Abstract:
A filtration system for a ventilation hood includes a first filter and a second filter, operatively disposed in series. The first filter is configured to be mounted within the ventilation hood, and has an air inlet, an air outlet, and a grease outlet. The second filter includes a filter material with an upstream surface and a downstream surface, an upstream housing element abutting the upstream surface of the filter material, and a downstream housing element abutting the downstream surface of the filter material. The housing elements include openings, and hold the filter material in compression.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. non-provisional application Ser. No. 13/363,128, filed Jan. 31, 2012, which claims priority to U.S. provisional application Ser. No. 61/438,226, filed Jan. 31, 2011, the disclosure of both of which are hereby incorporated by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to exhaust hoods, and, more particularly, to multi-stage filters for use with such hoods. 
         [0003]    In a typical restaurant kitchen, a plurality of cooking units are lined up side by side in a row under a common exhaust hood. The cooking units may include, for example, ranges, griddles, fryers, and broilers. The cooking processes performed on such equipment all produce air laden with grease, smoke, fumes, moisture, heat, and other particles in varying amounts and temperatures. The air is drawn in to the exhaust hood, where it is filtered. One known filtration system is disclosed in U.S. Pat. No. 6,394,083 to Lambertson, the disclosure of which is hereby incorporated by reference. 
         [0004]    Commercial exhaust hoods manufactured to be installed in the U.S. must comply with certain codes and standards, such as the National Fire Protection Associates (NFPA) Standard 96. This standard requires that all hoods used in commercial cooking establishments that are installed over cooking equipment that creates effluents other than heat and steam, such as grease, during the cooking process include grease removal devices that are individually listed in accordance with Underwrites Laboratories (UL) Standard 1046, or as components of UL 710 listed hoods. This standard requires grease removal devices to be able to prevent the spread of fire from the upstream face of the filter to an area downstream of the filter. 
       BRIEF SUMMARY 
       [0005]    A filtration system for a ventilation hood includes a first filter and a second filter, operatively disposed in series. The first filter is configured to be mounted within the ventilation hood, and has an air inlet, an air outlet, and a grease outlet. The second filter includes a filter material with an upstream surface and a downstream surface, an upstream housing element abutting the upstream surface of the filter material, and a downstream housing element abutting the downstream surface of the filter material. The housing elements include openings, and hold the filter material in compression. 
         [0006]    The second filter is disposed either downstream or upstream of the first filter. 
         [0007]    The second filter may be attached, such as removably attached, to the first filter. 
         [0008]    The housing elements may cooperate to define a housing for the filter material. The housing may be configured to be opened to allow access to the filter material. The upstream housing element may be hingedly attached to the downstream housing element such that the upstream housing element can be hinged open from the downstream housing element to thereby open the housing. A latch may be provided, to hold the housing closed, and may be manipulable by hand to open and close the housing without requiring tools. 
         [0009]    The ventilation hood may include a track, and the second filter may be configured to be inserted onto the hood by being moved along the track. The first filter may also be configured to be inserted onto the hood by being moved along the track. 
         [0010]    The first filter may be a cartridge filter or a baffle filter. The filter material of the second filter may be natural fiber or synthetic fiber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Exemplary embodiments will be described in more detail with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a schematic cross-sectional view of a known cartridge filter. 
           [0013]      FIG. 2  is a schematic cross-sectional view of a first exemplary embodiment. 
           [0014]      FIG. 3  is a schematic cross-sectional view of a second exemplary embodiment. 
