US20090317756A1

US20090317756A1 - Digital high turndown burner

Info

Publication number: US20090317756A1
Application number: US12/206,399
Authority: US
Inventors: James Hoverson; James Jagers
Original assignee: Mestek Inc
Current assignee: Mestek Inc
Priority date: 2008-06-18
Filing date: 2008-09-08
Publication date: 2009-12-24
Also published as: CA2709802A1; MX2010009273A; CA2709802C; WO2009154603A1

Abstract

A gas burner system for a heating device includes a burner, a valve assembly for controlling a flow of fuel to the burner, a blower assembly for directing air to the burner, and a control system. The burner includes one or more burner plates for facilitating the mixture of air and fuel to be combusted in a combustion chamber. The control system is configured to independently control the valve assembly and the blower assembly according to a control profile, for generating a plurality of air/fuel mixtures each configured for operation of the burner at a different firing rate. By mapping the characteristics of both the gas valve and the combustion blower independently, the burner system is assured of operating at the proper air/fuel mixture over a very wide range of firing rates, with a turndown ratio of 30:1 or greater, and within ANSI safety and performance standards.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of application Ser. No. 12/141,418 filed on Jun. 18, 2008, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to heating devices and, more particularly, to gas fueled, indirect-fired burners.

BACKGROUND OF THE INVENTION

Gas burners, incorporated for example into indirect heating devices, utilize the combustion of a gas or similar fuel (e.g., propane, natural gas, or fuel oil) for heating a work substance, oftentimes a flowable substance such as air or water. For example, heated air may be directed into the interior of a home for general comfort heating purposes. In operation, natural gas or other fuel is controllably forced through a nozzle or jet portion of the burner, where it is intermixed (most typically) with air, forming a gas spray or aerosol for enhancing combustion. In the case of an indirect heater, the gas spray is ignited, and the combustion product (heated air/plasma) is directed into a heat exchanger, where the energy produced by the combustion process is transferred to the work substance to be heated. The combustion exhaust is then moved to an exhaust exit, possibly after one or more recirculation steps or the like to further recapture heat from the combustion product.
For a gas heating device, the amount of fuel burned per unit time (e.g., liters or btu per hour) is referred to as the firing rate. Simple heating devices are configured to run at a single firing rate, with the heater being cycled on and off in cases where it is desired to achieve an average output that is less than the maximum possible output. If a heating device is capable of steady state operation at two or more firing rates within acceptable combustion parameters (e.g., combustion byproducts are kept to below a desired level, according to ANSI safety and performance standards or the like), this is referred to in the industry as “turndown.” In other words, while keeping within acceptable operational parameters, it is possible to “turn down” the heating device from the maximum possible firing rate to one or more lower firing rates. The ratio of the highest firing rate to the lowest firing rate in a heating device, at steady state operation and keeping within acceptable operational parameters, is referred to as the “turndown ratio” of the heating device.
High turndown ratios are desirable for achieving greater levels of efficiency in a heating device. For example, although it is possible to vary the average actual heat output of a single firing rate heating device by cycling the device between on and off operational modes, this can result in low levels of combustion efficiency, higher levels of fuel use per unit heat output, and a greater level of undesirable combustion byproducts. Among other reasons, this is because the conditions in the combustion chamber vary widely over time as the combustion process is turned on and off. When combustion is ongoing, the gas spray produced by the burner is consistent, and the temperature in the combustion chamber is high, factors that favor efficient operation. However, when combustion is turned off or restarted, this results in temperature variations in the combustion chamber, and variances in the quality of the gas spray input, factors that inhibit efficient operation.
