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22
Canopy Hood
®
Rotation Vane
A
nemometer
2 in.
Fig. 35
Fig. 36
Cartridge Filter Size
Imperial
Conversion Factor
Metric
Conversion Factor
16 in. (400 mm) high with 4 in. (100 mm) high inlet
1.63 1/
ft
3
5.35 1/m
3
20 in. (500 mm) high with 4 in. (100 mm) high inlet
2.15 1/
ft
3
7.05 1/m
3
16 in. (400 mm) high with 7 in. (120 mm) high inlet
1.24 1/
ft
3
4.07 1/m
3
20 in. (500 mm) high with 7 in. (120 mm) high inlet
1.58 1/
ft
3
5.18 1/m
3
Filter Readings (fpm)
470 440 425
482 430 453
455 431 441
399 439 465
Filter Readings (m/hr)
8595 8047 7772
8815 7864 8284
8321 7882 8065
7297 8028 8504
High Velocity Cartridge Filters
A. Exhaust
With all the filters in place, determine the total hood exhaust
volume with a rotating vane anemometer as follows:
1. All cooking equipment should be on. If the hood has
internal short circuit make-up air, it should be turned off.
2. Measuring Velocities
• Velocitymeasurementshouldbetakenatthreelocationsperfilter.
These must be over the inlet opening as shown in Fig. 35.
• Measurethevelocityofeachlocation.Adigital2.75in.(70mm)
rotating vane anemometer or its equivalent is suggested. The center
of the anemometer should be held 2 in. (50 mm) from the face of
the filters as in Fig. 31. It is helpful to make brackets to keep the
anemometer at the 2 in. (50 mm) distance and parallel to the filter.
Both squareness and distance are important for accuracy.
3. Calculate the average slot velocity.
4. Calculate the CFM per linear foot by dividing the average velocity by a
conversion factor listed in the following table.
5. Calculate the hood’s exhaust volume by multiplying the CFM per linear
foot by the length of hood.
1/4 Width
1/4 Width
1/2 Width
1/2 Height
Inlet Height
Filter Height
Example:
Measure the slot velocities in fpm for a 9 ft. (2.74 m) hood with four 20 x 20 in. (500 x 500 mm)
filters with standard opening, three readings per filter.
Average slot velocity =
Sum of Velocity Readings
Number of Readings
(Imperial)
=
5330
12
=
444.2 fpm
(Metric)
=
97474
12
=
8123 m/hr
CFM per linear foot =
Average Slot Velocity
Conversion Factor
=
444.2 fpm
2.15
=
206.6 cfm/linear foot
=
8123 m/hr
7.05
=
1152 m
3
/hr
Hood exhaust volume = CFM/linear foot (m
3
/hr / m) x Hood Length
= 206.6 x 9 ft. =
1859.4 cfm
= 1152 x 2.74 m =
3156 m
3
/hr