Abstract:
Various embodiments of fuel-fired low NOx water heaters are provided with burners having built-in venturi inlet sections for receiving fuel from a source thereof and combustion air from outside of the water heater. The burners are integrated in various manners with flammable vapor ignition resistance (FVIR) platforms to thereby reduce the tooling costs necessary to provide the water heaters with both lowered NOx emissions and flammable vapor ignition resistance.

Description:
BACKGROUND OF THE INVENTION 
   The present invention generally relates to fuel-fired heating appliances and, in representatively illustrated embodiments thereof, more particularly provides specially designed fuel-fired water heaters with low NOx burners having integral venturi fuel/air inlet structures therein, and being integrated with flammable vapor ignition resistance (FVIR) platforms. 
   Residential gas-fired water heaters are required to meet reduced NOx emission standards effective in 2005 for certain Air Quality Management Districts (AQMD&#39;s) of California and Texas. Recently, various gas-fired water heaters have been redesigned to provide them with flammable vapor ignition resistance (FVIR) in accordance with the Z21 ANSI standards. Significant tooling investment has been made to create new water heater platforms, complete with flame arrestors, damper plate assemblies with combustion air shutoff devices, and perforated jacket assemblies to channel and filter air. 
   It would be desirable to incorporate in these FVIR-redesigned water heaters low NOx fuel burners, which would provide the water heaters with the required lowered NOx emission rates, in a manner which would reduce or eliminate the need for platform redesigns. It is to this goal that the present invention is primarily directed. 
   SUMMARY OF THE INVENTION 
   In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a fuel-fired heating appliance, representatively but not by way of limitation a gas-fired water heater, is provided with a low NOx fuel burner which is integrated with a flammable vapor ignition resistance (FVIR) platform. In illustrated embodiments thereof, the water heater comprises a combustion chamber separated from a plenum area by a wall structure, an inlet space for receiving combustion air from outside the water heater, and a fuel burner. 
   The fuel burner has a hollow body with an outlet portion thereof projecting from the wall structure into the combustion chamber, and an inlet portion projecting from the wall structure into the plenum area. The inlet portion of the fuel burner has a venturi inlet structure associated therewith and operative to flow combustion air from the inlet space into the inlet portion of the burner body. To lower the NOx emissions of the burner, preferably all of the primary combustion air delivered to the burner comes from outside of the water heater and is illustratively flowed to the venturi inlet structure via the plenum area. 
   Illustratively, the fuel burner is a radiant burner having a perforate flame-holding wall section, which may be of a metal mesh construction, which is disposed on the outlet portion of the burner body. This perforate wall section provides the water heater with flammable vapor ignition resistance, the flame-holding wall section serving to preclude flame outflow from the combustion chamber. This flammable vapor ignition resistance may be augmented by disposing flame quenching openings in the bottom wall structure of the combustion chamber by, for example, placing a perforated flame arrestor plate therein. 
   According to one aspect of the invention, the venturi inlet structure of the burner is formed as an integral portion of its inlet portion disposed within the plenum area, thus integrating a low NOx burner with an FVIR platform. Alternatively, the venturi inlet structure, which is representatively an air inlet conduit structure extending through the plenum area or simply a venturi opening formed in an outer wall of the burner body inlet portion, may be a separate structure attached to the burner body inlet portion. Fuel is supplied to the burner via a fuel supply tube suitably routed through an interior portion of the water heater to the burner. 
   In one illustrated embodiment thereof, the water heater is also provided with a combustion shutoff system functioning to automatically terminate combustion in response to the presence of a predetermined, unacceptably high temperature within the combustion chamber which may be caused, for example, by the combustion therein of extraneous flammable vapors ingested from outside the water heater. In a representative embodiment thereof, the combustion shutoff system is operative to terminate combustion air flow to the burner and comprises a temperature sensing structure disposed within the combustion chamber an linked to a spring-loaded damper structure releasable by the temperature sensing structure, to close the inlet of the burner venturi inlet structure, in response to the combustion chamber temperature reaching a set point temperature of the temperature sensing structure. 
