Abstract:
A photocatalytic air purifier is disclosed. The photocatalytic purifier includes filter structures coated with a catalytic material such as titanium dioxide. One or more UV lamps are interposed between the filter structures. The catalytic layer reacts with airborne VOCs and bioaerosols when activated by the UV lamps to thereby oxidize the VOCs and destroy the bioaerosols. The photocatalytic air purifier does not need to be replaced or regenerated after a period of continuous usage. The photocatalytic purifier of the present invention substantially eliminates odors, VOCs, and bioaerosols from air directed through the fan coil. The photocatalytic air purifier includes a control system that optimizes operating costs. Because of these features, service, maintenance, and filter replacement are reduced to a minimum. At the same time, the well being of persons living in the space conditioned by the photocatalytic air purifier is improved.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional application of U.S. patent application Ser. No. 10/700,749, filed Nov. 4, 2003, now U.S. Pat. No. 7,758,821, the entirety of which is incorporated herein by reference, which is a divisional application of U.S. patent application Ser. No. 09/916,876, filed Jul. 30, 2001, now U.S. Pat. No. 6,884,399, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to air purifiers, and particularly to photocatalytic purifiers. 
     TECHNICAL BACKGROUND 
     Most fan coil units consist of a water coil or a direct expansion coil, a fan, and ductwork to distribute conditioned air. Before heating or cooling, air is directed through a filter of some sort. There are various types of filters. One type of filter is referred to as a media filter. This type of filter retains dust and other particulate matter. After prolonged usage, media filters become clogged and need to be replaced. 
     Another type of filter currently being used is known as a HEPA filter. HEPA is an acronym for “high efficiency particulate air.” HEPA filters can capture 99.9% of all particles, including sub-micron sized particles. These filters are useful in mitigating the effects of bioaerosols and dust. They are currently being used in hospitals, manufacturing clean rooms, and in other applications where clean air is considered vital. Typically, HEPA filters have an operational life span of twenty-four (24) months. After that, efficiency decreases markedly, and HEPA filters must be replaced. 
     Another type of filter currently being used are activated carbon adsorption filters. These filters were developed in response to industrial emissions of volatile organic compounds (VOCs). In an activated carbon adsorption system, contaminated air is directed across a bed of carbon. The carbon extracts the VOCs from the air and adsorbs the VOCs by holding them to its surface. One problem with activated carbon adsorption filters is that the air stream being filtered cannot have a high moisture content because carbon adsorbs moisture. Air having a high moisture content will quickly fill the carbon bed to capacity. Second, the air being filtered cannot include a large amount of particulate matter. The particulate matter will also clog the carbon bed. Thus, the activated carbon adsorption filter may require a pre-filter to reduce the particulate content and a dehumidifier to reduce moisture content to be effective. 
     An air filter is needed that substantially eliminates odors, VOCs, and bioaerosols from an air mass without requiring extensive service or maintenance. A need exists for a photocatalytic air purifier that can be conveniently installed and removed for maintenance purposes. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a photocatalytic air purifier that can be conveniently installed and removed for maintenance purposes. The photocatalytic purifier of the present invention substantially eliminates odors, VOCs, and bioaerosols from air that is directed through a duct or a fan coil. The photocatalytic air purifier of the present invention is suitable for both commercial and residential applications and can be installed in either original equipment or retrofitted into existing installations. 
     One aspect of the present invention is a modular photocatalytic air purifier. The photocatalytic purifier including a modular enclosure having a retractable alignment mechanism. The retractable alignment mechanism is configured to move the modular enclosure between an in-use position aligned within the fan coil unit and a retracted position. A plurality of support structures are disposed within the modular enclosure, each of the plurality of support structures having a catalytic layer disposed thereon. At least one UV lamp is interposed between the plurality of support structures. 
