Abstract:
The efficiencies of illustrative embodiments of vertical center flue type fuel-fired base water heaters are improved by installing in the water heaters variously configured tubular condensing type secondary heat exchangers of smaller diameters than the associated center flues. The efficiency increases are achieved with components and manufacturing processes similar to those utilized in the base water heaters and secondary heat exchanger materials similar to those in the tank portions of the base water heaters.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the filing date of provisional U.S. patent application Ser. No. 61/311,447 filed Mar. 8, 2010. The entire disclosure of the provisional application is incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to liquid heating apparatus and, in representatively illustrated embodiments thereof, more particularly provides variously configured fuel-fired high efficiency water heaters. 
     Fuel-fired water heaters of conventional construction typically have a glass-lined metal tank adapted to store a quantity of pressurized water received from a source such as a city water supply. A combustion chamber having a fuel burner associated therewith is positioned in a heat exchange relationship with the tank, usually at the upper or lower end thereof, and communicates with a central flue extending vertically through the tank water. During firing of the burner, hot combustion products created by the burner flow vertically through the flue to conductively transfer combustion heat to the stored water as required. Combustion products exiting the central flue are discharged to a suitable vent system external to the water heater. 
     While this relatively simple conventional water heater construction has for many years been well suited for its intended water heating purpose, fuel-fired water heaters of this general type are being subjected to increasingly stringent government efficiency requirements. These requirements have triggered a need in the water heater industry for a fuel-fired water heater design which meets the new efficiency requirements, preferably utilizing components and manufacturing techniques similar to those used in conventional water heater constructions, and utilizing improved heat exchanger materials similar to those used in fabricating the tank portion of the water heater, without unduly increasing the overall manufacturing cost of the more efficient water heater. It is to this need that the present invention is primarily directed. 
     SUMMARY OF THE INVENTION 
     In carrying out principles of the present invention, in accordance with representatively illustrated embodiments thereof, variously configured high efficiency fuel-fired liquid heating structures are provided which are representatively in the form of gas-fired water heaters. Each water heater has a tank portion for storing pressurized heated water for on-demand delivery to hot water-utilizing plumbing fixtures such as, for example, sinks, bathtubs, showers, dishwashers and the like. Extending vertically through the tank water, and communicating with a combustion chamber portion of the water heater is a central primary flue through which hot combustion products flow during firing of a fuel burner operatively associated with the combustion chamber. Such combustion products conductively transfer heat to the stored water when such heat is called for by a suitable water temperature sensing and control structure. 
     Utilizing principles of the present invention, this generally conventional fuel-fired water heater structure has its operational efficiency substantially increased in a relatively inexpensive manner, using conventional components, materials and fabrication techniques, with the unique addition thereto of secondary condensing type heat exchanger apparatus centered around various configurations of a smaller diameter secondary condensing type heat exchanger flue disposed extending through the interior of the tank and communicating with the central primary flue. 
     In representatively illustrated upflow versions of the high efficiency water heater the hot combustion products sequentially flow upwardly through the central primary heat exchanger flue and then, adjacent the upper end thereof, are flowed downwardly through a straight vertical portion of the secondary flue within the tank water external to the central flue. Finally, the combustion products flow through a lower section of the smaller diameter secondary flue, is illustratively coiled around a lower portion of the central flue, representatively around only a lower one third to one half of the central flue, before exiting the water heater. 
     Such flow of the combustion products may be induced by a blower interposed between the primary and secondary heat exchanger flues or downstream of both flues external to the water heater. Various ones of these water heater embodiments are provided with baffle structures isolating combustion products exiting the water from burner heat. According to a feature of the present invention the surface area of the lower coiled section of the secondary flue is illustratively sixty to ninety percent of the total secondary flue surface area in various ones of these water heater embodiments. According to a further feature of the present invention a baffle is illustratively installed in the primary flue and is operative, during firing of the water heater, to cause approximately sixty to eighty percent of the total combustion heat transferred to the water from the primary and secondary flues to be transferred to the water through the primary flue. 
