Application

Sequence of Operation
Fail Mode Operation
28
Siemens Industry, Inc.
Application Note, Application 6759
140-1335
2015-07-07
AVS Failure and AVS FAILMODE Table Values.
AVS FAILMODE
4
Close Supply, Hold General Exhaust
5
Close Supply, Open General Exhaust
6
Open Supply, Close General Exhaust
7
VENTILATION
8
PRESSURE
AVS FAILMODE values are not additive. For example, if AVS FAILMODE equals
3,
this means to open the supply Damper and hold the general exhaust Damper if an
AVS fails.
The first seven values of AVS FAILMODE (0 through 6) describe specific actions taken
when an AVS fails. For example, if AVS FAILMODE equals
5, then whenever an AVS
fails, the supply Damper will always close and the general exhaust Damper will always
open.
The last two values of AVS FAILMODE do not describe specific actions; that is, when
an AVS fails, the supply and general exhaust will react differently depending on the
circumstances.
If AVS FAILMODE equals
7, the supply Damper will hold. The general exhaust
Damper will also hold if a fume hood is present (that is, if MAX HOOD VOL > 0). If a
fume hood is absent, then the general exhaust Damper will close if the room is being
positively pressurized and open if the room is neutral or negatively pressurized (that is
if VOL DIF STPT is equal to or greater than 0).
If AVS FAILMODE equals
8, the supply Damper will open if the room is being positively
pressurized and close if the room is neutral or negatively pressurized. The general
exhaust Damperwill hold if a fume hood is present. If a fume hood is absent, the
general exhaust Damper will close if the room is being positively pressurized and open
if the room is neutral or negatively pressurized.
NOTE:
If AVS FAILMODE is set greater than 8, it will default to 0.
Fail Mode Operation
If one of the controller’s accessories (inputs) fails, a failure mode sequence is initiated
that leads to the failure of VOL DIFFRNC. The following figure shows the order in
which points will fail.