Patent Application
20120247444
Not applicable.
Not applicable.
The invention relates generally to gas-fired indoor and outdoor furnaces. More particularly, the invention relates to intake manifolds for premix gas-fired furnaces. Natural gas and propane fired furnaces are widely used in commercial and residential environments for heating, including space heating for air conditioning interior spaces. Gas and propane fired furnaces are known to generate and emit oxides of nitrogen (NOx). In general, NOx refers to a group of highly reactive gases that contain nitrogen and oxide in various amounts (e.g., NO, N2O, NO2).
These and other needs in the art are addressed in one embodiment by a gas-fired air conditioning furnace. In an embodiment, the furnace comprises a monolithic intake manifold including an inlet at a first end and a plurality of outlets at a second end opposite the first end. In addition, the furnace comprises a burner assembly including a plurality of burners, each burner is configured to combust an air-fuel mixture at least partially within an interior space of the burner. Further, each burner extends into one of the outlets of the intake manifold.
These and other needs in the art are addressed in another embodiment by an intake manifold for a gas-fired device. In an embodiment, the intake manifold comprises a monolithic body having a first end and a second end opposite the first end. In addition, the intake manifold comprises an inlet at the first end of the body. Further, the intake manifold comprises a plurality of outlets at the second end of the body. The body includes a distributor section including the inlet and a plurality of supply tubes extending from the distributor section. Each supply tube includes one of the plurality of outlets. The distributor is configured to receive an air-fuel mixture through the inlet and divide the air-fuel mixture among the plurality of supply tubes.
These and other needs in the art are addressed in another embodiment by a method of operating a gas-fired furnace. In an embodiment, the method comprises (a) supplying an air-fuel mixture to a single-piece intake manifold. The intake manifold has an inlet at a first end and a plurality of outlets at a second end opposite the first end. The intake manifold also includes a distributor extending from the first end and a plurality of supply tubes extending from the second end to the distributor. In addition, the method comprises (b) flowing the air-fuel mixture through the inlet of the intake manifold into the distributor. Further, the method comprises (c) dividing the air-fuel mixture in the distributor into a plurality of portions. Still further, the method comprises (d) flowing each portion of the air-fuel mixture through one of the supply tubes to a burner extending into the supply tube, one burner extends into each supply tube. Moreover, the method comprises (e) combusting the portion of the air-fuel mixture within each burner to form a hot flue gas.
Thus, embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings.
For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:
In some cases, NOx emissions from furnaces may contribute to less than optimal air-fuel mixtures and combustion temperatures, and may generally be considered pollutants. Consequently, air pollution regulatory agencies, such as South Coast Air Quality Management District (SCAQMD), may limit the emission of NOx from furnaces. Some regulations may limit NOx emissions from gas-fired furnaces to less than 40 nano-grams per Joule (ng/J) of energy used. However, some stricter regulations that may become effective in 2012 may limit NOx emissions from gas-fired furnaces to less than 14 ng/J of energy used.
Some conventional natural gas and propane fired furnaces include a burner assembly having a plurality of discrete parts coupled together. For example, burner assemblies often includes a gas valve, a gas manifold pipe with fixed orifices, atmospheric type burners (i.e., unenclosed or open burners), and a burner holder or box. Air may be sucked through the pipe and gas may be injected at the burners. Such natural gas and propane furnaces may emit NOx at a much higher level, around 40 Ng/J, than a premix burner system in which the air and gas are mixed upstream of the burner assembly.
In some cases, an approach to obtain the lower NOx emissions from a gas-fired furnace is to employ premix burners, in which the air and fuel are mixed upstream of the burner. Some premix burners need to be sealed so as to not allow air leakage downstream of the air and fuel inlets. Although gaskets may be utilized in the connections between the different parts employed in gas-fired furnace employing premix burners, undesirable air leakage between the connections may occur. Such air leakage may undesirably alter the air-fuel ratio, increase NOx emissions, reduce furnace capacity, and/or increase the likelihood for flashbacks.
Accordingly, there may be a need to provide furnaces that generate a substantially reduced quantity of NOx by providing gas-fired furnaces and premix burner intakes that reduce the potential for ingress of air downstream of the air-fuel mixing device. Such furnaces and intakes may be particularly well received if they provided cost advantages and reduced NOx emissions. As such, the present disclosure, in some embodiments, provides a gas-fired furnace with reduced ingress of air into a pre-mixed air/fuel mixture along an intake assembly to lower NOx emissions. In some embodiments, a furnace is provided that emits NOx at lower than 14 nano-grams per joule (ng/J) of energy used. In some embodiments, a furnace comprising a single-piece or monolithic intake manifold that eliminates connections typically in conventional furnace intake assemblies is provided to accomplish the above-described reductions in NOx emissions.