High turndown burners exist in the industry, typically for use in process heating, that is, for heating a work substance for an industrial or manufacturing process. Current technology tends to use techniques such as pre-mixing of the combustion air and gas mixture to assure a proper air/fuel ratio prior to ignition, ceramic liners or “targets” that retain heat in the combustion chambers to assure ignition at low gas flow rates, multiple individual burners that are “staged” using electromechanical or electronic controls, rudimentary mechanical linkages between the gas valve and a damper on the combustion air blower, or simple electronic controls that modulate the gas valve and blower together but are auxiliary or add-on systems to the basic HVAC unit controls. The published range of operation of any of these systems tends to peak at a turndown ratio of 20:1 for a single burner, again, referring to the ratio of highest firing rate to lowest firing rate. (Higher turndown ratios than this may be achieved in a heating device by using a multiple burner approach, where the turndown ratio is directly related to the number of burners. However, such devices are not directly relevant to the present case, since each individual burner has a low or unitary turndown ratio.)
One of the limiting factors in achieving higher turndown ratios is the loss of control of the air/fuel mixture at low flow rates. Failing to achieve the theoretically ideal fuel/air mixture can result in emissions of carbon monoxide, aliphatic aldehydes, nitrous oxides, and other contaminants that are judged to be harmful. Producing those contaminants will cause a burner design to fail ANSI (American National Standards Institute) safety and performance standard tests. A second limitation of these designs is the inability to consistently ignite or maintain combustion of the air/fuel mixture at very low flow rates. The ability to do so is also part of the ANSI safety and performance standards.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a burner system having a very high turndown ratio, typically 30:1, 60:1, or 90:1 that meets all applicable safety and performance standards across an entire range of firing rates.
It is another object of the present invention to provide a gas burner system having a very high turndown ratio, typically of 90:1 or greater, that meets both ANSI safety and performance standards (or similar standards) across an entire range of firing rates.
To achieve this and other objects, an embodiment of the present invention relates to a gas burner system for a heating device, e.g., an air heater. The system includes a burner, a valve assembly for controlling a flow of fuel to the burner, a blower assembly for directing air to the burner, and a control system. The burner includes one or more burner plates for facilitating the mixture of air and fuel to be combusted in a combustion chamber portion of the heating device. The control system is configured to independently control the valve assembly and the blower assembly according to a control profile, for generating a plurality of air/fuel mixtures each for operation of the burner at a different firing rate, with a turndown ratio of 30:1, 60:1, or 90:1 and higher.
In another embodiment, the control profile in effect maps an optimal range of operation of the gas valve assembly to an optimal range of operation of the blower assembly. The control profile is generated by testing the gas burner system across the operational ranges (or portion thereof) of both the valve assembly and the blower assembly, which enables data to be captured for any non-linear operational modes. Thus, the burner system is assured of operating at the proper air/fuel mixture over a very wide range of firing rates, i.e., for each air/fuel mixture, the burner system/heating device operates within ANSI safety and performance standards or similar official standards in countries other than the United States.
In another embodiment, the control system receives a control signal that indicates a desired or designated firing rate. For example, the control signal might be generated by an HVAC system, based on a user control input of a desired heat output. The control system cross-references the control signal to the control profile, for determining a first operational signal to apply to the valve assembly, and another, second operational signal to apply to the blower assembly. Application of the respective operational signals to the valve assembly and the blower assembly results in the generation of the proper air/fuel mixture for the firing rate designated by way of the control signal.
In another embodiment, the burner includes two burner or aeration plates. The burner plates are arranged in a generally V-shaped configuration, and each has a number of circular aeration apertures for facilitating the mixture of air and fuel. the apertures are sized so as to help with achieving the proper air/fuel mix across a wide range of firing rates.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

