Optimizing fuel combustion in a gas fired appliance

Abstract

A process and apparatus for optimizing fuel combustion at various ambient atmospheric pressures in a gas-fired appliance having a combustion chamber. The gas-fired appliance has an air blower and is capable of delivering a variable flow of combustion air to the combustion chamber. This may be accomplished by varying the speed of the blower motor. Alternatively, the appliance combustion air intake or exhaust conduit may be throttled to vary the amount of combustion air delivered to the combustion chamber. An ambient atmospheric pressure sensor is provided to sense ambient atmospheric pressure and generates a signal representative of ambient atmospheric pressure to a microprocessor. Alternatively, a signal representative of ambient atmospheric pressure may be provided to the microprocessor by manual input. Based on this signal the microprocessor generates a control signal to the air blower to either increase or decrease the amount of combustion air delivered to the combustion chamber to provide optimal fuel combustion at the sensed ambient atmospheric pressure. Alternatively, the throttle may be used to vary the amount of combustion air delivered to the combustion chamber. Optionally, the microprocessor can be used to regulate the amount of fuel delivered to the combustion chamber in relation to the sensed ambient atmospheric pressure. Additional sensors to sense and provide signals to the microprocessor representative of ambient air temperature and blower exhaust air temperature may be provided to further optimize fuel combustion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/182,559, filed on Feb. 15, 2000, the entire scope and content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates to optimizing fuel combustion in a gas-fired appliance, specifically, optimizing fuel combustion in a gas-fired appliance with a combustion chamber by varying the amount of fuel and/or combustion air delivered to the combustion chamber as a function of elevation.

BACKGROUND OF THE INVENTION

[0003] Gas-fired appliances, such as a residential heating furnace, operate by combusting a mixture of fuel and air in a combustion chamber. Such appliances are typically equipped with motor-driven air blowers to force or induce combustion air into the combustion chamber in such a quantity to provide for the complete combustion of the fuel. Gas-fired appliances are frequently equipped with atmospheric pressure-sensitive safety switches that will prevent the operation of the appliance if insufficient static or differential air pressure is detected in the combustion air delivery system. Such insufficiencies could be caused by system blockages. The safety switches are generally set in the factory to respond at a fixed set point representative of a particular pressure.

[0004] Problems arise when such gas-fired devices are used at higher elevations. The ambient atmospheric pressure surrounding the gas-fired appliances lessens as a result of increases in elevation. The reduced atmospheric pressure at higher elevations, in turn, reduces the amount of combustion air that is normally delivered to the combustion chamber. This will lead to insufficient combustion of fuel in the combustion chamber. Additionally, the atmospheric pressure-sensitive safety switch may require adjustment at higher elevations to ensure that the appliance does not operate under conditions of insufficient combustion air and that the safety switch does not operate spuriously because of either changes in ambient atmospheric pressure or intake conduit pressure.

[0005] To resolve this problem, it is current industry practice to modify gas-fired appliances that are destined to operate at higher elevations where atmospheric pressure is reduced. The modification restricts the amount of fuel delivered to the combustion chamber in order to compensate for the decreased delivery of combustion air. The process of restricting fuel input as a function of elevation is called “derating”. Where there are significant changes in elevation from one area to another, such as in the United States, the practice is to derate fuel input by an amount equal to 4% of fuel input at sea level for every 1000 feet rise in elevation. In Canada fuel input is derated by an amount equal to 10% of sea level values for operating altitudes of 2000 feet to 4500 feet. The fuel derating modification is generally accomplished by resizing the orifice of the fuel discharge nozzle by physically changing the installed orifice to a derated orifice or by reducing the delivery pressure of the fuel to the combustion chamber.

[0006] This manual process of derating causes a number of problems for the manufacturers, maintainers of gas-fired appliances and regulatory authorities. For example, the manufacturer of these appliances must also manufacture and stock a large variety of alternative orifice sizes to accommodate various derating practices. As well, the actual derating of fuel supply is only approximated and therefore the result is not ideally uniform from area to area. Maintainers and appliance regulatory personnel have to assume a greater responsibility to monitor and inspect gas-fired appliances to ensure that the derating has been done properly and that the appliance will function safely.

