FORM
Purge
When this purge sequence is selected and activated, the Supply Fan is controlled ON and the Exhaust Fan is controlled ON. The Outside Air damper is opened full and the Return Air damper is closed full. If the unit is a VAV unit, the VAV boxes are also driven full open to prevent duct
Purge With Duct Pressure Control (VAV Only)
When this purge sequence is selected and activated, the Supply Fan is cycled ON and controlled to maintain the duct static pressure setpoint. The Exhaust Fan is also controlled ON (Exhaust Damper driven full open) and the Outside Air Damper is driven full open. This mode is maintained until the smoke purge input is de- activated and the unit returns to normal operation.
VAV SPECIFIC SEQUENCES
Supply fan operation
For VAV units, the supply fan is controlled ON and OFF based on the occupancy state or the G input from a Thermostat (Unit must be configured for Thermostat operation to respond to the G input). When the unit goes into the Occupied mode of operation (or “G” is called) the Supply Fan will be controlled ON. The OptiLogic™ controller will monitor the static pressure within the supply duct system and control the speed of the supply fan to maintain a specified Duct Static Pres- sure setpoint. A Variable Frequency Drive (VFD) is used on all VAV units to vary the speed of the supply fan. Note, the use of a VFD in lieu of inlet guide vanes pro- vides for higher energy efficiency for the unit by elimi- nating the losses (air pressure drop) typical of inlet guide vane systems.
COOLING OPERATION
Thermostat Control
When a VAV unit is configured for thermostat opera- tion, the OptiLogic™ controller will command the Sup- ply Fan to start when the unit goes into the Occupied mode or a thermostat “G” signal is received by the con- trol. With no thermostat calls for cooling, the unit shall remain idle with the Supply Fan operating as required.
When a Cooling Stage 1 call (“Y1”) is received, and the unit is equipped with an economizer, the OptiLogic™ controller will check the Outside Air conditions to de- termine if conditions are suitable for economizing and modulate the outside air damper and or stage up com- pressors as required to maintain the VAV High Supply Air Temperature Setpoint. This setpoint is user select- able at the OptiLogic™ User Interface. The OptiLogic™ controller will control to this setpoint as long as Cooling Stage 1 (“Y1”) remains active.
When a Cooling Stage 2 call (“Y2”) is received, and the unit is equipped with an economizer, the OptiLogic™ controller will check the Outside Air conditions to de- termine if conditions are suitable for economizing and modulate the outside air damper and or stage up com- pressors as required to maintain the VAV Low Supply Air Temperature Setpoint. This setpoint is user select- able at the OptiLogic™ User Interface. The OptiLogic™ controller will control to this setpoint as long as Cooling Stage 2 (“Y2”) remains active.
The VAV High SAT Setpoint is always greater than the VAV Low SAT Setpoint and because of this essentially makes this control sequence a Supply Air Tempera- ture Reset algorithm based on Zone Temperature.
Zone Sensor Control
When a VAV unit is configured for Zone Sensor opera- tion, the OptiLogic™ controller will monitor a reference Zone Temperature and command the Supply Fan to start when the unit goes into the Occupied mode.
If the zone temperature is above the VAV Setpoint for SAT Reset, the OptiLogic™ controller will modulate the outside air damper (Economizer available and condi- tions suitable) and/or stage compressors up and down, as required, to maintain the VAV High Supply Air Tem- perature Setpoint.
If the zone temperature is below or falls below the VAV Setpoint for SAT Reset, the OptiLogic™ controller will modulate the Outside Air Damper (Economizer avail- able and conditions suitable) and/or stage compres- sors up and down, as required, to maintain the VAV Low Supply Air Temperature Setpoint.
As with thermostat operation, this sequence is also a Supply Air Temperature Reset algorithm based on Zone Temperature.
YORK INTERNATIONAL | 29 |
