Push/pull furnace and methods related thereto

Example furnaces and methods related thereto include a burner box including at least one burner configured to combust a fuel/air mixture. In addition, the furnace includes a first blower including an inlet nozzle having an air inlet and fuel inlet. The inlet nozzle is configured such that operation of the first blower is to pull air and fuel into the inlet nozzle to produce the fuel/air mixture at a fuel/air ratio that is configured to produce flue products having less than 14 Nano-grams per Joule of nitrogen oxides when combusted. Operation of the first blower is configured to push the fuel/air mixture into the burner box. Further, the furnace includes a heat exchanger assembly fluidly coupled to the burner box through a vestibule, and a second blower configured to pull the flue products through the heat exchanger assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

Not applicable.

BACKGROUND

A furnace may provide heated air to a defined space, such as, for instance an internal space of a home, office, retail store, etc. Furnaces may transfer heat to a defined space via a number of different methods. In some instances, furnaces may combust a hydrocarbon fuel source, such as, for example, propane or natural gas, and then transfer the heat of the combustion process to heat an airflow that is circulated throughout the defined space. Specifically, in some of these furnaces, hot flue products resulting from the combustion process are flowed through one or more heat exchanger tubes, and an airflow is simultaneously flowed over the outer surfaces of the heat exchanger tubes so as to increase the temperature thereof.

BRIEF SUMMARY

Some embodiments disclosed herein are directed to a furnace. In an embodiment, the furnace includes a burner box including at least one burner that is configured to combust a fuel/air mixture. In addition, the furnace includes a first blower including an inlet nozzle having an air inlet and fuel inlet. The inlet nozzle is configured such that operation of the first blower is to pull air and fuel into the inlet nozzle via the air inlet and fuel inlet, respectively, to produce the fuel/air mixture at a fuel/air ratio that is configured to produce flue products having less than 14 Nano-grams per Joule (ng/J) of nitrogen oxides (NOx) when combusted in the at least one burner. Operation of the first blower is configured to push the fuel/air mixture into the burner box. Further, the furnace includes a heat exchanger assembly fluidly coupled to the burner box through a vestibule, and a second blower configured to pull the flue products through the heat exchanger assembly.

In some embodiments, the furnace includes a housing including first compartment and a second compartment separated by a vestibule. In addition, the furnace includes a combustion assembly disposed in the first compartment. The combustion assembly includes a first blower including an inlet nozzle having an air inlet and a fuel inlet, and a burner that is configured to receive a fuel/air mixture from the first blower. Further, the furnace includes a heat exchanger assembly. The heat exchanger assembly includes a heat exchanger disposed in the second compartment that is configured to receive flue products from the burner. In addition, the heat exchanger assembly includes a second blower fluidly coupled to the heat exchanger that is disposed within the first compartment. The second blower is configured to pull the flue products through the heat exchanger. Still further, the furnace includes a second blower fluidly coupled to the heat exchanger that is disposed within the first compartment. The second blower is configured to pull the flue products through the heat exchanger.

Other embodiments disclosed herein are directed to a method of operating a furnace. In an embodiment, the method includes pulling air into an air inlet of an inlet nozzle and fuel into a fuel inlet of the inlet nozzle with a first blower to form an fuel/air mixture at a fuel/air ratio. In addition, the method includes pushing the fuel/air mixture into a burner box with the first blower. Further, the method includes combusting the fuel/air mixture within a burner of the burner box to produce flue products having less than 14 ng/J of NOx. Still further, the method includes pulling the flue products through a heat exchanger assembly with a second blower.

Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

DETAILED DESCRIPTION

The following discussion is directed to various exemplary embodiments. However, one of ordinary skill in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection of the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a given axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the given axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Further, when used herein (including in the claims), the words “about,” “generally,” “substantially,” “approximately,” and the like mean within a range of plus or minus 10%.

