0
High Velocity Cartridge Filters
Rotating V ane
Anemometer
2 in.
Fig. 7
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.
. Measuring Velocities
• Velocity measurement should be taken at three locations per filter.
These must be over the inlet opening as shown in Fig. 7.
• Measure the velocity of each location. A digital .75 in. (70 mm)
rotating vane anemometer or its equivalent is suggested. The center
of the anemometer should be held in. (50 mm) from the face of
the filters as in Fig. 8. It is helpful to make brackets to keep the
anemometer at the 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
Fig. 8
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
0 in. (500 mm) high with 4 in. (100 mm) high inlet
.15 1/
ft
3
7.05 1/m
3
16 in. (400 mm) high with 7 in. (10 mm) high inlet
1.4 1/
ft
3
4.07 1/m
3
0 in. (500 mm) high with 7 in. (10 mm) high inlet
1.58 1/
ft
3
5.18 1/m
3
Filter Readings (fpm)
470
440
45
48
430
453
455
431
441
399
439
465
Filter Readings (m/hr)
8595
8047
777
8815
7864
884
831
788
8065
797
808
8504
Example:
Measure the slot velocities in fpm for a 9 ft. (.74 m) hood with four 0 x 0 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
1
= 444. fpm
(Metric)
= 97474
1
= 813 m/hr
CFM per linear foot
=
Average Slot Velocity
Conversion Factor
=
444. fpm
.15
= 06.6 cfm/linear foot
=
813 m/hr
7.05
= 115 m
3
/hr
Hood exhaust volume
= CFM/linear foot (or m
3
/hr / m) x Hood Length
=
06.6
x
9 ft.
= 1859.4 cfm
=
115
x
.74 m
= 3156 m
3
/hr
