Note: Descriptions are shown in the official language in which they were submitted.
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DRAFT INDUCER PERFORMANCE CONTROL
FIELD OF THE INVENTION
The invention generally relates to air movement and, more particularly, the
invention relates to draft inducers.
BACKGROUND OF THE INVENTION
Fuel burning furnaces commonly have an attached draft inducer that mixes
ambient air with exhaust fumes produced by burning fuel. After the exhaust
fumes
and ambient air are mixed, they are vented from the furnace through an exhaust
pipe. Among other benefits, draft inducers can improve heater efficiency by
controlling the flow of exhaust fumes from their furnaces.
More particularly, when exhausting fumes, inducers necessarily draw heat
away from their corresponding furnace. Idealized inducers draw exactly the
minimum amount of fumes (and thus, the minimum amount of heat) to ensure that
carbon monoxide is sufficiently exhausted. For example, an inducer that draws
excess air from a hot water heater necessarily increases the amount of time
required
to heat the water. Accordingly, such an inducer wastes energy. Conversely,
carbon
monoxide can build up if the inducer does not draw enough air from the heater.
This clearly is a very dangerous condition and thus, must be avoided.
Accordingly,
some prior art inducers inefficiently draw too much air to avoid this
dangerous
build-up condition.
By mixing exhaust fumes with ambient air to create an exhaust/air mixture,
a draft inducer lowers the concentration of carbon dioxide and carbon
monoxide.
An elevated concentration of carbon dioxide can result in drowsiness, and
prolonged exposure to a consequently oxygen deficient environment can lead to
suffocation. Exposure to elevated concentrations of carbon monoxide is more
dangerous. By inactivating hemoglobin within red blood cells, carbon monoxide
may cause death even in the presence of an otherwise adequate oxygen
concentration.
One approach to maintaining carbon dioxide and carbon monoxide levels in
the exhaust/air mixture below thresholds known to cause problems is to control
the
speed of the draft inducer on the basis of those concentrations. The proper
draft
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creates the proper combustion efficiency. Optimum combustion is consistent
with
low carbon dioxide and carbon monoxide concentrations. The higher the speed,
the
more ambient air added, and the lower the concentration of the unwanted
constituents. However, measurement of gas concentrations may be relatively
expensive and complex as gas sensors may be costly and exposure of sensors to
an
exhaust/air mixture may require protecting sensors or withdrawing a sample of
the
exhaustlair mixture.
SUMMARY OF THE INVENTION
l0 In accordance with one aspect of the invention, the composition of the
output of a draft inducer is controlled by associating a desired temperature
with
desired concentrations of one or more constituents of the draft inducer output
and
controlling an air flow so as to substantially maintain the desired
temperature.
Optionally, the constituents may be carbon dioxide, carbon monoxide, and
water.
15 The controlling of an air flow may be accomplished with a look up table. In
certain
cases, the temperature at the output of the draft inducer may be measured, as
with a
thermistor. The desired temperature to associate with the desired
concentrations
may also be determined. On occasion, an audible signal may be generated, as by
a
speaker or by a piezo alarm.
20 In some embodiments, a desired temperature may be associated with desired
concentrations of constituents and with an ambient temperature. Association
may
be accomplished by accessing a look up table. The temperature of ambient air
entering the draft inducer, as well as the temperature of the draft inducer
output,
may be measured, as with thermistors.
25 In accordance with another aspect of the invention, a system for
controlling
the composition of the output of a draft inducer includes means for
associating a
desired temperature of the draft inducer output with one or more desired
concentrations of constituents and means for controlling an air flow so as to
substantially maintain the desired temperature. Certain embodiments may
include a
30 microprocessor where the microprocessor may include a memory and the memory
may include a look up table that may include the desired temperature and the
desired concentrations of the constituents. The constituents may include
carbon
dioxide, carbon monoxide, and water. The temperature of the draft inducer
output
may be measured with a thermistor.
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Certain embodiments may include means for measuring the temperature of
ambient air entering the draft inducer, as with a thermistor. There may be a
microprocessor where the microprocessor may include a memory and the memory
may include a look up table that may include the desired temperature, the
desired
concentrations of the constituents, and the ambient temperature. The
constituents
may include carbon dioxide, carbon monoxide, and water. Some embodiments may
include means for generating an audible signal, as with a speaker or with a
piezo
alarm.
