Basic Documentation

Chapter 4—Room Static Pressure
Control
Chapter 4 discusses static pressure control in rooms in the following facilities:
• Laboratories
• Healthcare Facilities
The most appropriate method of controlling a room's static pressure is dependent upon the
room application. Since the purpose for maintaining a differential pressure relationship
between rooms is to prevent cross contamination, the consequences of cross contamination
must be known in order to determine the most appropriate method of control. If the main
concern is to contain unpleasant odors, the consequences might be very small. On the other
hand, very serious consequences result if occupant safety and health are involved. These
are most typically associated with laboratories involved with highly infectious biological
aerosols, highly toxic laboratory chemicals and others such as radioactivity.
This section covers room pressurization control applications for many applications and
provides detailed recommendations for achieving the desired pressurization relationship
between a particular space and adjacent areas.
Laboratories
Airflow Tracking Static Pressure Control
Airflow tracking is the preferred room static pressurization control approach for most
laboratories. Airflow tracking can maintain desired room pressurization for both constant air
volume (CAV) ventilation systems as well as variable air volume (VAV) ventilation systems.
Figure 4 shows the essential components of a typical chemical laboratory room ventilation
system using a single duct supply terminal. This room ventilation system arrangement
enables using airflow tracking for maintaining room pressurization. The Room Controller and
the Fume Hood Controllers precisely control the room airflow as described below.
The Fume Hood Controllers modulate the exhaust airflow of the FUME HOODS to always
maintain the proper amount of exhaust. For constant air volume (CAV) fume hoods, the fume
hood exhaust is maintained at a constant value regardless of the amount that the fume hood
sash is open. For variable air volume (VAV) fume hoods the fume hood exhaust is modulated
so that the fume hood face velocity (incoming airflow) is maintained at the desired constant
value.
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