U.S. patent application number 11/143833 was filed with the patent office on 2006-12-07 for low power control system and associated methods for a water heater with flammable vapor sensor.
Invention is credited to Jozef Boros, Walter T. Castleberry, Bruce A. Hotton, Randy R. Koivisto.
Application Number | 20060275720 11/143833 |
Document ID | / |
Family ID | 37480417 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060275720 |
Kind Code |
A1 |
Hotton; Bruce A. ; et
al. |
December 7, 2006 |
Low power control system and associated methods for a water heater
with flammable vapor sensor
Abstract
A transistor used as a normally open switch is connected in the
millivolt electrical circuit of a fuel-fired natural draft water
heater in series with a thermopile device impinged upon by a
standing pilot flame, and the solenoid coil portion of the pilot
fuel valve. A variable resistance type flammable vapor sensor is
connected in a control circuit which is powered by a DC battery and
is coupled only to the transistor portion of the millivolt circuit.
In the absence of flammable vapor detection by the sensor the
control circuit outputs an electrical signal to the transistor that
holds it in a closed position to thereby maintain the standing
pilot flame. In response to sensor detection of flammable vapor,
the control circuit output signal terminates to cause the
transistor to return to its normally open switch position, thereby
shutting off the pilot flame.
Inventors: |
Hotton; Bruce A.;
(Montgomery, AL) ; Castleberry; Walter T.; (Pike
Road, AL) ; Koivisto; Randy R.; (Fort Smith, AR)
; Boros; Jozef; (Montgomery, AL) |
Correspondence
Address: |
HAYNES AND BOONE, LLP
901 MAIN STREET, SUITE 3100
DALLAS
TX
75202
US
|
Family ID: |
37480417 |
Appl. No.: |
11/143833 |
Filed: |
June 2, 2005 |
Current U.S.
Class: |
431/80 ;
431/66 |
Current CPC
Class: |
F23N 5/102 20130101 |
Class at
Publication: |
431/080 ;
431/066 |
International
Class: |
F23N 5/10 20060101
F23N005/10 |
Claims
1. Fuel-fired heating apparatus comprising: a burner adapted to
receive fuel and combustion air and create a flame therefrom; a
normally closed fuel valve coupled to said burner for supplying
fuel thereto when opened; a thermoelectric circuit having connected
in series therein (1) a thermoelectric device positioned to receive
heat from said flame and responsively generate an electrical
voltage, (2) a solenoid structure operative to receive electrical
power from said thermoelectric device and responsively hold said
normally closed fuel valve in an open position, and (3) a normally
open switch device; and a low power electrical control circuit,
operable by an electrical power source and coupled to said
thermoelectric circuit only via said normally open switch device,
for protecting said heating apparatus against an undesirable
operating condition, said low power electrical control circuit
having connected therein a variable resistance sensor operative to
detect said undesirable operating condition, said control circuit,
in the absence of detection by said sensor of said undesirable
operating condition, outputting an electrical signal to said switch
device to maintain it in a closed state, and terminating said
electrical signal upon detection by said sensor of said undesirable
operating condition to return said switch device to its normally
open state.
2. The fuel-fired heating apparatus of claim 1 wherein: said
fuel-fired heating apparatus is a water heater.
3. The fuel-fired heating apparatus of claim 1 wherein: said burner
is a pilot burner.
4. The fuel-fired heating apparatus of claim 1 wherein: said
thermoelectric device is a thermopile structure.
5. The fuel-fired heating apparatus of claim 1 wherein: said
normally open switch device is a normally open solid state switch
device.
6. The fuel-fired heating apparatus of claim 5 wherein: said
normally open solid state switch device is a field effect
transistor.
7. The fuel-fired heating apparatus of claim 1 wherein: said
electrical power source is a non-thermoelectric electrical power
source.
8. The fuel-fired heating apparatus of claim 7 wherein: said
non-thermoelectric electrical power source is a DC battery.
