Kitchen Hoods • Type I and Type II18
Grease-X-Tractor™ High Efficiency Filters or
Grease Grabber™ Multi-Filtration System -
Rotating Vane Method
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 off. If the hood has
internal short circuit make-up air, it should be turned
off.
2. Measure velocities
Measurement should be taken at six locations per
filter. They must be over the inlet opening as shown
in Fig. 14.
Measure the velocity of each location. A digital
2.75 in. (69.85 mm) rotating vane anemometer
or its equivalent is suggested. The center of the
anemometer should be held 2 in. (50.8 mm) from
the face of the filters as in Fig. 15. It is helpful to
make brackets to keep the anemometer at the 2 in.
(50.8 mm) distance and parallel to the filter. Both
squareness and distance are important for accuracy.
3. Calculate the average velocity for the filter.
4. Determine the filter’s conversion factor from the
table.
5. Calculate each filter’s volumetric flow rate in CFM by
multiplying the average velocity for each filter by the
conversion factor.
2 in.
(50.8 mm)
Rotating Vane
Anemometer
1/2 Width
1/4 Width
1/4 Width
1/2 Height
Fig. 15
Nominal Filter Size (H x L)
Imperial
Conversion
Factor
Metric
Conversion
Factor
Inches Millimeters
16 x 16 400 x 400
1.31
ft
2
.122 m
2
16 x 20 400 x 500
1.65
ft
2
.153 m
2
20 x 16 500 x 400
1.23
ft
2
.114 m
2
20 x 20 500 x 500
1.65
ft
2
.153 m
2
2 in.
(50.8 mm)
Rotating Vane
Anemometer
1/2 Width
1/4 Width
1/4 Width
1/2 Height
Fig. 14
Filter 1
225 201 187
210 238 197
Filter 2
228 222 226
237 240 220
Filter 3
230 245 240
250 223 219
Filter 4
225 265 219
245 221 200
Average slot velocity for Filter 1 =
Sum of Velocity Readings
Number of Readings
=
1258
6
= 209.7 ft/min.
(repeat for each filter)
For a nominal filter size of 20 x 20, the conversion factor is 1.65
Volume for Filter 1 = Conversion Factor x Average Velocity
= 1.65 ft
2
x 209.7 ft/min.
= 346.0 cfm (repeat for each filter)
Example: (Imperial)
Hood Length: 7 feet 0 inches with four 20 x 20 filters.
Measure the velocities in ft/min. for each 20 x 20 filter
(six readings per filter)
Total hood volume
=
Filter 1
Volume
+
Filter 2
Volume
+
Filter 3
Volume
+
Filter 4
Volume
= 346.0 + 377.6 + 386.9 + 378.1 =
1488.6 cfm
Filter 1
4114.80 3675.88 3419.86
3840.48 4352.54 3602.74
Filter 2
4169.66 4059.94 4133.08
4334.26 4389.21 4023.36
Filter 3
4420.12 4480.56 4389.12
4572.00 4078.22 4005.07
Filter 4
4114.80 4846.52 4005.07
4480.56 4041.65 3657.60
Example: (Metric)
Hood Length: 2.13 meters, with four 500 x 500 mm filters.
Measure the velocities in m/hr for each 500 x 500 mm filter
(six readings per filter)
Average slot velocity for Filter 1 =
Sum of Velocity Readings
Number of Readings
=
23006
6
= 3834 m/hr
(repeat for each filter)
For a nominal filter size of 500 x 500, the conversion factor is .153
Volume for Filter 1 = Conversion Factor x Average Velocity
= .153 m
2
x 3834 m/hr
=
586.7 m
3
/hr (repeat for each filter)
Total hood volume
=
Filter 1
Volume
+
Filter 2
Volume
+
Filter 3
Volume
+
Filter 4
Volume
= 587 + 642 + 657 + 642 =
2528 m
3
/hr
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