Application

Sequence of Operation

Fail Mode Operation

Siemens Industry, Inc.

BACnet LCM-OAVS, Application 6754

140-1325

2015-07-07

If AVS FAILMODE equals 7, the supply Damper will hold. The general exhaust Venturi

Air Valve 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 Venturi Air Valve 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 Venturi Air Valvewill hold if a fume hood is present. If a fume hood is absent,

the general exhaust Venturi Air Valve 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.

* If MAX HOOD VOL is set to 0, a “Failed” status of HOOD VOL will not initiate a failure

in TOTL EXHAUST or VOL DIFFRNC. See

Fume Hood Flow Input

Air Velocity Sensors – If one or both of the LCM air sensor signals (SUP AIR VOL,

GEX AIR VOL) are out of range (for example, improper wiring to/from the Offboard Air

Module(s), tubing not connected or connected backward), then the actions of the

supply and general exhaust Venturi Air Valves will depend on the value of AVS

FAILMODE. Once GEX AIR VOL and SUP AIR VOL are normal, the supply and

general exhaust Venturi Air Valves return to normal operation.

See

Operation of AVS FAILMODE

for more information.