Application

Sequence of Operation
Wiring Diagrams
40
Siemens Industry, Inc.
Application Note, App 2926
140-1308
2015-07-07
 OCC GEX MIN and UOC GEX MIN to 0.
If these two points are not set to 0, GEX AIR VOL— will read 0 since GEX FLO
COEF was set to 0—will be less than the general exhaust box minimum, resulting
in a false ventilation alarm.
 VOLUME STATE
The application varies the supply airflow as the fume hood flow changes, in order
to maintain the proper room pressurization. The supply airflow is not varied for
cooling purposes; all temperature control is done by the reheat valve. Because of
this, VOLUME STATE should be set to 0 to prevent the BTU Compensator from
trying to use the supply airflow for cooling.
The application varies the supply airflow as the fume hood flow changes, in order to
maintain the proper room pressurization. The supply airflow is not varied for cooling
purposes; all temperature control is done by the reheat valve.
Operating Without a Supply Box
This application can operate without a supply box. If a supply box is not being
controlled, set TRACK METHOD to FLOW and set the following points:
 TRACK MODE to 3.
(a value of 3 = ETS Flow Tracking, should be used for both the occupied and
unoccupied modes).
 SUP FLO COEF to 0.
When SUP FLO COEF equals 0, SUP AIR VOL will always read 0, but will never
show as Failed.
 OCC SUP MIN and UOC SUP MIN to 0.
If these two points are not set to 0, SUP AIR VOL— will read 0 since SUP FLO
COEF was set to 0—will be less than the supply box minimum, resulting in a false
ventilation alarm.
This setup is useful when the room has a constant source of supply air from other
equipment or sources not connected to the controller. If you enter this constant supply
air volume value into OTHER SUP, the application will vary the general exhaust airflow
as the fume hood flow changes, in order to maintain the proper room pressurization.
Since all temperature control will be done by the reheat valve, VOLUME STATE should
be set to 0 and both OCC SUP MAX and UOC SUP MAX should be set equal to
OTHER SUP. This will prevent the BTU Compensator from trying to use the supply
airflow as a source of cooling.
Wiring Diagrams
Offboard Air Module Wiring.