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Measure the velocity of each location.
A digital .75 in. (70 mm) rotating
vane anemometer or equivalent
is suggested. The center of the
anemometer should be held in.
(50 mm) from the face of the filters
as shown in Fig. . It is helpful
to make a bracket to keep the
anemometer at the in. (50 mm)
distance and parallel to the filter.
Both squareness and distance are
very important for accuracy.
Calculate the average velocity for the filter.
3. Determine the filter's conversion factor from the table.
4. Calculate the filter's volume in CFM (m
conversion factor.
5. Calculate the hood's volume by repeating the process for the remaining filters and summing the
individual filter volumes.
Nominal Filter Size (H x L)
Inches
16 x 16
16 x 0
0 x 16
0 x 0
Example: Exhaust Only Hood with three 20 x 16 Filters
Measured velocities in fpm for one 0 x 16 Filter
Average Velocity
(Imperial)
(Metric)
For a nominal filter size of 0 x 16, the conversion factor is 1.90 Imperial (.177 Metric)
Volume for one filter
Total hood volume
Millimeters
400 x 400
500 x 400
400 x 500
500 x 500
Sum of Velocity Readings
=
Number of Readings
55 + 50 + 56 + 48 + 40
=
5
4663 + 457 + 4681 + 4535 + 4389
=
5
= Conversion Factor x
=
1.90
=
.177
= (Filter 1 Volume) + (Filter Volume) + (Filter 3 Volume)
=
474.6
+
=
809
+
2 in.
x
3
/hr) by multiplying the average velocity by the
x
x
Imperial
Conversion Factor
1.63
.13
1.90
.48
= 49.8 fpm
= 4568 m/hr
Average Velocity
x
49.8 fpm
x
4568 m/hr
455.4
+
880
+
Rotating Vane Anemometer
x
x
Metric
Conversion Factor
H/4
.157
.198
.177
.30
255
(4663.44 m/h)
(4572 m/h)
256
(4681.73 m/h)
248
(4535.42 m/h)
(4389.12 m/h)
=
474.6 cfm
=
809 m
3
/hr
470.1
= 1400.1 cfm
799
= 488 m
Fig.
H/4
H
H/2
250
240
3
/hr
17
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