Operating Instructions

Laboratory Room Controller Owner's Manual
3-4 Siemens Building Technologies, Inc.
Setting the Flow Difference for Pressurization
The LRC adjusts the supply and general exhaust flows in a way that causes the measured
difference (VOL DIFFRNC, Point 83) to match the set point (VOL DIF STPT, Point 88). These
points can be accessed through the Overview report. This report is available through CIS, the
field panel and Insight. When the controller successfully maintains the flow difference at the
set point, the room should be effectively pressurized and an inward airflow should be
observable at the door of the room.
NOTE:
Pressurization can only be effective when the doors to the room are closed.
However, it is possible that even when the controller maintains the selected flow difference,
that the room is not correctly pressurized and air is not flowing in at the door. In effect, the
value of the set point may be too small to generate a reliable infiltration flow. A possible
solution is to increase the set point for the flow difference, VOL DIF STPT (Point 88).
Although it is likely that this adjustment took place at the time the system was commissioned,
pressurization can be corrected this way.
While adjusting pressurization at a later time may be an appropriate response, be aware that
doing this can mask another problem that should be corrected. Although many pressurization
problems can be overcome by increasing the set point for the flow difference, it is better to
identify and correct any problems that exist. The following sections describe some possible
pressurization problems.
Improperly pressurized building environment
If an improperly pressurized building environment is causing problems in the laboratory, verify
the following:
• Check the corridor and make sure that all doors are closed.
• Make sure there is adequate supply in the hallway.
• Check for other large exhaust sources.
Leakage from other spaces
Pressurization problems can be caused when excess air flows in from other spaces. This
means that some space inside or outside the building is pushing enough air into the
laboratory that it overcomes the controlled flow difference and causes a loss of pressurization
at the doorway. Look for any possible source of infiltration in the room. Pay particular
attention to windows and penetrations from above and below the laboratory. When it is
practical, sealing those penetrations is a better solution than increasing the flow difference. A
Siemens Building Technologies, Inc. representative can help you identify and correct the
problem.