Abstract:
A gas treatment system for treating a gas stream containing contaminants includes first and second gas treatment members in fluid communication with each other. Each of the first and second gas treatment members is selectively controllable between an on and an off condition. A third gas treatment member is in fluid communication with the first and second gas treatment members, and the third gas treatment member selectively retains or releases the contaminants based upon the on or off condition of at least one of the first or second gas treatment members.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a Divisional Application which claims priority to application Ser. No. 11/011,730 filed Dec. 14, 2004. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to air treatment modules and, more particularly, to protecting a photocatalyst in the air treatment module using a corona discharge device to remove contaminants from the air handling air stream. 
         [0003]    Air treatment modules are commonly used in automotive, commercial and residential heating, ventilating, and air conditioning (HVAC) systems to move and purify air. Typically, an air stream flowing through the air treatment module includes trace amounts of contaminants such as biospecies, dust, particles, odors, carbon monoxide, ozone, semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs) such as formaldehyde, acetaldehyde, toluene, propanol, butene, and silicon-containing VOCs. 
         [0004]    Typically, a filter and a photocatalyst are used to purify the air stream by removing and/or destroying the contaminants. A typical filter includes a filter media that physically separates contaminants from the air stream. A typical photocatalyst includes a titanium dioxide coated monolith, such as a honeycomb, and an ultraviolet light source. The titanium dioxide operates as a photocatalyst to destroy contaminants when illuminated by ultraviolet light. Photons of the ultraviolet light are absorbed by the titanium dioxide, promoting an electron from the valence band to the conduction band, thus producing a hole in the valence band and adding an electron in the conduction band. The promoted electron reacts with oxygen, and the hole remaining in the valence band reacts with water, forming reactive hydroxyl radicals. When contaminants in the air stream flow through the honeycomb and are adsorbed onto the titanium dioxide coating, the hydroxyl radicals attack and oxidize the contaminants to water, carbon dioxide, and other substances. The ultraviolet light also kills the biospecies in the airflow that are irradiated. 
         [0005]    Disadvantageously, typical air treatment module filters have a finite contaminant capacity. Once the contaminant capacity is reached, the filter does not physically separate additional contaminants from the air stream. Contaminants in the air stream may then flow through the filter and become oxidized by the photocatalyst. This is particularly troublesome when the photocatalyst oxidizes silicon-containing VOCs or SVOCs to form a silicon-based glass on the photocatalyst surface. The silicon-based glass may insulate the titanium dioxide from the passing air stream, thereby passivating the titanium dioxide. In severe instances, much of the catalytic activity of the photocatalyst may be lost within two weeks of reaching the contaminant capacity of the filter. To prevent photocatalyst passivation, the filter may be replaced before reaching the contaminant capacity or additional filters may be utilized to physically separate a greater amount of the contaminants, however, the maintenance required to replace a filter in short time intervals or continually monitor a filter may be expensive and inconvenient. 
         [0006]    Accordingly, an air treatment module that more effectively protects the photocatalyst from passivating contaminants is needed. 
       SUMMARY OF THE INVENTION 
       [0007]    A gas treatment system for treating a gas stream containing contaminants includes first and second gas treatment members in fluid communication with each other. Each of the first and second gas treatment members is selectively controllable between an on and an off condition. A third gas treatment member is in fluid communication with the first and second gas treatment members, and the third gas treatment member selectively retains or releases the contaminants based upon the on or off condition of at least one of the first or second gas treatment members. 
         [0008]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a HVAC system including an air treatment module. 
           [0010]      FIG. 2  is a perspective view of an example air treatment module. 
           [0011]      FIG. 3  is a schematic view of an example filter, plasma device, and photocatalyst. 
           [0012]      FIG. 4  is a schematic view another example of the filter of  FIG. 3 . 
           [0013]      FIG. 5  is a schematic view an example air treatment module that includes an ozone-destroying material. 
           [0014]      FIG. 6  is a schematic view of another air treatment module configuration that includes a second plasma device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]      FIG. 1  illustrates a residential, commercial, vehicular, or other structure  10  including an interior space  12 , such as a room, office or vehicle cabin. An HVAC system  14  heats or cools the interior space  12 . Air in the interior space  12  is drawn into the HVAC system  14  through an inlet path  16 . The HVAC system  14  changes the temperature and purifies the air drawn using an air treatment module  18 . The purified, temperature-changed air is then returned to the interior space  12  through an outlet path  20 . 