As previously described, a furnace may heat an airflow within a heat exchanger using the flue products resulting from the combustion of a hydrocarbon fuel, and then deliver the heated airflow to a defined space. Upon exiting the heat exchanger, the flue products may be vented to the atmosphere. During these operations, the combustion of the hydrocarbon fuel may produce undesirable by-products in the flue products, such as NOx. As used herein, “NOx” refers to nitrogen oxides, such as, for instance, nitrogen dioxide and nitric oxide.

Without being limited to this or any other theory, utilizing a “rich” fuel/air ratio within a fuel/air mixture (i.e., a mixture containing a relatively high amount of fuel compared to the amount of combustion air) provided to the combustion process of the furnace may generate higher levels of NOxin the flue products. As a result, it may be desirable to maintain a lean fuel/air ratio within the fuel/air mixture provided to the combustion process so that NOxlevels are reduced within the flue products. However, richer fuel/air mixtures are also typically associated with higher combustion temperatures, which may directly improve the operating efficiency of the furnace (e.g., since more enthalpy is transferred to the airflow within the heat exchanger as the combustion temperature increases). In addition, it can be difficult to maintain the combustion process if the proportion of fuel supplied to the furnace is reduced too severely.

Accordingly, embodiments disclosed herein include furnaces and associated methods of operation that provide a precise balance of the fuel/air ratio within the furnace in order to minimize NOxproduction, while still achieving reliable and stable combustion for delivering adequate heating capacity to the defined space. In some embodiments, the disclosed furnaces may be comprise a “push-pull” furnace that employs a first blower to “push” pressurized air and fuel to a burner box (where the air and fuel is combusted), and a second blower to “pull” the flue products resulting from the combustion through one or more heat exchanger tubes. In some embodiments, the furnaces of the embodiments disclosed herein may produce less than 14 Nano-grams per Joule (ng/J) of NOxduring operation.

Referring now toFIG.1, a schematic view of a furnace100according to some embodiments is shown. As generally noted above, furnace100may be utilized to heat an airflow that is circulated throughout a defined space (e.g., an interior of a home, office, retail store, etc.).

Furnace100generally includes a housing110that includes a plurality of chambers or compartments to house various components and assemblies of furnace100. For instance, in the embodiment ofFIG.1, housing110includes a first compartment112and a second compartment114that are separated by an internal wall or vestibule115. First compartment112encloses a combustion assembly150for combusting the hydrocarbon fuel during operations, and second compartment114encloses a heat exchanger assembly120for transferring heat from the combustion process in combustion assembly150to an airflow (not shown) that is then provided to the defined space (not shown). As a result, the first compartment112may be referred to herein as a combustion compartment112, and the second compartment114may be referred to herein as a heat exchanger compartment114.

Generally speaking, combustion assembly150is a premix combustion assembly whereby fuel and air are mixed at a desired fuel/air ratio before they are flowed to the burner(s) (e.g., see e.g., burner(s)170) and then combusted. In particular, combustion assembly150includes a first or premix blower152and a burner box164downstream from the premix blower152(e.g., with respect to the flow of air and fuel within the combustion assembly150).

Referring still toFIG.1, premix blower152is coupled to an inlet nozzle153that includes a first or air inlet158and a second or fuel inlet159. The air inlet158is coupled to a source of air, which in this embodiment comprises the available air disposed within the combustion compartment112. In some embodiments, the air inlet158may draw air directly from the environment outside of the housing110of furnace100(e.g., via a snorkel or other suitable conduit). The fuel inlet159is coupled to a source157of fuel via a fuel valve156. The source157may comprise a tank, pipe or other suitable storage or conveyance of hydrocarbon fuel. In some embodiments, the fuel comprises natural gas (e.g., a mixture of various hydrocarbons such as methane, ethane, etc.) that is delivered to the furnace100via a pipe (e.g., source157).

