CA1294344C - Gas-fired furnace control apparatus and method for maintaining an optimum fuel air ratio - Google Patents
Gas-fired furnace control apparatus and method for maintaining an optimum fuel air ratioInfo
- Publication number
- CA1294344C CA1294344C CA000520974A CA520974A CA1294344C CA 1294344 C CA1294344 C CA 1294344C CA 000520974 A CA000520974 A CA 000520974A CA 520974 A CA520974 A CA 520974A CA 1294344 C CA1294344 C CA 1294344C
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- Prior art keywords
- combustion
- fuel
- pressure
- heat exchanger
- air
- Prior art date
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Abstract
GAS-FIRED FURNACE CONTROL APPARATUS
AND METHOD FOR MAINTAINING AN
OPTIMUM FUEL AIR RATIO
ABSTRACT OF THE DISCLOSURE
A control apparatus and method are provided for maintaining an optimum fuel air ratio in a direct vent gas-fired furnace.
The control and method regulate the flow of fuel to the combustion chamber as a function of the pressure drop across the heat exchangers, thereby compensating for changes in certain operating parameters, such as vent pipe length, barometric pressure, and the like.
AND METHOD FOR MAINTAINING AN
OPTIMUM FUEL AIR RATIO
ABSTRACT OF THE DISCLOSURE
A control apparatus and method are provided for maintaining an optimum fuel air ratio in a direct vent gas-fired furnace.
The control and method regulate the flow of fuel to the combustion chamber as a function of the pressure drop across the heat exchangers, thereby compensating for changes in certain operating parameters, such as vent pipe length, barometric pressure, and the like.
Description
~ 43~4 GAS-FIRED FURNACE CONTROL APPARATUS
AND METHOD FOR MAINTAINING AN
OPTIMUM FUEL AIR RATIO
Background of the Invention This invention pertains to furnaces, and more particularly to a control apparatus and method for a ga~-fired furnace which maintains an optimum fuel air combustion ratio therefor.
Present technology for direct vent gas-fired furnace design generally requires the furnace to be operated at less than the optimum fuel air combustion ratio due to variations in certain parameters, such as vent pipe length, barometric pressure, and BTU content of the natural gas. As a result, the present technique is to design the furnace to operate for anticipated maximum vent pipe length, anticipated highest altitude at which the furnace might be installed, and anticipated maximum BTU content of the gas. Therefore, when the furnace is installed at other than these three anticipated conditions, the furnace will operate with excess combustion air, and as a result thereof, will operate at reduced efficiency.
Summary of the Invention The present invention provides a control apparatus and method for automatically regulating the manifold gas pressure to provide an optimum gas flow in response to varying parameters. This is accomplished by measuring the pressure drop across the heat exchangers by means of a differential pressure transducer and generating a signal indicative of the changing pressure drop. Since the pressure drop varies with vent pipe length, barometric pressure, gas line pressure, temperatures, and the like, the pressure drop signal is used as an input to a microprocessor control that has its control logic preprogrammed to automatically regulate the manifold gas pressure to a desired optimum level as a function of heat 12943'~4 exchanger pressure drop. Consequently, a furnace operated in accordance with the present invention will operate generally at a higher level efficiency than previously possible.
It is an object of the present invention to provide an improved control apparatus for a gas fired furnace that compensates for variation in certain operating parameters.
Another object of the present invention is to provide a method for maintaining opti~um fuel air combustion ratio in a gas-fired furnace.
Yet another obiect of the present invention is to provide a control apparatus for a gas-fîred furnace that utilizes the pressure drop across the heat exchangers to maintain an optimum fuel air combustion ratio.
A further object of the present invention is to provide a method that uses the pressure drop across the heat exchangers for maintaining an optimum fuel air combustion ratio.
Further objects of the present invention will appear as the description proceeds.
In one form of the invention, there is provided in a gas-fired furnace a fuel regulator connected to a combustion chamber for supplying a regulated flow of fuel thereto in response to a received control signal, a pressure differential measuring device for measuring the pressure drop across heat e~changers in the furnace and for generating a pressure differential signal in response thereto, and a control device for receiving the pressure differential signal and for generating in response thereto a control signal to the fuel regulator, whereby the flow of fuel to the combustion chamber is regulated as a function of the pressure lZ~3'~4 i!
drop across the heat exchangers to maintain an optimum fuel air combustion ratio.
In other form of the invention, there is provided a method for maintaining,an optimum fuel air combustion ratio in a gas-fired furnace comprising the steps of supplying a flow of fuel from a fuel source to a combustion apparatus for combusting with the combustion air, measuring the pressure drop across heat eY.changers in the furnace caused by the flow of combusted fuel air mixture, and regulating the supply of fuel flow to the combustion apparatus as a function of the measured pressure drop across the heat e~,;changers to maintain an optimum fuel air combustion ratio.
Brief Description of the Drawings The above-mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Figure 1 is a partially broken-away side elevational view of a furnace incorporating the principles of the present invention;
Figure 2 includes a sectional view of a gas supply valve in conjunction with a schematic of a furnace control system incorporating the principles of the present invention;
Figure 3 is a plot of a curve indicating the relationship between heat exchanger pressure differential and optimum manifold gas pressure; and Figure 4 is a block diagram of a portion of the furnace control system.
4 lZ9~3~
Detailed Description Referring to Figure 1, ~here is illustrated a gas-fired furnace which may be operated according to the principles of the present invention. The following description is made with reference to condensing furnace 10, but it should be understood that the present invention contemplates incorporation with a noncondensing-type furnace. Referring now to Figure 1, condensing furnace 10 includes in major part steel cabinet 12 housing therein burner asse~bly 14, gas regulator 16, heat exchanger assembly 18, inducer housing 20 supporting inducer motor 22 and inducer wheel 24, and circulating air blower 26. Gas regulator 16 includes pilot circuitry for controlling and proving the pilot flame. This pilot circuitry or control can be a BDP model 740A pilot obtainable from BDP Company, Indianapolis, Indiana.
Burner assembly 14 includes at least one inshot burner 28 for at least one primary heat exchanger 30. Burner 28 receives a flow of combustible gas from gas regulator 16 and injects the fuel gas into primary heat exchanger 30. A part of the injection process includes drawing air into heat exchanger assembly 18 so that the fuel gas and air mixture may be combusted therein. A flow of combustion air is delivered through combustion air inlet 32 to be mixed with the gas delivered to burner assembly 14.
Primary heat exchanger 30 includes an outlet 34 opening into chanber 36. Connected to chamber 36 and in fluid communication therewith is at least one condensing heat exchanger 38 having an inlet 40 and an outlet 42. Outlet 42 opens into chamber 44 for venting exhaust flue gases and condensate.