         [0016]      FIG. 2  illustrates a perspective view of an example air treatment module  18 . The air treatment module  18  includes a compressor  30  for drawing and returning the air. Air drawn from the interior space  12  flows in an air stream  32  into a filter cabinet  34 , which forms an air flow path through the air treatment module  18 . The filter cabinet  34  encloses a filter  36 , plasma device  38 , and photocatalyst  40  that cooperate to purify the air stream  32 . The air stream  32  continues through the filter cabinet to the coils  42 . The coils  42  heat or cool the air stream  32 , depending on the desired interior space  12  temperature. After being heated or cooled, the compressor  30  returns the air stream  32  to the interior space  12  through the outlet path  20 . It is to be understood that the air treatment module  18  shown is only one example and that the invention is not limited to such a configuration. 
         [0017]      FIG. 3  illustrates a schematic view of an example filter  36 , plasma device  38 , and photocatalyst  40 . The filter  36  receives the air stream  32  and adsorbs contaminants from the air stream  32 . The filter  36  includes a known activated carbon filter media held between layers of a fibrous mesh  44 . In one example, the known activated carbon is modified, impregnated, or pore-controlled. As is known, a modifier such as potassium permanganate or other modifier may be impregnated in the activated carbon to modify the adsorptive properties of the activated carbon. The pore volume of the activated carbon may also be controlled within a desired range to modify the adsorptive properties. These features may provide the advantage of designing the filter  36  to preferentially adsorb certain contaminants, such as formaldehyde, acetaldehyde, toluene, propanol, butene, silicon-containing VOCs, or other VOCs. 
         [0018]    In another example, the filter  36  may additionally utilize a zeolite and/or other type of filter media mixed with the activated carbon between the layers of fibrous mesh  44  to obtain preferential adsorption of certain contaminants. Alternatively, the activated carbon filter media may be integrated with the fibrous mesh  44  by coating the activated carbon onto fibers that make the fibrous mesh  44 . 
         [0019]    In another example, the activated carbon filter media is provided in a first layer  46  and the zeolite media and/or other filter media may be provided in an adjacent second layer  48 , as illustrated in  FIG. 4 . 
         [0020]    A heating element  50 , which is discussed in more detail below, surrounds the filter  36  and is selectively operable between and on and an off condition. 
         [0021]    In one example, the plasma device  40  is located generally downstream from the filter  36  and is selectively operable between an on and an off condition. Preferably the plasma device  38  is a corona discharge device that generates a plasma glow discharge. Even more preferably, the plasma device  38  includes a biased electrode  54 , such as a wire cathode. 
         [0022]    The photocatalyst  40  is, in one example, located downstream from the plasma device  38 . Preferably the photocatalyst  40  is a titanium dioxide coated monolith, such as a honeycomb, that operates as a photocatalyst to destroy contaminants when illuminated with an ultraviolet (UV) light  56 . It is to be understood that photocatalyst materials other than titanium dioxide and configurations other than shown (for example, integrating the photocatalyst  40  with the filter  36  in a single unitary fibrous or honeycomb structure) may be utilized. 
         [0023]    The UV light  56  is selectively operable between an on condition in which the photocatalyst  40  operates to destroy contaminants, and an off condition in which the photocatalyst  40  is inoperable. In one example, the UV light  56  illuminates the photocatalyst  40  with UV-C range wavelengths, however, other UV wavelength ranges may be utilized depending on the type of photocatalyst and/or air purifying needs of the air treatment module  18 . 
         [0024]    Operationally, the exemplary air treatment module  18  functions in two different modes. In the first mode, the air treatment module  18  functions primarily to move air from and return air to the interior space  12  and to purify the air. In the first mode, the heating element  50  is selectively turned off, the plasma device  38  is selectively turned off, and the UV light  56  is selectively turned on. Thus, the filter  36  captures, traps, and adsorbs certain contaminants from the air stream  32 , such as VOCs and SVOCs, and the photocatalyst  40  operates to destroy other contaminants that pass through the filter  36 . The heating element  50  and plasma device  38  do not function in the first mode, however, in other examples it may be advantageous to simultaneously operate the heating element  50  and plasma device  38  with the functions of filtering and moving the air. 