FIG. 1 is a perspective view of a burner system according to an embodiment of the present invention;

FIG. 2 is a top plan view of the burner system;

FIG. 3 is a side elevation view of the burner system;

FIG. 4 is a front elevation view of the burner system;

FIG. 5 is a cross-section view of the burner system, taken generally along line 5-5 in FIG. 1;

FIG. 6 is a perspective view of a burner plate portion of the burner system;

FIG. 7 is a schematic view of the burner system;

FIGS. 8 and 9 are schematic views of a control profile; and

FIGS. 10A-10C are various schematic views illustrating one method for determining the control profile.

DETAILED DESCRIPTION

With reference to FIGS. 1-10C, an embodiment of the present invention relates to a digital high-turndown burner system 20, for use as part of an indirect-fired heating device 22, e.g., for comfort or make-up air heating. The system 20 includes a burner unit 24 attached to and disposed within a housing 26, a gas valve assembly 28 for controlling a flow of natural gas or other fuel 30 to the burner unit 24, and a blower assembly 32 attached to the housing 26 for directing air 34 to the burner unit 24. The high-turndown burner system 20 also includes a control system 36, which independently controls the gas valve assembly 28 and blower assembly 32 according to a control profile 38. The control profile 38 maps an operational range 40 of the gas valve assembly to an operational range 42 of the blower assembly, for generating a plurality of air/fuel mixtures 44 each for operation of the burner at a different firing rate. The control profile 38 is customized according to the particular physical characteristics of the burner system 20, such that: (i) the ratio of highest firing rate of the burner system 20 to the lowest firing rate (i.e., the turndown ratio) is 30:1, 60:1 or 90:1 and greater; and (ii) the burner system 20 meets ANSI safety and performance standards across the entire turndown ratio ranges. In particular, for each air/fuel mixture generated according to the control profile 38 and combusted in the heating device 22, the air/fuel mixture is consistently ignited, combustion is consistently maintained, and harmful combustion exhaust byproducts are kept below designated limits.
With reference to FIG. 7 initially, and as mentioned above, the burner system 20 will typically be used as part of an indirect-fired heating device 22. Most such heating devices include a heat exchange unit 48, a combustion chamber 46 inside or downstream from the heat exchange unit 48, and an exhaust system 50. In operation, an air/fuel mixture from a burner system (such as the system 20 described herein) is ignited in or just before entering the combustion chamber 46. The combustion product is directed to the combustion chamber 46, where it heats a working substance outside the heat exchange unit. For example, the working substance might be ambient air, kept separate from the combustion air, which is heated and directed to a particular location for comfort purposes. The combustion exhaust is then vented through the exhaust system 50 (which may simply be a vent or passage) to ambient.
The housing 26 is a generally rectangular enclosure, made of sheet metal or the like, which is connected directly to the end of the combustion chamber 46. The blower assembly 32 includes a blower fan 52, an AC or other motor 54, and a blower motor controller 56. An output shaft of the motor 54 rotatably drives an impeller portion of the fan 52, which is located inside a fan housing 58 connected to the burner housing 26, for moving air from outside the fan housing 58 (and outside the burner housing) to inside the burner housing 26. The blower motor controller 56 has a control input for receiving a blower operational signal 60 from the control system 36, e.g., a 0-10 VDC signal, and a power output terminal electrically connected to the blower motor 54. The controller 56 outputs a PWM (pulse width modulation) power signal to the motor 54, for controlling the speed of the motor, based on the blower operational signal 60 as received from the control system. For example, it may be a linear relationship, such that a 0 V operational signal 60 from the control system 36 corresponds to a “motor off” condition, and a 10 V operational signal 60 from the control system 36 corresponds to a maximum speed of the motor. Typically, the power output terminal of the blower motor controller 56 will include from 2 to 3 electrical outputs, each of which is attached to one of the electrical terminals of the motor by an electrical line or cable. The PWM power signal applied to the motor by the blower motor controller 56 includes one or more separate electrical power signals applied to each of these cables/lines, according to a standard power waveform for powering the type of motor 54 in question. Thus, in operation, the blower motor controller 56 converts the 0-10 VDC blower operational signal 60 into an appropriate proportional power output signal for power the fan motor 54.
The gas valve assembly 28 includes an AC gas valve actuator 62 and a ball-type valve 64, which is interfaced with a gas supply line 66. The gas supply line 66 runs from a gas main (or other gas source), through the housing 26, and into the burner unit 24, as discussed in more detail below. The ball-type valve 64 is operably disposed in the path of the supply line 66, and the gas valve actuator 62 positions the ball-type valve 64 to control the flow rate of gas 30 through the supply line 66 and into the burner unit 24. The gas valve actuator 62 receives a valve operational signal 68 from the control system 36, which governs the position of the ball-type valve 64 and therefore the flow rate of gas into the burner. Like the blower operational signal 60, the valve operational signal 68 may be a 0-10 VDC signal, with the gas valve actuator 62 controlling the valve 64 proportional to the level of the received signal 68. For example, if the valve actuator 62 receives a 0 VDC signal 68 from the control system 36, the gas valve actuator 62 closes the valve 64 (or maintains the valve in a closed state), and if the valve actuator 62 receives a 10 VDC signal 68 from the control system 36, the gas valve actuator 62 opens the valve 64 to a fully open state. The gas supply line and/or gas valve assembly may be outfitted with other standard components for safety or operational purposes, such as a gas pressure regulator (not shown).
