PERFORMANCE OF A GAS-FIRED APPLIANCE BY USE OF FUEL INJECTION TECHNOLOGY

FIELD

Embodiments relate to gas-fired appliances (such as but not limited to, water heaters) including fuel injection systems.

SUMMARY

Gas-fired appliances may incorporate gas trains designed for gaseous fuel flow control. The gas flow control may be a pneumatic device, relying on an inlet gas supply pressure and a pressure differential across the regulator diaphragm within the gas control to closely regulate a preset gas flow into the burner. In addition, certain gas trains may include pneumatic devices that allow the gas flow to vary with respect to the speed of a blower providing combustion air to the burner such that the quantity of air mixed with the quantity of gas remains constant (i.e., a constant air/fuel ratio). However, these gas trains do not compensate for internal and external influences that the appliance may experience. In such cases, the appliance may not operate at peak performance, or may not operate until manual adjustments are made to the system components. For example, environmental changes from the effect of high altitude, increased vent length, prevailing wind conditions impacting the vent termination, subzero outside combustion air temperature, and/or transient changes in gas properties can have an adverse effect on the ability of traditional pneumatic controls to provide the desired constant air/fuel ratio to the burner.

Additionally, typical gas-fired fuel appliances designed for multiple fuel applications include costly redundant gas trains on board to handle each specific fuel source. Accordingly, there is usually a requirement for the appliance to be manually converted with components and adjustment procedures for a specific alternate fuel before operating the appliance.

One embodiment provides a water heater including a tank configured to hold a fluid, a burner configured to manipulate a temperature of the fluid within the tank, one or more sensors configured to sense one or more characteristics of the burner, a fuel injector (or fuel injector array) positioned upstream of the burner, and a controller. The controller includes an electronic processor and a memory. The controller is configured to receive one or more signals from the one or more sensors corresponding to the one or more characteristics, and control the opening sequence of the fuel injector (or fuel injector array) based on the one or more signals.

Another embodiment provides a method of operating a water heater. The method includes manipulating, via a burner, a temperature of a fluid and sensing, via a sensor, the characteristics of the burner. The method further includes injecting, via a fuel injector array, a fuel upstream the burner and supplying, via a blower, an air/fuel mixture to the burner. The method further includes controlling, via a controller, the fuel injector based on the characteristic.

Another embodiment provides a gas-fired appliance including a burner configured to manipulate a temperature of the fluid within the tank, a fuel injector (or fuel injector array) configured to inject fuel upstream of the combustion chamber, a blower configured to provide an air/fuel mixture to the burner, a sensor configured to sense a characteristic of the burner, and a controller having an electronic processor and a memory. The controller is configured to receive a signal from the sensor corresponding to characteristic of the burner, and control the fuel injector and the blower based on the signal.

Another embodiment provides a gas-fired appliance including electronic fuel injection controls that are customized specifically for operation of a gas-fired appliance. The gas-fired appliance also includes an electronic control unit that receives inputs from pre-combustion and post-combustion sensing devices, and controls an amount of gaseous fuel that is injected upstream of a burner to maintain a relatively constant air/fuel ratio at the burner. In some embodiments, the gaseous fuel is injected via multiple fuel injectors (array) located upstream of the burner to mix the gaseous fuel with the combustion air before the mixture is delivered to the burner. The electronic control unit may control the opening and closing time of each fuel injector within the array. In some embodiments, the opening and closing time is recalculated on a real time basis to provide a precise and steady stream of gas and air mixture to the burner.

In some embodiments, the gas-fired appliance includes onboard intelligence that, should the effects of altitude start to reduce the input (for example, as a result of normal density changes of air and fuel), respond in concert with an air mass flow sensor to speed up the blower and seek to maintain full input status rather than operate in a derated state. Traditionally, gas-fired appliances today are not equipped to make this adjustment. With this on-board intelligence, the customer does not need to automatically purchase an oversized appliance to receive the desired input rate. Therefore, adjusting the speed of the blower in response to environmental conditions (and to maintain a constant air/fuel ratio), reduces costs and maintains the desired output of the gas-fired appliance.

