Operating Instructions

Laboratory Room Controller Owner's Manual
3-18 Siemens Building Technologies, Inc.
Problem 4: Unstable Airflow
If people in the room notice that one of the airflows in or out of the room continually cycles up
and down, complete the following steps:
1. Verify that the airflow really is unstable by reading flow values (SUP AIR VOL, etc.) from
the system. Look for significant fluctuation in the values. An Insight trend graph and CIS
work best for this task.
2. Check to see if the set point is constant by reading the setpoint for that flow. If it
fluctuates, trace that point back to the source of the variation. Some possibilities to check
include the fume hood flow, the general exhaust flow, occupancy, and TEMP CTL VOL.
The Overview Report contains most of the requested information.
If the setpoint is stable, continue with Step 3.
3. Determine if the instability is in the central system or the local control loop. To do this,
temporarily interrupt the flow control. Set the appropriate damper command point (SUP
DMPR CMD, etc.) to zero. Read the flow values. If the values stabilize, then the flow
control loop is out of tune. Contact your Siemens Building Technologies, Inc. branch for
assistance.
If the flow continues to fluctuate with the damper locked in place; the instability is in the
central system.