Turning in particular to FIGS. 4-6, the burner unit 24 is a cast “line burner” that includes upper and lower stainless steel aeration plates 70 a, 70 b, two side plates 72 a, 72 b, and a gas inlet manifold 74. The manifold 74 has a generally tubular main body 76, each end of which is outfitted with a mounting flange 78. At least one end of the main body 76 is open, for providing an inlet aperture 80 for the passage of natural gas 30 or other fuel. A longitudinal slot 82 extends partway down one side of the main body 76, for providing a passageway that extends from the interior of the body 76 through to the space or area located between the aeration plates 70 a, 70 b. The upper aeration plate 70 a, 70 b includes a first planar portion 84 attached to the manifold main body 76 just above the longitudinal slot 82. A second planar portion 86, either angled slightly with respect to the first planar portion 84 or coplanar therewith, is integrally attached to the trailing edge of the first planar portion 84, and extends towards the outlet end of the burner system, in the direction of the combustion chamber 46. A third planar portion 88 is integrally attached to the trailing edge of the second planar portion 86, but is angled significantly upwards, e.g., 30-50° with respect to the second planar portion 86, so as to meet an upper inner surface of an outlet chute portion 90 of the housing 26. The lower aeration plate 70 b is configured symmetrically to the upper aeration plate 70 a, but is angled downwards for extending from just below the longitudinal slot 82 to a lower inner surface of the outlet chute 90. As indicated in the figures, the upper and lower aeration plates 70 a, 70 b are generally oriented relative to one another to form a “V”-like shape. Additionally, each aeration plate 70 a, 70 b is provided with a plurality of circular aeration holes or apertures 92, 94. Each of a first set of the aeration apertures 92 is located either in the trailing edge area of the second planar portion 86 of the aeration plate, or in the third planar portion 88. Each of the second set of the aeration apertures 94 is located generally in the leading area of the second planar portion 86 of the aeration plate, or in the first planar portion 84. In each aeration plate 70 a, 70 b, there is an area of the aeration plate, between the trailing line of small-diameter aeration apertures 94 and the leading line of large-diameter aeration apertures 92, in which the aeration plate has no apertures.
The aeration plates 70 a, 70 b are sized according to the desired heat capacity and/or gas input range of the burner system. For example, a 200-400 MBH burner system might utilize 6-inch (width) aeration plates, and a 600 MBH burner system might utilize 12-inch aeration plates. (“MBH” refers to thousands of BTU's per hour, e.g., 1 MBH=1 MBTU/hour, where “MBTU” is a standard abbreviation for 1000 BTU's.)
The burner unit side plates 72 a, 72 b are attached to and extend between the side edges of the aeration plates 70 a, 70 b and the main body 76 of the manifold 74. Thereby, the side plates 72 a, 72 b enclose the sides of burner unit, for facilitating the passage of air from the interior of the housing 26 (e.g., air blown therein by the blower assembly 32) through the aeration apertures 92, 94 of the aeration plates 70 a, 70 b. The entire burner unit 24 is disposed in the housing 26 as best shown in FIG. 5. As indicated, the manifold 74 is connected to and extends between the two side walls of the housing 26. The aeration plates 70 a, 70 b and side plates 72 a, 72 b extend from the manifold 74 to the inner surface area of the housing chute 90. The trailing edges of all four of the aeration plates 70 a, 70 b and side plates 72 a, 72 b are attached to the inner surface of the chute 90, such that the only fluidic passageway (e.g., passage for air) from the interior of the housing 26 to the exit end of the chute 90 (e.g., the end of the chute that lies in the combustion chamber) is through the aeration apertures 92, 94 of the aeration plates 70 a, 70 b. The mounting flange 78 of the inlet aperture end 80 of the manifold 74 is attached to the gas supply line 66 by way of one or more adapters, gaskets, or the like 96 that create a gas-tight connection between the supply line 66 and inlet aperture 80, i.e., the purpose of the gaskets 96 is to prevent gas from leaking into the housing interior.
As should be appreciated, the chute 90 is a rectangular extension of the housing 26, made of sheet metal or otherwise, which provides an exit from the housing and burner unit for passage of the combustion product into the combustion chamber 48. Because the chute 90 “sticks out” from the housing proper, it also acts to project the exit or trailing end of the burner unit, defined by the trailing ends of the aeration plates and side plates attached to the inner surface of the chute, further into the combustion chamber 46 than if the burner terminated coextensively with the housing side walls.
In general operation (without yet referring to the control profile 38, which is discussed in more detail below), the control system 36 receives a control signal 98 from an HVAC controller 100 or otherwise. The control signal 98 contains information relating to a desired heat output level of the heating device 22. For example, the control signal 98 may be a DC voltage signal having a range from “Vmin” to “Vmax,” with the intended or designated heat output of the heating device being linearly proportional to the DC voltage level of the signal 98. Thus, “Vmin” might indicate a minimum heating output level, or that the heating device remain or enter a “turned off” state, whereas “Vmax” might indicate a maximum heating output level of the heating device. Based on the control signal 98, the control system 36 outputs a blower operational signal 60 and a valve operational signal 68, for independent control of the blower assembly 32 and the gas valve assembly 28, respectively, so as to produce the desired heat output of the heating device 22.
