Patent Abstract:
A filter unit heat exchanger is provided that may include a housing substantially surrounding a heat exchange assembly. Provided through the housing are one or more tortuous fluid flow paths used to direct airflow therethrough around portions of the heat exchange assembly for efficient operation. The tortuous path(s) may be provided by one or more nozzle openings on an input side of the housing and one or more diffuser openings on an output side of the housing, where the nozzle openings and diffuser openings are offset to cause desired airflow deflection. The filter unit may include desired symmetries to improve manufacturability and/or installation.

Full Description:
The application is a continuation-in-part of U.S. patent application Ser. No. 12/807,653, filed Sep. 10, 2010, the entirety of which is incorporated by reference herein. 
     This application is also related to U.S. Pat. No. 5,456,244, titled “Combination Cook Stove Fluid Heater and Grease Filter,” U.S. Pat. No. 5,687,707, titled “Combination Cook Stove Heat Exchanger and Filter,” and U.S. Pat. No. 6,543,526, titled “Combination Cook Stove Heat Exchanger, Filter, and Recirculation Assembly,” the entire disclosures of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the present invention generally relate to air filters and, more particularly, to an improved grease trap air filter that is also used as a heat transfer device. 
     BACKGROUND OF THE INVENTION 
     Commercial or institutional kitchens generally include cook stoves, hot plates, deep fat fryers, and other cooking devices that produce heat energy and particulates, i.e. grease. The extreme heat and particulates must be exhausted to atmosphere usually through flue chimneys or similar venting devices for the safety and comfort of the kitchen workers. This process replaces the hot kitchen air with cooler, clean outside air. Although this circulation process is necessary to provide a constant source of clean air to the kitchen environment, it is inefficient and uneconomical, especially in colder climates where the cost to heat internal air and water is significant. 
     Another problem encountered in commercial kitchens is that the generated particulates must be filtered. The particulates, that most commonly includes grease can eventually cause malfunction of air ventilation systems, which may create fire hazards. Accordingly, air filters located in flume hoods positioned over cooking surfaces must be cleaned often, which is time-consuming and expensive. 
     Venting and filtering systems may employ heat exchangers to capture thermal energy from the hot gases. For example, some systems employ a heat exchanger positioned downstream of a grease filter. This configuration is unfavorable for many reasons. First, these designs may be inefficient as the heat exchanger is usually located a significant distance from the heat source, which means heat is lost before the hot air encounters the heat exchanger. That is, the thermal energy is lost through heat dissipation before the heat exchanger is reached. Second, the existing grease filters significantly impede air flow, especially when congested with grease, which reduces the efficiency of the air ventilation system as heat is absorbed by the filter before the hot air reaches the heat exchanger. Third, when the heat source is turned off, the grease quickly solidifies within existing filters, which usually include fins that capture and maintains the particulate matter. 
     Many existing kitchens fail to incorporate any kind of heat exchanger because of integration costs. Retrofitting existing kitchen equipment with heat exchanger systems may require an entirely new flue hood assembly and substantial piping and accessories. Thus, conversion is time-consuming and expensive. 
     While some improvements have been made to combine a filter and heat exchanger, such as disclosed in U.S. Pat. No. 5,456,244, there remains a need to provide a filter system of simplified construction and that provides more efficient heat transfer than existing devices. To address this long-felt need, one embodiment of the present invention is a system for filtering and heat capture that is efficient and that may be retrofitted into existing flue systems. 
     SUMMARY OF THE INVENTION 
     It is one aspect of some embodiments of the present invention to provide a system that simultaneously filters grease and airborne particulate matter from hot gas flumes and transfers heat from the hot gas to a circulating fluid. The heated circulating fluid then transfers heat to a heat transfer medium, water, or air. The system of one embodiment can be retrofitted into existing flue hood ventilation systems of varying designs and dimensions. 