Inducer housing 20 is connected to chamber 44 and has mounted therewith inducer motor 22 with inducer wheel 24 for drawing the combusted fuel air mixture from burner assembly 14 12~3 ~4 through heat exchanger assembly 18. Air blower 26 delivers air to be heated upwardly through air passage 52 and over heat exchanger assembly 18, and the cool air passing over condensing heat exchanger 38 lowers the heat exchanger wall temperature below the dew point of the combusted fuel air ~ixture causing a portion of the water vapor in the combusted fuel air mixture to condense, thereby recovering a portion of the sensible and latent heat energy. The condensate formed within heat exchanger 38 flows through chamber 44 into drain tube 46 to condensate trap assembly 48. As air blower 26 continues to urge a flow of air to be heated upwardly through heat exchanger assembly 18, heat energy is transferred from the combusted fuel air mixture flowing through heat exchangers 30 and 38 to heat the air circulated by blower 26.
Finally, the combusted fuel air mixture that flows through heat exchangers 30 and 38 exits through outlet 42 and is then delivered by inducer motor 22 through exhaust gas outlet 50 and thence to a vent pipe (not shown).
Cabinet 12 also houses microprocessor control assembly 54, LED display 56, pressure tap 58 at primary heat exchanger inlet 60, pressure tap 62 at condensing heat exchanger outlet 42 and limit switch 64 disposed in air passage 52; the purposes of which will be explained in greater detail below.
If condensing furnace 10 is replaced with a noncondensing-type furnace, then naturally pressure tap 62 would be disposed st primary heat exchanger outlet 34, since there would be no condensing heat exchanger 38.
Referring now to Figure 2, gas regulator 16 generally comprises valve body 66 having an inlet 68 and outlet 70.
~etween inlet 68 and outlet 70 are a series of chambers, in particular, inlet chamber 72, intermediate chamber 74, regulator chamber 76, and main chamber 78. These chambers are in fluid communication, directly or indirectly, with val~e body inlet 68 and outlet 70; inlet 68 communicates with 6 lZ~3~
inlet chamber 72 through inlet cha~ber seat 80, inlet chamber 72 communicates with intermediate chamber 74 through intermediate chamber seat 82, intermediate chamber 74 communicates with regulator chamber 76 through regulator seat 84, regulator chamber 76 communicates with main chamber 78 through main seat 86, and main chamber 78 communicates with outlet 70. The use of the term "seat" is equivalent to terms such as "opening", "hole", and the like.
Each of the above mentioned seats are closed and opened by particular members. IIIlet chamber seat 80 is closed and opened by manually-operated valve head 88. Valve head 88 is connected to plunger 90, which is slidably received through valve body 66 in a fluid-tight manner. The externally remote end of plunger 90 is suitably connected to manual on-off lever 92, which is surrounded by indicator bracket 94.
Bracket 94 is connected to valve body 66 in any suitable manner. Spring 96 is disposed within inlet 68 and between valve head 88 and the valve top cover plate 91 50 as to bias valve head 88 into seating engagement with inlet chamber seat 80, thereby to prevent fluid communication between inlet 68 and inlet chamber 7 O-ring 89 insures a fluid tight fit between valve head 88 and seat 80. To open or move valve head 88 to an open position to allow fluid communication between inlet 68 and inlet chamber 72, manual on-off lever 92 is rotated in a counter-clockwise direction, as viewed in Figure 2. Manual on-off lever 92 includes an enlarged end portion 98 that has a camming surface 100. Camming surface 100 is defined by two relatively flat surfaces 102 and 104 that are generally perpendicularly disposed to each other and joined by a generally curved surface 106. As seen in Figure 2, manual lever 92 is in the closed position so that spring 96 is biasing valve head 88 into seating engagement with inlet chamber seat 80 in a fluid-tight manner. ~s manual lever 92 is rotated counter-clockwise, the action of camming surface 100 and enla~ged end portion 98 causes plunger 90 to 7 :1Z~3.~4 be pulled upwardly a~ainst the force of spring 96 to separate val~e head 88 from inlet chamber seat 80, thereby permitting fluid communication between inlet 68 and inlet chamber 72.
Manual lever 92 is held in the open position by the engaging force or friction existing between flat surface 102 and the flat exterior surface portion of valve body 66. Naturally, to close inlet chamber seat 80, manual lever 92 i5 rotated clockwise to permit spring 96 to extend plunger 90 downwardly, thereby permitting valve head 88 to engage inlet chamber seat 80.
Intermediate chamber seat 82 is opened and closed by valve seat disc 108, which is disposed in inlet chamber 72. ~alve seat disc 108 has a secondary plunger 110 connected thereto in any suitable manner and secondary plunger 110 is slidably received in bore 112 disposed in valve head 88 and plunger 90. Spring 114 is disposed in inlet chamber 72 between valve seat disc 108 and oppositely disposed inlet chamber upper surface 116. Spring 114 biases valve seat disc downwardly to close intermediate chamber seat 82 in a fluid tight manner.
A rubber portion 109 insures a fluid tight fit between disc lQ8 and seat 82. Valve seat di8c 108 is connected to secondary plunger 110 so that valve seat disc 108 moves in a generally vertical or straight line dlrection generally perpendicular to the plane of intermediate chamber seat 82, thereby insuring a fluid tight closure of intermediate chamber seat 82 when valve seat disc 108 is in the closed position, as illustrated in Figure 2. Disposed on the opposite side of valve seat disc 108 and in general axial alignment with secondary plunger 110 is push rod 118. Push rod 118 abuts agAinst the undersurface of valve seat disc 108, and upon being moved in an upwardly direction, push rod 118 moves valve seat disc 108 upwardly against spring 114 to open intermediate chamber seat 82, thereby permitting fluid communication between inlet chamber 72 and ~ntermediate chamber 74. Push rod 118 is moved in an up and down 8 1Z~3~4 direction, as viewed in Figure 2, by pick and hold solenoid 120. Solenoid 120 is connected to valve body 66 in any suitable manner and includes a joining segment 122 extending slightly inwardly of intermediate chamber 74. Joining segment 122 provides a fluid tight fit or connection between solenoid 120 and intermediate chamber 74. Joining segment 122 has an axial passage 124 for slidably receiving push rod 118 therein, with the lower remote end of push rod 118 being fiY.ed loosely to movable plunger 126 of solenoid 120. When solenoid 120 is in a de-energized state, plunger 126 and push rod 118 are located in a lowermost position, a~ illu~trated in Figure 2, so that spring 114 biases valve seat disc 108 in fluid tight engagement with intermediate chamber seat 82.
Upon energizing solenoid 120, plunger 126 and push rod 118 move upwardly against valve seat disc 108 and spring 114, thereby to open intermediate chamber seat 82 to allow fluid communication between inlet chamber 72 and inter~ediate chamber 74.
