FORM 100.50-EG1
29
YORK INTERNATIONAL
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 over-pressurization. This mode is main-
tained until the smoke purge input is deactivated and
the unit returns to normal operation.
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.