[0007] One attempt to regulate combustion air delivery to a combustion chamber is found in U.S. Pat. No. 4,703,747 entitled “Excess Air Control” issued to Thompson, Dempsey and Peitz on Nov. 3, 1987 and assigned to the Carrier Corporation. The Carrier patent teaches a method and apparatus for delivering excess air control in a gas furnace having a variable speed inducer motor. The Carrier patent attempts to maintain excess combustion air in the combustion chamber specifically for two predetermined input rates by adjusting speed of the inducer motor accordingly and monitoring the pressure drop across the combustion chamber. However, there are a number of deficiencies in the Carrier patent that make it unsuitable for automatically adjusting the operation of the gas-fired appliance as a function of elevation or modifying the appliance safety set point. For example, the Carrier patent is unable to compensate for restrictions in the combustion air intake conduit that may impair operational efficiency and safety. As well, the Carrier patent does not detect ambient atmospheric pressure and therefore it is unsuitable for adjusting appliance operation as a function of ambient atmospheric pressure.

[0008] Derating practices remain mandatory in the industry and therefore there is a requirement for an apparatus and process that is able to adjust the operation of a gas-fired appliance as a function elevation in order to ensure the safe and efficient operation thereof.

[0009] It is therefore an objective of my invention to provide a process and apparatus that balances combustion air delivery to fuel input as a function of elevation without having to manually change the orifice size.

[0010] It is a further objective of my invention to provide a process and apparatus that balances combustion air delivery to fuel input as a function of changes in air conduit pressures caused by restrictions in the combustion air intake or combustion chamber exhaust conduit.

[0011] Another objective of my invention is to automatically adjust the set point of the safety shut off device as a function of elevation.

[0012] Yet another objective of my invention is to reduce the cost of manufacture of gas-fired appliances by reducing the need to manufacture and store a variety of different sized fuel injection orifices.

[0013] A further objective of my invention is to reduce the need for on-going maintenance and regulatory oversight of derating practices for gas-fired appliances.

SUMMARY OF THE INVENTION

[0014] In accordance with the present invention there is provided, for a fuel-fired appliance having a combustion chamber, an apparatus and process for optimizing fuel combustion at various elevations. The process uses a combustion air delivery system that is capable of delivering a variable flow rate of combustion air to the combustion chamber. The amount of air delivered is sufficient for ensuring the complete combustion of the fuel. The process further includes the activity of generating a signal representative of elevation. The elevation signal may be derived automatically from a device measuring ambient atmospheric pressure or by manual input of a signal representative of a desired elevation. This signal is relayed to a microprocessor having a memory. Based on this signal, the microprocessor determines the necessary incremental changes to the volume of combustion air delivered to the combustion chamber in order to maintain an efficient and safe combustion of fuel in the combustion chamber for the operating elevation. The microprocessor then converts the determined incremental changes to control signals that are capable of controlling the amount of combustion air delivered to the combustion chamber. Feedback signals may be provided to the microprocessor to confirm the correct combustion airflow. The combustion air delivery system may be a forced draught system or an induced draught system.

[0015] In accordance with another embodiment of my invention the process includes controlling the delivery of fuel to the combustion chamber as a function of elevation. The delivery of fuel and of combustion air to the combustion chamber is controlled in a cooperative manner by the microprocessor.

[0016] To ensure that the fuel-fired appliance operates in a safe manner, another embodiment of my invention includes the measuring of differential pressure across the combustion air delivery system and generating a signal proportional to the measured differential pressure. The microprocessor compares this signal to a value stored in its memory representing a safe operating value for the fuel-fired appliance. If necessary, the microprocessor will prevent the operation of the appliance or adjust its operation so that the measured differential pressure conforms to the required safe operating value.

