Abstract:
A system for sanitizing and filtering air includes a chamber through which air passes, the chamber containing an ultraviolet light source. A sanitizing filter is removably mounted in the chamber, the filter containing a mechanical filtration media and a photocatalytic agent. The ultraviolet light illuminates the photocatalytic agent, and air passing through the chamber is purified by the photocatalytic agent and filtered by the mechanical filtration media. The system may also ionize the air, thereby polarizing particles in the air. When the polarized particles are caught in the filter they polarize the filter media, causing it to electrostatically attract other polarized particles in the air, thereby improving its filtration efficiency.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention relates to air cleaners and more specifically to an air cleaner sanitizing the air through use of a photocatalyst.  
         BACKGROUND OF THE INVENTION  
         [0002]    Indoor air quality has a tremendous impact on human health. The three major strategies for improving the quality of indoor air are controlling the sources of indoor pollution to reduce their production, diluting pollutants in indoor air with outside air through ventilation, and removing pollutants from indoor air using an air cleaner.  
           [0003]    Air cleaners work to remove both particulate and gaseous pollutants. Particulate pollutants include, for example, inorganic and organic compounds, tobacco smoke, fungal spores, mold, pollens, and living organisms such as bacteria and viruses. Gaseous pollutants include, for example, carbon monoxide, nitrogen oxide, and other combustion byproducts, as well as volatile organic compounds (VOCs), aldehydes, ketones and other gasses given off by construction products, adhesives, paints and varnishes.  
           [0004]    Particulate pollutants are generally removed with a mechanical filtration system, which employs a fibrous material or media through which polluted air is drawn. Particulate pollutants are trapped in the filter media and thereby removed from the air. Gaseous pollutants are generally too small to be trapped by mechanical filtration media. Living particulate pollutants may be removed from the air by mechanical filtration media, however they continue to live within the media. As a result they may be released back into the air when the filtration media is removed from the air cleaner.  
           [0005]    Live particulate pollutants and some gaseous pollutants may be treated with ultraviolet (UV) radiation. This kills live pollutants by causing mutations in their DNA, thereby preventing reproduction of the organism. UV radiation also can break the electron bonds of organic pollutants, reducing them to harmless component molecules. However, high intensity UV light is required to achieve these effects, which is harmful to humans and animals and which can produce ozone as a byproduct.  
           [0006]    Photocatalytic oxidation can be used to kill live pollutants, and to oxidize VOCs, carbon monoxide and other gaseous pollutants. When a photocatalyst, such as titanium dioxide (TiO 2 ) is irradiated with UV light it behaves as a catalyst, enabling the oxidation of the pollutants described above. However, the killed organisms and other oxidation byproducts can collect on the surface of the photocatalyst, leading to a reduction in its efficiency and a degradation in the performance of the air cleaner.  
           [0007]    As such, many air cleaners suffer from deficiencies in removing both particulate and gaseous pollutants from indoor air without producing harmful byproducts and without a decrease in filtration efficiency over the lifetime of the air cleaner. Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a sanitizing air cleaner that substantially eliminates or reduces disadvantages and problems associated with previously developed systems.  
           [0009]    More specifically, aspects of the invention can be found in a system for sanitizing and filtering air that has a chamber through which air passes. An ultraviolet light source is mounted in the chamber and illuminates a sanitizing filter removably mounted in the chamber. The filter includes a mechanical filtration media and a photocatalyst. The ultraviolet light activates the photocatalyst and the air passing through the chamber is purified by the photocatalytic agent and filtered by the mechanical filtration media.  
           [0010]    The system may include an ionization unit in the air passage that ionizes the air before it reaches the sanitizing filter, the ionized air polarizing the particulate pollutants in the air, and the polarized particles polarizing the surface of the mechanical filtration media when trapped therein. The ultraviolet light source may include means to evenly distribute the light across the photocatalyst.  
