Air filtration unit

A modular, low-profile ceiling air filtration unit is disclosed having a diffuser plate with an unperforated zone along one edge, the remainder of the plate being perforated. A blower in the unit plenum directs air toward the end of the plenum having the unperforated zone. Turbulent air impinging on the housing end wall is prevented from passing through to a filter by the unperforated zone of the diffuser plate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an air filtration unit and, more 
particularly, to a low-profile, ceiling mountable module or unit specially 
and economically constructed to provide a uniform, low-velocity, downward 
flow of filtered air. 
2. Description of the Related Art 
In the construction of clean rooms used for the manufacture of electronic 
components, medical devices, and the like, it is usually necessary to 
provide a supply of filtered air. The air must not only be clean, but 
should be provided in a low velocity, downward, generally laminar flow so 
as not to create turbulent zones within the room and to carry contaminants 
from the room. 
Air filtration units are known in the prior art in which the unit is 
constructed to be supported within one of the grid openings of a ceiling 
grid. Such units typically include a housing defining a plenum, an upper 
air inlet, a blower, and a filter medium at the lower opening of the 
plenum. Low-profile units have been provided in which the blower is 
mounted within the plenum. 
Whatever the construction of the air filtration unit, it is necessary to 
reduce any turbulence created by the blower, and to arrange the plenum 
such that a uniform flow of air through the filter medium is attained. In 
the past, air filtration units have been constructed with baffle plates or 
internal passageways intended to direct and distribute the flow of air 
from the blower to the filter. Such measures have tended to make the 
filtration units more complicated and expensive. Furthermore, the addition 
of such internal structures makes it more difficult to minimize the height 
of the unit. 
Accordingly there is an unmet need for a clean room air filtration unit 
having a minimal height or profile and that is simply and economically 
constructed. 
SUMMARY OF THE INVENTION 
The present invention satisfies the aforementioned need by providing an air 
filtration unit having a diffuser plate disposed between the blower and 
the filter medium, the diffuser plate having an unperforated zone at one 
end opposite the blower, the remainder of the diffuser plate being 
perforated. The blower is situated within the plenum, preferably toward 
one end of the plenum adjacent the perforated zone. The air outlet of the 
blower is directed toward a second, opposite end of the plenum. The 
unperforated zone of the diffuser plate is situated along the second end 
of the plenum. The flow of air exiting the blower travels across the 
diffuser plate and impinges on the housing wall at the second end of the 
plenum. The turbulent region of air at the second end is precluded from 
entering the filter medium by the unperforated zone of the diffuser plate. 
Air is allowed to pass through the diffuser plate to the filter medium 
only at the remainder of the plenum away from the turbulent region. In 
this manner, a uniform, low-velocity, substantially laminar flow of air is 
attained without the need for additional baffles or passageways within the 
plenum. 
These and other objects, advantages, and features of the present invention 
will be more fully understood and appreciated by reference to the written 
specification and appended drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
By way of disclosing a preferred embodiment, and not by way of limitation, 
there is shown in the figures an air filtration unit 10 which includes in 
its general organization an air inlet 12, a housing 14, a blower 16, a 
filter 18, and a diffuser plate 20. Preferably, the filter is a HEPA 
filter, as is well known in the art. The housing 14, which is generally 
rectangular in plan, includes an upper portion 22 which defines a plenum 
24 and a lower portion 26 suitably configured to receive and retain the 
filter 18. The housing further includes opposed, spaced-apart first and 
second end walls 28, 30, side walls 32, 34, and an outlet opening defined 
by the lower edges of the end and side walls. The diffuser plate 20 is 
disposed within the outlet opening of the housing between the plenum and 
the filter medium. The lower portion 26 of the housing is suitably 
dimensioned and constructed to be supported by a ceiling grid G 
substantially coextensively with one of the grid openings. 
The air inlet 12 includes a grille or prefilter 35 through which air is 
drawn by the blower 16. In a completed installation, the air inlet 12 will 
either be connected to suitable ductwork or will draw air from the space 
above the suspended ceiling. The flow of air passes through an opening 36 
of the upper wall to the blower 16. The blower is a centrifugal or 
squirrel cage type mounted with its axis of rotation substantially normal 
to the diffuser plate 20. The blower is mounted within the plenum closer 
to the first end wall 28 than the second end wall 30. The blower 16 
includes a blower housing 38 having a blower outlet opening 40 directed 
generally toward the second end wall 30. 
The diffuser plate 20 includes an unperforated zone 42 disposed across an 
end portion of the diffuser plate adjacent the housing second end wall 30. 
The remainder of the diffuser plate comprises a perforated zone 44 which 
is formed with a large number of closely spaced openings through which the 
flow of air may pass. In the preferred embodiment illustrated in the 
Figures, the diffuser plate 20 is an assembly of an unperforated plate and 
a perforated plate which are overlapped as at 46 and joined together by 
spot welding or other suitable means. Those with ordinary skill in the art 
will realize that the diffuser plate 20 may also be formed as a unitary 
plate being solid at one extent and perforated at the other. 
As shown by the air flow lines 50 of FIG. 2, air leaving the blower outlet 
40 passes within the plenum across the inner surface of the diffuser plate 
toward the second end wall 30. A region of turbulence is caused by the air 
flow impinging on the wall 30. This region of turbulent flow is disposed 
in the plenum generally adjacent to and coextensive with the unperforated 
zone 42 of the diffuser plate. In this manner, turbulent air in this 
region is prevented from passing through the diffuser plate to the filter. 
Air is able to flow through the diffuser plate only in the region adjacent 
the perforated zone as indicated by flow lines 52. In this region, the 
turbulence is much reduced, thus promoting a uniform, more laminar flow of 
air to the filter. 
As shown in FIG. 2, the underside of the diffuser plate 20 is spaced apart 
a small distance from the upper side of the filter 18. This spacing 
enables a flow of air to reach under the unperforated zone as indicated by 
flow arrows 54 and pass through the entirety of the filter. 
Preferably the unperforated zone of the diffuser plate will extend over a 
minor extent of the housing opening, while the perforated zone will extend 
over the major extent. For an air filtration unit dimensioned to fit 
within a nominal 2 feet by 4 feet ceiling grid opening, the unperforated 
zone is preferably approximately 8 inches wide. The diffuser plate is 
preferably made of 18 gauge metal plate having 5/64 inch diameter holes 
staggered on 5/32 inch centers. The width of the unperforated zone, as 
well as the other dimensions of the unit, may easily be modified according 
to the ceiling configuration, air flow rate, and other pertinent factors. 
It should be noted that the plenum is free of any baffles or specially 
arranged passageways. The plenum need only accommodate the blower, so that 
the height or profile of the air filtration unit may be minimized. 
The above description is that of a preferred embodiment of the invention. 
Various alterations and changes can be made without departing from the 
spirit and broader aspects of the invention as set forth in the appended 
claims, which are to be interpreted in accordance with the principles of 
patent law, including the Doctrine of Equivalents.