   In illustrated representative embodiments thereof, the water heater has an inner wall structure defining a tank for holding water to be heater, a combustion chamber extending downwardly from a lower end of the tank and having a bottom wall structure, and a skirt wall depending from a bottom peripheral portion of the combustion chamber and circumscribing a plenum area separated from the combustion chamber by the bottom wall structure, the skirt wall having an opening therein. 
   An outer wall structure outwardly circumscribes the inner wall structure and defines therewith an air inlet space at least partially circumscribing the skirt wall, the outer wall structure having a combustion air inlet opening area extending therethrough into the air inlet space. The fuel burner is illustratively a radiant burner and has a hollow body with an upper outlet portion thereof projecting from the combustion chamber bottom wall structure into the combustion chamber, and a lower inlet portion projecting from the bottom wall structure into the plenum area, the inlet portion having a venturi inlet structure associated therewith and having an inlet communicated with the air inlet space in a manner permitting combustion air entering the air inlet space through said combustion air inlet opening area from outside the water heater to be drawn into said inlet of the venturi inlet structure. Preferably, all of the primary combustion air delivered to the burner flows through its venturi inlet structure, comes from outside of the water heater, and is flows flowed to the inlet of the venturi structure via the interior of the skirted plenum area. 
   The water heater also includes fuel delivery apparatus for delivering fuel from a source thereof to the interior of said lower inlet portion of said hollow body for mixture with combustion air flowed thereinto via said venturi inlet structure. Representatively, the fuel delivery apparatus includes a fuel supply tube appropriately routed through an interior portion of the water heater to operatively supply fuel gas, from a source thereof, to the burner. 
   According to various other aspects of the invention, the flame-holding wall section of the radiant burner is removable from the balance of the burner for cleaning and inspection purposes, the combustion air inlet opening area includes a series of air filtering perforations formed in the outer wall structure, and the water heater may have incorporated therein the aforementioned combustion shutoff system together with the flammable vapor ignition resistance structure which includes the flame-holding wall section of the radiant burner. 
   In accordance with further features of the invention, in illustrated embodiments of the water heater the bottom wall structure of the combustion chamber is defined by a peripheral portion of the fuel burner captively and supportingly retained in a circumferential rolled portion of the inner wall structure. In another illustrated embodiment of the water heater the bottom wall structure of the combustion chamber is separate from the fuel burner and has an opening through which the fuel burner vertically extends. The fuel burner is releasably interlocked with the bottom wall structure and is downwardly removable from the combustion chamber through the opening in the separate bottom wall structure. The fuel burner is releasably interlocked with the bottom wall structure by cooperating tab and slot structures on the fuel burner and bottom wall structure, and is interlockable with and releasable from the bottom wall structure by rotating the fuel burner relative to the bottom wall structure about a vertical axis. 
   When released from the bottom wall structure the fuel burner may be removed from the water heater by withdrawing the released fuel burner outwardly through aligned access openings in the inner and outer wall structures. The venturi inlet structure of this burner embodiment has a cover member secured thereto and adapted to cover the access opening in the inner wall structure when the fuel burner is supportingly interlocked with the bottom wall structure. 
   According to another aspect of the invention, in one embodiment thereof the water heater further includes a flue pipe extending upwardly from a central portion of the lower end of the tank. The upper outlet portion of the hollow burner body has a nonperforate central top side portion underlying the flue pipe, and the perforate flame holding wall section of the burner at least partially circumscribes this nonperforate central top side portion and slopes downwardly and inwardly towards it. In this manner, clogging of the flame-holding wall section by scale falling from the interior of the flue pipe is substantially reduced. 
   Various combustion air inlet flow paths through the interior of the water heater are representatively utilized in illustratively depicted embodiments of the water heater. These combustion air inlet flow paths include one in which the inlet of the venturi inlet structure receives combustion air from the air inlet space via the interior of the plenum area, another in which the inlet of the venturi inlet structure is disposed within the plenum area, and a further one in which the inlet of the venturi inlet structure is disposed within the air inlet space, and the water heater further includes an inlet passage for flowing combustion air from outside the water heater through the air inlet opening area and into the plenum area for delivery outwardly therefrom, via the skirt wall opening, into the air inlet space. 