[0017] In accordance with yet another embodiment of my invention there is provided an apparatus for optimizing fuel combustion in a gas-fired appliance having a combustion chamber at various elevations. The apparatus comprises a controllable combustion air delivery system that can vary the volume of combustion air delivered to the combustion chamber while providing sufficient combustion air to ensure complete combustion of the fuel. The apparatus further comprises a means for generating a signal representative of elevation. The signal may be generated automatically using a device for measuring ambient atmospheric pressure. Alternatively, the signal corresponding to a desired elevation may be manually input. The apparatus also includes a microprocessor having a memory. The microprocessor receives the elevation signal and determines, based on that signal, incremental changes to the volume of combustion air delivered to the combustion chamber necessary to optimize fuel combustion at the operating elevation. The microprocessor will also convert the determined incremental changes to control signals capable of acting upon the combustion air volume delivery control system. Control circuits deliver control signals and a feedback circuit can be included to confirm that the proper amount combustion air is delivered to the combustion chamber.

[0018] In another embodiment of my invention the apparatus includes a variable speed electric motor coupled to an air blower that is controllable by the microprocessor as a function of elevation. Varying the speed of the electric motor controls the amount of air delivered to the combustion chamber.

[0019] In yet another embodiment of my present invention the apparatus includes a constant speed electrical motor coupled to the blower and a throttle within the air intake conduit of the appliance or combustion chamber exhaust discharge conduit capable of moving through a range of positions to control the amount of combustion air delivered to the combustion chamber as a function of elevation and/or reduced or increased conduit pressures in the combustion air intake or combustion chamber exhaust conduits.

[0020] In still another embodiment of my invention the apparatus includes a throttle acting in cooperation with a variable speed electric motor, both controllable by the microprocessor by way of said control circuits and capable of varying the flow of combustion air to the combustion chamber as a function of elevation and/or reduced or increased conduit pressures in the combustion air intake or combustion chamber exhaust conduits in either a forced draught or induced draught configuration.

[0021] In another embodiment of my invention the apparatus includes means to throttle fuel delivery to the combustion chamber controllable by the microprocessor as a function of elevation. The fuel throttle means may act independently or in cooperation with the controllable combustion air delivery system to regulate both the amount of fuel and air delivered to the combustion chamber as a function of elevation.

[0022] Still further objectives and advantages of my invention will become apparent from a consideration of the ensuing descriptions and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a schematic drawing of one embodiment of the invention.

[0024] FIG. 2 is a logic diagram used in one embodiment of the invention.

[0025] FIG. 3 is a schematic drawing of another embodiment of the invention.

[0026] FIG. 4 is a schematic drawing of yet another embodiment of the invention.

[0027] FIG. 5 is a schematic of still another embodiment of the invention.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] FIG. 1 shows a schematic representation of a gas-fired appliance in which the preferred embodiment of my invention is used. The gas-fired appliance is shown operating in the forced draught mode wherein the motor and blower operate in combination to force combustion air into the combustion chamber.

[0030] In the preferred embodiment the gas-fired appliance comprises an air intake conduit (10) with an open end (12) for drawing combustion air from the atmosphere. The other end is attached to blower housing (14). Blower (16) is housed within blower housing (14). Blower (16) is driven by variable speed electric motor (18) by way of shaft (20). The speed of motor (18) is controlled by the microprocessor (40). Microprocessor (40) includes a memory storage device (41). The electric motor may operate by direct current and its speed may be varied by varying the voltage supplied to the motor. Alternatively, the motor may operate by alternate current and its speed may be varied by varying the waveform of the alternating current, for example, by pulse width modulation or phase angle chopping.

