Air-filtration module with ionization for elimination of static electricity

A filtration module containing a filter element is provided with an ionization device on the outlet side of the filter module which utilizes the outlet grille and portions of the standard filter element as components of the ionization device.

BACKGROUND OF THE INVENTION 
Several manufacturing and research activities require so-called "clean 
room" environments to avoid contamination of the articles being handled. 
It is standard practice to arrange a number of filtration modules in the 
ceiling area of a clean room, with some form of air outlet provided 
adjacent the floor level. Air is admitted to the filtration modules by 
standard ducting extending to a blower system, with the air normally being 
recirculated. The wide use of this type of equipment has developed a 
generally similar configuration for the modules, which includes some form 
of housing providing an equalization space between the housing intake and 
a filter element, and a grille defining the outlet of the module into the 
room. Some types of the module provide for the replacement of the filter 
elements from the interior of the room, and other forms of the modules are 
essentially throw-away assemblies that are discarded when the filter can 
no longer perform its function. In the latter case, it is common to 
utilize the wooden frame of the standard filter element as a part of the 
housing of the module. In both types of module, a grille of some form is 
mounted in a position spaced downstream from the outlet side of the 
filter. The standard filter element is the same in both cases, and 
consists of a rectangular wooden frame containing densely convoluted 
paper-like material separated by aluminum foil separation panels. 
The filter element goes a long way toward the removal of particulate 
material suspended in the air flow, but can never remove all of the 
particles that might conceivably contaminate delicate instruments or 
electronic components. A valuable adjunct to clean room filtration 
equipment has been a type of air-ionization equipment that tends to 
neutralize any static charges that may develop on articles within the room 
so that they do not attract the suspended particles that still remain 
carried by the air stream, or which may exist as a result of being carried 
into the room by personnel, work articles, or equipment. Basically, the 
ionization devices consist of a group of electrostatically charged bars 
arranged in a generally planar configuration, with some form of ground 
grid disposed on opposite sides of the charged bars with respect to the 
direction of movement of the air. Normally, the entire air stream is 
subject to the influence of this assembly. 
SUMMARY OF THE INVENTION 
An air-filtration module has a housing defining an air passage, and a 
filter element disposed across this passage. On the outlet side of the 
filter element, an ionization unit has electrically charged bars in the 
path of the air flow, and ground elements on opposite sides of the bars 
with respect to the direction of air flow. In one form of the invention, 
one of these ground elements is a metallic foil employed in the filter 
elements; and in another form of the invention, the other ground element 
is a metalliic grille defining the exhaust outlet of the module.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The filtration module illustrated in the drawings includes a housing 
assembly formed by the hood 10 (covered by the insulation indicated at 
11), the frame 12 of the standard HEPA filter element 13, and the 
extension frame 14. The hood 10 is provided with an inlet collar 15 
controlled by a valve plate 16 supported on the screw 17. This screw 
engages the central boss 18 in threaded engagement, and is manipulated 
through a vertical opening in the filter element 13 covered by the plug 
19. Generally radial arms as indicated at 20 and 21 in FIG. 1 extend out 
to the collar 15 to maintain the position of the control assembly. The 
space 22 between the hood 10 and the filter element 13 provides for the 
equalization of the air flow over the top of the filter element, from 
which the air entering through the collar 15 passes through the filter 
element to exhaust into the room through the openings in the metal grille 
23 secured to the bottom edge of the extension frame 14 by screws as shown 
at 23 a-e in FIG. 1. The hood 10 has a lower flange 24 secured to the top 
edge of the frame 12 of the filter element by a number of peripherally 
spaced screws 25. The extension frame 14 is secured to the frame 12 by 
clips as shown at 26 secured to the sides of the frame 12 by screws as 
shown at 27, and to the sides of the extension frame 14 by the screws 
indicated at 28. This type of assembly is not designed for normal 
replacement of the filter element 13, and is essentially at throw away 
assembly that may be discarded, or subject to salvage, when the filter 
element 13 can no longer perform its function properly. The entire unit 
may be suspended in position adjacent the ceiling of a room through 
brackets as indicated at 29-31 in FIGS. 4 and 5. Normally, there will be 
four of these brackets, one of these (29a) being concealed behind the 
brackets 29 and 31 in FIGS. 4 and 5. FIGS. 4 and 5, incidentally, do not 
show the insulaton 11 in place. 
The ionization unit indicated at 32 is mounted in the space between the 
underside of the filter element 13 and the grille 23. The unit includes 
the non-conductive bars 33 and 34, the ends of which are received in 
convenient recesses in the walls of the extension frame 14. A conductive 
member 35 is received in suitable openings in the bars 33 and 34 in a 
serpentine configuration, and is connected to a high-voltage source (not 
shown) by the cable 36. The conventional form of this unit also includes a 
ground grid disposed on opposite sides of the plane of the charged member 
35, but the present invention provides these components through a second 
use of the aluminum foil spacing panels conventionally interposed between 
the folds of the paper-like material constituting the filter body of the 
element 13. These foil panels emerge at the lower face of the filter 
element, and this foil material is contacted by the conductive clip 37 
interposed between the filter element 13 and the bar 34 of the ionization 
unit. A wire 38 connects this clip also to the screw 39 engaging the 
aluminum grille 23 so that the foil and the grille form ground components 
on opposite sides of the plane of the charged member 35. The charged 
member 35 is normally provided with discharge points as indicated at 35a, 
and experience has shown that there should be a minimum of one and 
five-sixteenths of an inch between the ends of these points and the 
conductive grille 23. The ground wire or strap 38 is preferably connected 
to either an external ground, or to a ground wire in the cable 36. The 
structure of the usual grounding grids associated with the ionization unit 
is thus eliminated by a dual use of components performing other functions 
in the module. It should be noted that the incorporation of the ionization 
unit into the module simplifies the wiring problems, and improves the 
protection of the components.