Note: Descriptions are shown in the official language in which they were submitted.
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CONTROL SYSTEM FOR BURNER
RELATED APPLICATIONS
[0001] This application clams priority from U.S. Provisional Application
Serial No.
62/460,166, filed 17 February 2017, which is incorporated herein in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a furnace controller and, more
specifically, relates
to a system for controlling mass flow and noise in a furnace having an inducer
blower.
BACKGROUND
[0003] All combustion systems have a means of controlling the ratio of the
fuel and
combustion air flows in such a way as to achieve the desired combustion
results. In residential
furnaces, the simplest method is the use of a servo-controlled gas valve
regulating the manifold
pressure upstream of a fixed orifice, coupled with an orifice controlling the
air delivered from a
fixed-speed combustion air blower. This method is very cost-efficient and
provides sufficient
control for the typical use of in-shot burners, with which variations in the
mass flows of the fuel
and combustion air is tolerated in varying field settings.
[0004] These control systems became more sophisticated with the advent of
modulating
input appliances, where the input rate through the appliance is varied to meet
the heating demand
of the structure. In these systems, the air and fuel must be modulated
simultaneously to maintain
the desired combustion characteristics throughout the modulated range. To meet
these
requirements, the development of controls and algorithms have emerged to
include modulating
gas valves, variable speed combustion blower motors, pressure and mass flow
sensors. In North
America, these systems have been developed to support the furnace industry
with primary focus
on induced draft, in-shot burner configurations applied to indirect, forced
air heating
applications.
[0005] With the passing of codes requiring NO, emissions in the 10¨ 12 ppm
range, the
traditional in-shot burners, which have served the industry so well for so
many years, are no
longer capable of meeting the newly regulated combustion requirements. To
achieve these
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"ultra-low NO," (ULN) emission standards, the industry has moved to pre-mixed
burners that
are capable of meeting the standards. Pre-mixed burners are nothing new, as
they have been used
for many years in applications including residential hot water boilers.
[0006] However, the application of pre-mixed burners in North America for
residential
warm air furnaces must be designed differently than those used in boilers and
other applications.
The North American furnace market demands that the flue side of the heat
exchanger be
maintained at a negative pressure with respect to the air side of the system.
This is a legacy
design requirement to insure that if there is a heat exchanger failure, the
possibility is reduced of
combustion products, including deadly carbon monoxide, entering the living
space via the
circulating air in the distribution ductwork. Therefore, premixed burners in
residential furnaces
are configured to be induced draft to meet this legacy requirement. This
presents an engineering
challenge due to the characteristics of the burner and combustion air blower,
the available means
to control these devices, and the cost-sensitive nature of the market.
[0007] As compared to an in-shot burner, which is very forgiving to
variations in the
air/gas mixture in which it operates, the pre-mixed burner operates properly
under much tighter
air/fuel ratios. If the pre-mixed burner is running too rich, it cannot
achieve the combustion
performance required. If it runs too lean, the flame can become unstable and
lift from the burner.
[0008] This not normally a problem when the burner is applied in a power
burner
application because the combustion air is entering the blower upstream of the
burner and
therefore at predictable and somewhat stable conditions with respect to
temperature, density and
composition. But in an induced draft system, the combustion blower is
downstream of the burner
and combustion chamber, thereby seeing significant changes in flue gas
temperatures and
composition, which results in density and mass flow changes.
[0009] Moreover, in induced-draft systems for pre-mixed burners, the heat
exchangers
normally used in residential furnaces are of a tubular design that provide the
conduit for the
products of combustion and provide the heat exchanger surface for heat
transfer. As a result,
each pipe is capable of generating specific audible tones at specific
frequencies and at specific
mass flow rates. Some of these resonant frequencies occur during operational
conditions and
produce undesirable noise levels.
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[0010] Typically, "soft start" strategies are used wherein the burner is
ignited at a
reduced rate and then, once the system has warmed up and stabilized, the rate
is increased to a
desired level. This approach, however, requires the burner system to be
capable of modulating
the operating rate ¨ normally both combustion air and fuel ¨ in such a way
that maintains a
relatively constant air/fuel ratio. This undesirably adds to the level of
complexity and cost in that
such systems need a modulating gas valve, a modulating combustion air blower
motor, and a
complex control to control these elements accordingly.
SUMMARY
[0011] In one embodiment of the present invention, a method of controlling
operation of
a furnace having a pre-mixed burner, a heat exchanger, and an inducer blower
downstream of the
heat exchanger includes monitoring a pressure drop across the heat exchanger.
The speed of the
inducer blower is controlled in response to the monitored pressure drop to
thereby control mass
flow through the furnace.
