Abstract:
A filter element having a frame defining an interior volume and having exterior surfaces. Filter media is mounted within the frame so as to allow fluid to enter an upstream side of the media and exit a downstream side of the media. At least one component of a multi-component filter frame seal, the at least one component being positioned on an outer surface of the frame and substantially circumscribing the filter frame at a location selected to align to a complementary component of the multi-component filter frame seal. The complementary component is provided separately from the filter element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates, in general, to electrically enhanced air filtration and, more specifically, systems and methods for reducing air bypass between adjacent filter assemblies and between filter assemblies and adjacent surfaces of housings and/or racks in which the filter assemblies are mounted.  
         [0003]     2. Relevant Background  
         [0004]     Gas filtration, and more specifically air filtration, is used in a wide variety of applications ranging from automobiles, homes, office buildings and manufacturing facilities. In many cases filtration systems are used to remove pollutants such as dust, particulates, microorganisms and toxins from breathing air, although filtration systems and processes may be used to purify manufacturing environments, process gasses, combustion gasses and the like.  
         [0005]     One particular application is for heating, ventilation, and air conditioning (HVAC) systems within buildings. HVAC systems are designed to circulate air throughout a building. HVAC systems comprise a motor and blower that moves air from a supply through ductwork that distributes the air throughout building spaces. The air supply may be outside air, re-circulated from inside the building, or a mixture of outside and re-circulated air. Toxic material entering an intake will spread quickly through the entire building. Moreover, any duct that is accessible can be used to spread contaminants. Hence, although HVAC systems contribute significantly to occupant comfort, safety, and health, and are one of the prime lines of defense against emergencies and hazards they can also quickly become a threat to the security and safety of a facility and its occupants.  
         [0006]     Conditioning systems such as heat exchangers, humidifiers, dehumidifiers, and the like are positioned in-line with the ductwork to adjust various characteristics of the supplied air before it is delivered to building spaces. Air filtration systems are placed in-line with the ductwork to filter out particulates, organisms, odors and noxious gases from the air that are present within the flow of air. Air filtration systems used in commercial environments typically comprise a filter rack mounted inside a main duct. Small systems may include a single replaceable filter mounted in the rack. More frequently, however, the filter rack forms a grid defining multiple cells where a filter is positioned in each cell. The filter rack can be formed of extruded metal having protrusions forming integral tracks for holding filter elements. Filter elements comprise a paper or plastic frame, usually square or rectangular in shape, with filter media mounted inside the frame. A wide variety of filter media are available including loose pile fibers, woven fibers, pleated fabric, and the like. Filter elements are positioned in the tracks by sliding them in from the side (or top in unusual configurations), or by placing them in from the front or back of the rack.  
         [0007]     In many buildings, air bypassing the filter cells is a significant problem. Air bypass means that some portion of the air is not being filtered. Air bypass can be caused by air leaking around the rack, leaking between the filter cells and the rack, old or missing gasket material, or leakage between the filter cells. Originally, the purpose of filtration in HVAC equipment was to prevent contaminants from fouling the motor/blower and cooling coils, and the like. Hence, filters were initially installed for equipment protection, not human protection. Since equipment protection mainly involved removing large particles, there was little perceived need to install a filter that was efficient at removing small particles. Filters for equipment protection are very open and therefore relatively inexpensive, since they contain relatively little filter media, and inexpensive frame material can be used as there was little concern regarding air bypass. Although such filters have a characteristically low purchase/replacement cost and low operating cost rather than improved indoor air quality, they only filter out large particulate matter such as dust, allowing smaller particulates to pass through. Air bypass has been a low-priority concern for systems in which low-cost, low-efficiency filter media already allow so much particulate matter that eliminating air bypass would provide negligible improvement. Moreover, air bypass actually reduces air resistance, and so can reduce operating energy costs.  
         [0008]     There has been little effort to develop systems that reduce air bypass except in high-end filtration system used in, for example, electronics manufacturing, medical research facilities, and the like. In these high-end systems air bypass is specifically addressed by gel or grease seals between mating surfaces of filter elements and between the frame and filter elements. These systems work well, but are expensive to install and maintain. As a result, they are used primarily for special-purpose installations and are not practical for general-purpose commercial HVAC systems.  
