U.S. patent application number 14/201231 was filed with the patent office on 2014-10-23 for control system for monitoring and adjusting combustion performance in a cordwood-fired heating appliance.
The applicant listed for this patent is REGINALD JAMES DAVENPORT. Invention is credited to REGINALD JAMES DAVENPORT.
Application Number | 20140311477 14/201231 |
Document ID | / |
Family ID | 51728052 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140311477 |
Kind Code |
A1 |
DAVENPORT; REGINALD JAMES |
October 23, 2014 |
CONTROL SYSTEM FOR MONITORING AND ADJUSTING COMBUSTION PERFORMANCE
IN A CORDWOOD-FIRED HEATING APPLIANCE
Abstract
A system including temperature measuring devices, a controller,
and an actuator, maintains a desired gas temperature range in the
secondary combustor by proportionally making adjustments to the
primary air orifice or other primary air valve of a cordwood
burning appliance. Heat output of the appliance is directly related
to the temperature of the gases in the secondary combustor, and
sufficient engagement of the second combustor during off-gassing of
volatiles from the wood will control emissions from the appliance.
The operator can select a desired room temperature via the
thermostat and the controller will use different secondary gas
temperature target ranges in order to meet the desired room
temperature as commanded by the thermostat throughout the burn
event. The controller also controls the start-up phase of
combustion and charcoal phase of combustion.
Inventors: |
DAVENPORT; REGINALD JAMES;
(EVANS, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAVENPORT; REGINALD JAMES |
EVANS |
WA |
US |
|
|
Family ID: |
51728052 |
Appl. No.: |
14/201231 |
Filed: |
March 7, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61851343 |
Mar 7, 2013 |
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Current U.S.
Class: |
126/502 |
Current CPC
Class: |
F24B 5/026 20130101;
F24B 1/028 20130101; F24B 1/026 20130101 |
Class at
Publication: |
126/502 |
International
Class: |
F24B 1/02 20060101
F24B001/02 |
Claims
1. A control system in a solid-fuel-burning appliance for reducing
emissions, the appliance having a primary combustion zone for
receiving and burning solid fuel, a secondary combustion zone for
burning combustible compounds outgassed from said burning of solid
fuel, a primary air stream entering the primary combustion zone
wherein a portion of the primary air stream flows with the
outgassed organic compounds to the secondary combustion zone, and a
primary air valve openable to increase flowrate of the primary air
stream and closable to reduce flowrate of the primary air steam,
the control system comprising: a temperature sensor located in the
secondary combustion zone and measuring secondary combustion zone
temperature (SCT); and a controller adapted to receive a signal
from said temperature sensor indicating measured SCT, wherein the
controller is adapted to adjust flowrate of the primary air stream
in response to the signal to raise or lower said SCT.
2. A control system as in claim 1, wherein the controller is
adapted to adjust said flowrate in incremental amounts in response
to said signal until the measured SCT is within a predetermined SCT
target range.
3. A control system as in claim 2, wherein the SCT target range is
a range of about 120 degrees Fahrenheit.
4. A control system as in claim 1, wherein said controller is
adapted to adjust said flowrate in incremental amounts in response
to said signal until the SCT is within a first range selected from
a plurality of predetermined SCT target ranges.
5. A control system as in claim 4, wherein said plurality of
predetermined SCT target ranges comprises at least two SCT target
ranges selected from a group consisting of: a high SCT target range
for high heat output from the appliance, a low SCT target range for
low heat output from the appliance, and a medium SCT target range,
between said high and low SCT target ranges, for medium heat output
between said high and low heat outputs, and wherein said first
range is selected from said plurality of SCT target ranges by means
of at least one signal from an operator-controlled unit selected
from the group consisting of a heat-out selection switch and a
thermostat.
6. A control system as in claim 1, comprising a room thermostat and
wherein said controller is adapted to adjust said flowrate of the
primary air stream in response to the signal from said temperature
sensor until the measured SCT is within a higher SCT target range
when the thermostat is calling for heat and until the measured SCT
is within a lower SCT target range when the thermostat is not
calling for heat.
7. A control system as in claim 6, wherein, when the thermostat is
not calling for heat, said controller incrementally adjusts said
flowrate of primary air until the first of: the SCT falling within
the lower SCT target range or the valve closing to a preset minimum
valve opening.
8. A control system as in claim 6, wherein the controller includes
a preset low threshold temperature, which generally corresponds to
SCT at an end of an organic release phase of solid-fuel combustion
in the primary combustion zone and the beginning of a charcoal
combustion phase in the primary combustion zone, and wherein, when
said signal from the temperature sensor indicates that the measured
SCT has fallen to said preset low threshold temperature, the
controller is adapted to completely close the valve to stop the
primary air stream from flowing into the primary combustion
zone.
9. A control system as in claim 8, wherein the controller is
adapted to increase the primary air stream flowrate, after the end
of the organic release phase, only if the thermostat calls for
heat.
10. A control system as in claim 1, wherein the primary air valve
is a sliding plate system forming one or more orifice openings.
11. A method of controlling emissions from burning of wood, the
method comprising: providing a solid-fuel-burning appliance having
a primary combustion zone receiving and burning solid fuel, a
secondary combustion zone for burning combustible compounds
outgassed from said burning of solid fuel, a primary combustion air
stream entering the primary combustion zone wherein a portion of
the primary combustion air stream flows with the outgassed organic
compounds to the secondary combustion zone, and a primary air valve
openable to increase flowrate of the primary air stream and
closable to reduce flowrate of the primary air steam, and a
secondary air stream supplied into the secondary combustion zone;
providing a temperature sensor located in the secondary combustion
zone and measuring second combustion zone temperature (SCT); and
adjusting flowrate of the primary air stream in response to
measured SCT to maintain the secondary combustion zone above a
temperature required for combustion of volatiles from the primary
combustion zone.
12. A method as in claim 11, wherein the method does not comprise
controlling flow of the secondary air stream.
13. A method as in claim 11, wherein said adjusting comprises
iteratively adjusting said flowrate in incremental amounts until
measured SCT is within a predetermined SCT target range.
14. A method as in claim 13, wherein the SCT target range is a
range of about 120 degrees Fahrenheit.
15. A method as in claim 13, wherein said adjusting comprises
adjusting said flowrate in incremental amounts until measured SCT
is within a first range selected from a plurality of predetermined
SCT target ranges.
16. A method as in claim 15, wherein said plurality of
predetermined SCT target ranges comprises at least two SCT target
ranges selected from a group consisting of: a high SCT target range
for high heat output from the appliance, a low SCT target range for
low heat output from the appliance, and a medium SCT target range,
between said high and low SCT target ranges, for medium heat output
between said high and low heat outputs, and wherein said first
range is selected from said plurality of SCT target ranges by means
of a signal from an operator-controlled unit selected from the
group consisting of: a heat-out selection switch and a
thermostat.
17. A method as in claim 15, comprising providing a room thermostat
and said adjusting flowrate of the primary air stream is done until
measured SCT is within a higher SCT target range when the
thermostat is calling for heat and until measured SCT is within a
lower SCT target range when the thermostat is not calling for
heat.
18. A method as in claim 17, comprising, when the thermostat is not
calling for heat, adjusting said flowrate until the first of the
measured SCT falling within the lower SCT target range or the valve
closing to a preset minimum valve opening.
19. A method as in claim 17, comprising completely closing the
valve to stop the primary air stream from flowing into the primary
combustion zone when measured SCT falls to a preset low threshold
temperature that generally corresponds to SCT at an end of an
organic release phase of solid-fuel combustion in the primary
combustion zone and the beginning of a charcoal combustion phase in
the primary combustion zone.