     Embodiments of the present invention include systems and methods related to filter units having simplified construction, using less material and providing more complete heat transfer than prior devices. More specifically, a filter unit according to one embodiment of the present invention comprises a housing generally comprised of a base and cover that surrounds a heat exchanger. The housing includes at least one entrance opening on an upstream side of the heat exchanger. The housing includes at least one baffle on a downstream side of heat exchanger opposite the upstream side. At least one exit opening is also provided through the housing on the downstream side of the heat exchanger. The at least one baffle may be aligned with the at least one entrance opening. In operation, hot gas is drawn through the at least one entrance opening and across the heat exchanger. The baffles will then redirect the gas towards the heat exchanger before the gas can leave the cavity through the at least one exit opening. In this way, hot air exposure to the heat exchanger is maximized. 
     It is another aspect of some embodiments of the present invention to provide a heat exchanger that increases heat transfer efficiency. More specifically, the heat exchanger may employ a heat-conductive material at least partially coated with a reduced friction material, such as polytetrafluoroethylene. The reduced-friction material enhances fluid flow, thereby increasing the rate at which the hot gases encounter heat transfer elements of the heat exchanger. The reduced-friction material also allows any captured particulates to drip from the heat transfer elements into a catch pan, instead of clinging to it. 
     Heat transfer is also increased by some embodiments of the present invention that employ an equal number of heat transfer fluid conduits, which may have equal surface area. Other embodiments of the present invention employ heat transfer fluid conduits that have heat exchange fins. The fins may surround one conduit or multiple conduits. The finned conduits are positioned in the fluid flow cavity provided by the housing, and increase thermal conductivity because the fins increase surface area of the heat exchanger fluid conduits. Other embodiments the present invention employ heat exchanger fluid conduits having dimples, turbulators, or other surface irregularities that help dissipate heat. 
     These and other advantages will be apparent from the disclosure of the invention(s) contained herein. The above-described embodiments, objectives, and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible using, alone or in combination, one or more of the features set forth above or described below. Further, the Summary of the Invention is neither intended nor should it be construed as being representative of the full extent and scope of the present invention. Moreover, references made herein to “the present invention” or aspects thereof should be understood to mean certain embodiments of the present invention and should not necessarily be construed as limiting all embodiments to a particular description. The present invention is set forth in various levels of detail in the Summary of the Invention as well as in the attached drawings and the Detailed Description of the invention and no limitation as to the scope of the present invention is intended by either the inclusion or non-inclusion of elements, components, etc. in this Summary of the Invention. Additional aspects of the present invention will become more readily apparent from the Detail Description, particularly when taken together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description of the invention given above and the detailed description of the drawings given below, serve to explain the principles of these inventions. 
         FIG. 1  is a perspective view of a filter unit according to one embodiment of the present invention; 
         FIG. 2  is an exploded view of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of  FIG. 2  showing a heat exchanger employed by the embodiment of  FIG. 1 ; 
         FIG. 5  is a perspective view of a base portion of a filter housing employed by the embodiment of  FIG. 1 ; 
         FIG. 6  is a perspective view of a cover portion of a filter housing employed by the embodiment of  FIG. 1 ; 
         FIG. 7  is a partial cutaway view of a venting and filtering system of one embodiment of the present invention; 
         FIG. 8  is a schematic of another embodiment of a venting and filtering system; 
         FIG. 9  is a partial cutaway view of another embodiment of a closed venting and filtering system; 
         FIG. 10  is a front perspective view of a filter unit according to another embodiment of the present invention; 
         FIG. 11  is a rear perspective view of  FIG. 10 ; 
         FIG. 12  is a exploded view of  FIG. 10 ; and 
         FIG. 13  is a cross-sectional view of  FIG. 10 . 
     
