static Pressure Setpoint bythe Deadband amount.If the Static Pressure ever rises 0.5” above the Duct Static PressureSetpoint, the Duct Static Pressure Control Output Signal will be cutin half every control period until the Static Pressure is brought undercontrol. This is to prevent damage to the ductwork if all the VAVboxes are closed or some other blockage occurs in the ductwork.WARNING: The manufacturer does not assume responsibilityfor protecting the equipment from over-pressurization! Youshould always install mechanical high static protection cutoffsto protect your system!Any time the Supply Fan is off, the Duct Static Pressure ControlOutput Signal will remain at zero volts. If Duct Static PressureControl is not configured, the Static Pressure can still be monitoredif a Static Sensor is installed, however, no control will occur.Duct Static Setpoint ResetIf the VCCX2 Controller is being used with AAON VAV boxcontrollers in a VAV system, the Duct Static Pressure Setpoint canbe dynamically reset based on the most-open VAV box associatedwith that unit. As long as the most-open box is less than 80% open,the Duct Static Setpoint will be reset downward at a user-adjustableReset Rate from the Max Static Pressure Reset Limit Setpoint downto the Minimum Static Pressure Reset Limit. Once the most-openbox exceeds 80%, the setpoint will begin to be reset back up towardthe Maximum Static Pressure Reset Limit Setpoint. A MiniLink PD5 is required in order to poll the VAV boxes for their damper position.