           [0011]    Further aspects of the invention may be found in a sanitizing air filter, for use in an air passage having a source of ultraviolet light. The sanitizing filter includes a mechanical filtration media and a photocatalytic agent. The sanitizing air filter is removably mounted in the air passage such that the ultraviolet light illuminates the photocatalytic agent. The air passage may also have an ionization source that ionizes the air in the air passage, which polarizes the particles in the air, and the mechanical filtration media may be made of electrically non-conductive material, whereby polarized particles trapped in the media polarize the media, and other polarized particles are electrically attracted to the polarized media.  
           [0012]    Further aspects of the invention may be found in a method of sanitizing and filtering air. The steps of the method include inserting a sanitizing air filter in a chamber through which air passes, the filter containing a mechanical filtration media and a photocatalytic agent, and illuminating the photocatalytic agent with ultraviolet light. The steps of the method also include renewing the photocatalytic agent by removing the sanitizing air filter and inserting a new sanitizing air filter, the air being sterilized by passing over the photocatalytic agent and filtered by passing through the mechanical filtration media. The mechanical filtration media may be electrically non-conductive and the steps of the method may further include creating ions in the air in the chamber which polarize the particles in the air. A further step of trapping the polarized particles in the mechanical filtration media causes the surface molecules of the media to become polarized, with the result that the polarized particles in the air are electrostatically attracted to the polarized media, improving its filtration efficiency.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:  
         [0014]    [0014]FIG. 1 shows an embodiment of the present invention in front, top and side views;  
         [0015]    [0015]FIG. 2 is a cross-sectional view of a filter embodying the present invention;  
         [0016]    [0016]FIG. 3 is an isometric view of a free-standing air cleaner embodiment of the present invention;  
         [0017]    [0017]FIG. 4 is an isometric view of a duct mounted embodiment of the present invention;  
         [0018]    [0018]FIG. 5 is a top view of a vacuum cleaner incorporating an air filter according to the present invention;  
         [0019]    [0019]FIG. 6 is a view of the ultraviolet light in an embodiment of the present invention;  
         [0020]    [0020]FIG. 7 is a view of a compound reflector used with the ultraviolet light in an embodiment of the present invention; and  
         [0021]    [0021]FIG. 8 is a view of a compound lens used with the ultraviolet light in an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Exemplary embodiments of the invention are illustrated in the Figures, like numerals being used to refer to like and corresponding parts of the various Figures.  
         [0023]    [0023]FIG. 1 shows three views of sanitizing air cleaner unit  10  embodying the present invention. FIG. 1A is a front view, FIG. 1B a top view and FIG. 1C a side view. Referring to FIG. 1A, air filter unit  10  is enclosed in high-quality galvanized steel housing  34 , which has apertures  26  and  28  at opposite ends. Polluted air  12  enters housing  34  via inlet aperture  26 , passing through grille  30 , which also acts as a light baffle to prevent ultraviolet (UV) radiation  24  emitted by UV lamp  22  from escaping housing  34 . The polluted air then passes over ion brushes  36 , through sanitizing filter  14  and emerges through grille  32  in outlet aperture  28  as filtered, purified air  20 . Fan  16 , coupled to filter  14  by shroud  18 , pulls the air into housing  34  and through filter  14 . Ultraviolet lamp  22  illuminates filter  14  with UV radiation  24 . Filter  14  has a layer coated with titanium dioxide (TiO 2 ) that is activated by UV radiation  24 .  
         [0024]    [0024]FIG. 1B shows a top view of air cleaner unit  10 . Ultraviolet lamp  22 , mounted on one side of housing  34  in this embodiment of the invention, illuminates sanitizing filter  14  with UV radiation  24 . Fan  16 , driven by motor  18 , draws air in through grille/light baffle  30  in inlet aperture  26 , past ion brushes  36 , through filter  14 , coupled by shroud  18 , and blows the treated air out through grille  32  in outlet aperture  28 .  