[0012] Another embodiment of the present invention includes a control
system for a
furnace having a pre-mixed burner, a heat exchanger, and an inducer blower
downstream of the
heat exchanger. The control system includes a sensor for measuring one of
pressure and mass
flow through the heat exchanger. A controller is connected to the sensor and
the inducer blower
and controls the speed of the inducer blower in response to receiving a signal
from the sensor
indicative of the pressure or mass flow.
[0013] In yet another embodiment a method of reducing noise in a furnace
includes
determining a resonant frequency of heat exchanger tubes in the furnace and
controlling the mass
flow of combustion products into the heat exchanger such that the combustion
products have a
different resonant frequency than the heat exchanger tubes.
[0014] Other objects and advantages and a fuller understanding of the
invention will be
had from the following detailed description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Fig. 1 is a schematic illustration of a furnace including a control
system of the
present invention.
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[0016] Fig. 2 is another schematic illustration of the control system of
Fig. 1.
[0017] Fig. 3 is a front view of a burner in accordance with an embodiment
of the present
invention;
[0018] Fig. 4 is a front view of a distributor for producing multiple
flame outputs for the
burner of Fig. 1;
[0019] Fig. 5 an exploded view of a furnace constructed in accordance with
one
embodiment of the invention;
[0020] Fig. 6 is a side view of the furnace of Fig. 5 with the side panel
removed;
[0021] Fig. 7 is an isometric view of cabinet portions of the furnace
shown in Fig. 5; and
[0022] Fig. 8 is an isometric view of an alternative burner in accordance
with an aspect
of the invention.
DETAILED DESCRIPTION
[0023] The present invention relates to a furnace controller and, more
specifically, relates
to a system for controlling mass flow and noise in a furnace having an inducer
blower. The
inducer blower runs at a reduced speed during the ignition cycle to control
the air flow through
the burner for a smooth, consistent light-off. The speed control can be
achieved by wave-
chopping the input voltage to the inducer blower motor while maintaining a
target pressure
feedback signal from a sensor. Once flame is established, the inducer speed is
increased to
deliver the proper amount of combustion air for the duration of the heating
cycle. The inducer
blower is therefore modulated to maintain a constant pressure setpoint, which
relates closely to
mass flow, as determined by the functional needs of the furnace.
[0024] Figs. 1-2 illustrate a furnace 10 including an example control
system 12 in
accordance with the present invention. The control system 12 can be configured
to operate with
any furnaces having a capacity of from about 40,000 ¨ 140,000 Btu/H. The
control system 12
can be used with a natural gas furnace 10 or a liquid propane furnace. One
example furnace 10
for use with the control system 12 is shown and described in U.S. Patent
Publication No.
2015/0369495, filed July 24, 2015, the entirety of which is incorporated by
reference herein. The
furnace 10 can be a mid- or high efficiency residential furnace.
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[0025] The furnace 10 includes a pre-mix burner 20, e.g., an ULN, pre-mix
burner. The
burner 20 is considered pre-mix because the combustion air and fuel are pre-
mixed upstream of
the burner. To this end, an air supply (shown schematically at 30) provides
air from outside the
furnace to a mixer 34. A single stage gas valve 40 supplies fuel, e.g., gas,
to the mixer 34 at a
constant flow rate. Alternatively, the gas valve 40 can be a modulating or
multi-stage gas valve
(not shown). The choice in gas valves 40 can be dictated by the type of
furnace 10. For example,
a single stage gas valve 40 can be used for the basic, most economical
furnace. A two stage or
modulating gas valve 40 can be used for more costly, feature-rich furnaces.
Limit
switches 42, 44 are provided in series with the gas valve 40 and close the gas
valve in response
to the supply air exceeding a prescribed temperature a predetermined number of
times.
[0026] The mixer 34 delivers the pre-mixed air/fuel mixture to the burner
20, where it is
ignited by an igniter 50. The igniter 50 can be a hot surface igniter that
changes temperature
based on the voltage, e.g., about 0 to 120VAC, applied thereto. A flame sensor
52 is used as a
flame-proving device.
[0027] Once the pre-mixed mixture is ignited, heated combustion products
exit the
burner 20 and flow into a heat exchanger 60. The heat exchanger 60 can include
a series of
serpentine tubes with indentations or dimples along their lengths (not shown).
A blower 62
blows air across the heat exchanger 60 such that the high temperature
combustion/flue products
heat the blown air. The blower 62 is driven by a motor 64. The motor 64 can be
a multi-speed,
permanent split capacitor (PSC) motor. As shown, the motor 64 is a four speed
PSC motor that
runs at different spends depending on whether the blower 62 is providing
heating or cooling.
