Abstract:
A heat exchanger coil has its fins coated with a photocatalytic semi-conductor material in such a manner that its fins may then be illuminated by UV light to activate the material so as to cause the oxidation of organic pollutants which are on the fin coils themselves or in the air passing therethrough. A preferred photocatalytic semi-conductor material is titanium dioxide, which may be applied to the fin stock prior to the fabrication of the coil.

Description:
This invention relates generally to air conditioning systems and, more particularly, to an air conditioning system having means to treat the air for microbial contaminants. 
     BACKGROUND OF THE INVENTION 
     The term “dirty socks syndrome” refers to the offensive smell that can emanate from a poorly maintained air conditioning system in which mold and/or bacteria grow on the indoor coil or in the drain pan. In addition to the undesirable smell, this microbial growth may cause the release of spores and toxins into the air so as to cause allergy related problems. Further, the buildup of mold tends to create maintenance problems because of the dirty coils, an increase in pressure drop, loss of heat exchange efficiency and possibly dirty and plugged drain pans. 
     Microbial growth can be temporarily treated by using chemicals such as bleach and the like. However, many of the most aggressive cleaning solutions, such as those which are chlorine based, have been banned from use in air conditioning systems. But even where approved biocidal agents are used on coils and drain pans, they do not provide a permanent solution. 
     The use of UV germicidal lamps have been found to be effective in controlling the growth of microbes in air conditioning systems. One of the most effective ways is to direct the light onto the coil and the drain pan so as to attack the growth directly. One example of such a system is shown in U.S. Pat. No. 5,755,103. There are also systems which filter the impurities from the air and the direct ultraviolet light onto the filter to neutralize the impurities such as are shown in U.S. Pat. Nos. 5,879,435 and 5,891,399. In addition, there is some systems which use the UV light to attack the growth indirectly by the use of a reactor structure which directs the light source on the air flow so as to provide a fly-by control of airborne contaminants. Examples of such systems are shown in U.S. Pat. No. 5,833,740 and U.S. Pat. No. 5,902,552. 
     More recently, it has been found that the effectiveness of UV irradiation in the conversion of contaminants can be substantially enhanced by the use of a catalyst, such as TiO 2 , in the reactor environment. U.S. Pat. Nos. 5,835,840; 5,790,934 and 5,865,959 show examples of such systems. It should be mentioned that, while these systems have been shown to be effective in the control of microbial growth, they are relatively expensive to implement since they require a dedicated reactor structure in order to accommodate that single function. 
     It is therefore an object of the present invention to provide an improved method and apparatus for the treatment of air. 
     Another object of the present invention is the provision for reducing microbial growth in an air conditioning system. 
     Yet another object of the present invention is the provision in an air conditioning system for the effective treatment of microbial growth without substantial investment. 
     Still another object of the present invention is the provision for an air conditioning system, which is capable of treating microbial growth, and which is economical to manufacture and effective in use. 
     These objects and other advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings. 
     SUMMARY OF THE INVENTION 
     Briefly, in accordance with one aspect of the invention, a photocatalytic agent is applied directly to the surface of the fins of the indoor heat exchanger of an air conditioning system, and the fins are irradiated with a UV light source having a wave length which is capable of activating the photocatalyst. The air passing through the evaporator then comes in contact with the photocatalyst and is purified by the activated photocatalyst. In this way, the photocatalyst process is used to simultaneously treat the surface of the heat exchanger and the air passing therethrough. 
     By another aspect of the invention, the UV light sources are so located that they irradiate both the evaporator coil and drain pan for purposes of directly attacking microbial growth, but also they simultaneously irradiate the coated surfaces of the evaporator coil fin surface such that the contaminated air passing therethrough is also treated. 
     By yet another aspect of the invention, the evaporator coil fin material is coated with a photocatalyst such as titanium dioxide, either in a pre-coating process wherein the fin is coated prior to being inserted into the heat exchanger structure or in a post-coat process wherein it is coated after it has been assembled into a heat exchanger device. 
     In the drawings as hereinafter described, a preferred embodiment is depicted. However, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a air conditioning system having the present invention incorporated therein; 
     FIG. 2 is a simplified perspective view of a fan coil with the present invention incorporated therein; and 
     FIG. 3 is schematic view of the coil portion of the present invention incorporated herein. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, the invention is shown generally at  10  as installed in an otherwise conventional air conditioning system having a compressor  11 , a condenser coil  12 , an expansion device  13 , and an evaporator coil  14 . 
     The evaporator coil  14  includes a plurality of parallel spaced fins  16  through which a plurality of tubes  17 , carrying refrigerant in liquid or vapor form, is circulated for purposes of exchanging heat with the air passing through the evaporator coil  14 . A fan  18  is provided to circulate the air through the evaporator coil. Similarly, a fan  19  is provided to circulate the outdoor air through the condenser coil  12  for heat exchange purposes. Although shown as blow-through fan they can also be of the drawn-through type. Also, it may be of any type such as a centrifugal blower. 