           [0015]      FIGS. 4A-4L  illustrate a third exemplary embodiment, where: 
           [0016]      FIGS. 4A ,  4 B, and  4 C are isometric views of a filter assembly in the closed, open, and filter material removed states, respectively; 
           [0017]      FIG. 4D  is an isometric view of the filter assembly of  FIGS. 4A-4C  as viewed from the other side; 
           [0018]      FIGS. 4E and 4F  are a top and rear view, respectively, of the filter assembly of  FIGS. 4A-4D ; 
           [0019]      FIGS. 4G ,  4 H, and  4 I schematically illustrate removal of the second filter from the filter assembly of  FIGS. 4A-4F ; 
           [0020]      FIG. 4J  is a cross-sectional view of the filter assembly of  FIGS. 4A-4I  mounted within a hood; 
           [0021]      FIG. 4K  is a bottom plan view thereof, looking up at the hood from underneath; and 
           [0022]      FIG. 4L  schematically illustrates the filter assembly of  FIGS. 4A-4K  mounted in a hood above an item of cooking equipment; 
           [0023]      FIGS. 5A-5N  illustrate a fourth exemplary embodiment, where: 
           [0024]      FIGS. 5A ,  5 B, and  5 C are isometric views of a filter assembly in the closed, open, and filter material removed states, respectively; 
           [0025]      FIG. 5D  schematically illustrates removal of the first filter from the filter assembly of  FIGS. 5A-5C ; 
           [0026]      FIGS. 5E and 5F  are side views of the second filter of  FIGS. 5A-5D , illustrating the closed and open states, respectively; 
           [0027]      FIGS. 5G ,  5 H, and  5 I are a rear, front, and top view, respectively, of the filter assembly of  FIGS. 5A-5F ; 
           [0028]      FIGS. 5J and 5K  are cross-sectional views of the filter assembly of  FIGS. 5A-5I  mounted within a hood, with the second filter in the closed and open states, respectively; 
           [0029]      FIGS. 5L and 5M  are bottom plan views thereof, looking up at the hood from underneath, with the lefthand second filter in the closed and open states, respectively; and 
           [0030]      FIG. 5N  schematically illustrates the filter assembly of  FIGS. 5A-5M  mounted in a hood above an item of cooking equipment; and 
           [0031]      FIGS. 6A-6H  illustrate a fifth exemplary embodiment, where: 
           [0032]      FIG. 6A  is a top view of a filter assembly; 
           [0033]      FIGS. 6B ,  6 C, and  6 D are isometric views of the filter assembly of  FIG. 6A  in the closed, open, and filter material removed states, respectively; 
           [0034]      FIG. 6E  is a front view of the filter assembly of  FIGS. 6A-6D ; 
           [0035]      FIG. 6F  is a cross-sectional view taken along line VIF-VIF in  FIG. 6E ; 
           [0036]      FIG. 6G  is a rear view of the filter assembly of  FIGS. 6A-6F ; and 
           [0037]      FIG. 6H  is a side view of the filter assembly of  FIG. 6A-6G  in the open state. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0038]    Exemplary embodiments of the invention provide a filtration system for a ventilation hood including a first filter, which drains grease out of the filter, and at least one second filter located either upstream or downstream of the first filter. The first filter is preferably effective at preventing the spread of fire from the upstream face of the filtration system to an area downstream of the system. The second filter includes filter material sandwiched between two perforated sheets of relatively more rigid material. 
         [0039]    The first filter may be any filter that drains grease out of the filter, and is preferably also an effective fire barrier. One example of a filter for a ventilation hood that drains grease to a grease drain and is an effective fire barrier is the adjustable ventilator cartridge filter disclosed in U.S. Pat. No. 6,394,083 to Lambertson (the inventor of the present application), and shown in  FIG. 1 . A ventilation hood  1  is disposed above one or more cooking units (not shown). The ventilation hood  1  employs a fan (not shown) to remove the polluted air and exhaust it out of the kitchen, as generally indicated by the curved arrows. A cartridge filter  102  is disposed in the upper rear portion of the ventilator to regulate the air flow through the hood. As seen in  FIG. 1 , the air enters the cartridge filter  102  from one side and exits the filter on the other side in a controlled manner. It is noted that other arrangements are possible. A grease drain  104  is disposed below the cartridge filter  102 . The cartridge filter  102  desirably has a substantially open and unobstructed bottom so that grease does not accumulate inside the cartridge filter  102 , but flows to the grease drain  104 . In the embodiment illustrated in  FIG. 1 , the cartridge filter  102  is inclined by about 45°, but other arrangements are possible. 
         [0040]    The polluted air enters the filter at the topmost arrow and encounters two immediate direction changes forced by the configuration of the walls of the filter. These immediate direction changes start the segmenting of the heavier pollutants from the lighter air. The air flow then enters a high velocity corridor at the second arrow. The entire flow is sped up and then goes through a drastic turn of direction of about 180° at the third arrow. The high rate of air speed and the sudden change in direction facilitate grease extraction. The separated heavier pollutants are unable to follow the lighter air flow around the sudden change of direction at the third arrow. Thus the momentum of the grease carries it to the bottom of the cartridge filter where it impinges with the hood, and then drains into the grease trough provided in the ventilation hood. 
         [0041]    Another example of a filter for a ventilation hood that drains grease to a grease drain and is an effective fire barrier is a baffle-type filter, such as that disclosed in U.S. Pat. No. 3,910,782 to Struble et al, the disclosure of which is hereby incorporated by reference. 