[0028] An inducer blower 70 located downstream of the heat exchanger 60
and in fluid
communication with the interior of the heat exchanger tubes draws in
combustion products from
the heat exchanger and delivers them to a vent 72 to be exhausted from the
furnace 10. The
inducer blower 70 can have a forward curved construction and is configured for
variable capacity
operation. To this end, the inducer blower 70 can driven by a motor 74, e.g.,
shaded pole PSC
motor driven with a wave-chopped control signal.
[0029] In another example, the motor 74 can be an electronically
commutated motor
(ECM) driven through a serial communications bus or pulse width modulation
(PWM) control
signal. In another example, a mechanical damper (not shown) can be installed
at the inlet or
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outlet of the inducer blower 70 to vary the flow therethrough. Alternatively,
the motor 74 can be
a variable speed motor (not shown).
[0030] A sensor 80 extends into the heat exchanger 60 and monitors the air
pressure of a
designated/predetermined control volume therein. The sensor 80 can be a mass
flow sensor,
pressure sensor, pressure transducer or other device capable of outputting a
usable/useful signal
indicative of conditions within the heat exchanger 60.
[0031] A controller 90 is connected to the blower motor 64, the gas valve
40, the inducer
blower motor 74, and the sensor 80 for actively controlling one or more of the
gas valve 40 and
blowers 62, 70. The controller 90 has a circuit for receiving signals from the
sensor 80 that can
include a high frequency noise filter and an analog-to-digital converter (not
shown). The
controller 90 can be integrated into the main controller of the furnace 10 or
be a stand-alone
controller integrated into the furnace control via serial communications
interface, digital or
analog control signal.
[0032] In a normal operating cycle of the burner 20, the inducer blower 70
initially
moves ambient air at about 25 C through the burner and heat exchanger 60
prior to the ignition
process. Immediately after ignition, the inducer blower 70 transitions to
moving a mixture of flue
products of steadily increasing temperature through the burner 20 and heat
exchanger 60.
Finally, during a steady-state operating period of the burner 20, the inducer
blower 70 will move
a steady flow of flue products in excess of 120 C through the burner 20 and
heat exchanger 60.
[0033] The inducer blower 70 is a constant volume device. Consequently,
the mass flow
variations of the combustion air coming into the burner 20 due to the changing
temperature and
composition of the flue gases at the inducer blower 70 can be significant.
Potential issues that
result from such mass flow variations range from noisy ignitions. failed
ignitions, unstable
burner operation resulting in continued noisy operation, and/or failure to
meet the required
combustion performance levels (high NON).
[0034] To combat these issues, the control system 12 utilizes the
controller 90 to adjust
the inducer blower 70 speed in response to changing system
parameters/conditions. To this end,
the sensor 80 sends a signal to the controller 90 indicative of the magnitude
and direction of the
parameter changes. In particular, the sensor 80 continuously measures a
pressure drop across the
control volume of the heat exchanger 60 and delivers a proportional signal to
the controller 90
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based on the measured pressure drop. The pressure drop is indicative of the
mass flow of air
and/or flue products through the control volume in the heat exchanger 60. The
sensor 80
continuously sends signals to the controller 90 which, in response thereto,
varies the speed of the
inducer blower 70 to stabilize the combustion process and thereby meet desired
performance
results.
[0035] Instead of using a traditional variable speed motor to control the
inducer
blower 70, the controller 90 of the present invention instead relies on a
single speed motor 74
and can use wave chopping to vary the speed thereof. In one example, the motor
74 speed is
controlled with a zero-cross wave chopping circuit on the controller 90.
Regardless of the wave-
chopping method used, the controller 90 cooperates with the sensor 80 to form
a pressure
feedback control loop in order to maintain the motor 74 at a desired speed. As
a result, the
desired mass flow rate through the burner 20 and heat exchanger 60 can be
maintained for a
particular operating condition. The feedback loop also makes the control
system 12 self-adapting
to varying field conditions, such as the vent 72 length/configuration or vent
system blockage, to
maintain the target mass flow rate regardless of these or any other
variations.