    
    
     To assist in the understanding of one embodiment of the present invention the following list of components and associated numbering found in the drawings is provided herein: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 # 
                 Component 
               
               
                   
                   
               
             
             
               
                   
                 100 
                 Filter unit 
               
               
                   
                 110 
                 Housing 
               
               
                   
                 112 
                 Base 
               
               
                   
                 114 
                 Cover 
               
               
                   
                 118 
                 Base wall 
               
               
                   
                 120 
                 Lateral sidewall 
               
               
                   
                 122 
                 Gap 
               
               
                   
                 123 
                 Base cavity 
               
               
                   
                 124 
                 Opening 
               
               
                   
                 124a 
                 Upstream side 
               
               
                   
                 124b 
                 Downstream side 
               
               
                   
                 126 
                 Fin 
               
               
                   
                 127 
                 Fin plate 
               
               
                   
                 128 
                 Retainer or tab 
               
               
                   
                 130 
                 Handle 
               
               
                   
                 132 
                 Handle bracket 
               
               
                   
                 133 
                 Drain hole 
               
               
                   
                 134 
                 Plate 
               
               
                   
                 136 
                 Lateral side member 
               
               
                   
                 138 
                 Baffle 
               
               
                   
                 140 
                 Opening 
               
               
                   
                 150 
                 Airflow path 
               
               
                   
                 170 
                 Heat exchanger 
               
               
                   
                 172 
                 Header pipe 
               
               
                   
                 174 
                 Fluid flow conduit 
               
               
                   
                 176 
                 Fluid flow chamber 
               
               
                   
                 178 
                 Fluid port 
               
               
                   
                 179 
                 Threads 
               
               
                   
                 180 
                 Vibration pad 
               
               
                   
                 200 
                 Exhaust housing 
               
               
                   
                 202 
                 Cooking surface 
               
               
                   
                 203 
                 Grease trap 
               
               
                   
                 204 
                 Angle 
               
               
                   
                 205 
                 Coupler 
               
               
                   
                 210 
                 Supply tank 
               
               
                   
                 212 
                 Conduit 
               
               
                   
                 214 
                 Storage tank 
               
               
                   
                 216 
                 Water heating tank 
               
               
                   
                 218 
                 Pump 
               
               
                   
                 220 
                 Check valve 
               
               
                   
                 222 
                 Shut-off valve 
               
               
                   
                 310 
                 Pump 
               
               
                   
                 312 
                 Radiator 
               
               
                   
                 314 
                 Heat exchanger 
               
               
                   
                 316 
                 Roof 
               
               
                   
                 318 
                 Heat exchanger 
               
               
                   
                 320 
                 Walkway 
               
               
                   
                 400 
                 Filter unit 
               
               
                   
                 401 
                 Fin 
               
               
                   
                 403 
                 Fastener 
               
               
                   
                 404 
                 Flange 
               
               
                   
                 405 
                 Hose 
               
               
                   
                 407 
                 Pressure relief valve 
               
               
                   
                 408 
                 Heat exchanger fin 
               
               
                   
                 412 
                 Base 
               
               
                   
                 414 
                 Cover 
               
               
                   
                 418 
                 Base wall 
               
               
                   
                 420 
                 Lateral side member 
               
               
                   
                 423 
                 Cavity 
               
               
                   
                 424 
                 Opening 
               
               
                   
                 424 
                 Entrance opening 
               
               
                   
                 426 
                 Fin 
               
               
                   
                 433 
                 Drain hole 
               
               
                   
                 438 
                 Baffle 
               
               
                   
                 440 
                 Opening 
               
               
                   
                 441 
                 Fin 
               
               
                   
                 450 
                 Fluid flow path 
               
               
                   
                 470 
                 Heat exchanger 
               
               
                   
                 474 
                 Fluid flow conduit 
               
               
                   
                   
               
             
          
         
       
