Patent Application
20140199643
1. Field of the Invention
The present invention relates generally to a modulating burner apparatus, and more specifically, but not by way of limitation, to a gas fired appliance incorporating a modulating burner.
2. Description of the Prior Art
Most conventional gas fired burner technologies utilize a single chamber burner designed to operate at a fixed flow rate of combustion air and fuel gas to the burner. Such technologies require that the burner cycles on and off in response to a control system which determines when the demand for energy has been met, and cycles back on at a predetermined setpoint when there is a demand for more energy. One example of such a typical prior art system which is presently being marketed by the assignee of the present invention is that shown in U.S. Pat. Nos. 4,723,513 and 4,793,800 to Vallett et al., the details of which are incorporated herein by reference.
The assignee of the present invention has also developed a continuously variable modulating burner apparatus for a water heating appliance with variable air and fuel input, as shown in U.S. Pat. No. 6,694,926 to Baese et al. In the Baese apparatus combustion air and fuel are introduced separately in controlled amounts upstream of a blower and are then premixed and delivered into a single chamber burner at a controlled blower flow rate within a prescribed blower flow rate range. This allows the heat input of the water heating appliance to be continuously varied within a substantial flow range having a burner turndown ratio of as much as 4:1. It should be understood by those skilled in the art that a 4:1 burner turndown capability will result in the appliance remaining in operation for longer periods of time during a typical seasonal demand than an appliance with less than 4:1 burner turndown ratio, or with appliances with no turndown ratio at all.
More recently, the assignee of the present invention has developed a water heating appliance including a dual-chamber burner, with dual blower assemblies providing fuel and air mixture to the chambers of the burner, as shown in U.S. Pat. No. 8,286,594 to Smelcer, the details of which are incorporated herein by reference. Through the use of the dual blower assemblies this system is capable of achieving turndown ratios of as much as 25:1 or greater. It should be understood by those skilled in the art that a 25:1 burner turndown capability will result in the appliance remaining in operation for longer periods of time during a typical seasonal demand than an appliance with less than 25:1 burner turndown ratio, or with appliances with no burner turndown ratio at all.
There is a continuing need for improvements in modulating burners which can provide modulation of heat input over a wider range of heat demands. Particularly there is a need for systems providing high turndown ratios with reduced mechanical complexity at significantly reduced cost as compared to known practices today.
In one embodiment a modulating burner apparatus includes one and only one source of pressurized pre-mixed fuel and air mixture, the source including at least one variable speed blower. The apparatus includes a multi-chamber burner configured to burn the pre-mixed fuel and air mixture, the burner including at least a first burner chamber and a second burner chamber. The apparatus further includes a flow controller configured to provide fuel and air mixture from the one and only one source to only the first burner chamber at lower blower speeds of the blower and to both the first and second burner chambers at higher blower speeds of the blower.
In another embodiment a modulating burner apparatus includes a variable speed blower, the blower including a blower outlet, and a multi-chamber burner configured to burn a pre-mixed fuel and air mixture, the burner including at least a first burner chamber and a second burner chamber. The second burner chamber is located adjacent the first burner chamber so that the second burner chamber can be ignited by the first burner chamber. A supply manifold communicates the blower with the burner, the supply manifold including a first passage portion communicated with the blower outlet, a second passage portion communicating the first passage portion with the first burner chamber, and a third passage portion communicating the first passage portion with the second burner chamber. A valve is located between the first passage portion and the third passage portion, the valve being configured such that as the blower speed increases from a lower speed range through a transition speed range to a higher speed range, the valve moves from a closed position when blower-speed is in the lower speed range to an open position when blower speed is in the higher speed range.
In another embodiment an apparatus for heating water includes a water conduit having an inlet and an outlet, a heat exchanger having a water side defining a portion of the water conduit, and a pre-mix burner configured to burn a pre-mixed fuel-air mixture. The burner is operatively associated with the heat exchanger to heat water in the water side of the heat exchanger. The burner includes a first plenum communicated with a first foraminous burner surface, and a second plenum communicated with a second foraminous burner surface, the first and second foraminous burner surfaces being sufficiently close to each other so that flame from the first foraminous burner surface will ignite fuel-air mixture exiting the second foraminous burner surface. A variable flow blower has a blower outlet communicated with the first and second plenums. A damper is located between the second plenum and the blower outlet. A biasing spring biases the damper toward a closed position, the damper being movable toward an open position when fluid pressure from the blower acting on the damper overcomes the biasing spring.