         [0025]    [0025]FIG. 1C shows a side view of air cleaner unit  10 , looking in through inlet aperture  26 . Grille/light baffle  30  has been removed in this view. Ultraviolet lamp  22  can be seen mounted on one side of housing  34 , illuminating sanitizing filter  14 . Ion brushes  36  can also be seen extending vertically in front of filter  14 . The outline of fan  16  and shroud  18 , which is behind filter  14  in this view, can be seen in broken lines.  
         [0026]    The mechanical filter media of sanitizing filter  14  is composed of an electrically non-conductive material, preferrably polypropylene fibers. Ion brushes  36  are connected to one terminal, preferrably the negative terminal, of a high voltage source (not shown) to form an ionization unit. Alternatively, a corona tip or corona wire could be used in the ionization unit in place of the ion brushes  36  shown in FIG. 1.  
         [0027]    Particulate pollutants become polarized as the airflow through the air cleaner unit  10  draws them past ion brushes  36 . Free electrons on the surface of the particles are drawn to the side of the particle closer to or farther from the ion brushes, respectively, depending on whether the ion brushes are positively or negatively charged. When these polarized particles are trapped in the mechanical filter media of sanitizing filter  14 , they polarize the surface molecules of the filter fibers. Subsequent polarized particles that are drawn through the mechanical filter media are electrically attracted to the polarized filter fibers, improving the filtration efficiency of filter  14 .  
         [0028]    This polarizing technique allows a less dense mechanical filter media to be used than would be needed in a filter unit that does not use the technique, while still meeting the HEPA filtration standard. The use of a less dense filter media makes it easier to draw air through the filter. Therefor, a lower fan speed can be used to filter a specified volume of air in a specified period of time than would be required with a denser filter. As a result of this lower fan speed, air cleaner unit  10  can can achieve HEPA standard filtration while operating more quietly than a unit not using this polarizing technique. Additionally, operating at a lower fan speed enables air cleaner unit  10  to draw less electrical power than a unit with a fan operating at higher speed.  
         [0029]    It should be understood that use of this polarizing technique is not essential to the present invention. Other mechanical filtration media, as described hereinbelow, may be used without departing from the techniques of the present invention. Furthermore, the ionization unit may be omitted from the air cleaner unit while still remaining within the scope of the present invention.  
         [0030]    While this embodiment of the invention utilizes a single inlet aperture  26  and a single outlet aperture  28 , it should be understood that multiple apertures can be used for air inflow or outflow without departing from the techniques of the present invention. Similarly, while grille  30  is described in this embodiment of the invention as also serving as a light baffle, it should be understood that it is within the scope of the invention to use a serpentine air passage or other light blocking technique between inlet aperture  26  and UV lamp  22  to prevent UV radiation  24  from escaping housing  34 .  
         [0031]    An embodiment of sanitizing filter  14  of FIG. 1 is illustrated in cross-section in FIG. 2. Mechanical filter media  40  is typically a fibrous material in a non-woven sheet, however woven fibrous material, sintered metal or plastic particles, or other filter materials may also be used. Preferrably, mechanical filter media  40  meets the HEPA standard for particulate filtration. Photocatalytic filter  42 , made in this embodiment from a wire mesh coated with TiO 2 , is sandwiched next to mechanical filter media  40  by frame  44 .  
         [0032]    It should be understood that other photocatalysts, such as compounds of TiO 2 , may be used within the scope of the present invention. Other techniques for supporting the photocatalyst in the airstream may also be used without departing from the techniques of the present invention, such as coating a substrate other than a wire mesh or coating the mechanical filtration medium directly. Further, either the mechanical filtration medium or a separate substrate could be fabricated with a photocatalyst embedded in its surface.  
