Abstract:
A high efficiency air filter for use in a standard return air grille is provided. Standard return air grilles possess filter receptacles for accepting air filters, a closeable cover with a cover flange for engaging air filters and a duct interface that leads away from the air grille to the remainder of the return air ducts. The air filter has a filter flange with a gasket that is sized to fit within the filter receptacle of the air grille, such that when the cover is closed, the cover flange seals against the cover and the filter receptacle. The gasket is affixed to a housing that is sized to extend beyond the filter receptacle into the duct extending beyond the return air grille. An extended pleat air filter is contained within and sealed to the walls of the housing such that air passing through the return air grille substantially passes through the air filter prior to entering the remainder of the return air duct.

Description:
TECHNICAL FIELD 
   The present invention relates to air filters for home and light commercial ventilation systems, and more particularly to extended surface air filters that fit into a standard, unmodified return air grille. 
   BACKGROUND 
   Air filters provide two important functions in any ventilation system, the first function is to remove particulates from the air circulating through the system and the second function is to provide adequate airflow for the system to operate efficiently. The most common method employed to remove particulates from a ventilation system is an air filter. Air filters can be placed at various locations throughout a ventilation system, but a common place for installation is in the return air grille. A standard return air grille is normally one inch deep and thus only accommodates at most a one inch thick air filter. The amount of pressure drop or airflow restriction through an air filter is dictated by the level of filtration needed and the surface area of the air filter presented to the air flow. As the level of filtration or filtration efficiency increases, the airflow reduction or pressure drop resulting from the filter is increased. There are two approaches to overcoming the increased pressure drop from higher efficiency air filters. The first, installing a larger fan to overcome the increased pressure drop, results in increased energy consumption and reduced fan life. The second approach involves modifying the return air grille to accommodate an air filter with greater surface area, which is costly and difficult due to the modification of the ductwork and return air grille required. 
   Thus, there is a need for a high efficiency filter that has improved filtration efficiency without the need to use a larger fan or modify the return air grille or ductwork. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying figures depict multiple embodiments of an air filter for residential and light commercial ventilation systems that enables an extended pleat air filter to be housed in a standard return air grille providing enhanced filtration with reduced pressure drop across the air filter. A brief description of each figure is provided below. Elements with the same reference numbers in each figure indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawings in which the reference number first appears. 
       FIG. 1  is a perspective view of one embodiment of an air filter. 
       FIG. 2  is a sectional view of one embodiment of an air filter looking from a side. 
       FIG. 2A  is a close up view of one embodiment of a filter flange with a single gasket. 
       FIG. 2B  is a close up view of another embodiment of a filter flange with a gasket sandwich. 
       FIG. 3  is a perspective view of one embodiment of an air filter installed in a standard return air grille. 
       FIG. 4  is a perspective view of one embodiment of the extended pleat filter medium with excess filter medium folded to create a seal around the extended pleat filter medium. 
   

   DETAILED DESCRIPTION 
     FIG. 1  depicts a first embodiment of the front face  114  of an air filter  100 . The air filter  100  is comprised of a housing  104  where the housing  104  has walls  108 , a front cover  106 , and a back cover (not shown). Surrounding the periphery of the housing  104  is a filter flange  110 . The filter flange  110  in the embodiment of an air filter  100  depicted in  FIG. 1  is wholly comprised of a gasket  112 . The gasket  112  in the embodiment depicted extends around the full periphery of the housing  104  and forms the full extent of the filter flange  110 . 
   The housing  104  in one embodiment of the air filter is comprised of polymer coated paperboard. In yet another embodiment, the housing  104  is comprised of laminated cardboard. In still other embodiments, the housing  104  is formed from materials selected from the following group consisting of paper, cardboard, plastic, and metal. The selection of housing  104  materials may be accomplished by one of ordinary skill in the art with the objective of providing a means to support the extended surface air filter  102  and be affixed to the filter flange  110 . The housing  104  is sized and shaped to substantially slide within a standard air duct disposed behind a filter receptacle  302  of a return air grille  300  as shown in  FIG. 3 . 
   Contained within the housing  104  and the front cover  106  and back cover (not shown) of the air filter  100  is an extended pleat filter medium  102 . Referring now to  FIG. 2 , the extended pleat filter medium  102  is disposed within an interior volume defined by the housing  104  and affixed to the interior surface of the walls  108  of the housing  104  to hold it in place. The front cover  106  and back cover are substantially open such that they assist in retaining the extended pleat filter medium  102  within the interior volume of the housing  104  while allowing incoming air  220  to pass through the air filter  100  by traveling through the front cover  106 , through the extended pleat filter medium  102 , and through the back cover to emerge as filtered air  222 . 