The fluid communication between intermediate chamber 74, regulator chamber 76, and main chamber 78 are closely related in that the opening and closing of regulator seat 84 and main seat 86 are controlled by a ~ingle regulator valve disc 128 disposed in regulator chamber 76. It should be noted that regulator seat 84 and main seat 86 are generally oppositely disposed from each other in regulator chamber 76 and are in generally axial alignment with each other, whereby the axial or linear movement of regulator valve disc 128 regulates the fluid communication between intermediate chamber 74, regulator chamber 76, and main chamber 78. Regulator valve disc 128 is connected in any suitable manner to re~ulator plunger 130 of regulator solenoid 132. A sprin~ 134 is disposed against the underside of regulator valve disc 128 and through regulator seat 84, and biases regulator valve disc 128 upwardly to close main seat 86 in a fluid tight fashion. The upper portion 136 of regulator valve disc 128 is made of a rubber material to ensure fluid tight engagement between valve disc 128 and main seat 86. Regulator ~alve disc 128 is moved downwardly from its uppermost position where it clo~es main seat 86 to a lowermost position where it closes regulator seat 84, thereby opening main seat 86 to permit fluid communication between regulator chamber 76 and main chamber 78. Re~ulator valve disc 128 is moved to its lowermost position upon energizing regulator solenoid 132, which pulls regulator plunger 130 downwardly until valve disc 128 seats aga~nst regulator seat 84. By controlling the voltage to regulator solenoid 132, which will be explained in greater detail below, regulator valve disc 128 is positionable to an infinite number of positions between its uppermost position where it closes main seat 86 and its lowermost position where it closes re~ulator seat 84.
Naturally, any position, other than the uppermost and lowermost positions, will provide simultaneous fluid communication bet~een intermediate chamber 74, regulator chamber 76, and main chamber 78.
Disposed in fluid communication with intermediate chamber 74 are pilot filter 138 and pilot conduit 140 for respectively filtering the portion of the ~as flowing through ~ilter 138 and delivering it through pilot conduit 140 to the pilot flame sssembly, which is part of gas regulator and pilot circuitry 16 (Figure 4).
A pressure-tap port 142 is disposed in regulator chamber 76 for transmitting ~ariations in fluid pressure from chamber 76 through line 144 to pressure transducer 146. Pressure transducer 146 then generates an analog signal to microprocessor control 148 indicative of a change in fluid pressure in regulator chamber 76. Microprocessor control 148 is located in microprocessor control assembly 54 in condensing furnace 10, and is capable of being preprogr2mmed to generate a plurality of control signals in response to ~:2~ 3~
received input signals. Microprocessor control 148 is also connected electrically to thermostat 150 to receive signals therefrom, to pick and hold solenoid 120 by electric~l lines 152, and to regulator solenoid 132 by electrical lines 154.
Referring to Figure 4, there is illustrated a simplified block diagram illustrating the interconnection between microprocessor control 148 and pressure taps 58, 62 through differential pressure transducer 156. As illustrated in Figure 2, differential pressure transducer 156 receives pressure tap inputs from pressure taps 58, 62 and generates an analog signal indicative of the differential pressure to microprocessor control 148 via electrical lines 158.
Still referring to Figure 4, it can be seen that microprocessor control 148 is electrically connected to limit switch 64 (Figure 1), gas valve 16 through electrical lines 152, 154, and also to air blower motor control 160 of air blower 26 through electrical lines 162, and inducer motor control 164 of inducer motor 22 through electrical lines 166.
Air blower motor control 160 and inducer motor control 164 respectively control the rate of fluid flow created by air blower 26 and inducer wheel 24.
With the manual on-off lever 92 moved in a counter-clockwise position to open inlet chamber seat 80, and upon closing of contacts in thermostat 150 indicating a need for heat, microprocessor control 148 is programmed to send a signal via electrical lines 166 (Figure 4) to inducer motor control 16~
to start inducer motor 22 to rotate inducer wheel 24~ thereby causing a flow of combustion air through combustion air inlet 32, burner assembly 14, heat exchanger assembly 18, inducer housing 20, and out eY~haust gas outlet 50. After a predetermined period of time, for example, ten seconds, to ensure purging of the furnace, microprocessor control 148 generates a signal through electrical lines 152 ~o pick and 11 ~2943-~
hold solenoid 120, thereby energizing it to move plunger 126 upwardly so that push rod 118 separates valve seat disc 108 from intermediate chamber seat 82 to permit gas flow from inlet chamber 72 to intermediate chamber 74. The gas flows then to and through pilot filter 138 and pilot conduit 140 to initiate the pilot flame, and flows also into regulator chamber 76 where the pressure is sensed at pressure-tap port 142. Ignition of the pilot flame is p~oved by the pilot circuitry in the pilot control of gas regulator 16 and a signal is generated to microprocessor control 148 through electrical lines 152, 154 (Figure 4) to indicate the flame is proved.
During this period of time, microprocessor control 148 (Figure .~) is monitoring the pressure drop across heat exchanger assembly 18, which is provided by pressure taps 58, 62 transmitting pressure readings to differential pressure transducer 156. Differential presSUre transducer 156 sends a pressure differential signal through electrical lines 158 to microprocessor control 148 indicative of the presSure drop reading. Pressure-tap port 142 is also transmitting increasing gas pressure in regulator chamber 76 through line 144 to pressure transducer 146, which generates an analog signal indicative of the increasing gas pressure to microprocessor control 148. After microprocessor control 148 determines a sufficient pressure drop exists across heat exchanger assembly 18, that the g&S pressure in regulator chamber 76 is at or above a predetermined pressure, and the pilot flame has been proved, microprocessor control 148 is programmed to generate a voltage signal through electrical lines 154 to regulator solenoid 132. During this period of time, regulator valve disc 128 is closing off main seat 86 of main chamber 78 to prevent gas flow therethrough.
Because of the relatively high pressure existing in regulator chamber 76, the signal generated from microprocessor control 12 ~Z~ 4 3~4 148 to regulator solenoid 132 is of a relatively high voltage to cause solenoid 132 to pull regulator plunger 130 to its lowermost position, whereby regulator valve disc 128 opens main seat 86 and closes regulator seat 84. This prevents fluid communication between regulator chamber 76 and intermediate chamber 74, but does permit fluid communication between regulator chamber 76 and main chamber 78. Thus, the increased gas pressure in regulator chamber 76 bleeds off through main seat 86, main cha~ber 78, and through outlet 70.
This decreasing gas pressure in reglllator chamber 76 is continually monitored by microprocessor control 148 through port 142 and upon rPaching a predetermined low pressure, microprocessor control 148 generates a relati~ely low voltage signal to re~ulator solenoid 132 to open regulator seat 84 by moving regulator plunger 130 to an intermediate position between its uppermost position where it closes off main seat 86 and its lowermost position where it close6 off regulator seat 84. Microprocessor control 148 is preprogrammed to position ~egulator valve disc 128 in regulator chamber 76 to provide a desired gas flow rate and pressure in main chamber 78.
Thereafter, gas flow is provided by gas regulator 16 to burner assembly 14 and the fuel air mixture is combusted by inshot burner 28. The combusted fuel air mixture is then drawn through heat exchanger assembly 18 and out exhaust gas outlet 50 by the rotation of inducer wheel 24 by motor 22.
Af~er a preselected period of time, for example, one minute, to ensure heat exchanger assembly 18 has reached a predetermined temp2rature, microprocessor control 148 is preprogrammed to generate a signal through electrical lines 162 (Figure 4) to air blower motor control 160, which starts air blower 26 to provide a flow of air to be heated over condensing heat exchanger 38 and primary heat exchanger 30.
