ASHRAE Journal - August 2024 - 17

COLUMN HVAC FUNDAMENTALS
One more value to calculate is the total static pressure
for the system. This is a large way that dust collector
systems vary from standard HVAC ducted systems.
Dust collectors are designed to handle very high static
pressures. It is common to have static pressures of
5 in. w.g. to 8 in. w.g. (1.2 kPa to 2 kPa) or higher. Thus,
it is crucial to calculate the expected static pressure
for your system to ensure the collector will be able to
perform correctly. In addition, it is benefi cial to limit the
amount of fl exible ductwork that is in the system. Flex
ductwork allows for greater dust accumulation by having
a corrugated interior surface. For the same reason, it is
also benefi cial to limit any unneeded duct transitions
or junctions. These connections reduce air velocity and
allow for dust to build up in the duct.
Dust Collector Placement
The next important factor in dust collector design
is the placement of the central dust collector, and the
International Mechanical Code 511 (IMC 511) gives the
requirements for this. The section states that " collectors
and separators...shall be constructed of noncombustible
materials and shall be located on the exterior of the
building or structure. A collector or separator shall
not be located nearer than 10 ft [3 m] to combustible
construction. " The code does provide two exceptions
to this outdoor requirement. (To see those exceptions,
please refer to the Relevant Codes section.)
Even if your system is allowed to be indoors, it is still
considered best practice to place collectors outdoors.
It is worth clarifying that if the outside of the building
you are collecting from is noncombustible, like a brick
or metal exterior, then you may place the unit right
next to the side of the wall. Be mindful of snow or ice
accumulation from the roof if you choose to place the
unit near or under the overhang of the roof.
Figure 1 shows a medium-sized dust collector outside
on a concrete pad. Note the two stainless steel panels
on the unit's left side. These are explosion vents. We
will discuss safety accessories in the next section, but
in short, these allow for a safe point of failure and
pressure release in case of an explosion within the
collector. They are engineered to be able to withstand
normal operating static pressures and loads, but under
elevated pressures, like when dust explodes, these
metal panels burst and allow the collector to relieve
the pressure safely.
TABLE 1 Kst values of common dusts.
COMMON DUSTS
Activated Carbon
Aluminum Grit
Aluminum Powder
Asphalt
Barley Grain Dust
Brown Coal
Charcoal
Cotton
Magnesium
Methyl Cellulose
Milk Powder
Paper Tissue Dust
Pectin
Polyurethane
Rice Starch
Silicon
Soap
Soy Bean Flour
Sulphur
Tobacco
Toner
Wood Dust
TABLE 2 Typical airflow through woodworking machines.
MACHINE
Circular Saw (Includes Table Saw, Radial-Arm Saw, and Miter Saw)
Band Saw
Belt Sander, up to 6 in.
Belt Sander, 7 in. to 9 in.
Disc Sander, up to 12 in.
Disc Sander, 13 in. to 18 in.
Drum Sander, up to 200 in.2 of sanding surface
Drum Sander, 201 in.2 to 400 in.2 of sanding surface
Jointer, up to 6 in.
Jointer, 7 in. to 12 in.
Thickness Planer, up to 13 in.
Thickness Planer, 14 in. to 20 in.
Router, Table-Mounted
Shaper
Lathe
MICRON
18
41
22
29
51
41
29
44
28
37
165
54
59
3
18
10
65
20
20
49
23
43
KST VALUE
44
100
400
117
240
123
117
24
508
209
90
52
162
156
190
126
111
110
151
12
145
102
cfm
350
350
440
550
350
440
350
550
350
440
400
785
195
350
350
A U G U ST 2 0 2 4 ashrae.org ASHRAE JOURNAL
17
WOOD MAGAZINE
http://www.ashrae.org
ASHRAE Journal - August 2024

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