[0031] Blower housing (14) is connected to combustion air delivery conduit (22) located between the exhaust port of blower housing (14) and combustion chamber (24). Located within combustion chamber (24) is combustion bed (26) upon which combustion (28) takes place. Fuel is supplied to the combustion bed (26) by a fuel injection nozzle (30). Fuel injection nozzle (30) is located at the terminus of the fuel delivery pipe (32) that is connected to a source of fuel (33). When the appliance is operating, motor (18) drives blower (16) by way of shaft (20) to draw combustion air into intake conduit opening (12), through intake conduit (10) and into blower housing (14). The air is compressed within blower housing (14) by the action of rotating blower (16) and is exhausted into combustion air delivery conduit (22). The combustion air travels the length of combustion air delivery conduit (22) to combustion chamber (24) wherein it is mixed with fuel delivered by the fuel injection nozzle (30) on the combustion bed (26) and ignited. Air in excess of combustion needs is heated and exhausted from the combustion chamber (24) by the exhaust conduit (34).

[0032] To accomplish the objectives of the preferred embodiment of my invention there is provided a means to determine gas-fired appliance operating elevation as a function of ambient atmospheric pressure. An ambient atmospheric pressure measuring device (36) is provided to measure ambient atmospheric pressure and relay a signal representing and proportional to measured ambient atmospheric pressure by way of a control circuit (38) to a microprocessor (40). As an alternative to or in cooperation with the ambient air pressure measuring device (36) there may be installed manual device (42) that can be set to send a signal to the microprocessor (40) representing a predetermined elevation.

[0033] For any signal received by the microprocessor (40) from either the pressure measuring device (36) or the manual input device (42) the microprocessor will determine the amount of combustion air that should be delivered by blower (16) to combustion chamber (24). To effect any necessary change in the amount of combustion air delivered to combustion chamber (24), the microprocessor (40) generates a control signal and relays the control signal by way of control circuits (44) to variable speed electric motor (18) demanding that it either increase its speed or decrease its speed. A feedback signal (46) may be generated by motor (18) and relayed to microprocessor (40) to confirm that the motor is operating at the desired speed.

[0034] In determining the appropriate amount of combustion air to deliver to the combustion chamber for a given elevation, microprocessor (40) executes a series of mathematical algorithms upon receiving an elevation signal from device (36) or device (42):

[0035] Using the following algorithm, the microprocessor relates measured ambient atmospheric pressure (BP) or a manual input value to altitude (ALT) as follows:

[0036] BPalt=29.92−0.001078136*ALT+1.439618E-8*ALT2, where altitude (ALT) in is feet above sea level and barometric pressure (BP) is in inches mercury.

[0037] Once measured ambient atmospheric pressure or the manual input signal is related to altitude, microprocessor (40) determines the required speed of the electric motor using the following equation:

[0038] RPMalt=RPMmaxalt*(Qalt/QSTP)*(RHOmaxalt/RHOalt), where RPMmaxalt is the maximum motor RPM (designed to occur at maximum design altitude range)

[0039] wherein

[0040] RHOalt=RHOSTP*(BPalt/BPSTP*(520/(460+VTalt)), where RHOSTP is sea level density of the vapour, BPSTP is sea level barometric pressure (29.92 “HG) and VT is vapour temperature (degrees F.).

[0041] And wherein

[0042] The fuel gas specific gravity (s) at a given altitude can be represented by the equation Salt=SSTP*(BPalt/BPSTP), where SSTP is sea level fuel specific gravity.

[0043] And wherein

[0044] Fuel gas normal reduction in calorific value (CV) per actual cubic foot due to altitude and temperature can be represented by the equation; CValt=CVSTP*BPalt/BPSTP*(520/(460+FTalt)), where CVSTP is sea level calorific value and FTalt is fuel temperature in degrees Farenheit.

[0045] And wherein

[0046] Appliance input (Q) at altitude where normal deration occurs, can be represented by the equation; Qalt=QSTP*SQRT(SSTP/Salt)*(CValt/CVSTP), where QSTP is sea level appliance input.

[0047] In confirming the correct operation of the microprocessor, the above equations were used to determine values of motor/blower speed as a function of elevation based upon measured ambient atmospheric pressure. These values are shown in Table 1 which shows predicted blower speed as a function of elevation under conditions of a steady blower exhaust temperature. Table 2 shows predicted blower speed as a function of elevations under conditions of varying blower exhaust air temperatures.