9. The fuel-fired heating apparatus of claim 1 wherein: neither of
said thermoelectric circuit and said low power electrical control
circuit is operative to receive an electrical current flow from the
other of said thermoelectric circuit and said low power electrical
control circuit.
10. The fuel-fired heating apparatus of claim 1 wherein: said
variable resistance sensor is a flammable vapor sensor.
11. The fuel-fired heating apparatus of claim 1 wherein: said low
power electrical control circuit further includes a multi-resistor
bridge section, and said variable resistance sensor forms a
resistive portion of said bridge section.
12. The fuel-fired heating apparatus of claim 11 wherein: said low
power electrical control circuit further includes an operational
amplifier having an input portion operatively connected across said
bridge section, and an output portion coupled to said normally open
switch device.
13. The fuel-fired heating apparatus of claim 12 wherein: said
operational amplifier is an open collector output type operational
amplifier.
14. The fuel-fired heating apparatus of claim 13 wherein: said low
power electrical control circuit further includes a first
electrical lead interconnecting said output portion of said
operational amplifier to said normally open switch device, a second
electrical lead interconnected between said first electrical lead
and said bridge section, and a pull-up resistor connected in said
second electrical lead.
15. A method of inhibiting extraneous flammable vapor ignition by a
fuel-fired heating appliance having a burner adapted to receive
fuel and combustion air and create a flame therefrom, a normally
closed fuel valve coupled to said burner for supplying fuel thereto
when opened, a thermoelectric circuit having connected in series
therein a thermoelectric device positioned to receive heat from
said flame and responsively generate an electrical voltage, and a
solenoid structure operative to receive electrical power from said
thermoelectric device and responsively hold said normally closed
fuel valve in an open position, said method comprising the steps
of: installing a normally open switch device in said thermoelectric
circuit in series with said thermoelectric device and said solenoid
structure; providing a low power electrical control circuit having
an electrical power source and a variable resistance type gas
sensor incorporated therein, said control circuit having an output
portion operative to create and maintain an electrical output
signal in the absence of said sensor being exposed to a
predetermined concentration of a gas, and to terminate said
electrical signal when said sensor is exposed to at least said
predetermined concentration of the gas; and coupling said output
portion to said thermoelectric circuit, only via said normally open
switch device so that the resistance of said sensor is not present
in said thermoelectric circuit, in a manner such that said normally
open switch is closed during the presence of said electrical
signal, and is open in the absence of said electrical signal.
16. The method of claim 15 wherein: said fuel-fired heating
appliance and said thermoelectric circuit are existing apparatus,
and said method is performed as a retrofit method in which said low
power electrical control circuit and normally open switch device
are operatively coupled to the existing thermoelectric circuit.
17. The method of claim 15 wherein: said installing step is
performed using a solid state switch.
18. The method of claim 15 wherein: said installing step is
performed using a field effect transistor.
19. The method of claim 15 wherein: said providing step includes
the step of using a DC battery as said electrical power source.
20. The method of claim 15 wherein: said providing step is
performed using a flammable vapor sensor as said variable
resistance type gas sensor.
21. The method of claim 15 wherein: said providing step includes
the step of incorporating said gas sensor as a resistive portion of
a multi-resistor bridge section of said low power electrical
control circuit.
22. The method of claim 21 wherein: said providing step includes
the step of connecting the output side of an operational amplifier
across said bridge section, and said coupling step is performed by
electrically connecting the output side of said operational
amplifier to said normally open switch device.
23. The method of claim 22 wherein: said operational amplifier is
an open collector output type operational amplifier, said coupling
step includes the step of connecting a first electrical lead
between said output side of said operational amplifier and said
normally open switch device, and said providing step includes the
steps of interconnecting a second electrical lead between said
first electrical lead and said bridge section, and connecting a
pull-up resistor in said second electrical lead.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to fuel-fired
heating apparatus and, in a representatively illustrated embodiment
thereof, more particularly provides a fuel-fired, natural draft
water heater having a specially designed, low power control system
which includes a flammable vapor sensor and is operatively
connected to a pilot valve millivolt circuit portion of the water
heater.