In another embodiment, a method of modulating energy input to a multi-stage burner includes steps of:
(a) modulating blower speed of a variable speed blower within a lower speed range to modulate energy input to a first stage of the burner within a lower burner input range while a second stage of the burner is inoperative;
(b) opening a valve to allow flow of fuel and air mixture to the second stage of the burner; and
(c) modulating blower speed of the variable speed blower within a higher speed range to modulate energy input to the combined first and second stages of the burner within a higher burner input range.
In any of the above embodiments, the blower may include one and only one blower.
In any of the above embodiments the control valve may include a spring pre-load adjuster configured to adjust an opening force required to move the valve member from the closed position.
In any of the above embodiments the valve member may include a disc shaped valve member operatively associated with a coil compression biasing spring.
In any of the above embodiments the blower may be a centrifugal blower having a blower output versus blower speed curve for a given flow restriction downstream of the blower, and the first burner chamber may define a higher flow restriction and the first and second burner chambers together may define a lower flow restriction, so that at the lower blower speeds when fuel and air mixture is provided to only the first burner chamber the blower output follows a first curve corresponding to the higher flow restriction, and at the higher blower speeds when fuel and air mixture is provided to both the first and second burner chambers the blower output follows a second curve corresponding to the lower flow restriction.
In any of the above embodiments an energy input to the burner can be continuously modulated over a lower input range modulation curve corresponding to operation of only the first burner chamber, and the energy input to the burner can be continuously modulated over a higher input range modulation curve corresponding to operation of both the first and second burner chambers together, there being an intermediate modulation curve between the lower and higher input range modulation curves, the intermediate modulation curve being steeper than the lower and higher input range modulation curves.
In any of the above embodiments the apparatus may have an overall modulation range of at least 16 to 1, and more preferably at least 25 to 1.
An object of the invention is to provide a high turndown burner apparatus having reduced complexity and reduced cost.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.
Referring now to the drawings, and particularly to
The modulating burner apparatus 10 includes a source 52 of pressurized pre-mixed fuel and air mixture including a variable speed blower 54, a multi-stage burner 42 configured to burn the pre-mixed fuel and air mixture, and a flow controller or flow control valve 74 configured to provide fuel and air mixture to only a first burner chamber at lower blower speeds and to both the first and a second burner chamber at higher blower speeds.
The modulating burner apparatus disclosed herein makes use of a dual chamber burner similar to that disclosed in U.S. Pat. No. 8,286,574 discussed above, but with a greatly simplified blower and control system. The modulating burner apparatus 10 uses one and only one source of pressurized pre-mixed fuel and air mixture, as opposed to the use of separate low range and high range blower assemblies as was shown in U.S. Pat. No. 8,286,574. That one and only one source of pressurized pre-mixed fuel and air mixture is preferably provided by one and only one variable speed blower, although as is shown below multiple blowers can be combined to provide one common source of pressurized pre-mixed fuel and air mixture.
As used herein, the terms water heating apparatus or water heating appliance or water heating system or water heater apparatus or water heater all are used interchangeably and all refer to an apparatus for heating water, including both boilers and water heaters as those terms are commonly used in the industry. Such apparatus are used in a wide variety of commercial and residential applications including potable water systems, space heating systems, pool heaters, process water heaters, and the like. Also, the water being heated can include various additives such as antifreeze or the like.
The water heating apparatus 11 illustrated in
The water heating apparatus 11 shown in the system 13 of
As best shown in
A burner assembly or burner apparatus 42 is located within the combustion chamber 32. The burner assembly 42 burns pre-mixed fuel and air within the combustion chamber 32. The hot gases from the combustion chamber 32 flow down through the fire tubes 36 to an exhaust collector 44 and out an exhaust flue 46.
