Abstract:
A duct-free air filtration system including a housing having a hood for capturing air, grease, and smoke, and an elongated exhaust section in fluid communication with the hood. A grease extracting blower unit takes in air, grease, and smoke through the hood and exhausts air and smoke through the exhaust section of the housing with a substantial amount of the grease removed by centrifugal force. A charcoal filter disposed in the exhaust section removes odors from the air exhausted from the grease extracting blower unit and a smoke filter removes smoke from the air passed through the charcoal filter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/281,657, filed Nov. 20, 2009. 
    
    
     FIELD OF INVENTION 
     The present invention relates in general to air filtration techniques and in particular to ductless cooking air filtration systems and methods. 
     BACKGROUND OF INVENTION 
     Cooking creates undesirable by-products such as smoke and odor that can pollute an inhabited airspace if they are not removed or reclaimed. Consequently, many devices have been invented for addressing the problem of airborne cooking contaminants. For example, ducted range hoods remove the contaminated air from the inhabited area, while ductless range hoods intake air from the cooking area, remove at least some of the contaminants, and then re-circulate the resulting exhaust air back into the inhabited space. 
     Currently available re-circulating (ductless) residential cooking ventilation systems typically rely on an ineffective grease separator and even less effective optional thin odor “filter”. Laboratory testing of these conventional re-circulating systems has indicated that, at best, only a portion of the cooking contaminants are removed from the exhaust air. These conventional systems are particularly ineffective in removing smoke and lingering odors. Furthermore, conventional grease separators and odor filters, when used, block the natural inflow into the range hood “collector” and eliminate necessary capture space. 
     Hence, given the significant disadvantages of currently available cooking ventilation systems, new cooking ventilation apparatus and methods are desirable for removing cooking by-products, including grease, odors, and smoke, from inhabited areas. 
     SUMMARY OF INVENTION 
     The principles of the present invention are embodied in a cooking air recovery system including a housing having a hood for capturing air, grease, and smoke, and an elongated exhaust section in fluid communication with the hood. A grease extracting blower unit takes in air, grease, and smoke through the hood and exhausts air and smoke through the exhaust section of the housing with a substantial amount of the grease removed by centrifugal force. A charcoal filter disposed in the exhaust section removes odors from the air exhausted from the grease extracting blower unit and a smoke filter removes smoke from the air passed through the charcoal filter. 
     Embodiments of the present principles realize substantial advantages over the prior art. Among other things, an unobstructed hood, without screens or filters at the hood aperture, allows for smoke, grease, and odor to be efficiently captured and passed to the centrifugal blower-separator. The centrifugal blower—grease extractor in turn liquefies and removes grease from the air flow and deposits it in a pan for easy disposal. Furthermore, by removing a substantial portion of the grease, the centrifugal blower—extractor ensures that the media in the following charcoal filter is not contaminated. 
     A thick, heavy charcoal filter advantageously ensures that the exhaust air flow remains in contact with the activated filter media for a sufficiently long period of time to remove odor. Finally, a high-density filter with a large contact area removes smoke from the exhaust air flow. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram of a representative duct-free cooking air filtration system, embodying the principles of the present invention, shown in a typical home cooking environment; 
         FIG. 2A  is a diagram providing a prospective view of the duct-free air filtration system of  FIG. 1 ; 
         FIG. 2B  is a diagram providing a partially exploded view of the duct-free air filtration system shown in  FIG. 1 ; 
         FIG. 3A  is a diagram providing a cut-away view of the duct air filtration system of  FIG. 1 ; 
         FIG. 3B  is a conceptual diagram of a conventional ductless hood system; and 
         FIG. 4  is a diagram of the blower-grease extractor assembly of the duct-free air filtration system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in  FIGS. 1-4  of the drawings, in which like numbers designate like parts. 
       FIG. 1  is a diagram of an exemplary duct-free hood system  100  embodying the principles of the present invention. Duct-free hood system  100  is shown disposed over a conventional home kitchen stove  101 , which during normal cooking generates cooking byproducts including grease, odors, and smoke. While duct-free hood system  100  is shown the preferred home kitchen environment, the present inventive principles are not limited thereto, and may be applied to other environments, such as commercial kitchens. In addition to stoves, the cooking byproducts can be generated by other cooking appliances, such as frying pans and similar electric apparatus. 
       FIG. 2A  is line drawing showing the internal structures of duct-free hood system  100 . In particular, duct-free hood system  100  includes a hood  201 , which provides a wide-open aperture, without obstructing screens or filters, for receiving intake air flow containing cooking byproducts. Hood  201  and/or exhaust housing  203  are constructed from stainless steel, glass, or a similar material that is sufficiently rugged yet provides for an ornamental design. Intake air flow is inducted by a centrifugal blower-grease extractor  202 , which in the illustrated embodiment is constructed and operates in accordance with co-assigned U.S. Pat. No. 6,820,609 to Woodall, I I I et al. for Low-profile Ventilation Hood. 
     The exhaust air discharged from centrifugal blower-grease extractor  202  is passed into exhaust housing  203  of duct-free hood system  100  towards exhaust vents  204   a - 204   b . Exhaust housing  203  includes a thick odor removing activated charcoal filter  205  and a pleated fiber smoke filter  206 . As shown in the exploded view of  FIG. 2B , activated charcoal filter  205  and smoke filter  206  are preferably discrete units, which can be removed from exhaust housing  203  for servicing or replacement. 
