YORK INTERNATIONAL
56
Controls
(continued)
through the Air Measurement Station. The unit control-
ler shall control the Outside Air damper to this flow rate
as long as the unit is in the Occupied mode, and the
economizer is not suitable for cooling.
Demand Ventilation
If an optional CO
2
sensor is connected to the unit, the
unit controller can reset the minimum OA damper
position(s) or minimum flow rate based on demand.
The unit controller shall monitor the CO
2
level within
the building. If the CO
2
level rises above the CO
2
setpoint,
the controller will temporarily increase the Minimum OA
Damper Position or Minimum OA flow rate to increase
ventilation. If the CO
2
level drops below the CO
2
setpoint,
the controller will decrease the Minimum OA Damper
Position or Minimum OA flow rate to decrease ventilation.
Demand Ventilation shall remain active as long as the
unit is in the Occupied mode of operation.
EXHAUST CONTROL SEQUENCES
Barometric
The optional barometric exhaust system consists of a
lightweight barometric relief damper installed on the end
of the unit in the Return Air section. As more outside air
is introduced into the controlled zone due to Econo-
mizer and Ventilation control sequences, the pressure
inside the building rises. This increase in building pres-
sure forces the barometric relief damper open to allow
exhaust air to escape. Because this type of exhaust
system is not powered, it is limited to small amounts of
exhaust.
Powered Fixed Volume Exhaust Based on
Outside Air Damper Position
This optional fixed volume powered exhaust system
consists of a fixed speed fan that is controlled ON and
OFF based on the position of the Outside Air Damper.
During operation, when the Outside Air Damper opens
to a selected turn-on point, the Exhaust Fan is cycled
ON. The fan remains on as long as the Outside Air
damper is above a selected turn-off point. If the Out-
side Air Damper closes to the selected turn-off point,
the Exhaust Fan is cycled OFF. The turn-on and turn-
off points are user selectable from the OptiLogic
™
User
Interface panel.
Powered Fixed Volume Exhaust Based on
Building Pressure
The optional fixed volume powered exhaust system
consists of a fixed speed fan that is controlled ON and
OFF based on the pressure inside the building. During
operation, the pressure within the building in monitored
by the OptiLogic
™
controller. If the pressure rises to or
above a selected turn-on pressure, the Exhaust Fan is
cycled ON. The fan shall remain on as long as the pres-
sure within the building remains above a selected turn-
off pressure. If the building pressure falls to or below
the selected turn-off pressure, the Exhaust Fan is cycled
OFF. The turn-on and turn-off pressure setpoints are
user selectable from the OptiLogic
™
User Interface.
Powered Variable Volume Exhaust-Discharge
Damper Controlled
This optional variable volume powered exhaust system
consists of a fixed speed fan configured with a propor-
tionally controlled discharge damper. The OptiLogic
™
controller monitors the pressure inside the building and
controls the Exhaust Damper and the Exhaust Fan. If
the Building Pressure rises, the Exhaust Damper is pro-
portionally controlled open and the Exhaust Fan is con-
trolled ON. If the Building Pressure falls, the Exhaust
Damper is proportionally controlled closed and the Ex-
haust Fan is controlled OFF. The position of the Ex-
haust Damper in which the Exhaust Fan is controlled
ON and OFF as well as the Building Pressure setpoint
is user selectable from the OptiLogic
™
User Interface.
Powered Variable Volume Exhaust-VFD Controlled
This optional variable volume powered exhaust system
consist of an Exhaust Fan driven by a Variable Fre-
quency Drive (VFD), which is controlled by the
OptiLogic
™
controller. The OptiLogic
™
controller moni-
tors the pressure within the building. As the pressure
rises, the VFD is controlled to increase Exhaust Fan
speed. As the pressure falls, the VFD is controlled to
decrease Exhaust Fan speed. The Building Pressure
Setpoint is user selectable from the OptiLogic
™
User
Interface. On/Off control is maintained the same as
Exhaust-Discharge Damper control stated above.
LOW AMBIENT OPERATION
The OptiLogic
™
controller continuously monitors the
outside air temperature to determine if mechanical cool-
ing should be allowed. As a safety, if the Outside Air
temperature falls to or below the Low Ambient Lockout
temperature, mechanical cooling is prevented from
operating. For units with economizers, the Low Ambi-
ent Lockout temperature is typically low enough that
mechanical cooling will rarely be required. However,
for some applications mechanical cooling is required
when the Outside Air temperature is lower than the Low
Ambient Lockout temperature.
