Fantech AEV 1000 Nstallation, Operation And Maintenance Manual - Air Flow Balancing (Cont’)
AIR FLOW BALANCING (CONT’)
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.
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.
3 The airflow is regulated by a
balancing damper located inside the
collar of the AEV. Adjust the “Supply
Air Out” damper until you reach
the desired velocity. Follow the
previous
steps to adjust the “Exhaust Air
Out” damper.
B
PITOT TUBE BALANCING PROCEDURE
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 down-
stream 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 air-
flow. For general balancing it is suffivient 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 read-
ing 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 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 section-
al 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
= [3014x(6” 12)2 4
=0.2 squeare feet
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)
CROSS SECTION AREA (sq ft.)
5 0.14
6 0.20
7 0.27
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 out-
lined in the literature supplied with the Pitot tube.
9
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