20. A method as in claim 19, comprising increasing the primary air
stream flowrate, after the end of the organic release phase, only
if the thermostat calls for heat.
21. A method of limiting emissions from a wood-burning appliance
having a primary combustion zone for burning wood, and a secondary
combustion zone for burning volatiles outgassed from the burning
wood, the method comprising: measuring secondary combustion zone
temperature during a wood-burning event, and adjusting primary air
supplied to the primary combustion zone to maintain the measured
secondary combustion zone temperature above a temperature
corresponding to sufficient activation energy for combustion of the
volatiles.
22. A method of claim 21 wherein the secondary combustion zone is
provided with secondary air flow, and wherein the secondary air
flow is not adjusted in response to the measured secondary
combustion zone temperature.
23. A method of claim 21, wherein the wood-burning event comprises
a start-up phase, an organic release phase, and a charcoal-burning
phase, and wherein said adjusting of primary air occurs during the
organic release phase to combust said volatiles, and occurs during
the charcoal-burning phase only in response to a room thermostat
calling for heat.
Description
DESCRIPTION
[0001] This application claims priority of Provisional Application
Ser. No. 61/851,343, filed Mar. 7, 2013, entitled "Control System
for Monitoring and Adjusting Combustion Performance in a Cord Wood
Fired Residential Heating Appliance", the entire disclosure of
which is incorporated herein by this reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to control systems designed to
operate on wood stoves, furnaces, fire places, and/or other types
of appliances that are designed to burn solid fuel, preferably
wood, and that are equipped with secondary combustion systems,
frequently called "secondary combustors". Certain embodiments are
for residential wood-burning appliances. Certain embodiments are
designed to optimize burn characteristics to reduce emissions,
maximize efficiency, and make operation simple for the
operator.
[0004] 2. Discussion of Related Art
[0005] Cordwood burning appliances must contend with a huge amount
of variation in physical and environmental factors that is realized
in the field. These physical and environmental variables may
include, for example, different operators, wood type, wood moisture
content, load density, altitude, chimney installation, etc., and
may all have impacts on the particulate emissions profile that the
appliance will produce while in operation. Typically, modern
wood-burning appliances have already been "tuned" to an EPA mandate
and tested in a laboratory for particulate emissions from the
appliance. However, this "standard" does not reflect real world
conditions, and likely never will, as the number of permutations
needed to understand the field emissions profile, based on the
aforementioned contributing factors, are far too many. There is
increasing pressure from air regulatory authorities to clean up air
sheds, but, given that laboratory testing and realized field
emissions do not and will likely never correlate, the only tool
regulators currently have is to lower the passing threshold for new
appliances coming to market.
[0006] Wood combustion may be categorized generally into three
phases of combustion: the start up or "wood alcohol" phase, the
organic release phase or "organic phase", and, finally, the
charcoal phase. Wood combustion, through all phases, is a dynamic
phenomenon, and each refueling event into an appliance is a
different event. The inventor believes that the only things
consistent from wood-burning event to event are that wood will burn
and volatiles (combustible gaseous compounds from the wood) may
burn in the secondary combustor under some circumstances.
Therefore, success in obtaining a low emissions profile during
operation of a wood burning appliance can be difficult for
operators. Units generally will not operate with minimal emissions
unless a skilled operator remains present to make adjustments. Due
to the manual system that most appliances employ, and the many
physical and environmental variables mentioned above, the operator
must stay with the appliance, "watching" its performance during the
various stages of the combustion process, and making adjustments to
the air inlet control. For example, if the air control for the
appliance is closed off prematurely in order to provide a low heat
output and prolong the length of the burn, then excessive emissions
and low efficiency are often the result. Therefore, the multiple
goals, of trying to heat a room comfortably during use of the room,
burning wood cleanly, extending length of a burn, and/or use less
wood, are entirely at the discretion of the operator and are seldom
all achievable by conventional, manual equipment and methods.
[0007] Therefore, there is a need for improved control of
solid-fuel-/wood-burning appliance operation, to improve multiple,
and preferably all, of emissions, comfort, and convenience.
Embodiments of the invention meet this need, using the temperature
of the secondary combustor gases (or "secondary combustion
temperature", SCT), which indicate said level of secondary
combustor engagement, to control air during at least one combustion
phase. With the secondary combustor engaged to a certain level, the
combustion event will tend to exhibit minimal emissions and
increased efficiency due to heat production from the volatiles.
Certain embodiments use SCT sensing, a controller comprising
control algorithm(s) specially-adapted to respond to said SCT
sensing, and an actuator performing primary air adjustments in
response to the controller, resulting in every refueling event
exhibiting improved or optimal burn characteristics regardless of
the above-mentioned physical and environmental variables. For
example, improved or optimal burn characteristics may be exhibited
regardless of operator, absence of operator, wood type,
installation, etc.
[0008] 3. Previous Attempts
[0009] Several mechanisms have been devised previously that attempt
to control wood combustion in an automatic fashion. These include
mechanical-type thermostats that make adjustments to the air
control via referencing the temperature of the appliance cabinet,
or by utilizing a timer of some sort on the primary air control.
Others are electronic in nature and utilize oxygen sensors or some
temperature measurement of the exhaust (flue) stream, or utilize
the appliance cabinet temperature in order to make adjustments to
the air control(s). None of the aforementioned systems directly
measure the temperature of the gases within the secondary
combustion system.
SUMMARY OF THE INVENTION
[0010] The present invention comprises apparatus, and/or methods,
for automatic control of a solid-fuel-burning appliance to reduce
emissions, during at least one and preferably multiple phases on
combustion. Certain embodiments comprise measuring temperature of
the secondary combustion system of the appliance, and controlling
the amount of air into the appliance to maintain a desired level of
said secondary combustion temperature(s) during at least one
combustion phase. Certain embodiments comprise secondary combustion
temperature (SCT) sensing apparatus, a controller responding to
said SCT sensing, and an actuator adjusting the air supply to the
appliance in response to the controller. Certain embodiments obtain
low emissions, while also increasing efficiency and/or extending
the length of the burn and providing great convenience for the
operator. Certain embodiments maintain combustion in the secondary
combustor that is sufficient to reduce emissions/pollution while
satisfying the desired room temperature, and then, if possible
while satisfying these two goals, reducing the rate of burning of
wood to conserve fuel.
[0011] In certain embodiments of the invention, automatic control
of air to the appliance is done chiefly or entirely by controlling
the primary air flow into the appliance. In certain embodiments,
this is done during all phases of combustion, with monitoring and
maintaining proper gas temperatures in the secondary combustion
system of the appliance being particularly important at all times
wherein combustible gasses from the wood, or "volatiles", are
flowing from the primary combustion zone (also, herein, "main
firebox") to the secondary combustion zone. Time-iterative sampling
of the temperature data provided from sensors in the secondary
combustor allow adjustment of the primary air orifice(s)/valve(s)
via an actuator. The automatic control may comprise throttling the
primary air, during periods when the desired room temperature is
satisfied, to an extent that reduces wood combustion to a
longer-lasting burn, but that sustains secondary combustion of
volatiles to reduce emissions. If room temperature is not
satisfied, the automatic control may comprise increasing primary
air to increase combustion of wood or charcoal in the main firebox,
and of volatiles when produced, even if this results in reducing
the total length of the burn.
[0012] The invented apparatus and/or methods may be retrofit,
manufactured OEM, or otherwise incorporated, into various
solid-fuel-burning, preferably wood-burning, appliances, such as
wood fireplaces, stoves, inserts or furnaces, that include a
secondary combustion system. The invented apparatus/methods are
expected to work well with all current conventional, and future,
secondary combustion systems, for example, those of various
physical structures with or without catalytic properties. Secondary
combustion systems not yet existing may use embodiments of the
present invention.
