Accurex XBEW Installation, Operation And Maintenance Manual page 21

Perforated Face Supply or External Supply
Plenum - Shortridge VelGrid Method
1. Hood set up.
Turn on both exhaust and supply air. If the make-up
air unit has temperature control, it should be used to
keep the supply air at the desired room discharge air
temperature.
2. Measure velocities.
Take two velocity readings on the first perforated
panel on the supply plenum. Center the VelGrid
along the width and 2 in. (50.8 mm) from each end
of the perforated panel as shown in Fig. 19. Take the
average of these two values and record.
Fig. 19
2.0 inches
(50.8 mm)
Center of
Perforated
Panel
(Width)
Length of Perforated Panel
3. Measure the length and width of the perforated
panel.
Example: Air supply plenum with three 24 inch (.610 m) by 12 inch (.305 m) perforated panels
Measured velocities in ft/min. for one perforated panel
Average Velocity =
=
(Imperial)
=
(Metric)
Measure length and width of perforated panel. 24 inches (.610 m) long by 12 inches (.305 m) wide
Volume for one panel = Conversion Factor x
=
(Imperial)
=
(Metric)
Total system volume =
=
(Imperial)
=
(Metric)
2.0 inches
(50.8 mm)
Sum of Velocity Readings
Number of Readings
256 + 259
2
4682 + 4737
2
Average Velocity
0.005 x
0.72 x
(Panel 1 Volume) + (Panel 2 Volume)
370.8 +
630.9 +
4. Calculate the perforated panel volume using the
following formula:
CFM = avg. velocity x length (in.) x width (in.) x 0.005
3
m /hr = avg. velocity x length (m) x width (m) x 0.72
5. Calculate the system's volume by repeating the
process for the remaining perforated panels and
FIGURE 6.3 VELGRID ASSEMBLY
adding the individual panel volumes together.
Place standoff spacers against
face of outlet or inlet grill,
filter, coil, etc.
Maintain 1½ inch
(38.1 mm) margin
Swivel bracket
Tubing connectors
Extension rods
= 257.5 ft/min.
= 4709.5 m/hr
x Length
257.5 ft/min. x 24
4709.5 m/hr x .610
+ (Panel 3 Volume)
373.1 +
633.9 +
Edge of outlet/inlet
active face area
Maintain 1½ inch
(38.1 mm) margin
Tubing harness
Pressure input ports
Neckstrap
External read jack
Pushbutton handle and plug
Handle bracket
Captive knob screws
x Width
x 12 = 370.8 cfm
x .305 = 630.9 m
369.0 = 1112.9 cfm
626.9 = 1891.7 m
Kitchen Hoods • Type I and Type II
3
/hr
3
/hr
21