Basic Documentation

Room Pressurization Control Application Guide
Room Pressurization Reference Data
As indicated in Table 1, good ventilation system design for chemical laboratory rooms should
ensure that the rooms are at a negative static pressure of approximately 0.01 inches w.c.
with respect to adjacent non-laboratory spaces, such as a corridor
3
.
The specific relationship between Room Differential Pressure, Room Leakage Area, and the
Differential Airflow is expressed by the following equations
4
based on inch-pound (IP) or
metric (SI) units.
(IP) Q = 2610 A (dP)
1/2
where:
Q is the differential airflow in Cubic Feet per Minute (cfm)
A is the total room leakage area in Square Feet
dP is the differential pressure in Inches of Water (inches w.c.)
(SI) Q = 840 A (dP)
1/2
where:
Q is the differential airflow in Liters per Second,
A is the total room leakage area in Square Meters
dP is the differential pressure in Pascals
The graph in Figure 3 depicts the relationship between room differential pressure, room
leakage area and differential airflow. Figure 3 also shows room leakage area in square feet
as a family of curves on the graph. The differential airflow (difference between the total room
supply and total room exhaust airflows) is shown as Cubic Feet per Minute (cfm) along the
horizontal axis of the graph. The resulting room differential (static) pressurization values are
shown as Inches of Water (inches w.c.) along the vertical axis.
To determine what room differential airflow is needed to provide a particular differential
pressure, the desired differential pressure value on the vertical axis is followed to where its
horizontal line intersects the room leakage area curves. The required differential room airflow
is then indicated along the bottom of the graph directly below the points of intersection.
3
In applications where it is necessary to prevent contamination by air flowing into the laboratory room from adjacent spaces, the
laboratory room can be maintained at a positive static pressure. However, the laboratory room must be separated from the
adjoining area (a corridor) by a vestibule room that is maintained at a negative static pressure.
4
Equations taken from 1999 ASHRAE Application Handbook, Fire and Smoke Management Section, Page 51.5.
14 Siemens Building Technologies, Inc.