[0013] Automatic control of the primary air orifice(s)/valve(s) is
preferably provided during all the stages or "phases" of the
combustion event, including a startup phase wherein a fresh load of
solid-fuel/wood has just been added, an organic burn phase, and
finally a charcoal phase. Preferably, operator input and effort is
minimal other than placing wood in the main firebox and lighting
the fire. In especially-preferred embodiments, the operator input
to the controller comprises, consists essentially of, or consists
of, selection of a desired room temperature via a wall mounted
"off-the-shelf thermostat" and pressing of the "cycle start" button
upon loading a fresh load of fuel.
[0014] Another inventive aspect of certain embodiments relates to
what feature(s)/element(s) is/are automatic and non-adjustable to
the user and what is/are adjustable. In order to provide low
emissions, it is necessary to define secondary zone gas temperature
presets (also "preset targets" or "targets") that are stored in
memory of the controller. Users do not have the ability to change
these temperature values. In preferred embodiments, a thermostat
allows a user to set a desired room temperature, and the
controller/algorithm has multiple, different preset targets for
secondary combustion gas temperature (SCT), the selection of which
different targets is determined by whether or not the thermostat is
calling for heat. A higher preset SCT target is used if room
temperature is not met, so that higher heat output is achieved from
the appliance to heat-up the room. A lower preset SCT target is
used if room temperature is met, as one may expect that maintaining
the room temperature to require a lower heat output from the
appliance and that said lower preset SCT target result in a longer
burn-time. The lower preset SCT target, however, is not so low that
it reduces secondary combustion to an extent that causes high
emissions from the secondary combustion system, and, hence, from
the appliance.
[0015] These and/or other features of the invention will be
apparent to those of skill in the art after reviewing this document
and the attached drawings. The preferred embodiments described
below are presented to show some, but not all, exemplary elements,
structure, means, and methods that may be used in certain
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a front view of a wood stove with control system
according to an embodiment of the present invention.
[0017] FIG. 2 is a cross-sectional side view of the wood stove with
control system of FIG. 1, viewed along the line 2-2 in FIG. 1.
[0018] FIG. 3 is a bottom perspective view of the tube style
secondary combustion system of the wood stove of FIGS. 1 and 2,
showing a location of the temperature sensors that send data to the
controller.
[0019] FIG. 4 is a front view of an alternative embodiment of wood
stove with control system that comprises a catalytic-style
secondary combustion system.
[0020] FIG. 5 is a side cross-section side view of the wood stove
with control system of FIG. 4, viewed along the line 5-5 in FIG.
4.
[0021] FIG. 6 is a front perspective view of the catalytic unit of
the wood stove and control system of FIGS. 4 and 5.
[0022] FIG. 7 is a cross-sectional side view of a wood stove such
as the one in FIGS. 1 and 2 (shown without most of the control
elements of embodiments of the invention), wherein the flow of
primary air, gases from the burning wood, and secondary air are
shown.
[0023] FIG. 8 is a graph of primary air orifice position vs time
for certain embodiments capable of operating under several heat
output selections, specifically selection of high, medium, or low
heat output modes.
[0024] FIG. 9 is a graph of the temperature (SCT) of the gases in
the secondary combustion zone/system, vs. time, generally
corresponding to the low heat output mode of FIG. 8.
[0025] FIG. 10 is a graph of primary air orifice position vs time,
for certain embodiments an operation wherein the SCT target starts
out the burn in high heat output mode, but then switches to a low
heat output mode partway through the organic combustion phase, for
example, because a thermostat signals the controller that the
design room temperature has been met.
[0026] FIG. 11 is a graph of the temperature (SCT) of the gases in
the secondary combustion zone/system, vs. time, generally
corresponding to the operation shown in FIG. 10.
[0027] FIGS. 12A, 12B, 12C are portions of a block flow diagram
showing some methods of operating a wood stove comprising certain
embodiments of the invented automatic control apparatus.
[0028] FIG. 13 shows additional steps that may supplement the
methods of FIGS. 12A-12C, for certain embodiments wherein either: a
user-operated thermostat is instrumental in causing the controller
to select the SCT target range (box at top left), in that a first
SCT target range is used if the thermostat is calling for heat, but
a second, lower SCT target range is used if the thermostat is no
longer calling for heat, or a user-operated heat output selection
switch (box at top right) is instrumental in causing the controller
to select the SCT target ranges.
DETAILED DESCRIPTION
[0029] Conventional appliances comprise a primary combustion
chamber (also "main combustion chamber", "main firebox", or
"firebox") for receiving the wood or other solid fuel during the
combustion event. The main firebox is an insulated volume, where
the solid-fuel/wood resides, that has air passage openings that
deliver primary air to one or more specific areas of the main
firebox mainly for combustion of the solid fuel. The appliance is
typically air-tight except for the primary air and secondary air
inlets into the primary and secondary combustion zones. Typically,
a variable orifice/valve controls the flow of primary air to the
various passage openings to the main firebox. The variable
orifice/valve may be comprised of a generally tight sealing valve,
for example, a sliding plate orifice system or rotating valve
allowing various amounts of air to enter the main firebox. An
electronic actuator is typically attached to this orifice, allowing
for full-open or full-closed positions and any position in between
full-open and full-closed. Therefore, the term "primary air" herein
means the air stream provided to the main firebox at one or more
locations in said firebox, mainly for the purpose of oxidation of
the wood or other solid-fuel. In other words, the primary air is
responsible for the primary combustion that occurs on or very near
the solid fuel. It is responsible for the immediate elevation in
temperature of the solid fuel in order to cause further outgassing.
Under certain circumstances, excess oxygen from the primary air
(not consumed by combustion in the main firebox) flows to the
secondary combustion zone, described below, and may react in
combustion of the volatiles reaching the secondary combustion zone.
Preferred embodiments control primary air, which control has the
synergistic effect of affecting the primary combustion of solid
fuel (in the main firebox), the outgas sing of volatiles to the
secondary combustion zone, and the amount of excess oxygen (in a
"portion of the primary air stream") leaving the primary combustion
zone to arrive in the secondary combustion zone.
[0030] Preferred embodiments of the invention are adapted for use
in appliances that, as a supplement to the main firebox, comprise a
secondary combustion system/zone (also "secondary combustor"
herein). Such secondary combustors are between the main firebox and
the flue, that is, downstream (regarding gas flow) from the
solid-fuel/wood chamber but upstream from the outlet of the
appliance, which is typically a receiver ring that allows
connection of the appliance to a flue pipe. The secondary combustor
is typically above or behind the main firebox, in fluid
communication with the main firebox. The secondary combustor is
intended for supplemental, "secondary" combustion, specifically,
burning of combustible gaseous compounds ("volatiles" from the
fuel) inside the appliance but downstream from the main firebox. In
other words, a secondary combustor in a wood-fired appliance is
constructed with the specific purpose of introducing air, and/or
working in conjunction with a catalytic element, in a proper amount
to maintain its activation energy during the active combustion
phase in order to combust the gas-rich mixture that is delivered
from the firebox area. It specific location and construction are
typically bound by maintaining this activation energy and
delivering the necessary amount of air to maintain proper gas
mixture that results in a near stoichiometric combustion that
results in a clean combustion pattern.
[0031] It should be noted that, for proper operation of the
secondary combustor, the temperature of the gases in the secondary
combustor must be maintained at or above the activation energy of
the specific type of combustor. For a tube-style combustor, this is
generally approximately 1200 degrees F., and for a catalytic-type
combustor, this temperature is above approximately 600 degrees F.
The specific location of the combustor must take this activation
energy into account therefore dictating it position in the stove.
For example, this need for high temperature is one reason most
secondary combustors are typically inside the cabinet and directly
above the location wherein the solid-fuel/wood is burning.
