Burner ignition system and method using a sensorless constant mass flow induced draft fan

Abstract

A motor controller for a burner system includes an inverter that supplies current to a motor for rotating a forced draft fan. A processor is coupled to the inverter and receives signals from a system controller and, in response, commands the inverter to supply a first current to the motor during a first period to rotate the fan, thereby generating a first mass flow through the burner system, the first mass flow having a first mass flow rate greater than a threshold to initiate a vacuum switch. The processor then commands the inverter to supply a second current to the motor during a second period beginning when the first period expires to rotate the fan, thereby generating a second mass flow through the burner system, the second mass flow having a target mass flow rate for normal operation of the burner.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Non - Provisional Patent Application No. 16 / 549,441, filed on August 23, 2019, the entire disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The field of the present invention generally relates to induced draft fans in burner systems, and more particularly to burner ignition systems and methods using a sensorless constant mass flow induced draft fan. Background Art

[0004] At least some known induced draft fans pass air through a gas burner and a heat exchanger to provide an adequate mass flow of air for combustion. The induced draft fan typically includes a fan that rotates to draw combustion gases from a collection manifold through the burner system. Generally, a pressure drop occurs as the combustion gases pass through the burner and the heat exchanger. To ensure an adequate mass flow exists prior to starting the gas burner, heating devices typically include a vacuum switch in or near the collection manifold or other low - pressure zone and are configured to actuate due to the pressure drop when the mass flow through the burner system reaches a specific level for safe ignition of the burner. At least some known variable - speed induced draft fans also include another sensor in or near the collection manifold to verify that the fan produces an adequate mass flow rate to activate the vacuum switch and enable the burner to operate.

[0005] At least some known fan motors operate without an air flow sensor that uses a constant mass flow technique, where the speed of the fan is determined based on the required mass flow rate and a known relationship between the fan speed and the motor torque. Thus, a fan motor using a constant air flow technique does not require a sensor to measure the air flow rate. Although the mass flow rate is typically calculated as a function of speed and torque, the mass flow rate produced by a given speed or a given torque depends on the air temperature and atmospheric pressure, and ultimately on the air density in the burner system. According to Bernoulli's equation, prior to ignition, when the air is cooler and denser in the burner system, the rotation of the fan to produce a given mass through the burner system will produce a smaller pressure drop across the burner and the heat exchanger than during normal operation when the air is warmer and less dense. Thus, when the temperature and / or atmospheric pressure in the burner system fluctuate over a wide range, a constant mass flow fan may not produce an adequate mass flow rate to activate the vacuum switch. Additionally, in such a case, the burner system will not operate. At least for this reason, available sensorless constant mass flow fan motors are generally not used in the induced draft fans of burner systems. Accordingly, there is a need for a sensorless motor that can operate a fan to produce an adequate mass flow to ignite / light the burner. Summary of the Invention

[0006] In one aspect, the present invention discloses a motor controller for a burner system. The burner system includes an induced draft fan and a vacuum switch, and the induced draft fan is configured to draw air through the burner system via an air flow path. The motor controller includes an inverter and a processor. The inverter is configured to supply current to a motor configured to rotate the induced draft fan. The processor is communicatively coupled to the inverter and is configured to receive an induced draft control signal from a system controller. The processor is configured to, in response to the induced draft control signal, instruct the inverter to supply a first current to the motor during a first period to rotate the induced draft fan, thereby generating a first mass flow through the burner system, the first mass flow having a first mass flow rate greater than a threshold mass flow rate to activate the vacuum switch. The processor is configured to instruct the inverter to supply a second current to the motor during a second period starting at the end of the first period to rotate the induced draft fan, thereby generating a second mass flow through the burner system, the second mass flow having a target mass flow rate for normal operation of the burner.