Based on the blower operational signal 60 received from the control system 36, the blower assembly motor controller 56 powers the motor 54 for operation of the blower fan 52. The fan 52 draws in air 34 from an ambient external source, and blows it into the interior of the housing 26. Because the aeration apertures 92, 94 of the aeration plates 70 a, 70 b represent the only egress for air 34 in the housing (considering the positive pressure generated by the fan output), the air is forced through the aeration apertures 92, 94 and into the space between the two aeration plates 70 a, 70 b. Concurrently, based on the valve operational signal 68 received from the control system 36, the gas valve actuator 62 operates the ball-type valve 64 for allowing natural gas or other fuel 30 to flow through the supply line 66 at a particular rate. The gas 30 passes into the interior of the burner manifold 74, where it is directed through the longitudinal slot 82 for passage into the space located between the V-oriented aeration plates 70 a, 70 b. The air 34 mixes with the gas 30 to form an air/fuel mixture 44, and is ignited by a standard ignition system 102. The ignition system may include, for example, a spark igniter, a flame rod, and/or the like. The ignited air/fuel mixture 44 then passes out the exit end of the burner system, out of the chute 90, and into the combustion chamber 46 for transferring heat energy to the working substance in the heat exchanger. The aeration plates 70 a, 70 b generally facilitate the mixing of air and fuel in the burner, before, during, and after ignition, and it has been found that the particular aeration aperture size and pattern discussed above enhances this mixing effect across a very wide range of air and fuel flow rates.
As noted above, the control profile 38 in effect maps the operational ranges of the gas valve assembly 28 and the blower assembly 32 to one another, for operation of the burner system at the proper air/fuel mixture over a very wide range of flow rates. As has been shown in many cases of prior development of burner technology, maintaining a proper air/fuel mixture is not a linear relationship. This is due to the non-linear nature of fluid flows through valves and fans. By “mapping” the characteristics of both the gas valve assembly and the blower assembly in effect independently, and then embedding those characteristics in the control system, the burner is assured of operating at the proper air/fuel mixture over a very wide range of flows. The control system uses two independent output channels 60, 68 to achieve this result.
As implemented, the control profile 38 can take several forms. In a first, with reference to FIG. 8, the control profile is a lookup table mapping the range of HVAC control signals 98 to a range of gas valve assembly operational signals 68 and to a range of blower assembly operational signals 60. Thus, for each of a plurality of discreet values of the control signal, from “Vmin” to “Vmax” divided into, e.g., 0.1 V intervals, there is a corresponding pair 104 of signals that include a valve operational signal 68 and a blower assembly operational signal 60. For example, as shown in FIG. 8, the maximum control signal Vmax correlates to a valve operational signal “m” VDC and a blower operational signal “x” VDC, where m and x are within the range of operational signals for the gas valve assembly and blower assembly, respectively. Similarly: (i) the minimum control signal Vmin correlates to another valve operational signal “n” and another blower operational signal “y”; and (ii) each intermediate control signal, e.g., a control signal “A” volts, where Vmin<A<Vmax, correlates to an intermediate valve operational signal “B” and a blower operational signal “C,” where n (and B) and y (and C) are within the range of operational signals for the gas valve assembly and blower assembly, respectively. The valve operational signals m and n may correspond to the maximum and minimum operational signals, respectively, but this is not necessarily the case. The same is true for the blower assembly operational signals.
As shown in FIG. 8, each pair 104 of gas valve and blower assembly operational signals results in a particular air/fuel mixture 44 for a designated firing rate, e.g., valve signal B and blower signal C result in an air/fuel mixture “d.”¹(Generally speaking, the firing rate is proportional to the received control signal 98, so that the higher the control signal, the greater the rate of gas or other fuel burned in the burner system and the greater the heat output of the heating device.) In operation, the control system 36 receives a control signal 98 from the HVAC controller 100 or otherwise. The control system 36 cross-references the received control signal 98 to the control profile 38, which results in a pair of operational signals 60, 68, one for the gas valve assembly and one for the blower assembly, that correlate to the received control signal. The operational signals are then applied to the gas valve assembly and blower assembly, which output gas and air into the burner unit 24. The burner unit 24 mixes the gas and air, thereby producing an air/fuel mixture 44, which is ignited and combusted in the combustion chamber 46 for heat exchange. The control profile 38 is configured for producing a high turndown ratio for the single-burner unit 24, e.g., the ratio of the highest firing rate (typically corresponding to Vmax and air/fuel mixture “e” in FIG. 8) to the lowest firing rate (typically corresponding to Vmin and air/fuel mixture “f” in FIG. 8) is 30:1, 60:1 or even 90:1 and greater. Additionally, the control profile 38 is configured so that across the entire turndown range, for each air/fuel mixture generated according to the control profile 38 and combusted in the heating device 22, the burner unit and heating device meet ANSI safety and performance standards, namely, the air/fuel mixture is consistently ignited, combustion is consistently maintained, and harmful combustion exhaust byproducts are kept below designated limits.
FIG. 9 shows a sample graph of the range of blower assembly and valve assembly operational signals, such as those that would be found in a lookup table as in FIG. 8. As indicated, it will typically be the case that the relationship between the blower assembly operational signals and the valve assembly operational signals is non-linear, which enables the system to meet ANSI safety and performance standards across all the firing rates of a very high turndown ratio.