Any condensate that forms in condensing heat exchanger 38 is 13 12943~4 delivered through drain tube 46 to condensate trap assembly 4~.
After the heating load has been satisfied, the contacts of thermostat 150 open, and in response there~o microprocessor control 148 de-energizes pick and hold solenoid 120 and regulator solenoid 132. Plunger 126 then moVes downwardly, as viewed in ~igure 2, under the influence of spring 114, and valve seat disc 108 closes intermediate chamber seat 82 due to the downwardly directed force provided by spring 114, thereby preventing 1uid communication between inlet chamber 72 and intermediate chamber 7~. In addition, upon de-energizing regulator solenoid 1~2, regulator plunger 130 moves upwardly under the influence of spring 134 and regulator valve disc 128 is moved to its uppermost position under the force exerted by spring 134 to thereby close off main seat 86. Thus, both intermediate chamber seat 82 and main seat 86 are closed to prevent gas flow through gas regulator 16. This naturally causes the pilot flame and burner flame to be extinguished, and upon cooling down of the pilot assembly, all switch contacts are re6et.
After regulator solenoid 132 is de-energized, microprocessor control 148 generates a signal over electrical lines 166 to inducer motor control 160 to terminate operation of inducer motor 22. After inducer motor 22 has been de-energized, microprocessor control 148 is further preprogrammed to generate a signal over lines 162 to air blower motor control 160, thereby terminating operation of air blower 26, after a preselected period of time, for example, 60-240 seconds.
This continual running of air blower 26 for this predetermined amount of time permits further heat transfer between the air to be heated and the hea~ being generated through heat exchanger assembly 18, which also r.aturally serves to cool heat exchanger assembly 18.
14 ~9L~3~
Because the pressure drop across heat exchanger assembly l&
can vary due to changing condition~ or parameters, microprocessor control 148 is preprogrammed to ensure an optimum manifold ga~ pressure as a function of the amount of combustion air flowing through combustion air inlet 32 under the influenc~ of inducer wheel 24. The pressure drop across heat exchanger assembly 18 is measured by pressure taps 58, 62 which transmit their individual pressure readings to differential pressure transducer 156 (Figures 1 and 2).
Transducer 156 then generates a pressure differential signal to microprocessor control 148 over electrical lines 158 indicative of the pressure drop across heat exchanger assembly 18. Figure 3 illustrates a plot or graph of an empirically determined equation for optimum manifold gas pressure versus heat exchanger pressure drop~ Although the graph is a straight line, it can be of any geometry, such as a curved line. Irregardless of the shape of the line, the graph represents that for one heat exchanger pressure drop value, there is one optimum manifold gas pressure. This equation, as represented by Figure 3, is programmed into microprocessor control 148 whereby it determines the optimum manifold gas pressure for a partlcular pressure drop across heat exchanger ~ssembly 18, as indicated by the pressure differential si~nal received from differential pressure transducer 156. As the pressure drop varies, microprocessor control 148 generates a si~nal over electrical lines 154 to regulator solenoid 132, which moves regulator valve disc 128 relative to main seat 86 to provide the desired ~as flow rate through main seat 86 and outlet 70. Durir.g continued operation of furnace 10, microprocessor control 148 continues to make adjustments in the gas flow rate and pressure as a function of certain ~ariable parameters, such as line pressure, supply voltage, temperature changes, vent pipe length, furnace altitude, and the like. Thus, gas regulator 16 and microprocessor control 148 pro~ides essentially an infinite number of gas flow rates between a zero flow rate i~9434~
and a maximum flow rate in a selected range of, for example, two inches - fourteen inches W.C.
While this invention has been described as having a preferred embodiment, it will be understood thst it is capable of further modifications. This application is therefore intended to cover any variations, uses, or adaptations of the invention following the general principles thereof, and including such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and fall within the limits of the appended claims.
AND METHOD FOR MAINTAINING AN
OPTIMUM FUEL AIR RATIO
Background of the Invention This invention pertains to furnaces, and more particularly to a control apparatus and method for a ga~-fired furnace which maintains an optimum fuel air combustion ratio therefor.
Present technology for direct vent gas-fired furnace design generally requires the furnace to be operated at less than the optimum fuel air combustion ratio due to variations in certain parameters, such as vent pipe length, barometric pressure, and BTU content of the natural gas. As a result, the present technique is to design the furnace to operate for anticipated maximum vent pipe length, anticipated highest altitude at which the furnace might be installed, and anticipated maximum BTU content of the gas. Therefore, when the furnace is installed at other than these three anticipated conditions, the furnace will operate with excess combustion air, and as a result thereof, will operate at reduced efficiency.
Summary of the Invention The present invention provides a control apparatus and method for automatically regulating the manifold gas pressure to provide an optimum gas flow in response to varying parameters. This is accomplished by measuring the pressure drop across the heat exchangers by means of a differential pressure transducer and generating a signal indicative of the changing pressure drop. Since the pressure drop varies with vent pipe length, barometric pressure, gas line pressure, temperatures, and the like, the pressure drop signal is used as an input to a microprocessor control that has its control logic preprogrammed to automatically regulate the manifold gas pressure to a desired optimum level as a function of heat 12943'~4 exchanger pressure drop. Consequently, a furnace operated in accordance with the present invention will operate generally at a higher level efficiency than previously possible.
It is an object of the present invention to provide an improved control apparatus for a gas fired furnace that compensates for variation in certain operating parameters.
Another object of the present invention is to provide a method for maintaining opti~um fuel air combustion ratio in a gas-fired furnace.
Yet another obiect of the present invention is to provide a control apparatus for a gas-fîred furnace that utilizes the pressure drop across the heat exchangers to maintain an optimum fuel air combustion ratio.
A further object of the present invention is to provide a method that uses the pressure drop across the heat exchangers for maintaining an optimum fuel air combustion ratio.
Further objects of the present invention will appear as the description proceeds.
In one form of the invention, there is provided in a gas-fired furnace a fuel regulator connected to a combustion chamber for supplying a regulated flow of fuel thereto in response to a received control signal, a pressure differential measuring device for measuring the pressure drop across heat e~changers in the furnace and for generating a pressure differential signal in response thereto, and a control device for receiving the pressure differential signal and for generating in response thereto a control signal to the fuel regulator, whereby the flow of fuel to the combustion chamber is regulated as a function of the pressure lZ~3'~4 i!
drop across the heat exchangers to maintain an optimum fuel air combustion ratio.
In other form of the invention, there is provided a method for maintaining,an optimum fuel air combustion ratio in a gas-fired furnace comprising the steps of supplying a flow of fuel from a fuel source to a combustion apparatus for combusting with the combustion air, measuring the pressure drop across heat eY.changers in the furnace caused by the flow of combusted fuel air mixture, and regulating the supply of fuel flow to the combustion apparatus as a function of the measured pressure drop across the heat e~,;changers to maintain an optimum fuel air combustion ratio.
