US20070221142A1 - Ultra low NOx water heater - Google Patents

Abstract

A low NO_xwater heater including a water container; a combustion chamber adjacent the water container having an opening covered with an open flame arrestor; a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, the burner including a plenum chamber having a combustion surface and a fuel/air conduit adapted to receive fuel and air and extending between and sealed to the plenum and a wall of the combustion chamber; and a heat resistant acoustic absorber positioned on the wall.

Description

RELATED APPLICATION
• This patent application claims the benefit of U.S. Provisional Application No. 60/783,882, filed Mar. 20, 2006. This earlier provisional application is hereby incorporated by reference.
TECHNICAL FIELD
• The technology in this disclosure relates to water heaters, particularly to ultra low NO_xgas-fired water heaters.
BACKGROUND
• Reducing polluting emissions from gas-fired water heaters, such as NO_xemissions, continues to be an important objective. Water heater manufacturers have attempted to reduce NO_xemissions through a variety of approaches, one approach utilizing radiant screen-type burners. However, there have been issues associated with simultaneously achieving: 1) the low NO_xgoal, 2) providing a water heater that is resistant to build up of lint, dirt, oils and the like or that can shut itself off when too much of a build-up occurs, 3) manufacture of a gas-fired water heater in an economical fashion and 4) producing a water heater that is safe, has excellent longevity and is noise free upon either initial ignition of the burner or during continued combustion of the burner.
SUMMARY
• We provide a water heater including a water container, a combustion chamber adjacent the water container having an opening covered with a flame arrestor, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, the burner including a plenum chamber having a combustion surface and a fuel/air conduit adapted to receive fuel and air and extending between and sealed to the plenum and a wall of the combustion chamber, and a heat resistant acoustic absorber positioned on the wall.
• We also provide a water heater including a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber and arranged to combust fuel to heat water in said water container, the burner having a combustion surface and a fuel/air conduit extending from the plenum and adapted to receive fuel, and a fuel nozzle positioned to supply fuel into the fuel/air conduit at an angle that is between about 1.5° and about 2.5° out of horizontal relative to a horizontal plane extending along a central axis of the fuel/air conduit.
• We further provide a water heater including a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the container, the burner having a combustion surface and adapted to receive fuel, and a fuel/air conduit sealed between a wall portion of the combustion chamber and the plenum, wherein an end portion of the conduit adjacent the wall portion is substantially conically shaped.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic partial sectional view of a water heater which emphasizes selected features of the water heater proximate the combustion chamber and omits others for ease of understanding.
• FIG. 2 is a schematic top plan view of a combustion chamber of the water heater shown inFIG. 1.
• FIG. 3 is a front elevational view of a combustion chamber and burner taken fromFIG. 1.
• FIG. 4 is a schematic perspective view of a burner taken fromFIG. 1 sealed to a combustion chamber door.
• FIG. 5 is a schematic perspective view of the burner and door ofFIG. 4 connected to a fuel supply line.
• FIG. 6 is a schematic perspective view of a fuel nozzle.
• FIG. 7 is a front elevational view of a venturi.
• FIG. 8 is a side elevational view of the venturi shown inFIG. 7.
• FIG. 9 is a schematic side elevational view of a burner, a venturi and a fuel nozzle.
DETAILED DESCRIPTION
• It will be appreciated that the following description is intended to refer to specific aspects of the structure selected for illustration in the drawings and is not intended to define or limit the disclosure, other than in the appended claims.
• Turning now to the drawings generally andFIGS. 1 and 2 in particular, awater heater10 is shown. It includes a water tank/container12 having a water inlet14 and awater outlet16. Aflue18 extends upwardly through the tank and outwardly from the top ofwater heater10.Tank12 is surrounded byinsulation20 and ajacket21. Such insulation may be made from a number of known foam type insulations and/or fiberglass insulation such as around the lower portion of the water heater. Various substitutions may be made.
