48
CNT-SVX05A-EN
Sequence of operation
Outdoor air damper operation
The controller operates the modulating outdoor air damper according to the
effective occupancy, outdoor air temperature (communicated or hardwired
sensor), space temperature, effective space temperature setpoint, discharge air
temperature, and discharge air temperature setpoint. Default minimum damper
positions are provided and can be changed using Trane's Rover service tool for
occupied and occupied standby ventilation.
The controller can also receive a communicated outdoor air damper minimum
position from Tracer Summit
™
. A communicated minimum position from Tracer
Summit has priority over all configured minimum setpoints. When a
communicated minimum position is not present, the controller uses the
configured minimum setpoints.
Table 27 — Determining the economizer damper minimum position setpoint
During occupied modes, the damper remains at a minimum damper position,
whether a configured minimum position or communicated from Tracer
Summit.
Mixed air temperature control
The Tracer
™
AH.540 controller provides minimum ventilation requirements
according to the effective occupancy mode. Ventilation requirements are
maintained by mixed air control depending on available heating and cooling
sources, unit configuration, and mixed air control type (configurable). Low
mixed air temperatures can be a concern for units with hydronic heating and
cooling.
Mixed air control is used to maintain the mixed air temperature above the
mixed air low limit setpoint (configurable). See Table 27 below. If the air
handling unit does not have a mixing box section, then mixed air control is not
required.
Heat only, cool only, or cool reheat air handling configurations with a mixing
box can be configured for mixed air control. If cold outdoor air conditions exist,
depending on ventilation requirements, the mixed air temperature can create
freezing conditions.
Mixed air control
reduces the outdoor air damper below
the minimum position to maintain mixed air temperature above the mixed air
temperature low limit.
Air handling units with preheat can use
mixed air preheat control
to maintain
mixed air temperature before reducing ventilation. Cold entering air conditions
from the mixing box can be heated with the preheat capacity to maintain the
mixed air temperature above the mixed air temperature low limit.
Mixed air
preheat control
attempts to use preheat until it has reached 100% capacity.
At 100% preheat capacity, if mixed air temperature is below the low limit
temperature, the
mixed air preheat control
then lowers the outdoor air damper
below the minimum position to maintain mixed air above the mixed air
temperature low limit.
Occupancy
Tracer Summit setpoint
Active minimum damper setpoint
Unoccupied
Valid or Invalid
Closed
Occupied
Occupied bypass
Occupied standby
Valid
Tracer Summit
Occupied
Occupied bypass
Invalid
Occupied minimum
Occupied standby
Invalid
Occupied standby minimum