Brief Description of the Drawings The above-mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Figure 1 is a partially broken-away side elevational view of a furnace incorporating the principles of the present invention;
Figure 2 includes a sectional view of a gas supply valve in conjunction with a schematic of a furnace control system incorporating the principles of the present invention;
Figure 3 is a plot of a curve indicating the relationship between heat exchanger pressure differential and optimum manifold gas pressure; and Figure 4 is a block diagram of a portion of the furnace control system.
4 lZ9~3~
Detailed Description Referring to Figure 1, ~here is illustrated a gas-fired furnace which may be operated according to the principles of the present invention. The following description is made with reference to condensing furnace 10, but it should be understood that the present invention contemplates incorporation with a noncondensing-type furnace. Referring now to Figure 1, condensing furnace 10 includes in major part steel cabinet 12 housing therein burner asse~bly 14, gas regulator 16, heat exchanger assembly 18, inducer housing 20 supporting inducer motor 22 and inducer wheel 24, and circulating air blower 26. Gas regulator 16 includes pilot circuitry for controlling and proving the pilot flame. This pilot circuitry or control can be a BDP model 740A pilot obtainable from BDP Company, Indianapolis, Indiana.
Burner assembly 14 includes at least one inshot burner 28 for at least one primary heat exchanger 30. Burner 28 receives a flow of combustible gas from gas regulator 16 and injects the fuel gas into primary heat exchanger 30. A part of the injection process includes drawing air into heat exchanger assembly 18 so that the fuel gas and air mixture may be combusted therein. A flow of combustion air is delivered through combustion air inlet 32 to be mixed with the gas delivered to burner assembly 14.
Primary heat exchanger 30 includes an outlet 34 opening into chanber 36. Connected to chamber 36 and in fluid communication therewith is at least one condensing heat exchanger 38 having an inlet 40 and an outlet 42. Outlet 42 opens into chamber 44 for venting exhaust flue gases and condensate.
Inducer housing 20 is connected to chamber 44 and has mounted therewith inducer motor 22 with inducer wheel 24 for drawing the combusted fuel air mixture from burner assembly 14 12~3 ~4 through heat exchanger assembly 18. Air blower 26 delivers air to be heated upwardly through air passage 52 and over heat exchanger assembly 18, and the cool air passing over condensing heat exchanger 38 lowers the heat exchanger wall temperature below the dew point of the combusted fuel air ~ixture causing a portion of the water vapor in the combusted fuel air mixture to condense, thereby recovering a portion of the sensible and latent heat energy. The condensate formed within heat exchanger 38 flows through chamber 44 into drain tube 46 to condensate trap assembly 48. As air blower 26 continues to urge a flow of air to be heated upwardly through heat exchanger assembly 18, heat energy is transferred from the combusted fuel air mixture flowing through heat exchangers 30 and 38 to heat the air circulated by blower 26.
Finally, the combusted fuel air mixture that flows through heat exchangers 30 and 38 exits through outlet 42 and is then delivered by inducer motor 22 through exhaust gas outlet 50 and thence to a vent pipe (not shown).
Cabinet 12 also houses microprocessor control assembly 54, LED display 56, pressure tap 58 at primary heat exchanger inlet 60, pressure tap 62 at condensing heat exchanger outlet 42 and limit switch 64 disposed in air passage 52; the purposes of which will be explained in greater detail below.
If condensing furnace 10 is replaced with a noncondensing-type furnace, then naturally pressure tap 62 would be disposed st primary heat exchanger outlet 34, since there would be no condensing heat exchanger 38.
Referring now to Figure 2, gas regulator 16 generally comprises valve body 66 having an inlet 68 and outlet 70.
~etween inlet 68 and outlet 70 are a series of chambers, in particular, inlet chamber 72, intermediate chamber 74, regulator chamber 76, and main chamber 78. These chambers are in fluid communication, directly or indirectly, with val~e body inlet 68 and outlet 70; inlet 68 communicates with 6 lZ~3~
inlet chamber 72 through inlet cha~ber seat 80, inlet chamber 72 communicates with intermediate chamber 74 through intermediate chamber seat 82, intermediate chamber 74 communicates with regulator chamber 76 through regulator seat 84, regulator chamber 76 communicates with main chamber 78 through main seat 86, and main chamber 78 communicates with outlet 70. The use of the term "seat" is equivalent to terms such as "opening", "hole", and the like.
Each of the above mentioned seats are closed and opened by particular members. IIIlet chamber seat 80 is closed and opened by manually-operated valve head 88. Valve head 88 is connected to plunger 90, which is slidably received through valve body 66 in a fluid-tight manner. The externally remote end of plunger 90 is suitably connected to manual on-off lever 92, which is surrounded by indicator bracket 94.
Bracket 94 is connected to valve body 66 in any suitable manner. Spring 96 is disposed within inlet 68 and between valve head 88 and the valve top cover plate 91 50 as to bias valve head 88 into seating engagement with inlet chamber seat 80, thereby to prevent fluid communication between inlet 68 and inlet chamber 7 O-ring 89 insures a fluid tight fit between valve head 88 and seat 80. To open or move valve head 88 to an open position to allow fluid communication between inlet 68 and inlet chamber 72, manual on-off lever 92 is rotated in a counter-clockwise direction, as viewed in Figure 2. Manual on-off lever 92 includes an enlarged end portion 98 that has a camming surface 100. Camming surface 100 is defined by two relatively flat surfaces 102 and 104 that are generally perpendicularly disposed to each other and joined by a generally curved surface 106. As seen in Figure 2, manual lever 92 is in the closed position so that spring 96 is biasing valve head 88 into seating engagement with inlet chamber seat 80 in a fluid-tight manner. ~s manual lever 92 is rotated counter-clockwise, the action of camming surface 100 and enla~ged end portion 98 causes plunger 90 to 7 :1Z~3.~4 be pulled upwardly a~ainst the force of spring 96 to separate val~e head 88 from inlet chamber seat 80, thereby permitting fluid communication between inlet 68 and inlet chamber 72.
Manual lever 92 is held in the open position by the engaging force or friction existing between flat surface 102 and the flat exterior surface portion of valve body 66. Naturally, to close inlet chamber seat 80, manual lever 92 i5 rotated clockwise to permit spring 96 to extend plunger 90 downwardly, thereby permitting valve head 88 to engage inlet chamber seat 80.
Intermediate chamber seat 82 is opened and closed by valve seat disc 108, which is disposed in inlet chamber 72. ~alve seat disc 108 has a secondary plunger 110 connected thereto in any suitable manner and secondary plunger 110 is slidably received in bore 112 disposed in valve head 88 and plunger 90. Spring 114 is disposed in inlet chamber 72 between valve seat disc 108 and oppositely disposed inlet chamber upper surface 116. Spring 114 biases valve seat disc downwardly to close intermediate chamber seat 82 in a fluid tight manner.