     Downfiring embodiments of these high efficiency water heaters are also encompassed in principles of the present invention, as are representative water heaters in which the coiled lower end portion of the secondary condensing flue is eliminated and provided in a vertically straight configuration. In all of the representatively illustrated water heater embodiments various types of heat transfer-enhancing baffle structures are installed in the interior of the central primary flue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view through a fuel-fired high efficiency water heater embodying principles of the present invention; and 
         FIGS. 2-13  are schematic cross-sectional views through representative alternate embodiments of the  FIG. 1  water heater, with similar components in the various embodiments having identical reference numbers in order to facilitate ready comparison between and among the various depicted embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Turning first to  FIG. 1 , schematically depicted fuel-fired liquid heating apparatus  10  is representatively a gas-fired water heater, which could be a residential, commercial or industrial type, but could alternatively be apparatus for heating another type of liquid, and/or could be fired using a fuel other than gas. Water heater  10  has a vertically extending tank  12  adapted to hold a quantity of water  14  to be heated, the tank  12  being outwardly surrounded by a suitable insulated jacket structure  16  (only a vertical portion thereof being shown) of conventional construction. Tank  12  has an upper end  18 , and a lower end  20  which forms the upper wall of a combustion chamber  22  that underlies the tank  12 . Suitable cold water inlet and hot water outlet fittings  24 , 26  are provided on the upper end  18  of the tank  12 . 
     Water heater  10  is provided with a flue system including a tubular central metal primary flue  28  which longitudinally extends vertically through a central portion of the interior of the tank  12  and is connected to the upper and lower tank end walls  18 , 20 . The lower end of the primary flue  28  communicates with the interior of the combustion chamber  22 , and the open upper end of the primary flue  28  extends upwardly through the upper tank end wall  18  and is capped off as at  30 . A heat transfer-enhancing baffle  32 , of a suitable conventional construction, is illustratively inserted into the interior of the primary flue  28  and functions in a known manner to increase the heat transfer from the flue  28  to the tank water  14  when hot combustion products are flowed upwardly through the flue  28  as later described herein. 
     The flue system also includes a specially designed tubular secondary flue  34  disposed within the tank interior and formed from metal piping having a smaller diameter than the diameter of the primary flue  28 . Illustratively, but not by way of limitation, the primary flue  28  has a 4″ diameter, and the secondary flue  34  has a 1.5″ diameter. However, either or both of these flue diameters could be varied as desired or necessary to suit the particular liquid heating application. The secondary flue  34  has a straight upper portion  36  that longitudinally extends vertically through an upper portion of the tank interior and has an inlet portion connected, as at  38 , to an upper end portion of the primary flue  28  within the tank interior adjacent the upper tank end wall  18 . 
     At the lower end of the upper secondary flue portion  36  is a lower portion  40  of the secondary flue  34  that preferably coils downwardly around a bottom portion of the primary flue  28 , and then exits the tank  12  through a side wall portion thereof as shown in  FIG. 1 . The coiled lower portion  40  of the secondary flue  34  vertically extends only through a lower portion of the tank  12 , representatively only through about a bottom third to about a bottom half of the interior of the tank  12 , thereby greatly concentrating the secondary flue-to-water heat transfer in such bottom third to bottom half of the tank water when hot combustion products are flowed through the secondary flue  34  as subsequently described herein. 
     The surface area of the coiled lower portion  40  of the secondary flue  34  is illustratively greater than the surface area of the straight upper portion  36  of the secondary flue  34 . Illustratively, but not by way of limitation, the percentage ratio of (1) the surface area of the secondary flue coiled portion  40  exposed to interior of the tank  12  (and thus to the water  14  therein) to (2) the total secondary flue coil area exposed to the interior of the tank  12  (and thus to the water  14  therein) is in the range of from about sixty percent to about ninety percent. 
