U.S. patent application number 12/720222 was filed with the patent office on 2010-06-24 for ultra low nox water heater.
Invention is credited to Thomas A. Edds, Michael A. Garrabrant, Gregory A. Ruston, Mingde Song, Garry D. Statzer, Roger D. Veen.
Application Number | 20100154723 12/720222 |
Document ID | / |
Family ID | 38520958 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154723 |
Kind Code |
A1 |
Garrabrant; Michael A. ; et
al. |
June 24, 2010 |
ULTRA LOW NOx WATER HEATER
Abstract
A low NO.sub.x 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 water container, the burner comprising a
plenum chamber having a combustion surface and a fuel/air conduit
adapted to receive fuel and air, and a fuel nozzle positioned to
supply fuel into the fuel/air conduit at an angle that is between
about 1.5.degree. and about 2.5.degree. out of horizontal relative
to a horizontal plane extending along a central axis of the
fuel/air conduit.
Inventors: |
Garrabrant; Michael A.;
(Unicoi, TN) ; Edds; Thomas A.; (Jonesborough,
TN) ; Ruston; Gregory A.; (Elizabethton, TN) ;
Statzer; Garry D.; (Abingdon, VA) ; Veen; Roger
D.; (Johnson City, TN) ; Song; Mingde;
(Johnson City, TN) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Family ID: |
38520958 |
Appl. No.: |
12/720222 |
Filed: |
March 9, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11724828 |
Mar 16, 2007 |
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12720222 |
|
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60783882 |
Mar 20, 2006 |
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Current U.S.
Class: |
122/17.1 |
Current CPC
Class: |
F23M 11/02 20130101;
F23M 2900/11021 20130101; F24H 1/205 20130101 |
Class at
Publication: |
122/17.1 |
International
Class: |
F24H 1/18 20060101
F24H001/18 |
Claims
1. A low NO.sub.x water 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 a fuel nozzle positioned to
supply fuel into the fuel/air conduit at an angle that is between
about 1.5.degree. and about 2.5.degree. out of horizontal relative
to a horizontal plane extending along a central axis of the
fuel/air conduit.
2. The water heater defined in claim 1, wherein the angle is about
2.degree..
3. The water defined in claim 1, wherein an end portion of the
fuel/air conduit extending from the plenum is sealed to a wall
portion of the combustion chamber.
4. The water heater defined in claim 3, wherein the wall portion is
a door sealed to an opening in the combustion chamber.
5. The water heater defined in claim 1, wherein the fuel/air
conduit extends into the plenum a distance of about 3/4 of the
length of the plenum.
6. The water heater defined in claim 5, wherein a distal portion of
the fuel/air conduit extending into the plenum is angled at about
45.degree..
7. The water heater defined in claim 1 wherein the angle is less
than 3% out of horizontal relative to the horizontal plane
extending along the central axis of the fuel/air conduit.
8. The water heater defined in claim 6 wherein a top portion of the
distal portion of the fuel/air conduit extends further into the
plenum than a bottom portion of the distal portion of the fuel-air
conduit.
9. A low NO.sub.x water 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 a fuel nozzle positioned to
supply fuel into the fuel/air conduit at an angle that is greater
than 0.degree. and less than 3.degree. out of horizontal relative
to a horizontal plane extending along a central axis of the
fuel/air conduit.
Description
RELATED APPLICATIONS
[0001] This patent application is a continuation of U.S.
application Ser. No. 11/724,828, filed Mar. 16, 2007, and claims
the benefit of U.S. Provisional Application No. 60/783,882, filed
Mar. 20, 2006, the entire contents of which are incorporated herein
by reference.
TECHNICAL FIELD
[0002] The technology in this disclosure relates to water heaters,
particularly to ultra low NO.sub.x gas-fired water heaters.
BACKGROUND
[0003] Reducing polluting emissions from gas-fired water heaters,
such as NO.sub.x emissions, continues to be an important objective.
Water heater manufacturers have attempted to reduce NO.sub.x
emissions 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.sub.x goal,
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
[0004] 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.
[0005] 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.degree. and about 2.5.degree. out of horizontal relative to a
horizontal plane extending along a central axis of the fuel/air
conduit.
[0006] 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
[0007] 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.
[0008] FIG. 2 is a schematic top plan view of a combustion chamber
of the water heater shown in FIG. 1.
[0009] FIG. 3 is a front elevational view of a combustion chamber
and burner taken from FIG. 1.
