U.S. patent application number 12/419065 was filed with the patent office on 2009-10-08 for water heater with pressurized combustion.
Invention is credited to Marc W. Akkala, Ray O. Knoeppel.
Application Number | 20090250017 12/419065 |
Document ID | / |
Family ID | 36190859 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090250017 |
Kind Code |
A1 |
Akkala; Marc W. ; et
al. |
October 8, 2009 |
WATER HEATER WITH PRESSURIZED COMBUSTION
Abstract
A water heater includes a sealed combustion chamber and one or
more fans for raising pressure in the combustion chamber to
increase efficiency of the water heater. The pressure permits a
more restrictive baffle to be used in the flue compared to baffles
used in atmospheric water heaters. The water heater may include a
water temperature sensor that activates the fan without activating
the burner if water temperature raises above a desired temperature.
The water heater may also include pressure and vapor sensors to
ensure the combustion chamber is properly sealed and there are no
flammable vapors present prior to igniting the burner. The fans are
relatively small and run off the same DC power that runs an
electric gas valve. The fans may be, for example, 12 or 24 Volt
fans with power inputs of about 10 Watts or less.
Inventors: |
Akkala; Marc W.; (Cedarburg,
WI) ; Knoeppel; Ray O.; (Hartland, WI) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Family ID: |
36190859 |
Appl. No.: |
12/419065 |
Filed: |
April 6, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
11034130 |
Jan 12, 2005 |
7032543 |
|
|
12419065 |
|
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|
|
11329793 |
Jan 11, 2006 |
7513221 |
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11034130 |
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Current U.S.
Class: |
122/14.2 ;
122/15.1; 122/18.3 |
Current CPC
Class: |
F24H 9/1836 20130101;
F24H 1/205 20130101 |
Class at
Publication: |
122/14.2 ;
122/15.1; 122/18.3 |
International
Class: |
F24H 9/20 20060101
F24H009/20; F24D 19/00 20060101 F24D019/00; F24H 1/00 20060101
F24H001/00 |
Claims
1. A water heater comprising: a water tank adapted to contain water
to be heated; a flue extending through the water tank and having an
inlet end and an outlet end; a combustion chamber in communication
with the inlet end of the flue, the combustion chamber having an
air intake defining an air inlet, said combustion chamber being
substantially air-tightly sealed except for the air inlet and the
inlet end of the flue; means for introducing air into the
combustion chamber and raising the pressure in the combustion
chamber above atmospheric pressure; and a main burner within the
combustion chamber and operable to combust a mixture of air and
fuel to create products of combustion; wherein the products of
combustion flow out of the combustion chamber into the inlet end of
the flue, heat the water in the tank through the flue, and exit the
water heater through the outlet end of the flue; wherein primary
air is mixed with fuel prior to combustion at the main burner;
wherein secondary air within the combustion chamber combines with
the primary air and fuel mixture to complete the combustion process
at an outlet of the burner.
2. The water heater of claim 1, further comprising a flammable
vapor sensor; and a controller that initiates ignition of the main
burner only after the flammable vapor sensor senses an acceptable
concentration of flammable vapors.
3. The water heater of claim 1, further comprising a flammable
vapor sensor; and a controller that shuts down operation of the
main burner in response to the flammable vapor sensor sensing an
unacceptable concentration of flammable vapors.
4. The water heater of claim 1, further comprising a pressure
sensor that senses pressure in the combustion chamber; and a
controller that initiates ignition of the main burner only after
the pressure sensor senses a rise in pressure in the combustion
chamber.
5. The water heater of claim 1, further comprising an
electrically-powered fuel valve, the valve and the means for
introducing air into the combustion chamber being powered with
electricity from a single source.
6. The water heater of claim 1, further comprising a baffle in the
flue operable to slow the rate at which products of combustion flow
through the flue to thereby increase heat transfer through the flue
wall to the water in the tank.
7. The water heater of claim 1, wherein the air intake includes an
air plenum between the air inlet and the combustion chamber, the
water heater further comprising a flame arrester sealed between the
plenum and combustion chamber such that substantially all air
flowing into the combustion chamber from the plenum flows through
the flame arrester, the flame arrester permitting ingress of
flammable vapors into the combustion chamber but substantially
preventing egress of flame out of the combustion chamber into the
plenum.