     Unlike a conventional evaporator coil, that of the present invention has fins  16  which are coated with a photocatalytic agent such as TiO 2  or the like which, when exposed to UV light will be activated to convert microbial contaminants that may reside on the surface of the fins  16 , as well as microbial contaminants that are in the air which passes through the evaporator coil  14 . 
     Disposed downstream of the evaporator coil  14  is a plurality of ultraviolet lamps  21 , powered by a power source  22 , and situated so as to illuminate not only the elements of the evaporator coil  14  and its condensate pan  15 , but also the surfaces of the individual fins  16  on which the photocatalyst has been coated. The wave length of the UV lamps is chosen so as to properly activate the photocatalyst such that it tends to purify the microbial growth both on the surfaces of the fins and within the condensate pan  15 , but also the microbial contaminants that are caused to flow through the evaporator coil  14  by way of the fan  18 . 
     In FIG. 2, there is shown a fan coil unit  23  with the present invention incorporated therein. Here, an evaporator coil  14 , with its tubes  17  and fins  16 , is disposed at an oblique angle in the lower portion of the fan coil unit  23 . The fins  16  are coated with a photocatalytic semi-conductor as previously described. A blower (not shown) is located in the upper portion of the fan coil  23  and acts to draw air up through the evaporator coil  14  to be cooled and purified. An ultraviolet lamp  21  is located downstream of the evaporator coil  14  and is aligned with its axis being substantially in parallel relationship with the tubes  17  as shown. In this way, the lamp  21  acts to irradiate the surfaces of the fins  16  which, in the presence of water vapor, tend to thereby form hydroxial radicals which, in turn, oxidizes the organic pollutants on the fins  16  and also those which are entrained in the air flowing through the coil  14 . 
     FIG. 3 shows an enlarged view of the coil  14  with its parallel fins  16  and refrigerant carrying tubes  17 . The particular coil  14  shown is a two row coil (i.e. with two rows of tubes across the thickness of the coil in the direction of the air flow. However, it should be recognized that any number of single row or multiple row coils can be used. As will be seen, the fins  16  are arranged in spaced parallel relationship in substantial parallel alignment with the air flow. The density of the fins are on the order of 8-20 fins per inch. The longitudinal profile of the individual fins is generally that of a sine wave as shown, the purpose being to promote air turbulence and increased air transfer characteristics of the coil  14 . However, this form is also considered to be useful in furtherance of the function of the present invention as will be described more fully below. 
     The fins  16  are coated with a photocatalytic semi-conductor coating on at least one side and preferably on both sides and on the entrance and exit edges thereof. The coating may be any of various types of metal oxides such as tin dioxide (SnO 2 ), titanium dioxide (TiO 2 ), zinc oxide (ZnO), tungsten trioxide (WO 3 ), lead oxide (PbO), iron titanium trioxide (FeTiO 3 ), vanadium pentoxide (V 2 O 5 ), iron oxide (Fe 2 O 3 ). Titanium dioxide is a preferred coating because: it has an optical absorption band close to visible light and therefore is readily activated by ultraviolet (UV) light with wave lengths less than about 400 nanometers; it is not readily poisoned by compounds in the air such as organic pollutants, it does not self-oxidize or evaporate; and it is inexpensive, stable, and environmentally sound. The coating can be applied to an otherwise finished evaporator coil but is preferably applied to the fin stock prior to its being assembled into the finished coil structure. 
     As will be seen, the UV lamp  21  is placed downstream of the coil  14  and is preferably aligned in parallel relationship with the tubes  14  so as to illuminate the individual fins  16  substantially equally. The lamp  21  is designed and optimized for operation within a 40-45° F., high humidity environment, and one in which there is a moving air stream. Typical output ratings at 45° F. and at a 400 FPM air flow are 120 microwatts per square centimeter at a one meter range. Although the invention is shown with a single lamp, multiple lamps may be used. In general, a single lamp is used for every 8-10 square feet of coil face area. 
     Because of the need for the coated fins to be irradiated by the UV light, it should be recognized that the wavy longitudinal pattern of the fins  16  lends itself to increased illumination characteristics because of the reflectivity that occurs on the variable geometry surfaces of the fins. That is, the effectiveness of the lamp  21  in its illumination of the coatings on the fins  16  is substantially enhanced over an installation wherein flat fins would be used. 
     The photocatalytic reaction is also enhanced by the wavy shape of the coated fins which produce turbulence in the contaminated air flowing through the coil maximizing fin contact by the airborne microbial particles. 
     Other features can also be used to make the light more effective in its irradiation of the coated surfaces. For example, the unit may be formed with a double wall, with sheet metal on the outside and fiberglass insulation on the inside. A second skin made of a reflective material, such as aluminum foil, can thereby be placed on the inner side of the insulation in order to reflect the light inwardly toward the fin surfaces of the coil. 
     Although the present invention has been shown and described with respect to a preferred embodiment, it will be understood by those skilled in the art that various changes in the form and detail thereof can be made without departing from the true spirit and scope of the invention. For example, although the invention is shown with the lamps located downstream of the coil, it should be understood that they could be placed in the upstream position as well.