Basic Documentation

Glossary
Airflow Tracking (Flow Tracking)
A means of maintaining a positive or negative static pressure in a particular room with
respect to an adjoining room, corridor, or building exterior. Airflow tracking consists of always
maintaining a fixed amount of airflow difference between the total supply air and total exhaust
air provided by the room or space ventilation system. Although the specific room supply and
exhaust airflow may periodically change, airflow tracking maintains a constant airflow (cfm or
l/s) differential. By maintaining more supply airflow than exhaust, a room is maintained at a
positive static pressure with respect to a non-pressurized adjacent space. By maintaining
less supply airflow than exhaust, a room is maintained at a negative static pressure with
respect to a non-pressurized adjoining space.
Differential Pressure (Differential Static Pressure)
Space or room static pressure value with reference to another room, space or location.
Fume Hood Static Pressure
The (negative) static pressure measured in the exhaust duct just after its connection to a
chemical fume hood's exhaust outlet. The static pressure value is measured just a few duct
diameters (normally 2 to 5) downstream of where the exhaust duct connects to the fume
hood.
Inches of Water (Inches Water Column; Inches W.C.)
An IP unit used to express very low air pressure values. It is typically used in ventilation
system applications. One inch of water is equal to the pressure exerted by a water column 1
inch in height at 39.2°F.
Manometer
Instrument for measuring relatively low pressures as are commonly associated with
ventilation system airflow. A manometer consists of a transparent vertical or slanted tube
containing a liquid (oil, water, or mercury). A manometer is an accurate and very repeatable
means of pressure measurement since it does not have any mechanical or electrical
components. As such, it is not subject to deterioration in accuracy (drift) due to the effects of
component wear and aging as is the case with instruments utilizing springs, gears, levers,
and various electrical components. However, due to the difficulty in reading very small
pressure values, manometers are not well suited for the very low pressure measurements
that are typically associated with room pressurization (for example, 0.01 inches w.c.).
Siemens Building Technologies, Inc. Glossary-1