         [0009]     Filter frame elements may be formed by injection molding or similar type processes. In its simplest variation, the frame is directly formed as a unitary structure. A simple technique for this is described in U.S. Pat. No. 2,032,262 where a pleated filter is held in a jig with only the edge portions extending out of the jig. Filter frames can also be formed from multiple pieces, which are then assembled by use of adhesive, welding, friction fit, snap fits, mechanical fasteners or the like. This type of approach permits more flexibility in terms of frame forms and functionality than unitary filter frames, however, it generally results in framed filters which are complicated to manufacture while often not providing an airtight seal around the filter media. U.S. Pat. No. 6,406,509, which is incorporated herein by reference, describes a framed filter media produced using a continuous extruded frame that is notched so that the extrusion can be bent at the notches to form an enclosing frame. Each of these structures fails to prohibit air bypass between adjacent filter elements or between filter elements and the housing or filter rack in which they are positioned.  
         [0010]     Accordingly, a need exists for filters and filter assemblies with bypass seal to reduce or prevent air bypass between adjacent filter elements or between filter elements and the housing or filter rack in which they are positioned.  
       SUMMARY OF THE INVENTION  
       [0011]     Briefly stated, the present invention involves a filter element having a frame defining an interior volume and having exterior surfaces. Filter media is mounted within the frame so as to allow fluid to enter an upstream side of the media and exit a downstream side of the media. The element further comprises at least one component of a multi-component filter frame seal, the at least one component being positioned on an outer surface of the frame and substantially circumscribing the filter frame at a location selected to align to a complementary component of the multi-component filter frame seal. The complementary component is provided integrally with the filter frame element or separately from the filter element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  shows an assembly for an air handling system that provides an array of replaceable filter elements having bypass seals in accordance with the present invention;  
         [0013]      FIG. 2  shows a cross sectional view of a portion of an exemplary filter frame in which the present invention is implemented;  
         [0014]      FIG. 3  illustrates a cross sectional view of the filter frame of  FIG. 3  in an engaged position;  
         [0015]      FIG. 4  illustrates a perspective view of an extrusion used to produce a filter frame in accordance with the present invention;  
         [0016]      FIG. 5  is a perspective view of another portion of an extrusion used to produce a filter frame in accordance with the present invention;  
         [0017]      FIG. 6  shows a cut-away perspective view of a filter element in accordance with an embodiment of the present invention; and  
         [0018]      FIG. 7  shows an alternative implementation of the present invention in engagement with a filter rack of an air handling system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     The present invention is illustrated and described in terms of an active electrically enhanced air filtration system. Active electrically enhanced air filtration operates using externally applied electricity to polarize the filter media and improve particulate capture efficiency without the air flow restriction normally encountered with purely mechanical high capture efficiency solutions. Using externally applied electricity enables higher voltages and corresponding higher collection efficiencies. For example, U.S. Pat. No. 5,549,735 and U.S. Pat. No. 5,593,476, incorporated herein by reference and which are assigned to StrionAir, Inc., describe an electrically enhanced fibrous air filter that uses polarized filter medium in combination with an upstream pre-charge system to impart a charge on particulates before they reach the polarized filter media. However, the present invention provides improvements in a wide variety of air filtration systems where air bypass between filter elements or between filter elements and the housing or racks in which they are positioned are problems.  
         [0020]      FIG. 1  shows an assembly for an air handling system that provides an array of replaceable filter elements having bypass seals in accordance with the present invention. Housing  101  is a supporting structure that houses one or more rows of filter elements. Housing  101  defines an array of cells where each cell comprises an ionization array  102 , upstream electrode  105 , an optional prefilter (not shown), a filter element  104 , and/or other components that are used in a particular application. A bypass seal, visible in the subsequent Figures, is provided on filter element  104 . The various components are arranged sequentially in the direction of air flow. The cellular or modular arrangement defined by housing  101  allows the system to be scaled to larger and smaller systems to meet the needs of a particular application.  
         [0021]     Housing  101  is formed integrally with or affixed to the ductwork of an air handling system such that air passes from an upstream side facing the viewer in  FIG. 1  to a downstream side that is away from the viewer in  FIG. 1 . In the case of an electrically enhanced air filtration shown in  FIG. 1 , ionizing arrays  102  and filter elements  104  are connected to electrical power supply  106 . In implementations that do not use active electrical enhancement, ionization array  102  and power source  106  would not be present and housing  101  would define a simple array of filter elements  104 . In some embodiments, housing  101  would not be provided at all.  
