Basic Documentation

Room Pressurization Factors
DIFFERENTIAL
PRESSURE
INCHES
of
WATER
0.020
0.019
0.018
0.017
0.016
0.015
0.014
0.013
0.012
0.011
0.010
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0.000
ROOM DIFFERENTIAL AIRFLOW - CFM
0.1 Ft
2
0.2 Ft
2
0.3 Ft
2
0.4 Ft
2
0.5 Ft
2
0.6 Ft
2
0.75 Ft
2
1.0 Ft
2
ROOM LEAKAGE AREA CURVES
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400
LAB0194R1
1.5 Ft
2
Figure 3. Room Differential Airflow vs. Differential Pressure for Various Room Leakage Areas.
Room Pressurization Factors
As Figure 3 shows, a room’s static pressurization value is wholly dependent on the
differential airflow and the room’s leakage area. For instance, the graph shows that for a
room with 1.0 sq. ft. of leakage area, a differential pressure (dP) of just under 0.010 inches
w.c. occurs when the difference between the room’s supply air and the total room exhaust is
250 cfm. This relationship exists regardless of what the room’s ventilation rate is (air changes
per hour). Therefore, to maintain a specific room pressurization value, the room’s differential
airflow must be controlled and maintained at the appropriate value.
Leakage Area
Most modest sized rooms, such as a two-person laboratory with two hinged doors, will have
a total room leakage area of about 0.5 to 1.0 sq. ft. even with relatively tight construction. To
obtain a tighter room, extensive sealing and meticulous attention to poke-throughs (places
where conduit, piping, ducts and other items pass through the room’s walls, ceiling, and floor)
is required. However, room pressurization can be more easily maintained at a constant value
if the room construction is not extremely tight.
Siemens Building Technologies, Inc. 15