[0036] The control system 12 is an integrated furnace control which
integrates the
operation of all functions desirable to operate the furnace 10. These
functions include, but are not
limited to, sequencing; ignition control; safety functions; control of the gas
valve, inducer motor,
and blower motor. With this in mind, in the development/calibration process of
the furnace 10,
the pressure drop through the heat exchanger 60 control volume detected by the
sensor 80 is
mapped to the mass flow of the air and/or flue products flowing through the
system. This signal
naturally compensates for temperature variations and composition flowing
through the heat
exchanger 60. Also, the optimum combustion air flow for consistent, quiet
light-off of the pre-
mixed burner 20 is identified empirically, recorded, and stored in flash
memory of the control
system 12 for future use. This light-off setting may or may not provide the
same stoichiometric
mixture used for steady-state operation, as the burner 20 may prefer a richer
or leaner mixture for
the most robust light-off.
[0037] In the same way, the optimum steady-state operating condition is
noted for stable
operation and desired combustion performance once the burner 20 has been
ignited and
sufficiently warmed for continuous operation. All of these parameters, along
with related
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timings, are recorded and stored in the non-volatile memory of a
microprocessor in the control
system 12.
[0038] In the case of a single-stage furnace, the gas valve 40 is either
energized or de-
energized, and supplies a constant heat input to the heat exchanger 60 when
energized. During
development, the inducer blower 70 timing settings for pre-purge, post-purge,
and warm-up
cycles of the furnace 10 are also defined based on desired pressure settings
within the heat
exchanger 60 according to the table below. The actual settings can be in
accordance with ANSI
standard Z21.20, another ANSI standard or have non-ANSI standard values.
State Pressure Setting (in.w.c.)
Time (examples in seconds)_
Pre-purge P1 Ti (1.0)
Ignitor Warm-up P2 T2
Ignition P3 T3
Flame Stabilization Period P4 T4 (.45)
Run P5
Until heating call is satisfied (1.0)
Post-purge P6 T6 (1.0)
Inter-Purge P7 T7 (1.0)
[0039] In this example, when the furnace 10 receives a call for heat,
typically from a
thermostat 76 in the living space, the controller 90 energizes the inducer
blower 70 for the pre-
purge cycle and selects the blower speed such that the sensor 80 returns a
signal correlating to
the system pressure drop of P1. The inducer blower 70 is maintained in this
state for duration Ti.
The pre-purge cycle is intended to allow for the dissipation of any unburned
gas or residual
products of combustion at the beginning of the furnace 10 operating cycle
prior to initiating
ignition.
[0040] After the pre-purge time Ti, the controller 90 energizes the
igniter 50 for a warm-
up period and adjusts the inducer blower 70 speed such that the sensor 80
returns a signal
correlating to the system pressure drop of P2. The igniter 50 is warmed up
prior to initiating gas
flow, and includes both a period of time in which the voltage to the igniter
is ramped from 0 to
120 VAC and a period of time in which the voltage is maintained at a constant
120 VAC.
[0041] Once the igniter 50 is sufficiently heated, the controller 90
adjusts the inducer
blower 70 to reach a sensor 80 feedback of P3. When this occurs, the
controller 90 opens the gas
valve 40 for duration T3 to allow the pre-mixed mixture to flow from the mixer
34 to the
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burner 20. Since the igniter 50 is already sufficiently heated, the flowing
pre-mixed mixture is
ignited by the igniter. The flame sensor 52 sends a signal to the controller
90 to confirm
successful ignition. The period of time allowed for the ignition of the main
burners in the
burner 20 [during which the igniter 50 is energized and the gas valve 40 open]
is known as the
trial for ignition, and is built into the time T2 and/or T3.
[0042] The inducer blower 70 is adjusted again to achieve a sensor 80
pressure of P4 and
maintained for duration T4 to stabilize the flame. The flame stabilization
period T4 is the time
permitted, after successful ignition, for the main burner flame to stabilize
before entering the
"Run" state.
[0043] It should be noted that during operation of the burner 20 from this
point forward,
the temperature will vary at the induced draft blower 70, which would normally
cause
unacceptable fluctuations in the mass flow through the burner 20. Due to the
control system 12,
however, the sensor 80 detects these variances as increased or decreased
pressure drop across the
control volume and reports these variations to the controller 90. In response,
the controller 90
increases or decreases the inducer blower 70 speed to maintain a constant
pressure drop reading
at the sensor 80. It is this response that allows the system 12 to maintain
the desired mass flow
through the burner 20.
[0044] At this point in the process, a stable flame is established on the
surface of the
burner 20 and the system is set to the "Run" pressure setting P5 for the
duration of the heating
cycle. Once the thermostat 76 is satisfied and the call for heat is removed by
the controller 90,
the gas valve 40 is de-energized, the inducer blower 70 is adjusted to achieve
a sensor 80
pressure of P6, and the post-purge cycle is continued for duration T6. The
post-purge cycle
allows for the dissipation of any unburned or residual products of combustion
at the end of the
furnace burner operating cycle. Post-purge begins when the flame sensor 52
determines there is
no flame at the burner 20 surface.
