Application

Sequence of Operation
Alarms
33
Siemens Industry, Inc.
BACnet LCM-OAVS, Application 6754
140-1325
2015-07-07
The ventilation alarm, VENT ALM, indicates that there is something wrong with the
ventilation to the room. VENT ALM has an adjustable alarm level that can vary with the
occupancy status of the room. An adjustable delay timer, VENT ALM DEL, prevents
nuisance alarms.
VENT ALM is turned on when at least one of the following conditions is true:
 The supply flow to the room, TOTL SUPPLY, stays below the alarm level, for a
time at least equal to VENT ALM DEL.
 SUP AIR VOL stays below the currently active supply minimum, for a time at least
equal to VENT ALM DEL.
 GEX AIR VOL stays below the currently active general exhaust box minimum, for a
time at least equal to VENT ALM DEL.
It is turned off only when all of the following conditions are true:
 The TOTL SUPPLY stays above the alarm level, for a time at least equal to the
alarm delay.
 SUP AIR VOL stays above the currently active supply minimum, for a time at least
equal to VENT ALM DEL.
 GEX AIR VOL stays above the currently active general exhaust box minimum, for a
time at least equal to VENT ALM DEL.
If the current conditions will neither turn on the ventilation alarm nor shut off the alarm,
then VENT ALM will keep its current value.
Setting the alarm level to zero means the ventilation alarm will not turn on just because
of a low value for TOTL SUPPLY.
Even if the alarm level is set to zero, the ventilation alarm will still turn on if:
 SUP AIR VOL stays below the currently active supply minimum, for a time at least
equal to VENT ALM DEL.
and/or
 GEX AIR VOL stays below the currently active general exhaust box minimum, for a
time at least equal to VENT ALM DEL.
Pressurization Alarm
The pressurization alarm, VOL DIF ALM indicates that the difference between supply
and exhaust flow is not what it should be, or that the controller can't calculate the flow
difference, VOL DIFFRNC, because it has lost a flow signal. The Figure
Failure Mode
Sequence
lists reasons why VOL DIFFRNC may fail.
The pressurization alarm point is turned on when at least one of the following
conditions occurs:
 VOL DIFFRNC has a status of Failed.
 VOL DIFFRNC stays below VOL DIF STPT – DIF ALM DBD for a time at least
equal to DIF ALM DEL.
 VOL DIFFRNC stays above VOL DIF STPT + DIF ALM DBD for a time at least
equal to DIF ALM DEL.