         [0033]    [0033]FIG. 3 illustrates freestanding air cleaner unit  10 , which is portable and suitable for placement in a room or other enclosed space where air filtration and purification are desired. As shown, sanitizing filter  14  is inserted through filter replacement aperture  48  into its operative position within air cleaner unit  10 . A door or cover plate (not shown in FIG. 3) is then closed to cover aperture  48  and to seal the unit so that air flows in through inlet aperture  26 , rather than through filter replacement aperture  48 . As killed organisms and oxidation byproducts gradually accumulate to coat the photocatalytic filter within sanitizing filter  14 , they reduce both the efficiency of the filter and the sanitizing functionality of air cleaner unit  10 . Filter efficiency and filter unit functionality can be restored by removing the used filter and inserting a new one with a clean, efficient photocatalytic filter.  
         [0034]    Replacement of sanitizing filter  14  preferrably occurs at least every six months to maintain an appropriate level of sanitizing functionality. Ultraviolet lamp  22  is preferrably cleaned with a brush or dry cloth at least every 3 months to remove dust and debris that reduce the amount of UV radiation falling upon the photocatalyst in sanitizing filter  14 . Because the amount of UV radiation emitted by UV lamp  22  gradually declines over the lifetime of the lamp, the lamp is preferrably replaced after 9000 hours or one year of use  
         [0035]    [0035]FIG. 4 illustrates air filter unit  50 , an embodiment of the present invention intended to be mounted within the air handling equipment or ductwork of a ventilation system. Such a ventilation system might be found in a building or in a vehicle, such as a car, an airplane, or a ship. Ultraviolet lamp  52  is mounted inside the unit to illuminate sanitizing filter  54 , which is shown installed in the unit through filter replacement aperture  64 . As in FIG. 3, a door or other cover plate (not shown in FIG. 4) is used to seal aperture  64  while unit  50  is in operation. Inlet aperture  56  and outlet aperture  58  (not visible in FIG. 4) are not covered with decorative grilles in this embodiment. Flanges  60  and  62  are provided to bolt air filter unit  50  to the air handling equipment or ductwork of the ventilation system. Because air is moved though the system by ventilation system fans, unit  50  does not have an internal fan.  
         [0036]    [0036]FIG. 5 shows an embodiment of the techniques of the present invention in vacuum cleaner  80 . Fan  86 , powered by motor  88 , draws particle-laden air  82  from suction hose  96  into bag  102 . While larger particles are removed from the air stream by bag  102 , finer particles and dust remain. These are purified and further filtered by exhaust filter  84  embodying the techniques of the present invention. Exhaust filter  84  is inserted into position to cover outlet aperture  96  through the filter replacement aperture covered by door  100 . Ultraviolet lamp  92  illuminates sanitizing filter  84  with UV radiation  94 , activating the photocatalyst in filter  84 .  
         [0037]    Other techniques for securing exhaust filter  84  in place over outlet aperture  96  may be used. In one embodiment, filter  84  is fitted in a housing that screws into aperture  96 . In another embodiment, filter  84  is fitted in a housing with molded features that mate with catch mechanisms mounted on the exterior of vacuum cleaner housing  104 , the catches securing the filter against outlet aperture  96 .  
         [0038]    [0038]FIG. 6 depicts UV lamp  112  illuminating surface  116  of a sanitizing filter with UV radiation  114  as taught in the hereinbefore described embodiments of the present invention. While all of surface  116  is illuminated, region A of the surface receives more illumination than region B. If UV lamp  112  is too dim or too far away from region B, the photocatalyst in region B may not receive enough UV radiation to be activated. Thus, it may be desirable to utilize the techniques described below to provide a more even distribution of the UV radiation  114  from lamp  112  over surface  116 .  
         [0039]    A reflector  118  is employed to spread the light more evenly in FIG. 7. By reflecting the radiation from the side of lamp  112  that faces away from surface  116  toward region B, the illumination level in regions B can be increased. A compound lens  120  is shown in FIG. 8. A stepped lens with regions of different curvature can redirect light rays from lamp  112  that would have illuminated region A toward region B, to more evenly illuminate surface  116 .  
         [0040]    As such, an apparatus and method are described for a sanitizing air filter. In view of the above detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the present invention as set forth in the claims that follow.