Whereas FIG. 8 shows a control profile that maps each value in a range of control signals 98 to a pair of blower assembly and valve assembly operational signals, the control profile may be arranged in other manners. For example, each value in the range of control signals may be mapped to a particular gas valve assembly flow rate and a particular blower assembly flow rate. In turn, the range of possible flow rates for the gas valve assembly, and the range of possible flow rates for the blower assembly, are each mapped to a set or range of operational signals. Thus, in operation: (i) based on a received control signal, the control system correlates the control signal to a gas valve assembly flow rate and to a blower assembly flow rate; (ii) based on the gas valve assembly flow rate, the control system determines a gas valve assembly operational signal for achieving that flow rate, based on a graph, lookup table, algorithm calculation, etc.; (iii) based on the blower assembly flow rate, the control system determines a blower assembly operational signal for achieving that flow rate, based on a graph, lookup table, algorithm calculation, etc.; and (iv) the blower assembly operational signal and gas valve operational signal are applied to the blower assembly and gas valve assembly, respectively. As should be appreciated by way of this example, the term “control profile” as used herein therefore includes any mapping or other relationship or group of relationships, such as graphs, lookup tables, databases, algorithms, or the like, for determining a blower assembly operational signal and gas valve operational signal for each of a plurality of possible control signal values, again, for operation of the burner unit/heating device according to ANSI safety and performance standards across a very high turndown ratio, e.g., 30:1, 60:1 or even 90:1 and greater.
In a preferred embodiment, the gas valve operational signal is the primary control signal and the blower operational signal is secondary. That is, the control system employs the gas valve operational signal before the blower operational signal when generating air/fuel mixtures. It will be appreciated, however, that either the gas or blower operational signals may be employed as the primary signal without departing form the scope of the invention. It will also be appreciated that the sequence of the claimed components, in particular, the blower and valve assemblies, may be varied without departing from the present invention.
Moreover, while the present invention facilitates very high turndown ratios of 30:1, 60:1, or 90:1 and greater, other intermediate ratios, e.g., 40:1, 50:1 or 70:1, are possible. As stated, the inventive system allows for very high turndown ratios while meeting or exceeding both ANSI safety and performance standards across the entire ratio.
As mentioned above, because blower assemblies, gas valve assemblies, burner units, combustion chambers, etc. all involve the control, flow, and/or mixing of one or more fluids (e.g., gas/fuel or air) in a confined space with a varying geometry (e.g., flow through a valve opening), heating devices of the type disclosed herein are non-linear systems. Thus, the combustion output of the heating device is not a linear function of the control inputs, across the operational range of the heating device. In certain heating devices, non-linear effects are minimized by having a small turndown ratio. For achieving a high-turndown ratio, however, the burner system of the present invention takes into account non-linear system effects. Thus, despite the fact that very low flow rates may be especially non-linear, the system of the present invention is able to achieve such low flow rates, and thereby achieve a very high turndown ratio (again, while meeting ANSI standards across the entire range of operation).
Because non-linear flow characteristics are dependent on the particular geometry and configuration of a burner system, the control profile 38 is tailored for individual use with the burner system and/or heating device. (In other words, for different burner systems, each system has its own customized control profile 38.) To prepare a control profile 38 for a particular burner system or heating device, a prototype (i.e., physical implementation) of the heating device is first constructed, according to a desired heat capacity, size, operational characteristics, and the like. Then, the prototype heating device is tested in operation, across a designated, wide range of fuel and air flow rates, all the while collecting data points relating to the combustion product or output of the heating device, in terms of heat output, combustion exhaust, and other combustion performance characteristics. If the measured data points for a particular fuel and air flow rate fall outside a desired range (e.g., ANSI safety and performance standards), that fuel and air flow rate is not used as part of the control profile. Instead, the control profile is an amalgam/grouping of those air/fuel data points that exhibit the best operational characteristics for providing the designated range of heat output.
The process is explained in more detail in FIGS. 10A-10C. As indicated at Step 200 in FIG. 10A, and as mentioned above, for generating a control profile 38, a prototype heating device is first constructed. At Step 202, the heating device is interfaced with a standard testing and data acquisition system. The testing and data acquisition system includes a plurality of sensors disposed in the heating device at different locations of interest, and a computer system (with appropriate testing and data logging software) operably connected to the sensors through a sensor interface device or the like. The sensors are configured to measure or sense various operational characteristics of the heating device while in use, such as: (i) levels of CO (carbon monoxide) exiting the exhaust, in PPM or otherwise; (ii) actual gas/fuel input into the burner unit; (iii) actual air input; (iv) levels of NO (nitric oxide) and/or NOx (other mono-nitrogen oxides) in the exhaust; (v) oxygen levels; (vi) heat output; and the like. Also measured is the operational signal 68 applied to the gas valve assembly, and the operational signal 60 applied to the blower assembly. The computer system monitors sensor output, records data values received from the sensors, and organizes the data for further use. Suitable testing and data acquisition systems are available from National Instruments.
Once the prototype heating device is interfaced with the testing and data acquisition system, it would be possible to commence testing by running the heating device at every possible iteration and combination of possible operational signals 60, 68. This could be done by dividing the gas valve operational signal into a plurality of testing points, such as 100 or 1000 divisions between 0-10 VDC. Each test signal would then be sequentially applied to the gas valve assembly, e.g., 0 V, 0.1 V, 0.2 V, and so on. For each of these input signals, the blower assembly would be run across its entire operational signal range, again, according to a designated level of granularity, such as 100 or 1000 divisions between 0-10 VDC. Thus, for a 0.1 V gas valve operational signal, the blower assembly would be sequentially run according to a 0 V, 0.1 V, 0.2 V, 0.3 V signal and so on. At each iteration, the testing and data acquisition system would record data received from the sensors.