[0045] It should be noted that the trial for ignition can fail
periodically. When this occurs,
inter-purge step is performed for duration T7 to allow for the dissipation of
any unburned gas or
residual products of combustion between the failed trial for ignition and the
retry period. The
inter-purge is performed while the sensor 80 indicates a pressure P7.
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[0046] In another example operation of the furnace 12, once a call for
heat from the
thermostat 76 is indicated at the controller 90, the inducer blower 70 is
energized and controlled
to a pre-determined pressure output for a predetermined time to achieve a pre-
purge of the
combustion chamber/heat exchanger 60. The igniter 50 is then energized.
[0047] The inducer blower 70 is then set to a new pressure setting for the
ignition
process. This inducer blower 70 setting purposely operates at a setting
calculated to operate the
burner 20 at a different air/fuel ratio than the normal target. Typically, the
burner 20 is lit off at a
rich ratio (less combustion air) but at full rate (single stage gas valve) to
achieve an acceptably
quiet light-off.
[0048] Once the flame is established and proved by the flame sensor 52, a
flame
stabilization mode is initiated at which the inducer blower 70 is operated at
a designated pressure
for a pre-determined time to stabilize the flame and warm up the burner 20 and
heat
exchanger 60. This operating point also runs a rich air/fuel ratio and serves
to get the flue gas
temperatures closer to the normal operating temperatures, which brings the
flue gas density
closer to normal.
[0049] After the flame stabilization period, the inducer blower 70 is
ramped up to the
normal operating pressure and the system enters the "Run" mode. The flame has
been stabilized
by this time by warming up the burner 20 media, warming up the heat exchanger
60, and raising
the temperature of the flue products to a "normal" temperature. This
stabilizes the density such
that the mass flow is nearly constant for stable burner 20 operation and
targeted combustion
efficiencies.
[0050] The control system 12 of the present invention is advantageous in
that a
predetermined combustion air flow across the igniter 50 is achieved during
igniter warm-up,
which ensures the desired ignition temperature can be achieved. This might be
considerably less
than other operating states. Furthermore, corrections can be made to the
air/fuel ratio flowing
through the burner 20 during light-off, which ensures a stable, quiet
ignition. To this end, pre-
mixed burners operate better when lit in a slightly rich environment.
[0051] Additionally, combustion air can selectively flow during the flame
stabilization
period, again possibly slightly rich, to allow the flame to stabilize prior to
steady state operation.
A consistent air/fuel ratio can be achieved during the "Run" cycle of the
furnace to optimize the
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combustion process for compliance with ULN regulations and codes. Since the
control system of
the present invention does not simultaneously vary the fuel and combustion air
the control
hardware and software algorithms can be simplified, thereby making the control
system less
expensive and the sequence of operation less complication.
[0052] This description mentions only variations in flue gas temperature
and composition
as possible causes for mass flow changes in the appliance. It will be
appreciated, however, that
once installed in the field, there are a number of other factors that can
cause the mass flow of the
system to shift, thereby resulting in noisy operation or poor combustion
performance, e.g.,
venting configurations ¨ direct vs. non-direct vent applications, venting
length, excessive wind
applied to the vent terminations, altitude, and venting system blockages, such
as ice or debris.
The control system 12 can include additional sensors and/or furnace 10
components that can be
monitored/controlled by the controller 90 to maintain the desired mass flow
rate in view of these
additional factors. In any case, the mass flow rate is controlled for each
operating stage of the
furnace to help maintain flame stability and combustion quality.
[0053] The control system of the present invention is also advantageous in
its ability to
reduce noise in the furnace. Instead of the aforementioned "soft start"
strategy, the control
system of the present invention specifically tailors the system pressure to
reduce undesirable
furnace noise. More specifically, during the development/calibration process,
tests are conducted
to identify the harmonic resonance operating conditions for the specific
furnace being used. Once
these operating points are identified, the combustion air pressure settings
used during the light-
off, flame stabilization, and run modes indicated above are selected to avoid
operating the pre-
mixed burner and heat exchanger in these specific resonance operating points.
In this way,
desirable furnace operating conditions in combustion performance, quiet
operation, and stable
burner control are achieved.
[0054] Figs. 3-5 illustrate a burner 30 in accordance with an aspect of
the present
invention. The burner 30 includes a body 32 that extends from a first end 34
to a second end 36.