   As will be readily appreciated by those of skill in this particular art, the present invention is not limited to water heaters, but could also be advantageously incorporated in other types of fuel-fired heating appliances such as, for example, boilers and fuel-fired air heating furnaces. Additionally, while the various water heater embodiments representatively illustrated and described herein have been indicated as incorporating radiant fuel burners therein, it will also be readily appreciated by those of skill in this particular art that other types of fuel burners could alternatively be utilized if desired without departing from principles of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional view through a lower end portion of a gas-fired water heater embodying principles of the present invention; 
       FIG. 2  is a partial cross-sectional view through the water heater taken along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  is an enlarged scale cross-sectional view through the water heater taken along line  3 — 3  of  FIG. 2 ; 
       FIG. 4  is an enlarged scale cross-sectional view through the water heater taken along line  4 — 4  of  FIG. 2 ; 
       FIG. 5  is a schematic cross-sectional view through a lower end portion of a first alternate embodiment of the  FIG. 1  water heater; 
       FIG. 6  is a partial cross-sectional view through the  FIG. 5  water heater taken along line  6 — 6  of  FIG. 5 ; 
       FIG. 7  is a schematic cross-sectional view through a lower end portion of a second alternate embodiment of the  FIG. 1  water heater; 
       FIG. 8  is a cross-sectional view through the  FIG. 7  water heater taken along line  8 — 8  of  FIG. 7 ; and 
       FIG. 9  is a schematic cross-sectional view through a lower end portion of a third alternate embodiment of the  FIG. 1  water heater. 
   

   DETAILED DESCRIPTION 
   Cross-sectionally illustrated in schematic form in  FIG. 1  is a fuel-fired heating appliance, representatively a gas-fired water heater  10 , embodying principles of the present invention. Water heater  10  rests upon a horizontal support surface, such as the illustrated floor  11 , and has a vertically oriented tubular inner wall structure  12 . Inner wall structure  12  defines, along an upper portion thereof, a tank  14  adapted to hold a quantity of water  16  to be heated and having a domed bottom end wall  18 , a combustion chamber  20  extending downwardly from a peripheral portion of the end wall  18 , and an annular skirt wall  22  extending downwardly from the periphery of the combustion chamber  20  to the floor  11  and circumscribing a plenum  24  disposed beneath the combustion chamber  20 . A circumferentially spaced series of air transfer openings  26  extend through the skirt wall  22  into the plenum  24 . Extending upwardly from the bottom tank end wall  18 , through the stored water  16 , is a flue pipe  28  that communicates at its lower end with the interior of the combustion chamber  20 . 
   A vertically oriented tubular metal outer wall structure, representatively in the form of a metal jacket  30 , outwardly circumscribes the inner wall structure  12  and forms therewith an annular space, an upper portion of which is filled with a suitable insulation material  32 , and a lower end portion of which forms an annular air inlet or receiving space  34  which outwardly circumscribes the skirt wall  22 . A circumferentially spaced series of combustion air inlet openings  36  extend through a lower end portion of the jacket  30  into the annular space  34 . 
   Water heater  10  also includes a radiant gas burner  40 , the hollow body of which is formed from abutting upper and lower metal pan structures  42 , 44  having circular peripheral edge flange portions supportingly received in a circumferentially rolled portion  46  of the inner wall structure  12 . As can be seen in  FIG. 1 , a peripheral flange portion of the burner  40  defines the bottom wall of the combustion chamber  20 , with an upper or outlet portion of hollow body of the burner  40  projecting upwardly from such bottom wall into the interior of the combustion chamber  20 , and a lower or inlet portion of the hollow body of the burner  40  projecting downwardly from such bottom wall into the skirt plenum  24 . 