[0002] Fuel-fired, natural draft water heaters typically maintain a
standing pilot flame which is used to ignite a main burner flame
when the control system of the water heater calls for heat to be
added to its tank-stored water from the main burner. The pilot
burner is supplied with fuel gas through a normally closed valve
having an electrically operated solenoid portion used to keep the
valve open during the presence of the pilot flame.
[0003] The valve solenoid portion is part of what is customarily
referred to as a "millivolt" circuit and is wired in series with a
thermoelectric device, such as a thermocouple or a
multi-thermocouple thermopile structure, which is impinged upon by
the pilot flame. Such thermoelectric device operates to convert
pilot flame heat to a relatively small amount of electrical current
that flows through the millivolt circuit and, via the solenoid,
holds the normally closed pilot valve in an open position to
maintain the standing pilot flame. Conventionally, the pilot valve
is linked to the main burner valve in a manner such that if the
pilot valve shuts off the main burner valve automatically does so
as well to thereby shut off the water heater combustion
process.
[0004] In recent years considerable design effort has been expended
to provide fuel-fired water heaters with flammable vapor ignition
resistance (FVIR) of various sorts in an attempt to prevent the
ignition by the water heater of extraneous flammable vapors that
may be present (from, for example, spilled gasoline on the floor)
adjacent the water heater. One suggested technique to achieve this
protective result is to use a flammable vapor sensor which detects
flammable vapors adjacent the water heater and terminates or
precludes combustion initiation in the water heater combustion
chamber. A common type of flammable vapor sensor used in this
application is of a chemiresistor type in which the electrical
resistance of the sensor increases as a function of the
concentration of flammable vapors to which the sensor is exposed.
It is this flammable vapor-created sensor resistance increase which
is utilized to prevent ignition of such flammable vapors.
[0005] One previously proposed technique for using a variable
resistance flammable vapor sensor in this application is
illustrated and described in published U.S. Patent application
2001/0042564 to Abraham et al, which is hereby incorporated by
reference herein, in which a variable resistance flammable sensor
22 is placed in the water heater millivolt circuit in series with
the valve solenoid 28 and a thermocouple 36 or thermopile that is
position so as to be heated by a standing pilot flame 34.
Electrical energization of the solenoid coil 28 with sufficient
voltage holds the fuel valve 24 open against the force of a spring
26 urging the valve to its normally closed position.
[0006] A disadvantage of this approach of interposing a variable
resistance flammable vapor in a fuel-fired water heater millivolt
circuit is noted in U.S. published Patent Application 2001/0042564
as being " . . . it is necessary to increase the internal
resistance of the solenoid coil. This can be accomplished by for
example the use of higher gauge wire (smaller diameter) and an
increase in number of coils in the electromagnet".
[0007] Thus, if it desired to add the flammable vapor ignition
protection of a variable resistance type flammable vapor sensor by
interposing the sensor in the millivolt circuit in a retrofit
application it is necessary to modify or replace the valve solenoid
to accommodate the additional electrical resistance (and the
corresponding decrease in voltage available to operate the valve
solenoid) created by the sensor. This, of course, undesirably adds
to the overall installation and materials cost of this retrofit
effort. And, of course, a modified solenoid structure would also
have to be provided if the flammable vapor sensor was incorporated
in the millivolt circuit in the original manufacture of the water
heater.
[0008] From the foregoing it can readily be seen from the foregoing
that it would be desirable to provide a technique for associating a
variable resistance flammable vapor sensor with the millivolt
circuit of a fuel-fired water heater without the previous necessity
of modifying the valve solenoid portion of the millivolt circuit.