[0010] FIG. 4 is a schematic perspective view of a burner taken
from FIG. 1 sealed to a combustion chamber door.
[0011] FIG. 5 is a schematic perspective view of the burner and
door of FIG. 4 connected to a fuel supply line.
[0012] FIG. 6 is a schematic perspective view of a fuel nozzle.
[0013] FIG. 7 is a front elevational view of a venturi.
[0014] FIG. 8 is a side elevational view of the venturi shown in
FIG. 7.
[0015] FIG. 9 is a schematic side elevational view of a burner, a
venturi and a fuel nozzle.
DETAILED DESCRIPTION
[0016] 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.
[0017] Turning now to the drawings generally and FIGS. 1 and 2 in
particular, a water heater 10 is shown. It includes a water
tank/container 12 having a water inlet 14 and a water outlet 16. A
flue 18 extends upwardly through the tank and outwardly from the
top of water heater 10. Tank 12 is surrounded by insulation 20 and
a jacket 21. 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.
[0018] A combustion chamber 22 is located below tank 12 and formed
by tank bottom 24, substantially vertically oriented skirt 26 and
bottom pan 28. Bottom pan 28 sits on legs 30. A burner 32 formed
from a plenum 68 is positioned in combustion chamber 22. Burner 32
is also positioned to receive fuel from fuel line 34, which
connects to gas valve 36, which connects to a fuel supply line 38
connected to a fuel supply that is not shown.
[0019] Burner 32 is positioned within combustion chamber 22 and
above an opening 40 shown in FIG. 2 in bottom pan 28. Burner 32 is
a so-called "low NO.sub.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.sub.x burners
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.
[0020] Opening 40 may be covered with an air inlet/flame trap/flame
arrestor such as an air inlet/flame trap/flame arrestor 42 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 enters combustion chamber 22
through opening 40 and open flame arrestor 42. Although FIG. 2
shows combustion chamber 22 having an opening 40 and open flame
arrestor 42 positioned at a particular location in bottom pan 28,
it is possible to construct water heater 10 such that opening 40
and open flame arrestor 42 have different locations with respect to
combustion chamber 22 and burner 32.
[0021] Fuel line 34 connects to a fuel nozzle 46 fixed to door 44
such that the end of fuel line 34 is held in a selected position by
mounting bracket 31 proximate an opening 48 in the end of a venturi
50. Fuel exits nozzle 46 and flows directly into opening 48. Pilot
fuel line 35 extends between gas valve 36 and a pilot burner (not
shown). Venturi 50 connects directly between plenum 68 and door 44.
Venturi 50 is substantially air-tightly sealed to door 44 and
plenum 68.
[0022] Combustion chamber 22 also contains heat resistant acoustic
absorber 27. Absorber 27 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.RTM.. Other types of acoustically absorbing material may be
used. An adhesive may be employed to adhere absorber 27 to the
interior surface of skirt 26. Also, a metallic backing layer 29 may
be applied to the surface of absorber 27. Backing layer 29 provides
stiffness and further heat resistance.
[0023] In operation, fuel is supplied through nozzle 46 to venturi
50 and ambient combustion air is mixed at opening 48 of venturi 50
and the mixed fuel/air flows into plenum 68 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 of screen 70 in
the usual manner. Primary combustion air is introduced solely
through opening 48 in venturi 50. Secondary air flows through
opening 40 and open flame arrestor 42.
[0024] FIG. 3 shows burner 32 in one possible position relative to
skirt 26 and opening 60 in skirt 26. Burner 32 is sized and shaped
to be removable from combustion chamber 22 through opening 60.
Burner 32 is preferably rectangular in shape and sized slightly
smaller than opening 60, although it need not be so shaped and/or
sized. Door 44 (not shown in FIG. 3) is removably sealed to skirt
26, typically by screws (not shown) which extend through holes 62
in skirt 26.
[0025] Burner 32, including rectangularly-shaped plenum 68, has a
substantially flat or planar bottom 73. Burner 32 has a combustion
surface 70 as shown in FIGS. 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.RTM. screen, most preferably having portions of
the screen formed into reinforcing ribs.
[0026] As previously noted, burner 32 and plenum 68 may have a
construction completely different from that shown in the figures
and may be a shape other than the burner 32 and plenum 68
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.
