Abstract:
A fuel-fired water heater is provided with a combustion chamber assembly, representatively a sealed combustion chamber assembly, operative to create from combustion air delivered thereto via a circumferentially limited vertical side portion thereof a flow of primary combustion air to the underside of a centrally disposed fuel burner within the assembly via a first location underlying the burner, a first flow of secondary combustion air delivered to the burner via the first location, and a second flow of secondary combustion air delivered to the burner via a second location outwardly circumscribing the first location.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to fuel-fired heating appliances and, in a representatively illustrated embodiment thereof, more particularly relates to a fuel-fired direct vent water heater having a specially designed sealed combustion chamber assembly incorporated therein. 
     Modern fuel-fired direct vent water heaters are commonly provided with a “sealed” combustion chamber. In this context, the term “sealed” means that the water heater combustion chamber does not exceed the internal pressure-created leakage test flow rates set forth in section 2.33.3 of the American National Standard/CSA Standard for Storage Water Heaters With Input Ratings of 75,000 Btu Per Hour or Less. 
     While this sealed combustion chamber design provides the direct vent water heater with a variety of operational advantages, including facilitating a flammable vapor ignition resistant design of the water heater, it also tends to introduce a variety of undesirable operational characteristics including diminished ignition performance leading to sooting in the combustion chamber, decreases in burner flame stability, increased NOx emissions and a lessening in combustion performance. It would thus be desirable to provide a combustion chamber assembly for a fuel-fired heating appliance, such as a water heater, in which these potential design problems are eliminated or at least substantially diminished. 
     SUMMARY OF THE INVENTION 
     In carrying out principles of the present invention, in accordance with an illustrated embodiment thereof, a fuel-fired heating appliance is provided with a specially designed combustion chamber assembly. Representatively, but not by way of limitation, the appliance is a direct vent water heater, and the combustion chamber assembly incorporated therein is of a sealed configuration. 
     The combustion chamber assembly, which forms a bottom portion of the water heater disposed beneath the storage tank portion of the water heater through which a flue upwardly extends, comprises a hollow body having an interior circumscribed by a side wall, a plate member extending generally transversely to the side wall and dividing the interior into a combustion chamber, from which a flue upwardly extends through the tank, and an air intake plenum disposed beneath the combustion chamber. A fuel burner is centrally disposed in the combustion chamber in a spaced relationship with the plate member, and in a facing relationship with a central portion thereof. An air transfer opening extends through the central portion of the plate member. 
     According to one aspect of the invention, a first wall structure is disposed in the air intake plenum and extends inwardly from the combustion air intake opening. The first wall structure forms a first passage for receiving air drawn inwardly through the combustion air intake opening and flowing a portion of the received air to the air transfer opening for transfer therethrough into the combustion chamber, the first passage having a volume substantially less that that of the air intake plenum. Illustratively, the first passage has a progressively narrowing configuration operative to funnel the portion of the received air to the air transfer opening, and the first wall structure includes two elongated, opposite sloped support leg structures underlying the plate member. Additional combustion air entering the air intake plenum may bypass the air transfer opening and flow into the combustion chamber via openings in the support legs and a peripheral gap circumscribing an outer edge portion of the plate member and disposed between such outer edge portion and a facing portion of the interior surface of the hollow body. 
     According to another aspect of the invention, a second wall structure is disposed in the combustion chamber and extends from the central portion of the plate member to adjacent the fuel burner, the second wall structure forming a second passage for receiving combustion air exiting the air transfer opening and flowing the received combustion air to the fuel burner. Illustratively, the second passage has a progressively narrowing configuration and is operative to funnel the received combustion air to the fuel burner. Preferably, the second wall structure includes an air transfer member having a hollow, generally frustroconical configuration with an open inlet end portion positioned against the plate member and circumscribing the air transfer opening therein, and a smaller area open outlet end portion positioned adjacent the fuel burner and separated therefrom by a gap through which combustion air may outwardly pass. 