A rubber portion 109 insures a fluid tight fit between disc lQ8 and seat 82. Valve seat di8c 108 is connected to secondary plunger 110 so that valve seat disc 108 moves in a generally vertical or straight line dlrection generally perpendicular to the plane of intermediate chamber seat 82, thereby insuring a fluid tight closure of intermediate chamber seat 82 when valve seat disc 108 is in the closed position, as illustrated in Figure 2. Disposed on the opposite side of valve seat disc 108 and in general axial alignment with secondary plunger 110 is push rod 118. Push rod 118 abuts agAinst the undersurface of valve seat disc 108, and upon being moved in an upwardly direction, push rod 118 moves valve seat disc 108 upwardly against spring 114 to open intermediate chamber seat 82, thereby permitting fluid communication between inlet chamber 72 and ~ntermediate chamber 74. Push rod 118 is moved in an up and down 8 1Z~3~4 direction, as viewed in Figure 2, by pick and hold solenoid 120. Solenoid 120 is connected to valve body 66 in any suitable manner and includes a joining segment 122 extending slightly inwardly of intermediate chamber 74. Joining segment 122 provides a fluid tight fit or connection between solenoid 120 and intermediate chamber 74. Joining segment 122 has an axial passage 124 for slidably receiving push rod 118 therein, with the lower remote end of push rod 118 being fiY.ed loosely to movable plunger 126 of solenoid 120. When solenoid 120 is in a de-energized state, plunger 126 and push rod 118 are located in a lowermost position, a~ illu~trated in Figure 2, so that spring 114 biases valve seat disc 108 in fluid tight engagement with intermediate chamber seat 82.
Upon energizing solenoid 120, plunger 126 and push rod 118 move upwardly against valve seat disc 108 and spring 114, thereby to open intermediate chamber seat 82 to allow fluid communication between inlet chamber 72 and inter~ediate chamber 74.
The fluid communication between intermediate chamber 74, regulator chamber 76, and main chamber 78 are closely related in that the opening and closing of regulator seat 84 and main seat 86 are controlled by a ~ingle regulator valve disc 128 disposed in regulator chamber 76. It should be noted that regulator seat 84 and main seat 86 are generally oppositely disposed from each other in regulator chamber 76 and are in generally axial alignment with each other, whereby the axial or linear movement of regulator valve disc 128 regulates the fluid communication between intermediate chamber 74, regulator chamber 76, and main chamber 78. Regulator valve disc 128 is connected in any suitable manner to re~ulator plunger 130 of regulator solenoid 132. A sprin~ 134 is disposed against the underside of regulator valve disc 128 and through regulator seat 84, and biases regulator valve disc 128 upwardly to close main seat 86 in a fluid tight fashion. The upper portion 136 of regulator valve disc 128 is made of a rubber material to ensure fluid tight engagement between valve disc 128 and main seat 86. Regulator ~alve disc 128 is moved downwardly from its uppermost position where it clo~es main seat 86 to a lowermost position where it closes regulator seat 84, thereby opening main seat 86 to permit fluid communication between regulator chamber 76 and main chamber 78. Re~ulator valve disc 128 is moved to its lowermost position upon energizing regulator solenoid 132, which pulls regulator plunger 130 downwardly until valve disc 128 seats aga~nst regulator seat 84. By controlling the voltage to regulator solenoid 132, which will be explained in greater detail below, regulator valve disc 128 is positionable to an infinite number of positions between its uppermost position where it closes main seat 86 and its lowermost position where it closes re~ulator seat 84.
Naturally, any position, other than the uppermost and lowermost positions, will provide simultaneous fluid communication bet~een intermediate chamber 74, regulator chamber 76, and main chamber 78.
Disposed in fluid communication with intermediate chamber 74 are pilot filter 138 and pilot conduit 140 for respectively filtering the portion of the ~as flowing through ~ilter 138 and delivering it through pilot conduit 140 to the pilot flame sssembly, which is part of gas regulator and pilot circuitry 16 (Figure 4).
A pressure-tap port 142 is disposed in regulator chamber 76 for transmitting ~ariations in fluid pressure from chamber 76 through line 144 to pressure transducer 146. Pressure transducer 146 then generates an analog signal to microprocessor control 148 indicative of a change in fluid pressure in regulator chamber 76. Microprocessor control 148 is located in microprocessor control assembly 54 in condensing furnace 10, and is capable of being preprogr2mmed to generate a plurality of control signals in response to ~:2~ 3~
received input signals. Microprocessor control 148 is also connected electrically to thermostat 150 to receive signals therefrom, to pick and hold solenoid 120 by electric~l lines 152, and to regulator solenoid 132 by electrical lines 154.
Referring to Figure 4, there is illustrated a simplified block diagram illustrating the interconnection between microprocessor control 148 and pressure taps 58, 62 through differential pressure transducer 156. As illustrated in Figure 2, differential pressure transducer 156 receives pressure tap inputs from pressure taps 58, 62 and generates an analog signal indicative of the differential pressure to microprocessor control 148 via electrical lines 158.
Still referring to Figure 4, it can be seen that microprocessor control 148 is electrically connected to limit switch 64 (Figure 1), gas valve 16 through electrical lines 152, 154, and also to air blower motor control 160 of air blower 26 through electrical lines 162, and inducer motor control 164 of inducer motor 22 through electrical lines 166.
Air blower motor control 160 and inducer motor control 164 respectively control the rate of fluid flow created by air blower 26 and inducer wheel 24.
With the manual on-off lever 92 moved in a counter-clockwise position to open inlet chamber seat 80, and upon closing of contacts in thermostat 150 indicating a need for heat, microprocessor control 148 is programmed to send a signal via electrical lines 166 (Figure 4) to inducer motor control 16~
to start inducer motor 22 to rotate inducer wheel 24~ thereby causing a flow of combustion air through combustion air inlet 32, burner assembly 14, heat exchanger assembly 18, inducer housing 20, and out eY~haust gas outlet 50. After a predetermined period of time, for example, ten seconds, to ensure purging of the furnace, microprocessor control 148 generates a signal through electrical lines 152 ~o pick and 11 ~2943-~
hold solenoid 120, thereby energizing it to move plunger 126 upwardly so that push rod 118 separates valve seat disc 108 from intermediate chamber seat 82 to permit gas flow from inlet chamber 72 to intermediate chamber 74. The gas flows then to and through pilot filter 138 and pilot conduit 140 to initiate the pilot flame, and flows also into regulator chamber 76 where the pressure is sensed at pressure-tap port 142. Ignition of the pilot flame is p~oved by the pilot circuitry in the pilot control of gas regulator 16 and a signal is generated to microprocessor control 148 through electrical lines 152, 154 (Figure 4) to indicate the flame is proved.
During this period of time, microprocessor control 148 (Figure .~) is monitoring the pressure drop across heat exchanger assembly 18, which is provided by pressure taps 58, 62 transmitting pressure readings to differential pressure transducer 156. Differential presSUre transducer 156 sends a pressure differential signal through electrical lines 158 to microprocessor control 148 indicative of the presSure drop reading. Pressure-tap port 142 is also transmitting increasing gas pressure in regulator chamber 76 through line 144 to pressure transducer 146, which generates an analog signal indicative of the increasing gas pressure to microprocessor control 148. After microprocessor control 148 determines a sufficient pressure drop exists across heat exchanger assembly 18, that the g&S pressure in regulator chamber 76 is at or above a predetermined pressure, and the pilot flame has been proved, microprocessor control 148 is programmed to generate a voltage signal through electrical lines 154 to regulator solenoid 132. During this period of time, regulator valve disc 128 is closing off main seat 86 of main chamber 78 to prevent gas flow therethrough.