[0032] The secondary combustor is typically constructed to receive
additional air and/or to comprise catalytic element(s) to encourage
combustion of the overly-rich mixture of gases that may be
generated in the firebox, particularly during the organic
combustion phase. For example, said additional air may be a
secondary air stream, which is separate from the primary air and
which is injected directly into the secondary combustor (see stream
27 in FIGS. 3 and 7, and/or simply "excess" primary air (or a
"portion of the primary air") that flows from the main firebox to
the secondary combustion zone.
[0033] An important aspect of the preferred embodiments is the use
of temperature measurement devices directly within the secondary
combustion zone. The secondary combustion system may be selected,
for example, from several variants commonly employed in the
industry, for example, tube-style systems, catalytic element
systems, and downdraft-style systems. It may be noted that an
example of a tube-style system and an example of a catalytic
element system are shown in the drawings. A downdraft-style system
is not shown in the drawings, but will be understood by those of
skill in the art; they are small boxes that are on the back of the
appliance unit and basically force the volatiles thru a coal bed
and then in a highly insulated box introduce secondary air to burn
the gases.
[0034] Temperature measurement device(s) placed inside the
secondary combustion zone provide temperature information to an
electronic controller. The temperature information will typically
comprise, consist essentially of, or consist of, the temperature of
the gas that is directly contacting the measurement device, which
typically may be considered representative of the temperature of
substantially the entire secondary combustion area/zone.
Alternatively, temperature measurement device(s) may be designed or
placed so that it/they is/are in direct contact with, or
covered/protected by, metallic or other heat-conducting structure
inside the secondary combustion zone, rather than being in direct
contact with the gasses; however, said metallic/heat-conducting
structure and the covered/protected sensors are located generally
centrally and appropriately in the zone so that the temperature
sensed by said measurement device may be considered equal to the
gas temperature, and, therefore, the temperature of the
substantially the entire secondary combustion area/zone.
[0035] An important aspect of the preferred embodiments is that
multiple phases, and preferably all three phases, of combustion of
solid fuel are controlled. Upon reloading of fuel into the
appliance, control of the start-up phase of combustion may comprise
an operator depressing a "cycle start" button located on or near
the appliance initiating a startup mode. A status indication light
may be provided, for example, that illuminates after depression of
the cycle start button to indicate that the unit is ready for a
burn event. The startup mode of the controller preferably opens the
primary air control all the way in order to provide ample air
supply to the new load of fuel to ignite the fuel. Once the level
of fuel combustion has progressed to a preset threshold point (also
"high threshold" or "start-up threshold" SCT) measured by the
temperature sensors in the secondary combustor, then the controller
may in certain embodiments close the primary air orifice a certain
amount in preparation for the modulation mode of the organic
combustion. The preset high threshold SCT may be, for example,
about 1200 degrees F. for a non-catalytic secondary combustion unit
and for a catalytic combustion unit, regardless of the size of the
fuel load, which represents a temperature wherein one may be
certain that a good fire is going before further decisions are
made.
[0036] Control during the organic phase of the combustion may be
described as "modulation" control conducted in conjunction with
operator input, preferably, the setting of a wall-mounted
thermostat by the operator. The modulation control comprises the
system monitoring and making decisions and consequential
adjustments of the primary air orifice in order to adjust
performance of the appliance, and repeating same until the SCT
falls within a preset SCT target range, that is selected from two
(a higher and a lower) preset SCT target ranges depending on
whether the thermostat is calling for heat or not calling for heat,
respectively. It may be noted that certain embodiments may be
designed to respond to an operator's adjusting the thermostat in
the middle of the burn cycle, for example, the operator changing
the desired room temperature by changing the thermostat setting in
the middle of the organic phase or even the charcoal phase. It will
be understood from this document that the controller/algorithms
(including code, programming, firmware, software, and/or hardware)
would respond to the thermostat change as predetermined for that
phase. For example, if the thermostat change were done in the
organic phase, the controller would continue or begin iterative
adjustments of primary air in response to the thermostat, so that
the thermostat adjustment might result in the controller moving
from a thermostat-satisfied SCT target range to a
thermostat-not-satisfied SCT target range, or vice versa, at any
point in the organic phase.
[0037] The cycle of monitor, decide and adjust includes an
evaluation time period after adjustment, in order to give the
performance of the appliance time to equilibrate. The evaluation
time is established based upon the temperature of the secondary
combustor at the time the modulation cycles are being conducted. If
the SCT is much higher than the selected preset SCT target range,
then a short evaluation time period (approximately 90 seconds, for
example, a "short timer") is used before making the ensuing
decision to incrementally reduce (partially close) the primary air
orifice. If the SCT is only slightly higher than the selected
preset SCT target range, then a longer evaluation time frame
(approximately 240 seconds, for example, a "long timer") is used
before making the ensuing decision to incrementally reduce
(partially close) the primary air orifice. In either case, upon
fulfillment of the selected timer (the end of the evaluation time),
if the SCT is higher than the preset SCT target range, then the
primary air orifice will be closed by a predetermined
distance/amount via the electronic actuator. Having multiple timer
options available allows the system to respond to a "typical"
startup of generally dry wood and a cool firebox, or more quickly,
for example, if the fire really "takes off" due to really dry wood
or a hot reload. The iterative orifice closure distance is
generally defined by the design of the primary air orifice, however
generally will be from 1/2'' to 0.050''. If, at the time of
fulfillment of the evaluation timer, the secondary combustion
temperature is within the preset SCT target range, then no action
is taken by the controller other than to restart the evaluation
timers and continue the process. In normal operation/combustion,
this multiple iteration, wait-evaluate-decide process will result,
after some amount of time, in the primary air control having been
closed to a preset minimum opening that is set within the
controller. This minimum opening is preset in order to guarantee
that sufficient primary air and oxygen will reach the secondary
combustion zone to minimize emissions during the entire organic
combustion phase. When this occurs, then, upon the fulfillment of
the next evaluation timer event, no further closing will occur even
if the secondary combustion temperature is above the preset
range.
[0038] As mentioned above, input to the controller from the
wall-mounted thermostat, of certain embodiments, determines what
target SCT range is used during various portions of the organic
phase modulation mode. While the thermostat is calling for heat,
the controller uses a relatively high SCT target range that results
in a relatively high heat output from the appliance. When the
thermostat does not call for heat, indicating that the room has
reached the desired temperature, then the controller switches to a
relatively lower SCT target range that results in a relatively
lower heat output from the appliance. In other words, during
organic phase portions (periods) wherein the thermostat is
satisfied, the controller closes the air flow iteratively according
to the lower secondary combustion temperature range, that is, the
range of a low burn. The iterative process (of measuring,
adjusting, and then a timed evaluation (waiting) period before
another measurement) is continued to reach whichever SCT target
range is appropriate given the signal from the thermostat. It
should be noted that fully-open or mainly-open primary air may be
called-for while the thermostat is calling for heat, but at least
partial closing, or full closure, of the primary air may be done
even when the thermostat is calling for heat, if safety-based
high-temperature limits that are held in memory of the controller
are reached in the secondary combustion zone.
[0039] After the modulation mode of the system has satisfied the
room temperature setting (thermostat setting) and has switched to a
low burn by modulating to meet the lower SCT target range, the
controller will typically make no further adjustments to the
primary air control orifice while the organic combustion phase
continues. The controller will typically make no further
adjustments until the wood has burned to a great extent so that the
SCT falls to another, significantly-lower preset temperature, that
may be called the "charcoal-phase temperature" and that is preset
as the indicator of the end of the organic phase of combustion and
the start of the charcoal phase of combustion. The charcoal-phase
temperature may be, for example, approximately 900 degrees F., as
will be typical for the end of a successful burn during the organic
phase. For example, for either a non-catalytic or a catalytic
secondary combustion unit, the charcoal-phase temperature is
expected to be about 932 degrees F. for a large load of fuel, or
about 842 degrees F. for a small load of fuel.
