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20
Canopy Hood
®
B. Supply (If Applicable):
Example for Perforated Face Supply
1. Hood set up
If the make-up air unit has a temperature control, it should be used to keep the supply air at the
desired room discharge air temperature.
2. Measure Velocities
Divide the perforated face panel into a grid of equal areas, each approximately 4 in. (100 mm)
square.
Measure the velocity at the center of each grid area. A digital 2.75 in. (70 mm) rotating vane
anemometer or equivalent is suggested. The center of the anemometer should be held tight to
the face of the panel, and parallel to the filter. Both squareness and distance are important for
accuracy. Calculate the average velocity of the panel.
3. Measure the length, height, and width of the perforated face panel.
4. Calculate the perforated face panel volume in CFM by using the following formula:
Volume = Avg. Velocity
*
Length (in.)
*
Height (in.)
*
0.005
Volume = Avg. Velocity
*
Length (m)
*
Height (m)
*
0.72
5. Calculate the system’s volume by repeating the process for the remaining panels and adding
the individual panel volumes together.
Total system volume = (Panel 1 Volume) + (Panel 2 Volume) + (Panel 3 Volume)
= 606.4 + 614.3 + 593.8 =
1814.5 cfm
= 1029 + 1044 + 1009 =
3082 m
3
/hr
Example: Face Supply Hood with three 28 in. (.711 m) Perforated Panels
Measured velocities in FPM for one perforated panel
Average Velocity =
Sum of Velocity Readings
Number of Readings
(Imperial)
=
260 + 250 + … + 265 + 260
28
=
270.7 fpm
(Metric)
=
4755 + 4572 + … + 4846 + 4755
28
=
4951 m/hr
Measure Length and Height = 28 in. (.711 m) long perforated panels x 16 in. (.406 m) high
Volume for one panel =
Conversion
Factor
x
Average
Velocity
x Length x Height
= 0.005 x 270.7 fpm x 28 x 16 =
606.4 cfm
= 0.72 x 4951 m/hr x .711 x .406 =
1029 m
3
/hr
Filter Readings (fpm)
260 250 255 260 250 255 265
270 275 270 280 265 265 270
290 285 280 280 275 290 295
285 275 280 260 270 265 260
Filter Readings (m/hr)
4755 4572 4663 4755 4572 4663 4846
4938 5029 4938 5121 4846 4846 4938
5304 5212 5121 5121 5029 5304 5395
5212 5029 5121 4755 4938 4846 4755