[0007] In another aspect, the present invention discloses a method of operating a motor of an induced draft fan in a burner system. The motor is coupled to the induced draft fan, and the induced draft fan is configured to move air through an air flow path. The method includes receiving, by a motor controller configured to supply current to the motor, an induced draft control signal from a system controller. The method includes supplying a first current to the motor in response to the induced draft control signal during a first period to rotate the induced draft fan, thereby generating a first mass flow through the burner system, the first mass flow having a first mass flow rate greater than a threshold mass flow rate to activate a vacuum switch of the burner system. The method includes supplying a second current to the motor during a second period starting at the end of the first period to rotate the induced draft fan, thereby generating a second mass flow through the burner system, the second mass flow having a target mass flow rate for normal operation of the burner.

[0008] In yet another aspect, the present invention discloses a burner system. The burner system includes a burner, a heat exchanger, a collection manifold, an electric motor connected to and configured to rotate a draft fan, a vacuum switch, and a motor controller. The draft fan is configured to draw an air stream from the collection manifold through an air flow path, through the burner, and through the heat exchanger. The vacuum switch is configured to activate when the mass flow rate through the air flow path is sufficient to create a vacuum above a vacuum threshold, enabling the burner to operate. The motor controller is coupled to a system controller and the electric motor and is configured to receive a draft fan control signal from the system controller. The motor controller is configured to operate the electric motor during a first period to rotate the draft fan, thereby creating a first mass flow through the air flow path, the first mass flow having a first mass flow rate greater than a threshold mass flow rate. The motor controller is configured to operate the electric motor during a second period beginning at the end of the first period to rotate the draft fan, thereby creating a second mass flow through the air flow path, the second mass flow having a target mass flow rate for normal operation of the burner. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of an exemplary burner system.

[0010] Figure 2 is a perspective view of a water heater including Figure 1 an exemplary embodiment of the burner system shown;

[0011] Figure 3 is available for Figure 1 a cross-sectional perspective view of an exemplary draft fan assembly for the burner system shown;

[0012] Figure 4 is a flowchart depicting an exemplary method of operating Figure 1 the electric motor shown; and

[0013] Figure 5 is a graph showing an example of the variation of vacuum pressure over time during system startup of a burner system such as Figure 1 the one shown. DETAILED DESCRIPTION

[0014] The implementation of the system described herein uses a constant mass flow fan motor to generate an air stream to start the burner. More specifically, when the ignition process begins, the fan motor operates at an increased speed and mass flow to ensure sufficient air flow within the system for ignition of the burner and for activation of the vacuum switch. After a predetermined period of time, the fan motor operates at a reduced speed and mass flow to generate a target air flow for normal operation of the burner. Additional features of the system will be described in more detail herein.

[0015] As used herein, an element or step recited in the singular and preceded by the word "a" or "an" should be understood as not excluding a plurality of elements or steps, unless such exclusion is explicitly recited. Further, references to "example implementations" or "an implementation" of the present disclosure are not to be construed as excluding the existence of additional implementations that also incorporate the recited features.

[0016] Figure 1 is a schematic diagram of an exemplary burner system 100. The burner system 100 includes a system controller 102, a burner 104, a collection manifold 105, a draft inducer assembly 106, a vacuum switch 108, and an air flow path 110. The draft inducer assembly 106 includes a motor controller 112, a motor 114, and a draft inducer fan or fan 116. Combustion gases are collected in the collection manifold 105 before being ignited. Typically, these combustion gases are cooler and denser than the gases during operation of the burner system 100. The fan 116 is fluidly connected to the air flow path 110 and draws an air flow from the collection manifold 105 through the air flow path 110, through the burner 104, and through a heat exchanger 117. When a sufficient mass flow rate is generated, the vacuum switch 108 is actuated and causes the burner 104 to operate.

[0017] The motor controller 112 includes a processor 118 and a storage device 120. In some alternative embodiments, the processor 118 and / or the storage device 120 are physically separated from the motor controller 112 and communicatively connected to the motor controller 112.