[0048] Since there are many different designs and thermal capacities of gas-fired appliances my invention contemplates modification to the above equations to suit the design of each gas-fired appliance so that each gas-fired appliance is capable of matching the delivery of combustion air to operating elevation and operate within the guidelines stipulated by regulatory bodies. For example, one variation for which modification of the equations could be required are changes in water vapour condensation rates within high efficiency condensing appliances that would affect volumetric flow being conveyed by the blower.

[0049] In the preferred embodiment of my invention and to ensure the safe operation of the gas-fired appliance at various elevations, it is possible to modify the safety shut-off device set point as a function of elevation. The safety shut-off set point is stored in the memory device (41) of microprocessor (40). Signal (38) is received by the microprocessor (40) from ambient atmospheric pressure measuring device (36) or manual input (42). Microprocessor (40) adjusts the safety shut-off set point stored in memory (41) as a function of elevation as determined by ambient atmospheric pressure.

[0050] In one embodiment of my invention, the safety shut-off device comprises a device (48) that measures the differential pressure between combustion air intake conduit (10) and combustion air delivery conduit (22). Signal (51) proportional to the measured differential pressure is sent to microprocessor (40). Microprocessor (40) compares the received signal (52) with the elevation-modified set-point stored in memory (41). If the received signal (52) falls within an predetermined acceptable range but is not optimum when compared to the set-point the microprocessor (40) will adjust the speed of the electric motor (18) so that measured differential pressure remains within safe operating parameters. If the received signal falls outside an acceptable range and into an unsafe operating configuration then the microprocessor will shut down the appliance. The microprocessor (40) follows the logic as shown in FIG. 2. Upper limits for the speed of the combustion air blower motor (18) may also form a part of the control strategy. Should a predetermined maximum blower motor speed be reached without satisfying the flow or pressure targets determined by the microprocessor (40) then the microprocessor will shut down and lock-out the appliance. A trouble shooting diagnostic indicator may also be included to indicate the nature of the cause of the lockout condition to service personnel. Automatic recycling of a lockout condition on a predetermined time period could also be included in control system logic.

[0051] Now referring to FIG. 3, another embodiment of my invention is illustrated. In this embodiment, the variable speed electric motor of the previous embodiment is replaced with a constant speed electric motor (60) connected by shaft (20) to drive the blower (16). Since the speed of the motor (60) is constant the amount of combustion air delivered to the combustion chamber (24) is controlled by way of a throttle (52). The throttle (52) is actuated by an actuator (54). Actuator (54) is controlled by the microprocessor (40) by way of control circuit (56) as a function of elevation and/or changes in conduit air pressure in either the combustion air intake conduit or the combustion chamber exhaust conduit resulting from blockages. Throttle (52) may be one of a damper, a butterfly valve or an orifice valve. The throttle is capable of movement to provide variable airflow. In the operation of the alternative embodiment a signal representing elevation is produced by measuring device (36) or input manually through device (42). The signal is conveyed to the microprocessor (40). The microprocessor (40) determines the volume of air required for the combustion chamber and converts that value into a control signal and relays that to the actuator (54). The air intake conduit is opened to conform to the required delivery of combustion air to the combustion chamber. A feedback circuit (58) may be provided to ensure that the throttle is in its correct position. Advantageously, this feature of my invention enables a gas-fired appliance to self-adjust and compensate for a drop in combustion air delivery due to physical restrictions in the air delivery conduit such a blockages.

