Pitot Tube Balancing Procedure - SystemAir Fantech AEV Serie Manuel D'installation

Airflow balancing (Cont'd)
1 For this flow measuring station, cut the duct
and place the flow measuring station
between each station. Make sure that the
flow measuring station's air direction arrow
points in the direction of the airflow. Secure
the flow measuring station with duct tape.

Pitot tube balancing procedure

The following is a method of field balancing an AEV using a Pitot tube,
advantageous in situations when flow stations are not installed in the
ductwork. Procedure should be performed with the AEV on high speed.
The first step is to operate all mechanical systems on high speed,
which have an influence on the ventilation system, i.e. the AEV itself and
the forced air furnace or air handler if applicable. This will provide the
maximum pressure that the AEV will need to overcome, and allow for a
more accurate balance of the unit.
Drill a small hole in the duct (about 3/16), three feet downstream of any
elbows or bends, and one foot upstream of any elbows or bends.
These are recommended distances but the actual installation may limit
the amount of straight duct. The Pitot tube should be connected to a
magnehelic gauge or other manometer capable of reading from 0 to 0.25
in (0-62 Pa) of water, preferably to 3 digits of resolution. The tube coming
out of the top of the pitot is connected to the high pressure side of the
gauge. The tube coming out of the side of the pitot is connected to the
low pressure or reference side of the gauge.
Insert the Pitot tube into the duct; pointing the tip into the airflow. For
general balancing it is sufficient to move the pitot tube around in the duct
and take an average or typical reading. Repeat this procedure in the other
(supply or return) duct. Determine which duct has the highest airflow
(highest reading on the gauge). Then damper that airflow back to match
the lower reading from the other duct. The flows should now be balanced.
Actual airflow can be determined from the gauge reading. The value read
on the gauge is called the velocity pressure. The Pitot tube comes with
2 Before taking the reading, make sure that
the magnehelic gauge is level and at 0.
Refer to the flow measuring station's chart
to determine your unit's airflow velocity.
a chart that will give the air flow velocity based on the velocity pressure
indicated by the gauge. This velocity will be in either feet per minute
or metres per second. To determine the actual airflow, the velocity is
multiplied by the cross sectional areas of the duct being measured.
This is an example for determining the airflow in a 6" duct.
The Pitot tube reading was 0.025 inches of water.
From the chart, this is 640 feet per minute.
The 6" duct has cross sectional area of
The airflow is then:
640 ft./min.x0.2 square feet-128cfm
For your convenience, the cross sectional area of some common round
duct is listed below:
DUCT DIAM. (inches)
The accuracy of the air flow reading will be affected by how close to any
elbows or bends the readings are taken. Accuracy can be increased
by taking an average of multiple readings as outlined in the literature
supplied with the Pitot tube.
3 The airflow is regulated by a balancing
damper. Adjust the "Supply Air Out" damper
until you reach the desired velocity. Follow
the previous steps to adjust the "Exhaust Air
Out" damper.
= [3014x(6" 12)2 4
=0.2 squeare feet
CROSS SECTION AREA (sq ft.)
5 0.14
6 0.20
7 0.27
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