     In another aspect, the present invention includes a fan coil unit having an air return, a coil unit, a fan, and an air supply. The fan coil unit includes at least one photocatalytic purifier disposed adjacent the coil unit. The at least one photocatalytic purifier includes a modular enclosure having a retractable alignment mechanism. The retractable alignment mechanism is configured to move between an in-use position aligned within the fan coil unit and a retracted position. A plurality of support structures are disposed within the modular enclosure, each of the plurality of support structures having a catalytic layer disposed thereon, and at least one UV lamp interposed between the plurality of support structures. A control unit may be coupled to the at least one photocatalytic purifier, whereby the control unit energizes the at least one UV lamp in accordance with a fan coil operating mode. 
     In yet another aspect, the present invention includes a method for filtering air in a unit having an air return, and an air supply. The method includes providing at least one modular photocatalytic purifier. The at least one photocatalytic purifier includes a modular enclosure having a retractable alignment mechanism, and at least one UV lamp interposed between a plurality of titanium dioxide coated filter structures. The retractable alignment mechanism is used to dispose the at least one modular photocatalytic purifier in an in-use position within the unit. Air is directed from the air return into the at least one photocatalytic purifier. Contaminants borne by the air are brought into contact with the titanium dioxide coated filter structures. UV radiation is directed from the at least one UV lamp onto the titanium dioxide coated filter structures, whereby the titanium dioxide coated filter structures are activated to react with the contaminants to produce carbon dioxide and water. 
     Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a photocatalytic purifier in accordance with the present invention; 
         FIG. 2  is a cross-sectional view of the photocatalytic purifier taken through line A-A in  FIG. 1 ; 
         FIG. 3  is a detail view of the honey-combed filter element depicted in  FIG. 2 ; 
         FIG. 4  is a diagrammatic depiction of a fan coil unit in accordance with a first embodiment of the invention showing the photocatalytic purifier depicted in  FIGS. 1-3  in an in-use position; 
         FIG. 5  is a diagrammatic depiction of a fan coil unit in accordance with the first embodiment of the invention showing the photocatalytic purifier depicted in  FIGS. 1-3  in a retracted position; and 
         FIG. 6  is a diagrammatic depiction of a fan coil unit in accordance with a second embodiment of the invention showing the photocatalytic purifier depicted in  FIGS. 1-3  in a retracted position. 
         FIG. 7  is a plan view of a photocatalytic purifier in accordance with one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the photocatalytic purifier of the present invention is shown in  FIG. 1 , and is designated generally throughout by reference numeral  10 . 
     In accordance with the invention, the present invention includes a photocatalytic air purifier for use in a fan coil unit or a duct. The purifier features a modular enclosure having a retractable alignment mechanism. The retractable alignment mechanism is configured to move the enclosure between an in-use position aligned within the fan coil unit and a retracted position. The photocatalytic purifier includes a first honey-combed filter structure having a catalytic layer disposed thereon. A second honey-combed filter structure is disposed adjacent to the first honey-combed filter structure, the second honey-combed filter structure also having the catalytic layer disposed thereon. At least one UV lamp is disposed between the first honey-combed filter structure and the second honey-combed filter structure. The catalytic layer reacts with airborne VOCs and bioaerosols when activated by UV light to thereby oxidize the VOCs and destroy the bioaerosols. 
     Thus, the photocatalytic purifier of the present invention substantially eliminates odors, VOCs, and bioaerosols from air directed through a fan coil while reducing service and maintenance to a minimum. Further, the photocatalytic air purifier is conveniently installed and removed for maintenance purposes. 
     As embodied herein and depicted in  FIG. 1 , a plan view of a photocatalytic purifier in accordance with the present invention is disclosed. Photocatalytic purifier  10  is disposed in fan coil housing  102 , between media filter  50  and fan coil unit  30 . One of ordinary skill in the art will recognize that this embodiment of the present invention can also be employed in a duct system instead of a fan coil unit. Photocatalytic purifier  10  includes at least one filter layer  12  having at least one UV lamp  20  disposed between honey-combed filter element  14  and honey combed filter element  16 . In the embodiment depicted in  FIG. 1 , a second photocatalytic purifier layer  12 ′ is formed by disposing UV lamps  22  between filter element  16  and filter element  18 . Each additional filter layer  12  increases the efficiency of filter  10 . Thus, photocatalytic purifier  10  may include a plurality of filter layers  12  that include at least one UV lamp  20  disposed between honey-combed filter elements  14  and  16 . 