[0040] Once the charcoal-phase temperature is reached, the
preferred controller enters the charcoal phase of combustion
control by closing the primary air orifice all the way, and then
responds to true or false signals from the wall-mounted thermostat.
If the thermostat is false (room temperature is above the set
point) at any time during the charcoal phase of combustion, the
controller will leave the primary air orifice closed all the way.
If the thermostat becomes true (room temperature is below the set
point), the controller will open the primary air control all the
way in order to increase the charcoal burn to raise the temperature
of the appliance, thus providing more heat to the room. Thus, it is
the thermostat that signals the controller during most of the
charcoal phase. After the initial closing based on SCT, the SCT is
preferably ignored during this combustion phase. This is due to the
fact that charcoal has virtually no organic compounds that would
volatilize and enter the secondary combustor, so specific burn
conditions related to obtaining clean combustion by optimizing the
secondary combustor are negated.
[0041] Referring Specifically to the Drawings:
[0042] Referring to the drawings, there are shown several, but not
the only, embodiments of the invented apparatus and/or methods of
automatic control for a solid-fuel-burning, preferably
wood-burning, appliance. The apparatus and/or methods are adapted
to improve emissions, while achieving one or more of the goals of
meeting a desired room temperature selected by an operator,
increasing efficiency, and lengthening burn time of a single load
of wood.
[0043] In general, "efficiency" herein is defined as the
combination of combustion efficiency (how much chemical losses are
realized in the flue stream, i.e. combustible gases that leave the
appliance without being burned) and the heat transfer efficiency
(which is how well the hot burned gases are cooled off while in the
appliance prior to entering the flue). It may be noted that certain
embodiments of the invented system are specially-adapted to affect
efficiency mainly by maximizing combustion efficiency, specifically
by minimizing chemical losses. Therefore, an efficient burn may be
a fast burn or a slow burn, and certain embodiments of the
invention may produce an efficient burn that is fast, or an
efficient burn that is slow, for example.
[0044] One embodiment 1 of the invention is illustrated by the
cordwood burning appliance in FIGS. 1 and 2, with an integrated
system comprising a controller and actuator, temperature sensor(s),
thermostat , and operator input switches (for example, a cycle
start button) to provide control of heat output. Referring to the
reference numbers in FIGS. 1 and 2, cordwood burning appliance 20
is constructed in a conventional fashion and employs a tube-style
secondary combustion system 2. An embodiment of the invented
combustion and emission control system is integrated into the
appliance 20. It includes a combustion chamber 19 into which the
cordwood fuel is loaded and combusted. An air tight door is not
shown but is normal to the construction of a cordwood burning
appliance 20. The secondary combustion system (secondary combustor)
2' is shown in more detail in FIG. 3, and is a conventional style
known in the art except for the adaptation of receiving temperature
sensors 14, typically thermocouples, and/or protection for the
sensors according to embodiments of the invention. A receiver ring
45 is attached to the appliance that allows for combustion
by-products to exit the appliance into a flue or chimney (not shown
in FIGS. 1 and 2). A controller 13 is responsible for the
combustion control of the appliance and is located under and far
away from the hot combustion chamber 19. Temperature sensors 14
located in direct proximity to the gases being combusted in the
secondary combustor 2 send information to the controller 13
typically by means of a wired connection W1. After the controller
interprets data from the temperature sensors 14, it sends a signal
(via W2) to the electronic actuator 12 based on the
controller/algorithm(s) (including "logic", "programming", "code",
"software", "firmware" and/or "hardware"), discussed elsewhere in
this document.
[0045] The status indication light 10 serves several functions. For
example, if the status indication light 10 is illuminated after a
fire has been recently started (in the start-up phase), it
indicates to the operator that fuel can be added without having to
press the cycle start momentary switch 11. Further, if light 10 is
illuminated during the organic phase, it indicates that the SCT IS
above the lowest target range of the controller (even if the target
range being used by the controller at the time is a higher target
range), and the operator may add more fuel to the stove without
having to reset the cycle (without having to press the start
button). This is because the inventor has found that if the SCT is
above the lowest sct target range of the controller, there is
enough thermal inertia to add more fuel to the stove and it will
burn well even without having to reset the cycle. Thus, an operator
may put "one more piece" on the fire before retiring to bed, for
example, without restarting the cycle. The light 10 goes out once
the SCT is below the lowest SCT target of the controller,
indicating that if more wood is to be added the cycle should be
reset. Also, the status indication light 10 serves the purpose of
sending a blinking message to the operator that a fault has
occurred, such as a burned out thermocouple, etc.
[0046] The cycle start momentary 11 pushbutton sends a signal to
the controller 13 (via W3) that resets the control algorithm and
opens the primary air orifice 16 to full open in anticipation of a
re-fueling of the appliance. The electronic actuator 12 is attached
to a control rod 15 that, by means of mechanical attachment to the
primary air control rod 18, moves the orifice plates that are part
of the primary air orifice 16. An operator selector unit 21, such
as a heat output selection switch or a thermostat, is also
connected to the controller 13 (via W4), and provides information
to the controller 13 regarding the desired heat output or the room
temperature, respectively.
[0047] In the organic combustion phase, the preferred thermostat
(21) sends a signal to the controller 13 if the indicated (sensed)
room temperature is lower than the thermostat set-point room
temperature and the controller 13 controls the primary air orifice
16, according to the methods discussed elsewhere in this document,
to attain a secondary combustor temperature (SCT) within a certain
predetermined target range that is relatively high compared to a
different, lower, predetermined SCT target range that is used if
the thermostat is satisfied. This relatively high target SCT range
typically requires the controller keep the orifice 16 entirely or
substantially open, thus providing more air for combustion and
raising the temperature of the room. Once the room temperature is
high enough to satisfy the thermostat (21), a different signal sent
to the controller 13 then controls the primary air orifice 16,
again according to the methods discussed elsewhere in this
document, to attain said lower predetermined SCT target range. This
lower target SCT range typically allows/requires the controller to
reduce (close an incremental amount) the orifice 16 an incremental
mount once or iteratively until the lower SCT target range is
obtained.
[0048] In the charcoal combustion phase, the controller again
responds to the thermostat, but according to a somewhat simpler
method, because the lack of organic volatiles escaping the charcoal
to the secondary combustor allows for said simpler method. In this
phase, if the thermostat calls for heat (room temperature lower
than the set-point), then the controller opens the orifice. If the
thermostat is satisfied (room temperature at or higher than the
set-point), then the controller closes the orifice, typically all
the way to 100% closed to conserve the remaining charcoal fuel.
[0049] FIG. 3 shows a close up view of the tube style secondary
combustion system 2 of FIGS. 1 and 2, removed from the appliance
20. Metered or unmetered secondary air 27 (in dashed line) enters
the manifold 24 that is generally sealed to the side of the
combustion chamber 19 (see FIG. 2). The secondary air is then
distributed to the individual tubes 22 and then enters the
secondary combustion zone (FIG. 2). The baffle board 23, a
generally horizontal board above the tubes 22, serves to block the
gasses from rising and diverts the gases to flow generally
horizontally along/across multiple tubes 22 toward the front of the
appliance (FIG. 2). Temperature sensors 14 are located in a
separate tube 26, typically parallel to the tubes 22, and between
two of the tubes, that serves to hold and protect the sensors 14.