         [0042]    Other grease-draining and fire barrier filters are within the scope of the appended claims. 
         [0043]    The inventor of both U.S. Pat. No. 6,394,083 and the instant application has noted that the cartridge filter of U.S. Pat. No. 6,394,083 and  FIG. 1  is very effective at preventing fires from traveling both from the downstream portion of the filter to the upstream portion, and vice versa, as is required by UL Standard 1046. 
         [0044]    The grease that is filtered by the cartridge filter is drained rather than being stored inside the filter. In other words, the cartridge filter is an example of a “non-loading” filter, in that the grease does not load up within it. Therefore, if a fire enters the filter, there is very little grease inside of the filter to serve as fuel. The shape of the cartridge filter is also such that a flame cannot travel through the entire filter. 
         [0045]    However, the filter of U.S. Pat. No. 6,394,083 and  FIG. 1  is satisfactory at filtering out grease with a particle size of greater than about 5 micrometers (μm), but less effective with smaller particles. 
         [0046]    Therefore, embodiments of the present invention further include a second disposable or permanent filter, located either upstream or downstream of the first filter, the second filter being permanently or removably attached to the first filter, or mounted within the hood separately from the first filter. 
         [0047]    A recent change in the UL  1046  standard now allows for testing of so-called “multi-stage” filters. Materials that cannot and could not pass the fire safety requirement of the standard individually may be utilized if the filter assembly as a whole can pass the tests mandated by the standard. 
         [0048]    Embodiments of the present invention thus provide a filtration system with both a first and a second filter, where the first filter is a very effective fire barrier, and the second filter is a very effective at entrapping particulates. The resulting combination provides superior performance in both respects. 
         [0049]    In some embodiments, the second filter is made, in part, of fibers, such as natural, synthetic, and/or hybrid fibers, such as, for example and without limitation, wool fibers, wood-based viscose fibers, and cellulose-based synthetic fibers. In some embodiments, the second filter is made of organic material, such as natural organic material. In some embodiments, the second filter is made of animal-derived organic material, such as wool. 
         [0050]    Other filter materials are within the scope of the appended claims. 
         [0051]    The material of the second filter is sandwiched between two perforated sheets of relatively more rigid material. While fiber filters are prized for their particle filtration abilities, their consistency is similar to that of paper towels, and they are known to collapse during use, particularly with age. For this reason, they are not used as often as might be expected given their excellent filtration properties. The present inventor has discovered that by sandwiching the fiber material between two perforated sheets, the problems caused by the consistency can be rectified. In a presently preferred embodiment, the two sheets are placed very close together to squeeze and hold the material between them. In this way, the material remains in place, regardless of how much grease and other particulates it has absorbed. 
         [0052]    As was mentioned above, the second filter can be placed either upstream or downstream of the first filter. There are three presently preferred configurations: first, the second filter is downstream of the first filter. This configuration is similar to that discussed in the parent application and particularly in the embodiments of  FIGS. 2 and 4  therein. Second, the second filter is disposed upstream of the first filter, by being retrofit into an existing hood that already includes a first filter but not a second filter. And third, the second filter is disposed upstream of the first filter, where both filters are retrofit into an existing hood that does not yet include any filters. 
         [0053]      FIG. 2  shows a first example of the second filter being disposed downstream of the first filter. This embodiment is similar to that illustrated in  FIG. 2  in the parent application. In this embodiment, the first filter is a cartridge filter  202  with associated pitched grease tray  203  and grease drain  204 , and the second filter is a fiber, organic, or other filter  206  located downstream of the first filter  202 . The second filter  206  is mounted to the first filter  202  at its downstream end, between the air outlet of the first filter and the air outlet of the ventilation hood  2 . The second filter may be permanently or removably attached to the first filter, or merely installed in the hood separately. 
         [0054]    Also illustrated in  FIG. 2  are two sheets of perforated material  208 ,  210 , such as metal, one immediately upstream of the fiber filter material  206  and one immediately downstream of the filter material  206 . These sheets may each have a cross-section substantially identical in shape and size to the filter material  206 , to act as a backing for the filter and sandwich it therebetween. They may be approximately 0.5 mm thick and made, for example, of stainless steel. The perforations may take any number or configuration that can be selected by a person of ordinary skill in the art based on the teachings herein, and may take up, for example, approximately 60% of the total cross-sectional area of the sheet. The percent open of each perforated sheet can be selected so as to enable efficient flow resistance behavior for the multi-stage filter system, to allow for enhanced grease capture while not adversely impacting the flow resistance of the multi-stage filter system. Alternatively, the perforated sheets can be made of expanded metal, wire screen or mesh, or any other supporting material—preferably non-flammable—that can be selected by a person of ordinary skill in the art based on the teachings herein. 
