FORM 100.50-EG3 (802)
57
YORK INTERNATIONAL
For these applications, the unit must be equipped with
optional Low Ambient controls. For optional Low Ambi-
ent operation, the OptiLogic
™
controller monitors the
refrigeration system discharge pressure and controls
the speed of the condenser fans. If the discharge pres-
sure falls, the speeds of the condenser fans are re-
duced to maintain acceptable condensing pressures in
the refrigeration system. With the optional Low Ambi-
ent controls, mechanical cooling is allowed down to
Outside Air temperatures of -17.7°C.
SMOKE PURGE SEQUENCES
General
As a convenience, for when buildings catch fire or the
building is inundated with smoke or fumes from manu-
facturing processes, etc., the OptiLogic
™
control sys-
tem provides one of five ventilation override control
sequences for building purge. The five selectable purge
sequences are, Shutdown, Pressurization, Exhaust,
Purge and Purge with duct pressure control. Note, when
any of the purge sequences are activated, cooling and
heating modes are disabled. A contact closure input is
provided which indexes the OptiLogic
™
controller into
the selected purge sequence.
Shutdown
When this purge sequence is selected and activated,
the supply and exhaust fans are controlled OFF and
the Outside Air damper is overridden closed. This idle
state is maintained until the purge input is deactivated
and the unit returns to normal operation.
Pressurization
When this purge sequence is selected and activated,
the exhaust fan is controlled OFF and the Supply 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.
Exhaust
When this purge sequence is selected and activated,
the Supply Fan is controlled OFF and the Exhaust Fan
is controlled ON (Exhaust Damper driven full open and
the outside air damper is closed). This mode is main-
tained until the smoke purge input is deactivated and
the unit returns to normal operation.
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 deter-
