Application

Sequence of Operation
Flow Tracking – Supply Tracks Exhaust vs. Exhaust Tracks Supply
13
Siemens Industry, Inc.
Application Note, App 2928
140-1302
2015-07-07
NOTE:
If desired, the LCM can be used without any fume hoods attached. In this case, MAX
HOOD VOL should be set to 0 cfm to disable the alarming that would occur if the
fume hood flow input drops below 1 Vdc.
Flow Tracking – Supply Tracks Exhaust vs. Exhaust
Tracks Supply
The Supply Tracks Exhaust (STE) and Exhaust Tracks Supply (ETS) feature is
configured by setting TRACK MODE to STE or ETS to help the controller meet the
pressurization needs of the controlled space, such as for negative or positive pressure.
TRACK METHOD is used to determine what is being tracked – a flow value or a
setpoint value. Regardless of the mode (STE or ETS) in which the controller is
operating, the application will change the value of TRACK METHOD from STPT to
FLOW (that is, from setpoint tracking to flow tracking) if necessary to maintain proper
pressurization. This is important in situations where a room may lack sufficient supply
or general exhaust capacity. The following paragraphs explain this in greater detail.
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.