• Acombustion chamber22 is located belowtank12 and formed bytank bottom24, substantially vertically orientedskirt26 andbottom pan28.Bottom pan28 sits on legs30. Aburner32 formed from aplenum68 is positioned incombustion chamber22. Burner32 is also positioned to receive fuel fromfuel line34, which connects togas valve36, which connects to afuel supply line38 connected to a fuel supply that is not shown.
• Burner32 is positioned withincombustion chamber22 and above anopening40 shown inFIG. 2 inbottom pan28.Burner32 is a so-called “low NO_x” burner which is more specifically shown in other Figures and described later herein in detail. It is, however, possible to utilize other types of low NO_xburners having different sizes, shapes and modes of combustion in accordance with selected aspects of this disclosure. Other such burners are known and need not be discussed herein.
• Opening40 may be covered with an air inlet/flame trap/flame arrestor such as an air inlet/flame trap/flame arrestor42 of the type as disclosed in any of U.S. Pat. Nos. 5,797,355; 6,142,106; 6,085,699 or the like, for example. However and in any event, the flame arrestor should have about 30% or more open surface area. Such flame arrestors will hereinafter be referred to as an “open flame arrestor.” Combustion air enterscombustion chamber22 through opening40 andopen flame arrestor42. AlthoughFIG. 2 showscombustion chamber22 having an opening40 andopen flame arrestor42 positioned at a particular location inbottom pan28, it is possible to constructwater heater10 such that opening40 andopen flame arrestor42 have different locations with respect tocombustion chamber22 andburner32.
• Fuel line34 connects to afuel nozzle46 fixed todoor44 such that the end offuel line34 is held in a selected position by mountingbracket31 proximate anopening48 in the end of aventuri50.Fuel exits nozzle46 and flows directly intoopening48.Pilot fuel line35 extends betweengas valve36 and a pilot burner (not shown). Venturi50 connects directly betweenplenum68 anddoor44. Venturi50 is substantially air-tightly sealed todoor44 andplenum68.
• Combustion chamber22 also contains heat resistantacoustic absorber27. Absorber27 is substantially a belt of heat resistant acoustic absorption-type material. It is preferably made of fiberglass. One example of a suitable absorber material is Sewn E-glass®. Other types of acoustically absorbing material may be used. An adhesive may be employed to adhere absorber27 to the interior surface ofskirt26. Also, ametallic backing layer29 may be applied to the surface of absorber27.Backing layer29 provides stiffness and further heat resistance.
• In operation, fuel is supplied throughnozzle46 toventuri50 and ambient combustion air is mixed at opening48 ofventuri50 and the mixed fuel/air flows intoplenum68 and may further be mixed and distributed by a type of diffuser if desired. The air and fuel mixture is then combusted along the surface ofscreen70 in the usual manner. Primary combustion air is introduced solely through opening48 inventuri50. Secondary air flows through opening40 andopen flame arrestor42.
• FIG. 3shows burner32 in one possible position relative toskirt26 and opening60 inskirt26.Burner32 is sized and shaped to be removable fromcombustion chamber22 throughopening60.Burner32 is preferably rectangular in shape and sized slightly smaller than opening60, although it need not be so shaped and/or sized. Door44 (not shown inFIG. 3) is removably sealed to skirt26, typically by screws (not shown) which extend throughholes62 inskirt26.
• Burner32, including rectangularly-shapedplenum68, has a substantially flat or planar bottom73.Burner32 has acombustion surface70 as shown inFIGS. 4 and 5 which is most preferably in a curved configuration although any shape, including flat or substantially flat, is possible. The surface is porous and preferably Inconel® screen, most preferably having portions of the screen formed into reinforcing ribs.
• As previously noted,burner32 andplenum68 may have a construction completely different from that shown in the figures and may be a shape other than theburner32 andplenum68 illustrated herein. In any event, in essentially all burners and plenums suitable for use in connection with liquid or gaseous fuel, such burners have a combustion surface of some type wherein a multiplicity of ports are present on the surface itself or are located at or around the edge of that surface that permit egress of fuel and/or combustion air for formation of a flame adjacent such multiple holes or ports. Those ports/holes are typically arranged in a generally planar manner, typically in a generally horizontal orientation. Nonetheless, such burners and plenums may be utilized in accordance with this disclosure and fall within the scope of the appended claims.