8. A water heater comprising: a water tank adapted to contain water
to be heated; a flue extending through the water tank and having an
inlet end and an outlet end; a combustion chamber in communication
with the inlet end of the flue, the combustion chamber having an
air intake defining an air inlet, said combustion chamber being
substantially air-tightly sealed except for the air inlet and the
inlet end of the flue; means for introducing air into the
combustion chamber sealed with respect to the air inlet such that
the combustion chamber is downstream of the means for introducing
air and air flows through the means for introducing air into the
combustion chamber, wherein operation of the means for introducing
air raises the pressure in the combustion chamber above atmospheric
pressure; and a main burner within the combustion chamber and
operable to combust a mixture of air and fuel to create products of
combustion; wherein the products of combustion flow out of the
combustion chamber into the inlet end of the flue, heat the water
in the tank through the flue, and exit the water heater through the
outlet end of the flue; wherein primary air is mixed with fuel
prior to combustion at the main burner; wherein secondary air
within the combustion chamber combines with the primary air and
fuel mixture to complete the combustion process at an outlet of the
burner.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 11/034,130, filed Jan. 12, 2005, now U.S. Pat. No. 7,032,543
and a continuation of U.S. application Ser. No. 11/329,793, filed
on Jan. 11, 2006, now U.S. Pat. No. 7,513,221, the entire contents
of which are incorporated herein by reference.
BACKGROUND
[0002] The present invention relates to a water heater having a
pressurized combustion chamber.
SUMMARY
[0003] In one embodiment, the invention provides a water heater
comprising a water tank adapted to contain water to be heated; a
flue extending through the water tank and having an inlet end and
an outlet end; a combustion chamber in communication with the inlet
end of the flue, the combustion chamber having an air intake
defining an air inlet, said combustion chamber being substantially
air-tightly sealed except for the air inlet and the inlet end of
the flue; means for introducing air into the combustion chamber and
raising the pressure in the combustion chamber above atmospheric
pressure; and a main burner within the combustion chamber and
operable to combust a mixture of air and fuel to create products of
combustion. The products of combustion flow out of the combustion
chamber into the inlet end of the flue, heat the water in the tank
through the flue, and exit the water heater through the outlet end
of the flue; wherein primary air is mixed with fuel prior to
combustion at the main burner; wherein secondary air within the
combustion chamber combines with the primary air and fuel mixture
to complete the combustion process at an outlet of the burner.
[0004] In another embodiment, the invention provides a water heater
comprising a water tank adapted to contain water to be heated; a
flue extending through the water tank and having an inlet end and
an outlet end; a combustion chamber in communication with the inlet
end of the flue, the combustion chamber having an air intake
defining an air inlet, said combustion chamber being substantially
air-tightly sealed except for the air inlet and the inlet end of
the flue; means for introducing air into the combustion chamber
sealed with respect to the air inlet such that the combustion
chamber is downstream of the means for introducing air and air
flows through the means for introducing air into the combustion
chamber, wherein operation of the means for introducing air raises
the pressure in the combustion chamber above atmospheric pressure;
and a main burner within the combustion chamber and operable to
combust a mixture of air and fuel to create products of combustion.
The products of combustion flow out of the combustion chamber into
the inlet end of the flue, heat the water in the tank through the
flue, and exit the water heater through the outlet end of the flue;
wherein primary air is mixed with fuel prior to combustion at the
main burner; wherein secondary air within the combustion chamber
combines with the primary air and fuel mixture to complete the
combustion process at an outlet of the burner.
[0005] In some embodiments, the air intake may define an air plenum
and a flame arrester may be sealed between the plenum and
combustion chamber to contain flames within the combustion chamber.
The flue in some embodiments may include a baffle to slow the flow
of products of combustion through the flue. The water heater may
include a gas valve that is either electric or non-electric, a
pressure sensor for sensing pressure in the combustion chamber
and/or plenum, a gas pressure switch that activates the at least
one fan in response to a change of gas pressure at the gas valve
consistent with gas flow to the main burner, a flammable vapor
sensor for sensing the presence of flammable vapors in the
combustion chamber and/or plenum, and a high-limit water
temperature switch for sensing whether the water has exceeded a
high limit.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates water heater according to a first
embodiment of the invention.
[0008] FIG. 2 is a cross section view of the bottom portion of the
water heater of FIG. 1.