[0018] The system controller 102 is communicatively connected to the burner 104, the draft inducer assembly 106, and the vacuum switch 108. The system controller 102 generates a burner control signal 122 to control the burner 104. The burner 104 ignites, sustains, or extinguishes a gas flame based on the burner control signal 122. The system controller 102 also generates a draft inducer control signal 124 to control the draft inducer assembly 106. The efficiency of operation of the burner 104 depends on the mass flow through the air flow path 110. The burner 104 is configured to operate at a target mass flow rate at which the burner 104 can operate safely and with a desired efficiency. When the burner 104 is operating, the draft inducer assembly 106 causes air to flow through the air flow path 110 at the target mass flow rate.

[0019] For safe ignition, the burner 104 requires a mass flow rate greater than a threshold mass flow rate. The vacuum switch 108 is typically disposed in the air flow path 110 or some other low pressure zone. The vacuum switch 108 is configured to activate only when the vacuum pressure generated by the mass flow caused by the fan 116 at the vacuum switch 108 is greater than a threshold vacuum pressure. In response to activation, the vacuum switch 108 transmits a vacuum switch control signal 126 to the system controller 102, indicating that the mass flow in the air flow path 110 is above the threshold mass flow rate for safe ignition of the burner 104 and enabling the system controller 102 to instruct the burner 104 to ignite.

[0020] The motor controller 112 is communicatively coupled to the motor 114 and is configured to supply current 128 to the motor 114. The motor controller 112 may include, for example, a rectifier, a direct current (DC) link or bus, and an inverter 130 for generating the current 128. The motor controller 112 controls one or more of the frequency, amplitude, phase, or duty cycle of the current 128 based on instructions from the processor 118. The speed at which the motor 114 rotates is a function of, for example, the frequency of the current 128. Thus, the motor controller 112 can change the speed of the motor 114 by changing the frequency, amplitude, phase, and / or duty cycle of the current 128.

[0021] The motor 114 is mechanically coupled to the fan 116 and is configured to rotate the fan 116 to generate an air flow through the air flow path 110 and the burner system 100 by causing air to flow from the collection manifold 105 through the inlet 132 into the induced draft fan assembly 106 and out through the outlet 134. The air flow has a mass flow rate or is characterized by a mass flow rate. The mass flow rate through the air flow path 110 depends at least on the speed and torque output of the motor 114 and the fan 116, and the density of the combustion gas.

[0022] The processor 118 is configured to instruct the inverter 130 to supply the current 128 to rotate the motor 114 at a target speed (or torque) based on a specific required or target mass flow rate of the burner 104. The relationship between the mass flow rate through the air flow path 110 and the speed (or torque output) of the motor 114 can be represented as a formula or a "curve" defined by a function of speed, torque, and target mass flow rate, sometimes referred to as a mass flow curve. The mass flow curve can be stored in a storage device 120, for example, as a look-up table or an algorithm. The processor 118 determines the speed (or torque) at which the motor 114 operates for a given target mass flow based on the mass flow curve. Generally, as the mass flow increases, the torque output of the motor 114 will increase. Thus, when the combustion gas is heated, the mass flow curve or mass flow algorithm will result in a higher speed (or torque) command for the motor 114.

[0023] During the ignition process, the motor controller 112 is configured to operate the motor 114 at a mass flow rate higher than the target mass flow rate to cause a decrease in the temperature and an increase in the density of the combustion gas accumulated in the collection manifold 105 before the burner 104 ignites. Since the combustion gas in the collection manifold 105 is colder and denser before the burner 104 ignites, a given target mass flow of the fan 116 produces a vacuum pressure lower than the required vacuum pressure at the vacuum switch 108. Therefore, the processor 118 determines a first or starting mass flow rate greater than the target mass flow rate, for example, a mass flow rate equal to the target mass flow rate multiplied by a factor of 1.2. The processor 118 then calculates a starting speed (or torque) based on the determined starting mass flow rate using a mass flow curve and commands the inverter 130 to supply current 128 to the motor 114 at a corresponding frequency, amplitude, phase, and duty cycle to operate it at the starting speed (or torque). According to the mass flow curve, the actual mass flow rate through the burner 104 and through the heat exchanger 117 generated by operating the motor 114 at the starting speed is higher than the expected mass flow rate and is sufficient to activate the vacuum switch 108 and cause the burner 104 to ignite at a low flue temperature. After a period of time - for example, 30 seconds - sufficient to cause the mass flow to activate the vacuum switch 108, ignite the burner 104, and allow the heated combustion gas to reach the fan 116, the processor 118 then commands the motor controller 112 to supply current 128 at a corresponding frequency, amplitude, phase, and duty cycle to operate the motor 114 at the target mass rate for normal operation through the air flow path 110 and the burner system 100.