Secondary combustion of the combustible gasses may take place at or
near the tubes 22 and board 23, given appropriate oxygen content
and temperature in that zone 2. The temperature sensors 14 monitor
the temperature of the mixture of gasses (air and combustibles or
"volatiles") and this temperature is the "secondary combustion
temperature" (SCT) discussed herein. In this embodiment, two
sensors 14 are shown, but other numbers of sensors could be used.
Other means to hold and protect the temperature sensors may be
used.
[0050] Another embodiment 1' of the invention is illustrated by the
cordwood burning appliance in FIGS. 4 and 5, wherein the
combination of cordwood appliance 20' and the combustion and
emission control system includes much the same equipment as
embodiment 1 in FIGS. 1 and 2 (hence, many reference numbers are
the same), except that an alternative embodiment of the secondary
combustor is used, specifically, a catalytic combustion system 2'.
Referring to the reference numbers in FIGS. 4 and 5, cordwood
burning appliance 20' is constructed in a conventional fashion and
employs a catalytic secondary combustion system 2' such as is known
in the art. An embodiment of the invented combustion and emission
control system is integrated into the appliance 20'. The appliance
includes a combustion chamber 19 (also "main firebox") into which
the cordwood fuel is loaded and combusted. An air tight door is not
shown but is normal to the construction of a cordwood burning
appliance 20'. The secondary combustion system (secondary
combustor) 2' is shown in more detail in FIG. 6, and is a
conventional style known in the art except for the adaptation of
receiving temperature sensors 14, typically thermocouples, and/or
protection for the sensors according to embodiments of the
invention. A receiver ring 45 is attached to the appliance that
allows for combustion by-products to exit the appliance into a
flue/chimney F, shown in dashed lines in FIG. 5. A controller 13 is
responsible for the combustion control of the appliance and is
located under and far away from the hot combustion chamber 19.
Temperature sensors 14 located in direct proximity to the gases
being combusted in the secondary combustor 2' send information to
the controller 13. After the controller interprets data from the
temperature sensors 14, it sends a signal to the electronic
actuator 12 based on the controller algorithm(s), discussed
elsewhere in this document.
[0051] FIG. 6 shows a close up view of the catalytic element 30 of
system 2' of FIGS. 5 and 6. The catalytic element 30 is generally
located in the same location as the tubes 22 and baffle board 23 of
the secondary combustor 2 of FIGS. 1 and 2. Directed to flow
generally horizontally forward toward the front of the appliance 20
by the horizontal baffle board 23' (see FIG. 6), air 32 and
combustible gases 33 flow from the combustion chamber 19 to the
front of, and then rearward through, the catalytically-active
portion 130 of element 30. Top flange 131 and side flanges 133,
protruding forward from the catalytically-active portion 130,
further serve to direct the air/gas flow to portion 130. The
temperature of the mixture of gasses (air and combustibles or
"volatiles") is monitored by temperature sensors 14', typically
thermocouples, and this temperature is the "secondary combustion
temperature" (SCT) discussed herein. The temperature sensors 14'
can be located in the front of the catalytic element 30 (as shown
in FIG. 6). Or, temperature sensors 14' may also be located in the
space behind the catalytic element 30 but still upstream of the
ring 45 and flue F, or a combination thereof (as shown
schematically in dashed lines in FIG. 5). The catalytic element 30
serves as a location of oxidation of the combustible gases 33 and
air 32. The by-product gases 34 then exit the catalytic element 30
and exit the appliance 20' via the receiver ring 45 that is
attached to a flue or chimney F.
[0052] FIG. 7 shows the air flow and combustible gases that are
typical of the preferred appliances in which many embodiments of
the invention will be built/retrofit. The primary air streams 40,
41 and 42, all being air that is provided through primary air
orifice 16, is distributed to multiple locations within the
combustion chamber 19 (main firebox) in various proportions. For
example, primary air streams 40 and 41 are directed to enter the
chamber 19 generally below the burning solid-fuel/wood 46. Primary
air stream 42 is split-off from the other primary air, and directed
inside conduit/passageways inside the cabinet of the appliance, to
flow through an inlet 142 at a front side of the appliance but
still supplying the chamber 19 with oxygen for solid-fuel/wood 46
combustion. Therefore, all three streams 40, 41, and 42 are
controlled by the primary air orifice 16 and all three streams 40,
41 and 42 are brought in contact with the solid-fuel/wood 46.
Direct combustion occurs on the solid-fuel/wood 46, as well as
outgassing of combustible gases 47 that are carried upwards by
buoyancy to the secondary combustion system 2. Secondary air 27
(see FIG. 3) is introduced into the secondary combustion system (in
this example, through tubes 22 as in FIG. 3), that is, above the
solid-fuel/wood 46 and in a position to mix easily with the
combustible gases 47 rising up from the fuel 46. Thus, burning of
the combustible gases 47 occur in the region of the secondary
combustion system 2 (FIG. 1). The temperature of the combustion
process is monitored by temperature sensors 14 (see FIG. 1). The
by-product gases 44 then travel in a cavity formed between the top
48 of the appliance and the baffle board 23 (see also FIG. 3). The
top 48 of the appliance serves as the main heat exchanger in order
to provide heat to the ambient environment/room. The by-product
gases 44 then exit the appliance through the receiver ring 45.
Thus, the gasses 44 may be said to exit the appliance before
reaching the flue/chimney, and it is clear that the secondary
combustion system and zone, and the associated temperature sensors,
are located inside the appliance, upstream of the appliance's exit
to the flue. Preferably, the temperature sensors are located within
a few inches of the secondary combustion zone structure, for
example, within 0.5-4 inches, or within 1-3 inches of a secondary
air tube 22, baffle board 23, or catalytically-active portion 130.
In many embodiments, the controller does not receive any messages
from any temperature sensors (is any exist) in the primary
combustion zone.
[0053] It is clear that the preferred temperature sensors for
sensing secondary combustion are not in the flue. It is clear too
that the preferred temperature sensors for sensing secondary
combustion are neither near nor contacting, nor sensing the
temperature of, the appliance cabinet, which may also be called the
appliance "cabinet walls" or "outer housing".
[0054] FIG. 8 shows examples of some, but not all, heat-output
scenarios, wherein the different scenarios are created by the
controller using different predetermined SCT targets. Each SCT
target is typically a range of SCT temperature, for example, a
range of about 120 degrees F. For example, for a non-catalytic
secondary combustion zone, a relatively high heat output mode H
could use a high SCT target range of 1500 degrees F. to 1380
degrees F., a relatively medium heat output mode M could use a high
SCT target range of 1370 to 1250 degrees F., and the relatively low
heat output mode L could use a low SCT target of 1180 to 1060
degrees F. For example, for a catalytic secondary combustion zone,
a relatively high heat output mode H could use a high SCT target
range of 1470 degrees F. to 1350 degrees F., a relatively medium
heat output mode M could use a high SCT target range of 1120 to
1000 degrees F., and the relatively low heat output mode L could
use a low SCT target of 770 to 650 degrees F. It may be noted that
the differences between each range, that is, from the lowest
temperature of one range to the highest temperature of the
next-lowest range, is in the range of 150-250 degrees F., or in the
range or 200-250 degrees F., or preferably about 230 degrees F. It
may be noted that these high SCT target ranges are higher than the
preset high threshold temperature of about 1200 degrees F.,
discussed above. This is because the fire continues to build in
temperature after the first small closing of the primary air valve
(at the end of shutdown), so that the SCT will continue to build
for a time after said first small closing, so that, even with said
first small closing, the fire will take the SCT Into the high SCT
target range if the a high heat output selection or thermostat
setting is commanding the high SCT target range.
[0055] The high and low modes H, L, may be used to illustrate the
high and low SCT target ranges used in preferred embodiment, with
selection of the high SCT target range or the low SCT target range
being based on whether the thermostat is not satisfied and
therefore calling for more heat output, or whether the thermostat
is satisfied because the desired room temperature has been met.
