Molded fiberglass air return filter grille

An air return filter or air supply grille assembly having an interchangeable perforated face plate hingedly attached directly to a molded fiberglass plenum. The molded fiberglass plenum has a preformed recess for receiving and positioning a filter resting on the face plate when used as an air return filter grille assembly. The hinge system for the interchangeable perforated face plate is comprised of a pair of mating half hinges with one half secured to the plenum and the other half secured to each interchangeable face plate. The grille assembly can be mounted and a perforated face plate selected to provide an air return filter grille assembly or an air diffusing supply grille assembly. The air filter grille assembly is constructed to mount easily on T-bar suspended ceilings with the perforated face plate held closed by manually rotatable pawls.

FIELD OF THE INVENTION 
This invention relates to air return filter grilles and more particularly 
relates to a molded fiberglass air return filter grille having a molded 
fiberglass plenum with foil reinforcement and a grille hinged directly to 
the plenum. 
BACKGROUND OF THE INVENTION 
Air return filter grilles are comprised of a plenum which may be sheet 
metal or fiberglass, attached to a metal frame mounted in ceilings, walls, 
and sometimes mounted on T-bar ceilings. The frames are constructed 
usually of aluminum or sheet metal with a perforated face plate or grate 
hingedly attached on one side, closed and held in place by screws on the 
side opposite the hinge. The sheet metal frame has a cavity or recess for 
mounting a filter behind the face plate. Besides being quite heavy in 
construction, the replacement of the filters require special tools for 
releasing the screws holding the face plate in position. Another 
disadvantage is that the substantial metal construction can make them 
noisy when air is flowing through the return filter. Also the cost, weight 
and bulk of metal construction are additional substantial disadvantages. 
It is therefore one object of the present invention to provide an air 
return filter mounting grille substantially lightweight in construction. 
Yet another object of the present invention is to provide an air return 
filter grille, having a unique molded fiberglass plenum with foil 
reinforcement. 
Yet another object of the present invention is to provide a lightweight air 
return filter grille, having high acoustical absorption, surpassing the 
substantial steel or metal units presently in use. 
Still another object of the present invention is to provide an air return 
filter grille which makes it easy to change the filter without the need 
for special tools or equipment. 
Yet another object of the present invention is to provide an air return 
filter grille having an unique fiberglass construction with the perforated 
face plate attached by a hinge directly to the molded fiberglass to 
provide a substantial reduction in weight and allow easy mounting on T-bar 
ceilings. 
Still another object is to construct an air return filter grille which 
mounts flush in T-bar suspended ceilings and matches air supply units in 
appearance. The unique construction provides a clean uncluttered design 
without the usual metal frame around the perforated metal face. 
Yet another object of the present invention is to provide an air system 
grille assembly having a unique fiberglass construction with a perforated 
face plate attached by a separable split hinge directly to the molded 
fiberglass to provide a substantial reduction in weight and allow easy 
mounting on T-bar ceilings. The separable split hinge allows the system to 
be used for an air return filter grille, or for an air supply system by 
removing and exchanging perforated face plates. 
BRIEF DESCRIPTION OF THE INVENTION 
The purpose of the present invention is to provide an improved air return 
filter grille that is lightweight in construction designed for easy 
replacement of filters without the need for tools or special equipment. 
The air return filter grille of the present invention is comprised of a 
unique molded fiberglass plenum having a foil reinforced upper surface for 
connecting the plenum to a flexible air duct. A recess is molded into the 
plenum for receiving up to a one inch filter. The plenum dimensions are 
such that it will fit comfortably on the flange of bars forming suspended 
T-bar ceilings. The plenum is secured against movement on the T-bar by at 
least one flexible sheet metal tab on either side constructed to bend 
around the rib of a T-bar and be fastened by a sheet metal screw. 
The entrance or opening to the plenum is closed by a perforated sheet metal 
face plate hingedly attached to the molded fiberglass plenum. The hinges 
are supported by a sheet metal channel clamped securely along one skirted 
edge of the fiberglass plenum. One side of the hinge is securely riveted 
or welded to the sheet metal channel while the other is riveted or welded 
to a flanged border on the perforated sheet metal face plate. The sheet 
metal channel is secured along the skirted edge of the fiberglass plenum 
with rivets or teeth formed by punching the sides of the sheet metal 
channel. The perforated face plate hinges and sheet metal channel form the 
only metal parts of the air return filter grille. 