The body 32 is formed from a durable material such as metal and has a first or
front side 38 and
a second or rear side 40 opposite the front side. The body 32 is formed by a
sidewall 50 that has
an elongated shape such as, for example, rectangular or trapezoidal. The
sidewall 50 defines an
interior chamber 52 that receives a pre-mixed mixture of fuel and air. In
particular, an inlet
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conduit 60 in fluid communication with the interior chamber 52 extends from
the sidewall 50
and includes an opening 62 connected to a fuel and air mixer (not shown) in
order to supply the
pre-mix mixture to the interior chamber.
[0055] A flange 54 extends from the sidewall 50 along the front side 38 of
the body 32.
The flange 54 has a rectangular shape and includes an opening 56 in fluid
communication with
the interior chamber 52. The opening 56 in the flange 54 receives a
distributor 80 (Fig. 4). The
distributor 80 closes the opening 56 in the flange 54 and substantially seals
the front side 38 of
the body 32. The distributor 80 has an elongated shape that mimics the shape
of the opening 56
in the flange 54, e.g., rectangular. The distributor 80 extends along a
centerline 86 from a first
end 82 to a second end 84. When the distributor 80 is secured to the flange 54
(see Fig. 3) the
first end 82 of the distributor is positioned at the first end 34 of the body
32 and the second end
84 is positioned at the second end 36 of the body.
[0056] Referring to Fig. 4, the distributor 80 is formed from a thin,
durable, and heat-
resistant material such as metal, metal screen or expanded metal. The
distributor 80 includes a
first portion 88 and at least one dimple or second portion 90 formed or
provided on the first
portion. The number, size, and spacing of the second portions 90 coincides
with the number,
size, and spacing of downstream heat exchanger sections (not shown) in the
furnace in which the
burner 30 is used. In particular, each second portion 90 is aligned with an
open end of an
associated heat exchanger section such that the end of each section is in
fluid communication
with each second portion.
[0057] In one example, the first portion 88 has a planar configuration and
each second
portion 90 is curved or dimple-shaped, e.g., rounded, hemispherical, circular,
concave or convex.
Every second portion 90 may have the same configuration or different
configurations from one
another. A concave second portion 90 will provide a narrow, long or elongated
flame while a
convex second portion will provide a wider, more dispersed flame. Each second
portion 90 may
exhibit any circular or polygonal shape such as triangular, square or the
like. The planar portion
88 extends substantially along the centerline 86.
[0058] Perforations 92 formed in each concave portion 90 extend entirely
through the
distributor 80. The perforations 92 may exhibit any shape and may be randomly
spaced about the
concave portion 90 or may have predetermined spacing. The perforations 92
cooperate with the
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concave portions 90 to produce an elongated flame for each concave portion
that extends into the
corresponding heat exchanger section (not shown) during use of the burner 30.
[0059] Carryover perforations 94 may also extend through the planar
portion 88 of the
distributor 80. The carryover perforations 94 may be similar, identical or
different than the
perforations 92 in the concave portions 90. The carryover perforations 94
cooperate with the
perforations 92 to provide a flame path between adjacent concave portions 90.
The path allows a
flame initiated at one concave portion 90 to propagate to all the concave
portions 90 in the
distributor 80.
a. An axis (not shown) extends perpendicular to the planar portion 88
and through
the center of a concave portion 90. The perforations 94 extend substantially
parallel to the axis
and the perforations 92 are angled towards the axis. Consequently, flow
through the perforations
92 of each concave portion 90 is directed towards a common point along the
axis that coincides
with the center of that curved portion. This helps to focus the flame produced
therefrom along
the axis towards the center of the respective heat exchanger section (not
shown). Flow through
the perforations 94, however, is directed in a direction substantially
parallel to the axis.
[0060] A fiber mesh burner surface 100 overlies the distributor 80 and is
formed from a
material such as an iron-chromium alloy, e.g., FeCrA1M. The burner surface 100
is contoured to
match the contour of the distributor 80 and, thus, the burner surface includes
the same dimples or
rounded portion(s) as the distributor. A cover retainer 110 is secured to the
flange 54 of the body
32 to secure the fiber mesh burner surface 100 and distributor 80 between the
body and the cover
retainer.
[0061] In operation, and referring to Fig. 3, a 100% pre-mix mixture of
air and fuel is
supplied via a mixer, duct or the like (not shown) upstream of the burner 30
to the opening 62 of
the inlet conduit 60 in the manner indicated generally by the arrow A. The pre-
mix mixture flows
through the interior chamber 52 and towards the opening 56 in the flange 54.