   The housing  104  can be selected by one of ordinary skill in the art to house a variety of different sizes of extended pleat filter medium  102 . The housing  104  in one embodiment is flush mounted with the filter flange  110  such that the top surface  106  is substantially level with the surface of the filter flange  110  facing the front face  114  of the air filter  100 . The depth of the air filter  100  penetration beyond the return air grille  300  is limited primarily by the depth or size of the return air duct extending beyond the return air grille  300 . For most household and light commercial installations, the return air grille  300  is installed into a metal boot or other adaptor to join the return air duct to the return air grille  300 . In an alternative installations, the return air grille  300  is installed directly into the side or end of a metal duct. In either approach, the depth of the air filter  100  extending past the end of the filter receptacle  302  is limited primarily by the need for smooth flow of the filtered air  222  into the return air duct. In a typical installation with a 4-8″ deep metal boot, the housing  104  extends from about three inches to about five inches without disturbing the smooth flow of the filtered air  222 . 
   When mounted within the housing  104 , the extended pleat filter medium  102  is folded upon itself and held in an accordion or serpentine-like shape as depicted in  FIG. 2 . The accordion or serpentine-like shape increases the effective surface area of the extended pleat filter medium  102  exposed to the incoming air  220  entering through the front cover  106  of the air filter  100 . The multiple folds of the extended pleat filter medium  102  allows the air filter  100  to have a greater filter surface area per a linear distance  250  than otherwise possible. The incoming air  220  passes through the extended pleat filter medium  102  and the filtered air  222  emerges from the air filter  100  at the back face  202  of the air filter  100 . The front cover  106  that extends across the front face  114  and a back cover (not depicted) extends across the back face  214  to help retain the extended pleat filter medium  102  inside the housing  104 . 
   Extended Pleat Filters 
   The extended pleat filter medium  102  in the embodiment depicted in  FIG. 2  is formed from a commercially available reinforced non-woven cotton fiber sheet  140  also known as the filter medium  140  bonded to a metallic reinforcement  402 . The metallic reinforcement  402  is thin metal wire formed in a substantially repeating pattern. The metallic reinforcement  402  stiffens and substantially holds the filter medium  140  in the substantially accordion-like, pleated shape shown in  FIG. 2  while maximizing the exposed surface of the fiber sheet. In yet another embodiment, polymer reinforcement is used to stiffen the extended pleat filter medium  102 . In yet another embodiment, the extended pleat filter medium  102  is impregnated with a fire retardant for safety. 
   In an alternative embodiment the extended pleat filter medium  102  is comprised of synthetic filter medium made of thermally bonded, continuous hydrophobic (moisture repelling) polyolefin fibers that resist shredding and do not absorb moisture. Synthetic medium can be electrostatically charged creating a force that attracts particles, especially smaller diameter particles. 
   The side edges  206  of the extended surface filter medium  102  in the embodiment shown in  FIG. 2  are bonded with an adhesive compound to the inner surface of the housing  104  walls  108 . In one embodiment, the side edges  206  are bonded with an adhesive compound to a fabric  208  that provides a loose fitting seal between the side edges  206  of the extended pleat filter medium  102  and the inner surface of the walls  108 . The fabric  208  in one embodiment is a non-woven cotton fabric. In still another embodiment, the filter medium  140  extends beyond the length of the metallic reinforcement  402  on one side of the extended pleat filter medium  102  creating an excess  404  of filter medium  140 . The excess filter medium  404  is easily folded and manipulated into the space between the side edge  206  of the extended pleat filter medium  102  where the metallic reinforcement  402  stops and the wall  204 . The excess filter medium  404  is adhered to the inner surface of the wall  204  facing the excess filter medium  404  to substantially seal the extended pleat filter medium  102  on that side edge  206 . 
   One of ordinary skill in the art can select alternative materials for the fabric  208  that work in conjunction with the adhesive to provide an effective seal between the side edges  206  and the ends  210  of the extended pleat filer medium  102  and the walls  108  of the housing  104 . The ends  210  of the extended pleat filter medium  102  are bonded to a fabric  208  that provides a loose fitting seal between the ends  208  and housing  104  walls  108 . In still another embodiment, the side edges  206  and the ends  210  of the extended pleat filter medium  102  are bonded with adhesive directly to the inner surface of the walls  108  of the housing  104 . 
