High Velocity Cartridge Filters
A. Exhaust
With all the filters in place, determine the total hood exhaust | 1/4 Width |
volume with a rotating vane anemometer as follows: |
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1.All cooking equipment should be on. If the hood has internal short circuit
2.Measuring Velocities
•Velocity measurement should be taken at three locations per filter.
These must be over the inlet opening as shown in Fig. 35.
•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. 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.
1/2 Width
1/4 Width
Fig. 35
2 in.
Rotation Vane
Anemometer
Fig. 36
Cartridge Filter Size | Imperial | Metric | |||
Conversion Factor | Conversion Factor | ||||
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16 in. (400 mm) high with 4 in. (100 mm) high inlet | 1.63 | 1/ft3 | 5.35 | 1/m3 | |
20 in. (500 mm) high with 4 in. (100 mm) high inlet | 2.15 | 1/ft3 | 7.05 | 1/m3 | |
16 in. (400 mm) high with 7 in. (120 mm) high inlet | 1.24 | 1/ft3 | 4.07 | 1/m3 | |
20 in. (500 mm) high with 7 in. (120 mm) high inlet | 1.58 | 1/ft3 | 5.18 | 1/m3 | |
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 | |||||
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| Number of Readings | |||||
(Imperial) | = | 5330 | = | 444.2 fpm | |||
12 | |||||||
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(Metric) | = | 97474 | = | 8123 m/hr | |||
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CFM per linear foot | = | Average Slot Velocity | |||||
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| Conversion Factor | |||||
| = | 444.2 fpm | = | 206.6 cfm/linear foot | |||
| 2.15 |
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| = | 8123 m/hr | = | 1152 m3/hr | |||
| 7.05 |
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Filter Readings (fpm)
470 | 440 | 425 |
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482 | 430 | 453 |
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455 | 431 | 441 |
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399 | 439 | 465 |
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Filter Readings (m/hr) | ||
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8595 | 8047 | 7772 |
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8815 | 7864 | 8284 |
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8321 | 7882 | 8065 |
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7297 | 8028 | 8504 |
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Hood exhaust volume = | CFM/linear foot (m3/hr / m) | x | Hood Length |
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= | 206.6 | x | 9 ft. | = | 1859.4 cfm | |
= | 1152 | x | 2.74 m | = | 3156 m3/hr | |
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22 | Canopy Hood |
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