     
     It should be understood that the drawings are not necessarily to scale. In certain instances, details that are not necessary for an understanding of the invention or that render other details difficult to perceive may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION 
       FIGS. 1-3  and  5  depict a filter unit  100  according to one embodiment of the present invention that comprises a housing  110  and a heat exchanger  170 . The housing  110 , which may be comprised of one or more components, generally surrounds the heat exchanger  170 . For example, the housing  110  may comprise a base  112  and a cover  114 . The base  112  includes a base wall  118  and a plurality of lateral sidewalls  120 . The base  112  may be stamped or otherwise formed of a planar sheet material, such as a stainless steel sheet of a desired thickness. Once stamped, the lateral sidewalls  120  may be bent towards each other, thus forming a cavity  123 . Alternatively, the sidewalls  120  may be coupled to the base wall  118 , such as by welding. There may be a gap  122  (see  FIG. 5 ) between adjacent sidewalls  120 , or the gap  122  may be closed with a sealant or weld. Alternatively, the plurality of sidewalls  120  may be formed as a unitary member, such as in a ring formation, and coupled to a base wall  118 . Various shapes of the base, wall  118  are contemplated, although a generally planar, rectilinear shape is shown, which will facilitate manufacture and installation. In addition, such shape is easily adaptable to be utilized with filter assembly units or exhaust hoods that are presently provided in commercial cooking settings. Furthermore, it is the shape of the filter unit  100  may be at least laterally symmetrical, such that the unit may be inserted into a hood or exhaust assembly in a plurality of orientations, to provide ease of connectivity. Indeed, the filter unit may be rotationally symmetrical in at least one plane. 
     The base wall  118  is of one embodiment is perforate, including one or more air portals  124  that allow air to pass into the base cavity  123 . The openings  124  may be associated with fins  126  adapted to decrease the opening  124  size towards the cavity  113 . A pair of fins  126  may be provided for each opening  124 , wherein each fin  126  extends into the cavity  123 . This configuration acts as a nozzle, wherein each opening is wider at its upstream side  124   a  and narrower at its downstream side  124   b . The fins  126  may be formed from the same material as the base wall  118 , and may be stamped and formed from the same piece of material as the base wall  118 , and then bent into the cavity  123 . Alternatively, the fins  126  may be provided as separate components that are stationarily coupled with respect to the base wall  118 . If provided as separate components, two fins  126  may be provided as coupled together, perhaps as a unitary member including a fin plate  127  disposed between the two fins  126 . The fin plate  127  may include a substantially planar surface extending along a length, proximate end portions of which are secured to the base wall  118 . The nozzling function provided by the arranged fins  126  focuses the airflow towards a baffle  138  included on the cover  114  or disposed on the opposite side of the heat exchanger  170  from the fins  126 . This configuration therefore assists in the collection of grease particles. In addition, the airflow path creates turbulence that increases exposure time of the air with the heat exchanger  170 . Accordingly, one embodiment of the present invention allows no direct airflow path through the filter assembly  110 , or a majority of the airflow therethrough is not direct. Indeed, as shown in  FIG. 3 , the fins and baffles reverse airflow to a path oriented about 45-180° from the direction of flow at the upstream side of the filter unit. One or more tortuous airflow paths  150  are created, thereby creating turbulent flow that exposes the heat exchanger  170  to heated air for a sufficient amount of time to allow for adequate heat exchange to a fluid flowing through the heat exchanger  170 . 
     One or more retainer tabs  128  are formed on at least one of the lateral side members  120  of the base  112 . The retainer tabs  128  may be on two opposing lateral side members  120 . A retainer tab  128  is extruded from the lateral side number  120  so as to provide a resiliently deflectable retaining member. Also provided on the base  112  is at least one handle  130 , which may be formed in a variety of ways. The handles  130  are provided in opposing positions on the filter unit  100  to allow for balanced insertion and removal of the filter unit  100  from an exhaust system. The handles  130  are full or partially wire loop handles that are suspended from handle brackets  132  that may be formed integrally with or coupled to the base wall  118 . 
     The filter unit  100  according to some embodiments of the present invention serves as an air filter that assists in the collection of grease particles, which is especially advantageous to be used over commercial cooking surfaces. To aid in the drainage of collective grease particles, the base  112  may be provided with one or more drain holes  133 . A plurality of drain holes  133  may be employed which may be formed along the juncture of one or more lateral side members  120  and the base wall  118 . 