   In still another embodiment, the individual folds of the extended pleat filter medium  102  are held apart and separated by the presence of a pleat spacer  226 . The pleat spacer  226  in the embodiment shown is fabricated from the same material as the housing  104  and has fingers  228  that are inserted between the individual folds or pleats of the extended pleat filter medium  102  as mounted inside the housing  104 . The fingers  228  of the pleat spacer  226  separate the individual pleats from each other to prevent two adjacent pleats from collapsing together, thereby increasing air flow through the air filter  100 . In the preferred embodiment, the fingers  228  are generally triangular shaped pieces of material, a few inches in length, that are spaced at regular intervals along a common edge of a base strip. 
   In another embodiment, the side edges  206  of the extended pleat filter medium  102  are fitted into forms similar in shape and dimension to the pleat spacer  226 , a framework having receptacles each of which receives and holds a single pleat, of similar shape and configuration to the pleat spacer  226  except the forms are fitted against the internal surfaces of the wall  204  to substantially guide and hold the extended pleat filter medium  102  in its accordion-like shape. In this another embodiment, an adhesive is used to seal the extended pleat filter medium  102  into the forms. In still another embodiment, the forms are bonded to a fabric  208  such that the forms maintain the structure of the extended pleat filter medium  102  while forming a loosely fitting seal between the side edges  206  and the fabric  208 . In yet another embodiment, an adhesive is applied to bond the side edges  206  to the fabric  208  and the forms to fix the extended pleat filter medium  102  in place within the housing  104 . The loosely fitting seal formed between the extended pleat filter medium  102  and the walls  108  of the housing  104  substantially eliminates any airflow around the extended pleat filter medium  102  and effectively urges the incoming air  220  to pass through the extended pleat filter medium  102  prior to exiting the air filter  100  as filtered air  222 . 
   Gasket 
   Gasket  112  in the embodiment depicted in  FIG. 1 and 2  is a foam material. The filter flange  110 , in the embodiment depicted, is only a gasket  112  and is about 0.5 inches thick and about 0.75 inches wide. However, one of ordinary skill in the art will size the filter flange  110  and the gasket  112  such that the extents of the filter flange  110  are substantially equivalent or smaller than the filter receptacle  302  of the return air grille  300 . 
   Referring now to embodiments where the filter flange  110  is formed entirely of a gasket  112 . The gasket  112  in one embodiment is formed from a series of straight pieces of substantially rectangular foam that are affixed with an adhesive to the exterior surface of the walls  108  of the housing  104 , along the housing  104  periphery adjacent to the front cover  106 , and to the abutting ends of neighboring pieces of foam. In another embodiment, the gasket  112  is formed from a continuous strip that is affixed with an adhesive to the walls  108  of the housing  104  with the two ends of the continuous gasket  112  affixed to each other. In all of these embodiments, the gasket  112  surrounds the entire periphery of the front face  114  of the housing  104 . 
   In an alternative embodiment of the filter flange  110 , shown in detail in  FIG. 2A , the gasket  112  is affixed to a flange support  218 . The flange support  218  is an extension of the housing  104  that provides an additional mounting surface for the gasket  112 . The gasket  112  is affixed with adhesive to the filter flange  110  and the housing  104  to form a seal around the housing  104 . In one embodiment, the gasket  112  is affixed to the housing  104  such that the front face  114  of the housing  104  is substantially level with the top surface of the filter flange  110  or, in another embodiment, substantially level with the top surface of the gasket  112 . 
   In another alternative embodiment of the filter flange  110 , shown in detail in  FIG. 2B , two separate gaskets  112  are mounted to the top and bottom surfaces of the flange support  218 . The flange support  218  is an extension of the housing  104  that provides an additional mounting surface for the gaskets  112 . The gaskets  112  are then affixed with adhesive to the top and bottom surfaces of the filter flange  110  and the housing  104  to form a seal around the housing  104 . 
   The gasket  112  is formed of a foam rubber that retains some rigidity while remaining substantially deformable. In one embodiment, the foam rubber is polyurethane foam. In still other embodiments, the foam rubber is formed from materials such as latex, neoprene, polyvinylchloride (PVC), polyethylene, microcellular urethane, vinyl-nitrile, styrene butadiene (SBR), ethylene-Diene-Propylene-Monomer (EPDM) and ethyl vinyl acetate (EVA) or equivalents as known to those of ordinary skill in the art. In yet another embodiment, where the gasket  112  is affixed to a flange support  218 , the gasket  112  material is selected to be substantially more compliant to provide structural support to the filter flange  110 . 
