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Smoke capture and grease extraction efficiency are depen-
dent upon the proper air velocity at the inlet slot of the ventilator.
The "Air Velocity Chart" below gives the optimum inlet slot
velocity and the minimum and maximum allowed velocities. If
the slot velocity is below or above the minimum or maximum,
the exhaust fan must be adjusted accordingly.
NOTE: The height of the inlet slot can vary depending upon the
design of the ventilator. It is, therefore, important to first
measure the inlet slot and compare it to the chart below to
determine the required average inlet slot velocity. The de-
signed air volume per lineal foot is related to the velocity as
shown on the chart below. The total air volume for the ventilator
can be found on the ventilator nameplate. (Refer to Figure 25).
Air velocity readings less than what is specified on the "Air
Velocity Chart" may allow smoke and grease to escape the
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*The nominal height of the front inlet slot on "DS" series ventilators is always 3".
MEASURING INLET SLOT VELOCITY
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confines of the ventilator and/or reduce grease extraction
efficiency. This can result in grease deposits which lead to
sanitation problems or fire hazards if left uncorrected. If the air
velocity readings are higher than the maximum allowed, it will
require more energy to operate the exhaust fan, excessive
noise levels will result, and grease can be pulled through the
extractor depositing in the duct and fan.
Higher or lower velocities than the allowed will normally put the
entire heating and ventilating system out of balance.
When measuring the air velocity it is very important to take
readings across the inlet slot plane as illustrated in Figures 23
and 24. Positioning the sensing head incorrectly will give
velocity readings that cannot be compared to the "Air Velocity
Chart". The sensing heads shown in Figure 23 are of the design
typically used on anemometer type instruments.
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