     Water heater  10  further has a combustion system that includes a fuel burner  42  disposed within the combustion chamber  22  beneath the open lower end of the primary flue  28  and supplied with fuel gas via a suitable fuel supply line  44 ; an air intake structure  46  through which combustion air  48  may be delivered into the combustion chamber  22  for supply to the burner  42 , and a discharge conduit  50 , disposed externally of the tank  12 , connected at an inlet end thereof to the discharge end of the secondary flue portion  40 , and connected at an outlet end thereof to the inlet of a draft inducer fan  52 . 
     Various modifications could be made to the depicted combustion system without departing from principles of the present invention. For example, the illustrated air intake structure is a vertically extending air intake conduit having an elevated open upper end  54  through which the combustion air  48  inwardly flows for delivery through the air intake conduit into the combustion chamber  22 . Alternatively, however, the combustion air could be delivered directly into the combustion chamber  22  via suitable openings in its exterior wall. Moreover, the combustion air  48  could be obtained from adjacent the water heater  10  or remotely therefrom if desired. Additionally, the illustrated burner  42  could be a power burner in which case the draft inducer fan  52  could be eliminated. 
     With continuing reference to  FIG. 1 , during firing of the water heater  10 , the burner  42  creates within the combustion chamber  22  hot combustion products  56  which, with the assistance of the draft inducer fan  52 , are sequentially flowed upwardly through the primary flue  28 , downwardly through the secondary flue  34  and into the discharge conduit  50 , and then upwardly through the discharge conduit  50  to the draft inducer fan  52  for expulsion therefrom. While the hot combustion products are traversing this flow path, combustion product heat is transferred to the stored water  14  via both the primary and secondary flues  28 , 34 . The flue system is designed to cool the combustion products  56  to an extent such that the discharge conduit  50  depicted in  FIG. 1  may preferably be of a plastic pipe material such as, for example, PVC pipe, ABS pipe or CPVC pipe. 
     Secondary flue  34  functions as a condensing heat exchanger and creates therein condensate as the combustion products  56  downwardly traverse the flue  34 . To suitably carry away such condensate from the water heater, a discharge portion of the lower secondary flue section  40  is provided with a downward slope, toward the discharge conduit  50 , as indicated by the arrow  57  in  FIG. 1 . To provide for removal of this condensate, an appropriate condensate drain fitting  58  may be connected as shown at the lower end of the discharge conduit  50 . 
     Baffle  32  is representatively sized and configured to be operative, during firing of the water heater  10 , to cause the primary flue  28  to transfer from about 60% to about 80% of the total combustion product heat from the flue system to the tank water  14 , with the balance of the flue system combustion product heat being transferred to the water  14  via the secondary flue  34 . 
     The water heater embodiment  10   a  shown in  FIG. 2  is substantially identical to the previously described water heater  10  in  FIG. 1  with the exception that instead of the open top end of the primary flue  28  being capped off it is coupled to and communicates with the interior of a transfer plenum structure  59  above the upper end  18  of the tank  12 , with the upper inlet end of the upper secondary flue portion  36  also being coupled to and communicating with the interior of the transfer plenum structure  59 . During firing of the water heater  10   a , the hot combustion products  56  sequentially flow upwardly through the primary flue  28  into the transfer plenum structure  59 , downwardly through the secondary flue  34  into the discharge conduit  50 , and then upwardly through the discharge conduit  50  into the draft inducer fan  52  for expulsion therefrom. 
     The water heater embodiment  10   b  shown in  FIG. 3  is substantially identical to the previously described water heater  10  in  FIG. 1  with the exceptions that (1) the fuel burner  42  disposed within the combustion chamber  22  is isolated by a wall structure  60  from the balance of the combustion chamber  22 , (2) the primary flue  28  is provided with a horizontally widened bottom end portion  62  directly above the wall structure  60 , and (3) the discharge end portion of the lower secondary flue section  40  extends downwardly into the combustion chamber  22 , externally of the wall structure  60 , and then extends outwardly through an external side wall of the combustion chamber  22  for connection to the vertical discharge conduit  50 . The isolating wall structure  60  serves to desirably isolate the portion of the secondary flue section  40  within the combustion chamber  22  from burner heat. 