     In the illustrated embodiment, activated charcoal filter  205  is constructed of a double layered squared off inverted “U” shaped chamber made of perforated metal enclosed in a sheet metal box-shaped housing that is open top and bottom. Between the double layers of perforated metal is a one (1) inch thick bed of activated carbon pellets. (Other types of odor filtering media may be used in alternate embodiments.) The squared off inverted “U” shaped carbon bed advantageously maximizes the exposure time of the exhaust air stream to the carbon pellets within the space constraints. 
     Odor removal effectiveness increases with the time the contaminated air is in contact with the actuated charcoal and this design generates carbon pellet to exhaust air stream exposure approximately fifty (50) times longer than existing carbon thin mat filters. For example, for an embodiment of the present invention in which blower-grease extractor  202  provides an exhaust air flow of approximately 200 cubic feet per minute (cfm) and charcoal filter  205  provides approximately 221 cubic inches (cubic in.) of charcoal pellets, the exhaust air stream exposure ratio is approximately 220 cfm/231 cubic in or 0.85 cfm/cubic in. (The performance of charcoal filter  205  can be improved by reducing the cfm/cubic in. ratio or reduced by increasing the cfm/cubic in, as needed for the particular embodiment). 
     Smoke filter  206 , in the illustrated embodiment, mounts directly on the open top of the box shaped charcoal filter housing of charcoal filter  206 . This configuration forces all of the air flowing through the activated carbon bed into smoke filter  206 . Preferably, smoke filter  206  includes a filter element constructed of thin layer glass media folded into a multi-pleated pattern to maximize filter surface area within the space constraints. In the illustrated embodiment, the filter media is rated to trap 95 percent of particles measuring three microns and larger that enter the filter. Other ratings from 60 percent of particles measuring three microns and larger to 99.97 percent of particles measuring three microns and larger can also be utilized. (The smoke particles are permanently trapped within the filter element because they are larger than the openings in the filter media.) For an exhaust air flow of approximately 200 cfm, and a filter media providing approximately 35 square feet of surface area, the exhaust air stream exposure ratio is 200 cfm/35 sq. ft. or 5.5 cfm/sq. ft. (The performance of smoke filter can be increased by reducing the cfm/sq. ft. ratio, or reduced by reducing the cfm/sq. ft. ratio, as required by the particular embodiment. 
     The four-phase air recovery process implemented by duct-free hood system  100  is illustrated in  FIG. 3A . The first and second phases are implemented by blower-grease extractor  202 , which is shown in further detail in  FIG. 4 . In particular, blower-grease extractor includes a centrifugal blower  401 , circular intake aperture  402 , sidewalls  403 , grease pan  404 , and laterally offset exhaust aperture  405 . A complete description of blower-grease extractor  202  is provided in co-assigned U.S. Pat. No. 6,820,609, incorporated herein by reference. 
     In the first phase, a centrifugal blower  401  achieves active canopy collection by pulling air from hood (canopy)  201  in through intake aperture  402 . The wide-open design of hood canopy  201  allows blower-grease extractor  202  to efficiently capture the rising cooking byproducts from the underlying cooking appliance. 
     For the second phase, a temperature sensor ensures that blower  401  is operating at the optimum speed for centrifugal grease extraction. Such a temperature sensor is disclosed in co-assigned U.S. Pat. No. 6,142,142, also incorporated herein by reference. As the dirty air passes through aperture  402 , the grease is separated from the air as the air undergoes rapid radial acceleration. The grease is then gravity collected in grease collection pan  404  while the grease-free air passes through laterally offset exhaust aperture  405 . 
     In the third phase, the air stream exhausted from blower-grease extractor  202  is passed through charcoal odor filter  205 , discussed in detail above. Finally, in the fourth phase, the air stream is passed through smoke filter  206  and out of exhaust vents  204   a  and  204   b.    
     In additional embodiments of the principles of the present invention, apparatus may be provided within hood  201  or exhaust housing  203  for releasing an odor masking agent, freshening aroma, or disinfectant. A reactive device, such as an ultraviolet light source, may also be provided for killing bacteria, viruses, and other pathogens. 
     The illustrated embodiment of the present principles is contrasted with a conventional ductless ventilation hood  300  in  FIG. 3A . As shown in  FIG. 3A , the conventional system includes a restricted canopy  302  having a limited capability to capture cooking byproducts generated on the underlying cooking equipment (not shown). In particular, the aperture of canopy  302  is obstructed by a conventional filter system  303  formed by metal baffles and/or a thin layer of filter material. The metal baffles and/or thin layer of filter material are not only ineffective in stopping grease, smoke, and odors, from flowing through but also are difficult to remove and clean of those cooking byproducts that are captured. 
     Conventional ventilation system  300  utilizes a simply blower  301  for inducing air flow through the system housing. Blower  301  does not extract any of the grease that has passed through filter  303  and simply exhausts that grease back into the surrounding environment. Conventional ventilation system  300  does not include a thick charcoal filter for removing odors or a smoke filter for removing smoke pulled-in in from the stove. 
     In sum, the principles of the present invention are embodied in robust apparatus and methods for removing airborne cooking byproducts, including grease, odor, and smoke. These embodiments include a wide-open hood (canopy) and a centrifugal blower-grease extractor, which efficiently capture the cooking byproducts and remove grease. A thick odor filter ensures that the airstream exhausted from the blower-grease extractor is sufficiently exposed to the active filter material such that odors are substantially removed. A smoke filter, having a pleated-material filter element with a large surface area, ensures that smoke is substantially removed from the air stream. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     It is therefore contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.