     Illustratively, the fuel burner has a fuel/air mixture-receiving inlet structure generally aligned with the open outlet end portion of the air transfer member, and the water heater further comprises a fuel discharge nozzle disposed in the inlet end portion of the air transfer member and being operative to discharge received fuel for mixture with combustion air entering the air transfer member via the air transfer opening in the plate member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified, somewhat schematic cross-sectional view taken through a bottom end portion of a representative fuel-fired direct vent water heater incorporating therein a specially designed sealed combustion chamber assembly embodying principles of the present invention; 
         FIG. 2  is a schematic perspective view of the water heater portion cross-sectionally illustrated in  FIG. 1 ; 
         FIG. 3  is a reduced scale schematic cross-sectional view through the  FIG. 1  water heater portion taken generally along line  3 - 3  of  FIG. 1 ; and 
         FIG. 4  is an enlarged scale schematic cross-sectional view through the  FIG. 3  water heater portion taken generally along line  4 - 4  of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     This invention provides a fuel-fired heating appliance which is representatively a direct vent water heater  10 , a lower portion of which is somewhat schematically depicted in  FIGS. 1 and 2 . While principles of the present invention are representatively incorporated in a water heater, it will be readily appreciated by those of ordinary skill in this particular art that fuel-fired heating appliances of other types (such as, for example, boilers or fuel-fired furnaces) may be alternatively utilized without departing from principles of the present invention. 
     Water heater  10  is illustratively a gas-fired direct vent water heater and has a combustion chamber  12  underlying the bottom wall  13  a vertically oriented, generally circularly cross-sectioned water storage tank  14  through the interior of which a flue  16 , communicating with the combustion chamber  12 , upwardly extends. A gas burner  18  is disposed within the combustion chamber  12  and is supplied with fuel through a gas supply line  20  connected to the usual thermostatic gas valve  21  mounted on a side portion of the tank  14 . Combustion air  22  is also supplied to the burner  18 , in a unique manner subsequently described herein, via an air delivery passage  24  extending downwardly through an insulation space  26  disposed between the tank  14  and a metal jacket structure  28  outwardly surrounding the tank  14  in a manner similar to that shown in FIG. 3 of U.S. Pat. No. 7,013,841 (which is hereby incorporated herein by reference) assigned to the same assignee as the present application. Air passage  24 , which communicates at its inlet end with a source of air external to the location of the water heater  10  (illustratively outside air), is illustratively the sole path through which combustion air can enter the combustion chamber  12 . 
     Combustion chamber  12  forms a portion of a specially designed sealed combustion chamber assembly A that houses the burner  18  and embodies principles of the present invention. Combustion chamber  12  is bounded on its top side by the bottom wall  13  of the tank  14 , and on its side by a downward side wall extension  14   a  of the tank  14 . The bottom wall of the combustion chamber  12  is defined by a circular air transfer plate structure  30  which also forms the top wall of an air inlet plenum  32  that underlies the combustion chamber  12  and communicates with the air passage  24  via a side wall opening  34  of the plenum  32 . Air inlet plenum  32  has a bottom wall  35 . Air transfer openings  36  (see  FIGS. 2-4 ) are formed in a central portion of the air transfer plate  30 . For purposes later described herein, there is a circular gap  38  between the periphery of the air transfer plate  30  and the inner side surface of the combustion chamber side wall  14   a . As best illustrated in  FIGS. 1-3 , a peripheral portion  30   a  of the air transfer plate  30  at the side wall opening  34  of the plenum  32  is upwardly bent to clear the side wall opening  34 . 
     With reference now to  FIGS. 1-4 , sealed combustion chamber assembly A also includes a pair of elongated, generally strip-shaped support legs  40  underlying the air transfer plate  30  within the plenum  32 , and a generally frustroconically-shaped hollow air transfer member  42  disposed atop the air transfer plate  30  and overlying the air transfer openings  36  therein. 
     As illustrated in  FIGS. 1-4 , the widths of the support legs  40  extend between the bottom side of the air transfer plate  30  and the bottom wall  35  of the plenum  32  and have generally circular air outlet openings  44  therein. As viewed from the top (see  FIG. 3 ), legs  40  slope leftwardly and inwardly toward one another, with the right ends of the legs  40  being disposed closely adjacent the side wall section  14   a , on opposite sides of the air passage  24 , and being spaced further apart from one another than the left ends of the legs  40  which are spaced inwardly apart from the side wall section  14   a . As also can be best seen in  FIG. 3 , the air transfer openings  36  in the air transfer plate  30  are disposed above the lateral space between the oppositely sloped support legs  40 . 