Water from flow loop 16 to be heated flows in the water inlet 12, then around the exterior of the fire tubes 36 and up through a secondary heat exchanger portion 48 of water side 26, and continues up through a primary heat exchanger portion 50 of water side 26, and then out through water outlet 14. It will be appreciated that the interior of the water heating apparatus 11 includes various baffles for directing the water flow in such a manner that it generally uniformly flows around all of the fire tubes 36 and through the water chamber 50 of primary heat exchanger 28 between the outer jacket 24 and inner jacket 30. As the water flows upward around the fire tubes 36 of the secondary heat exchanger 40 the water is heated by heat transfer from the hot combustion gases inside of the fire tubes 36 through the walls of the fire tubes 36 into the water flowing around the fire tubes 36. As the heated water continues to flow upward through the water side 50 of primary heat exchanger 28 additional heat is transferred from the combustion chamber 32 through the inner jacket 30 into the water contained in water side 50.
The controller 200 also provides output signals to various components, such as a blower speed control signal over line 214 to blower 54, an ignition signal over line 216 to direct spark ignition element 128, and a control signal over line 218 to electric actuator 98 of the positive control valve 74B of
Referring again to
The blower assembly 52 includes a variable flow blower 54 driven by a variable frequency drive motor. A venturi 56 is provided for mixing combustion air and fuel gas. An air supply duct 58 provides combustion air to the venturi 56. A gas supply line 60 provides fuel gas to the venturi 56. A gas control valve 62 is disposed in supply line 60 for regulating the amount of gas entering the venturi 56. The gas control valve 62 includes an integral shutoff valve. In some embodiments the gas control valve and the venturi may be combined into a single integral unit. The gas control valve is preferably a zero governor or negative regulation type gas valve for providing fuel gas to the venturi 56 at a variable gas rate which is proportional to the negative air pressure within the venturi caused by the speed of the blower, hence varying the flow rate entering the venturi 56, in order to maintain a predetermined air to fuel ratio over the flow rate range within which the blower 54 operates.
The venturi 56 may be more generally described as a mixing chamber 56 upstream of the blower 54, the mixing chamber 56 being configured to at least partially pre-mix the fuel and air mixture prior to the fuel and air mixture entering an inlet of the blower 54. It is noted, however, that the blower assembly 52 could alternatively be of a construction wherein the fuel gas is added to the air at the outlet or shortly downstream of the outlet of the blower 54.
The blower assembly 52 as schematically illustrated in
Alternatively, as shown in
In still another alternative as shown in
As schematically illustrated in
The modulating burner apparatus 10 includes a flow controller or flow control valve schematically indicated as 74 in
In one embodiment as illustrated in
Optionally, a spring pre-load adjuster 80 is provided and is configured to adjust an opening force required to move the valve member 76 from the closed position. This adjustment may be used to offset the effects of changes in air density as a result of varying altitudes that may be encountered in the installation of the burner apparatus 10. The opening force may be adjusted by lengthening or shortening the coil compression spring 78 by the threaded makeup of threaded nut 84 on the threaded rod 82 of the spring pre-load adjuster 80.
In another embodiment as shown in
In yet another embodiment shown in
Referring now to
The two chamber burner 42 can generally be referred to as a multi-chamber burner 42 including at least a first burner chamber 104 and a second burner chamber 106. The multi-chamber burner 42 may also have more than two chambers. In such a case each additional burner chamber will have an associated flow control valve to bring that burner chamber into operation at a selected blower speed.
A duct 108 extends upward from interior wall 102. Duct 108 is welded or otherwise attached to interior wall 102. The lower end of duct 108 communicates through opening 110 in interior wall 102 with the second burner chamber 106.
The burner apparatus 42 further includes a cylindrical outer burner housing 112 extending from the flange 100 downward to a lower end plate 114. An upper portion 116 of cylindrical outer burner housing 112 is a solid cylindrical non-perforated structure, and a lower portion 118 of the cylindrical outer burner housing 112 includes rows of slotted perforations 120. The bottom plate 114 may also be perforated in a manner similar to the slotted perforations 120. A foraminous outer layer 122 is received about the perforated portion 118 and bottom plate 114. The foraminous outer layer 122 may for example be a ceramic fiber weave material, or it might also be a woven metal fabric, or any other suitable material providing many very small passageways for fuel and air mixture to flow therethrough.