   On the top side of the burner  40  is a metal mesh burner screen structure  48  (see.  FIGS. 1–4 ) which functions as a perforate flame-holding surface or wall structure during firing of the burner. The screen structure  48  may be removed from the balance of the burner  40  and withdrawn from the combustion chamber, for inspection and cleaning purposes, through suitable aligned access openings (not illustrated herein) formed in the outer wall structure  30  and a vertical side wall portion of the combustion chamber  20 . During firing of the burner  40 , as later described herein, the burner generates hot combustion products which flow upwardly through the flue  28  and heat the stored water  16  to maintain it at a predetermined heated temperature. 
   As can best be seen in  FIGS. 2–4 , the removable screen structure  48  (which may be of an alternative perforate construction such as a porous ceramic material), has a partially annular configuration as viewed from the top, and has opposite, circumferentially spaced apart ends  50 , 52 . Removable screen  48  circumscribes a generally circular, non-screened central area  56  of the upper burner pan structure  42  that underlies the open lower end of the flue  28 , with the screen  48  sloping downwardly and radially inwardly toward the non-screened central area  56 . In this manner, scale falling from the interior of the flue  28  tends to land in the central area  56  and thus does not tend to plug the screen  48 . Additionally, scale landing on the screen  48  tends to fall down its inwardly sloped surface onto the non-screened central area  56 . 
   The burner screen  48  provides the water heater  10  with flammable vapor ignition resistance (FVIR) to substantially prevent flames within the combustion chamber  20  (caused, for example, by ignition of extraneous flammable vapors ingested into the combustion chamber) from downwardly exiting the combustion chamber  28 , the various small openings in the screen area  48  serving as flame quenching openings that permit fuel and air to upwardly traverse the screen, but preclude the passage of flames downwardly therethrough. 
   As illustrated in  FIG. 1 , the lower burner pan structure  44  forms within the skirt plenum  24  a burner venturi inlet opening  58  that is an integral portion of the burner  40  and communicates the interior of the plenum  24  with the interior of the burner  40 . A fuel gas supply tube  60  is connected to a thermostatic gas valve  62  and extends downwardly therefrom through a portion of the combustion chamber  20  and into the interior of the burner  40 . A suitable gas discharge nozzle  64  is connected to the lower outlet end of the tube  60  within the interior of the burner  40  adjacent its integral inlet opening  58 . 
   During firing of the burner  40 , fuel gas  66  is discharged from the nozzle  64  into the interior of the burner  40 , and combustion air  68  from outside the water heater  10  sequentially flows inwardly through the combustion air inlet openings  36  into the annular space  34 , from the annular space  34  into the skirt plenum area  24  via the skirt wall openings  26 , and from the skirt plenum area  24  into the interior of the burner  40  through its integral venturi inlet opening  58 . Combustion air  68  entering the interior of the burner  40  in this manner is mixed with the discharged fuel gas  66  to form a fuel/air mixture that passes upwardly through the removable burner screen  48  and is suitably ignited to form the previously mentioned hot combustion products within the combustion chamber  20  and heat the stored tank water  16 . 
   As can be seen, all of the primary combustion air supplied to the burner  40  comes from outside the water heater  10 . Accordingly, the NOx emissions generated by the burner  40  are quite low. Thus, the representatively illustrated water heater  10 , in a simple, efficient and economical manner, integrates a low NOx fuel burner with a flammable vapor ignition resistance structure. 
   A first alternate embodiment  10   a  of the previously described water heater  10  is schematically shown in  FIGS. 5 and 6 . For ease in comparing the water heaters  10  and  10   a , components in the water heater  10   a  similar to those in the previously described water heater  10  have been given the same reference numerals to which the subscripts “a” have been added. Water heater  10   a  is similar in construction and operation to the previously described water heater  10  with the following exceptions. 