[0027] Plenum 68 has an opening 72 sized and shaped to receive
venturi 50 in a substantially sealed manner. The length of venturi
50 may be adjusted as desired. A small rib 74 may be manufactured
into the bottom of plenum 68 to provide an attachment point for the
inwardly extending end portion of venturi 50 as shown in FIG. 9.
The inwardly extending end portion of venturi 50 should extend
about three-quarters of the length of plenum 68. As shown in FIG.
9, venturi 50 extends about three-quarters of the length of plenum
68 as shown from the left side to the right side of that figure.
Also, venturi 50 has an angled portion 80 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.degree. angle.
[0028] Venturi 50 has a barrel portion 86 and a substantially
conical portion 82 that extends outwardly from barrel portion 86.
The distal most portion of conical portion 82 has a flange 84 that
is sealed to outer door 44. As better shown in FIGS. 7 and 8,
venturi 50 comprises a barrel portion 86, substantially conical
portion 82, flange 84 and radius portion 88. Utilization of venturi
50 in conjunction with plenum 68 at a length of about
three-quarters of the length of plenum 68 and the angled portion
80, helps facilitate complete combustion to reduce NO.sub.x
emissions.
[0029] Also, referring back to FIG. 9 and in conjunction with FIGS.
1 and 6, a schematic representation of nozzle 46 is shown. Nozzle
46 has a central bore 47 extending from an inlet side 49 to an
outlet side 51. Threads allow fuel nozzle 46 to be sealingly fixed
to fuel supply line 34. FIG. 9 particularly shows a dashed axis "X"
that extends longitudinally through venturi 50 as a center axis. A
dashed line "Y" is angled out of horizontal from axis "X" at angle
.alpha.. Angle .alpha. should be between about 1.5.degree. and
about 2.5.degree., preferably about 2.degree.. Dashed line "Y"
forms the angle at which a central axis extending through nozzle 46
should be tilted out of horizontal to further enhance complete
combustion of fuel emanating from nozzle 46 to further reduce
NO.sub.x emissions. Although we are not entirely sure of the
mechanism behind this phenomenon, we discovered that the normal
horizontal introduction of fuel into venturi 50 does not produce
the same combustion completion efficiency as does the about
1.5.degree.-about 2.5.degree. range. We also discovered that
increasing the angle to as much as 3.degree. results in a
degradation of combustion efficiency back to the horizontal
levels.
[0030] Conventional wisdom has suggested that achieving lowered
levels of NO.sub.x emissions 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.
[0031] 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.
[0032] 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.
[0033] Use of open flame arrestor 42 permits burner 32 to operate
without the noise commonly associated with radiant burners. The
secondary air is also relatively free to flow where needed within
combustion chamber 22 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 on screen 70, 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. The open flame arrestor
42 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 of burner 32. In fact, in normal operating conditions, most
combustion noise is eliminated.
[0034] Open flame arrestor 42 also allows air to travel to the
pilot burner independently of venturi 50. This allows the pilot
burner to remain lit when burner 32 consumes the main source of
air.
[0035] Open flame arrestor 42 also eliminates potential flash back
to nozzle 46 when it becomes slightly air deprived. Burner 32 no
longer seeks air from venturi 50 when abundant air is available on
the other side of the burner screen 70 due to open flame arrestor
42. In fact, extraordinary measures must be induced to force a
flash back. Open flame arrestor 42 also allows condensation
produced in heating cold water to safely drain away from combustion
chamber 22 without affecting combustion performance and minimizing
chamber corrosion over a long period.
[0036] Open flame arrestor 42 also allows water heater 10 to
operate during a flammable vapor incident and coordinate with
burner 32 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.
[0037] Open flame arrestor 42 also allows burner 32 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 as flue 18. 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.
[0038] 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
absorber 27, mounted along skirt 26 inside combustion chamber 22,
has substantially completely eliminated operational acoustics under
all conditions. Absorber 27 is used in conjunction with burner
32/venturi 50/open flame arrestor 42 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. Burner 32 and absorber 27 together
make a very quiet operating system. Sewn E-glass.RTM. is
particularly resistant to heat and is non-respiring during the
lifetime of the material. Metallic backing 29 mounts facing
combustion chamber 22 to add stiffness to the pad and speed the
assembly process. Adhesive may be applied to selected areas of the
metallic backing 29 to assist not only in assembly, but during
shipping. Also, it was found that absorber 27 provided thermal
insulation to chamber 22, thereby enhancing the efficiency and
making surfaces that are normally hot during operation completely
cool to the touch.
[0039] 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.
* * * * *