It is to this goal that the present invention is primarily
directed.
SUMMARY OF THE INVENTION
[0009] In carrying out principles of the present invention, in
accordance with a representative embodiment thereof, a fuel-fired
heating apparatus is provided which is illustratively a water
heater but could alternatively be another type of fuel-fired
heating apparatus such as, for example, a boiler or air heating
furnace.
[0010] The water heater has a burner, representatively a pilot
burner, adapted to receive fuel and combustion air and create a
flame therefrom, and a normally closed fuel valve coupled to the
burner for supplying fuel thereto when opened. A thermoelectric
circuit portion of the water heater has connected in series therein
(1) a thermoelectric device positioned to receive heat from the
burner flame and responsively generate an electrical voltage, (2) a
solenoid structure operative to receive electrical power from the
thermoelectric device and responsively hold the normally closed
fuel valve in an open position, and (3) a normally open switch
device operative to receive an electrical signal and responsively
close to thereby permit thermoelectric current flow through the
solenoid structure for the duration of said electrical signal.
[0011] A low power electrical control circuit, operable by an
electrical power source, preferably a long-life DC battery, is
coupled to the thermoelectric circuit only via the normally open
switch device and is operable to protect the heating apparatus
against an undesirable operating condition. The low power
electrical control circuit has connected therein a variable
resistance sensor operative to detect the predetermined undesirable
operating condition which is representatively the presence of a
predetermined concentration of extraneous flammable vapors adjacent
the heating apparatus. The control circuit, in the absence of
detection by the sensor of the undesirable operating condition,
outputs an electrical signal to the switch device to maintain it in
a closed state, and terminates the electrical signal upon detection
by the sensor of the undesirable operating condition to return the
switch device to its normally open state which automatically
returns the fuel valve to its normally closed position or precludes
it from being opened.
[0012] By associating the control system and switch with the
thermoelectric circuit in this unique manner, which forms a method
of the present invention that may be carried out in the initial
fabrication of the heating apparatus or later as a retrofit method,
the resistance of the sensor, illustratively a flammable vapor
sensor, is not incorporated into the thermoelectric circuit.
Accordingly, it is not necessary to modify the fuel valve solenoid
coil in any manner.
[0013] According to various other aspects of the present invention,
the normally open switch device is a solid state switch device,
preferably a field effect transistor, and the thermoelectric device
is preferably a thermopile structure. The low power electrical
control circuit preferably includes a multi-resistor bridge
section, with the variable resistance sensor forming a resistive
portion of the bridge section. Preferably, the control circuit
further includes an operational amplifier of the open collector
output type and has an input portion operatively connected across
the circuit bridge section, and an output portion coupled to the
normally open switch device. The control circuit also preferably
includes a first electrical lead interconnecting the output portion
of the operational amplifier to the normally open switch device, a
second electrical lead interconnected between the first electrical
lead and the circuit bridge section, and a pull-up resistor
connected in the second electrical lead.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic cross-sectional view through a
representative fuel-fired natural draft water heater embodying
principles of the present invention; and
[0015] FIG. 2 is a schematic diagram of a millivolt circuit portion
of the water heater to which a specially designed low power control
system, incorporating a variable resistance flammable vapor sensor,
is operatively coupled.
DETAILED DESCRIPTION
[0016] As schematically illustrated in FIG. 1, this invention
provides a fuel-fired, natural draft water heater 10 which
representatively rests on a floor 12 and includes the usual
insulated tank 14 that holds a quantity of pressurized water 16 for
on-demand delivery to various plumbing fixtures through a
tank-mounted outlet fitting 18. Pressurized hot water 16 delivered
to such plumbing fixtures is automatically replaced by pressurized
cold water delivered to the tank 14 via a tank inlet fitting
20.