[0056] Therefore, FIG. 8 illustrates the primary orifice relative
to time for the various target heat output scenarios. In high heat
output mode H, the orifice stays wide open (start-up phase, P1)
until a predetermined/preset (high) threshold temperature is
realized in the secondary combustor, as measured by the secondary
combustion zone temperature sensors. The orifice is then closed a
small amount (at C1) and the "high burn" SCT target referenced in
the control algorithm is used to control any further closing of the
primary air orifice during the modulation of the organic combustion
phase P2-H. This high heat output mode H in FIG. 8 would generally
correspond to a scenario wherein the thermostat continues to call
for heat throughout most of the burn so that a high target SCT
range is selected and maintained. At the end of the organic burn
phase P2-H, another (low) temperature threshold is reached (see
temperature 65 in FIG. 9), indicating that the fuel is gone and the
orifice can then be shut all the way to closed (at C2) assuming the
thermostat is satisfied by the end of the organic phase P2-H.
[0057] The same/similar operation occurs for the low heat output
mode L illustrated in FIG. 8, which except that a lower preset SCT
target range is referenced in the control algorithm, for example,
because the thermostat indicates the desired room temperature has
been met. In this low heat output mode L, the orifice stays wide
open (start-up phase, P1) until a predetermined/preset (high)
threshold temperature is realized in the secondary combustor, as
measured by the secondary combustion zone temperature sensors. The
orifice is then closed a small amount (C1) and, assuming the
thermostat is satisfied in this scenario, the "low burn" SCT target
range is referenced in the control algorithm is used to control any
further closing of the primary air orifice during the modulation of
the organic combustion phase P2-L. In this low heat output mode L,
the controller commands the electronic actuator to close further
than it does in the high heat output mode H, due to the lower SCT
target range that is referenced. This low heat output mode L would
generally correspond to a scenario wherein the thermostat is set so
low, or the room is already so warm, that the thermostat
immediately/soon does not, and continues not to, call for heat
throughout most of the burn, resulting in the low target SCT range
being selected and maintained. At the end of the organic burn phase
P2-L, another (low) temperature threshold (for example, 65 in FIG.
9) is reached indicating that the fuel is gone and the orifice can
then be shut all the way to closed (starting at C2 in FIG. 9).
Assuming the thermostat is still satisfied through the charcoal
phase P3-L, the orifice will remain closed.
[0058] Therefore, the steep change in slope after C2, in FIG. 8,
represents the beginning of the charcoal phase of combustion (P3-H
and P3-L) due to no further combustible gas compound from the
solid-fuel/wood ("volatiles") being available for the secondary
combustor to burn. Near the end of the organic combustion phase
P3-L of the low heat output mode L, for example, when the SCT first
drops to the low threshold temperature, the controller opens the
primary air orifice very slightly (at O-L) in order to raise the
temperature of the fuel load slightly and allow for further
outgassing of volatiles. Soon after that, the low temperature
threshold is reached again in the low heat output mode L, and the
primary air orifice is closed all the way.
[0059] One may note in FIG. 8 that the low heat output mode
exhibits a shorter organic phase than the medium and high heat
output modes, that is, more quickly reaching the point wherein the
primary air valve is reduced to zero percent open. This may occur
because, in the low mode, the stove is essentially "baking" the
wood, that is, by-and-large acting like a gasifier. The gross
result is that, fairly quickly, the volatiles are baked out of the
wood and a larger portion (compared to medium and high modes) of
charcoal is left that has no smoke (no volatiles). Thus, more
quickly than in medium and high mode, the low threshold temperature
is reached and the controller can shut down the primary air (if the
thermostat is satisfied in embodiments with a thermostat). On the
other hand, during high or medium mode, the organic phase is a
(longer) combination of burning through a significant portion of
the charcoal plus and burning volatiles, and this combination of
burning charcoal while burning volatiles typically makes it
necessary to hold the primary air orifice at least partly open for
a longer time. The fact that the primary air control goes to zero
at an earlier time in the low heat output mode does not mean that
heat output has stopped, it means that heat output is slowed down,
but that charcoal BTU's will be subsequently produced over a longer
charcoal phase (typically, a longer charcoal phase than in the
medium and high modes).
[0060] FIG. 9 is a graph that depicts the relationship of the
temperature (SCT) of the gases in the secondary combustor in
relation to time for a low heat output setting, for example, such
as low heat output mode L in FIG. 8. The steep line 60 shows the
rise in temperature of the gases after a refueling event has
occurred; this region is defined as the startup phase of combustion
P1-L. The temperature builds until it reaches the upper threshold
temperature depicted by 61. The upper threshold temperature 61, as
shown in FIG. 9, may be at the upper limit of the SCT target range.
Alternatively, in certain embodiments, the upper threshold
temperature 61' may be within or lower than the preset SCT
temperature range (TR-L), due to the fact that the fire may
continue to increase SCT even after a first small closing of the
primary valve, as discussed above. Or, alternatively, in certain
embodiments, the upper threshold temperature 61'' may be higher
than the preset SCT temperature range (TR-L). As explained
elsewhere in this document, an example upper threshold temperature
61 may be 1200 degrees F.
[0061] This following portion of combustion is referred to as the
organic combustion phase P2-L, or "organic portion". This first
peak then dips (trough 62) due to the controller closing primary
air control valve some set amount (see C1 in FIG. 8), which in this
scenario brings the SCT into the SCT target range TR-L. The
temperature then builds again (peak 63) and the controller closes
the primary air valve again to drop (trough 64) the SCT to the
predetermined level, that is, to be substantially within, and then
preferably entirely within, the SCT target range TR-L. As will be
understood by viewing FIG. 9, the iterative process of bringing SCT
to the SCT target range may comprise SCT being only slightly
outside (up to about 50 degrees F.) the SCT target range for short
periods of time, for example for up to about 5 minutes for each
occurrence, and this is within the definition of the term
"substantially within" in this context; such iterations would
typically use the "long timer". In other situations, iterations may
comprise SCT being greatly outside (for example, 100-300 degrees)
the SCT target range for a few iterations, in which case the "short
timer" would be used to make quicker adjustments in order to bring,
after said few iterations, the SCT to be substantially within, or
entirely within, the SCT target range. The iterations continue
until the primary air orifice is either closed to a programmed
(preset) minimum orifice opening or until the SCT remains within
the TR-L without further adjustment (see the flat slope in FIG. 8).
It may be noted from FIG. 9 that more than 4 iterations of closing,
evaluating, and readjusting the primary air valve are done, but
other numbers of iterations may be done in certain embodiments and
depending on the size and type of solid fuel load, for example. For
example, one might expect 1-8 iterations, or 2-7 iterations, or 3-6
iterations, in certain embodiments for each change in the SCT
target range. For a scenario wherein a large load of fuel is placed
in an appliance in a room with a thermostat and easily or
moderately-easily heated by the appliance, one might expect two SCT
target ranges to be used, that is, the high range in the beginning
of the organic phase and the low range once the thermostat is
satisfied. In such a scenario, for example, one might expect a
total of 4-14 (twice times 2-7) iterations for the two ranges
combined, or more typically 6-12 (twice times 3-6) iterations,
between the two ranges.
[0062] The air control is then held stationary (see flat slope in
FIG. 8) until the end of the organic phase, indicated by the steep
downward temperature slope 66 and reaching of the low threshold
temperature 65, due to the fuel being exhausted and the temperature
of the secondary combustor lowering naturally. The low threshold
temperature could be, for example, about 932 degrees F. for a large
fuel load initially placed into the appliance, or about 842 degrees
F. for a small fuel load initially placed into the appliance,
regardless of whether the non-catalytic or catalytic secondary
combustion zone is being used. This begins the stage of combustion
referred to as the charcoal phase P3-L. The primary air control is
then closed all the way via the controller. In certain embodiments,
as discussed earlier, the controller may open the primary air
during the charcoal phase P3-L, if the thermostat calls for
heat.