         [0022]     Housing  101  may include a rack system that define horizontal rails that support ionization units  102 , filter elements  104 , or other components of the air handling system. The rack system comprises an upper rail  111  and a lower rail  112  having channels formed therein to hold filter elements  104 , prefilters if used, and ionization units  102 . When more than one row of cells is provided one or more horizontal center rails  113  are provided to define each row. Although the rack shown in  FIG. 1  is oriented horizontally, (i.e., with horizontally oriented channels) it can be oriented vertically as well by essentially rotating the structure 90 degrees.  
         [0023]     One feature of the present invention is that edges of framed filter elements  104  are adapted with complementary or interlocking air bypass systems to lessen or prevent air flow between adjacent filter elements  104 . Another feature of the present invention is that the downstream edges of filter elements  104  may be fitted with gasket material so as to lessen or prevent air flow between filter frames  104  and the rack and/or housing in which they are positioned. In prior systems gasket material to prevent such air flow may have been provided on the rack or housing itself. As the system aged the gaskets would wear out and gradually allow air bypass. Replacing the gasket material was difficult and labor intensive. By placing the gasket material on the replaceable filter element  104 , the gasket material can be refreshed each time a filter element  104  is replaced.  
         [0024]      FIG. 2  shows a cross sectional view of a portion of an exemplary filter frame in which the present invention is implemented.  FIG. 2  and  FIG. 3  show an interface region between two adjacent (e.g., side by side) filter elements  104  looking downward. Frames  201  comprise a U-shaped channel formed from an extruded plastic, polymeric materials, metal, paper, chipboard, composite or other material that meets the needs of a particular application.  
         [0025]     Frame  201  has a base portion  203  that has a first or inner surface to which a filter media material  200  is affixed positioned. Filter media  200  comprises synthetic or natural fibers, woven or knitted materials, foams, or electret or electrostatically charged materials. The filter media  200  may also include sorbents, catalysts, and/or activated carbon (granules, fibers, fabric, and molded shapes). In a particular implementation, filter media  200  is formed as a pleated media that uses a thermosetting glue bead to hold the pleat shape and provide structural stability. A filter media of this type is available from Columbus Industries available under the product designation Microshield. The glue bead is applied before the folding of the filter media and connects the folds with one another at the point of application.  
         [0026]     An outer surface of base portion serves as an interface to an adjacent filter element  104 . The outer surfaces of filter elements  104  are fitted with complementary components  208  and  209  of a bypass sealing mechanism  204 . In the implementation shown in  FIG. 2  sealing strip  208  is positioned in a guide  207  to form a landing pad for knife edge  209 . Sealing strip  208  comprises a closed cell foam, open cell foam, gel, or other resilient or elastomeric material that will create a seal when engaged by knife edge  209 . Exemplary materials include neoprene, polyurethane, silicone, buna-N(Nitril), EPDM, polyethylene, vinyl, gum rubber, latex, natural rubber, styrene-butadiene rubber, viton, santoprene, polyester, epichlorohydrin, butyl, polyimide foam, ionomer foam, Hytrel®, hypalon, ethylene vinyl acetate, polystyrene, melamine foam and the like. As shown in  FIG. 3 , when two filter frames  104  are pressed together the knife edge  209  is pushed into sealing strip  208  to prevent air flow between adjacent filter frames  104 . Seal strip  208  may be formed as a flat structure shown in  FIG. 2 , or may have a complementary indentation that increases the surface area of contact between knife edge  209 . An advantage of increased contact area is an incrementally better seal.  
         [0027]     As shown in  FIG. 2 , each base region  203  is configured with one knife edge  209  and one sealing strip  208 . It is contemplated that the invention can be implemented with only one or the other component so long as an adjacent filter frame is configured with a complementary component of the sealing mechanism. Moreover, any number or knife edges  209  and/or sealing strips  208  may be provided. The implementation shown in  FIG. 2  provides a double seal as the complementary components  208 / 209  engage each other.  