[0017] Beneath the bottom end of the tank 14 is a combustion
chamber 22 in which a main fuel burner 24 and an associated pilot
burner 26 are operatively disposed. In a conventional manner, each
burner is operative to receive fuel and combustion air which it
combusts to create a burner flame. A main fuel supply line 28 is
connected to the main burner 24, and a pilot fuel supply line 30 is
connected to the pilot burner 26. Normally closed main and pilot
fuel supply valves 32,34 are respectively installed in the fuel
supply lines 28,30. The pilot valve 34 is linked to the main valve
32 in a conventional manner such that when the pilot valve 34
closes the main valve 32 also closes.
[0018] The pilot valve 34 has an electric solenoid coil 36 (see
FIG. 2) which circumscribes a movable metal core portion 38 of the
pilot valve 26 and, when electrically energized as later described
herein, moves the core 38 in a first direction (representatively
upwardly as indicated by the arrow 40 in FIG. 2) to open the
normally closed pilot valve 34. When coil 36 is de-energized, the
solenoid core 38 is spring-driven in the opposite direction 42 to
thereby close the pilot fuel supply valve 34, thus also closing the
main fuel supply valve 32.
[0019] With reference now to FIGS. 1 and 2, according to key aspect
of this invention, the water heater 10 is provided with a specially
designed low power fuel valve control system 44 which includes a
flammable vapor sensor 46. The vapor sensor 46 is positioned near
the floor 12 and is operative to sense flammable vapor 48 (such as
from spilled gasoline) near the floor 12 adjacent the bottom end of
the water heater 10 and responsively cause the pilot valve 34, and
thus the main valve 32, to close. The flammable vapor sensor 46 is
of the chemiresistor type and has an electrical resistance which
increases with increases in the concentration of the flammable
vapor 48 to which the sensor 46 is exposed.
[0020] Turning now to FIG. 2, the specially designed low power fuel
valve control system 44 of the present invention comprises
electrical circuitry that includes a millivolt circuit portion 50
and a control circuit portion 52. The millivolt circuit 50 includes
a pair of electrical leads 54,46 which are coupled as shown to the
pilot valve solenoid coil 36, and to a thermopile device 58 in
series with the coil 36. Thermopile device 58, which may
alternatively be a thermoelectric device of another suitable type
such as a thermocouple, is positioned to be impinged upon by the
standing flame 60 of the pilot burner 26 to thereby
thermoelectrically generate a small electrical current in the
millivolt circuit 50. A conventional ECO (emergency cutoff device)
is connected in lead 54 between the coil 36 and the thermopile 58,
and a field effect transistor 61 is connected in the lead 54
between the ECO and the coil 36. As will be seen, transistor 61
functions as a normally open solid state electrical switch
structure in the millivolt circuit 50. When it is in its normally
open mode, the transistor 61 blocks electrical current flow through
the solenoid coil 36. When it is in its closed mode the transistor
61 permits electrical current flow through the solenoid coil, and
does not add any appreciable additional resistance to the millivolt
circuit 50.
[0021] It is important to note at this point that the flammable
vapor sensor 46 is not directly connected in the millivolt circuit
50. Thus, the valve solenoid coil 36 does not have to be modified
in any manner to accommodate the extra electrical resistance of the
flammable vapor sensor 46. Instead of being connected in the
millivolt circuit 50, the variable resistance flammable vapor
sensor 46 is connected in the separate control circuit 52 as will
now be described.
[0022] Control circuit 52 includes a pair of electrical leads 62,64
between which, from left to right in FIG. 2, electrical leads
66,68,69,70 are connected. A 3.6V long life lithium DC storage
battery 72 is connected in lead 66. A 150 k.OMEGA. resistor R1 and
the flammable vapor sensor 46 (forming a variable resistor R2) are
connected in series in the lead 68, and a 150 k.OMEGA. resistor R3
and a 49.9 k.OMEGA. resistor R4 are connected in series in lead 70.