• Plenum68 has anopening72 sized and shaped to receiveventuri50 in a substantially sealed manner. The length ofventuri50 may be adjusted as desired. A small rib74 may be manufactured into the bottom ofplenum68 to provide an attachment point for the inwardly extending end portion ofventuri50 as shown inFIG. 9. The inwardly extending end portion ofventuri50 should extend about three-quarters of the length ofplenum68. As shown inFIG. 9,venturi50 extends about three-quarters of the length ofplenum68 as shown from the left side to the right side of that figure. Also,venturi50 has an angledportion80 at its distal end. The top portion of the venturi extends the furthest to the right side with the bottom portion of the venturi extending less far. Angled portion is formed at about a 45° angle.
• Venturi50 has abarrel portion86 and a substantiallyconical portion82 that extends outwardly frombarrel portion86. The distal most portion ofconical portion82 has aflange84 that is sealed toouter door44. As better shown inFIGS. 7 and 8,venturi50 comprises abarrel portion86, substantiallyconical portion82,flange84 andradius portion88. Utilization ofventuri50 in conjunction withplenum68 at a length of about three-quarters of the length ofplenum68 and theangled portion80, helps facilitate complete combustion to reduce NO_xemissions.
• Also, referring back toFIG. 9 and in conjunction withFIGS. 1 and 6, a schematic representation ofnozzle46 is shown.Nozzle46 has acentral bore47 extending from aninlet side49 to anoutlet side51. Threads allowfuel nozzle46 to be sealingly fixed tofuel supply line34.FIG. 9 particularly shows a dashed axis “X” that extends longitudinally throughventuri50 as a center axis. A dashed line “Y” is angled out of horizontal from axis “X” at angle α. Angle α should be between about 1.5° and about 2.5°, preferably about 2°. Dashed line “Y” forms the angle at which a central axis extending throughnozzle46 should be tilted out of horizontal to further enhance complete combustion of fuel emanating fromnozzle46 to further reduce NO_xemissions. Although we are not entirely sure of the mechanism behind this phenomenon, we discovered that the normal horizontal introduction of fuel intoventuri50 does not produce the same combustion completion efficiency as does the about 1.5°-about 2.5° range. We also discovered that increasing the angle to as much as 3% results in degradation of combustion efficiency back to the horizontal levels.
• Conventional wisdom has suggested that achieving lowered levels of NO_xemissions for radiant screen burners necessitates that the combustion air and fuel should be primarily pre-mixed and passed through the venturi. This required that a flammable vapor arrestor located in the bottom of the combustion chamber be blocked off or only very small amounts of secondary air be allowed in the chamber through small, tightly controlled areas or flapper doors. However, such arrangements exhibited unacceptable start-up (rumbling) and operational noise (100+ dB scream) due to a standing wave forming in the combustion chamber and passing up the flue. Additionally, burners in such arrangements were subject to flash back and pilot burner outages occurring due to the main burner starving the pilot burner for air. Also, the burner tended to be potentially affected by lint, dust and oil contamination under certain particular circumstances. This was indicated by the system producing higher levels of CO at relatively low levels of contamination due to incomplete combustion while lacking secondary air.
• We found that, by using an open flame arrestor, the start up rumble was eliminated and operational noise reduced. An open flame arrestor is a flammable vapor resistant structure that has about 30 percent or more of the available burner surface as open area. It was found that less than about 30 percent compromises both the acoustic levels and resilience to resist flash back. We also found that the pilot burner was also relatively unaffected by burner operation since it was easily able to draw sufficient secondary air through such a large volume opening.
• We also discovered that improving air flow characteristics of the burner to allow for an adequate amount of primary air is helpful. Previously, burners had enough air flow restriction within their mixing bodies that additional draft was needed to overcome such restriction. We minimized internal burner restriction and vastly improved internal flow characteristics of the burner. This allows full exposure to secondary air while continuing to introduce adequate amounts of primary air, thus allowing the use of a open flame arrestor.