         [0055]    In some embodiments, these perforated sheets provide resistance to the greasy air flowing through the filter material  206 , creating an additional static pressure drop across the filter  206 . This distributes the air flow more evenly throughout the filter, thus improving the particle extraction efficiency. 
         [0056]    In use, polluted air enters the first filter  202 , where it is first filtered, and the less-polluted air then enters the second filter  206  with an increased static pressure, and is further filtered there. The clean air then flows through the downstream perforated sheet  210  and exits the ventilation hood  2 . 
         [0057]      FIG. 3  shows a second example of the second filter being disposed downstream of the first filter. This embodiment is similar to that illustrated in  FIG. 4  in the parent application. This differs from the embodiment seen in  FIG. 2  of this application in that the first filter is a baffle filter  302  rather than a cartridge filter  202 . The second filter  306  is again a fiber, organic, or other filter with associated perforated sheets  308 ,  310 . The second filter  306  is mounted within the ventilation hood  3  downstream of the first filter  302 , between the air outlet of the first filter and the air outlet of the ventilation hood. As discussed above, the second filter may be permanently or removably attached to the first filter, or installed in the hood separately. 
         [0058]    Other embodiments provide the second filter upstream of the first filter. These embodiments are considered particularly suitable when retrofitting an existing hood. Most hoods, whether with or without first filters, have tracks near the upstream end of the hood. (See  212  and  214  in  FIGS. 2 , and  312  and  314  in  FIG. 3 .) The present inventor has discovered that these tracks can be used as rails on which to position a filter assembly: either only a second filter (filter material plus perforated sheets) or for hoods that have no filters yet, a second filter integrated with a first filter can be inserted onto the hood and slid on the tracks provided in the hood. The filter assembly can alternatively be attached to the hood by any other appropriate means. 
         [0059]      FIGS. 4A-4L  show a second filter  416  integrated with a cartridge filter  402 , to provide a filter assembly  400  that can be slid into an existing hood  4  that does not yet have a filter. As can be seen, the first and second filters are removable from one another by the pivoting motion shown in  FIG. 4H  or the sliding motion shown in  FIG. 41 . The filter material  406  can be removed from between the perforated sheets  408 ,  410  even when the second filter  416  is attached to the first filter  402 , as can be seen in  FIGS. 4A-4C . A latch or clamp  418  keeps the filter material  406  interior the perforated sheets  408 ,  410  during use. This latch  418  can be undone by hand, and the upstream perforated sheet  408  can be swung open on hinges to provide access to the fiber material  406  for cleaning or replacement. 
         [0060]      FIG. 4L  shows the assembly  400  mounted in a hood  4  over cooking equipment  420 . A stove  420  is illustrated for exemplary purposes. 
         [0061]      FIG. 5A-5N  show a configuration in which the assembly  500  includes a baffle filter  502 , rather than a cartridge filter  402 , provided as the first filter. In this configuration, the baffle filter  502  can be slid into a track  512 ,  514  provided on a frame attached to the second filter  516  from the side. The second filter  516  includes filter material  506  sandwiched between perforated sheets  508 ,  510 . A latch  518  keeps the material  506  interior the sheets  508 ,  510  during use.  FIGS. 5J-5N  show the assembly mounted in a hood  5  that did not previously have a filter.  FIG. 5N  shows the hood  5  over cooking equipment  520 ; a stove  520  is illustrated for exemplary purposes. 
         [0062]      FIGS. 6A-6H  show a standalone second filter  616  for attachment into a hood (not shown) that already has a first filter (such as a cartridge or baffle filter). This second filter  616  can be inserted as a standalone add-on item, such as by being inserted into the track of the hood to provide additional filtering capabilities. The filter assembly  616  includes filter material  606  sandwiched between perforated sheets  608 ,  610 . The filter assembly  616  also includes a latch  618  to keep the material  606  interior to the sheets  608 ,  610  during use. 
         [0063]    As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. Many other embodiments are possible without deviating from the spirit and scope of the invention. These other embodiments are intended to be included within the scope of the present invention, which is set forth in the following claims.