     Referring now to  FIGS. 2 ,  3 , and  6 , the cover  114  comprises a plate  134 , and may further include one or more lateral side members  136  extending from the plate  134 . The side members  136  are inserted between header pipes  172  of the heat exchanger  170 . Furthermore, the side members  136  may be formed with one or more heat exchanger interfaces which may contact and/or surround a portion of the heat exchanger  170  to maintain position during and after installation. The cover  114  may be formed as a symmetrical shape that may be inserted into the base  112  in a plurality of orientations. 
     One or more baffles  138  are formed integrally with or coupled to the plate  134 . The baffles  138  are disposed opposite the entrance openings  126  formed in the base  112 . The cover  114  also includes at least one opening  140  similar to that provided by the base. The baffles  138  act as a one or more diffusers, such that upstream side  140   a  of the openings  140  disposed between the baffles  138  is smaller than the downstream side  140   b . The baffles  138  may be formed similar or identical to the unitary fin members, discussed above. A flow construction created by the baffles  138  restrict and redirect flow laterally to create the tortuous airflow path  150  that aids in the collection of grease and maximizes heat transfer to the heat exchanger  170 . 
     The filter base  112  and cover  114  are formed of stainless steel, though other materials are contemplated, such as aluminum, copper, steel, and other materials adapted to transfer heat. A plastic housing could also be used. However, plastic has demonstrated affections for grease, which may be caused by its insulative properties, and therefore it may require more frequent cleaning. 
     The heat exchanger  170  is formed from two header pipes  172 , which may be provided in a parallel arrangement, and a plurality of fluid flow conduits  174 , which also may be provided in a parallel arrangement, extending between the two header pipes  172 . The heat exchanger  170  is sized to be positioned substantially within the cavity  123 . A fluid flow chamber  176  is provided within the header pipes  172  and conduits  174 . A fluid may be a potable fluid, such as water, or propylene glycol. While the heat exchanger  170  could be formed asymmetrically, it is at least rotationally symmetrical in at least one plane, such that it may be inserted into the cavity  123  in a plurality of orientations. In one embodiment, each header  172  is provided with a fluid port  178  in fluid communication with the fluid flow chamber  176 . The ports  178  may be provided with threads  179  or other coupling mechanisms, such as a fluid quick connect coupling that interfaces to a fluid supply or drain. In one embodiment of the present invention, the ports  178  are provided on opposite ends of their respective header  172 . Vibration pads  180  may be provided on one or more components of the filter unit  100 . A plurality of pads  180  may be adhered to each header pipe  172  in the heat exchanger  170 . The vibration pads  180  cooperate with the base wall  118  to prevent a rattling of two or more components. 
     A material for one or more components of the heat exchanger is copper, which may be coated with a non-stick material, such as a paint including polytetrafluoroethylene, available as a Teflon® material, available from E.I. du Pont de Nemours and Company of Wilmington, Del. The non-stick material may be painted onto the desired heat exchanger components. Another acceptable material for the heat exchanger headers  172  and conduits  174  is steel tube, which may also be painted with a non-stick material. 
     Generally, systems and methods according to some embodiments of the present invention collects heat generated by a cooking surface, which would otherwise be wasted as exhaust, and transfer such heat to other locations for use in an open or closed circulation system. As shown in  FIG. 7 , one or more filter units  100  may be installed in an exhaust housing  200  above a cooking surface  202 . While the filter  100  could be installed at any desirable angle, such as horizontal, some embodiments include a filter  100  installed at an angle  204  relative to horizontal level. The angle  204  may be between about 12 degrees to about 45 degrees to allow collected particles to drain. In this configuration, the longitudinal dimension of the fins and baffles are disposed at approximately the same angle. Thus, collected particles will drain from the drain holes and into one or more grease traps  203 . As further shown in  FIG. 7 , a plurality of filter units  100  may be coupled together to form an expanded filter unit. The units  100  may be coupled in series, as shown, or in parallel. If coupled in series, a coupler  205  may be connected at one end to a port  178  of one filter unit  100 A and at the other end to a supply port  178  of a subsequent filter unit  100 B. 