• Use ofopen flame arrestor42permits burner32 to operate without the noise commonly associated with radiant burners. The secondary air is also relatively free to flow where needed withincombustion chamber22 to aid in more complete combustion. This feature makes the water heater much more resilient to lint, dirt and oil contamination. When burner ports begin to clog from dirt accumulating onscreen70, this reduces the amount of fuel/air mixture that can flow through the ports, which usually reduces the amount of air available to complete combustion. With secondary air present on the other side of the burner screen surface, this reduction of air is compensated for and complete combustion occurs. This provides a distinct advantage over systems that only can allow a small amount of secondary air to enter. Theopen flame arrestor42 deals with the problem of start up rumble, which is caused by the initial ignition pressure wave pulse, because it is allowed to escape the chamber. It also aids in keeping the burner contaminant resistant by shocking surface build up and slowing total contaminant build up. It also reduces the high-pitched operation noises ofburner32. In fact, in normal operating conditions, most combustion noise is eliminated.
• Open flame arrestor42 also allows air to travel to the pilot burner independently ofventuri50. This allows the pilot burner to remain lit whenburner32 consumes the main source of air.
• Open flame arrestor42 also eliminates potential flash back tonozzle46 when it becomes slightly air deprived.Burner32 no longer seeks air fromventuri50 when abundant air is available on the other side of theburner screen70 due toopen flame arrestor42. In fact, extraordinary measures must be induced to force a flash back.Open flame arrestor42 also allows condensation produced in heating cold water to safely drain away fromcombustion chamber22 without affecting combustion performance and minimizing chamber corrosion over a long period.
• Open flame arrestor42 also allowswater heater10 to operate during a flammable vapor incident and coordinate withburner32 to combust the flammable vapors present in the incoming air at a much higher rate. This tends to keep the unburned hydrocarbons at a lower level throughout the event.
• Open flame arrestor42 also allowsburner32 to operate in a mode more compatible with basic water heater design because it provides more convection heat transfer by allowing greater airflow. This helps in transferring heat to surfaces not exposed directly to the infrared radiation, such asflue18. Water heaters are designed to have a great deal of the heat transfer occur through convection. We found that this system flows between about 10 and about 20 percent more air than a conventional water heater of the same size and BTU input while having comparable or less exhaust outlet temperatures.
• We discovered that, while the above-mentioned system eliminated operational noise during normally encountered conditions, a small and barely audible tone may be induced in unpredictable conditions. We found that a heat resistant,acoustic absorber27, mounted alongskirt26 insidecombustion chamber22, has substantially completely eliminated operational acoustics under all conditions.Absorber27 is used in conjunction withburner32/venturi50/open flame arrestor42 to be substantially completely noise free. Acoustic pads tested in closed chamber systems did not address start up rumble and did not completely address operational acoustics in various conditions.Burner32 andabsorber27 together make a very quiet operating system. Sewn E-glass® is particularly resistant to heat and is non-respiring during the lifetime of the material.Metallic backing29 mounts facingcombustion chamber22 to add stiffness to the pad and speed the assembly process. Adhesive may be applied to selected areas of themetallic backing29 to assist not only in assembly, but during shipping. Also, it was found thatabsorber27 provided thermal insulation tochamber22, thereby enhancing the efficiency and making surfaces that are normally hot during operation completely cool to the touch.
• Although this disclosure has been described in connection with specific forms of water heaters and associated components, it will be appreciated that a wide variety of equivalents may be substituted for the elements described herein without departing from the spirit and scope of this disclosure as described in the appended claims.