Another embodiment provides a gas-fired appliance including a water inlet configured to receive water from an external source, and a water outlet that delivers the heated water to a storage tank or to a direct use outlet. The gas-fired appliance also includes a combustion air supply, a gas supply line that provides gaseous fuel, and a plurality of fuel injectors (or a fuel injector array) coupled to the gas supply line such that each injector receives an independent gaseous fuel supply. The fuel injectors are configured to inject gaseous fuel in a sequential pattern into a common gas supply line to be mixed with combustion air and then delivered to the burner. The gas-fired appliance also includes a combustion air supply system coupled to the fuel injector (or fuel injector array) upstream of the burner. Additionally, the gas-fired appliance includes a blower coupled to the common manifold assembly to receive the mix of gaseous fuel and air, an air mass flow sensor positioned in the combustion air stream of the inlet side of the blower, and a burner coupled to the blower. The burner receives the mix of gaseous fuel and air from the blower and burns the mix of gaseous fuel and air to generate products of combustion. The gas-fired appliance further includes a heat exchanger coupled to the burner configured to extract heat from the products of combustion, a flue outlet configured to vent the products of combustion, an oxygen sensor mounted on the flue outlet, and an electronic control unit. The electronic control unit is electrically and/or communicatively coupled to the fuel injectors, the air mass flow sensor, and the oxygen sensor. The electronic control unit is configured to receive output signals from the air mass flow sensor and the oxygen sensor, control the fuel injectors in sequence based on the output signals from the air mass flow sensor and the oxygen sensor, and control a speed of the blower also based on the output signals from the air mass flow sensor and the oxygen sensor, and in synchronization with the control of the fuel injectors.

In some embodiments, an air/fuel ratio sensor replaces the oxygen sensor in the gas-fired appliance. In such embodiments, the air/fuel ratio sensor measures the combined total air/fuel ratio based on the oxygen content in the flue gases. The electronic control unit receives the air/fuel ratio from the air/fuel ratio sensor. In contrast, when the gas-fired appliance includes an oxygen sensor, the electronic control unit computes the air/fuel ratio based on the output of the air mass flow sensor and the oxygen sensor.

Another embodiment provides a gas-fired appliance including a water inlet configured to receive water from an external source, a combustion chamber, and a heat exchanger. The combustion chamber includes a fuel injector (or fuel injector array) and a burner. The fuel injector (or fuel injector array) is configured to provide gaseous fuel to the burner. The burner is operable to burn a mixture of air and gaseous fuel received from the fuel injector to generate products of combustion. The heat exchanger is configured to receive the products of combustion and transfer heat from the products of combustion to the water from the water inlet. The appliance also includes an electronic processor coupled to the fuel injector (or fuel injector array) and the burner. The electronic processor is operable to send an activation signal to the fuel injector to control a fuel/air ratio of the mixture of air and gaseous fuel.

Yet another embodiment provides a method of operating a gas appliance. The method includes determining, by an electronic processor, a target fuel/air ratio for operation of the water heater, and sending, by the electronic processor, an activation signal to a fuel injector (or fuel injector array) of the water heater based on the target fuel/air ratio. The method also includes providing, by the fuel injector (or fuel injector array) opening sequence, gaseous fuel to a burner of the appliance when the fuel injector (or fuel injector array) is activated, and generating, by the burner, products of combustion by burning a mixture of air and the gaseous fuel. The method further includes receiving, at the heat exchanger, the products of combustion, and transferring, by the heat exchanger, heat from the products of combustion to water received from a water inlet of the appliance.

Other aspects of the application will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary gas-fired appliance according to some embodiments of the application.

FIG. 2 is a schematic diagram of an exemplary fuel injector system as shown installed within a gas inlet train of the gas-fired appliance of FIG. 1 according to some embodiments of the application.

FIG. 3 is a flowchart illustrating a method of operation of a fuel injector of FIG. 2 within any multiple set of fuel injectors used for a particular input according to some embodiments of the application.

FIG. 4 is a block diagram of a control circuit for the gas-fired appliance of FIG. 1 according to some embodiments of the application.

FIGS. 5A & 5B are flowcharts illustrating a method of operation of the gas-fired appliance of FIG. 1 according to some embodiments of the application.

FIG. 6 is a flowchart illustrating a method of sending an activation signal to a fuel injector (or fuel injector array) of the gas-fired appliance of FIG. 1.

DETAILED DESCRIPTION

Before any embodiments of the application are explained in detail, it is to be understood that the application is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the aforementioned drawings. The application is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

FIG. 1 is a schematic diagram of a gas-fired appliance 100 according to some embodiments of the application. In the illustrated embodiment, appliance 100 is a storage-type gas-fired water heater 100, however, in other embodiments, the appliance 100 may be any appliance operable to heat a medium, for example but not limited to a gas-fired furnace, a gas-fired boiler, and/or a tankless gas-fired water heater. In the illustrated embodiment, the appliance 100 includes an enclosed water tank 105, a shell 110 surrounding the water tank 105, and foam insulation 115 filling an annular space between the water tank 105 and the shell 110. The water tank 105 may be made of ferrous metal and lined internally with a glass-like porcelain enamel to protect the metal from corrosion. In other embodiments, the water tank 105 may be made of other materials, such as plastic.