In accordance with a further aspect of the invention, a draft inducer capable
l0 ' of coupling with an exhaust pipe includes an input for detecting a
temperature of a
draft inducer output at a selected location in he exhaust port of the draft
inducer, an
air moving device, capable of rotating at a plurality of different rotational
speeds,
for generating air flow in the exhaust pipe, and a control module for
controlling the
rotational speed of the air moving device as a function of the difference
between the
temperature of the draft inducer output in the exhaust pipe and a desired
temperature reflective of desired concentrations of constituents, including
carbon
dioxide, carbon monoxide, and water in the exhaust pipe.
In certain embodiments, the control module may control the rotational speed
of the air moving device to maintain the temperature in the exhaust pipe at
2o substantially the desired temperature. The draft inducer output may be
coupled to
the exhaust pipe at the draft inducer exhaust port. In some embodiments, the
draft
inducer may include an audible alarm, such as a piezo alarm or a speaker.
In accordance with an additional aspect of the invention, a computer
program product for use on a computer system for controlling the composition
of
the output of a draft inducer includes a computer usable medium having
computer
readable program code. The computer readable program code contains program
code for associating a desired temperature with desired concentrations of one
or
more constituents of the draft inducer output and program code for controlling
an
air flow so as to substantially maintain the desired temperature. In some
3o embodiments, the desired temperature may be associated with desired carbon
dioxide, desired carbon monoxide, and water concentrations. There may be
program code for measuring a temperature of draft inducer output and for
accessing
a look up table.
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In another embodiment, there may be program code for associating a desired
temperature with a desired carbon dioxide concentration, with a desired carbon
monoxide concentration, with a desired water concentration and with the
ambient
temperature. There may also be program code for measuring draft inducer output
temperature and for determining the desired temperature to associate with the
desired concentration.
BRIEF DESCRIPTION OF THE DRAWINGS
1o The foregoing and advantages of the invention will be appreciated more
fully from the following further description thereof with reference to the
accompanying drawings wherein:
Figure 1 schematically shows a draft inducer system that may be configured
in accordance with illustrative embodiments of the invention.
15 Figures 2A and 2B schematically show a draft inducer configured in
accordance with illustrative embodiments of the invention.
Figure 3 schematically shows the electronic configuration and connections
between the draft inducer and a corresponding hot water heater.
Figure 4. shows an exemplary process executed by the electronic circuit
2o shown in figure 3.
Figure 5 schematically shows a processor system with various connections
to other circuit elements within the circuit shown in figure 3.
Figures 6A and 6B shows experimental maintenance of gas concentration
for various lengths of 2 inch and 3 inch diameter exhaust pipes.
25 Figure 7 shows an example of correction of desired exhaust/air mixture
temperature for ambient temperatures.
Figure 8 shows a look-up table that may be used by the processor system
shown in figure 5.
Figure 9 shows a process used by the processor system to control carbon
3o dioxide and carbon monoxide concentrations.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
An indirect approach may permit control of constituent concentrations
within the exhaust from a combustor of carbon-based fuels more simply and less
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expensively. Specifically, for a given ambient air temperature, one may
associate,
in illustrative embodiments, desired concentrations of carbon dioxide and
carbon
monoxide with a desired temperature of the exhaustlair mixture measured at an
exhaust port immediately after mixing ambient air and exhaust in a mixing
chamber. As a result, control of draft induces speed to produce the desired
mixture
temperature may also control the composition of the exhaust/air mixture,
thereby
limiting carbon dioxide and carbon monoxide concentrations to desired values.
In
addition, measurement of mixture temperature may employ a relatively
inexpensive
and easy to install sensor, such as a thermistor or a thermocouple.
1o Figure 1 schematically shows a draft induces system (the "system 10") that
may be configured in accordance with illustrative embodiments of the
invention.
The system 10 has a fuel burning device 12 with a draft induces 14 mounted to
its
top side. Among other things, the draft induces 14 forcibly vents exhaust
fumes
produced by the burning fuel.
In illustrative embodiments, the fuel burning device 12 is a conventional
natural gas hot water heater (also identified by reference number 12).
