Abstract:
An electronic air filter assembly includes filter media disposed on opposite sides of an electrified charging screen. The filter media and charging screen are held between outer screens. The outer screens are held together in an assembled condition by pressure-sensitive securements and can be pulled apart to disassemble the filter assembly by applying an outer screen-separating force sufficient to overcome the holding force of the securements.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/330,740 filed Oct. 30, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     Electrostatic filters have been developed for incorporation into heating ventilation and air conditioning (HVAC) systems. Such filters, having the same general overall dimensions as a conventional panel-type filter element, can be placed into the duct of an HVAC system and oriented transverse to the direction of air flow in the duct. In general, electrostatic filters include a central charging screen that is sandwiched between two fibrous filter elements, and the filter elements and charging screen are enclosed between outer screens, each having a rigid frame surrounding a mesh material. Power is applied to the central charging screen which induces a particle-attracting charge in the filter elements, thereby providing improved filtration as compared to a non-electrified filter. Examples of such filter assemblies are described in the following United States patents, the respective disclosures of which are hereby incorporated by reference: U.S. Pat. Nos. 5,846,302; 5,807,425; 5,573,577; 4,828,586; 4,549,887; 4,886,526; 4,978,372; and 5,108,470. 
     Prior art electronic filters include clumsy latches or other hardware for holding the multi-piece filter assembly together. Such hardware protrudes from the frames of the outer screens and can get hung up on screws or rivets securing c-channels for holding the filter assembly within the duct of the HVAC system, thereby making the installation and extraction of the filter assembly difficult. 
     Accordingly, there exists a need for an electronic air filter assembly in which the filter assembly is securely held together in a manner which does not interfere with the duct work in which the filter is installed and in a manner which permits easy disassembly. 
     SUMMARY OF THE INVENTION 
     The present invention includes a multi-piece electronic filter assembly whereby the pieces are held together by pressure-activated securements that do not protrude or otherwise extend outside of the outer frames of the assembly. Accordingly, there are no structures or latches to get caught when the filter is installed in or removed from a duct. Moreover, the filter assembly can be disassembled by pulling the outermost pieces of the assembly apart with sufficient force to overcome the securements. 
     In another aspect of the invention, the overall particle attraction of the assembly is improved by the use of tackified filters. 
     Other objects, features, and characteristics of the present invention, including the methods of operation and the function and interrelation of the elements of structure, will become more apparent upon consideration of the following description and the appended claims, with reference to the accompanying drawings, all of which form a part of this disclosure, wherein like reference numerals designate corresponding parts in the various figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the elements which make up the air filter assembly. 
     FIG. 2 shows the arrangement of the air filter assembly elements when the assembly is in the open position. 
     FIG. 3 is a partial, exploded view showing attachment of a securement to an outer screen of the filter assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the electrostatic air filter assembly  10  is illustrated in FIG.  1 . The assembly  10  comprises filter media preferably in the form of two filter elements  12 ,  14  formed from sheets of filter material for gas, preferably formed of battings of a tackified glass fiber material and being of the same rectangular shape and size. Most preferably, the filter elements are battings of unwoven long strand fiberglass web with a tackifier uniformly distributed on the glass fibers as described in U.S. Pat. Nos. 6,136,058 and 5,846,603, the disclosures of which are hereby incorporated by reference. Such tackified fiberglass filter material is available from Superior Fibers, Inc. The fiberglass batting of the filter elements  12 ,  14  are preferably 13 gram/ft 2  fiberglass web. Conventional electronic filter assemblies employ 16 gram/ft 2 , non-tackified fiberglass filter elements. The use of tackified filter material improves the efficiency of the filter assembly. The 13 gram/ft 2  filter elements of the present invention result in a smaller pressure drop across the filter assembly as compared to the pressure drop across filter assemblies employing 16 gram/ft 2  filter elements. In addition, the use of tackified filter elements ensures that the filter assembly of the present invention will be at least as effective as conventional filter assemblies employing more dense, but non-tackified filter elements. 
     A charging element, preferably in the form of a charging screen  16 , is sandwiched between elements  12 ,  14 , and comprises a rectangular frame  28 , preferably of extruded elongated members formed from rigid, nonconductive material onto which a rectangular mesh (preferably a metal wire mesh)  26  is disposed. The frame  28  is preferably made from rigid PVC. The mesh  26  of the charging screen  16  is preferably an 8×8 (i.e., eight openings per inch in either direction) mesh of 11 gauge bright aluminum wire. The charging screen  16  can have another structure, instead of the mesh  26 , such as a metal gauze or perforated metal sheet or a grill of wires or a punched metal lattice, but the mesh, grill, lattice, etc. should be made of an electrically conductive material and be of a construction that readily allows air flow therethrough. 