[0024] Figure 2 is a perspective view of a water heater 200 including an exemplary embodiment of the burner system 100. The water heater 200 includes a water tank 202. Combustion gas is discharged through the air flow path 110 and the induced draft fan assembly 106. The air flow through the air flow path 110 is regulated by the induced draft fan assembly 106. Heat is transferred from the air flowing through the air flow path 110 to heat the water in the water tank 202.

[0025] Figure 3 is a cross-sectional perspective view of an exemplary embodiment of the induced draft fan assembly 106 that can be used in the burner system 100 and the water heater 200. The motor controller 112, the motor 114, and the fan 116 can be contained within a housing 302. The housing 302 includes an inlet 132 and an outlet 134 and is connected to the air flow path 110 at the inlet 132. As described above, the motor controller 112 supplies current to the motor 114 and controls the speed of the motor 114 by changing the frequency of the current 128. The motor 114 rotates the fan 116 to draw air in through the inlet 132 and discharge it through the outlet 134, thereby creating an air flow in the air flow path 110.

[0026] Figure 4is a flowchart depicting an exemplary method 400 of operating an electric motor of an induced draft fan in a burner system, the electric motor being, for example, Figure 1 the electric motor 114 that drives the fan 116 in the burner system 100 as shown. The method 400 includes receiving 402, by the motor controller 112 from the system controller 102, an induced draft fan control signal 124. The motor controller 112 then supplies 404 a first current 128 in response to the induced draft fan control signal 124 during a first period. When the first current 128 is supplied to the electric motor 114, the first current causes the electric motor 114 to rotate the fan 116 at a starting speed corresponding to a first mass flow having a first mass flow rate through the air flow path 110. The first mass flow rate is sufficient to create a vacuum above a vacuum threshold to activate the vacuum switch 108. The motor controller 112 then supplies 406 a second current 128 during a second period that begins when the first period expires. When the second current 128 is supplied to the electric motor 114, the second current causes the electric motor 114 to rotate the fan 116 to produce a second mass flow having a target mass flow rate through the air flow path 110. The target mass flow rate is the target mass flow rate for the proper and efficient operation of the burner 104.

[0027] Figure 5 is a graph 500 showing the variation of vacuum pressure over time during the startup process of a burner system such as Figure 1 the burner system 100 as shown. The horizontal axis 502 corresponds to the time elapsed since the start of the startup process and is represented in seconds, ranging from 0 to 100. The vertical axis 504 represents the vacuum pressure at the vacuum switch 108 and is represented in inches of water column from 0 to 1.2. The curve 506 represents the vacuum pressure at the vacuum switch 108 at a given moment during the startup process. The vacuum pressure at the vacuum switch 108 is related to the mass flow rate through the air flow path 110.

[0028] During a first period 508 between time zero and time 510 at the start of the startup process, the motor controller 112 operates the electric motor 114 at a first or starting speed sufficient to cause the fan 116 to produce a first mass flow having a first mass flow rate. The first mass flow rate creates a vacuum pressure at the vacuum switch 108 that is greater than the threshold vacuum pressure 512 for activating the vacuum switch 108.

[0029] During a second period 514 after time 510, the motor controller 112 operates the electric motor 114 at a second or target speed sufficient to cause the fan 116 to direct a second mass flow having a second or target mass flow rate. The second mass flow rate is the target mass flow rate for the operation of the burner 104 and creates a vacuum pressure at the vacuum switch 108 that is the corresponding target vacuum pressure 516.

[0030] The methods and systems described herein can be implemented using computer programming or engineering techniques, including computer software, firmware, hardware, or any combination or subset thereof, where the technical effects can include at least one of the following: (a) enabling a constant mass flow fan motor without an air flow sensor to be used in the induced draft fan of a burner system by first operating the fan motor at an increased speed to ensure sufficient air flow in the system for burner ignition before operating the fan motor at a reduced speed to produce a target air flow for normal burner operation; (b) reducing the cost of the induced draft fan for a burner system by eliminating the need for an air flow sensor in the fan motor of the induced draft fan; and (c) increasing the ease of manufacture and installation of the fan motor of the induced draft fan for a burner system by eliminating the need for an air flow sensor in the fan motor.

[0031] Some embodiments relate to the use of one or more electronic processing or computing devices. As used herein, the terms "processor" and "computer" and related terms, e.g., "processing device", "computing device", and "controller" are not limited to those integrated circuits referred to as computers in the art, but rather broadly refer to processors, processing devices, controllers, general-purpose central processing units (CPUs), graphics processing units (GPUs), microcontrollers, microcomputers, programmable logic controllers (PLCs), reduced instruction set computers (RISC) processors, field programmable gate arrays (FPGAs), digital signal processing devices (DSPs), application specific integrated circuits (ASICs), and other programmable circuits or processing devices capable of performing the functions described herein, and these terms may be used interchangeably herein. The above embodiments are merely examples and are not intended to limit in any way the definition or meaning of the terms processor, processing device, and related terms.

[0032] In the embodiments described herein, the storage device may include, but is not limited to, non-transitory computer-readable media such as flash memory, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile random access memory (NVRAM). As used herein, the term "non-transitory computer-readable media" is intended to represent any tangible computer-readable media, including but not limited to non-transitory computer storage devices, including but not limited to volatile and non-volatile media, as well as removable and non-removable media such as firmware, physical and virtual memory, CD-ROM, DVD, and any other digital source such as a network or the Internet, and digital means yet to be developed, with the sole exception of transitory propagating signals. Alternatively, floppy disks, compact disc read-only memory (CD-ROM), magneto-optical disk (MOD), digital versatile disc (DVD), or any other computer-based device implemented by any method or technology for storing information for short and long terms such as computer-readable instructions, data structures, program modules and sub-modules, or other data may also be used. Thus, the methods described herein may be encoded as executable instructions, such as "software" and "firmware", embodied in a non-transitory computer-readable media. Further, as used herein, the terms "software" and "firmware" are interchangeable and include any computer program stored in a memory for execution by a personal computer, workstation, client, and server. When executed by a processor, such instructions cause the processor to perform at least a portion of the methods described herein.

[0033] In addition, in the embodiments described herein, the additional input channels may be, but are not limited to, computer peripherals associated with a runner interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used, including but not limited to, for example, a scanner. Further, in an exemplary embodiment, the additional output channels may include, but are not limited to, a runner interface monitor.

[0034] This written description uses examples to provide details of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including making and using any device or system and performing any combined methods. The patentable scope of the present invention is defined by the claims, and may include other examples that occur to those skilled in the art. If these other examples have structural elements that are not different from the literal language of the claims, or if these other examples include equivalent structural elements that are not substantially different from the literal language of the claims, then these other examples are intended to fall within the scope of the claims.

Claims

1. A motor controller for a burner system, the burner system including a forced draft fan and a vacuum switch, the forced draft fan configured to draw air through the burner system via an air flow path, the motor controller including: An inverter configured to supply current to a motor, the motor configured to rotate the forced draft fan; And A processor communicatively connected to the inverter, wherein the processor is configured to: Receive a forced draft control signal from a system controller; Determine a first mass flow rate based on a target mass flow rate, wherein the first mass flow rate is greater than the target mass flow rate; Calculate a starting speed based on the first mass flow rate using a mass flow curve; In response to the forced draft control signal, instruct the inverter to supply a first current to the motor during a first period to rotate the forced draft fan at the calculated starting speed, thereby generating a first mass flow through the burner system, the first mass flow having the first mass flow rate greater than a threshold mass flow rate to activate the vacuum switch; And Instruct the inverter to supply a second current to the motor during a second period starting from the end of the first period to rotate the forced draft fan, thereby generating a second mass flow through the burner system, the second mass flow having the target mass flow rate for normal operation of the burner.

2. The motor controller according to claim 1, wherein, The processor is configured to determine the first mass flow rate by multiplying the target mass flow rate by a factor of at least 1.

2.

3. The motor controller according to claim 1, wherein, The mass flow curve is represented as a formula or a look-up table stored in a memory.

4. The motor controller according to claim 1, wherein, The processor is further configured to determine the second mass flow based on the target mass flow rate using the mass flow curve.

5. The motor controller according to claim 4, wherein, The mass flow curve is represented as a formula or a look-up table stored in a memory.

6. The motor controller according to claim 1, wherein, The first period has a duration of at least 30 seconds.

7. A method of operating a motor of a forced draft fan in a burner system, the motor coupled to the forced draft fan, the forced draft fan configured to move air through an air flow path of the burner system, the method including: Receiving a forced draft control signal from a system controller by a motor controller configured to supply current to the motor; The motor controller determines a first mass flow rate based on a target mass flow rate, where the first mass flow rate is greater than the target mass flow rate; And Calculating a starting speed based on the first mass flow rate by the motor controller using a mass flow curve; During a first period, in response to the forced draft control signal, supplying a first current to the motor to rotate the forced draft fan at the calculated starting speed, thereby generating a first mass flow through the burner system, the first mass flow having the first mass flow rate greater than a threshold mass flow rate to activate the vacuum switch of the burner system; And During a second period starting from the end of the first period, supplying a second current to the motor to rotate the forced draft fan, thereby generating a second mass flow through the burner system, the second mass flow having the target mass flow rate for normal operation of the burner.

8. The method according to claim 7, further including determining the first mass flow rate by the motor controller by multiplying the target mass flow rate by a factor of at least 1.

2.

9. The method according to claim 7, wherein The mass flow curve is represented as one of a formula and a look-up table stored in a memory.

10. The method according to claim 7, further comprising calculating, by the motor controller, a second speed corresponding to the second mass flow based on the target mass flow rate using a mass flow curve.

11. The method according to claim 10, wherein, The mass flow curve is represented as at least one of a formula stored in a memory and a look-up table.

12. The method according to claim 7, wherein The first time period has a length of at least 30 seconds.

13. A burner system, comprising: A burner; A heat exchanger; A collection manifold; A motor coupled to a draft fan and configured to rotate the draft fan, the draft fan being configured to draw an air flow from the collection manifold through an air flow path, through the burner, and through the heat exchanger; A vacuum switch configured to activate when a mass flow rate through the air flow path is sufficient to create a vacuum above a vacuum threshold, thereby enabling the burner to operate; and A motor controller coupled to the motor, the motor controller being configured to: Receive a draft fan control signal from a system controller; Determine a first mass flow rate based on a target mass flow rate, wherein the first mass flow rate is greater than the target mass flow rate; and Calculate a starting speed using a mass flow curve based on the first mass flow rate; Operate the motor during a first time period to rotate the draft fan at the calculated starting speed, thereby creating a first mass flow through the air flow path, the first mass flow having the first mass flow rate that is greater than a threshold mass flow rate; and During a second time period beginning at the end of the first time period, operate the motor to rotate the draft fan, thereby creating a second mass flow through the air flow path, the second mass flow having the target mass flow rate for normal operation of the burner.

14. The burner system according to claim 13, wherein, The motor controller is further configured to determine the first mass flow rate by multiplying the target mass flow rate by a factor of at least 1.

2.

15. The burner system according to claim 13, wherein, The mass flow curve is represented as one of a formula stored in a memory and a look-up table.

16. The burner system according to claim 13, wherein, The motor controller is further configured to calculate a second speed using a mass flow curve based on the target mass flow rate.

17. The burner system according to claim 16, wherein, The mass flow curve is represented as at least one of a formula stored in a memory and a look-up table.

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