       FIG. 2  is a cross-sectional view of filter  10  taken through line A-A in  FIG. 1 . The cross-sectional view clearly shows the honey-combed structure of filter element  12 . Any suitable structure may be employed, however, the honey-combed structure of filter elements  12 ,  14 , and  16  is preferred because air pressure is maintained as air is directed through filter  10 . Filter elements  12 ,  14 , and  16  include catalytic coating  120  disposed thereon. As depicted in  FIG. 2 , UV lamps  20  are positioned to direct UV radiation into the interior of honey-combed filter elements  12  and  14 . As shown in  FIG. 2 , the cross-section of photocatalytic purifier  10  is equal to the cross-section of fan coil housing  102 . Thus, purifier  10  purifies the entire volume of air passing through the fan coil. 
       FIG. 3  is a detail view of honey-combed filter element  12 , showing catalytic coating  120  and substrate  122 . One of ordinary skill in the art will recognize that any suitable catalytic coating  120  may be disposed on elements  12 ,  14 , or  16 , but there is shown by way of example a coating of titanium dioxide. One of ordinary skill in the art will also recognize that any suitable material may be used as a substrate material for filter elements  12 ,  14 , and  16 , but there is shown by way of example a ceramic substrate. In other embodiments, an aluminum substrate or an FeCrAlY alloy substrate are used. Both the ceramic and aluminum substrates are desirable in applications requiring non-flammable filter elements. If non-flammability is not an issue, substrate  122  used in filter elements  12 ,  14 , and  16  could be fabricated using a paper material. One of ordinary skill in the art will also recognize that any suitable substrate geometry may be used. The geometry can include honey-combs, fins, mesh, a filter-type structure, a fibrous type, or a filamentous structure. 
     Photocatalytic purifier  10  employs photocatalytic oxidation technology to substantially eliminate odors, VOCs, and bioaerosols. Air propagating through purifier  10  passes over catalytic layer  120 . In gas-solid photocatalytic oxidation (PCO), a VOC laden air stream is brought into contact with a titania catalyst disposed on layer  120 . The UV light activates the catalyst. The VOCs react with the activated catalyst and are converted into carbon dioxide and water via oxidation. This process occurs at room temperature. Since the process occurs at room temperature, the operating cost is much lower than conventional high temperature thermal oxidizers. PCO destroys a wide range of contaminants in air streams. Filter elements  14 ,  16 , and  18  are not degraded over time by UV light and thus, they do not need to be replaced even after continuous prolonged usage. It should also be mentioned that bioaerosols are also destroyed by their exposure to UV light. 
     As embodied herein, and depicted in  FIG. 4 , fan coil unit  100  includes housing  102  which is connected to suspension casing  104 . Suspension casing  104  is attached to a ceiling or some other structural element of the building accommodating fan coil unit  100 . Fan coil unit  100  includes photocatalytic purifier  10  which is disposed in housing  102  between media filter  50  and fan coil  30 . Fan coil  30  includes cold water supply  34  and hot water supply  36 . Both cold water supply  34  and hot water supply  36  include valves (not shown) that are controlled by fan coil controller  110  to thereby regulate heating and cooling within the conditioned space. Fan coil unit  100  also includes fan  32  which draws an air stream from air return  42  through photocatalytic purifier  10  and fan coil  30 . The air stream is then directed into the conditioned space via air supply duct  40 . In  FIG. 4 , photocatalytic purifier  10  is shown in the in-use position, being disposed adjacent to filter  50 . Photocatalytic purifier  10  includes modular enclosure  60  having a retractable alignment mechanism  62 . Retractable alignment mechanism  62  is configured to move enclosure  60  between an in-use position aligned within the fan coil unit, and a retracted position. In this embodiment, alignment mechanism  62  is a hinged door structure. Mechanism  62  includes arm  64  that is used to hold enclosure  60  in the in-use position. The retracted position is depicted in  FIG. 5 . 