     When the filter assembly is in the assembled condition, the charging screen  16  and filter elements  12 ,  14  are held together by outer retaining elements, preferably in the form of outer screens  18 ,  20 . The first outer screen  18  comprises a rectangular frame  22 , preferably formed from four rectangular aluminum extrusions  34  interconnected, for example, by plastic 90° connectors  36 . A rectangular wire mesh  24  is located within frame  22 . The mesh  24  is preferably an 8×8 mesh of epoxy-covered 11-gauge aluminum wire. The epoxy covering gives the mesh some resiliency, thereby making the stretched mesh  24  less susceptible to denting. The second outer screen  20  is substantially the same as the first outer screen  18  and also comprises a rectangular frame  22  formed of extruded aluminum pieces  34  interconnected by plastic 90° connectors  36  and has a wire mesh  24  extending between the sides thereof and located in the same manner. 
     The two outer screens  18 ,  20  are of the same size and shape as each other. The wire mesh  24  is preferably secured to the outer surface of the frames  22  of the screens  18 ,  20 . Thus, when the screens  18 ,  20  are brought together, a space is defined between the respective meshes  24  of the screens  18 ,  20  that is approximately twice the thickness of each frame  22 . The filter elements  12 ,  14  are of the same size and shape as each other, but slightly smaller than frames  22  so as to be clampable therebetween with the edges of the filter material preferably abutting or even slightly overlapping the inner peripheral edges of the frames  22  so as to ensure that air passing through the wire meshes  24  also passes through the filter elements. The frame  28  of the charging screen  16  is smaller than the inner periphery defined by the frames  22 . 
     As shown in FIG. 2, the outer screens  18  and  20  are preferably hinged at one edge such that filter elements  12 ,  14  and the charging screen  16  can be clamped between them. Pressure-activated securements  42  are mounted to the edges of the frames  22  opposite the hinges, preferably in the corners. The securements  42  are mounted on corresponding facing surfaces in co-aligned positions such that they engage each other when the hinged outer screens  18 ,  20  are closed. The securements  42  are constructed and arranged to interlock with one another when pressed together and to release each other when pulled apart with sufficient force. 
     As shown in FIG. 3, the securement  42  comprises a circular plastic plug of upstanding fingers with enlarged heads. Self-lock, mushroom head fasteners, having a density of 400-heads per square inch and a {fraction (9/16)} inch diameter, manufactured by 3M and known as a dual lock washer are preferred for the securements. The mushroom heads of the fingers interlock with the enlarged heads of the upstanding fingers of a mating securement plug on the corresponding surface of the opposite screen frame. The plug is installed into a similarly sized circular recess  40  formed in the corner piece  36  and is fastened there by means of a screw  44 . The plug may be of some other shape, but circular is preferred because of the relative ease of forming a circular recess to receive the plug, as opposed to a recess of some other shape. Securements are preferably installed in the two corners opposite the hinged edges of the screens  18 ,  20 . In an alternate, though less preferred embodiment, securements  42  can be installed in all four corners of the screens  18 ,  20 , and the hinges can be omitted. 
     An electrode  32  in FIG. 2 is arranged such that the filter element  14  will fit between the electrode  32  and wire mesh  24 . Thus, when screens  18 ,  20  are closed, electrode  32 , preferably a wire with an exposed end, makes physical and electrical contact with the charging screen  16 . 
     A high voltage power supply  30 , an example of which is detailed in U.S. Pat. No. 5,846,302, hereby incorporated by reference, is attached to one edge of one of the screens  18 ,  20 . When the high voltage power supply  30  is connected to a source of electricity, e.g., a 24-volt power line, voltage is supplied, via the electrode  32 , to the charging screen  16 . The charging screen  16  is in contact with the nonconductive filter elements  12 ,  14  and induces a particle-attracting charge in the filter elements  12 ,  14 . The epoxy covering of the mesh  24  of outer screens  18 ,  20  acts as an electrical insulator, which reduces the incidence of arcing between the mesh  26  of the charging screen  16  and the mesh  24  of the outer screens  18 ,  20 , which are grounded when the filter assembly  10  is installed. 
     While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     Furthermore, those of the appended claims which do not include language in the “means for performing a specified function” format permitted under 35 U.S.C. §112(¶6), are not intended to be interpreted under 35 U.S.C. §112(¶6) as being limited to the structure, material, or acts described in the present specification and their equivalents.