     The water heater embodiment  10   c  shown in  FIG. 4  is substantially identical to the previously described water heater embodiment  10   a  in  FIG. 2  with the exceptions that (1) a vertical dividing wall  64  is installed in the combustion chamber  22  to isolate a portion  66  thereof from the burner  42 , and (2) a discharge end portion of the lower secondary flue section  40  is routed through the isolated combustion chamber portion  66  before being passed through a vertical outer wall portion of the combustion chamber for operative connection to the vertical discharge conduit  50 . This shields the portion of the secondary flue passing through the combustion chamber from undesirable exposure to burner heat. 
     The water heater embodiment  10   d  shown in  FIG. 5  is substantially identical to the previously described water heater  10   a  in  FIG. 2  with the exception that the draft inducer fan  52  in  FIG. 1  is removed and replaced with a draft inducer fan  68  disposed on the upper end wall  18  of the tank  12  and having a motor-driven impeller  70  rotatable about a vertical axis  71 . Fan  68  is interposed between the primary and secondary flues  28  and  34  in a manner such that the hot combustion products  56  generated by the burner  42  are sequentially drawn upwardly through the primary flue  28  into the fan  68 , discharged from the fan  68  downwardly through the secondary flue  34  and then flowed into and through the discharge conduit  50 . 
     The water heater embodiment  10   e  shown in  FIG. 6  is substantially identical to the previously described water heater embodiment  10   d  in  FIG. 5  with the exceptions that (1) a vertical dividing wall  64  (similar to the dividing wall  64  shown in  FIG. 4 ) is installed in the combustion chamber  22  to isolate a portion  66  thereof from the burner  42 , and (2) a discharge end portion of the lower secondary flue section  40  is routed through the isolated combustion chamber  66  before being passed through a vertical outer wall portion of the combustion chamber for operative connection to the vertical discharge conduit  50 . 
     The water heater embodiment  10   f  shown in  FIG. 7  is substantially identical to the previously described water heater embodiment  10   e  in  FIG. 6  with the exceptions that (1) the burner  42  in the combustion chamber  22  is isolated from the balance of the combustion chamber by a wall structure  60  similar to the wall structure  60  shown in  FIG. 3 , (2) the lower end of the primary flue  28  is widened as at  62 , (3) the coiled section  40  of the secondary flue is eliminated so that the straight vertical portion  36  thereof continues downwardly through the interior of the tank  12  into the combustion chamber  22  before turning outwardly through a vertical outer wall portion of the combustion chamber  22  for operative connection to the discharge conduit  50 . 
     The water heater embodiments  10   g  and  10   h  respectively shown in  FIGS. 8 and 9  are downflow variants of the previously described water heater  10  in  FIG. 1 . In the downfired water heater embodiment  10   g  shown in  FIG. 8 , a submerged combustion chamber  72  extends downwardly from the upper tank end wall  18  and receives a power fuel burner  74  operative to receive fuel  76  and air  78  and responsively form hot combustion products  56  and force them downwardly through the primary flue  28  which longitudinally extends downwardly from the bottom end of the combustion chamber  72  and into a chamber  82  positioned beneath the lower tank end wall  20 . 
     As shown in  FIG. 8 , the lower end of the primary flue  28  is capped off as at  84 . A vertical dividing structure, generally denoted by the reference numeral  86 , extends through the interior of the primary flue  28  and horizontally divides its interior into two communicating vertical chambers  88  and  90 . The vertical dividing structure  86  carries, at its upper end, a blocking plate  87  which blocks off the upper end of the vertical chamber  90  within the primary flue  28 . The previously described straight vertical portion  36  of the secondary flue is eliminated, with the coiled secondary flue portion  40  being connected at its upper end to the primary flue  28  and extending downwardly through the tank interior, around the exterior of the primary flue  28 , through only about a bottom one third to about a bottom one half of the tank interior. 