Referring now to
In this embodiment, furnace 100 includes a gas supply valve 105, an air/fuel mixing tube 110, an intake manifold 120, a partition panel 150, a burner assembly 160, a post combustion chamber 170, a plurality of heat exchangers 180, and a heat exchanger exhaust chamber 190. As best shown in
Mixing tube 110 has an open upstream end 110a defining an air inlet 111, and an open downstream end 110b defining an air/fuel mixture outlet 112. An annular connection flange 113 extends radially outward from mixing tube 110 proximal downstream end 110b. Connection flange 113 couples mixing tube 110 to intake manifold 120. Fuel and air are introduced to the air/fuel mixing tube 110 to allow mixing before combustion, and thus, furnace 100 may be described as a “pre-mix” furnace. Fuel is introduced to the air/fuel mixing tube 110 by gas supply valve 105 mounted thereto, and air is introduced to mixing tube 110 via air inlet 111. Gas supply valve 105 may be adjusted either electrically or pneumatically to obtain the correct air to fuel ratio for increased efficiency and lower NOx emissions. In addition, gas supply valve 105 may be configured for either staged operation, or modulation type operation. For example, staged operation may have two flame settings, where modulation type operation may be incrementally adjustable over a large range of outputs, for example from 40% to 100% output capacity. In general, gas-fired furnace 100 may be operated with any suitable gaseous fuel including, without limitation, natural gas or propane.
Within mixing tube 110, the air and fuel are mixed together to form an air/fuel mixture that is preferably a uniform or homogenous mixture. Accordingly, in this embodiment, mixing tube 110 may include internal features downstream of air and fuel inlets that aid in the mixing of air and fuel within tube 110 by increasing downstream turbulence within the air/fuel mixture. The mixing of the air and fuel may also be aided by an active mixing device to encourage homogeneous mixing of the fuel and combustion air in the air/fuel mixing tube 110. The air/fuel mixture flows through outlet 112 of mixing tube 110 into intake manifold 120.
Referring now to
The air/fuel mixture from mixing tube 110 flows through distributor 130 to each heat exchange supply tube 140. Specifically, distributor 130 receives the air/fuel mixture via an air/fuel inlet 131 at end 121a, and distributes the air/fuel mixture among the plurality of heat exchange supply tubes 140 via a plurality of air/fuel outlets 132 at the intersection of distributor 130 and supply tubes 140; each outlet 132 being in fluid communication with one of the heat exchanger supply tubes 140. In this embodiment, distributor 130 is configured to evenly distribute the air/fuel mixture among the heat exchanger supply tubes 140. In other words, each heat exchanger supply tube 140 receives substantially the same volumetric flow rate of the air/fuel mixture from distributor 130.
Referring still to
As previously described, the air/fuel mixture enters intake manifold 120 through inlet 131 of distributor 130, and exits intake manifold 120 through outlets 142 of supply tubes 140. Accordingly, inlet 131 functions as the inlet of distributor 130 and intake manifold 120, and outlets 142 function as the outlet of supply tubes 140 and intake manifold 120.
Referring briefly to
In general, intake manifold 120 may comprise any suitable material(s), but preferably comprises durable materials suitable for high temperature furnace applications. In addition, as previously described, body 121 of intake manifold 120 is monolithically formed. Thus, intake manifold 120 preferably comprises a material that may be cast, machined, or otherwise formed as a single-piece such as steel or aluminum.
Referring now to
Referring now to
By positioning burners 162 within the heat exchanger supply tubes 140, burners 162 are positioned within a combustion airflow path, therefore substantially all of the combustion air passes through burners 162. In this embodiment, each burner 162 has an associated heat exchanger 180 for venting hot flue gases such that the heat exchanger 180 is in the combustion airflow path of its associated burner 162. While four supply tubes 140 and four corresponding burners 162 are provided in this embodiment, in general, the total number of supply tubes (e.g., supply tubes 140) and burners (e.g., burners 162) may vary depending upon the desired capacity of the furnace (e.g., furnace 100).
Referring again to
The flame in the burners 162 may be counter-flow to the direction of combustion gas flow in the system, resulting in substantially all of the air/fuel mixture passing through the perforations in the burner assembly 160 to the flame. The combustion of the air/fuel mixture occurs substantially inside burners 162 along the inner perforated surfaces of burners 162. Combustion within burners 162 allows substantially all of the heat of combustion to be focused at open ends 164b of burners 162.
In the manner described, the air and fuel are mixed upstream of burners 162 in mixing tube 110, and then flowed into burners 162 for combustion. Accordingly the air and fuel are “premixed” prior to delivery to burners 162, in contrast to injection of the fuel at the burner, where the fuel mixes with air. Accordingly, as used herein, the terms “premix” and “premixed” are used to refer to burners and furnaces in which the air and fuel are mixed upstream of the burners.
Referring still to
Substantially enclosing burners 162 within heat exchanger supply tubes 140 and substantially containing combustion within burners 162 offers the potential to reduce the amount of thermal radiation emitted to parts of furnace 100 other than the heat exchangers 180. Open ends 164b of burners 162 are in fluid communication with post combustion chamber 170, which is attached to inlet 181 of each heat exchanger 180 to ensure that substantially all of the heat generated by the burners 162 is transferred directly into heat exchangers 180 by directing hot flue gases through inlets 181 into heat exchangers 180. Post combustion chamber 170 seals the system from secondary dilution air as well as positions heat exchangers 180 for transfer of the hot flue gasses from burners 162.
