Measure the velocity of each location.
A digital 2.75 in. (70 mm) rotating |
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vane anemometer or equivalent |
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is suggested. The center of the | Airflow |
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anemometer should be held 2 in. |
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(50 mm) from the face of the filters as |
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shown in Fig. 30. It is helpful to make |
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a bracket to keep the anemometer |
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at the 2 in. (50 mm) distance and |
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parallel to the filter. Both squareness |
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| Fig. 30 | ||
and distance are very important for |
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accuracy. |
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Calculate the average velocity for the filter.
3.Determine the filter’s conversion factor from the table.
4.Calculate the filter’s volume in CFM (m3/hr) by multiplying the average velocity by the conversion factor.
5.Calculate the hood’s volume by repeating the process for the remaining filters and summing the individual filter volumes.
Nominal Filter Size (H x L) | Imperial | Metric | |
Inches | Millimeters | Conversion Factor | Conversion Factor |
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16 x 16 | 400 x 400 | 1.63 | .157 |
16 x 20 | 500 x 400 | 2.13 | .198 |
20 x 16 | 400 x 500 | 1.90 | .177 |
20 x 20 | 500 x 500 | 2.48 | .230 |
Example: Exhaust Only Hood with three 20 x 16 Filters |
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Measured velocities in fpm for one 20 x 16 Filter |
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| 255 |
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Average Velocity | = |
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| 256 |
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| (4681.73 m/h) |
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| 248 |
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(Imperial) | = |
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(Metric) | = | 4663 + 4572 + 4681 + 4535 + 4389 | = 4568 m/hr |
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For a nominal filter size of 20 x 16, the conversion factor is 1.90 Imperial (.177 Metric) |
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Volume for one filter | = | Conversion Factor | x | Average Velocity |
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| = | 1.90 |
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| = | .177 |
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Total hood volume | = | (Filter 1 Volume) | + | (Filter 2 Volume) | + | (Filter 3 Volume) |
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| = | 474.6 | + |
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| = | 809 | + |
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| = | 2488 m3/hr | |||||||||||||
19 Canopy Hood
®