     As may be best seen in  FIG. 4 , the frustroconically shaped hollow air transfer member  42  has an open circular bottom end  46  that rests atop the air transfer plate  30  and circumscribes the plurality of air transfer openings  36  formed therein, and an open, smaller diameter circular top end  48  that is centrally positioned beneath the bottom side  50  of the burner  18  and circumscribes a fuel/air mixture inlet structure  52  extending downwardly therefrom. An annular gap  54  is formed between the top end  48  of the air transfer member  42  and the bottom side  50  of the burner  18 . The previously mentioned gas supply line  20  extends into the interior of the frustroconical air transfer member  42 , through a bottom end portion thereof, and is connected to a fuel discharge nozzle  56  disposed in the interior of the air transfer member  42  beneath the fuel/air mixture inlet structure  52 . 
     With reference now to  FIGS. 1 ,  3  and  4 , during firing of the water heater  10 , a flame  58  is created by the burner  18  within the combustion chamber  12 . The resulting hot combustion gases  60  (see  FIG. 1 ) are drawn upwardly through the flue  16 , with combustion heat from such gases  60  being transferred through the flue  16  to water  62  stored within the tank  14  for on-demand delivery therefrom in a conventional manner to various hot water-utilizing plumbing fixtures operatively communicated with the tank interior. 
     At the same time, combustion air  22  is drawn downwardly through the passage  24  and into the air transfer plenum  32  through its side wall opening  34 . Combustion air  22  drawn into the air transfer plenum  32  in this manner travels leftwardly therethrough (as viewed in  FIG. 3 ) and is funneled horizontally inwardly towards the openings  36  in the air transfer plate  30  by the oppositely sloped support legs  40  that underlie the plate  30 . 
     A first portion of the combustion air  22  entering the air transfer plenum  32  passes upwardly through the plate openings  36  (see  FIG. 4 ) into the interior of the frustroconical air transfer member  42  and forms primary combustion air  22   a  that mixes with fuel  64  being discharged from the nozzle  56  to form therewith a fuel/air mixture  66  delivered to the burner fuel/air mixture inlet structure  52 . 
     A second portion of the combustion air  22  entering the air transfer plenum  32  passes upwardly through the plate openings  36  (see  FIG. 4 ) into the interior of the frustroconical air transfer member  42  and forms secondary combustion air  22   b  (i.e., excess combustion air that is not mixed with the discharged fuel  64 ) which passes outwardly through the annular gap  54  and is fed to the flame  58  around the periphery of the burner  18 . 
     A third portion of the combustion air  22  entering the air transfer plenum  32  bypasses the transfer plate openings  36  and flows upwardly into the combustion chamber  12  via the gap  38  (see  FIG. 3 ) between the periphery of the air transfer plate  30  and the side wall portion  14   a . A first quantity of this third portion flow upwardly through the gap  38  before entering the funneled space between the support legs  40 , a second quantity flows outwardly through the support leg openings  44  and then upwardly through the gap  38 , and the remainder of the third portion exits through the left end space between the legs  40  and then flows upwardly through the gap  38  into the combustion chamber  12 . As schematically depicted in  FIG. 4 , this combustion air entering the combustion chamber  12  upwardly through the gap  38  flow from all around the gap to the periphery of the burner  18  as additional secondary combustion air  22   c.    
     As can be readily seen from the foregoing, despite the introduction of combustion air  22  to the plenum  32  via only a limited circumferential side wall portion thereof, the sealed combustion chamber assembly A of the present invention functions to provide accurate positional control of the delivered combustion air by routing primary combustion air  22   a  to a location directly beneath the centrally located burner  18 , for mixture with the discharged fuel  64 ), and by routing secondary air flows  22   b , 22   c  uniformly to the periphery of the burner  18  for supporting the flame  58  which it creates. Because of this positional control of incoming combustion air, the sealed combustion chamber assembly A provides the water heater  10  with enhanced ignition performance, decreased NOx emissions, and increased combustion performance. 
     As previously mentioned herein, the present invention is not limited to water heaters, but may also be utilized to advantage in a variety of other types of fuel-fired heating appliances such as, for example but not by way of limitation, boilers and furnaces. A variety of modifications may be made to the representatively disclosed heating appliance structure without departing from principles of the present invention. For example, the combustion air may be delivered to the water heater through a path external to the outer jacket portion of the water heater. Additionally, while the representatively depicted water is a direct vent water heater, it could be an alternative type of water heater. 
     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.