Note: Descriptions are shown in the official language in which they were submitted.
CA 02582309 2009-12-15
ULTRA LOW NOx WATER HEATER
Technical Field
The technology in this disclosure relates to water heaters, particularly to
ultra low NO,, gas-fired
water heaters.
Background
Reducing polluting emissions from gas-fired water heaters, such as NO,
emissions, continues to
be an important objective. Water heater manufacturers have attempted to reduce
NO,, 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,, 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
Ion-gevity and is
noise free upon either initial ignition of the burner or during continued
combustion of the burner.
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Summary
We provide a water heater including a water container, a combustion chamber
adja-cent 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 posi-tioned 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.
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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 in Fig. 1.
Fig. 3 is a front elevational view of a combustion chamber and burner taken
from Fig. 1.
Fig. 4 is a schematic perspective view of a burner taken from Fig. 1 sealed to
a com-bustion
chamber door.
Fig. 5 is a schematic perspective view of the burner and door of Fig. 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 in Fig. 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 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 maybe made
from a number
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of known foam type insulations and/or fiberglass insulation such as around the
lower portion of
the water heater. Various substitutions may be made.
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.
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 NON" burner which is more spe-
cifically shown
in other Figures and described later herein in detail. It is, however,
possible to utilize other types
of low NO, 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.
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 US Patents
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
dif-ferent
locations with respect to combustion chamber 22 and burner 32.
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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
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door 44. Venturi 50 is substantially air-tightly sealed to door 44 and plenum
68.
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 .
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 sur-
face of absorber 27. Backing layer 29 provides stiffness and further heat
resistance.
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 intro-
duced solely through opening 48 in venturi 50. Secondary air flows through
opening 40 and
open flame arrestor 42.
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.
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Burner 32, including rectangularly-shaped plenum 68, has a substantially flat
or plan-ar 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 screen, most preferably having
portions of the screen
formed into reinforcing ribs.
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 con-
nection with liquid or gaseous fuel, such burners have a combustion surface of
some type where-
in 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 man-
ner, 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.
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 angle.
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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 ven-turi 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,
emissions.
Also, referring back to Fig. 9 and in conjunction with Figs. 1 and 6, a
schematic rep-resentation
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 a.
Angle a 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 through nozzle 46 should be tilted out of
horizontal to further
enhance complete combustion of fuel emanating from nozzle 46 to further reduce
NO1,
emissions. Although we are not entirely sure of the mechanism behind this
phenomenon, we dis-
covered that the normal horizontal introduction of fuel into venturi 50 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,,
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
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CA 02582309 2007-03-20
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 con-
tamination 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 bur-ner. 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 of open flame arrestor 42 permits burner 32 to operate without the noise
com-monly
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
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CA 02582309 2007-03-20
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 com-
bustion. 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 bur-
ner 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 con-
ditions, most combustion noise is eliminated.
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.
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 cham-ber 22
without affecting combustion performance and minimizing chamber corrosion over
a long
period.
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
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much higher rate. This tends to keep the unburned hydrocarbons at a lower
level throughout the
event.
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 per-cent
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 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 oper-
ational acoustics in various conditions. Burner 32 and absorber 27 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 backing 29 mounts facing combustion chamber
22 to add stiff-
ness 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.
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CA 02582309 2007-03-20
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.
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