Because testing the prototype heating device in this manner would generate a very large set of data, e.g., 1,000 points of iteration for two 0-10 VDC signals each divided into 100 increments, most of which would not be useful, testing may be targeted or focused by first preparing a theoretical or projected characterization curve of burner unit performance, as in Step 204 in FIG. 10A. Here, the theoretical characterization curve is estimated as being linear, with data points being assigned to the curve based on the heat capacity of the burner unit/heating device and theoretical relationships between desired heat output, the fuel rate needed to achieve such a heat output, and the air rate needed for complete combustion at the fuel rate. Thus, for example, with reference to FIG. 10B, a theoretical or projected characterization curve might be populated by first assuming the desired heat output is linearly related to the control signal 98 and to the gas valve operational signal 68, i.e., a heat output of zero corresponds to a control signal of 0 VDC and a valve signal of 0 VDC (point “A” in FIG. 10B), and a max heat output corresponds to a control signal of 10 VDC and a valve signal of 10 VDC (point “B” in FIG. 10B), representing the maximum gas flow rate. The blower operational signal data is then determined by assuming a linear relationship between air flow rate and blower operational signal, and calculating the theoretical air flow rate needed for combustion at one or more of the gas flow rates. For example: (i) it could be assumed that the blower should be in an “off” state when the gas flow rate is zero (data point {min, A} in FIG. 10B); (ii) calculate the theoretical air flow rate needed for the maximum gas flow rate at point “B”; (iii) approximately determine the blower operational signal needed to achieve this air flow rate, resulting in data point {D, B} in FIG. 10B; and (iv) map the two points as a linear function.
As mentioned, the purpose of a theoretical or projected characterization curve as in FIG. 10B is merely to approximate the operational range of the heating device or burner unit, for narrowing the range of data points during actual testing. (In other words, this method eliminates data outliers, such as the case of the gas flow rate being at a maximum when the blower is turned off, which is highly unlikely to result in an ideal operational state of the burner unit.) Thus, for testing the unit as at Step 206 in FIG. 10A, and with reference to FIG. 10C, the range of gas valve operational signals 68 is again divided into a plurality of testing points, according to a desired level of granularity, e.g., 0.1 VDC signal increments, for a total of 100 testing points across a 0-10 VDC signal range. At each testing point of the gas valve assembly, e.g., point “Y” in FIG. 10C (which is approximately a 3.7 VDC operational signal for 0-10 VDC range), the projected curve is accessed for determining a projected blower assembly operational signal 110. A window is established around this value, say from “+X” to “−X,” and the window is divided into a desired number of test points. For example, “X” could be 2 volts, with the window around the “central” operational signal 110 thereby being 4 volts total. While the gas valve operational signal 68 is maintained at “Y” volts, each testing signal in the window is sequentially applied to the blower assembly 32. (Therefore, if the central operational signal 110 at point “Y” were “Z” volts, then the operational signal 60 applied to the blower assembly would range from Z+X volts to Z−X volts, in 0.1 volt or other increments.) At each testing signal, the testing and data acquisition system collects data 112 relating to burner operation, as described above.
Once the data 112 is collected for all testing points of the gas valve assembly and blower assembly, the data is analyzed as at Step 208 in FIG. 10A, for generating a control profile as at Step 210. This may be done using data analysis software (part of the testing and data acquisition system or otherwise), which determines, for each gas valve assembly testing point, the tested blower signal that provides the best performance characteristics while staying within ANSI safety and performance standards for CO output and the like. Other optimization techniques may be employed, using standard software-based or other methods, for taking into account all the variables present in the system. Once it is determined which operational signal pairs (e.g., blower operational signal and valve operational signal) provide the best level of performance at each level of control signal/heating output, these are used to populate the control profile.
The “window” testing approach discussed above might fall outside the optimum performance level for a given testing point. If so, the window may be adjusted until an optimum point is reached. Additionally, it will typically be the case that several iterations of the process is carried out for achieving the most fine-tuned control profile, e.g., the control profile generated in the first run-through (based on a theoretical characterization curve) is used as the theoretical characterization curve in the next run-through, and so on.
As should be appreciated, because the control profile 38 is generated based on actual testing data acquired across a wide operational range of the heating device, with independent control of the blower assembly and gas valve assembly, non-linear system effects are fully accounted for, i.e., even in instances where the system acts particularly non-linear, such instances are identified and compensated for through the testing data. This also enables operation of the system at a high turndown ratio. For example, in the case where a linear control profile might result in unsafe performance at a very low firing rate, vis-à-vis a high firing rate along the same linear profile, this is avoided by using a control profile according to the present invention, which can be non-linear.
The control system 36 is typically implemented as part of, and/or interfaced directly with, the HVAC controller 100.
Since certain changes may be made in the above-described digital high turndown burner, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.