A water inlet line 120 and a water outlet line 125 are in fluid communication with the water tank 105. In the illustrated embodiment, the water inlet line 120 is in fluid communication with the water tank 105 at a bottom portion of the water tank 105, while the water outlet line 125 is in fluid communication with the water tank 105 at a top portion of the appliance 100. In other embodiments, the water inlet line 120 may be at a bottom portion of the appliance 100, while the water outlet line 125 may be at the top portion of the appliance 100. In yet another embodiment, the water inlet line 120 may be the top portion of the appliance 100, while the water outlet line 125 may be at the bottom portion of the appliance 100. The inlet line 120 includes an inlet opening 130 for adding cold water to the water tank 105, and the outlet line 125 includes an outlet opening 135 for withdrawing hot water from the water tank 105 for delivery to a user.

The appliance 100 also includes a premix assembly 140, an exhaust structure 142, an air mass flow sensor 143, an oxygen sensor 145, an inlet temperature sensor 146, an outlet temperature sensor 147, a heat exchanger temperature sensor 148, an upper storage tank temperature sensor 149, and a lower storage tank temperature sensor 150. The appliance 100 analyzes the measurements from one or more of the sensors 143-150 to monitor and control the operation of the appliance 100. In the illustrated embodiment, the premix assembly 140 is supported by and positioned above the water tank 105. In other embodiments, the premix assembly 140 is positioned under the water tank 105 and supports the water tank 105. The appliance 100 also includes a heat exchanger 155 in fluid communication with the premix assembly 140 and the exhaust structure 142.

The premix assembly 140 includes an air intake vent pipe 160, a gas inlet manifold assembly 165, a plurality of fuel injectors 170a-d, a plurality of common gas lines 172a-d, a blower 175, an ignition device 180, a burner 185, and a flame sensor 190. In some embodiments, the premix assembly 140 is surrounded by a high temperature insulation to retain the heat from the hot products of combustion. The air intake vent pipe 160 is in fluid communication with the blower 175. Operation of the blower 175 draws air for combustion through the air intake vent pipe 160. The gas inlet manifold assembly 165 is in fluid communication with an external fuel source such as, for example, a natural gas source. Each fuel injector 170 is in fluid communication with the gas inlet manifold assembly 165 to receive the fuel and provide the gaseous fuel toward the blower 175 upon demand (e.g., in response to an activation signal from an electronic control unit 405 (FIG. 4)). As illustrated, in some embodiments, the plurality of fuel injectors 170a-d are located at various positioned spaced from each other. Although illustrated as a plurality of fuel injectors 170, in other embodiments, there may be a single fuel injector 170.

FIG. 2 illustrates a schematic diagram of an exemplary fuel injector 170. The fuel injector 170 includes an inlet 200 and an outlet opening 203. The fuel injector 170 also includes an electrical connector 205, a solenoid 210, a pintle spring 215, a plunger 220, a valve 225, and a nozzle 230. The solenoid 210 is electrically coupled to the electrical connector 205. The solenoid 210 is magnetically coupled to the pintle spring 215. The pintle spring 215 is connected to the plunger 220, which is in turn connected to the valve 225. The pintle spring 215 retracts and extends based on the activation of the solenoid 210. The plunger 220 is also slidably movable between a first position in which the plunger 220 is closer to the outlet opening 203 and a second position in which the plunger 220 is closer to the inlet 200. Since the valve 225 is physically connected to the plunger 220, the valve 225 also selectively moves toward the inlet 200 and toward the outlet opening 203 in response to movement of the plunger 220. The valve 225 is in an open position when the valve 225 is closer to the inlet 200, and is in a closed position when the valve 225 is closer to the outlet opening 203. The inlet 200 is in fluid communication with the outlet opening 203 of the fuel injector 170 through the nozzle 230 when the valve 225 is open. When the valve 225 is closed, the inlet 200 is not in fluid communication with the outlet opening 203.

In contrast to fuel injectors used in other industries such as the automotive industry, the fuel injectors 170a-d shown in FIGS. 1-2, comply with different requirements. In some embodiments, each fuel injector 170 may be located in the gas/air inlet stream and is designed to withstand temperatures of up to approximately 160° F. Additionally, in some embodiments, each fuel injector 170 controls the flow of gaseous fuels (for example, methane, propane, propane air, and the like). Furthermore, in some embodiments, each fuel injector 170, because of its position in the gas-fired appliance, withstands a pressure of approximately 0.253-0.361 psi, unless a fuel pump is used, and approximately 0.072-0.361 psi of negative pressure (for example, when positioned in a premix application). In some embodiments, each fuel injector 170 operates on approximately 24 VAC and requires a relatively low current (for example, when compared to the current required for the fuel injector 170 under different applications). In some embodiments, however, the volumetric flow rate is substantially higher for the same energy input of liquid to gaseous fuel sources.