   In the water heater  10   a , the removable burner screen  48   a  has a fully domed configuration, and the combustion air inlet openings  36   a  formed in the jacket wall  30   a  are particulate filtering perforations operative to filter out, for example, lint, dirt and oil from combustion air  68   a  entering the annular space  34   a  to reduce potential clogging of the burner screen  48   a . As an alternative to these filtering perforations in the jacket wall  30   a , a separate filtering structure could be appropriately installed in a suitable mounting opening in the jacket wall  30   a . The integral burner venturi inlet opening  58   a  disposed within the skirt plenum  24   a  faces downwardly and forms a portion of a combustion shutoff system  70  incorporated in the water heater  10   a.    
   The combustion shutoff system  70  functions to terminate combustion in the combustion chamber  20   a , representatively by precluding further combustion air flow to the burner  40   a , in response to the detection of an undesirably high temperature in the combustion chamber  20   a  which may be caused, for example, by the combustion therein of ingested extraneous flammable vapors from outside the water heater  10   a . Combustion shutoff system  70  representatively includes a temperature sensing structure  72  disposed within the combustion chamber  20   a  and linked to a spring-loaded shutoff damper assembly  74  which is normally held in its indicated open position in which it permits combustion air  68   a  to flow into the interior of the burner  48   a  through its integral venturi inlet opening  58   a.    
   Upon detecting a predetermined, undesirably high temperature within the combustion chamber  20   a , the temperature sensing structure  72  permits the damper structure  74  to be spring-driven upwardly in a manner causing the damper structure  74  to close off the burner inlet opening  58   a . The temperature sensing structure  72  is located over a perforated arrestor plate  76  (see  FIG. 6 ) inset into peripheral portions of the upper and lower burner pan structures  42 , 44 . The perforated arrestor plate  76  serves to prevent outflow of flames from the interior of the combustion chamber  20   a  (augmenting the flame outflow prevention of the burner screen  48   a ), and additionally functions to provide combustion chamber pressure relief during normal ignition and operation of the burner  40   a . Temperature sensing structure  72  and its associated spring-loaded shutoff damper structure  74  may be similar in construction and operation to any of those shown in U.S. Pat. No. 6,715,451 which is hereby incorporated by reference herein. 
   Like the previously described water heater  10 , the water heater  10   a  desirably integrates a low NOx fuel burner with an FVIR platform in a simple, efficient and economical manner. 
   Cross-sectionally illustrated in schematic form in  FIGS. 7 and 8  is a second alternate embodiment  10   b  of the previously described water heater  10  shown in  FIG. 1 . Water heater  10   b , with the exceptions noted below, is similar in construction and operation to the previously described water heater  10   a  shown in  FIGS. 5 and 6 . To facilitate the comparison of water heaters  10   b  and  10   a , components in the water heater  10   b  similar to those in water heater  10   a  have been given identical reference numerals to which the subscripts “b” have been added. 
   Water heater  10   b  representatively does not incorporate the previously described combustion shutoff system  70  therein, and, compared to the water heater  10   a , has a somewhat modified burner configuration. Specifically, as shown in  FIGS. 7 and 8 , the burner  40   b  has a generally horizontally extending venturi inlet conduit  78  formed as an integral portion of the bottom burner pan  44   b  and disposed within the skirt plenum area  24   b , the venturi inlet conduit  78  having, at its horizontally outer end, the inlet opening  58   b  as illustrated in  FIG. 7 . The fuel gas tube  60   b  extends horizontally into the conduit  78  through its inlet opening  58   b . The removable burner screen structure  48   b  is withdrawable from the combustion chamber  20   b , for inspection and cleaning, through an appropriately covered combustion chamber side wall access opening  80  and a corresponding jacket side wall access opening (not visible). Like the previously described water heaters  10  and  10   a , the water heater  10   b  desirably integrates a low NOx fuel burner with an FVIR platform in a simple, efficient and economical manner. 
   A third alternate embodiment  10   c  of the previously described water heater  10  shown in  FIG. 1  is schematically depicted in cross-sectional form in  FIG. 9 . Water heater  10   c , with the exceptions noted below, is similar in construction and operation to the previously described water heater  10   b  shown in  FIGS. 7 and 8 . TO facilitate the comparison of water heaters  10   c  and  10   b , components in the water heater  10   c  similar to those in water heater  10   b  have been given identical reference numerals to which the subscripts “c” have been added. 