Accordingly,
various embodiments are discussed as being used with a natural gas hot water
heater
12. Rather than having a hot water heater 12, however, the system 10 may have
other types of fuel burning devices, such as boilers. Discussion of a hot
water
heater 12 thus is exemplary and, consequently, not intended to limit all
.embodiments of the invention. Moreover, various embodiments may be
implemented with other types of burnable fuels, such as oil or wood.
Accordingly,
discussion of burning natural gas is not intended to limit all embodiments of
the
invention.
The draft induces 14 illustratively is mounted over an exhaust opening in the
hot water heater 12 to receive exhaust fumes produced by the burning fuel. In
illustrative embodiments, that mounting is between a cold water intake pipe 16
and
a hot water outlet pipe 18 at the top of the heater 12. When the system 10 is
on, the
draft induces 14 mixes the exhaust fumes with ambient air within its interior,
and
3o forces the resultant draft induces output or exhaust/air mixture 90 out of
the
premises via an exhaust pipe 20. Because the resultant mixture typically has a
much lower temperature than that of the exhaust fumes, the exhaust pipe 20 can
be
produced from a lower cost material, such as conventional PVC piping.
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An AC plug 22 that can be inserted into a conventional AC outlet powers the
overall system 10. Accordingly, installation requires no specialized
electrical
expertise. Draft inducer 14 also contains a connection plug 42 to provide
electrical
power to hot water heater 12.
Figures 2A and 2B schematically shows a draft inducer 14 configured in
accordance with illustrative embodiments of the invention. The draft inducer
14 has
a metal or plastic housing 24 (including sections 24A and 24B held together by
compression clips 52) containing a blower 25, a blower controller 27, and a
step-
down transformer 36 and forming an exhaust port 26 for directing the noted
1o exhaust/air mixture 90 of exhaust fumes and ambient air to the exhaust pipe
20.
The housing 24 also forms an interior mixing chamber 28 for mixing ambient air
with exhaust fumes. One or more ambient air inlets 30 formed in the side of
the
housing 24 permit the blower 25 to draw ambient air into the mixing chamber
28,
thus enabling the exhaust to mix with the air. A mixture thermistor 78 for
15 measuring the temperature of the output 90 of the draft inducer 14, i.e.,
the
exhaust/air mixture, and an over-temperature switch 72 are mounted in the
exhaust
port 26 of the inducer 14 in Figure 2B. An ambient air thermistor 80 for
measuring
the temperature of the ambient air may be mounted within ambient air inlet 30.
Plug 22, which brings AC wall voltage to draft inducer 14 through electrical
20 cord 38 has a pair of prongs 34 for mating with a wall plug (e.g., a home
AC outlet,
such as those in North America and Europe, or a power strip). The plug 22 may
be
produced from any conventional material used for these purposes, such as a
hard or
soft plastic.
Figure 3 schematically shows the general electronic configuration and
25 connections between the draft inducer 14 and the hot water heater 12. The
various
parts of the system 10 are divided by vertical dashed lines. In particular,
relevant
components of the, draft inducer 14 (i.e., noted as being within the housing
24
and/or exhaust pipe 20) are shown and identified by reference number 14, and
relevant components of the heater 12 are shown and identified by reference
number
30 12.
The step-down transformer 36 receives the wall voltage (e.g., 115 volts AC)
from plug 22 and produces a stepped-down AC voltage (e.g., 24 volts AC). The '
stepped-down voltage then is fed to a bridge rectifier 64 (within the draft
inducer
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housing 24), which converts the stepped-down AC voltage to a DC voltage (e.g.,
24
volts DC).
The draft inducer 14 also includes a first capacitor C1 that reduces ripple
from the bridge rectifier 64 and stores the DC voltage received from the
bridge
rectifier 64. A voltage regulator 24 maintains a 24 volt voltage at the input
to the
blower controller 27. A second capacitor C2 at the output of voltage regulator
24
maintains stable regulator operation. The second capacitor C2 does not provide
any
appreciable filtering. In alternative embodiments, the second capacitor C2 is
omitted.
l0 The blower controller 27 may include one or more program leads (shown
schematically at reference number 66) that permit it to perform in pre-
specified
ways. For example, as noted above, the blower controller 27 may be programmed
to cause the blower 25 to rotate at a speed (i.e., in RPMs) that is based upon
the
temperature of the exhaust/air mixture in the exhaust port 26. To that end,
the
blower 25 and the blower controller 27 may include hardware and/or software
that
perform the noted functions. For example, the blower controller 27 may include
a
processor system 68 that executes a specified function based upon computer
instructions. Different hardware within the blower 25 and the blower
controller 27
also may be configured to perform the noted functions. Additional details of
the
processor system 68 and some of its functions are discussed below with
reference to
figures 5-7.