As can be seen, the resistors R1-R4 form a bridge section of the
control circuit 52, with the flammable vapor sensor forming a
resistive element in one of the legs of such bridge circuit.
[0023] An operational amplifier 73, representatively of the open
collector output type, is interposed in lead 69 and has an input
lead 74 interconnected between its positive input terminal and the
lead 70 between the resistors R3 and R4, an input lead 76
interconnected between its negative input terminal and the lead 68
between resistor R1 and the flammable vapor sensor 46, and an
output lead 78 connected to gate G of the transistor 61. Thus, the
input side of the operational amplifier 73 is connected across the
bridge section of the control circuit 52. Additionally, an
electrical lead 80 having a 100 k.OMEGA. pull-up resistor R5
therein is interconnected between leads 62 and 78 as shown. Pull-up
resistor R5 functions to substantially reduce the electrical
current outflow from the control circuit 52.
[0024] When the flammable vapor sensor 46 is not exposed to
flammable vapor 48, its resistance is substantially less than the
49.9 k.OMEGA. resistance of resistor R4 so that the total
resistance of the R1,R2 circuit leg is similarly substantially less
than the total resistance of the R3,R4 circuit leg. Accordingly,
under this condition the operational amplifier 73 outputs an
electrical signal via lead 78 to the gate "G" of the transistor 61,
thereby maintaining the transistor 61 in its closed state and
permitting current flow through the transistor 61 to hold the pilot
valve 34 open. However, if the flammable vapor sensor 46 is exposed
to flammable vapor 48 and its electrical resistance rises to above
49.9 k.OMEGA., the operational amplifier output signal in lead 78
terminates. This causes the transistor 61 to return to its normally
open state in which it blocks electrical current flow therethrough,
thereby causing the pilot valve 34, and thus the main valve 32, to
close.
[0025] It should be noted that the control circuit 52 is
electrically coupled to the millivolt circuit 50 only by the single
electrical lead 78 extending between the operational amplifier 73
and the field effect transistor 61. The electrical power source for
the control circuit 52 (the battery 72) is separate from and not
coupled to the electrical power source (the thermopile 58). Thus,
to retrofit a fuel-fired water heater with the control
circuit/transistor structure of the present invention all that is
necessary is to connect the transistor 61 in the water heater's
millivolt circuit, and then provide the single lead interconnection
between the control circuit 52 and the installed transistor. In
accordance with principles of the present invention, the control
circuit 52, by itself or with the associated transistor 61, may
conveniently be provided in module form for original or retrofit
installation on an associated water heater.
[0026] Instead of the illustrated long-life battery 72 used to
power the control circuit 52, other suitable electrical power
sources, such as a thermoelectric source or an AC power source
converted to DC power, could be alternatively utilized if desired
without departing from principles of the present invention.
Moreover, in the representatively illustrated control circuit 52,
resistors of other suitable values could be utilized, and other
circuit components and arrangements could be utilized without
departing from principles of the present invention. Similarly,
electrical switch structures other than the illustrated field
effect transformer 61 could be utilized without departing from
principles of the present invention.
[0027] Although the present invention has been representatively
illustrated as being incorporated in a fuel-fired, natural draft
water heater, it will be readily appreciated by those of skill in
this particular art that principles of the present invention could
alternatively be utilized to advantage in other types of fuel-fired
heating apparatus such as, by way of example and not of limitation,
fuel-fired boilers and heating furnaces. Additionally, various
types of variable resistance type sensors other than a flammable
vapor sensor could be incorporated in the control circuit 52, to
detect an undesirable operating condition of the associated
fuel-fired heating apparatus, could be utilized without departing
from principles of the present invention. For example, but not by
way of limitation, various other types of gas sensors, or a
temperature sensor, could be used.
[0028] The foregoing detailed description is to be clearly
understood as being given by way of illustration and example only,
the spirit and scope of the present invention being limited solely
by the appended claims.
* * * * *