Because of the relatively high pressure existing in regulator chamber 76, the signal generated from microprocessor control 12 ~Z~ 4 3~4 148 to regulator solenoid 132 is of a relatively high voltage to cause solenoid 132 to pull regulator plunger 130 to its lowermost position, whereby regulator valve disc 128 opens main seat 86 and closes regulator seat 84. This prevents fluid communication between regulator chamber 76 and intermediate chamber 74, but does permit fluid communication between regulator chamber 76 and main chamber 78. Thus, the increased gas pressure in regulator chamber 76 bleeds off through main seat 86, main cha~ber 78, and through outlet 70.
This decreasing gas pressure in reglllator chamber 76 is continually monitored by microprocessor control 148 through port 142 and upon rPaching a predetermined low pressure, microprocessor control 148 generates a relati~ely low voltage signal to re~ulator solenoid 132 to open regulator seat 84 by moving regulator plunger 130 to an intermediate position between its uppermost position where it closes off main seat 86 and its lowermost position where it close6 off regulator seat 84. Microprocessor control 148 is preprogrammed to position ~egulator valve disc 128 in regulator chamber 76 to provide a desired gas flow rate and pressure in main chamber 78.
Thereafter, gas flow is provided by gas regulator 16 to burner assembly 14 and the fuel air mixture is combusted by inshot burner 28. The combusted fuel air mixture is then drawn through heat exchanger assembly 18 and out exhaust gas outlet 50 by the rotation of inducer wheel 24 by motor 22.
Af~er a preselected period of time, for example, one minute, to ensure heat exchanger assembly 18 has reached a predetermined temp2rature, microprocessor control 148 is preprogrammed to generate a signal through electrical lines 162 (Figure 4) to air blower motor control 160, which starts air blower 26 to provide a flow of air to be heated over condensing heat exchanger 38 and primary heat exchanger 30.
Any condensate that forms in condensing heat exchanger 38 is 13 12943~4 delivered through drain tube 46 to condensate trap assembly 4~.
After the heating load has been satisfied, the contacts of thermostat 150 open, and in response there~o microprocessor control 148 de-energizes pick and hold solenoid 120 and regulator solenoid 132. Plunger 126 then moVes downwardly, as viewed in ~igure 2, under the influence of spring 114, and valve seat disc 108 closes intermediate chamber seat 82 due to the downwardly directed force provided by spring 114, thereby preventing 1uid communication between inlet chamber 72 and intermediate chamber 7~. In addition, upon de-energizing regulator solenoid 1~2, regulator plunger 130 moves upwardly under the influence of spring 134 and regulator valve disc 128 is moved to its uppermost position under the force exerted by spring 134 to thereby close off main seat 86. Thus, both intermediate chamber seat 82 and main seat 86 are closed to prevent gas flow through gas regulator 16. This naturally causes the pilot flame and burner flame to be extinguished, and upon cooling down of the pilot assembly, all switch contacts are re6et.
After regulator solenoid 132 is de-energized, microprocessor control 148 generates a signal over electrical lines 166 to inducer motor control 160 to terminate operation of inducer motor 22. After inducer motor 22 has been de-energized, microprocessor control 148 is further preprogrammed to generate a signal over lines 162 to air blower motor control 160, thereby terminating operation of air blower 26, after a preselected period of time, for example, 60-240 seconds.
This continual running of air blower 26 for this predetermined amount of time permits further heat transfer between the air to be heated and the hea~ being generated through heat exchanger assembly 18, which also r.aturally serves to cool heat exchanger assembly 18.
14 ~9L~3~
Because the pressure drop across heat exchanger assembly l&
can vary due to changing condition~ or parameters, microprocessor control 148 is preprogrammed to ensure an optimum manifold ga~ pressure as a function of the amount of combustion air flowing through combustion air inlet 32 under the influenc~ of inducer wheel 24. The pressure drop across heat exchanger assembly 18 is measured by pressure taps 58, 62 which transmit their individual pressure readings to differential pressure transducer 156 (Figures 1 and 2).
Transducer 156 then generates a pressure differential signal to microprocessor control 148 over electrical lines 158 indicative of the pressure drop across heat exchanger assembly 18. Figure 3 illustrates a plot or graph of an empirically determined equation for optimum manifold gas pressure versus heat exchanger pressure drop~ Although the graph is a straight line, it can be of any geometry, such as a curved line. Irregardless of the shape of the line, the graph represents that for one heat exchanger pressure drop value, there is one optimum manifold gas pressure. This equation, as represented by Figure 3, is programmed into microprocessor control 148 whereby it determines the optimum manifold gas pressure for a partlcular pressure drop across heat exchanger ~ssembly 18, as indicated by the pressure differential si~nal received from differential pressure transducer 156. As the pressure drop varies, microprocessor control 148 generates a si~nal over electrical lines 154 to regulator solenoid 132, which moves regulator valve disc 128 relative to main seat 86 to provide the desired ~as flow rate through main seat 86 and outlet 70. Durir.g continued operation of furnace 10, microprocessor control 148 continues to make adjustments in the gas flow rate and pressure as a function of certain ~ariable parameters, such as line pressure, supply voltage, temperature changes, vent pipe length, furnace altitude, and the like. Thus, gas regulator 16 and microprocessor control 148 pro~ides essentially an infinite number of gas flow rates between a zero flow rate i~9434~
and a maximum flow rate in a selected range of, for example, two inches - fourteen inches W.C.
While this invention has been described as having a preferred embodiment, it will be understood thst it is capable of further modifications. This application is therefore intended to cover any variations, uses, or adaptations of the invention following the general principles thereof, and including such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and fall within the limits of the appended claims.
