Application

Sequence of Operation
Flow Tracking – Supply Tracks Exhaust vs. Exhaust Tracks Supply
12
Siemens Industry, Inc.
Application Note, App 6751
140-1331
2015-07-07
Supply Tracks Exhaust mode is useful when trying to maintain negative pressurization.
During Supply Tracks Exhaust, the supply air volume "tracks" or follows the exhaust air
volume. If the exhaust air is "broken" (for instance, if the general exhaust airflow control
device is stuck open or stuck closed), the supply air volume will be adjusted so that
VOL DIF STPT is maintained as much as possible. (The supply air volume cannot go
lower than zero and the application will not allow it to go higher than OCC SUP MAX
during occupied periods, or UOC SUP MAX during unoccupied periods.)
Exhaust Tracks Supply mode is useful when trying to maintain positive pressurization.
During Exhaust Tracks Supply, the general exhaust air volume "tracks" or follows the
supply air volume. If the supply air is "broken" (for instance, if the supply airflow control
device is stuck open or stuck closed), the general exhaust air volume will be adjusted
so that VOL DIF STPT is maintained as much as possible. (The general exhaust air
volume cannot go lower than zero and the application will not allow it to go higher than
OCC GEX MAX during occupied periods, or UOC GEX MAX during unoccupied
periods.)
The selected track mode is not affected by occupancy status (OCC or UNOCC), and is
set by the value of TRACK MODE.
TRACK MODE Values.
TRACK MODE
(value)
Description
0
default
Always STE (Supply Tracks Exhaust), exhaust only.
1
STE during occupancy, ETS during the unoccupied period.
2
ETS during occupancy, STE during the unoccupied period.
3
Always ETS (Exhaust Tracks Supply), supply only.
NOTE:
If TRACK MODE is set greater than 3, it will default to 0.
TRACK METHOD
TRACK METHOD is a point associated with TRACK MODE. TRACK MODE
determines which airflow (supply or general exhaust) gets tracked and which airflow
does the tracking. TRACK METHOD determines how tracking is accomplished.
 If TRACK MODE is set to ETS and TRACK METHOD is set for FLOW tracking, the
general exhaust flow setpoint is calculated according to the measured value, SUP
AIR VOL.
 If TRACK METHOD is set for STPT tracking, the general exhaust flow setpoint is
calculated according to the supply flow setpoint. However, this module changes
over to FLOW tracking mode if the supply cannot reach the setpoint.
This feature prevents the incorrect pressurization of rooms that lack the required
supply capacity. The changeover is based on the error of the supply flow loop. If the
error is greater than FAIL LIMIT, and stays that way for a time longer than FAIL TIME,
then the module changes from STPT tracking to FLOW tracking. It stays in that mode
until the error comes back to zero, then switches back to the STPT tracking mode.
 If TRACK MODE is set to STE and TRACK METHOD is set for FLOW tracking, the
supply flow setpoint is calculated according to the measured value, GEX AIR VOL.
 If TRACK METHOD is set for STPT tracking, the supply flow setpoint is calculated
according to the general exhaust flow setpoint. However, this module changes over
to FLOW tracking mode if the general exhaust cannot reach the setpoint.