The interior wall 102 divides the foraminous outer layer 122 into a first foraminous burner surface 124 and a second foraminous burner surface 126.
The apparatus 10 preferably utilizes a direct spark ignition element 128 (see
In the construction illustrated in
It will be appreciated that due to the presence of the interior wall 102 there will be a small gap between the exterior burner surfaces 124 and 126 associated with the first chamber 104 and second chamber 106 of the burner assembly 42. When the heating apparatus 10 is first fired up, there will only be flame on the exterior surface 124 of the first burner chamber 104. Hot combustion gases will be flowing downward past the outer surface 126 of second burner chamber 106 and upon opening of control valve 74 those hot gases will ignite fuel being provided to second burner chamber 106. Although the physical gap created by interior wall 102 is preferably kept to a minimum, it will be appreciated that so long as the first foraminous burner surface 124 is sufficiently close to second foraminous burner surface 126 that the gases exiting the second burner chamber 106 can be ignited, then the apparatus 10 can operate with only the single direct spark ignition element 128 initially igniting the flame from first burner chamber 104. Although it is preferred for practical reasons that the burner assembly 42 be an integrally constructed burner assembly, it is conceivable to completely physically separate the burner surfaces associated with the first and second burner chambers 104 and 106 so long as they are feeding a common combustion zone 32 and are sufficiently close that second foraminous burner surface 126 can take ignition from flame from first foraminous burner surface 124, and so long as the design prevents physical damage from occurring to the neighboring burner.
Due to the proximity of the burner surfaces 124 and 126 to each other, and because the same fuel/air mixture exits both burner surfaces, it is also only necessary to have one flame sensor 129 to confirm that flame is present at the burner assembly 42. The second foraminous burner surface 126 does not need a second flame sensor.
Referring now to
The manifold housing 130 has a radially inward extending upper flange 138 which is arranged to have the blower 54 mounted on top thereof with a blower mounting flange 140.
The valve housing 132 is a cylindrical member telescopingly received within the upper end of duct 108 of burner assembly 42 and attached thereto such as by weld 142. A radially inward extending flange 144 at the upper end of valve housing 132 has an opening 146 defined therein which in
The support rod 82 of the disc shaped valve element 76 is attached to a cross member 148 extending diametrically across the interior of valve housing 132.
Referring now to
The blower 54 may be a centrifugal blower. As will be understood by those skilled in the art, for any given conditions at the inlet of the blower regarding inlet pressure, inlet temperature, and the makeup of the gases being conveyed by the blower, the blower will have a blower output versus blower speed curve for a given flow restriction downstream of the blower. This blower output may be measured as a mass flow rate, or as a volumetric flow rate, or as a blower outlet pressure, but however measured the blower output will have a shape generally as shown in
With the system shown in
Referring to
Similarly, curve 152 defines the blower output versus blower speed curve for the blower 54 when the control valve 74 is open and both the first and second burner chambers are operative.
This blower output or flow rate of fuel and air mixture also directly corresponds to the energy input to the burner 42, so the curves of
In the example illustrated in
If it were possible to immediately open the control valve 74 and immediately transition to full operation of the first and second burner chambers, the input to the two stage burner 42 would jump from the curve 150 vertically along dashed line 156 to the second curve 152. Such an abrupt jump, however, does not actually occur because it takes some time for the control valve 74 to open and for the blower and the flow rate to respond. Thus during some transition range 158 of blower speeds the actual energy input to the burner apparatus will pass through an intermediate transition curve 160 until the flow rate is fully established through the second burner chamber at which point the blower speed will be in the range indicated on
Thus, as a result of the operation of the control valve 74 there is an intermediate input range 164 in which there is less precise control and a much steeper modulation curve than there is in the lower and upper input ranges 154 and 162.
The system represented in
When using the mechanical valve with mechanical biasing spring arrangement of either
On the other hand, if the positive control valve arrangement of
The energy input to the burner 42 can be described as being continuously modulated between a first energy input value 168 and a second energy input value 170 corresponding to the lower speed range of the blower 54. The energy input to the burner can also be continuously modulated between a third energy input value 172 and a fourth energy input value 166 corresponding to the higher speed range of the blower. The fourth energy input value 166 divided by the first energy input value 168, as previously noted, defines the overall modulation range of the heater apparatus. The steeper intermediate modulation curve, as previously noted, is defined between the second energy input value 170 and the third energy input value 172, corresponding to a transition of the blower output from the first curve 150 to the second curve 152 as the valve 74 opens.