     During firing of the water heater  10   g , the hot combustion products  56  created by the power burner  74  are sequentially forced thereby downwardly from the combustion chamber  72  through the vertical chamber  88 , upwardly through the vertical chamber  90  and into the inlet end of the coiled secondary flue portion  40 , downwardly through the coiled flue portion  40 , and then outwardly through the outlet end of the coiled secondary flue portion  40  into and upwardly through the external discharge conduit  50 . 
     The schematically depicted vertical dividing structure  86  is preferably a flue baffle which is configured to horizontally separate the vertical chambers  88 , 90  and also functions to increase the heat transfer from the primary flue  28  to the tank water when hot combustion products  56  are flowed through the primary flue  28 . Alternatively, the dividing structure could simply be a vertical dividing plate. Downfired water heater embodiment  10   h  shown in  FIG. 9  is substantially identical to the downfired water heater embodiment  10   g  shown in  FIG. 8  with the exception that the lower end portion of the coiled secondary flue portion  40  exits the tank through a vertical outer side wall portion thereof and then operatively connects to the vertical discharge conduit  50 . 
     The upfired water heater embodiments  10   i - 10   l  respectively shown in  FIGS. 10-13  are further variants of the previously described upflow water heater embodiment  10  shown in  FIG. 1 . 
     Water heater embodiment  10   i  shown in  FIG. 10  is substantially identical to the water heater embodiment  10   b  shown in  FIG. 3  with the exception that in the water heater embodiment  10   i  the coiled portion  40  of the secondary flue is eliminated, and the vertical straight portion  36  vertically extends downwardly into the combustion chamber  22  and then extends outwardly through a vertical side wall portion of the combustion chamber  22  for connection to the vertical discharge conduit  50 . 
     Water heater embodiment  10   j  shown in  FIG. 11  is substantially identical to the previously described water heater embodiment  10   c  in  FIG. 4  with the exception that in the water heater embodiment  10   j  the coiled portion  40  of the secondary flue is eliminated, and the vertical straight portion  36  vertically extends downwardly into the isolated combustion chamber portion  66  and then extends outwardly through a vertical side wall portion of the combustion chamber portion  66  for connection to the vertical discharge conduit  50 . 
     Water heater embodiment  10   k  shown in  FIG. 12  is substantially identical to the previously described water heater embodiment  10   i  in  FIG. 10  with the exception that the isolating wall structure  60  in  FIG. 10  is removed, and a horizontally widened lower end portion  92  of the primary flue  28  forms a central upstanding pocket portion  94  of the lower tank end wall  20 , the pocket portion  94  having an open bottom end  96  communicating with the underlying balance of the combustion chamber  22 . The fuel burner  42  is received in the pocket area  94  which functions to shield the portion of the secondary flue section  36  extending through the combustion chamber  22  from burner heat. 
     Water heater embodiment  10   l  shown in  FIG. 13  is substantially identical to the previously described water heater embodiment  10   k  shown in  FIG. 12  with the exception that the flue cap  30  shown in  FIG. 12  is removed and replaced with the transfer plenum structure  59  to which the upper end of the secondary flue section  36  is connected as shown in  FIG. 13 . 
     As can be seen from the foregoing, the present invention provides a fuel-fired liquid heating apparatus, representatively in the form of a gas-fired residential type water heater, that provides a high efficiency while at the same time being of a simple construction and which may be manufactured from standard materials and components. For example, the overall combustion product-to-water heat exchange structure may be fabricated from a standard center flue  28 , which is supportingly interconnected between the upper and lower tank end walls  18  and  20 , and a length of smaller diameter flue pipe which may be operatively connected to the center flue during construction of the water heater. More specifically, the secondary flue structure may be connected to the center flue  28  before it is operatively secured within the interior of the tank  12 . The smaller diameter secondary heater exchanger flue pipe may be of a glass-lined metal material similar to that used in the tank portion of the base water heater, and the manufacturing process for the efficiency-augmented may be similar to the manufacturing process utilized in fabricating the base water heater. Thus, a significant enhancement in the efficiency of a basic center flue fuel-fired water heater may be achieved in a simple and relatively inexpensive manner. 
     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.