A. Exhaust
With all the filters in place, determine the total hood exhaust |
| 1/2 Width |
volume with a rotating vane anemometer as follows: | 1/4 Width | 1/4 Width |
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1. All cooking equipment should be off. If the hood has internal |
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short circuit |
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2.Measuring Velocities
•Measurement should be taken at six locations per filter.
They must be over the inlet opening as shown in Fig. 39.
• Measure the velocity of each location. A digital 2.75 in. (70 mm) 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. 40. 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 velocity for the filter.
4.Determine the filter’s conversion factor from the table.
5.Calculate each filters volume in CFM by multiplying the average velocity by the conversion factor.
Nominal Filter Size (H x L) | Imperial | Metric | |
Inches | Millimeters | Conversion Factor | Conversion Factor |
16 x 16 | 400 x 400 | 1.31 ft2 | .122 m2 |
16 x 20 | 400 x 500 | 1.65 ft2 | .153 m2 |
20 x 16 | 500 x 400 | 1.23 ft2 | .114 m2 |
20 x 20 | 500 x 500 | 1.65 ft2 | .153 m2 |
2 in.
Rotating Vane
Anemometer
Fig. 40
Example: (Imperial)
Hood Length = 7 feet 0 inches with four 20 x 20 filters.
Measure the velocities in fpm for each 20 x 20 filter (six readings per filter)
| Filter 1 | 225 | 201 | 187 |
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| 210 | 238 | 197 |
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| Filter 2 | 228 | 222 | 226 |
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| 237 | 240 | 220 |
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| Filter 3 | 230 | 245 | 240 |
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| 250 | 223 | 219 |
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| Filter 4 | 225 | 265 | 219 |
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| 245 | 221 | 200 |
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Average slot velocity for Filter 1 = | Sum of Velocity Readings | |||||
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| Number of Readings | ||
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| = | 1258 | = 209.7 fpm | |
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(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 ft2 | x | 209.7 ft./min. |
= | 346.0 cfm (repeat for each filter) | ||
Total hood volume
=Filter 1 + Filter 2 + Filter 3 + Filter 4 Volume Volume Volume Volume
=346.0 + 377.6 + 386.9 + 378.1 = 1488.6 cfm
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)
| Filter 1 | 4114.80 | 3675.88 |
| 3419.86 |
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| 3840.48 | 4352.54 |
| 3602.74 |
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| Filter 2 | 4169.66 | 4059.94 |
| 4133.08 |
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| 4334.26 | 4389.21 |
| 4023.36 |
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| Filter 3 | 4420.12 | 4480.56 |
| 4389.12 |
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| 4572.00 | 4078.22 |
| 4005.07 |
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| Filter 4 | 4114.80 | 4846.52 |
| 4005.07 |
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| 4480.56 | 4041.65 |
| 3657.60 |
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Average slot velocity for Filter 1 | = | Sum of Velocity Readings | ||||
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| Number of Readings | |
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| = | 23006 | = 3834 m/hr |
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(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 m2 | x | 3834 m/hr |
= | 586.7 m3/hr (repeat for each filter) | ||
Total hood volume
=Filter 1 + Filter 2 + Filter 3 + Filter 4 Volume Volume Volume Volume
= 587 + 642 + 657 + 642 = 2528 m3/hr
24 Canopy Hood
®