This steeper modulation curve is the tradeoff that is made to achieve the high turndown ratios of the burner 42 without a complex dual blower system having individual blowers feeding each burner chamber. But a primary advantage of a high turndown ratio, namely high maximum energy input to the burner while maintaining the ability to operate at low minimum levels to avoid cycling the burner on and off, is still achieved, at a greatly reduced cost and reduced complexity. This avoids the off-cycle losses of energy that occur during off periods.
It is noted that during operation of the first burner chamber when blower speed is in the lower speed range, a positive pressure differential exists across the valve 74 from the first passage portion 66 to the third passage portion 72, thereby preventing back flow through the second burner chamber 106.
As described above, in the embodiment disclosed the blower 54 and the burner 42 are continuously modulated within the blower speed ranges of interest. In a broader aspect of the invention, however, the blower speed may be modulated in a non-continuous fashion resulting in a non-continuous modulation of burner input. For example, the blower 54 may be programmed to increase and decrease speed in a step-wise fashion. Also a multi-stage source 52 of pressurized air and fuel mixture may be provided using a series of gas valves that are placed into and out of service to provide a step-wise modulated source of pre-mixed air and fuel. For such a non-continuous modulation the source 52 of pressurized air and fuel mixture would provide a series of input levels of air and fuel mixture, with an appropriate substantially constant air to fuel ratio being maintained at each input level.
The following provides one example of a burner apparatus providing enhanced turndown capabilities using the principles described above. In this example, a total burner size for the area of outer burner surfaces 124 and 126 of chambers 104 and 106 is selected as if the total burner size were for a single chamber burner having a blower without the control valve system 74. The total burner size is selected for a maximum energy input of 400,000 BTU/Hr, and uses a blower having a turndown ratio of 5 to 1.
Based upon the maximum desired energy input of 400,000 BTU/Hr, the total size of the burner is selected and the blower 54 is sized so that at its maximum speed the blower 54 provides appropriate mass flow rate of fuel and air mixture to the burner so as to generate the desired 400,000 BTU/Hr energy input to the burner. Accordingly, when operating at its minimum speed the blower provides appropriate mass flow rate of fuel and air mixture to the burner so as to generate 80,000 BTU/Hr energy input to the burner based on the 5:1 turndown of the blower.
By incorporating the control valve system 74 in the manner described above to the same burner/blower/gas valve arrangement, the burner assembly can be arranged so as to provide a minimum turndown of 25,000 BTU/Hr (turndown ratio of 16:1) by selecting the burner area of the first foraminous burner surface 124. Thus, the position of the interior wall 102 within the cylindrical housing 112 is selected so as to define the proper area for the first foraminous burner surface 124 to achieve the desired 25,000 BTU input at the lowest blower output speed. This will depend upon the inherent characteristics of the foraminous burner surface 124 and the flow rates needed to achieve a stable flame front on the foraminous burner surface 124.
Next, the characteristics of the flow control valve 74 must be designed to allow the valve 74 to open at the desired speed. For example, utilizing the coil compression biasing spring arrangement of
In this example the chambers 104 and 106 of burner 42 may have an inside diameter of approximately 6.5 inches. The first foraminous burner surface 124 may have an axial length of approximately ⅝ inches and the second foraminous burner surface may have an axial length of 4.25 inches. The opening 146 closed by disc shape valve element 76 may have a diameter of 3.75 inches. The biasing spring 78 may be designed to allow the valve 74 to open at a force of 0.584 pound. The blower 54 may for example be a Model RG 148 available from EBM Pabst. The venturi and gas valve may be a combination venturi/gas valve model VR8615F available from Honeywell. In this example the burner lower end plate 114 is not perforated and the burner end does not have combustion taking place; it is not an active burner end.
Thus it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are embodied with the scope and spirit of the present invention as defined by the following claims.