The blower controller 27 includes internal circuitry (e.g., the processor or
control module 68) that produces a signal having a zero output state (e.g.,
logic
level of zero) when the blower 25 is running (i.e., rotating at or above a pre-
selected
RPM value), and an open output state (e.g., logic level one) when the blower
25 is
not running. This signal is transmitted directly to a switch 69 (via a
resistor R7)
that, consequently, is open when the blower 25 is off, and closed when the
blower
25 is on. In illustrative embodiments, the switch 69 is a NPN bipolar junction
transistor ("BJT") that is biased on when its base receives the noted zero
output
state.
The draft inducer 14 also includes an over temperature switch ("OTS 72") to
ensure that the temperature of the exhaust/air mixture in the exhaust port 26
does
not exceed a prescribed temperature. The inducer 14 further has a mixture
thermistor sensor 78 to measure the temperature of the exhaust/air mixture,
and may
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have an ambient air thermistor sensor 80 to measure the temperature of the
ambient
air. To that end, if the OTS 72 detects that the exhausdair mixture exceeds
such
temperature, it opens, thus breaking the circuit to the heater 12. As a
consequence,
the heater 12 cannot continue to operate. The exhaust/air mixture temperature
and
ambient air temperature, if available, are used to control the blower speed to
maintain a desired exhaust/air mixture temperature.
The heater 12 has a solenoid 74 that turns on the gas supply when on, and
turns off the gas supply when off. Accordingly, when either the OTS 72 or
switch
69 breaks the circuit, the solenoid 74 cannot function, consequently cutting
off the
to supply of gas to the heater 12. Consequently, the heater 12 cannot burn
gas, which
produces exhaust fumes.
The heater 12 also includes a low temperature switch ("LTS 76"), which
selectively turns the heater 12 on and off based upon water temperature within
the
tank. Specifically, the LTS 76 turns the heater 12 on (i.e., it closes) when
it detects
that the water temperature is below a pre-selected low temperature. In a
corresponding manner, the LTS 76 turns the heater 12 off (i.e., it opens) when
it
detects that the water temperature is at or above a pre-selected high
temperature.
Figure 4 shows an exemplary process executed by the electronic circuit
shown in figure 5. The process begins at step 500, in which the low
temperature
2o switch 76 is closed to begin heating water in the tank. This connection
provides the
ground return for the blower 25, which causes it to begin rotating.
It then is determined at step 502 if the blower 25 is running at a
predetermined minimum speed that can provide a sufficient pressure to perform
the
draft inducing function. This predetermined speed may be based upon a number
of
variables, such as the size of the hot water heater 12, the size of the blower
25 and
inducer 14, and other known parameters associated with the system 10. In
illustrative embodiments, the processor 68 makes this determination. The hot
water
heater 12 thus receives no power until the blower 25 reaches this minimum
speed.
After the blower 25 reaches the minimum speed, the process continues to
3o step 504, in which the solenoid 74 is connected to the power source. To
that end,
the processor 68 forwards a signal to the switch 69 (e.g., a logical zero).
Upon
receipt, the switch 69 closes, which connects the power source (i.e., the
transformer
36 and rectifier 64) with the solenoid 74. Consequently, the solenoid 74 turns
on
the gas supply, which enables the hot water heater 12 to begin heating the
water in
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its internal tank. After a certain delay from the time at which the blower
reaches the
minimum speed, the system increments the blower speed to create a temperature
at
the exhaust port 26 reflective of desired carbon dioxide and carbon monoxide
concentrations.
The hot water heater 12 continues to heat the water until it reaches a
predetermined maximum temperature (step 506). When that temperature is
reached,
the hot water heater 12 opens its low temperature switch 76 (step 508), which
effectively breaks the return path for the rectifier 64.
The water in the hot water heater 12 then cools until it reaches a
to predetermined minimum temperature (step 510). After it reaches the minimum
temperature, the process repeats by looping back to step 500, in which the low
temperature switch is closed.
It should be noted that this process can be interrupted at any time for
several
reasons. Primarily, if the blower 25 malfunctions by not rotating rapidly
enough,
15 the switch 69 opens, which stops the hot water heater 12 from burning its
fuel. In
other words, if the blower 25 does not reach its predetermined speed, then the
entire
system 10 effectively shuts down. In such case, the blower 25 may be replaced.
If
the various parameters are properly selected, then this feature should help
prevent
the hot water heater 12 from generating more exhaust fumes than the inducer 14
can
2o force from the system 10. The process also can be interrupted if the
exhaust/air
mixture is too hot, which causes the over temperature switch 42 to open.
In illustrative embodiments of the invention, the processor system 68
controls the speed of the blower 25 to ensure that the carbon dioxide and
carbon
monoxide concentrations in the exhaust port 26 are maintained at substantially
25 optimum gas concentration values.
To those ends, figure 5 shows the processor system 68 with various
connections to other circuit elements within the circuit shown in figure 3. In
particular, the processor system 68 includes a commutation processor U2 for
controlling normal blower commutation, and a control processor U1 for
controlling
30 the speed of the blower as a function of the temperature of the exhaust/air
mixture
within the exhaust port 26. In illustrative embodiments, the control processor
U1 is
a PIC processor (flash microprocessor), such as model number 16F818 from
Microchip, Inc., while the commutation processor U2 is an INFINEON
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POWERCH1P type of H-Bridge motor drive (e.g., model number 6LE6209), from
Infineon.
Figure 5 shows a number of other components, such as the bridge rectifier
64 (discussed above), various capacitors and resistors, and a speaker 81. The
5 speaker 81 may sound an audible signal if an error condition is detected to
inform
an operator that something is not correct. (A piezo alarm may also be used to
generate the audible signal.) For example, a signal corresponding to two beeps
may
indicate that the blower motor is running too fast, that there may be a
blockage, that
the water heater should not be used, and that service should be contacted.
Three
to beeps may indicate that the blower motor is running two slowly and that
service
should bring a replacement blower.
The control processor U1 includes memory for storing, among other things,
instructions relating to its operation, a look up table relating ambient air
temperature
with desired exhaust/air mixture temperatures, and a look up table with
information
for controlling the blower speed (in RPMs) as a function of duty cycle.
It has been experimentally determined (Figure 6) that combinations of
concentrations of carbon dioxide and carbon monoxide for a specific type of
hot
water heater (Bradford White 40 gallon gas hot water heater Model MITW
40L6BN12) can be associated with exhaust/air mixture temperatures at the
exhaust
2o port 26 of the draft inducer 14. An illustrative correlation between the
desired
exhaust/air mixture temperature measured at the outlet of the exhaust port 26
and
desired carbon dioxide and carbon monoxide concentrations there is shown in
Figure 7A for hot water heater (Bradford White 40 gallon gas hot water heater
Model MTTW 40L6BN12). It has been found that a desired carbon dioxide
concentration of 9 ppm and a desired carbon monoxide concentration of 30 ppm
may be maintained in a 2 inch diameter exhaust pipe, independent of the length
of
the pipe, if the speed (i.e., as measured in revolutions per minute or RPM) of
the
blower is adjusted to maintain the temperature of the exhaustlair mixture at
170 °F,
as measured at the exhaust port 26. It has also been found that the adjustment
of
3o blower speed required to maintain constant exhaust/air temperature
consistent with
desired carbon dioxide and carbon monoxide concentrations also maintains
constant
volume flow rate (i.e., as measured in cubic feet per minute or CFM) of the
exhaust/air mixture. Figure 7B illustrates maintenance of a carbon dioxide
concentration of 9 ppm and a carbon monoxide concentration of 30 ppm with an
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11
exhaust/air temperature of 140 °F for a 3 inch diameter exhaust pipe.
It has been
observed that control of the carbon monoxide concentration may become
problematic for carbon monoxide concentrations in excess of 30 ppm as the
carbon
monoxide concentration becomes very sensitive to changes in blower speed.
Correlation between desired exhaust/air mixture temperatures and the
desired carbon dioxide and carbon monoxide concentrations may be somewhat
affected by the ambient temperature. Additional control for ambient
temperature
may be achieved by adjustment of the desired temperature associated with
desired
concentrations of carbon dioxide and carbon monoxide. For example, for a
desired
to carbon dioxide concentration of 9 ppm and a desired carbon monoxide
concentration of 30 ppm, figure 7 illustrates the relationship between desired
exhaustlair mixture temperatures and ambient air temperatures of 60 °F,
70 °F, 80
°F, and 90 °F.
In general, the lower the desired exhaust/air mixture temperature, the higher
15 are the desired concentrations of carbon dioxide and carbon monoxide.
Consequently, control of blower RPM to control exhaust/air mixture temperature
also controls carbon dioxide and carbon monoxide concentrations by altering
the
proportions of exhaust and ambient air in the exhaust/air mixture. To that
end, for
the specific type of hot water heater (Bradford White 40 gallon gas hot water
heater
2o Model MITW 40L6BN12) a number of RPM values have been associated with
different duty cycles (which control blower speed) for exhaust pipe lengths of
5, 10,
and 20 feet in Figure 8. This data may be stored as a look-up table in
processor
system 68.
In operation, once the blower 25 has been determined to be running at a
25 predetermined speed, the blower speed may be increased or decreased and the
exhaust/air mixture temperature may be monitored by thermistor 78. As long'as
the
temperature indicated by the thermistor 78 is below the desired temperature,
in this
case, 170 °F, the duty cycle may be increased to increase the blower
speed. When
the temperature derived from thermistor 78 matches the desired temperature,
the
3o blower speed is kept constant. Beginning at a moderate speed and increasing
rather
than beginning at a high blower speed and decreasing minimizes the disturbing
effect that the sound from a suddenly energized blower may have. Another
reason
to start the blower 25 at a moderate speed is avoidance of Booting.
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12
As an example, to obtain a carbon dioxide concentration of 9 ppm (parts per
million) or less and a carbon monoxide concentration of 30 ppm or less in
exhaust
pipe 20 of a Bradford White 40 gallon gas hot water heater (Model MITW
40L6BN12), the temperature of the exhaust/air mixture may be controlled to be
170
°F, independent of the length of exhaust pipe 20, within the capability
of the blower
25. Different combinations of desired carbon dioxide and carbon monoxide
concentrations may be associated with different desired exhaust/air
temperatures
and may be contained in a look up table.
During operation, the processor U1 sets the duty cycle at one of the duty
to cycles in the table to establish a speed for blower 25. Hall effect sensor
90 gives
feedback to processor U1 to define blower speed (RPM). If the exhaust/air
mixture
temperature does not match the desired exhaust/air mixture temperature, then
the
processor U1 changes the duty cycle to another value in the table. For
example, the
processor Ul increases the RPM (i.e., increases the duty cycle) if the
exhaust/air
mixture temperature is below the desired exhaust/air mixture temperature, or
decreases the RPM (i.e., decreases the duty cycle) if the exhaust/air mixture
temperature is above the desired exhaust/air mixture temperature. After
increasing
or decreasing the RPM, the processor Ul again checks the exhaust/air mixture
temperature. This process iterates until there is a match between the measured
2o exhaustlair temperature and the desired exhaust/air temperature. Details of
the use
of this table are discussed below with reference to Figure 9.
The process of Figure 9 begins at step 800, where the initial duty cycle is
set. The processor U1 sets the initial duty cycle to a middle entry in the
look up
table appropriate for the length of exhaust pipe 20 to minimize sooting. For
example, the duty cycle may be set to DC8 for a 10 foot long exhaust pipe. In
alternative embodiments where, for example, sooting is not a concern, the
initial
duty cycle may be the first entry in the look up table (DC6 in the case of a
10 foot
long exhaust pipe).
Within seven seconds, ignition is initiated in step 803. A time limit is
3o imposed to avoid having excessive fuel vapor in the exhaust pipe 20. If a
time limit
is not imposed, ignition may result in an explosion.
It then is determined at step 804 if the actual exhaust/air mixture
temperature
indicated by mixture thermistor 78 in exhaust port 26 associated with the
currently
set duty cycle is higher or lower than the desired exhaustlair mixture
temperature
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13
associated with the desired carbon dioxide and carbon monoxide concentrations.
(For additional control, the desired exhaust/air mixture temperature may also
be
based upon the current ambient temperature.) In the example above, it is
determined if the actual exhaust/air mixture temperature exceeds 170
°F. If the
actual exhaust/air temperature is lower, then the process continues to step
806, in
which it is determined if the duty cycle is at a maximum value in the table.
If it is at
the maximum value in the table, (which, in the current example, is not the
case),
then the process continues to step 808, in which the system 10 is shut down.
In
such case, an error condition may have occurred, such as the blockage of the
to exhaust pipe 20, such as a nest built on the outlet. To that end, the
processor Ul
shuts down the blower 25, which causes the solenoid 74 to shut down.
Conversely, if at step 806 it is determined that the duty cycle is not at the
maximum value, then the process continues to step 810, in which the duty cycle
is
incremented by one look up table entry. Accordingly, at step 810, the duty
cycle is
increased from DC8 to DC9. The process then loops back to step 804.
Returning to step 804, rather than determining that the actual exhaust/air
mixture temperature is lower, if the actual exhaust/air mixture temperature is
higher
than the desired exhaust/air mixture temperature 170 °F, then the
process continues
to step 812. At that step, it is determined if the duty cycle is at a minimum
value in
2o the table. If at the minimum value, then the system 10 shuts down (as
discussed
above-step 808). This type of shut down could suggest some disconnection of
the
exhaust pipe 20. If the current entry is for DCB, however, then the minimum
duty
cycle has not been reached.
If the duty cycle is not at the minimum, as in the example, then the process
continues to step 814, in which the duty cycle is decremented. Accordingly, if
the
current duty cycle is DCB, then the duty cycle is decremented to the next
entry in
the table, which is DC7. The process then loops back to step 804.
Of course, if the processor U1 detects a match at step 804 (i.e., the actual
exhaust/air mixture temperature equals the desired exhaust/air mixture
temperature),
3o then the processor U1 remains at step 804 until it detects a difference.
Those skilled in the art should understand that if a fan is used instead of a
blower, then step 810 would decrement the duty cycle, while step 814 would
increment the duty cycle. This occurs because a blower generally rotates
faster as
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14
impedance increases. Indeed, such a reaction is opposite to that of a fan,
which
rotates slower as impedance increases.
Various embodiments of the invention may be implemented at least in part
in any conventional computer programming language. For example, some
embodiments may be implemented in a procedural programming language (e.g.,
"C"), or in an object oriented programming language (e.g., "C++"). Other
embodiments of the invention may be implemented as preprogrammed hardware
elements (e.g., application specific integrated circuits, FPGAs, and digital
signal
processors), or other related components.
l0 In an alternative embodiment, the disclosed apparatus and method may be
implemented as a computer program product for use with a computer system. Such
implementation may include a series of computer instructions fixed either on a
tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM,
ROM, or fixed disk) or transmittable to a computer system, via a modem or
other
interface device, such as a communications adapter connected to a network over
a
medium. The medium may be either a tangible medium (e.g., optical or analog
communications lines) or a medium implemented with wireless techniques (e.g.,
WIFI, microwave, infrared or other transmission techniques). The series of
computer instructions can embody all or part of the functionality previously
described herein with respect to the system.
Those skilled in the art should appreciate that such computer instructions
can be written in a number of programming languages for use with many computer
architectures or operating systems. Furthermore, such instructions may be
stored in
any memory device, such as semiconductor, magnetic, optical or other memory
devices, and may be transmitted using any communications technology, such as
optical, infrared, microwave, or other transmission technologies.
Such a computer program product may be distributed as a removable
medium with accompanying printed or electronic documentation (e.g., shrink
wrapped software), preloaded with a computer system (e.g., on system ROM or
3o fixed disk), or distributed from a server or electronic bulletin board over
the
network (e.g., the Internet or World Wide Web). Of course, some embodiments of
the invention may be implemented as a combination of both software (e.g., a
computer program product) and hardware. Still other embodiments of the
invention
are implemented as entirely hardware, or entirely software.
CA 02537192 2006-02-28
WO 2005/024303 PCT/US2004/027290
Although various exemplary embodiments of the invention are disclosed
above, it should be apparent that those skilled in the art can make various
changes
and modifications that will achieve some of the advantages of the invention
without
departing from the true scope of the invention.
