Operating Instructions

Application 2522: VAV with Electric Reheat or Baseboard Radiation
Siemens Building Technologies, Inc. 3-33
Recalibration of Damper when Autozero Module is Used
The Autozero Module is enabled when it is wired to DO 4 and CAL MODULE (Point 87) is set
to YES.
Under normal operation DMPR STATUS (Point 84) reads CAL. However, if using an
Autozero Module, it is possible after a period of operation for the calculated damper position
point, DMPR POS (Point 49), to differ from the actual (physical) damper position.
If this occurs, the controller automatically compensates for any difference by setting
DMPR STATUS to RECAL, which readjusts the value of DMPR POS, allowing accurate flow
control to continue. DMPR STATUS is set to RECAL if all of the following conditions are true:
• DMPR POS = 100%
• Air velocity > 200 ft/min (1.016 m/sec)
• FLOW (Point 75) < FLOW STPT (Point 93)
-or-
• DMPR POS = 0%
• Air velocity > 200 ft/min (1.016 m/sec)
• FLOW > FLOW STPT
NOTE: For a system using English units, air velocity (fpm) equals AIR VOLUME (Point
35, cfm) divided by DUCT AREA (Point 97, sq ft). For a system using SI units, air
velocity (mps) equals 0.001 times AIR VOLUME (lps) divided by DUCT AREA (sq
m).
NOTE: To change DMPR STATUS from RECAL back to CAL, set DMPR STATUS to
CAL, and then release it.
Fail-Safe Operation
If the air velocity sensor fails, the controller uses pressure-dependent control. The
temperature loop controls the operation of the damper.
If the room temperature sensor fails, the controller operates using the last known temperature
value.