Claims (12)
1. A gas-fired furnace control apparatus for maintaining an optimum fuel air combustion ratio, comprising:
a housing having a combustion air inlet and an exhaust gas outlet, a combustion means in said housing in communication with said combustion air inlet for receiving a flow of combustion air and for burning a mixture of combustion air and fuel, a fuel regulator means in said housing and connected to said combustion means for supplying a regulated flow of fuel to said combustion means in response to a received control signal, a heat exchanger means in said housing in communication with said combustion means and said exhaust gas outlet for delivering a flow of combusted fuel air mixture therethrough, a blower means in said housing in communication with said heat exchanger means for providing a flow of combustion air through said combustion air inlet and said combustion means and a flow of a combusted fuel air mixture through said heat exchanger means and said exhaust gas outlet, a differential pressure measuring means in said housing for measuring a pressure drop across said heat exchanger means and for generating a pressure differential signal in response thereto, and a control means in said housing for receiving said pressure differential signal from said differential pressure measuring means and for generating in response thereto said control signal to said fuel regulator means, whereby the flow of fuel to said combustion means is regulated as a function of the pressure drop across said heat exchanger means to maintain an optimum fuel air combustion ratio.
a housing having a combustion air inlet and an exhaust gas outlet, a combustion means in said housing in communication with said combustion air inlet for receiving a flow of combustion air and for burning a mixture of combustion air and fuel, a fuel regulator means in said housing and connected to said combustion means for supplying a regulated flow of fuel to said combustion means in response to a received control signal, a heat exchanger means in said housing in communication with said combustion means and said exhaust gas outlet for delivering a flow of combusted fuel air mixture therethrough, a blower means in said housing in communication with said heat exchanger means for providing a flow of combustion air through said combustion air inlet and said combustion means and a flow of a combusted fuel air mixture through said heat exchanger means and said exhaust gas outlet, a differential pressure measuring means in said housing for measuring a pressure drop across said heat exchanger means and for generating a pressure differential signal in response thereto, and a control means in said housing for receiving said pressure differential signal from said differential pressure measuring means and for generating in response thereto said control signal to said fuel regulator means, whereby the flow of fuel to said combustion means is regulated as a function of the pressure drop across said heat exchanger means to maintain an optimum fuel air combustion ratio.
2. The apparatus of claim 1 wherein said control means is a programmable microprocessor control means.
3. The apparatus of claim 1 wherein said heat exchanger means has an exchanger inlet and an exchanger outlet, and wherein said differential pressure measuring means includes an inlet pressure tap at said exchanger inlet and an outlet pressure tap at said exchanger outlet, and a differential pressure transducer connected between said pressure taps and said control means, said differential pressure transducer generating said pressure differential signal to said control means.
4. In a gas-fired furnace comprising a combustion means for receiving a flow of combustion air and for burning a mixture of combustion air and fuel, and a heat exchanger means in communication with said combustion means for delivering a flow of a combusted fuel air mixture therethrough; a fuel control apparatus for maintaining an optimum fuel air combustion ratio in said combustion means, comprising:
a fuel regulator means connected to said combustion means for supplying a regulated flow of fuel to said combustion means in response to a received control signal, a differential pressure measuring means for measuring a pressure drop across said heat exchanger means and for generating a pressure differential signal in response thereto, and a control means for receiving said pressure differential signal from said differential pressure measuring means and for generating in response thereto said control signal to said fuel regulator means, whereby the flow of fuel to said combustion means is regulated as a function of the pressure drop across said heat exchanger means to maintain an optimum fuel air combustion ratio.
a fuel regulator means connected to said combustion means for supplying a regulated flow of fuel to said combustion means in response to a received control signal, a differential pressure measuring means for measuring a pressure drop across said heat exchanger means and for generating a pressure differential signal in response thereto, and a control means for receiving said pressure differential signal from said differential pressure measuring means and for generating in response thereto said control signal to said fuel regulator means, whereby the flow of fuel to said combustion means is regulated as a function of the pressure drop across said heat exchanger means to maintain an optimum fuel air combustion ratio.
5. The furnace of claim 4 wherein said control means is a programmable microprocessor control means.
6. The furnace of claim 4 wherein said heat exchanger means has an exchanger inlet and an exchanger outlet, and wherein said differential pressure measuring means includes an inlet pressure tap at said exchanger inlet and an outlet pressure tap at said exchanger outlet, and a differential pressure transducer connected between said pressure taps and said control means, said differential pressure transducer generating said pressure differential signal to said control means.
7. The furnace of claim 4 further comprising a blower means in communication with said combustion means and said heat exchanger means for urging combustion air through said combustion means and for urging a combusted fuel air mixture through said heat exchanger means.
8. A method for maintaining an optimum fuel air combustion ratio in a gas-fired furnace including a combustion apparatus for receiving a flow of combustion air and for burning a mixture of combustion air and fuel, a fuel source connected to the combustion apparatus, and a heat exchanger in communication with the combustion apparatus for delivering a flow of a combusted fuel air mixture therethrough, comprising the steps of:
supplying a flow of fuel from the fuel source to the combustion apparatus for combusting with the combustion air, measuring the pressure drop across the heat exchanges caused by the flow of combusted fuel air mixture therethrough, and regulating the supply of fuel flow from the fuel source to the combustion apparatus as a function of the measured pressure drop across the heat exchanger to maintain an optimum fuel air combustion ratio.
supplying a flow of fuel from the fuel source to the combustion apparatus for combusting with the combustion air, measuring the pressure drop across the heat exchanges caused by the flow of combusted fuel air mixture therethrough, and regulating the supply of fuel flow from the fuel source to the combustion apparatus as a function of the measured pressure drop across the heat exchanger to maintain an optimum fuel air combustion ratio.
9. The method of claim 8 wherein the step of measuring includes generating a pressure differential signal in response to and as a function of the measured pressure drop.
10. The method of claim 9 wherein the step of regulating includes receiving the generated pressure differential signal and generating a control signal in response thereto to the fuel source to regulate the supply of fuel as a function of the pressure drop across the heat exchanger.
11. The method of claim 10 wherein the pressure differential signal is generated by a pressure transducer connected to the heat exchanger.
12. The method of claim 11 wherein a microprocessor control receives the generated pressure differential signal and generates the control signal in response thereto.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80227385A | 1985-11-26 | 1985-11-26 | |
| US802,273 | 1985-11-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1294344C true CA1294344C (en) | 1992-01-14 |
Family
ID=25183277
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000520974A Expired - Lifetime CA1294344C (en) | 1985-11-26 | 1986-10-21 | Gas-fired furnace control apparatus and method for maintaining an optimum fuel air ratio |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU573996B2 (en) |
| CA (1) | CA1294344C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110594778A (en) * | 2018-06-12 | 2019-12-20 | 芜湖美的厨卫电器制造有限公司 | Gas distributing rod assembly for gas water heater and gas water heater with same |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4706881A (en) * | 1985-11-26 | 1987-11-17 | Carrier Corporation | Self-correcting microprocessor control system and method for a furnace |
| CN108758774B (en) * | 2018-06-19 | 2021-01-05 | 广东美的暖通设备有限公司 | Control method and control system of gas furnace and gas furnace |
-
1986
- 1986-10-21 CA CA000520974A patent/CA1294344C/en not_active Expired - Lifetime
- 1986-11-25 AU AU65742/86A patent/AU573996B2/en not_active Ceased
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110594778A (en) * | 2018-06-12 | 2019-12-20 | 芜湖美的厨卫电器制造有限公司 | Gas distributing rod assembly for gas water heater and gas water heater with same |
| CN110594778B (en) * | 2018-06-12 | 2024-03-29 | 芜湖美的厨卫电器制造有限公司 | Gas distribution rod assembly for gas water heater and gas water heater with same |
Also Published As
| Publication number | Publication date |
|---|---|
| AU573996B2 (en) | 1988-06-23 |
| AU6574286A (en) | 1987-06-25 |
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