[0009] FIG. 3 is an exploded view of the base of the water heater
of both illustrated embodiments.
[0010] FIG. 4 illustrates a water heater according to a second
embodiment of the invention.
[0011] FIG. 5 is a cross section view of the bottom portion of the
water heater of FIG. 4.
DETAILED DESCRIPTION
[0012] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. Unless specified or limited otherwise,
the terms "mounted," "connected," "supported," and "coupled" and
variations thereof are used broadly and encompass both direct and
indirect mountings, connections, supports, and couplings. Further,
"connected" and "coupled" are not restricted to physical or
mechanical connections or couplings.
[0013] The present invention is intended for use on a flammable
vapor ignition resistant (FVIR) water heater of the kind disclosed
in U.S. Pat. Nos. 6,109,216; 6,216,643; 6,230,665; and 6,295,952,
the entire contents of those patents being incorporated herein by
reference. The concept of pressurized combustion may be applied to
non-FVIR water heaters as well, provided the water heater includes
a combustion chamber that is sufficiently sealed so that it will
permit a higher-than-atmospheric pressure condition. The present
invention should therefore not necessarily be limited to FVIR water
heaters, although the illustrated embodiments include an FVIR
application.
[0014] The present invention is described below in terms of two
illustrated embodiments. The first embodiment (FIGS. 1 and 2)
includes a water heater having a non-powered gas valve/thermostat,
and the second embodiment (FIGS. 4 and 5) includes a water heater
having an electric gas valve. The illustrated embodiments have in
common many features and the same reference numerals are used in
the drawings to indicate identical or similar parts in the two
embodiments.
[0015] FIGS. 1-5 illustrate a storage-type gas-fired FVIR water
heater 10 that includes a base pan 15 that provides the primary
structural support for the rest of the water heater 10. The base
pan 15 may be constructed of stamped metal or molded plastic, for
example, and includes a generally horizontal bottom wall 20, a
vertical rise 25 having an air inlet opening 27, and an elevated
step 30. The water heater 10 also includes a water tank 35,
insulation 40 surrounding the tank 35, and an outer jacket 45
surrounding the insulation 40 and the water tank 35. A skirt 50 is
supported by the base pan's elevated step 30 and in turn supports
the water tank 35. The elevated step 30 also supports the
insulation 40 and jacket 45. Metal tabs 55 are formed (e.g.,
punched and bent) out of the step 30 material or otherwise provided
and affixed on the step 30, and co-axially position the base pan 15
and skirt 50.
[0016] Also supported by the elevated step 30 is a divider 60 that
divides the space between the bottom of the tank 35, skirt 50, and
the base pan 15 into a combustion chamber 65 (above the divider 60)
and plenum 70 (below the divider 60).
[0017] A cold water inlet tube 75 and a hot water outlet tube 80
extend through a top wall of the water tank 35. A flue 85 extends
through the tank 35, and water in the tank 35 surrounds the flue
85. The flue 85 includes an inlet end 90 and an outlet end 95, and
has a baffle 100 in it. The baffle 100 slows down the flow of
products of combustion through the flue 85, and consequently
increases the time during which the products of combustion reside
within the flue 85. Generally, heat transfer from the products of
combustion to the flue 85 and ultimately to the water increases as
the baffle 100 is made more restrictive of fluid flow through the
flue 85. The practical restrictiveness of the baffle 100 has its
limits, however, due to condensation, combustion quality, and other
considerations.
[0018] The combustion chamber 65 and plenum 70 space is
substantially air-tightly sealed except for the air inlet opening
27 and inlet end 90 of the flue 85, and seals 105 between the skirt
50 and the tank 35 and base pan 15 assist in sealing the space. The
seals 105 may be, for example and without limitation, fiberglass
material or a high-temperature caulk material. A radiation shield
110 sits on the divider 60 within the sealed combustion chamber 65
and reflects radiant heat up toward the tank 35.