Mounted on the perforated face plate are a filter stop for positioning a 
filter in the perforated face plate and a spring for securely holding the 
filter against the recess in the plenum when the perforated face plate is 
closed. An additional, but unique feature of this system, is the inclusion 
of pawls which hold the perforated face plate closed by engaging the T-bar 
flange. Two such pawls are sufficient to hold the perforated face plate 
closed with the filter properly positioned in the recess in the plenum. 
The pawls are formed with large slots allowing them to be easily rotated 
by hand, a coin or similar object. Thus no special tools are necessary for 
opening the face plate to remove and replace the filter. 
In an alternate embodiment of the grille assembly, the perforated face 
plate is attached by a separable split hinge directly to the molded 
fiberglass plenum. This construction allows the molded fiberglass plenum 
to be used for either air return or air supply purposes. The split hinge 
allows the face plate to be easily removed for exchange with a perforated 
face plate having a stop for positioning a filter when used as an air 
return filter grille, or changed to a perforated face plate having 
adjustable louvers such as those disclosed and described in U.S. Pat. No. 
4,266,470. The latter separable hinge construction allows the assembly to 
be quickly and easily changed to an air diffuser or air supply system. 
The above and other features of the invention will be more fully understood 
from the following detailed description and the accompanying drawings, in 
which:

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1 an air return filter grille assembly 10 constructed 
according to the invention is shown mounted on a suspended T-bar ceiling 
12, connected to a flexible duct 14. The T-bar ceiling 12 is a suspended 
ceiling comprised of joists 16 and 18, suspended on wires or cables 20 
secured to a solid surface or roof (not shown). The air return filter 
grille 10 is supported on flanges 22 and 24 on the joist 16 and 18 and on 
flanges 26 and 28 forming a part of crossbars 30 and 32 respectively. The 
air return filter grille 10 is secured to the suspended t-bar ceiling as 
will be described in greater detail hereinafter. 
Air return filter grille assembly 10 has a unique very simple construction 
with a minimum of lightweight metal parts. In FIG. 2, air return filter 
grille 10 is shown comprised of a unique molded fiberglass plenum 34, 
having a perforated face plate 36, hingely attached directly to a skirted 
edge of the plenum. Molded fiberglass plenum 34 is uniquely molded to 
comfortably fit on a suspended T-bar construction and has a recess 38, 
constructed to receive half to one inch filters 44, supported by 
perforated face plate 36. Filter 44 lies on face plate 36, which when 
closed securely holds the filter in recess 38. Molded fiberglass plenum 
then tapers toward an upper surface 40 where the plenum is connected to 
duct 14 through hole 42. 
It should be noted that the exterior of surface 40 is reinforced with foil 
45 (FIG. 9) prescored for receiving flexible duct connections of from six 
to fourteen inches. This construction is similar to that shown and 
described in U.S. Pat. No. 4,266,470 issued May 12, 1981. As in this 
patent the reinforcing foil 45 protects the edges of hole 42 from fraying 
and provides a secure surface for connecting duct 14 to the plenum with 
duct tape (not shown) if desired. 
A bottom view of the air return filter grille is shown in FIG. 3 with face 
plate 36 closed and held in place by pawls 46 and 48, rotably mounted on 
face plate 36. The pawls 46 and 48 are secured to face plate 36 by rivets 
50 and resilient spacers 52, allowing the pawls 46, 48 to easily rotate. 
Slots 54 and 56 formed in the pawls 46, 48 are made large enough so they 
can be easily rotated manually or with a coin, or similar object 
eliminating the need for any special tools to open the face plate and 
replace filter 44. 
As can be seen in FIG. 4, filter 44 snugly fits into recess 38 formed in 
the molded fiberglass plenum. Recess 38 is formed in the plenum during the 
molding and is strengthened by slightly increasing the compression of the 
molded fiberglass at area 58 around the periphery of the recess. Skirt 60 
on fiberglass plenum 34 provides a cavity for receiving flanged border 62 
of face plate 36 so that face plate 36 is flush with lower edge 64 of the 
molded fiberglass plenum when closed. 
Perforated face plate 36 is attached to molded fiberglass plenum 34 by 
hinges 66 and sheet metal channel 68. Channel 68 having hinges 66 attached 
by rivets or welded 70 is mounted on skirt 60 of fiberglass plenum 34 by 
clamping the channel against the molded compressed fiberglass of the 
skirt. Additional gripping of the sheet metal channel 68 is provided by 
punching teeth 72 in the sheet metal which bite into the fiberglass of 
skirt 60 (FIG. 6). Perforated face plate 36 is secured to hinge 66 by spot 
welding. 