     An alternative embodiment is a sliding arrangement wherein the photocatalytic purifier  10  can be made to slide from its installed position to a retracted position as shown by the dashed lines in  FIG. 4 . 
     It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to fan coil control  110  of the present invention depending on cost requirements and the complexity of the application. For example, fan coil unit  100  can be deployed as a stand-alone unit in a single family dwelling, or as one unit among many in a complex architecture. For example, fan coil unit  100  may be employed in a multi-storied structure having a plurality of air-conditioned zones. Fan coil control  110  includes firmware containing the control program necessary to control the water valves, fan  32 , and UV lamps  20 ,  22 , and  24  included in photocatalytic purifier  10 . The control program is executed by an embedded microprocessor included in fan coil control  110 . In another embodiment, fan coil control  110  is implemented using a logic controller. 
     Fan coil control  110  includes several operational modes  80  that are selected by a switch  81 . The first mode is an “unoccupied mode.” In this mode, the level of comfort provided by fan coil unit  100  does not have to be at an optimum level because no one is in the conditioned space as determined by the sensor  82 . The heating and cooling of the air conditioned zone is regulated in accordance with a wider “dead-band.” Thus, controller  110  allows the ambient air temperature of the air conditioned zone to vary within a wide range temperatures before providing either heating or cooling. The UV lamps are generally inoperative during this mode but may be on for some lead/lay time before or after occupancy. 
     The second mode is referred to as the “occupied mode.” In this mode, the level of comfort provided by fan coil unit  100  is optimized because of the presence of people in the conditioned space. Thus, the UV lamps are always operating in this mode. The occupied mode includes a “demand” sub-mode wherein fan  32  is operating at a higher speed, and a “satisfied” sub-mode wherein fan  32  is operative at a lower speed. In other embodiments, controller  110  uses a “tolerance index” as a control metric. Controller  110  may include a motion detector input to determine whether the conditioned space is occupied. 
     A third mode is provided by controller  110 . It is known as the “frost protection mode.” The frost protection mode initiates heating within a conditioned space only to maintain a minimum air temperature within the air conditioned space. Since the air conditioned space is assumed to be unoccupied, the UV lamps are not operative in this mode. In addition to temperature sensors  86 , controller  110  may include a sensor  87  input coupled to window contacts, enabling it to recognize an open window condition. In another embodiment, the frost protection mode initiates heating during the open window condition. An indoor air quality (IAQ) sensor  88  provides feedback to the fan coil control  110  as to the quality of air in the particular zone being conditioned. 
     As embodied herein and depicted in  FIG. 5 , a diagrammatic depiction of fan coil unit  100  showing photocatalytic purifier  10  in a retracted position is disclosed. In the retracted position, hinged door structure  62  retracts to provide access to purifier  10  during maintenance or the removal of purifier  10 . Arm  64  is detached from purifier  10  during removal. 
     As embodied herein and depicted in  FIG. 6 , a diagrammatic depiction of photocatalytic purifier unit  100  in accordance with a second embodiment of the invention is disclosed. In this embodiment, unit  100  is disposed in media cabinet  70 . The enclosure  60  of photocatalytic purifier  10  is shown in a retracted position. Enclosure  60  is equipped with slider mechanism  72  on a top portion of enclosure  60 , and is equipped with slider mechanism  74  on a bottom portion of enclosure  60 . One of ordinary skill in the art will recognize that unit  100  can be a fan coil unit or part of a duct system. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.