   In the water heater  10   c  shown in  FIG. 9 , the burner  40   c  does not have peripheral portions which are supportingly received in the roll portion  46   c . Instead, the body of the operatively installed burner  40   c  extends downwardly through a central circular opening  82  formed in a separate circular metal plate  84  forming the bottom wall of the combustion chamber  20   c  and having a peripheral edge portion supportingly received in the roll portion  46   c . Diametrically opposite notches  86  are formed in the plate  84  and extend radially outwardly from the periphery of its central opening  82 . A pair of corresponding diametrically opposite tabs  88  project radially outwardly from an upper peripheral portion of the burner  40   c.    
   Horizontally extending outwardly from a lower portion of the burner  40   c  which projects downwardly into the skirt plenum area  24   c  is a venturi conduit  90  having, at its outer end, the venturi inlet  58   c . Conduit  90  extends outwardly through an access opening  92  in the skirt wall  22   c , with an outer end portion of the conduit  90  being fixedly secured within a removable access cover  94  extending across the access opening  92 . As illustrated, the inlet opening  58   c  of the venturi conduit  90  is disposed within the annular space  34   c  for receiving fuel  66   c  from the discharge orifice  64   c . An access opening  96  is formed through the jacket  30   c , in alignment with the combustion chamber access opening  92 , with a removable cover  98  extending across the access opening  96 . 
   With the covers  94 , 98  removed, the burner  40   c  is installed within the water heater  10   c  by inserting the burner body inwardly through the aligned access openings  96 , 92  in an orientation in which the burner tabs  88  underlie the plate notches  86  and the access cover  94  is closely adjacent the access opening  92 . The burner  40   c  is then moved upwardly to place an upper burner portion within the combustion chamber  20   c  and move the burner tabs  88  upwardly through the plate notches  86 . Finally, the inserted burner  40   c  is rotated about the indicated vertical axis  100  to cause the tabs  88  to overlie the plate  84  and operatively support the burner  40   c  within the water heater  40   c . This also brings the cover member  94  into a covering relationship with the access opening  92 . The other removable cover  98  is then installed over the jacket access opening  96 . TO remove the installed burner  40   c  for inspection and cleaning, this process is simply reversed. The wire mesh top side section  102  of the installed burner  40   c , in conjunction with the indicated perforated flame arrestor plates  76   c  installed in the plate  84 , provides the water heater  10   c  with flammable vapor ignition resistance. 
   The indicated particulate filtering perforations  68   c  formed in the jacket  30   c  are positioned diametrically oppositely from the venturi conduit inlet  58   c  and communicate with an enclosed passageway  104  extending through annular space  34   c  and opening into the skirt plenum area  24   c . During firing of the water heater  10   c , combustion air  68   c  from outside the water heater  10   c  flows sequentially through the combustion air inlet perforations  36   c  into the interior of the skirt plenum area  24   c  via the enclosed passageway  104 , outwardly from the skirt plenum area into the annular space  34   c  through the air transfer openings  26   c , and then into the venturi conduit inlet  58   c  for mixture with fuel  66   c  being discharged from the fuel nozzle  64   c  to form the fuel/air mixture ignited by the burner  40   c.    
   Like the previously described water heaters  10 ,  10   a  and  10   b , the water heater  10   c  desirably integrates a low NOx fuel burner with an FVIR platform in a simple, efficient and economical manner. 
   While various principles of the present invention have been representatively illustrated and described herein as being incorporated in a fuel-fired water heater, it will be readily appreciated by those of skill in this particular art that the present invention is not limited to water heaters, but could also be advantageously incorporated in other types of fuel-fired heating appliances such as, for example, boilers and fuel-fired air heating furnaces. 
   Additionally, while the various water heater embodiments representatively illustrated and described herein have been indicated as incorporating radiant fuel burners therein, it will also be readily appreciated by those of skill in this particular art that other types of fuel burners could alternatively be utilized if desired without departing from principles of the present invention. 
   The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.