[0052] Now referring to FIG. 4, another embodiment of my invention is illustrated. The gas appliance is operating in a forced draught mode. The electric motor may operate at a constant speed (60) or a variable speed (18). The electric motor is coupled to blower (16) by way of shaft (20). Throttle (52) may operate in a fully open position in the case where the appliance uses a variable speed electric motor (18) or throttle (52) may operate as controlled by actuator (54) when the appliance uses a constant speed motor (60). This embodiment further includes a means to regulate the flow of fuel into the combustion chamber (24) by way of fuel orifice (30). A regulating valve (62) is installed in fuel supply line (32) and is controllable by microprocessor (40) by way of control circuits (64). Upon receiving an elevation signal from either device (36) or device (42) controller will vary the amount of fuel permitted into the combustion chamber (24) by regulating valve (62). Valve (62) may be regulated by microprocessor (40) in cooperation with variable speed electric motor (18) and/or variable throttle (52). This control strategy may also include a fuel flow measuring device (66) that would measure fuel flow to the combustion chamber (24) and provide a signal representing fuel flow to the microprocessor (40) by way of control circuit (68). The microprocessor will then adjust the operation of the appliance as a function of elevation and/or changes in air pressure in the intake air conduit or exhaust air conduit due to blockages by varying fuel flow and/or by varying either the speed of motor (18) or position of throttle (52) to ensure sufficient combustion air is delivered to the combustion chamber permitting efficient fuel combustion.

[0053] Still referring to FIG. 4, my invention further contemplates the optional addition of an ambient air temperature input signal (70) and a blower exhaust air temperature input signal (72) to the microprocessor (40) to further optimize the combustion of fuel in the combustion chamber.

[0054] Referring to FIG. 5, in another embodiment of my invention the gas-fired appliance is shown operating in an induced draught configuration wherein the motor (18), blower housing (14) and blower (16) are installed on the exhaust conduit (34) of combustion chamber (24). The position of throttle (52), acutator (54) and differential pressure measuring device (48) are likewise located on the exhaust conduit (34).

[0055] Although the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of my invention. 1 TABLE 1 MATCHING NATURAL DERATION FOR 0 TO 10000 FEET OF ALTITUDE BASED ON MAX BLOWER RPM @ 10000 ft = 3450 ALTITUDE 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 BP 29.92 28.86 27.82 26.82 25.84 24.89 23.97 23.08 22.22 21.38 20.58 BP DENSITY 1.0000 0.9644 0.9299 0.8962 0.8636 0.8319 0.8011 0.7713 0.7425 0.7147 0.6878 FACTOR BLOWER AIR TEMP 400 400 400 400 400 400 400 400 400 400 400 BLOWER AIR 0.0463 0.0446 0.0430 0.0415 0.0399 0.0385 0.0371 0.0357 0.0343 0.0331 0.0318 DENSITY NATURAL DERATE 100000 98206 96429 94669 92928 91206 89505 87826 86170 84538 82932 INPUT (Btu/h) % OF SEA LEVEL 100.00 98.21 96.43 94.67 92.93 91.21 89.51 87.83 86.17 84.54 82.93 INPUT 4%/1000 ft DERATE 100000 96000 92000 88000 84000 80000 76000 72000 68000 64000 60000 METHOD INPUT PREDICTED 2861 2913 2967 3022 3079 3137 3197 3258 3320 3384 3450 BLOWER RPM

[0056] 2 TABLE 2 MATCHING NATURAL DERATION FOR 0 TO 10000 FEET OF ALTITUDE BASED ON MAX BLOWER RPM @ 10000 ft = 3450 ALTITUDE 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 BP 29.92 28.86 27.82 26.82 25.84 24.89 23.97 23.08 22.22 21.38 20.58 BP DENSITY 1.0000 0.9644 0.9299 0.8962 0.8636 0.8319 0.8011 0.7713 0.7425 0.7147 0.6878 FACTOR BLOWER AIR TEMP 400 405 410 415 420 425 430 435 440 445 450 BLOWER AIR 0.0463 0.0444 0.0425 0.0407 0.0390 0.0374 0.0358 0.0343 0.0328 0.0314 0.0301 DENSITY NATURAL DERATE 100000 98206 96429 94669 92928 91206 89505 87826 86170 84538 82932 INPUT (Btu/h) % OF SEA LEVEL 100.00 98.21 96.43 94.67 92.93 91.21 89.51 87.83 86.17 84.54 82.93 INPUT 4%/1000 ft DERATE 100000 96000 92000 88000 84000 80000 76000 72000 68000 64000 60000 METHOD INPUT PREDICTED 2704 2769 2837 2906 2977 3051 3126 3204 3284 3366 3450 BLOWER RPM