[0019] A flame arrester 115 is affixed in a sealed condition across
an opening 120 in the divider 60 such that all air flowing from the
plenum 70 into the combustion chamber 65 must flow through the
flame arrester 115. The air inlet 27, air plenum 70, and opening
120 in the divider 60 together define an air intake for the
combustion chamber 65, and all air flowing into the combustion
chamber 65 through the opening (see arrows in FIG. 2) 120 must flow
through this air intake and the flame arrester 115. It should also
be noted that the position and orientation of the flame arrester
115 are not limited to those shown in the drawings, and that
substantially any construction will work provided that the flame
arrester 115 acts as the gateway for all air flowing into the
combustion chamber 65 from the plenum 70. Sealing members 125 seal
the periphery of the flame arrester 115 to the divider 60 to reduce
the likelihood of air circumventing the flame arrester 115. In
alternative constructions, a single sealing member 125 may be used
to seal the flame arrester 115 with respect to the divider 60, or
if the flame arrester fits snugly against the divider 60, no
sealing members 125 may be needed.
[0020] The flame arrester 115 prevents flame within the combustion
chamber 65 from igniting flammable vapors outside of the combustion
chamber 65. To achieve this end, the flame arrester 115 may operate
according to one or both of two theories.
[0021] The illustrated flame arrester 115 operates according to the
first theory of operation, in which the flame arrester is
constructed of material characterized by high thermal resistance
such that heat on the top surface (i.e., the surface exposed to the
combustion chamber) does not spread to the bottom surface (i.e.,
the surface exposed to the plenum). This prevents the bottom
surface from reaching an incandescent temperature that could ignite
the flammable vapors near the bottom surface. This type of flame
arrester therefore tolerates the presence of flame on its top
surface and includes passageways that are sufficiently narrow to
prevent flame from propagating through the flame arrester.
[0022] This first type of flame arrester may, for example, have
through-holes or a random pattern of interconnected voids. A
conglomeration of randomly-oriented fibers or particles (e.g.,
carbon or glass fibers) may be bonded or compressed together to
form a cohesive unit including the random pattern of interconnected
voids. The size and shape of the particles or fibers are preferably
selected to avoid a chain of voids that would allow a flame to
travel through the flame arrester and to avoid the isolation of a
significant number of voids from other voids, which would
effectively increase the density of the flame arrester and unduly
restrict the air flow through the flame arrester. The air that is
necessary for combustion of the gaseous fuel during normal
operation of the water heater is allowed to flow from void to void
from the bottom surface to the top surface of the flame arrester.
The arduous air-flow path through the flame arrester further (i.e.,
in addition to the thermal resistance of the material itself)
reduces the thermal conductivity of the flame arrester, and
substantially ensures that the bottom surface of the flame arrester
will be below the ignition temperature of the flammable vapors
entering the flame arrester, even when vapors are burning on the
top surface of the flame arrester.
[0023] In the second theory of operation, the flame arrester
quickly extinguishes any flame on its top surface, and does not
rely on a high thermal resistivity. In fact, some flame arresters
that operate under this principle incorporate materials of high
thermal conductivity to quickly diffuse or absorb heat and
extinguish the flame. Flame arresters of this type may be
constructed of one or more wire mesh screens, for example.
[0024] With reference again to FIG. 3, the air inlet 27 is covered
by a screen 130 mounted to the outer surface of the base pan 15 and
by one or more fans 135 mounted to the inner surface of the base
pan 15. In the illustrated embodiment, a plate 140 having holes 145
therein is mounted to the inner surface of the base pan 15 over the
air inlet 27, and each fan 135 is mounted to the plate 140 over one
of the holes 145. The plate 140 is substantially air-tightly sealed
to the base pan 15 by way of a gasket 150 or other means for
sealing between the plate 140 and base pan 15, and all air passing
through the air inlet 27 flows through the screen 130 and one of
the fans 135. The screen 130 filters air flow into the plenum 70
and reduces the likelihood that the flame arrester 115 will become
occluded by lint or other debris.
[0025] Although two fans 135 are illustrated, the invention may
include a single fan or more than two fans depending on the size of
the water heater 10, air flow requirements, and other
considerations. Also, the fans 135 may in alternative constructions
be mounted to the outside of the base pan 15 and may have integral
screens in lieu of the illustrated screen 130, or the screen 130
may be mounted inside the base pan 15. The illustrated position of
the screen 130 was chosen to permit easy access for cleaning. Also,
the fans 135 may be mounted directly to the base pan 15 (i.e.,
without the plate 140), and with or without a gasket, depending on
the quality of the seal between the fans 135 and base pan wall),
provided the air inlet 27 is properly shaped so the fans 135 fully
cover it.
