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Sequence of operation
Occupied and unoccupied operation
The valid occupancy modes of the Tracer
• Occupied—Normal operating mode for occupied spaces or daytime
operation.
• Unoccupied—Normal operating mode for unoccupied spaces or nighttime
operation.
• Occupied Standby—Constant volume mode used to reduce the heating and
cooling demands during the occupied hours when the space is vacant or
unoccupied. For example, the controller may use occupied standby mode for
a classroom while the students are out of the room.
• Occupied Bypass—Mode used for timed override conditions. For example,
if the controller is in unoccupied mode and someone presses the On button
on the zone sensor, the controller is placed in occupied bypass mode for 120
minutes (adjustable) or until someone presses the Cancel button on the zone
sensor.
The occupancy mode can be hardwired to the controller via the occupancy
binary input or communicated to the controller.
Occupied mode
The Tracer AH.540 controller operates according to the configured control
mode:
• Constant volume space temperature control
• Constant volume discharge air temperature control
• Variable air volume control
When the controller is configured for constant volume space temperature
control, the unit attempts to maintain the space temperature at the active
occupied heating or cooling space setpoint, based on the measured space
temperature, the discharge air temperature, the active setpoint, and the
proportional/integral control algorithm. The modulating control algorithm used
when occupied or in occupied standby is described in the following sections.
Additional information related to the handling of the controller setpoints can be
found in the previous Setpoint operation section.
The Tracer AH.540 controller, when configured for constant volume discharge
air temperature control, maintains the discharge air temperature at the
configured discharge air temperature heating or cooling setpoint. The default
occupied mode of the controller is cooling. In the occupied mode, the
controller's communicated application mode input (nviAppicMode) and heat/
cool mode input (nviHeatCool) determine the controller's heating and cooling
setpoint. Refer to the Appendix for heating and cooling control modes of
operation.
When the controller is configured for variable air volume control, the duct static
pressure is always maintained at the configured or communicated duct static
pressure setpoint. The air volume is controlled by the supply fan speed analog
output to the variable frequency drive (VFD).
Variable air volume control also maintains the discharge air temperature at the
discharge air heating or cooling setpoint. The discharge air temperature and
supply fan speed are both modulated to maintain the duct static pressure at the
duct static setpoint and the discharge air at the discharge air temperature
setpoint.
Economizing is possible during any of the configured control types if a mixed
air sensor and outdoor air temperature sensor exist.
™
AH.540 controller are:
CNT-SVX05A-EN
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