         [0025]    In the second mode, the air treatment module  18  functions primarily to regenerate the filter  36 . That is, the activated carbon or other adsorbent filter media is conditioned to desorb the previously adsorbed contaminants. The air stream  32  is shut off such that there is essentially zero air flow in the filter cabinet  34 . The heating element  50  is selectively turned on and heats the filter  36  to approximately 100° C., although other heating temperatures or heating profiles may also be utilized. The filter  36  desorbs and releases the contaminants previously adsorbed. The plasma device  38  is selectively turned on and generates a plasma, and the UV light  56  is preferably turned off to prevent the photocatalyst  40  from oxidizing the released contaminants. 
         [0026]    The filter cabinet  34  holds the released contaminants and acts essentially as a reactor vessel for the plasma device  38 . The released contaminants, such as VOCs, SVOCs, or other contaminants that the filter  36  was designed to adsorb/release, contact the plasma generated by the plasma device  38 . The plasma chemically transforms the contaminants into solid contaminant products and deposits the solid contaminant products onto a receiving portion, the biased electrode  54 . Once deposited, the essentially immobile and inert solid contaminant products are unlikely to damage the photocatalyst  40 . In one example, the plasma deposits the solid contaminant products onto a wire cathode. After a predetermined number of deposit cycles, the wire cathode is removed from the plasma device  38  and discarded or cleaned. 
         [0027]    While in the second mode, the heating element  50  and plasma device  38  operate for a selected predetermined amount of time. Preferably, the time is adequate to i) release most of the contaminants from the filter  36 , and thus regenerate the filter  36  and ii) transform the contaminants to solid contaminant products. The time required will vary with temperature, size and type of filter media, size of the filter cabinet  34 , and the size and type of plasma device  38  used. 
         [0028]    Preferably, the UV light  56  remains off when switching from the second mode to the first mode to protect the photocatalyst  40  from any remaining contaminants that have not been transformed to solid contaminant products. The air stream  32  flows through the filter cabinet  34  for a selected predetermined amount of time to purge the remaining released contaminants before turning on the UV light  56  to operate the photocatalyst  40 . 
         [0029]    In another example, the contaminant products include organic silicon compounds, such as silicon-containing VOCs and silicon-containing SVOCs. The filter  36  releases the organic silicon compounds upon heating and the plasma generated by the plasma device  38  chemically transforms the organic silicon compounds into silicon dioxide or other silicon-based glass. The plasma deposits the silicon dioxide or other silicon-based glass on the biased electrode  54 . 
         [0030]    In another example, the filter  36  includes a single pleated layer with a pleating factor of about 8 and about 100 g of activated carbon filter media. The filter  36  adsorbs approximately 90% of the organic silicon compounds in the incoming air stream  32  and takes approximately twelve hours to reach full capacity in first mode operation. Near the twelve hour time, the air treatment module  18  utilizes, for example, a controller to automatically switch into the second mode and regenerate the filter  36 . Alternatively or in addition to the controller, an operator may control the switching between modes. 
         [0031]    In another example shown in  FIG. 5 , an ozone-destroying material  58 , such as a known metal oxide catalyst, is included between the plasma device  38  and the photocatalyst  40 . The ozone-destroying material  58  may be disposed on a honeycomb structure  60 , for example, and receives ozone from the plasma device  38  before switching the UV light  56  on. The ozone-destroying material  58  adsorbs ozone onto the surface and decomposes the ozone. This feature may provide the advantage of exposing the photocatalyst  40  to less ozone, which may contribute to photocatalyst  40  passivation. It is to be understood that the ozone-destroying material  58  may alternatively be positioned in other locations in the filter cabinet  34  than shown. 
         [0032]      FIG. 6  illustrates a schematic view of another air treatment module  18  configuration including a second plasma device  138  surrounding the filter  36 . The second plasma device  138  includes a biased electrode  154  and operates similarly to and in conjunction with the plasma device  38  to chemically transform released contaminants into solid contaminant products. Utilizing the second plasma device  138  may provide the benefit of shorter times to fully chemically transform the contaminants released from the filter  36  or greater efficiency in transforming the released contaminants. Likewise, a multitude of additional plasma devices may be used. 
         [0033]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.