FIG. 3 is a flowchart illustrating a method 300 of operation of the fuel injector 170 according to some embodiments. The fuel injector 170 receives gaseous fuel through the inlet 200 (block 305). The fuel injector 170 then receives an activation signal, from a control circuit 400 (FIG. 4), through the electrical connector 205 (block 310). More details regarding the activation signal from the control circuit 400 are discussed below with respect to FIG. 6. The solenoid 210 becomes activated due to the received activation signal (block 315). Since the solenoid 210 is magnetically coupled to the pintle spring 215, activation of the solenoid 210 causes retraction of the pintle spring 215 (block 320). As the pintle spring retracts, the plunger 220 moves toward the inlet 200 thus opening the valve 225 (block 325). In particular, the plunger 220 overcomes the preload force of the pintle spring 215, and the plunger 220 moves toward the inlet 200 lifting from an injector seat. When the valve 225 is open, the fuel injector 170 allow gaseous fuel to pass through the outlet opening 203 (block 330). Specifically, pressure from the gaseous fuel supply forces gaseous fuel through the outlet opening 203. The fuel injector 170 remains open while activated. When the fuel injector 170 becomes deactivated, the plunger 220 moves back toward the outlet opening 203, on the injector seat, thereby inhibiting any gaseous fuel to pass through the fuel injector 170.

Referring back to FIG. 1, the blower 175 includes an inlet side and an outlet side. The blower 175 receives the ambient air from the air intake vent pipe 160 and the gaseous fuel from the fuel injector 170 at the inlet side. The blower 175 then provides an air/fuel mixture to the burner 185 at the outlet side of the blower 175. In the illustrated embodiment, the blower 175 includes a variable speed blower, however in other embodiments, the blower 175 may be a single speed blower.

The ignition device 180 is electrically activated to ignite the gas/air mixture at the burner surface. The flame sensor 190 is positioned outside (for example, external to) the surface of the burner 185, and proximate to (for example, next to) the ignition device 180. The flame sensor 190 detects a signal indicating whether a flame is present. In one example, the flame sensor 190 detects a direct current generated by the electronic control unit 405 (FIG. 4) (or another separate device). When a flame is present, the conductive ionized combustion gases from the flame conduct the current such that it is detected by the flame sensor 190. When the flame is not present, the current is unable to find a path to the flame sensor 190. The electronic control unit 405 (FIG. 4) determines that a flame is present when the current detected by the flame sensor 190 is above a threshold level.

After the ignition device 180 ignites the flame, the combustion process begins to generate hot products of combustion. The oxygen sensor 145 (or the air/fuel ratio sensor in some embodiments) and air mass flow sensor 143 generate and transmit data to the electronic control unit indicative of an air/fuel ratio of the combustible air/fuel mixture. An inadequate air/fuel ratio of the combustible air/fuel mixture may affect, for example, an efficiency of the water heater and/or the ability of the water heater to rapidly heat water. In other words, the air/fuel ratio may affect the heat generated per amount of fuel used to generate the heat. As described in more detail below, the electronic control unit 405 (FIG. 4) adjusts the operation of the appliance 100, for example, of the fuel injectors 170 in particular, to reach various target air/fuel ratios and maintain the fuel at an optimum relationship with other performance characteristics. The target air/fuel ratios may change to, for example, achieve peak thermal efficiency, meet lowest emissions regulations, provide immunity to burner noise or resonance, exhibit lower burner surface temperatures, extend burner life, among other goals.

The hot products of combustion flow through the heat exchanger 155 toward the exhaust structure 142. As the products of combustion flow through the heat exchanger 155, heat is transferred from the products of combustion to the heat exchanger wall and to the water surrounding the heat exchanger 155. In the illustrated embodiment, the hot products of combustion flow downward through a first portion of the heat exchanger 155, upward through a second portion of the heat exchanger 155, and downward again through a third portion of the heat exchanger 155. In other embodiments, the hot products of combustion may flow downward through the entirety of the heat exchanger 155. In yet other embodiments (for example, when the premix assembly 140 is positioned under the water tank 105), the hot products of combustion flow upward through the heat exchanger 155. In such embodiments, the exhaust structure 142 may be positioned at an upper portion of the appliance 100. Although illustrated as having a substantially helical shape, in other embodiments, the heat exchanger 155 may take other forms or shapes, for example but not limited to, a substantially straight shape.

The air mass flow sensor 143 is positioned within the air intake pipe 160, upstream of the blower 175 and the point where gaseous fuel from the fuel injectors 170 is introduced into the air stream. The air mass flow sensor 143 detects a mass flow rate of air flowing into the blower 175. The air mass flow sensor 143 may help determine, for example, how much combustible air mixture is provided to the burner 185.

The oxygen sensor 145 is coupled to the exhaust structure 142. The oxygen sensor 145 detects excess oxygen levels within the products of combustion generated by the burner 185. In some embodiments, the oxygen sensor 145 may be replaced by an air/fuel ratio sensor 144 that generates an output signal indicative of the air/fuel ratio. A measure of the excess oxygen level may also be determined from the output of the air/fuel ratio sensor 144.

The inlet temperature sensor 146 is positioned at the water inlet line 120 and measures a temperature of the water entering the appliance 100. The outlet temperature sensor 147 is positioned at the water outlet line 125 and measures a temperature of the water leaving the appliance 100 (for example, to be provided to a user). The heat exchanger temperature sensor 148 is positioned within the heat exchanger 155 toward the exit of the heat exchanger 155. The heat exchanger temperature sensor 148 measures a temperature of the products of combustion exiting the heat exchanger 155 (also referred to as the flue gas temperature). The upper tank temperature sensor 149 is positioned in an upper portion of the water tank 105 and measures an average water temperature within an upper volume of the tank 105 (for example, an average water temperature for the upper one-third of the water tank 105). The lower tank temperature sensor 150 is positioned in a lower portion of the water tank 105 and measures an average water temperature within the lower volume of the water tank 105 (for example, an average water temperature for the lower one-third of the water tank 105). In other embodiments, the appliance 100 may include more or less sensors, and the sensors may be positioned elsewhere with respect to the appliance 100.

The operation of the plurality of fuel injectors 170a-d, as well as the other components of the appliance 100 are controlled by a control circuit 400 (FIG. 4). FIG. 4 illustrates a block diagram of the control circuit 400. The control circuit 400 includes an electronic control unit 405 (for example, an electronic processor), a power regulator 410, a set of input/output devices 415, and a memory 420. The control circuit 400 is coupled to the premix assembly 140 to control the plurality of fuel injectors 170a-d, the blower 175, and the ignition device 180. The control circuit 400 is also coupled to the sensors 143-150 of the appliance 100 to receive measurements of different operational parameters of the appliance 100 and adjust operation of the appliance 100 accordingly.

The control circuit 400 receives power from a power source 430 (for example, an alternating current (AC) power source or a direct current (DC) power source). In one embodiment, the power source 430 provides 120 VAC at a frequency of approximately 50 Hz to approximately 60 Hz. In another embodiment, the power source 430 provides approximately 220 VAC at a frequency of approximately 50 Hz to approximately 60 Hz. In yet another embodiment, the power source 430 provides a DC voltage (for example, approximately 12 VDC). The power regulator 410 receives the power from the AC power source 430 and converts the power from the power source 430 to a nominal voltage (e.g., a nominal DC voltage). The power regulator 410 provides the nominal voltage to the control circuit 400 (e.g., the electronic control unit 405, the input/output devices 415, and the like).

The input/output devices 415 output information to the user regarding operation of the appliance 100 and may also receive one or more inputs from the user. In some embodiments, the input/output devices 415 may include a user interface for the appliance 100. The input/output devices 415 may include a combination of digital and analog input or output devices required to achieve control and monitoring for the appliance 100. For example, the input/output devices 415 may include a touch screen, a speaker, buttons, and the like, to output information and/or receive user inputs regarding the operation of the appliance 100 (for example, a temperature set point at which water is to be delivered from the water tank 105). The electronic control unit 405 controls the input/output devices 415 to output information to the user in the form of, for example, graphics, alarm sounds, and/or other known outputs. The input/output devices 415 are operably coupled to the electronic control unit 405 to control temperature settings of the appliance 100. For example, using the input/output devices 415, a user may set one or more temperature set points for the appliance 100.

The input/output devices 415 may also be configured to display conditions or data associated with the appliance 100 in real-time or substantially real-time. For example, but not limited to, the input/output devices 415 may be configured to display characteristics of the burner 185 (e.g., whether the burner is activated or malfunctioning), temperature of the water, and/or other conditions of the appliance 100. In some embodiments, the input/output devices 415 may also generate alarms regarding the operation of the appliance 100.

The input/output devices 415 may be mounted on the shell of the appliance 100, remotely from the appliance 100, in the same room (e.g., on a wall), in another room in the building, or even outside of the building. The input/output devices 415 may provide an interface between the electronic control unit 405 and a user interface that includes a 2-wire bus system, a 4-wire bus system, and/or a wireless signal.

The memory 420 stores one or more algorithms and/or programs used to control the plurality of fuel injectors 170a-d, the blower 175, the burner 185, and/or other components of the appliance 100. In particular, the memory 420 may store firing algorithms for specifying the time of activation for each of the fuel injectors 170. The memory 420 may also store operational data of the water heater (e.g., when the burner 185 has been activated, historical data, usage patterns, and the like) to help control the appliance 100.

The electronic control unit 405 is coupled to the power regulator 410, the input/output devices 415, the memory 420, the fuel injectors 170a-d, the blower 175, the ignition device 180, the flame sensor 190, the air mass flow sensor 143, the oxygen sensor 145, the inlet temperature sensor 146, the outlet temperature sensor 147, the heat exchanger temperature sensor 148, the upper tank temperature sensor 149, and the lower tank temperature sensor 150. As discussed above, in some embodiments, the electronic control unit 405 may be coupled to the air/fuel ratio sensor 144 instead of the oxygen sensor 145. In other words, the electronic control unit 405 may determine the air/fuel ratio of the combustion gases based on the output signals from the air mass flow sensor 143 and the oxygen sensor 145, or from the air/fuel ratio sensor 144 directly.

The electronic control unit 405 receives the output signals from each of the sensors 143-150. In particular, the electronic control unit 405 controls operation of the burner 185 based on the inlet temperature, a desired or target outlet temperature, an upper temperature (for example, the water temperature detected by the upper tank temperature sensor 149), and a lower temperature (for example, the water temperature detected by the lower tank temperature sensor 150). For example, the electronic control unit 405 monitors the upper temperature and the lower temperature to determine when to activate the burner 185. By analyzing the upper temperature, the electronic control unit 405 determines a difference between the target outlet temperature and the upper temperature. When the difference exceeds a difference threshold, the electronic control unit 405 sends an activation signal to the burner 185 such that water can be heated. By analyzing the lower temperature, the electronic control unit 405 ensures that the lower temperature is at a temperature capable of preventing or inhibiting condensation to form within the water tank 105. Additionally, the electronic control unit 405 may use the lower temperature to estimate an average tank temperature and energy necessary to bring the water to a user-defined water setpoint (for example, the target outlet temperature).

The electronic control unit 405 accesses the memory 420 to retrieve information relevant to the operation of the appliance 100. For example, the electronic control unit 405 may retrieve information regarding the usage patterns for the appliance 100, the previous activations of the burner 185, firing algorithms for the fuel injectors 170, and the like. The electronic control unit 405 uses the information retrieved from the memory 420 to control the fuel injector 170. The electronic control unit 405 also outputs control signals to the blower 175 and the ignition device to light the burner 185. The fuel injector 170, the blower 175, and the burner 185 then operate according to the control signals.

FIGS. 5A & 5B are flowcharts illustrating a method 500 of operating the appliance 100. First, the electronic control unit 405 receives the output signals from the sensors 143-150 (block 505). The electronic control unit 405 then calculates an average temperature of the stored water based on the temperature sensors of the gas-fired appliance (block 510). In particular, the electronic control unit 405 calculated the average temperature for the stored water based on the inputs received from the upper tank temperature sensor 149, the lower tank temperature sensor 150, the inlet water temperature sensor 146, and the outlet water temperature sensor 147. The electronic control unit 405 then determines whether the average water temperature is below a predetermined setpoint temperature (block 515). The electronic control unit 405 accesses the predetermined setpoint temperature from the memory 420. When the electronic control unit 405 determines that the average water temperature is not below the predetermined setpoint temperature, the electronic control unit 405 continues to receive the inputs from the sensors 143-150 (block 505). On the other hand, when the electronic control unit 405 determines that the average water temperature is below the predetermined setpoint temperature, the electronic control unit 405 generates a demand signal (block 520). The demand signal indicates that heat is necessary to raise the average temperature of the water to the predetermined setpoint temperature.

The electronic control unit 405 then operates the blower 175 at a pre-purge speed (block 522) to purge the combustion chamber of any unburnt gases that may be present from a previous heating cycle or from a failed ignition attempt. The electronic control unit 405 activates the ignition device 180 (block 525) to readily generate a flame, and sends activation signals to the fuel injectors 170 (block 527). In some embodiments, the electronic control unit 405 activates the ignition device 180 and sends the activation signals to the fuel injectors 170 simultaneously such that a flame can be readily generated upon the air/fuel mixture reaching the burner 185.

Each fuel injector 170 receives the activation signal and provides gaseous fuel to the blower 175 (block 530). The fuel injectors 170 provide gaseous fuel to the blower 175 based on the activation signal from the electronic control unit 405. For example, in some embodiments, the electronic control unit 405 may utilize a pulse-width-modulation signal to control the fuel injectors 170. In such embodiments, each fuel injector 170 activates and deactivates the solenoid 210 based on the frequency of the pulse-width-modulation signal from the electronic control unit 405. In other embodiments, however, the electronic control unit 405 provides a continuous activation signal to each fuel injector 170 such that each fuel injector 170 opens the valve 225 for a duration of the continuous activation signal. Thereby, the fuel injectors 170 provide a constant output of gaseous fuel for the duration of the continuous activation signal. As described below with respect to FIG. 6, the fuel injectors 170 may be activated based on a particular firing algorithm.

After the fuel injectors 170 provide the gaseous fuel, the electronic control unit 405 determines whether a flame is present at the burner 185 through the flame sensor 190 (block 532). When the electronic control unit 405 determines that a flame is not present, the electronic control unit 405 generates a fault alert to the user (block 533). In some embodiments, the electronic control unit 405 deactivates and reactivates the ignition device 180 and the fuel injectors 170 to attempt to generate a flame again. In other embodiments, the electronic control unit 405 simply deactivates the ignition device 180 and the fuel injectors 170. When the electronic control unit 405 determines that a flame is present, the electronic control unit 405 controls the blower 175 to operate at an ignition speed (block 534). The burner 185 then burns the fuel/air mixture received from the blower 175 and generates products of combustion (block 535). The heat exchanger 155 receives the products of combustion (block 540) as the products of combustion flow toward the exhaust structure 142. The heat exchanger 155 then transfers heat from the products of combustion therein to the water surrounding the heat exchanger 155 (block 545), thereby heating the water inside the water tank 105.

During operation of the water heater 100, as described in more detail below, the electronic control unit 405 receives the output signals from the sensors 146-150, and adjusts the operation of the fuel injectors 170 and/or the blower 175 accordingly. The electronic control unit 405 continues to compare the temperature of the water with the setpoint temperature and deactivates the fuel injectors 170 and the burner when the temperature of the water reaches the setpoint temperature. The blower 175 may then operate at a post-surge speed and deactivate.

In some embodiments, before the activation signal is sent to each of the fuel injectors 170a-d, and/or the ignition device 180, the electronic control unit 405 determines whether any faults exist in the water heating system. When faults are detected by the electronic control unit 405, a message is output to a user, for example, via the input/output devices 415 (similar to, for example, the alert generated when no flame is detected in block 533). In some embodiments, operation of the water heater 100 ceases while faults are detected. When the electronic control unit 405 does not detect any faults, the electronic control unit 405 sends the activation signal to the fuel injectors 170.

FIG. 6 is a flowchart illustrating a method 600 of sending an activation signal to the fuel injectors 170a-d, as discussed with respect to block 525 of FIGS. 5A & 5B. The method 600 is triggered by the generation of the demand signal by the electronic control unit 405. After the electronic control unit 405 generates the demand signal, the electronic control unit 405 determines a target air/fuel ratio for operating the appliance 100 (block 605). As discussed above, the air/fuel ratio determines the efficiency at which fuel is utilized and an efficiency at which water is heated. The electronic control unit 405 determines the target air/fuel ratio for operation based on the output signals from the oxygen sensor 145, the air mass flow sensor 143, the air/fuel ratio sensor 144, or a combination thereof. The amount of free oxygen present in the products of combustion is used to determine the amount of excess air in the fuel/air mixture. The electronic control unit 405 may compare the amount of excess oxygen (as measured, for example, by the oxygen sensor 145) to an ideal amount of oxygen in the products of combustion, and may determine the target air/fuel ratio accordingly. Specifically, when the amount of oxygen determined by the electronic control unit 405 (e.g., based on the output signals from one or more of the oxygen sensor 145, the air mass flow sensor 143, or the air/fuel ratio sensor 144) is outside predetermined limits or thresholds (for example, as specified by the electronic control unit 405), a different air/fuel ratio is calculated.

The electronic control unit 405 may access a firing algorithm for the fuel injectors 170a-d from the memory 420 (block 610). The firing algorithm determines how and when each fuel injector is to be opened based on feedback inputs from the air mass flow sensor 143 (or air/fuel ratio sensor 144), the oxygen sensor 145, the temperature sensors 146-150, the flame sensor 190, and other safety limiting devices sometimes used in the application of a gas-fired appliance to control the rated input of the burner in addition to maintaining a constant air/fuel ratio entering the burner 185. The electronic control unit 405 then calculates a time of activation for each fuel injector 170 (block 615). The time of activation is based on, for example, the firing algorithm used by the electronic control unit 405. The electronic control unit 405 then sends the activation signal to each fuel injector 170 based on the calculated time of activation (block 620).

Although the blocks for the flowcharts above have been described as being performed serially, in some embodiments, the blocks may be performed in a different order and two or more blocks may be carried out in parallel to, for example, expedite the control process.

In some embodiments, the gas-fired appliance 100 includes the air mass flow sensor 143 and the oxygen sensor 145, or the air/fuel ratio sensor 144 without including the plurality of the fuel injectors 170. In such embodiments, the electronic control unit 405 controls a valve (or a plurality of valves) of a gas train system based on the outputs from the air mass flow sensor 143 combined with the outputs from the oxygen sensor 145, or from the output of the air/fuel ratio sensor 144, instead of controlling the fuel injectors 170. The electronic control unit 405, however, may perform similar control algorithms (e.g., logic) as described above in FIGS. 5-6, but may send activation signal(s) to a valve instead of a fuel injector 170. The control of the gas-fired appliance 100 based on these sensors 143-145 may increase the operation efficiency of the gas-fired appliance 100.

The use of fuel injectors 170, however, significantly improves (e.g. increase the speed of) the response time to the control signals from the electronic control unit 405 to maintain a more constant air/fuel relationship to the burner 185 in contrast to appliances that do not include fuel injectors. For example, when external influences (such as, but not limited to, changes in pressure) may cause changes that affect the air/fuel ratio, in embodiments illustrated in the application, the electronic control unit 405 may correct the air/fuel ratio by controlling the fuel flow though the injectors 170. The fuel injectors 170 are configured to respond, for example, on the order of milliseconds to correct the air/fuel ratio through direct control of the fuel flow. In contrast, pressure driven controls may not be able to respond as quickly or precisely, if at all, and may instead result in extended periods of time during which the appliance continues to operate with an inadequate air/fuel ratio.

Additionally, using the fuel injectors 170 allows the operating range of the blower speeds to increase the burner turndown range (allowing for maximum output to minimum input of the burner in Btu/Hr (British thermal units per hour)). Increasing the burner turndown range when operating a heating boiler allows the boiler to match the load as long as possible without cycling the burner 185 off. For example, an appliance that does not include fuel injectors typically has a modulation range limited by the ability of the blower to provide a minimum stable negative pressure signal to the regulator of a gas valve. This minimum stable negative pressure signal typically corresponds to the minimum blower speed of approximately 1250 RPM (revolutions per minute). On the other hand, the appliance 100 including the fuel injectors 170 is independent of the negative pressure signal, and therefore the minimum blower speed (i.e., the minimum input) is specific only to the requirements for lubrication of the bearing system of the blower 175 as specified by the manufacturer of the blower 175. The minimum blower speed in an appliance 100 with fuel injectors 170 may be, for example, 500 RPM, thereby expanding the range of modulation of the burner 185. The appliance 100 is then able to operate for longer periods of time without cycling during moderate and light heating load periods.

Additionally, the electronic control unit 405 determines the target air/fuel ratio based on the sensor output signals. By analyzing the sensor output signals, the electronic control unit 405 can adjust to changing operating conditions of the appliance 100 without requiring additional instructions or manual adjustments. In particular, the electronic control unit 405 may directly or indirectly sense different changes in operating conditions and adjust the target air/fuel ratio as necessary. For example, operating a gas-fired appliance in higher altitudes differs from operating the gas-fired appliance in lower altitudes since the concentration of oxygen in the air decreases as the altitude increases. The electronic control unit 405, however, receives an output signal from the air mass flow sensor 143 and the oxygen sensor 145 (or, alternatively, from the air/fuel ratio sensor 144) and determines that the air/fuel ratio is too low (for example, the air/fuel mixture burnt by the burner 185 is too rich). The electronic control unit 405 can then adjust the activation signal sent to each fuel injector 170 such that the fuel injectors 170 provide a decreased amount of gaseous fuel to the burner 185.

Analogously, the electronic control unit 405 may detect different external conditions that affect the quality of combustion. For example, the electronic control unit 405 may detect when a vent length (for example, a length of a vent from an end of the heat exchanger 155 to the exhaust structure 142) is excessively long, when sidewall wind conditions increase backpressure to the blower 175 due to high winds, or when fuel constituency changes. In some embodiments, the electronic control unit 405 receives inputs from the oxygen sensor 145, the air mass flow sensor 143 (or, alternatively, from the air/fuel ratio sensor 144) to detect when the amount of excess air is not within a predetermined range. When the amount of excess air is outside the predetermined range, the electronic control unit 405 adjusts the activation sequencing of the fuel injectors 170 to reestablish the air/fuel ratio to the target air/fuel ratio.

Such precise monitoring of the operating conditions, and particularly of the air/fuel ratio, enables the appliance 100 to operate more efficiently. Additionally, including fuel injectors 170 in the appliance 100, due to the small nature of the valve 225, allows for stricter, more precise control of the amount of gaseous fuel provided to the burner 185. Therefore, including fuel injectors in the appliance 100 to provide gaseous fuel to the blower 175 increases the efficiency of the appliance 100 and provides greater adaptability to changing operating conditions.

Thus, the application provides, among other things, a system and method for operating gas appliance using fuel injection technology. Various features and advantages of the application are set forth in the following claims.

PERFORMANCE OF A GAS-FIRED APPLIANCE BY USE OF FUEL INJECTION TECHNOLOGY

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