In general, combustion air may be introduced into furnace 100 either in induced draft mode, by pulling air through the system, or in forced draft mode by pushing air through the system. In this embodiment, induced draft mode is employed by pulling the hot flue gases from exhaust chamber 190 with a blower or fan 195 by creating a relatively lower pressure at the exhaust of heat exchanger exhaust chamber 190. Alternatively, forced draft mode may be accomplished by placing a blower or fan between the air/fuel mixing tube (e.g., mixing tube 110) and the manifold inlet (e.g., manifold inlet connection flange 122) and forcing air into the system through the manifold (e.g., manifold 120). A control system may control the fan or blower (e.g., blower 195) to an appropriate speed to achieve adequate air flow for a desired firing rate through the burners (e.g., burners 162). Increasing the fan speed of the combustion blower will introduce more air to the air/fuel mixture, thereby changing the characteristics of the combustion within the burners.
Referring again to
As previously described and shown in
Referring now to
In this embodiment, intake manifold 120 of furnace 100 is monolithically formed as a single piece, thereby eliminating several discrete couplings that are common along the air/fuel intake assembly of most conventional gas-fired furnaces. In particular, many conventional gas-fired furnaces include a mixing box that is coupled to the upstream end of each of a plurality of discrete heat exchanger inlet tubes. The mixing box functions to distribute the air/fuel mixture among the heat exchanger inlet tubes. In addition, many conventional gas-fired furnaces include a separate and distinct burner box that is coupled to the downstream end of each heat exchanger inlet tube and positioned between the heat exchanger inlet tubes and the burner assembly. Accordingly, each heat exchanger inlet tube is independently coupled to the mixing box and the burner box. Although gaskets are typically employed in each of the connections with the heat exchanger inlet tubes, these connections are susceptible to leaks and frequently allow external air to access the intake assembly, thereby altering the air-fuel ratio and potentially increasing NOx emissions. However, in furnace 100, many of these connections have been eliminated. Specifically, heat exchanger supply tubes 140 are monolithically formed with distributor 130 and outlet connection flange 123, thereby eliminating the mechanical couplings with each supply tube inlet 141 and each supply tube outlet 142. As a result, embodiments of furnace 100 and intake manifold 120 offer the potential to reduce ingress of external air into the air/fuel mixture and NOx emissions.
Method 200 continues at block 230 where the air/fuel mixture flows into intake manifold 120 and is evenly divided among heat exchanger supply tubes 140 by distributor 130. Moving now to block 240, the air/fuel mixture in each supply tube 140 flows to a burner 162 disposed within that particular supply tube 140. At each burner 162, the air/fuel mixture flows through holes in end 164a and tubular 164 to the interior of the burner 162. Within burners 162, the air/fuel mixture is ignited with igniter 175 according to block 250. Combustion may occur at least partially within the interior burners 162 so that generated heat is forced out of open ends 164b and into post combustion chamber 170 and heat exchangers 180. It should be appreciated that combustion may occur just outside burner cavities 162, for example, slightly downstream of open ends 164b. Open ends 164b of each burner 162 face post combustion chamber 170 and a corresponding inlet of one heat exchanger 180 attached to combustion chamber 170. Thus, hot flue gases resulting from combustion of the air/fuel mixture in each burner cavities 162 pass through chamber 170 and vent into heat exchangers 180 in block 260.
Moving now to block 270, as the hot flue gases travel through heat exchangers 180 in route to heat exchanger exhaust chamber 190, thermal energy is transferred from the flue gas to the heat exchangers 180. Air that is exterior to heat exchangers 180 is moved across the outer surface of heat exchangers 180 with a circulation blower. As the air moves across heat exchangers 180, thermal energy is transferred from heat exchangers 180 to the air, thereby heating the air. Method 200 concludes at block 280 by venting the heated air into an air conditioned space, for example, an office space or living area of a home. The heated air may be used to warm the space in order to increase comfort levels for occupants or to maintain the contents of the space at a pre-determined temperature.
Referring now to
Referring now to
The air/fuel mixture flow through an air/fuel inlet 331 in distributor section 330 at end 321a and is distributed among the plurality of heat exchange supply tubes 340 via air/fuel outlets 332 of distributor section 330—one outlet 332 is provided for each heat exchanger supply tube 340. As with distributor 120 previously described, in this embodiment, distributor 330 is configured to evenly distribute the air/fuel mixture among the heat exchanger supply tubes 340.
Referring still to
Referring briefly to
In general, intake manifold 320 may comprise any suitable material(s), but preferably comprises durable materials suitable for high temperature furnace applications. In addition, as previously described, body 321 of intake manifold 320 is monolithically formed. Thus, intake manifold 320 preferably comprises a material that may be cast, machined, or otherwise formed as a single-piece such as steel or aluminum.
Referring now to
Referring again to
At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, RI, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=RI+k*(Ru−RI), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention.