Claims (23)

1. A low NO_xwater heater comprising:

a water container;

a combustion chamber adjacent the water container having an opening covered with an open flame arrestor;

a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, the burner comprising a plenum chamber having a combustion surface and a fuel/air conduit adapted to receive fuel and air and extending between and sealed to the plenum and a wall of the combustion chamber; and

a heat resistant acoustic absorber positioned on the wall.

2. The water heater defined inclaim 1, wherein the wall is substantially vertically oriented and the absorber is adhered to the wall.

3. The water heater defined inclaim 2, wherein the absorber extends vertically between a bottom portion of the water container and a bottom portion of the water heater.

4. The water heater defined inclaim 1, wherein the absorber is an insulation pad.

5. The water heater defined inclaim 1, wherein the absorber comprises fiberglass.

6. The water heater defined inclaim 1, further comprising a metallic backing layer applied to the absorber.

7. A low NO_xwater heater comprising:

a water container;

a combustion chamber adjacent the water container;

a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, the burner having a combustion surface and a fuel/air conduit extending from the plenum and adapted to receive fuel; and

a fuel nozzle positioned to supply fuel into the fuel/air conduit at an angle that is between about 1.5° and about 2.5° out of horizontal relative to a horizontal plane extending along a central axis of the fuel/air conduit.

8. The water heater defined inclaim 7, wherein the angle is about 2°.

9. The water defined inclaim 7, wherein an end portion of the fuel/air conduit extending from the plenum is sealed to a wall portion of the combustion chamber.

10. The water heater defined inclaim 9, wherein the wall portion is a door sealed to an opening in the combustion chamber.

11. The water heater defined inclaim 7, wherein the fuel/air conduit extends into the plenum a distance of about ¾ of the length of the plenum.

12. The water heater defined inclaim 11, wherein a distal portion of the fuel/air conduit extending into the plenum is angled at about 45°.

13. A low NO_xwater heater comprising:

a water container;

a combustion chamber adjacent the water container having an opening covered with an open flame arrestor;

a burner associated with the combustion chamber and arranged to combust fuel to heat water in the container, the burner having a combustion surface and adapted to receive fuel; and

a fuel/air conduit sealed between a wall portion of the combustion chamber and the plenum, wherein an end portion of the conduit adjacent the wall portion is substantially conically shaped.

14. The water heater defined inclaim 13, wherein the end portion further comprises a flange connected to the conically shaped portion and the flange is located exteriorly of the wall portion and is sealed to the wall portion.

15. The water defined inclaim 13, wherein the wall portion is a door sealed to an opening in the combustion chamber.

16. The water heater defined inclaim 13, wherein the fuel/air conduit extends into the plenum a distance of about ¾ of the length of the plenum.

17. The water heater defined inclaim 13, wherein a distal portion of the fuel/air conduit extending into the plenum is angled at about 45°.

18. A low NO_xwater heater comprising:

a water container;

a combustion chamber adjacent the water container;

a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, the burner comprising a plenum chamber having a combustion surface and a fuel/air conduit adapted to receive fuel and air and extending between and sealed to the plenum and a wall of the combustion chamber; and

a heat resistant acoustic absorber positioned on the wall.

19. The water heater defined inclaim 18, wherein the wall is substantially vertically oriented and the absorber is adhered to the wall.

20. The water heater defined inclaim 19, wherein the absorber extends vertically between a bottom portion of the water container and a bottom portion of the water heater.

21. The water heater defined inclaim 18, wherein the absorber is an insulation pad.

22. The water heater defined inclaim 18, wherein the absorber comprises fiberglass.

23. The water heater defined inclaim 18, further comprising a metallic backing layer applied to the absorber.

Images