The pre-mix
mixture then flows through the perforations 92, 94 in both the concave
portions 90 and the planar
portion 88 of the distributor. When activated, an igniter (not shown)
positioned adjacent to the
leftmost concave portion 90 (as viewed in Fig. 3) ignites the pre-mix mixture
flowing through
the leftmost concave portion. The air and fuel mixture is ignited to produce a
flame, indicated
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generally by arrow F1 in Fig. 1 that extends from the surface of the fiber
mesh burner surface 100
outward away from the burner 30 into the associated heat exchanger section
(not shown).
[0062] The flame F1 in the leftmost concave portion 90 carries over or
propagates across
the planar portion 88 via the carryover perforations 94 and ignites the pre-
mix mixture flowing
through each successive concave portion until a flame F,, is produced in the
rightmost concave
portion of the distributor 80 (as viewed in Fig. 3). This directs the flame
F11 into the
corresponding heat exchanger section in the furnace (not shown). A flame
sensor (not shown)
may be positioned adjacent to the rightmost concave portion 90 that produces
the flame Fõ in
order to provide proof of ignition and propagation.
[0063] Figs. 5-7 illustrate a furnace 820 that includes a furnace cabinet
housing and
supporting a burner assembly 821 similar to the burner 30, along with
peripheral components,
including heat exchangers, blowers, etc. The furnace 820 includes a furnace
cabinet 822, a
primary heat exchanger 824 that comprises a plurality of serpentine tubes
824a, a secondary,
condensing heat exchanger 826, and a circulating air blower 828.
Alternatively, the primary heat
exchanger 824 may have a clamshell design known in the art. Components of the
burner
assembly 821 that are similar to the components of the burner 30 are given the
same reference
numeral with the added suffix " ' ".
[0064] The furnace cabinet includes a pair of vertical side panels 830 and
a vertical rear
panel 832. An intermediate plate assembly 834 is supported between the side
panels 830 and the
rear panel 832 and includes a blower deck plate 835 and an inverted L-shaped
support plate 836.
A vertical section 836a of the L-shaped support plate 836 forms a vest panel
which, as will be
explained, supports the burner 821. A horizontal segment 835a of the blower
deck plate 835 and
portions of the side panel 830 and rear panel 832 define a heat exchange
chamber 838 (best
shown in Fig. 5). The furnace 820 also includes a base 837 that cooperates
with the horizontal
segment 835a and portions of the side panel 830 and rear panel 832 to define a
blower chamber
for receiving the blower 828.
[0065] The secondary heat exchanger 826 (Fig. 5) sits atop and is
supported by the deck
plate segment 835a and overlies a rectangular opening 840. The blower 828 is
supported below
the deck plate 835 and includes a rectangular exit (not shown) aligned with
the deck plate
opening 840. Air discharged by the blower 828 enters the heat exchange chamber
838 through
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the opening 840. A control panel 843 is attached to the blower 828 and/or the
blower deck plate
835 and mounts conventional controls for the blower 828 and burner assembly
821.
[0066] The burner assembly 821 is attached to the vest panel 836a and is
received in a
rectangular opening 842 (Fig. 7) defined in the vest panel 836a of the plate
836. In particular, the
burner body 32' is shaped and sized to conform to the rectangular opening 842
in the vest panel
836a. The burner body 32' includes tapered end sections which operate to
provide a more even
flow of gas/air mixture to the distributor 80'. The burner body 32' is
suitably attached to the
exterior side of the vest panel 836a and includes a fuel/air inlet 60'. The
distributor 80' that
defines the perforated portions 90' is clamped between the body 32' and the
exterior of the vest
panel 836a. A combustion chamber defining cover 844 is attached to the
interior side of the vest
panel 836a in alignment with the burner body 32'. The component 100' defining
the burner
surface (which may be the previously disclosed fiber mesh burner surface 100)
is supported
between the distributor 80' and the interior of the combustion chamber cover
844. The
component 100' may be formed by, for example, sintering, weaving and/or
knitting techniques.
[0067] The combustion chamber cover 844 includes a plurality of openings
844a each
aligned with one of the burner portions 90' defined in the distributor 80'.
The openings 844a
each receive an associated inlet side 846 of an associated heat exchange
section 824a (Fig. 5). It
should be apparent that the portions 90' are therefore aligned with associated
heat exchange
sections 824a. The inlet sides 846 of the heat exchange sections 824a may be
attached to the
combustion chamber cover 844 by means of a known swaging process. The flame F
of each
portion 90' extends through the associated opening 844a of the cover 844 and
into the inlet side
846 of the associated heat exchange section 824a. The flames F are tailored
such that the tip of
each flame terminates at or adjacent to the inlet side 846 of each section
824a, i.e., the flames
may barely extend into the interior of each tube.
