Basic Documentation

Room Pressurization Control Application Guide
With respect to the ventilation system design, the vestibule exhaust would normally be a
constant air volume (CAV) exhaust while the laboratory room could employ either a CAV or
VAV ventilation arrangement. The important element is that the laboratory room controller
must ensure that the total exhaust of the room combination is always greater than the room
supply air. Each entryway into the laboratory room requires a vestibule unless the entryway
connects to an adjoining laboratory room that is also protected against contamination by
positive pressurization. If an adjoining area is not at the same static pressure as the
laboratory room, a vestibule entry arrangement should then be used for that respective entry.
When implementing a dual pressurization arrangement, it is advisable to ensure that the
laboratory, vestibule walls, and ceilings be completely sealed to minimize the opportunity for
transfer air to pass directly into the adjacent area from the laboratory. Depending on
individual situations, an airlock type of entry for the vestibules may also be desirable. An
airlock door arrangement uses electric door releases to ensure that only one door of the
vestibule is opened at a time.
SUPPLY
TERMINAL
ROOM
CONTROLLER
FUME
HOOD
CONTROLLER
ROOM
GENERAL
EXHAUST
CFM
CFM
CFM
VESTIBULE
DOORS
EXHAUST
CFM
+
-
TRANSFER
AIRFLOW
TOTAL
ROOM
EXHAUST
AIRFLOW
TRACKING
OFFSET
ROOM
SUPPLY
AIRFLOW
VESTIBULE
EXHAUST
LABORATORY
LAB0197R1
Figure 6. Preventing Room Contamination by Room Positive Pressure & Vestibule Negative
Pressure.
26 Siemens Building Technologies, Inc.