Basic Documentation

Chapter 2—Pressurization Applications
Chapter 2 defines room pressurization and discusses these topics:
• Room Static Pressure
• Building Pressurization
• Room Pressurization Applications
Room Static Pressure
When referring to room pressurization, the term static pressure is usually applied to establish
the fact that the pressure is not due to any air motion. Rather, the pressure exists
independently of any motion of the air.
Every pressure measurement or pressure value is based on a difference between two points
or locations. Therefore, a room's static pressure value is the difference in static pressure
between the room and another location. Most often the other location is an adjoining room or
corridor. However, the other location can also be:
• The outdoors.
• The floor above or below.
• A stairwell.
• A more distant area in the building.
It is important to use the terms positive and negative when referring to room static pressure
values since it is not always apparent which location is at the higher (or lower) static
pressure. Positive indicates that the location has the higher static pressure while negative
indicates that the location has the lower value. So, stating that a room is positively
pressurized indicates that the room has a higher static pressure than the reference area.
Conversely, stating that a room is negatively pressurized indicates that the room has a lower
static pressure than the reference area. Note also that a room can, and often does, have
multiple static pressure values. For example, a room may be negative 0.01 inches w.c. with
respect to an adjoining corridor and it could also be positive 0.01 inches w.c. with respect to
another room or area. Because pressure values are always referenced to another area, there
is no limit to the number of pressure values that a given room or space may have with
respect to other locations.
If the static pressure of a certain room were negative 0.02 inches w.c. with reference to an
adjacent corridor, it would be equivalent to saying that the static air pressure of the room is
0.02 inches w.c. lower than the static pressure of the corridor. It could also be stated that the
corridor is positive 0.02 inches w.c. with respect to the room.
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