Claims

1. A gas burner system for a heating device, said system comprising:

a burner having at least one burner plate for facilitating the mixture of air and fuel to be combusted in a combustion chamber;

a valve assembly for controlling a flow of fuel to the burner;

a blower assembly for directing air to the burner; and

a control system that independently controls the valve assembly and the blower assembly according to a control profile, said control profile mapping an operational range of the valve assembly to an operational range of the blower assembly for generating a plurality of air/fuel mixtures each for operation of the burner at a different firing rate.

2. The system of claim 1, wherein:

the valve assembly is controlled according to a valve assembly control value, and the blower assembly is controlled according to a blower assembly control value; and

the control profile maps a range of possible valve assembly control values to a range of corresponding blower assembly control values, each corresponding blower assembly control value and valve assembly control value establishing one of said plurality of air/fuel mixtures.

3. The system of claim 2, wherein the control system determines a corresponding valve assembly control value and blower assembly control value from the control profile by applying a control signal to the control profile, said control signal relating to a desired heat output rate of the gas burner system.

4. The system of claim 3, wherein:

the valve assembly comprises a ball valve for controlling the flow of fuel into the burner, and a valve actuator for controlling the ball valve based on a first operational signal received from the control system, said first operational signal corresponding to the valve assembly control value determined by the control system; and

the blower assembly comprises a motor, a fan driven by the motor, and a blower control circuit configured to run the motor based on a second operational signal received from the control system, said second operational signal corresponding to the blower assembly control value determined by the control system.

5. The system of claim 1, wherein each of the plurality of air/fuel mixtures generated according to the control profile is configured for combustion, in conjunction with the burner and combustion chamber, within ANSI regulatory safety and performance parameters for indirect-fired gas burners.

6. The system of claim 1, wherein the burner is a single burner unit, and the control system is configured for operation of the single burner unit at a turndown ratio of at least 30:1.

7. The system of claim 6, wherein each of the plurality of air/fuel mixtures generated according to the control profile is configured for combustion, in conjunction with the single burner unit and combustion chamber, within ANSI regulatory safety and performance parameters for indirect-fired gas burners.

8. The system of claim 1, wherein:

the valve assembly comprises a ball valve for controlling the flow of fuel into the burner, and a valve actuator for controlling the ball valve based on a first operational signal received from the control system,

the blower assembly comprises a motor, a fan driven by the motor, and a blower control circuit configured to run the motor based on a second operational signal received from the control system; and

wherein said first and second operational signals being determined by the control system by applying a control signal to the control profile, said control signal relating to a desired heat output rate of the gas burner system

9. The system of claim 8, wherein:

the control system is operably interfaced with an HVAC controller that controls the heating device, said HVAC controller providing the control signal to the control system.

10. The system of claim 9, wherein the control system is imbedded in the HVAC controller.

11. The system of claim 1, wherein the burner comprises at least two burner plates, said burner plates being arranged in a generally V-shaped configuration.

12. A heating device comprising:

a combustion chamber;

a housing in fluid communication with the combustion chamber;

a burner disposed in the housing, said burner comprising at least one burner plate for facilitating the mixture of air and fuel to be combusted in the combustion chamber;

a blower assembly connected to the housing for directing air into the interior of the housing;

a valve assembly connected to the housing for controlling a flow of fuel into the burner; and

13. The system of claim 12, wherein each of the plurality of air/fuel mixtures generated according to the control profile is configured for combustion, in conjunction with the burner and combustion chamber, within ANSI regulatory safety and performance parameters for indirect-fired gas burners.

14. The system of claim 12, wherein the burner is a single burner unit, and the control system is configured for operation of the single burner unit at a turndown ratio of at least 30:1.

15. The system of claim 14, wherein each of the plurality of air/fuel mixtures generated according to the control profile is configured for combustion, in conjunction with the single burner unit and combustion chamber, within ANSI regulatory safety and performance parameters for indirect-fired gas burners.

16. A heating device comprising:

a combustion chamber;

a housing in fluid communication with the combustion chamber;

a single-burner unit disposed in the housing, said single-burner unit having at least one burner plate for facilitating the mixture of air and fuel to be combusted in the combustion chamber;

a blower assembly connected to the housing for directing air into the interior of the housing, said blower assembly being controlled according to a first operational signal;

a valve assembly connected to the housing for controlling a flow of fuel to the single-burner unit, said valve assembly being controlled according to a second operational signal; and

a control system that independently controls the valve assembly and the blower assembly by generating the first and second operational signals, respectively, wherein the control system determines the first and second operational signals by applying a control signal, indicative of a desired heat output level of the heating device, to a control profile, said control profile mapping an operational range of the valve assembly to an operational range of the blower assembly for generating a plurality of air/fuel mixtures each for operation of the burner at a different firing rate;

wherein a ratio of the highest of said firing rates to the lowest of said firing rates is at least 30:1; and

wherein each of the plurality of air/fuel mixtures generated according to the control profile is configured for combustion, in conjunction with the single-burner unit and combustion chamber, within ANSI regulatory safety and performance parameters for indirect-fired gas burners.

17. A method of controlling a gas burner, said method comprising the steps of:

determining a gas valve control signal and an air blower control signal by cross-referencing information associated with a received control signal to a gas burner control profile, said information relating to a desired heat output of the gas burner, wherein the control profile correlates a range of gas valve control signals to a range of air blower control signals for operation of the gas burner at a turndown ratio of at least 30:1;

outputting the gas valve control signal to a gas valve unit, for controlling the gas output of the gas valve; and

outputting the air blower control signal to an air blower unit, for controlling the air output of the air blower unit, said gas output and air output being combined for combustion in the gas burner.