[0068] As best seen in Fig. 5, discharge ends 847 of each heat exchange
section 824a are
connected (as by swaging) to an intermediate collector box 850 having
associated ports 850a.
The intermediate collector box 850 receives the hot exhaust gasses from the
heat exchange
sections 824a and causes the exhaust gas to pass through the secondary heat
exchanger 826.
After passing through the secondary heat exchanger 826, the exhaust gasses are
received and
collected in a collector chamber 854 which communicates with an induced draft
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inducer blower 856. The exhaust gasses are drawn out by the induced draft
blower 856 and are
discharged to an outlet conduit 858 to be vented.
[0069] Referring to Fig. 6, the furnace cabinet 822 includes conduit ports
843a, 843b.
The conduit port 843a receives a combustion air conduit (not shown) that
provides a source of
combustion air which is delivered to the vestibule 871 and, thus, is delivered
to the mixer 870.
The port 843b receives the exhaust conduit 858 or vent (not shown) through
which the products
of combustion are exhausted to the outside.
[0070] As best seen in Figs. 6-7, the blower opening 840 in the blower
deck plate 835 is
located near the inlet side 846 of the heat exchange sections 824a and, thus,
air to be heated is
discharged near the burner side of the heat exchange chamber 838, i.e., near
the vest panel 836a.
In conventional furnaces, the flames extend deep into the heat exchange tubes
and therefore the
blower ¨ and associated blower opening ¨ is located further down the length of
the tubes from
the burner side. Since the flames from the burner assembly 821, 821', 821"
terminate at or
adjacent to the openings in the heat exchange sections 824a the blower opening
840 and blower
828 can be aligned with the inlets to the heat exchange sections on a side of
the vest panel 836
opposite to the burner assembly, i.e., within the heat exchange chamber 838.
Air from the blower
828 therefore washes over the heat exchange sections 824a where the flames are
the hottest.
[0071] Fig. 8 illustrates portions of another burner 930 in which the
distributor and fiber
mesh are omitted for brevity and clarity. In Fig. 8, features that are similar
to those in Figs. 3-4
have a reference numeral that is 900 greater than the reference numerals in
Figs. 1-3. In Fig. 8,
the burner 930 is configured such that the igniter 911 and flame sensor 913
are positioned
outside the heat exchanger compartment 838 and within the vestibule 871. More
specifically, the
burner 930 includes a body 932 having a substantially trapezoidal sidewall 950
that defines an
interior chamber 952. The sidewall 950 includes an extension 953 that extends
along the front
side 938 of the body 932. The vest panel 836' includes a series of bends 839
that form a notch
which defines a passage 841 extending along and above the extension 953 for
receiving the
extension. The bends 839 position the extension 953 outside of the heat
exchanger compartment
838 and the passage 841 is sized to allow the igniter 911 and flame sensor 913
to be inserted
through the extension 953 into the interior 952 of the body 932.
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[0072] A viewing window 915 formed in the extension 953 allows for visual
inspection
of the interior chamber 952. A series of pressure relief sections constituting
openings 917 may be
formed along the extension 953 for mitigating pulsing and resonance within the
interior chamber
952. It is believed that these openings 917 may allow secondary air to flow
into the combustion
chamber during operation of the burner assembly 930.
[0073] The combustion chamber cover 944 is attached to the interior or
heat exchanger
compartment 838 side of the vest panel 836a'. The combustion chamber cover 944
includes an
interior space 946 and a plurality of openings 944a each aligned with one of
the burner portions
(not shown) defined in the distributor (not shown). The openings 944a each
receive an associated
inlet side 846 of an associated heat exchange section 824a (Fig. 5) to align
the burner portions
with associated heat exchange sections 824a. The inlet sides 846 of the heat
exchange sections
824a may be attached to the combustion chamber cover 944 by means of a known
swaging
process. The flame of each burner portion extends through the associated
opening 944a of the
cover 944 and into the inlet side 846 of the associated heat exchange section
824a. Both the
igniter 911 and the flame sensor 913 may extend through the combustion chamber
cover 944 to
the interior space 946 within the heat exchange chamber 838.
[0074] The burner has been described in connection with a condensing type
furnace. It
should be noted that the burner of the present invention can be used in a non-
condensing type
furnace.
[0075] What have been described above are examples of the present
invention. It is, of
course, not possible to describe every conceivable combination of components
or methodologies
for purposes of describing the present invention, but one of ordinary skill in
the art will
recognize that many further combinations and permutations of the present
invention are possible.
Accordingly, the present invention is intended to embrace all such
alterations, modifications and
variations that fall within the spirit and scope of the appended claims.
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