Filter 44 is positioned on perforated face plate 36 by stop 74 secured to 
the face plate by rivet 76 and resilient spacer 78. To install the filter 
it is placed on face plate 36 in abutment with stop 74 as shown in FIG. 2. 
Filter 44 is held firmly in place in recess 38 by a resilient leaf spring 
80, also secured to perforated face plate 36 by a rivet 82 and resilient 
spacer 84. Spring 80 is configured to press against the surface of filter 
44 maintaining the edges of filter in firm engagement with recess 38. This 
prevents any air from entering the duct that does not pass through filter 
44. The leaf spring also keeps the filter in position as the unit cycles 
on and off thus preventing accumulating dust from shaking loose. 
The mounting of the air return filter assembly in the suspended T-bar 
ceiling is illustrated in FIG. 9. Molded fiberglass plenum skirt 60 rests 
on flange 22 of joist 16. Likewise the other skirt portions of molded 
fiberglass plenum 34 rest on the respective flanges of the other joist and 
T-bar cross members. The molded fiberglass plenum is then secured against 
movement by thin sheet metal tabs 86 bent around skirt 60 as shown at 90 
and secured by rivets 88. The sheet metal tab 86 is also bent around joist 
rib 92 as shown at 94 and secured by a sheet metal screw 96. This 
minimizes movement and vibrations of the air return filter grille 
assembly. 
FIGS. 10 through 14 illustrate an alternate embodiment of the grille 
assembly shown in FIGS. 1 through 9. The grille assembly of this 
embodiment uses the same plenum 34 as in the previous embodiment and is 
constructed to fit the T-bar construction having joists 16 and 18 and 
crossbar 32. However, in this embodiment the perforated face plate of the 
grille assembly 110 is interchangeable from an air return filter face 
plate to a louvered air supply face plate. 
Perforated face plate 112 is mounted on plenum 34 by a hinge 114 attached 
to metal channel 116 secured to plenum 34 by rivets as before. However, in 
this embodiment hinge 114 is a separable split-hinge as can be seen more 
clearly in FIGS. 12 through 14. Hinge 114 is comprised of socket half 118 
fastened be rivets 120 to channel 116 and has a cylindrical socket 122. 
The second half of hinge 114 is comprised of a plate 124 secured by rivets 
129 to face plate 112. Plate 124 has a hinge pin 126 fitting aperture 128 
in hinge socket 122. Thus, the grille assembly can be quickly and easily 
changed from an air return filter grille assembly as illustrated in FIG. 
2, to an air supply filter grille assembly by simply opening the grille 
and sliding pins 126 from each socket 122. 
Thus, the same plenum and assembly arrangement can be used to convert the 
air filter assembly of FIG. 2, to an air return assembly. The change is 
accomplished by simply detaching the perforated face plate by separating 
the hinges and replacing the face plate with the appropriate assembly. For 
an air return, a perforated face plate 34 having pinned half hinges as 
shown in FIG. 14 is slipped into the mating half hinge. For an air supply, 
a perforated face plate 12 having a half hinge as shown in FIG. 14 is 
fitted into the socket. Preferably a perforated face plate 112 for use as 
air supply may have adjustable louvers as shown and described in U.S. Pat. 
No. 4,266,470 incorporated herein by reference. 
Thus, the system disclosed can use the same plenum for either an air supply 
grille assembly or air return filter grille assembly by simply and quickly 
removing and changing the perforated face plate. For an air return filter 
grille, a perforated face plate as shown in FIG. 2 is installed using the 
split separable hinge with stop 74 and leafspring 80. For an air supply, a 
perforated face plate 112 having adjustable louvers and a half hinge is 
inserted in the hinges mounted on the plenum, as shown in FIGS. 10 through 
14. 
Thus, there has been described a novel and unique air return filter grille 
assembly or air supply grille assembly comprised of a unique molded 
fiberglass plenum having an interchangeable perforated face plate attached 
directly to the plenum. A perforated face plate is connected directly to 
the molded fiberglass plenum by a sheet metal channel mounted on the 
plenum skirt, having separable hinges mounted on the plenum and the 
perforated face plate. The molded fiberglass plenum has a recess for 
receiving a filter and unique pawls holding the selecting interchangeable 
perforated face plate in position against the plenum when mounted on a 
suspended T-bar ceiling. 
This invention is not to be limited by the embodiment shown in the drawings 
or described in the description, which is given by way of example and not 
of limitation but only in accordance with the scope of the appended 
claims.