ENGINEERING MANUAL OF AUTOMATION CONTROL
BUILDING AIRFLOW SYSTEM CONTROL APPLICATIONS
280
AIRFLOW MEASURING DEVICES
Va rious devices for measuring airflow are available. Figure
19 shows a flow measuring station that consists of:
— An air straightener section to eliminate swirl type
airflow and help normalize the velocity profile
—Total pressure sensors aligned into the air stream and
spaced on an equal area basis
—Static pressure sensors with ports perpendicular to the
airflow direction and positioned on an equal area basis
— Separate manifolds for static and total pressure
averaging
The flow measuring station in Figure 19 uses a tube as an air
straightener (Fig. 20) with total and static pressure sensors at
the downstream end. These tubes are arranged on an equal area
basis.
C2659
AIR
STRAIGHTENER
TOTAL
PRESSURE
SENSOR
STATIC
PRESSURE
SENSOR
MANIFOLD
ASSEMBLY
TOTAL PRESSURE
CONNECTION
STATIC
PRESSURE
CONNECTION
A
IR
F
L
O
W
Fig. 19. Averaging Flow Measuring Station.
C2660
Fig. 20. Air Straighteners/Sensors and Manifolds.
Electronic flow stations use the tube type construction with
thermal velocity sensors instead of static and total pressure
sensors. Other flow sensing arrangements use holes in round
tubing (Fig. 21A and 21B) or airfoil designs (Fig. 21C). It is
important to consult the manufacturer of each type of flow
station for specifications, calibration data, and application
information (location limitations within ducts).
Fig. 21. Miscellaneous Flow Sensing Arrangements.
AIRFLOW
39.25 39.25
TOTAL PRESSURE
PORT
STATIC PRESSURE
PORTS
A. B.
C2661
AIR PROFILE
TOTAL
PRESSURE
STATIC
PRESSURE
FLOW
AIR PROFILE
NOTE: STATIC PRESSURE SIGNAL WILL BE LESS THAN ACTUAL
STATIC PRESSURE AND CANNOT BE USED FOR STATIC
PRESSURE CONTROL. AS DEPRESSION VARIES WITH
AIR VELOCITY, VELOCITY PRESSURE (VP=TP - SP) WILL
BE AMPLIFIED.
˚˚
TOTAL
PRESSURE
TUBE
STATIC
PRESSURE
TUBE
TOTAL
PRESSURE
TUBE
STATIC
PRESSURE
TUBE
(SEE NOTE)
C.
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