         [0028]      FIG. 4  illustrates a perspective view of an extrusion  400  that can be continuously extruded with integrally formed protrusions to form knife edge  209  and guides  207 . Sealing strip  208 , which is typically of a more resilient material composition than the remaining portions of extrusion  400 , can be affixed separately using a foam tape, for example. Alternatively, sealing strip  208  can be co-extruded using a suitably resilient material in which case guides  207  may be omitted. Extrusion  400  may include sidewalls that extend substantially orthogonally from the base portion  203  to provide a more rigid construction and better attachment to filter media  200  shown in  FIG. 2  and  FIG. 3 .  
         [0029]     To assemble a frame  201  from extrusion  400 , sidewalls  401  are cut or notched at desired corner locations. The distance between corner locations defines the length and width of a completed framed filter element  104 . The notching allows extrusion  400  to be folded at the corner locations into a frame shape with a single joint used to join ends of extrusion  400  into a continuous frame. At any point filter material  200  may be placed in the channel defined by extrusion  400  and preferably glued to the inside surface of portion  203 . Knife edge  209  and sealing strip  208  are positioned symmetrically with respect to a centerline of extrusion  400  so that when the extrusion is flipped the knife edge  209  of a first piece is aligned with the sealing strip  209  of a second frame piece.  
         [0030]      FIG. 5  is a perspective view of another portion of an extrusion used to produce a filter frame in accordance with the present invention. The sidewalls  401  will eventually face in the direction of airflow such that one sidewall  401  will be an “upstream sidewall” and the other sidewall  401  will be a downstream sidewall. In operation, air flow will urge the downstream sidewall into contact with the rack or housing in which the framed filter element  104  is mounted. As shown in  FIG. 5 , a gasket  501  is positioned on the downstream sidewall  401 . Gasket  501  is implemented, for example, as a brush gasket which eases the installation, repositioning, and removal of framed filter elements  104  as the brush gasket can move relatively freely against the rack and/or housing. The brush gasket  501  is similar to that found in many high performance sliding windows where it is used to improve air sealing. Gasket  501  may be implemented with a variety of other sealing mechanisms including rubber bulb seals, woven fabric tadpole seals, weather stripping, rope seals, gasket tape, cork, rubber, silicone gel and the like to meet the needs of a particular application.  
         [0031]      FIG. 6  shows a cut-away perspective view of a filter element in accordance with an embodiment of the present invention.  FIG. 6  is taken looking downward towards the downstream side of the completed framed filter element  104 . In the electrically enhanced filter implementation of the preferred embodiment, downstream electrode  601  is attached so as to be in frequent electrical and physical contact with the filter media  200 . This arrangement provides improved performance as described in U.S. patent application Ser. No. 10/721,940 which is incorporated herein by reference. As noted hereinbefore, gasket material  501  may be placed at the top and bottom of frame  201 , or may be provided so as to substantially circumscribe the downstream sidewall  401  of frame  201 . The gasket seal  501  is not necessary on edges where the knife edge/sealing strip provide adequate bypass inhibition, however, it may reduce material cost to only place gasket seal  501  on edges where it is necessary. On the other hand, it may be more cost effective to place it on edges, even edges where it is not strictly required, to make the filter element a more universal, standardized part that needs little attention to field preparation/modification/alignment when being installed. Similarly, sealing strip  208  and knife edge  209  substantially circumscribe the outer surface of base portion  203  of the frame  201 . In the case of knife edge  209  and sealing strip  208  there will be a discontinuity at the comers when a sharp corner is made. Discontinuities such as these that make up a relatively small portion (i.e., less than 10%) of the circumference are considered within the meaning of “substantially continuous” as that term is used herein.  
         [0032]      FIG. 7  shows an alternative implementation of the present invention in engagement with a filter rack of an air handling system.  FIG. 7  illustrates the operation of brush gasket  501  as airflow pushes the filter assembly so that the gasket  501  forms a seal, or at least a high resistance air path, with the rack  704 . As shown in  FIG. 7 , the complementary sealing mechanism  204  can optionally be omitted on the frame/rack interfaces. This is because many installations have existing racks that will not have components of the complementary sealing mechanism  204  (e.g., knife edge  209  and sealing strip  208 ) formed on the surfaces of rack  704 . Alternatively, the rack surfaces can be outfitted with complementary sealing components to provide even better air-bypass inhibition.  
         [0033]      FIG. 7  also illustrates an alternative configuration in which frame  701  is adapted to allow for a filter volume  700  that extends beyond the rack  704 . This configuration allows larger, deeper filters and/or filter bags to be used in conjunction with the present invention.  
         [0034]     Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed.