U.S. patent application number 15/624797 was filed with the patent office on 2018-12-20 for thermistor system for temperature measurement in a gas water heater combustion chamber.
The applicant listed for this patent is Haier US Appliance Solutions, Inc.. Invention is credited to Thomas Allen Bailey.
Application Number | 20180363950 15/624797 |
Document ID | / |
Family ID | 64657278 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180363950 |
Kind Code |
A1 |
Bailey; Thomas Allen |
December 20, 2018 |
THERMISTOR SYSTEM FOR TEMPERATURE MEASUREMENT IN A GAS WATER HEATER
COMBUSTION CHAMBER
Abstract
A gas water heater that includes a sheathed thermistor placed
into the combustion chamber near a gas burner to provide for more
accurate measurements of the temperature therein. The thermistor
may be used in combination with a thermopile to provide additional
measurements for determination of temperature conditions requiring
a closure of a valve controlling the flow of gas to the burner
Inventors: |
Bailey; Thomas Allen;
(Louisville, KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Haier US Appliance Solutions, Inc. |
Wilmington |
DE |
US |
|
|
Family ID: |
64657278 |
Appl. No.: |
15/624797 |
Filed: |
June 16, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24H 1/186 20130101;
F24H 9/2035 20130101; F24H 2240/08 20130101 |
International
Class: |
F24H 9/20 20060101
F24H009/20; F24H 1/18 20060101 F24H001/18 |
Claims
1. A gas fueled water heater, comprising: a tank for storage of
water for heating; a chamber wall at least partially enclosing a
combustion chamber; a gas burner positioned adjacent to the tank
and within the combustion chamber, the gas burner configured for
heating the water in the tank; a thermistor positioned within the
combustion chamber near the gas burner, the thermistor not
contacting the chamber wall, the thermistor configured for
providing temperature measurements of the combustion chamber; and a
sheath positioned around the thermistor.
2. The gas fueled water heater of claim 1, further comprising a
controller in communication with the thermistor for the receipt of
temperature measurements from the thermistor.
3. The gas fueled water heater of claim 2, further comprising: a
gas valve for controlling the flow of gas to the gas burner;
wherein the controller is in communication with the gas valve and
is configured to close the flow of gas through the gas valve upon
determining that the temperature in the combustion chamber as
measured by the thermistor has reached or exceeded a predetermined
maximum temperature, TS.sub.MAX.
4. The gas fueled water heater of claim 2, a gas valve for
controlling the flow of gas to the gas burner; wherein the
controller is in communication with the gas valve and is configured
to close the flow of gas through the gas valve upon determining
that the temperature in the combustion chamber as measured by the
thermistor has reached or exceeded a predetermined maximum
temperature, TS.sub.MAX, for a predetermined period of time,
.DELTA..sub.ts.
5. The gas fueled water heater of claim 1, further comprising: a
pilot burner for providing a pilot light to ignite the gas burner;
and a thermopile positioned adjacent to the pilot burner and
configured for detecting the presence of a pilot light at the pilot
burner.
6. The gas fueled water heater of claim 1, further comprising: a
pilot burner for providing a pilot light to ignite the gas burner;
and a thermopile positioned adjacent to the pilot burner and
configured for detecting the presence of a pilot light at the pilot
burner and for providing a secondary measurement of temperature in
the combustion chamber.
7. The gas fueled water heater of claim 6, further comprising: a
gas valve for controlling the flow of gas to the gas burner;
wherein the controller is in communication with the gas valve and
is configured to close the flow of gas through the gas valve upon
determining that both i) the temperature in the combustion chamber
as measured by the thermistor has reached or exceeded a
predetermined maximum temperature, TS.sub.MAX, and ii) the
temperature in the combustion chamber as measured by the thermopile
has reached or exceeded a predetermined maximum temperature,
TP.sub.MAX.
8. The gas fueled water heater of claim 6, further comprising: a
gas valve for controlling the flow of gas to the gas burner;
wherein the controller is in communication with the gas valve and
is configured to close the flow of gas through the gas valve upon
determining that both i) the temperature in the combustion chamber
as measured by the thermistor has reached or exceeded a
predetermined maximum temperature, TS.sub.MAX, for a predetermined
period of time, .DELTA..sub.ts, and ii) the temperature in the
combustion chamber as measured by the thermopile has also reached
or exceeded a predetermined maximum temperature, TP.sub.MAX, for
the predetermined period of time, .DELTA..sub.tp.
9. The gas fueled water heater of claim 1, wherein the thermistor
is supported by the chamber wall.
10. The gas fueled water heater of claim 9, wherein the sheath is
attached to the chamber wall.
11. The gas fueled water heater of claim 10, wherein the sheath
comprises a metal.
12. The gas fueled water heater of claim 11, wherein the sheath
comprises a ceramic.
13. A gas fueled water heater, comprising: a tank for storage of
water for heating; a chamber wall supporting the tank and forming a
combustion chamber; a gas burner centrally located within the
combustion chamber and positioned below the tank, the gas burner
spaced apart from the chamber wall; a thermistor located with the
combustion chamber and adjacent to the gas burner without being
located within a flame of the burner, the thermistor configured for
providing a signal representing temperature within the combustion
chamber, wherein the thermistor is not in contact with the chamber
wall; and a sheath completely surrounding the thermistor and
configured for protecting the thermistor.
14. The gas fueled water heater of claim 13, further comprising a
controller in communication with the thermistor for the receipt of
temperature measurements from the thermistor, and a gas valve for
controlling the flow of gas to the gas burner; wherein the
controller is in communication with the gas valve and is configured
to close the flow of gas through the gas valve upon determining
that the temperature in the combustion chamber as provided by a
signal from the thermistor has reached or exceeded a predetermined
maximum temperature, TS.sub.MAX.
15. The gas fueled water heater of claim 13, further comprising a
controller in communication with the thermistor for the receipt of
temperature measurements from the thermistor, and a gas valve for
controlling the flow of gas to the gas burner; wherein the
controller is in communication with the gas valve and is configured
to close the flow of gas through the gas valve upon determining
that the temperature in the combustion chamber as determined from a
signal provided by the thermistor has reached or exceeded a
predetermined maximum temperature, TS.sub.MAX, for a predetermined
period of time, .DELTA..sub.ts.
16. The gas fueled water heater of claim 13, further comprising: a
pilot burner for providing a pilot light to ignite the gas burner;
and a thermopile positioned adjacent to the pilot burner and
configured for detecting the presence of a pilot light at the pilot
burner and for providing a secondary measurement of temperature in
the combustion chamber.
17. The gas fueled water heater of claim 16, further comprising a
controller in communication with the thermistor for the receipt of
a signal representing temperature measurements from the thermistor;
and wherein the controller is in communication with the gas valve
and is configured to close the flow of gas through the gas valve
upon determining that both i) the temperature in the combustion
chamber as measured by the thermistor has reached or exceeded a
predetermined maximum temperature, TS.sub.MAX, and ii) the
temperature in the combustion chamber as measured by the thermopile
has reached or exceeded a predetermined maximum temperature,
TP.sub.MAX.
18. The gas fueled water heater of claim 16, further comprising: a
gas valve for controlling the flow of gas to the gas burner;
wherein the controller is in communication with the gas valve and
is configured to close the flow of gas through the gas valve upon
determining that both i) the temperature in the combustion chamber
as measured by the thermistor has reached or exceeded a
predetermined maximum temperature, TS.sub.MAX, for a predetermined
period of time, .DELTA..sub.ts, and ii) the temperature in the
combustion chamber as measured by the thermopile has also reached
or exceeded a predetermined maximum temperature, TP.sub.MAX, for
the predetermined period of time, .DELTA..sub.tp.
Description
FIELD OF THE INVENTION
[0001] The subject matter of the present disclosure relates
generally to temperature measurement in the combustion chamber of a
gas water heater.
BACKGROUND OF THE INVENTION
[0002] A variety of energy sources are used in creating hot water
for commercial and residential use including electric, solar, and
various fuels. Natural gas and propane are preferred by some
customers due to e.g., the relatively quick heating rate. These
fuels are supplied as a gas that is burned in a combustion chamber
to provide heat energy to raise the water temperature.
[0003] Temperatures in the combustion chamber are relatively high
and can e.g., reach 600 degrees Fahrenheit during normal operation.
A flame is created by burning a mixture of the gaseous fuel and
air. Proper combustion requires that the air and fuel are provided
within a particular ratio to ensure e.g., complete combustion and
avoid wasted fuel or the production of unwanted by-products such as
carbon monoxide.
[0004] If the water heater is e.g., installed in a dusty area
containing above average levels of e.g., dirt, oil, or lint, the
air intake of water heater can become clogged. The lack of enough
air can cause the temperature of the combustion chamber to become
too hot. As another example, a flammable vapor event such as a the
ignition of vapor from liquid fuel present near the water heater
can also create elevated temperatures in the water heater
combustion chamber.
[0005] Accordingly, it is desirable to monitor temperature and
terminate the combustion process by e.g., shutting off the gas flow
if the temperature reaches unsafe levels.
[0006] One conventional approach is the use of a bi-metal switch
placed in direct contact with the wall of the combustion chamber so
as to activate the switch. The metals of the bi-metal switch have
different thermal expansion characteristics. Once the temperature
of the bi-metal switch reaches a predetermined maximum temperature,
the switch is activated so as to cause a control system to close
off the flow of gas--even if the temperature is only high for a
relatively short period of time. Then, the bi-metal switch must
cool before allowing the water heater to operate again or,
alternatively, the bi-metal switch must be manually reset. Such
reset requirement can be undesirable, particularly if the increased
temperature was not due to a unwanted event such as clogging of the
air flow.
[0007] Also, because the bi-metal switch must be placed in contact
with the combustion chamber wall, it does not provide a direct
measurement of the temperature of the combustion process. Instead,
heat must be transmitted to the wall of the combustion chamber
before the bi-metal switch can be triggered due to an unsafe
condition. Furthermore, the bi-metal switch does not provide for
multiple temperature measurements or adjustment of the temperature
at which it is activated. Instead, the bi-metal switch is simply
activated upon reaching a predetermined maximum temperature.
[0008] Accordingly, an improved system for measuring and monitoring
the temperature of the combustion chamber of a gas water heater is
needed.
BRIEF DESCRIPTION OF THE INVENTION
[0009] The present invention provides a gas water heater that
includes a sheathed thermistor placed into the combustion chamber
near a gas burner to provide for more accurate measurements of the
temperature therein. The thermistor may be used in combination with
a thermopile to provide additional, confirmatory measurements for
determination of temperature conditions requiring a closure of a
valve controlling the flow of gas to the burner. Additional aspects
and advantages of the invention will be set forth in part in the
following description, or may be apparent from the description, or
may be learned through practice of the invention.
[0010] In one exemplary embodiment, the present invention provides
a gas fueled water heater having a tank for storage of water for
heating. A chamber wall at least partially encloses a combustion
chamber. A gas burner is positioned adjacent to the tank and within
the combustion chamber. The gas burner is configured for heating
the water in the tank. A thermistor is positioned within the
combustion chamber near the gas burner. The thermistor does not
contact the chamber wall. The thermistor is configured for
providing temperature measurements of the combustion chamber. A
sheath is positioned around the thermistor.
[0011] In another exemplary embodiment of the present invention, a
gas fueled water heater is provided that includes a tank for
storage of water for heating. A chamber wall supports the tank and
forms a combustion chamber. A gas burner is centrally located
within the combustion chamber and is positioned below the tank. The
gas burner is spaced apart from the chamber wall. A thermistor is
located within the combustion chamber and is adjacent to the gas
burner without being located within a flame of the burner. The
thermistor is configured for providing a signal representing
temperature within the combustion chamber. The thermistor is not in
contact with the chamber wall. A sheath completely surrounds the
thermistor and is configured for protecting the thermistor.
[0012] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A full and enabling disclosure of the present invention,
including the best mode thereof, directed to one of ordinary skill
in the art, is set forth in the specification, which makes
reference to the appended figures, in which:
[0014] FIG. 1 provides a partially cut away, side view of an
exemplary embodiment of a water heater of the present
invention.
[0015] FIG. 2 provides a perspective view of an exemplary gas
combustion chamber as may be used with the exemplary water heater
of FIG. 1.
[0016] FIG. 3 is a schematic of a gas flow control system as may be
used with the exemplary water heater of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment can be used with
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0018] FIG. 1 illustrates a partial sectional, side view of an
exemplary water heater 100 of the present invention. Water heater
100 includes a tank 102 where water is stored and heated. Water is
supplied to tank 102 by inlet line 104. Heated water is supplied by
tank 102 through outlet line 106. Water heater 100 is fluidly
connected with lines 104 and 106 using connections 132 and 134. In
turn, lines 104 and 106 connect with the water supply system of
e.g., a residence or a commercial structure.
[0019] From line 104, water travels into tank 102 through a cold
water dip tube 122 that extends along vertical direction V towards
the bottom 114 of tank 102. After being heated, water exits tank
102 by travelling vertically upward and out through outlet line
106. Anode rod 126 provides protection against corrosion attacks on
tank 102 and other metal components of water heater 100. A pressure
relief valve 128 provides for a release of water from tank 102 in
the event the pressure rises above a predetermined amount.
[0020] Water heater 100 includes a combustion chamber 110 in which
a gas burner 108 is centrally located. Gas burner 108 is supplied
with a gaseous fuel e.g., propane or natural gas. Air travels into
combustion chamber 110 through air intake 112 in cabinet 130. The
resulting mixture of air and gas is ignited and burned to heat
bottom 114 of tank 102 and its water contents. Hot combustion gas
120 exits combustion chamber 110 through a vent or flue 124
centrally located within tank 102. Heat exchange with flue 124 also
helps heat water in tank 102. A baffle 120 promotes this heat
exchange. Gas 120 exits water heater 100 though vent hood 136,
which may be connected with additional vent piping (not shown).
[0021] A thermostat 116 measures the temperature of water in tank
102 and provides a signal to gas control valve module 118. As used
herein, "a signal" is not limited to a single measurement of
temperature and, instead, may include multiple measurements over
time or continuous measurements over time. Depending upon whether
the desired temperature has been reached as determined e.g., from
the signal from thermostat 116, gas control valve module 118
regulates the flow of gas to burner 108 as will be more fully
described herein.
[0022] Referring now to FIG. 2, combustion chamber 110 is formed by
a chamber wall 138 that at least partially encloses combustion
chamber 110 and may also provide support for tank 102 along top
edge 160. As shown, chamber wall 138 encircles burner 108 and is
spaced apart from burner 108. Chamber wall 138 may be part of
cabinet 130 (FIG. 1) or may be a separate component.
[0023] A thermistor 140 is positioned within combustion chamber 110
near gas burner 108 and is configured for providing a signal
T.sub.S representing the temperature in combustion chamber 110. As
will be understood by one of skill in the art, a thermistor can
include one or more resistors having a resistance in an amount that
depends on the temperature. The amount of resistance can be
correlated to temperature and used to provide a signal representing
a measurement of the temperature. For water heater 100, the
resistance to a current through the thermistor (and the changes in
that resistance) provide a measurement of temperature in combustion
chamber 110.
[0024] For this exemplary embodiment, thermistor 140 is located
close to burner 108 without being directly in the flame 162 (FIG.
1) created by burner 108. Thermistor 140 does not contact chamber
wall 138 as such might give an inaccurate temperature measurement.
Instead, for this embodiment, thermistor 140 is supported on
chamber wall 138 by a sheath 142 that surrounds thermistor 140 and
connects with chamber wall 138 to support thermistor 140. For this
exemplary embodiment, sheath 142 completely encloses thermistor
140. Sheath 142 protects thermistor 140 from damage by the heat and
flame from burner 108 while still allowing conduction for
temperature measurement. By way of example, sheath 142 may be
constructed from a metal such as aluminum, a ceramic, and
combinations thereof. Electrical conductors 144 connect thermistor
140 with gas control module 118 to provide the signal representing
temperature from thermistor 140.
[0025] FIG. 3 provides a schematic representation of combustion
chamber 110 and gas valve control module 118, which includes at
least one controller 154. By way of example, controller 154 may
include memory and one or more processing devices such as
microprocessors, CPUs or the like, such as general or special
purpose microprocessors operable to execute programming
instructions or micro-control code associated with operation of
water heater 100 as further described herein. The memory can
represent random access memory such as DRAM, or read only memory
such as ROM or FLASH. The processor executes programming
instructions stored in the memory. The memory can be a separate
component from the processor or can be included onboard within the
processor. Alternatively, controller 154 may be constructed without
using a microprocessor, e.g., using a combination of discrete
analog and/or digital logic circuitry (such as switches,
amplifiers, integrators, comparators, flip-flops, AND gates, and
the like) to perform control functionality instead of relying upon
software.
[0026] Water heater 100 includes a gas valve 146 positioned along
main gas supply line 168. Controller 154 is in communication with
gas valve 146 to control the flow of gas therethrough by
determining when valve 146 is energized. For this exemplary
embodiment, gas valve 146 operates so that when energized, valve
146 is fully open to allow a flow of gaseous fuel to burner 108.
When not fully energized, valve 146 is fully closed (i.e. a
"fail-closed" type valve) so as to prevent the flow of gaseous fuel
to burner 108.
[0027] Water heater 102 includes a pilot burner 148 that provides a
pilot light 150 to ignite the mixture of air and fuel at burner 108
when gas valve 146 is open. Gaseous fuel for pilot burner 148 is
supplied by pilot burner fuel line 152. Gas valve control module
118 controls the flow of gaseous fuel through pilot burner fuel
line 152. A thermopile 156 is positioned adjacent to the pilot
burner 148. Thermopile 156 can convert heat from pilot burner 148
into electrical energy.
[0028] Thermopile 156 may be constructed from e.g., a plurality of
thermocouples connected in a series, for example. The output
voltage from thermopile 156 is proportional to the temperature. As
such, thermopile 156 provides a signal to controller 154 through
conductors 164 indicating whether a pilot light 150 is present at
pilot burner 148. In addition, thermopile 156 can provide enough
energy to power gas control module 118.
[0029] In one exemplary aspect of operation, if the signal from
thermopile 156 indicates the measured temperature T.sub.P is at
room temperature (e.g., 72.degree. F.), then the pilot light 150 is
not present. In such state, gas valve 146 would remain unenergized
or closed so that no gaseous fuel flows to burner 108. If the
signal from thermopile 156 indicates a pilot flame 150 is present
(e.g., temperature is above 500.degree. F.), then module 118 can
place gas valve 146 in either an open or closed state depending
upon whether water in tank 102 needs to be heated. Specifically, by
comparing temperature measurement using thermostat 116 with the
desired set point temperature, module 118 can determine whether to
open or close gas valve 146.
[0030] Additionally, if pilot light 150 is not present, gas control
valve module 118 would also prevent the flow of gas to pilot burner
148 unless the user has placed gas control module 118 in a start or
ignition state. In the ignition state, gas valve 146 would remain
closed but module 118 would allow gas to flow through pilot burner
fuel line 152 while igniter 158 (FIG. 2) provides one or more
sparks so as to ignite gaseous fuel flowing from pilot burner 148
to create pilot light 150. Once pilot light 150 is detected by
thermopile 156, controller 154 would continue to allow gaseous fuel
to flow through pilot burner fuel line 152 while pilot light 150 is
detected.
[0031] The signal from thermopile 156 can also be used to measure
the temperature in combustion chamber 110. While the temperature
measured at thermopile 156 may not be identical to the temperature
as measured by thermistor 140, the signal from thermopile 156 can
still be used to determine whether the temperature is such that the
desired level of combustion it taking place in chamber 110. In
addition, as stated, the signal from thermopile 156 provides a
voltage sufficient to power controller 154 and other components of
gas control valve module 118 such that an external power source is
not required.
[0032] As previously described, for various reasons, the combustion
of gaseous fuel in combustion chamber 110 may be
incomplete--potentially creating carbon monoxide and undesirable,
elevated temperatures. For example, air intake 112 may be clogged
or blocked such that the supply of air for combustion is
insufficient. As will now be further described, exemplary water
heater 100 can detect when elevated temperatures are occurring and
take precautionary steps.
[0033] In one exemplary aspect, controller 154 receives a signal
from thermistor 140 representing the temperature in combustion
chamber 110. When such temperature reaches or exceeds a
predetermined maximum temperature, TS.sub.MAX, controller 154
terminates the flow of gaseous fuel to burner 108 by closing gas
valve 146. As gas valve 146 is a "fail-closed" valve, controller
154 ceases to energize gas valve 146 thereby allowing a spring or
other biasing element to force gas valve 146 into a closed state.
In one exemplary embodiment of the invention, TS.sub.MAX is
750.degree. F. Other settings for TS.sub.MAX may also be used,
however.
[0034] It is desirable to avoid nuisance trips or unnecessary
closings of gas valve 146. For example, if the temperature, TS,
sensed by thermistor 146 is at or above TS.sub.MAX only momentarily
and then falls below TS.sub.MAX, then it may not be necessary to
close gas valve 146 because e.g., incomplete combustion may not
actually be occurring in chamber 110 or may have already ended.
[0035] Accordingly, in another exemplary aspect of the invention,
controller 154 receives a signal from thermistor 140 representing
the temperature TS in combustion chamber 110. When such temperature
reaches or exceeds a predetermined maximum temperature, TS.sub.MAX,
for at least a predetermined amount of time, .DELTA..sub.ts, then
controller 154 terminates the flow of gaseous fuel to burner 108 by
closing gas valve 146. In one exemplary embodiment, .DELTA..sub.ts
is ______ seconds. Other values may be used as well.
[0036] In another exemplary aspect of the invention, thermopile 156
can be used to provide a secondary measurement of temperature in
combustion chamber 110 that can be used to determine whether to
close gas valve 146. During operation of water heater 100,
controller 154 receives a signal from thermistor 140 representing
the temperature TS in combustion chamber 110 as measured by
thermistor 140 and receives a signal from thermopile 156
representing the temperature TP in combustion chamber 110 as
measured by thermopile 156.
[0037] By way of example, when the temperature TS as measured by
thermistor 140 reaches or exceeds a predetermined maximum
temperature, TS.sub.MAX, gas valve 146 it not closed unless the
temperature TP as measured by thermopile 156 also exceeds a
predetermined maximum value, TP.sub.MAX. In certain embodiments,
TP.sub.MAX is not necessarily the same value as TS.sub.MAX and may
be different due e.g., the difference in the location of thermistor
140 relative to thermopile 156. In one exemplary embodiment,
TP.sub.MAX is less than TS.sub.MAX. In still another exemplary
embodiment, TS.sub.MAX is less than 725.degree. F. As such, if both
TP and TS exceed TP.sub.MAX and TS.sub.MAX, respectively, then
controller 154 can operate to close gas valve 146. In this way,
water heater 100 is able to avoid potentially unnecessary closings
of valve 146 based on e.g., momentary temperature spokes detected
thermistor 140.
[0038] In still another exemplary aspect, controller 154 receives a
signal from thermistor 140 representing the temperature TS in
combustion chamber 110. When such temperature ST reaches or exceeds
a predetermined maximum temperature, TS.sub.MAX, for at least a
predetermined amount of time, .DELTA..sub.ts, controller 154 does
not close gas valve 146 unless the temperature TP as measured by
thermopile 156 also exceeds a predetermined maximum value,
TP.sub.MAX for at least a predetermined amount of time,
.DELTA..sub.tp.
[0039] In certain embodiments, .DELTA..sub.tp is not necessarily
the same value as .DELTA..sub.ts. In one exemplary embodiment,
.DELTA..sub.tp is less than .DELTA..sub.ts. In still another
exemplary embodiment, .DELTA..sub.tp is one second less than the
value of .DELTA..sub.ts. Other values may be used as well. As such,
if both TP and TS exceed TP.sub.MAX and TS.sub.MAX for
predetermined time periods .DELTA..sub.tp and .DELTA..sub.ts,
respectively, then controller 154 can operate to close gas valve
146. Again, this exemplary aspect, water heater 100 is able to
avoid potentially unnecessary closings of valve 146 based on e.g.,
momentary temperature spokes detected thermistor 140.
[0040] Accordingly, by using thermistor 140 placed in combustion
chamber 110, more accurate temperature measurements of the
combustion process can be provided to gas control valve module 118
with controller 154 than a typical bi-metal switch positioned
against combustion chamber wall 138 as used in conventional
constructions. In addition, thermistor 140 does not require a reset
or period of cooling off as with such bi-metal switch
constructions. In addition, one or more aspects as described above
may be used with thermistor 140 to avoid unnecessary closings of
gas valve 146.
[0041] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they include structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *