Patent Application
20180087775
The field of the disclosure relates generally to airflow in gas-burning appliances, and more specifically to a motor controller for a blower in gas-burning appliances.
Known gas-burning appliances require sufficient airflow to exhaust, and to reduce the concentration of, dangerous combustion gas by-products, such as, for example, NO3 and NO4, among others, otherwise referred to as NOx. In some known high efficiency furnaces, water heaters, and other gas-burning appliances, standard chimney air-draw effects are not sufficient to assure the required airflow through the gas burners and heat exchangers, and therefore, some known gas-burning appliances utilize draft inducers to provide sufficient airflow through the heat exchangers of the furnace and to reduce the concentration of combustion by-products. The generated airflow is typically drawn in from the ambient or through an inlet duct by a blower, and typically exhausted through an exhaust duct. Inlet ducts and exhaust ducts generally pose a restriction on the generated airflow, as do the gas burner, heat exchanger, and the blower itself. Blowers installed in gas-burning appliances are typically selected to operate at a sufficient speed and volume to generate the necessary airflow for efficient heat transfer within the appliance and to exhaust combustion gases with an acceptable by-product concentration.
Inlet ducts and exhaust ducts for gas-burning appliances generally vary in length per installation. Many known gas-burning appliances utilize a blower that generates a sufficient airflow for the longest, most restricted, ducts for a particular gas-burning appliance. Many known gas-burning appliances specify a maximum restriction or duct length to ensure sufficient airflow. For example, a water heater may specify that inlet and exhaust ducts may not exceed 150 feet in length. Many installations of such gas-burning appliances utilize inlet ducts and exhaust ducts that are below the specified maximum length and, consequently, utilize blowers that far exceed the necessary airflow for the gas-burning appliance. In such installations, the blower generates excessive airflow that, although sufficiently exhausts combustion gases, reduces the efficiency of combustion and heat exchange within the gas-burning appliance.
In one aspect, a motor controller for a blower in a gas-burning appliance is provided. The motor controller includes a processor configured to receive a measured pressure differential measured by a sensor disposed in an airflow generated by the blower. The processor is configured to compute a motor speed based on the measured pressure differential and a pressure differential set-point for the gas-burning appliance. The processor is configured to operate the blower at the motor speed to drive the measured pressure differential toward the pressure differential set-point.
In another aspect, an exhaust system for gas-burning appliance is provided. The exhaust system includes a blower, a motor, a pressure sensor, and a motor controller. The blower is configured to generate an airflow through a duct comprising a gas burner, a non-variable airflow restriction, and an exhaust duct. The motor is coupled to the blower and is configured to operate the blower at a variable motor speed. The pressure sensor is disposed in the airflow and is configured to measure a pressure differential across the non-variable airflow restriction by the airflow. The motor controller is coupled to the motor and the pressure sensor. The motor controller is configured to compute a motor speed based on the pressure differential and a pressure differential set-point. The motor controller is further configured to operate the blower at the motor speed to converge the pressure differential onto the pressure differential set-point.
In yet another aspect, a method of controlling a blower in a gas-burning appliance is provided. The method includes operating a blower at a first motor speed to generate an airflow through a duct comprising a gas burner, a non-variable airflow restriction, and an exhaust duct. The method includes measuring a pressure differential across the non-variable airflow restriction. The method includes comparing the pressure differential to a pressure differential set-point. The method includes computing a second motor speed based on the comparing. The method includes operating the blower at the second motor speed to modify the airflow.
As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “example implementation” or “one implementation” of the present disclosure are not intended to be interpreted as excluding the existence of additional implementations that also incorporate the recited features.
Gas-burning appliances, such as, for example, and without limitation, furnaces and water heaters, burn a mixture of air and a fuel to generate heat that is carried by combustion gasses. The combustion gasses are typically drawn through a heat exchanger by a blower, and then vented out through an exhaust duct. While flowing through the heat exchanger, the combustion gasses heat another medium, such as, for example, water. If the airflow is too little, combustion gasses are not properly evacuated from the gas-burning appliance and can potentially leak into the ambient air, creating a hazardous condition. If the airflow is too great, combustion gasses are properly vented, but the combustion and heat exchange become less efficient. The airflow necessary to properly vent the combustion gasses generally depends on the length of the inlet ducts, if any, and the exhaust duct. Longer ducts require greater airflow to vent combustion gasses. Blowers in gas-burning appliances are typically configured to operate at a fixed speed that is sufficient, i.e., high enough, to exhaust combustion gasses for the longest possible duct for the gas-burning appliance. Motor controllers described herein regulate motor speed for the blower based on measured pressure differentials within the duct to achieve both sufficient ventilation of combustion gasses and high-efficiency combustion and heat exchange.
Embodiments of the present disclosure provide a motor controller for a blower in gas-burning appliances. More specifically, embodiments of the motor controller described herein operate a blower to sufficiently exhaust combustion gasses and to achieve high-efficiency combustion and heat exchange. Embodiments of the motor controller described herein utilize pressure differential measurements across a non-variable airflow restriction within the gas-burning appliance to adjust a variable motor speed at which the blower is operated. Measured pressure differential is compared to a pressure differential set-point to adjust motor speed using a proportional-integral (PI) control loop. Motor controllers described herein achieve sufficient exhaust and high-efficiency combustion and heat exchange regardless of inlet duct length and further regardless of exhaust duct length.