[0026] A main burner 155 in the combustion chamber 65 burns a
mixture of gas fuel and air to create the products of combustion
that flow up through the flue 85 to heat the water in the tank 35,
as discussed above. The main burner 155 receives gas fuel through a
gas manifold tube 160 that extends in a sealed condition through an
access door 165 mounted in a sealed condition over an access
opening in the skirt 50. The two illustrated embodiments differ
primarily in the type of ignition system used to ignite the main
burner 155, and also in the type of gas valve used to control gas
fuel to the main burner 155.
[0027] The first embodiment (illustrated in FIGS. 1 and 2), employs
a non-powered gas valve/thermostat 170 mounted to the water tank
10. A gas main 175 provides gas fuel to the input side of the
non-powered gas valve/thermostat 170. The non-powered gas
valve/thermostat 170 includes a water temperature probe 180
threaded into the tank side wall 35. Connected to the output side
of the non-powered gas valve/thermostat 170 are the burner manifold
tube 160, a pilot burner 185, a thermocouple 190, a spark igniter
195, and a gas pressure switch or relay 200. The pilot burner 185,
thermocouple 190, and spark igniter 195 extend into the combustion
chamber 65 in a sealed condition through a grommet in the access
door 165.
[0028] The non-powered gas valve/thermostat 170 provides a flow of
gas fuel to the pilot burner 185 to maintain a standing pilot
flame, and this construction is therefore generally referred to as
a "continuous pilot ignition" system. The spark igniter 195 is used
to initiate flame on the pilot burner 185 without having to reach
into the combustion chamber with a match. A spark is generated by
the spark igniter 195 in response to pushing a button on the
non-powered gas valve/thermostat 170. The thermocouple 190 provides
feedback to the non-powered gas valve/thermostat 170 as to the
presence of flame at the pilot burner 185. More specifically, the
non-powered gas valve/thermostat 170 includes an interrupter valve
or some other means for selectively shutting off fuel flow to the
pilot burner 185 and main burner 155. The interrupter valve is
biased toward a closed position. The interrupter valve is held open
by a voltage arising in the thermocouple 190 in response to the tip
of the thermocouple 190 being heated by the pilot burner flame. If
the pilot burner 185 loses its flame, the thermocouple 190 will
cool down and not provide the voltage to the interrupter valve, and
the interrupter valve will close and shut off fuel flow to the
pilot burner 185 and main burner 155.
[0029] The non-powered gas valve/thermostat 170 permits gas fuel to
flow to the main burner 155 in response to a water temperature
sensor (e.g., the water temperature probe 180) indicating that the
water temperature in the water tank 35 has fallen below a selected
temperature. When gas fuel flows to the main burner 155, it is
mixed with air and the mixture is ignited when it contacts the
pilot burner flame. Once the water temperature sensor indicates
that the water has reached the desired temperature, the non-powered
gas valve/thermostat 170 shuts off gas fuel flow to the main burner
155, and the water heater 10 is in "standby mode" until the water
temperature again drops to the point where the non-powered gas
valve/thermostat 170 must again provide gas fuel to the main burner
155.
[0030] A transformer/converter 205 plugs into a standard outlet
providing 110-volt alternating current (A/C) electricity. The
transformer/converter 205 steps the voltage down and converts it to
12 or 24 volt direct current (D/C) electricity, which is delivered
to the electric fans 135. The fans 135 are preferably standard 12
volt or 24 volt D/C electric fans. The fans 135 preferably have
permanent magnet D/C motors to avoid sparks or discharges that may
ignite flammable vapors.
[0031] The pressure switch 200 is part of the electrical circuit
providing electricity to the fans 135 and is connected in series
between the transformer/converter 205 and the fans 135. The
pressure switch 200 includes a tube 210 that references the
pressure switch 200 to the gas pressure at the manifold tube 160
connection. The pressure switch 200 senses an increase in pressure
when gas fuel is permitted to flow to the main burner 155, and
closes the electrical circuit in response to the pressure increase
to permit electricity to flow to the fans 135 to thereby energize
or activate the fans 135. The gas pressure switch 200 opens the
electrical circuit when the pressure at the main burner manifold
160 drops in response to gas fuel flow to the main burner 155 being
shut off. The fans 135 in this embodiment therefore run during main
burner operation.