   These multiple embodiments are non-exhaustive examples of the multiple methods of affixing a gasket  112  to the housing  104  of an air filter  100  to create a filter flange  110 . Regardless of the specific method of attachment or materials used, one of ordinary skill in the art is capable of affixing a filter flange  110  to the housing  104  that substantially fits within the extents of a filter receptacle  302  within a standard return air grille  300  and the cover flange  304  such that a seal is formed whereby the incoming air  220  is forced to pass through the air filter  100  prior to entering the duct work behind the return air grille  300  as filtered air  222 . 
   Installation Within Standard Return Air Grille 
     FIG. 3  depicts a standard return air duct filter mount or return air grille  300 . The return air grille  300  includes a removable or rotatable cover  308 . The cover  308  includes a series of louvered grates  306  that enable incoming air  220  to enter the air filter  100  while, in the embodiment shown, cloaking the air filter  100  from easy view. The cover  308  also includes a cover flange  304 . The return air grille  300  also includes an outer housing  310  that is mounted to a wall of a house and attached to the return air duct within the house. Inside the return air grille  300  is a filter receptacle  302 . The filter receptacle  302  provides a recess around the periphery of the passage where the return air grille  300  is fit into the duct work. The recess in the filter receptacle  302  is sized for a standard air filter and, in the embodiment depicted, the filter receptacle  302  is sized for a standard one inch air filter. The most common size filter receptacle  302  is sized for one inch filter, however two, three, four, and five inch filter receptacles are also available, but they are uncommon. The air filter  100  fits within the standard filter receptacle  302 . The filter flange  110  of the air filter  100  fits within the filter receptacle  302  while the housing  104  is sized to fit within the return air duct beyond the return air grille  300  and extend beyond the filter receptacle  302  into the duct. When the rotatable cover  308  is fitted to the outer housing  310 , the cover flange  304  contacts the filter flange  110  and compresses the gasket  112  against the filter receptacle  302 . The cover flange  304  holds the air filter  100  in place and by virtue of the deformable nature of the gasket  112 , seals the space around the air filter  100  and the filter receptacle  302  thereby substantially preventing the flow of air around the air filter  100 . When installed within the return air grille  300 , the housing  104  is sized to pass through the filter receptacle  302  and be accepted into the duct emerging beyond the return air grille  300 . In such a manner the extended pleat filter medium  102  is extended into the air duct and occupies a greater volume of space then otherwise available in a standard filter receptacle  302 . 
   Extended Pleat Filter Performance 
   The extended pleat filter medium  102  mounted in the air filter  100  depicted in the embodiments shown provides significant additional performance over a standard filter designed to fit within the extents of a standard return air grille  300  filter receptacle  302 . In comparison, a traditional 1″ pleated air filter (not depicted) with a Minimum Efficiency Reporting Value (MERV) of 8 with 14 pleats per a foot of filter length  250  provides 7.5 square feet of filter medium presented to the incoming air  220 . The MERV rating is developed for filters based on ASHRAE Standard 52.2 promulgated by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). In contrast, the air filter  100  of the embodiment depicted in  FIG. 1 and 2  with an extended pleat air filter medium  102  with 12 pleats per a foot of filter length  250  provides 33.4 square feet of filter medium presented to the incoming air  220 . The increased surface air of the extended pleat air filter medium  102  reduces the initial resistance to air flow through the filter (about 0.12 in WG (water gauge) for an air filter  100  with an extended pleat air filter medium  102  versus about 0.17 in WG for a standard 1″ MERV 8 filter) as well as enables additional particulates to be captured resulting in an increase in service life (more than 180 days service life for an extended pleat air filter medium  102  versus 30 days service life for a standard 1″ MERV 8 filter). Although the comparisons above were provided for a MERV 8 filter, the air filter  100  presented herein can be configured for multiple different MERV rating, including for example MERV 6, 10, and 13. 
   Conclusion 
   The embodiments of the invention shown in the drawing and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is contemplated that numerous other configurations of an extended pleat filter medium air filter may be created taking advantage of the disclosed approach. It is the applicant&#39;s intention that the scope of the patent issuing herefrom will be limited only by the scope of the appended claims.