Claims

1. In a fuel-fired appliance having a combustion chamber, a process for optimizing fuel combustion at various elevations comprising the steps of:

(a) using a combustion air delivery means capable of delivering a variable flow rate of combustion air to said combustion chamber, said variable flow rate sufficient for ensuring complete fuel combustion;

(b) generating a signal representative of elevation;

(c) using a microprocessor having a memory device to:

1. receive said signal and, based on said signal, determine incremental changes to said rate of combustion air delivered to the combustion chamber said changes commensurate with predetermined volumes of delivered combustion air necessary to optimize fuel combustion at said elevation; and,

2. convert said determined incremental changes to control signals capable of controlling said combustion air delivery means; and,

(d) relaying said control signals by way of control circuits to said combustion air delivery means,

whereby the operation of said combustion air delivery means is appropriately adjusted to ensure that the necessary volume of combustion air is delivered to the combustion chamber to optimize combustion at said elevation without the need for manual intervention or physical modifications to the gas-fired appliance.

2. The process as claimed in

claim 1 further comprising the step of measuring flow or differential pressure representative of flow across a portion of the combustion air delivery means, generating a signal proportional to said flow, sending said signal to the microprocessor, comparing said signal to a predetermined value stored in said memory device and adjusting the operation of said combustion air delivery means to comply with the said acceptable value in the event that said measured flow is not substantially at said acceptable value.

3. The process as claimed in

claim 1 further comprising the step of providing a feedback signal from the combustion air delivery means to the microprocessor to confirm correct airflow to the combustion chamber.

4. The process as claimed in

claim 1 wherein said signal representative of elevation is based upon measuring ambient atmospheric pressure wherefrom a signal proportional to ambient atmospheric pressure is generated and relayed to the microprocessor.

5. The process as claimed in

claim 1 wherein said signal representative of elevation is based on a manually input signal to the microprocessor.

6. The process as claimed in

claim 1 further comprising the step of using a variable speed electric motor in cooperative combination with a fuel delivery means capable of delivering a variable flow of fuel to the combustion chamber and further wherein the microprocessor determines incremental changes to the rate of combustion air and fuel delivered to the combustion chamber to optimize fuel combustion at the elevation.

7. The process as claimed in

claim 1 or

6 further comprising the step of using a variable throttle means to regulate the amount of combustion air delivered to the combustion chamber said throttle means positioned within said combustion air delivery means to regulate the amount of combustion air delivered to the combustion chamber said throttle means controllable by the microprocessor by way of the control circuits.

8. In a fuel-fired appliance having a combustion chamber, an apparatus for optimizing fuel combustion at various elevations comprising:

(a) means for controlling the volume of combustion air delivered to said combustion chamber, said variable flow rate sufficient for ensuring complete fuel combustion;

(b) means for generating a signal representative of elevation;

(c) a microprocessor having a memory device that will:

1. receive said signal and determine, based on the signal, incremental changes to said volume of combustion air delivered to the combustion chamber said changes commensurate with predetermined volumes of air necessary to optimize fuel combustion at said elevation; and,

2. convert said determined incremental changes to control signals capable of controlling said combustion air volume delivery control means; and,

(d) control circuits to relay said control signals to the combustion air volume delivery control means to obtain a desired volume of combustion air in the combustion chamber,

whereby the operation of the combustion air delivery means is appropriately adjusted to ensure that the necessary volume of combustion air is delivered to the combustion chamber to optimize combustion at said elevation without the need for manual intervention or physical modifications to the gas-fired appliance.

9. The apparatus as claimed in

claim 8 further comprising control circuits to provide a confirmatory feedback signal to the microprocessor to verify that a desired combustion air volume is being delivered to the combustion chamber.

10. The apparatus as claimed in

claim 8 wherein said means for generating a signal representative of elevation comprises an ambient atmospheric pressure measuring device wherefrom a signal proportional to ambient atmospheric pressure is generated and relayed to the microprocessor and translated to a value representative of elevation.