       FIG. 7  depicts an open system. Here, the heated fluid flowing through the heat exchangers is removed and put to some other use, such as dishwashing, or it is stored for future use. Water or other desirable fluid may be provided by gravity feed, such as from an elevated supply tank  210  or municipal water supply, or it may be pumped to the system. Conduit  212  and standard connections may couple the water supply to a first filter unit  100 A. The fluid flows through one or more filter units  100 , and then drain into a storage tank  214  for future use, such as by a dishwasher, hot water supply in a restroom, or for other purposes. 
     Another example of an open system is shown in  FIG. 8 . Here, in addition to the storage tank  214 , this system includes a water heating tank  216  and a recirculating pump  218 . The associated plumbing includes various check valves  220  and shut-off valves  222 . One advantage to this enhanced system is that if fluid usage exceeds the supply of heated fluid, fluid stored in the storage tank  214  may be recirculated to keep the water in the plumbing system warm. The recirculating pump  218  may be selectively activated and deactivated with a timer or as a function of a measured temperature of the fluid in the storage tank  214 . 
       FIG. 9  shows a closed system, that uses heat from the exhaust gases elsewhere. In this system, water or other fluid is introduced and substantially all of any residual air is purged. The fluid may be pumped through the system by an inline pump  310 , through conduit  212  and through one or more filter units  100 . After traveling through the one or more filter units  100 , in which the fluid is heated by exhaust from the cooking surface  202 , the fluid travels through one or more additional heat exchangers. For instance, the fluid may be pumped to a radiator  312  to heat a room. Additionally or alternatively, the fluid may be pumped through a roof heat exchanger  314  disposed along the edge of the roof  316  of the building to prevent ice damming. The fluid may be pumped through a sidewalk heat exchanger  318  disposed beneath or embedded in a concrete or other external walkway  320  to reduce the buildup of ice thereon. It is to be appreciated that the function of a system according to some embodiments of the present invention may be changed depending upon the time of year. For instance, in summer months, it may not be desirable to use a closed system for heating as described above. In such situations, the fluid may remain static and the filter units  100  may be used to collect particulates from the exhaust air. Alternatively, the closed system could be changed to an open system in the summer months, thereby providing hot water for use. Those of skill in the art will appreciate that the heat energy can be converted to electrical or mechanical energy using common methods. 
       FIGS. 10-13  show a filter unit  400  of another embodiment of the present invention. Similar to the embodiments described above, filter unit  400  includes a base  412  interconnected to a cover  414 . The cover  414  and a base wall  418  of the base  412  define a cavity  423  that surrounds the heat exchanger  470  that receives the airflow  450 . As in the embodiments described above, the base  412  includes a plurality of fins  426  that direct airflow into the cavity  423 . Here, however, the openings  424  are bounded by the fins  426  and a fin  401  that is generally parallel to the base wall  418 . The fin  401  directs gas towards the angled fins  426  and define a circuitous flow path  450 , which is described in further detail below. 
     Similarly, the cover  414  includes a plurality of baffles  438  that are angled into the cavity  423 . Again, the baffles  438  define an exit opening  440 . A fin  441  is positioned between adjacent baffles  438  and helps shield the fluid conduits  474  of the heat exchangers  470 . Accordingly, a fluid flow path  450  is provided that redirects or at least partially reverses fluid flow. As gas enters the entrance opening  424 , it is directed by the fin  401  and the fins  426  into contact with a baffle  438 . These features redirect fluid flow between about 45-180° from its original path, which increases contact with fluid conduits  474 . The base wall  418  and fin  426  of an adjacent entrance opening  424  will then direct the redirected airflow so it will exit the space between the baffle  438  and the fin  441 . In this fashion, the hot air exposure to the fluid conduits  474  is dramatically increased without unduly slowing fluid flow. 
     As shown in  FIG. 12 , the fluid flow conduits  474  may include a plurality of heat exchanger fins  408 . The fins  408  may extend the entire length of the fluid flow conduits  474  or portion thereof. Further, the fins may encapsulate one or more fluid flow conduits  474 . Some of the fluid flow conduits  474  do not include exchanger fins  408 . The exchanger fins  408  increase the amount of surface area that contact the hot gas. 
       FIG. 12  also shows that the cover for 12 may be interconnected to the base for 12 by way of a plurality of fasteners  403  in incorporated onto a flange  404 . 
       FIG. 11  also shows a pressure relief valve that opens when high-pressure is encountered within the system which is a safety feature. 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Technology Classification (CPC): 5