Application

Sequence of Operation
Alarms
23
Siemens Industry, Inc.
Application Note, App 2927
140-1311
2015-07-07
 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.
WARNING
To ensure that VOL DIF ALM turns on before the pressure in the room changes sign,
DIF ALM DBD must be less than the absolute value of VOL DIF STPT.
For example, if negative pressure is desired and VOL DIF STPT equals 70 cfm and
DIF ALM DBD is 200 cfm, then the room could go positive by almost 130 cfm without
the pressure alarm turning on. In this case, if you want the alarm to turn on before the
room changes sign, then you must set DIF ALM DBD to be less than 70 cfm.
The pressurization alarm point is turned off when all of the following conditions occur:
 VOL DIFFRNC has a status of Normal.
 VOL DIFFRNC stays above VOL DIF STPT – DIF ALM DBD for a time at least
equal to DIF ALM DEL.
 VOL DIFFRNC stays below VOL DIF STPT + DIF ALM DBD, for a time at least
equal to DIF ALM DEL.
 DIF ALM DBD and DIF ALM DEL can be configured to prevent nuisance alarms.