Trane Tracer VV550 Installation, Operation And Maintenance Manual page 58

Sequence of Operations
The minimum can be adjusted down at anytime, but only as far as the configured
minimum airflow.
Figure 3. UCM local ventilation operations
Is unit in pressure dependent
(PD) mode?
Ventilation ratio = effective
ventilation setpoint/airflow
Is communicated ventilation
ratio limit valid?
Ventilation limited by system
UCM takes action to change the active minimum.
If ventilation ratio > communicated ventilation ratio limit, then
ventilation ratio = communicated ventilation ratio limit.
Ventilation minimum flow = effective ventilation
setpoint/communicated ventilation ratio limit.
Limit ventilation minimum flow to the active maximum flow.
Ventilation minimum flow is used in the minimum flow
setpoint arbitration logic to determine the active minimum
flow setpoint.
If the zone temperature drops below the heating setpoint -1°F
(cooling), rises above the cooling setpoint +1°F (heating), or if
the space temperature input fails, ventilation is deemed
uncontrollable. Ventilation minimum flow is not allowed to
increase above its current position (it is allowed to decrease).
Increasing ventilation minimum flow can begin again when
zone temperature rises above the heating setpoint + 1°F
(cooling), drops below the cooling setpoint -1°F (heating), or
space temperature is regained.
UCM sends:
– Ventilation ratio (invalid)
– Effective ventilation setpoint
– Active minimum flow setpoint
– Minimum airflow setpoint source
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Figure 3 provides a flow diagram of local ventilation actions.
Invalid ventilation ratio
Ventilation = uncontrollable (see Note 1)
UCM sends:
Yes
– Ventilation ratio (invalid)
– Effective ventilation setpoint
– Active minimum flow setpoint
– Minimum airflow setpoint source
No
No
Assume communicated
ventilation ratio limit = 1.0
Yes
No limit on ventilation. A properly
designed system requires no local
action, but local action is possible.
Ventilation minimum flow = effective
ventilation setpoint
Limit ventilation minimum flow to
active maximum flow
UCM sends:
– Ventilation ratio (invalid)
– Effective ventilation setpoint
– Active minimum flow setpoint
– Minimum airflow setpoint source
Note 1: On a transition to occupied or a
change in primary air temperature
(change in heat/cool mode), ventilation
is assumed to be uncontrollable until
proven otherwise.
CNT-SVX17G-EN