[0032] When operating, the fans 135 raise the pressure within the
plenum 70 and combustion chamber 65. Fuel and primary air are mixed
upstream of the burner 155 within the combustion chamber 65 (there
is no fuel mixing within the plenum 70) and is combusted at the
burner 155. Secondary air within the combustion chamber 65 combines
with the primary air and fuel mixture to complete the combustion
process at the outlet of the burner 155. In this regard, the fans
135 pressurize both primary and secondary air. The
higher-than-atmospheric pressure within the plenum 70 aids in the
flame arrester's functionality because it reduces the likelihood of
vapors and fuel flowing out of the combustion chamber 65 into the
plenum 70 (i.e., it biases the flow of gases out of the plenum 70
into the combustion chamber 65 and further into the flue 85).
[0033] The second illustrated embodiment (FIGS. 4 and 5) includes
an electric gas valve 215 that includes a power cord 220 to be
plugged into a standard 110-volt wall socket. The electric gas
valve 215 preferably runs on 12 or 24 volt D/C power, and includes
an internal transformer and rectifier that step the voltage down to
12 or 24 volts and convert the current to D/C. The electric gas
valve 215 provides power to the fans 135 through a power cord 225.
Because of the relatively small size (as compared to, for example,
a power vent blower) of the fans 135, the fans 135 can be run off
the same power source as the gas valve 215. The illustrated fans
135, for example, have power inputs of less than about 10 Watts.
The electric gas valve 215 includes a controller or CPU 230.
[0034] The second embodiment also includes a flammable vapor sensor
235 (FIG. 5) mounted in the plenum 70, and a pressure sensor 240
and pressure sensing tube 245 (FIG. 4) mounted outside the base pan
15. The sensors 235, 240 communicate with the electric gas valve
215 through sensor conduits 250. The flammable vapor sensor 235
could alternatively be mounted in the combustion chamber 65, but
then the sensor 235 would need to withstand the temperature
conditions in the combustion chamber 65. The second illustrated
embodiment employs an intermittent ignition system, which includes
a hot surface igniter 255 and a flame sensor 260 in place of the
pilot burner 185, thermocouple 190, and spark igniter 195 of the
first embodiment.
[0035] Control logic in the controller 230 initiates operation of
the fans 135 and checks the conditions in the plenum 70 prior to
energizing the igniter 255 and permitting fuel flow to the main
burner 155. More specifically, if the flammable vapor sensor 235
indicates that flammable vapors are present in the plenum 70 or
combustion chamber 65 (depending on where the sensor 235 is
mounted), the controller 230 activates the fans 135 and gives them
enough time to purge such vapors through the plenum 70, combustion
chamber 65, and flue 85, and confirms through the sensor 235 that
the vapors have in fact been purged, prior to energizing the
igniter 255 and permitting fuel flow to the main burner 155. The
controller 230 may be programmed with a set point for acceptable
levels or concentrations of flammable vapors prior to initiating
burner ignition. For example, the controller 230 may be set to only
permit main burner 115 ignition after the flammable vapor sensor
235 indicates zero flammable vapors in the plenum 70, or the
controller 230 may be set to permit main burner 115 ignition when
flammable vapors are still present in the plenum 70, but at
concentrations less than the lower explosive limit of the flammable
vapor. The controller 230 includes a timer function to de-energize
the fans 135 in the event flammable vapors do not purge after
extended fan operation (e.g., if there is a saturated flammable
vapor environment around the water heater 10 that the fans 135
cannot clear and that requires other intervention).
[0036] Also, after energizing the fans 135 and prior to energizing
the igniter 255 and permitting fuel flow to the burner 155, the
controller 230 monitors the pressure sensor 240. The pressure
sensor 240 compares ambient pressure to pressure in the tube 245
(communicating with the plenum 70 or combustion chamber 65) to
determine whether there is an increase in pressure in the plenum 70
or combustion chamber 65 in response to fan operation. If pressure
does not sufficiently increase, the controller 230 concludes that
there is a leak in the plenum 70 or combustion chamber 65, a fan
malfunction, or a blockage of the airflow into the plenum 70 or
combustion chamber 65, and will not energize the igniter 255 or
permit fuel flow to the burner 155.
