Greenheck Fan Grease Grabber H2O Auto-Cleaning Hood GGH20 - Manual (Page 21)

21 Model GGH2O
®
Airflow Testing Procedure
NOTE
The constants 4.846 and 2.47 are factory derived for
use with the Grease Grabber™ H
2
O.
Calculation Example:
Five (5) inlet slot velocity readings (minimum)
Average Velocity (FPM) =
(175 + 210 + 250 + 190 + 160)  5 = 197 FPM
Hood Exhaust Rate (CFM) =
[(96 x 4.846) x (197 x 2.47)]  144 = 1572 CFM
After the appropriate number of readings have been
taken from the inlet slot of the hood, an average
reading can be calculated by summing the velocity
readings and dividing the total value by the number of
readings taken.
Next calculate the total hood airflow volume (CFM) by
using the following equation:
Hood CFM = [(Length of Hood in inches x 4.846) x
(Average inlet slot velocity x 2.47)]  144
Average Velocity =
Sum of Velocity Readings
Number of Readings
Hood Length
48 to 72
inches
72 to 120
inches
120 to 192
inches
Minimum Number
of Test Locations
3 5 7
For measuring exhaust airflow rates (cubic feet per
minute = CFM), use a short ridge meter to measure
velocities along the inlet slot of the hood. To ensure
accurate data, all appliances should be on. Multiple
locations need to be tested as outlined below to
ensure an accurate reading.
To take velocity readings along the length of the hood,
the edge of the short ridge meter must start/stop six
(6) inches from the end of the hood. Vertical placement
of the short ridge meter along the inlet is shown.
Hood Length 96 inches
Test Location
(off left; in inches)
6 27 48 69 90
Velocity Reading (fpm) 175 210 250 190 160
Short Ridge Meter Components