[0063] In certain embodiments, there may be situations in which,
after the first, small closing of the primary air, the SCT drops
quickly in the organic phase to a level that is below the lowest
SCT target range; this may occur when a very small amount of fuel
is placed in the appliance for the first and only fuel load, for
example. In such cases, the controller will not further adjust the
primary air, until a value of SCT is reached that triggers entrance
into the charcoal phase. Due to the single adjustment of the
primary air (said first, small closing), the controller may select
a lower-than-normal "value of SCT" to signal the start of the
charcoal phase. In other words, the controller may select a lower
than the normal low threshold temperature (charcoal phase
temperature) for such cases wherein there are very few iterative
adjustments of the primary air because the SCT drops quickly. In
such situations, the fire is still clean, but the secondary
combustor is not engaged (or minimally) and the fire is burning
more like a fireplace rather than an airtight wood stove.
[0064] FIGS. 10 and 11 illustrate a preferred embodiment, which
provides a scenario wherein the appliance is controlled for high
heat output, until the desired room temperature is met according to
the user's thermostat, and then the appliance is controlled for
lower heat output. FIG. 10 illustrates the primary orifice relative
to time for one example of this preferred scenario, wherein a high
heat output mode H is used during the beginning of the organic
combustion phase, but said high heat output heats the room to the
point where the thermostat is satisfied midway through the organic
combustion phase. When the thermostat is satisfied, the controller
switches at transition T to referencing the low heat output SCT
target. Then, the controller iteratively closes the primary air
orifice until the SCT falls within the low target range, and the
organic phase continues in a low heat output mode L such as
described above for FIG. 8. FIG. 11 illustrates the SCT profile
during the primary air orifice adjustments of FIG. 10. This
embodiment allows for convenient heating of the room to a desired
temperature, but, after that, maintenance of that room temperature
typically may be done by controlling the appliance to output less
heat while still reducing/minimizing emissions. Thus, this scenario
comprises a start-up phase P1 and a first portion of organic phase
P2 typical of a high heat output mode H, but a latter portion of
the organic phase P2 and an organic phase P3 typical of low heat
output mode L.
[0065] FIG. 12A-C illustrate methods of control and operation of
certain embodiments, which methods have been generally or
specifically discussed above. One may note that FIGS. 12A-C use the
term "selected SCT target range TR", wherein selection is a broad
term that may include several types of "selection".
[0066] The preferred embodiments utilize, in FIGS. 12A-C and 13, a
thermostat in a room that the user will use in a conventional
manner to enter a set-point corresponding to the desired room
temperature. The true or false signals from the wall-mounted
thermostat, sent to the controller, determine whether what SCT
target range TR is "selected" by the controller/algorithm(s). As
illustrated by FIG. 13, if the thermostat changes its signal
partway through the organic combustion phase (with or without the
user changing the thermostat), this results in the new "selection"
of SCT target range, and a new iterative process for bringing the
SCT into compliance with the newly-selected SCT target range.
[0067] In alternative embodiments, the selection, in FIGS. 12A-C
and 13, could be done by other methods/apparatus. For example,
certain embodiments may be adapted so that the user selects a heat
output via a switch, for example, a wall switch or switch near the
controller. The controller then responds by using a SCT target
range preprogrammed for that heat output. As illustrated by FIG.
13, if the user changes the heat output selection changes partway
through the organic combustion phase, this results in the new
"selection" of SCT target range, and a new iterative process for
bringing the SCT into compliance with the newly-selected SCT target
range.
[0068] This may result in an appliance that can operate in all of
the high, medium, and low modes of FIG. 8, and may result in an
operation wherein the operator may switch the heat output selection
in the middle of the burn cycle, for example, in the middle of the
organic phase. One may understand from this document, including the
disclosure of the provisional application, that said switching
would result in iterative adjustments of primary air to reach the
newly-selected heat output mode. Examples of such adaptations and
methods are focused on in the provisional application of which this
non-provisional claims priority, that is, Provisional Application
Ser. No. 61/851,343, filed Mar. 7, 2013, incorporated herein by
reference.
[0069] The main objective of the preferred embodiments is to
provide ease of use to the user and ensure clean emissions at all
available burn rates/heat-output modes. The electronic-based system
may use a parameter table, for the high threshold temperature that
triggers/signals the end of the start-up phase, the multiple SCT
target ranges, the low threshold temperature that triggers/signals
the end of the organic phase, and failsafe temperature safety
limit(s) to ensure that the automatic operation of the appliance
does not enter dangerous scenarios. The parameters/table may be
established by a manufacturer and/or retrofitter, and the
controller may be programmed without undue experimentation, given
the teachings of this document and the figures. For example,
fine-tuning of the parameters, relative to those disclosed herein,
may be determined for each appliance model either without undue
experimentation, and then the parameters would be entered into
memory of the controller during the manufacturing process of the
controller.
[0070] The process of evaluating the temperature of the gases in
the secondary combustor via a wait, evaluate and make decision
process is not the only method of control possible when considering
the present invention. Other algorithms based on PID
(proportional-integral-derivative) control of the relationship
between secondary gas temperature and control of the primary air
orifice may be used in certain embodiments. The process of
adjusting primary air into the combustion chamber of a cordwood
fired appliance based upon gas temperature of the secondary
combustor is important to most or all embodiments of the invention,
and may be incorporated into several types of secondary combustors
and ones not yet invented. If the gas temperature of the secondary
combustor is sufficient then by proxy the appliance is burning
clean and efficiently. Secondarily, this gas temperature also
indicates various stages of the combustion process and decisions
can be made by the controller to influence burn time and heat
output.
[0071] It will be noticed that the preferred embodiments do not
comprise adjustment or other control of secondary air. Thus,
certain embodiments may be said to be control apparatus and/or
methods that comprise, consist essentially of, or consist of
adjusting primary air in response to one or more temperatures
measured inside or immediately adjacent to the secondary combustion
zone of a solid-fuel burning appliance. Said temperature will be
the temperature, or extremely close to the temperature, of the
gasses burning in the secondary combustion zone, which will be a
mixture of gasses from the main firebox burning of solid fuel,
including "excess" primary oxygen that is not consumed in the main
firebox and combustible volatiles from the wood, and in some,
particularly unanalyzed embodiments, secondary air added directly
to the secondary combustion zone. Thus, it is important to note
that the preferred embodiments control air stream(s) added to the
appliance for combustion of the solid fuel in the main firebox, but
that this primary air control has a synergistic effect of
controlling and improving secondary combustion zone performance and
emissions performance of the appliance.
[0072] In certain embodiments that comprise adjusting primary air
according to teachings herein, secondary air stream(s) also may be
controlled via the same control system or a supplemental control
system. Therefore, in certain embodiments of the invention, it may
be advantageous to also control the air stream(s) that enter(s)
directly into the secondary combustor (in addition to controlling
the primary air that first enters the main firebox for solid-fuel
combustion) in order to maximize efficiency and to control SCT even
further. The inventor believes that if a system were built to
control only secondary air, rather than primary air and possibly
also secondary air, then the unit would be "stuck on high" due to
there being no control of the primary combustion zone (main
firebox) and the level of volatile gas production.
[0073] Although this invention has been described above with
reference to particular means, materials and embodiments, it is to
be understood that the invention is not limited to these disclosed
particulars, but extends instead to all equivalents within the
scope of the following claims.
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