Greenheck Fan Canopy Type Kitchen Hoods 452413 - Manual (Page 20)

20 Kitchen Hoods • Type I and Type II
Testing Hood Air Volume - Rotating Vane
Method
Short Circuit Hoods
A. Supply
All cooking equipment should be off. The hood exhaust
should also be off.
1. Measure Velocities
Velocity measurements should be made with a digital
2.75 in. (69.85 mm) rotating vane anemometer or its
equivalent.
One velocity measurement should be taken for
every 8 in. (203.2 mm) of short circuit opening
length, starting tight against one edge of the
opening, and finishing tight against the other edge.
The anemometer should be placed at the bottom
edge of the opening, flush with the bottom lip.
Both squareness and placement are important for
accuracy.
2. Calculate the average slot velocity.
3. Calculate the volumetric flow rate per linear foot by
dividing the average velocity by a conversion factor
of 5.52 per ft. If metric units are used, divide the
average velocity by a conversion factor of 1.68 per
meter.
4. Calculate the hoods supply volume by multiplying the
CFM per linear foot by the total hood length.
Hood supply volume = CFM/linear foot (m
3
/hr / m) x Hood Length
(Imperial) = 183.8 x 4 ft. = 735.2 cfm
(Metric) = 1026 x 1.22 m = 1252 m 3 /hr
Example: 4 ft. (1.22 m) short circuit hood (36 inch (.914 m) short circuit opening
Number of readings = 36 in. / 8 in. => 6 readings (.914 m / .2 m => 6 readings)
CFM per linear foot =
Average Slot Velocity
Conversion Factor
(Imperial) =
1014.3 ft/min.
5.52
= 183.8 cfm/linear ft.
(Metric) =
1723 m/hr
1.68
= 1026 m 3 /hr
Average Velocity =
Sum of Velocity Readings
Number of Readings
(Imperial) =
786 + 900 + 1126 + 1048 + 1111 + 1115
6
=
6086
6
= 1014.3 ft/min.
(Metric) =
1335 + 1529 + 1913 + 1780 + 1888 + 1894
6
=
10339
6
= 1723 m/hr
®