[0037] Once the controller 230 is satisfied that there are no
flammable vapors in the plenum 70 and that the combustion chamber
65 is sufficiently pressurized (as evidenced by the pressure rise
in response to fan operation), the controller 230 energizes the hot
surface igniter 255, waits for a period of time sufficient for the
hot surface igniter 255 to reach a temperature sufficient to ignite
a combustible mixture of fuel and air, and then permits fuel flow
into the burner 155 where it is mixed with air and the mixture
flows out of the burner 155. The air/fuel mixture ignites upon
contact with the hot surface igniter 255.
[0038] The controller 230 then uses flame rectification principles
and methods to determine with the flame sensor 260 whether flame is
present at the burner 155. More specifically, the controller 230
applies alternating voltage to the flame sensor 260 and uses the
flame (if present) as the ground for the circuit. The controller
230 continues to provide gas fuel to the burner 155 while a D/C
offset current is measured between the flame sensor 260 and the
flame, and shuts down gas flow to the burner 155 in the absence of
current flow. If flame is not present at the main burner 155, the
controller 230 may be programmed to purge the combustion chamber 65
of gas fuel by energizing the fans 135, and then try again to
ignite the main burner 155.
[0039] In both illustrated embodiments, the water heater's
efficiency is increased due to the combined use of the
pressurization fans 135 and the baffle 100, which in tandem
increase the heat transfer to the flue 85. In atmospheric water
heaters, the restrictiveness of a flue baffle 100 is limited by the
force of the natural convection currents in the flue 85 caused by
the buoyancy of the hot products of combustion. In the present
invention, however, the positive pressure created by the fans 135
forces the products of combustion up through the flue 85, and a
more restrictive baffle 100 can be used.
[0040] It should be noted that, while the first and second
embodiments include a non-powered gas valve and an electric gas
valve, respectively, it is possible to use a hybrid system that
uses an electric valve in combination with continuous pilot
ignition. Such hybrid system may include an electric gas valve that
includes a voltage sensor that tells the controller the magnitude
of the voltage in the thermocouple. The controller would therefore
be able to monitor the strength of the pilot flame and determine
when a low-oxygen condition is arising in the combustion chamber.
In such a situation, the controller may activate the fans to add
oxygen-rich ambient air to the combustion chamber and purge the
low-oxygen air from the combustion chamber. If the low-oxygen
condition is due to a cause that is not overcome by activation of
the fans, the controller would diagnose such conditions when
activation of the fan does not help strengthen the pilot flame, and
the controller may shut down fuel flow to the pilot and main
burners. Use of an electric gas valve having a controller with a
continuous pilot ignition system would also enable the use of
flammable vapor and/or pressure sensors as discussed above with
respect to the second embodiment.
[0041] Another way for such hybrid system to determine when a
low-oxygen condition arises is to monitor water temperature. When
the water temperature is hot, the flue and any gases within the
flue remain warm, and convection currents caused by the pilot
burner alone will be able to flow up through the flue (even with
the restrictive baffle in place). If, however, the water in the
tank becomes cold, but not so cold as to trigger operation of the
main burner (e.g., when the set point of the water heater is low,
as when in a vacation or temperature set-back mode), the flue may
become cool enough to retard convection currents caused by the
pilot burner alone. Under such circumstances, the hot products of
combustion created by the pilot burner alone will be insufficient
to support convection currents of sufficient strength to flow up
through the cold flue (especially with the restrictive baffle in
place). Thus, the controller may be programmed to activate the fans
when the temperature probe senses a cold water condition in which
it is likely that the pilot burner products of combustion are not
able to flow through the flue on their own. Activation of the fans
will force the products of combustion of the pilot flame out of the
combustion chamber and replenish fresh air into the combustion
chamber.
[0042] A hybrid system with a continuous pilot ignition and
electric gas valve would also be able to energize the fans in
response to sensing the water temperature exceeding a high limit. A
high water temperature situation may occur with a continuous pilot
ignition system during long periods of standby. During standby, the
baffle may retain products of combustion generated by the pilot
flame in the flue 85 long enough to heat the water in the tank
beyond the water heater's set point. If such a high water
temperature situation occurs, the controller in the electric gas
valve may be programmed to activate the fans without permitting
fuel flow to the main burner. The resulting influx of relatively
cool ambient air into the combustion chamber and flue strips heat
from the water in the tank and reduces the water temperature. When
the water temperature is again safely below the high temperature
set point, the controller would be programmed to deactivate the
fans.
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