Gas-burning appliance 100 further includes a motor 116 for turning blower 112. Gas-burning appliance 100 further includes a motor controller 118 and a sensor 120. Motor controller 118 controls motor 116 by transmitting a control signal representing a variable motor speed. The control signal may be implemented, for example, and without limitation, as a square wave. In certain embodiments, the control signal may undergo pulse width modulation to affect a change in duty cycle that represents a motor speed set-point. Sensor 120 may include, for example, and without limitation, a pressure sensor that approximates airflow 104 by measuring a pressure differential across a portion of duct 102.
Airflow 104 enters gas-burning appliance 100 at inlet duct 106, which is illustrated by inlet airflow 122. Airflow 104 is generated by the turning of blower 112 by motor 116 to draw-in inlet airflow 122. Inlet duct 106 has a length and, in certain embodiments, one or more turns in its path to burner 108. The length and turns of inlet duct 106 at least partially define the airflow restriction it poses to airflow 104. Burner 108 carries out combustion of inlet airflow 122 and a fuel, producing combustion gasses that may include NOx gasses. Combustion gasses pass through heat exchanger 110, where heat is transferred from the combustion gasses to another medium, such as, for example, and without limitation, water. Airflow 104 carries the combustion gasses from heat exchanger 110, through blower 112, and through exhaust duct 114. Exhaust duct has a length and, in certain embodiments, one or more turns in its path. The length and turns of exhaust duct 114 at least partially define the airflow restriction it poses to airflow 104. Combustion gasses are vented from exhaust duct 114 as exhaust airflow 124.
Motor controller 118 controls motor 116, at least, by transmitting a control signal representing a variable motor speed. Motor controller 118 determines a motor speed set-point based on a pressure differential measured by sensor 120. Sensor 120 measures a pressure differential across a non-variable airflow restriction. A measured pressure differential across a non-variable airflow restriction generally does not change from installation to installation. Conversely, airflow 104 can change from installation to installation based on at least the respective lengths and paths of inlet duct 106 and exhaust duct 114. Changes in airflow 104 are reflected in the pressure differential measured by sensor 120, however, because sensor 120 measures the pressure differential across a non-variable airflow restriction, any changes in measured pressure differential are attributed to variables external to that non-variable airflow restriction, such as, for example, respective lengths and paths of inlet duct 106 and exhaust duct 114.
In the embodiment of
Motor controller 118 adjusts the variable speed of motor 116 by setting a motor speed set-point via a control signal. The control signal may include a pulse width modulated square wave having a duty cycle that represents the motor speed set-point. Motor controller 118 computes the motor speed set-point using a PI control loop. In alternative embodiments, motor controller 118 may utilize a proportional-integral-derivative (PID) control loop or any other suitable control scheme for computing the motor speed set-point. Within the PI control loop, the difference between the measured pressure differential across non-variable airflow restriction 130 and the pressure differential set-point is utilized as an error value upon which the proportional term and the integral term of the PI control loop operate. The output of the PI control loop is the motor speed set-point, i.e., the desired motor speed to turn blower 112 and to generate airflow 104. The PI control loop ensures the measured pressure differential converges on the pressure differential set-point and, more specifically, airflow 104 converges on the desired airflow 104 that is sufficient to achieve sufficient ventilation of combustion gasses through exhaust duct 114, high-efficiency combustion in gas burner 108, and high-efficiency heat transfer in heat exchanger 110.
Similar to the embodiment of
Motor controller 118 controls motor 116, at least, by transmitting a control signal representing a variable motor speed. Motor controller 118 determines a motor speed set-point based on a pressure differential measured by sensor 120. Sensor 120 measures a pressure differential across non-variable airflow restriction 310. The measured pressure differential across non-variable airflow restriction 310 generally does not change from installation to installation. Conversely, airflow 104 can change from installation to installation based on at least the respective lengths and paths of inlet duct 106 and exhaust duct 114. Changes in airflow 104 are reflected in the pressure differential measured by sensor 120, however, because sensor 120 measures the pressure differential across non-variable airflow restriction 310, any changes in measured pressure differential are attributed to variables external to non-variable airflow restriction 310, such as, for example, respective lengths and paths of inlet duct 106 and exhaust duct 114.
In the embodiment of
Motor controller 118 adjusts the variable speed of motor 116 by setting a motor speed set-point via a control signal. The control signal may include a pulse width modulated square wave having a duty cycle that represents the motor speed set-point. Motor controller 118 computes the motor speed set-point using a PI control loop. In alternative embodiments, motor controller 118 may utilize a proportional-integral-derivative (PID) control loop or any other suitable control scheme for computing the motor speed set-point. Within the PI control loop, the difference between the measured pressure differential across non-variable airflow restriction 310 and the pressure differential set-point is utilized as an error value upon which the proportional term and the integral term of the PI control loop operate. The output of the PI control loop is the motor speed set-point, i.e., the desired motor speed to turn blower 112 and to generate airflow 104. The PI control loop ensures the measured pressure differential converges on the pressure differential set-point and, more specifically, airflow 104 converges on the desired airflow 104 that is sufficient to achieve sufficient ventilation of combustion gasses through exhaust duct 114, high-efficiency combustion in gas burner 108, and high-efficiency heat transfer in heat exchanger 110.
Unlike the embodiments of
Motor controller 118 controls motor 116, at least, by transmitting a control signal representing a variable motor speed. Motor controller 118 determines a motor speed set-point based on a pressure differential measured by sensor 120. Sensor 120 measures a pressure differential across heat exchanger 110 and gas burner 108, otherwise referred to as a non-variable airflow restriction 420. Non-variable airflow restriction 420 is composed of non-variable airflow restrictions 426 and 428, which respectively correspond to gas burner 108 and heat exchanger 110. The measured pressure differential across gas burner 108 and heat exchanger 110 generally does not change from installation to installation. Conversely, airflow 104 can change from installation to installation based on at least the length and path of exhaust duct 114. Changes in airflow 104 are reflected in the pressure differential measured by sensor 120, however, because sensor 120 measures the pressure differential across non-variable airflow restriction 420, any changes in measured pressure differential are attributed to variables external to non-variable airflow restriction 420, such as, for example, the length and path of exhaust duct 114.
In the embodiment of
Motor controller 118 adjusts the variable speed of motor 116 by setting a motor speed set-point via a control signal. The control signal may include a pulse width modulated square wave having a duty cycle that represents the motor speed set-point. Motor controller 118 computes the motor speed set-point using a PI control loop. In alternative embodiments, motor controller 118 may utilize a proportional-integral-derivative (PID) control loop or any other suitable control scheme for computing the motor speed set-point. Within the PI control loop, the difference between the measured pressure differential across non-variable airflow restriction 420 and the pressure differential set-point is utilized as an error value upon which the proportional term and the integral term of the PI control loop operate. The output of the PI control loop is the motor speed set-point, i.e., the desired motor speed to turn blower 112 and to generate airflow 104. The PI control loop ensures the measured pressure differential converges on the pressure differential set-point and, more specifically, airflow 104 converges on the desired airflow 104 that is sufficient to achieve sufficient ventilation of combustion gasses through exhaust duct 114, high-efficiency combustion in gas burner 108, and high-efficiency heat transfer in heat exchanger 110.
Processor 510 periodically receives pressure differential measurements from sensor 120 and gains access to the pressure differential set-point. Processor 510, in certain embodiments, is configured to implement a PI control loop for computing a motor speed set-point for motor 116. Processor 510 computes the motor speed set-point based on a difference between a time-average pressure differential and the pressure differential set-point. Processor 510 then generates a control signal for motor 116 and may further include a pulse width modulation component to adjust the duty cycle of the control signal to represent the motor speed set-point. Processor 510, in certain embodiments, updates the motor speed set-point for motor 116 on a periodic basis. For example, in one embodiment, processor 510 updates the motor speed set-point once every 10 seconds. In alternate embodiments, processor 510 is configured to update the motor speed set-point at any suitable frequency that produces stable control and convergence of the measured pressure differential to the pressure differential set-point.
Motor controllers described herein operate a blower to sufficiently exhaust combustion gasses and to achieve high-efficiency combustion and heat exchange. Embodiments of the motor controller described herein utilize pressure differential measurements across a non-variable airflow restriction within the gas-burning appliance to adjust a variable motor speed at which the blower is operated. Measured pressure differential is compared to a pressure differential set-point to adjust motor speed using a PI control loop. Motor controllers described herein achieve sufficient exhaust and high-efficiency combustion and heat exchange regardless of inlet duct length and further regardless of exhaust duct length.
The methods and systems described herein may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect may include at least one of: (a) operating a blower for a gas-burning appliance at a variable speed; (b) controlling airflow through a gas-burning appliance based on measured pressure differentials; (c) ensuring proper ventilation of combustion gasses from the gas-burning appliance; (d) improving efficiency of combustion and heat transfer in the gas-burning appliance; (e) simplifying selection, installation, and configuration of gas-burning appliances by eliminating the duct-length variable; (f) simplifying selection, installation, and configuration of gas-burning appliances by eliminating considerations of line voltage fluctuations and altitude; and (g) achieving proper ventilation and high-efficiency regardless of duct lengths.
Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor, processing device, or controller, such as a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field programmable gate array (FPGA), a digital signal processing (DSP) device, and/or any other circuit or processing device capable of executing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processing device, cause the processing device to perform at least a portion of the methods described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the terms processor, processing device, and controller.
In the embodiments described herein, memory may include, but is not limited to, a computer-readable medium, such as a random access memory (RAM), and a computer-readable non-volatile medium, such as flash memory. Alternatively, a floppy disk, a compact disc—read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, an operator interface monitor.
As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by a processor, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are examples only, and are thus not limiting as to the types of memory usable for storage of a computer program.
The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein.
This written description uses examples to provide details on the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