11. The apparatus as claimed in

claim 10 wherein said means for generating a signal representative of elevation further comprises a manual input device.

12. The apparatus as claimed in

claim 8 wherein the means for controlling the volume of combustion air delivered to said combustion chamber comprises:

(a) an air intake conduit having a first end and a second end, said first end open for drawing combustion air from the atmosphere and said second end connected to;

(b) a blower housing having an air intake port and an air discharge port wherein said second end of said air intake conduit is connected to said air intake port;

(c) a combustion air delivery conduit having a first end and a second end wherein said first end connected to the discharge port of said blower housing and said second end is connected to the combustion chamber;

(d) a blower located in said blower housing for drawing combustion air through the air intake conduit and exhausting it down said combustion air delivery conduit to the combustion chamber; and,

(e) an electric motor coupled to said blower, said motor speed controllable by the microprocessor by way of said control circuits.

13. The apparatus as claimed in

claim 12 wherein the means for controlling the volume of combustion air delivered to said combustion chamber further comprises a combustion air throttle means to regulate the amount of combustion air delivered to the combustion chamber said throttle means controllable by the microprocessor.

14. The apparatus as claimed in

claim 8 wherein the means for controlling the volume of combustion air delivered to said combustion chamber comprises:

(a) an air intake conduit having a first end and a second end, said first end open for drawing combustion air from the atmosphere and said second end connected to the combustion chamber;

(b) a combustion products delivery conduit having a first end and a second end wherein said first end is connected to the combustion chamber and said second end is connected to;

(c) a blower housing having an air intake port and an air discharge port wherein;

(d) a blower located in said blower housing for drawing combustion air through the air intake conduit and combustion chamber; and

(e) wherein said discharge port of the blower housing is connected to a combustion products discharge conduit for delivery to the atmosphere; and,

(f) an electric motor coupled to said blower, said motor speed controllable by the microprocessor by way of said control circuits.

15. The apparatus as claimed in

claim 12 or

14 further comprising means for controlling the volume of fuel delivered to the combustion chamber said fuel volume control means acting in cooperation with said combustion air volume control means wherein the microprocessor determines incremental changes to the volume of combustion air and fuel delivered to the combustion chamber commensurate with predetermined volumes of air and fuel necessary to optimize fuel combustion at the elevation.

16. The apparatus as claimed in

claim 15 further comprising means to provide a feedback signal proportional to fuel delivery volume to the microprocessor to confirm correct fuel flow to the combustion chamber.

17. The apparatus as claimed in

claim 16 wherein the means for controlling the volume of fuel delivered to the combustion chamber comprises a fuel delivery pipe connected to a fuel supply said pipe terminating in the combustion chamber said pipe having a fuel injection nozzle at its terminal end and a fuel flow regulating valve located between the fuel supply and the fuel injection nozzle wherein said valve is controlled by the microprocessor.

18. The apparatus as claimed in

claim 8 wherein said apparatus further includes a differential pressure sensor located between the combustion air intake conduit and the combustion air delivery conduit for sensing the difference in pressure between the blower housing intake port and discharge port, providing a signal proportional to sensed differential pressure to the microprocessor wherein the microprocessor receives and processes said signal and compares said signal to an acceptable value stored in the memory device and in the event that said signal is not substantially at the acceptable value adjusts the operation of the air delivery means to bring the differential pressure to substantially the acceptable value.

19. The apparatus as claimed in

claim 8 wherein said microprocessor uses a timer to permit a recheck of the appliance operation after it has shut-down based on insufficient differential pressure across the combustion air delivery means to determine if the appliance is safe to restart.

20. The apparatus as claimed in

claim 12 further including a blower exhaust temperature sensor, a fuel temperature sensor and an ambient air temperature sensor for sending signals to the microprocessor wherein said microprocessor receives and processes said signals and appropriately adjusts the volume of air and fuel delivered to the combustion chamber.