The premix blower152may generally comprise a centrifugal blower comprising a blower housing151, a blower impeller154at least partially disposed within the blower housing151, and a blower motor155configured to selectively rotate the blower impeller154. The premix blower152may generally be configured as a modulating and/or variable speed blower capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the premix blower152may be a single speed blower. The blower motor155may comprise any suitable driver for rotating the impeller154within blower housing151. For instance, in this embodiment, the blower motor155comprises an electric motor.

During operations, the premix blower152may be operated (e.g., by rotating the blower impeller154) to draw in air and fuel via the inlets158and159, respectively, of inlet nozzle153. The air drawn into the inlet158may be referred to herein as “primary air.” The fuel valve156may comprise a negative pressure regulator valve that opens in response to a sub-atmospheric pressure generated by the operation of the premix blower152. In particular, in some embodiments, the inlet nozzle153may form a Venturi nozzle that creates a negative pressure at the fuel inlet159with a flow of air entering the inlet nozzle153via air inlet158. During these operations, the fuel valve156may open according to the magnitude of the negative pressure created at the fuel inlet159, which is in turn related to the flow rate of air into and through the inlet nozzle153via the air inlet158. As a result, the flow rate of fuel into the inlet nozzle153via the fuel inlet159may be proportional to the flow rate of air into the inlet nozzle153via the air inlet158. Therefore, the size, shape, and other parameters of the inlets158,159, inlet nozzle153, fuel valve156, etc. may be chosen so as to produce a desired fuel/air ratio for limiting or minimizing the production of NOxduring combustion.

More particular, in some embodiments, the inlets158,159, inlet nozzle153, fuel valve156, etc. may be configured to provide more than a Stoichiometric amount of air needed to combust all of the fuel (e.g., fuel flowing from source157) that is provided to burner box164during operations, so that a resulting air/fuel mixture emitted from the premix blower152and provided to burner box164may be “lean” with respect to the volume of fuel included therein. In some embodiments, the inlets158,159, inlet nozzle153, fuel valve156, etc. may be configured to provide approximately 20-30 vol. % of air, or 27-30 vol. % of air in the air/fuel mixture. Without being limited to this or any other theory and as generally described above, a lean air/fuel mixture may produce a generally lower flame temperature, which may reduce a heating performance of the furnace100, but may also produce lower levels of NON. As a result, the inlets158,159, inlet nozzle153and fuel valve156, etc. may be configured to strike a balance between sufficiently high flame temperature for occupant comfort and furnace efficiency, but while maintaining NOxemissions below an upper limit (e.g., such as 14 ng/J as previously described above). In some embodiments, the target flame temperature within the burners (e.g., burners170) of burner box164is about 1900 to 2100° F., or about 1950 to 2100° F. so as to achieve this balance.

In some embodiments, the inlet nozzle153may expand the inner diameter when moving downstream from the air inlet158to premix blower152so as to generate a sufficient negative pressure to draw a desired amount of fuel through the fuel inlet159(and therefore result in the desired fuel/air ratio as mentioned above). For instance, in some embodiments, the diameter of the air inlet158in inlet nozzle153may range from about 0.50 inches to about 1.50 inches, or from about 0.75 to about 1.10 inches, and the inlet nozzle153may include an outlet (not specifically shown) that communicates the air and fuel with the premix blower152that has a diameter of about 1.25 inches to about 1.50 inches, or from about 1.30 inches to about 1.50 inches. In some specific embodiments, the diameter of the air inlet158may be about 0.75 inches and the diameter of the outlet of inlet nozzle153may be about 1.34 inches. In some specific embodiments, the diameter of the air inlet158may be about 1.10 inches and the diameter of the outlet of inlet nozzle153may be about 1.45 inches.

Because the flow rate of fuel into the inlet159and thus into the premix blower152is proportional to the flow rate of air flowing with inlet158, the fuel/air ratio may be maintained regardless of the operating speed of the blower152(e.g., such as in embodiments where the premix blower152is a variable speed blower as previously described above). As the air and fuel flow into and within the inlet nozzle153and blower housing151of premix blower152, they are sufficiently agitated so as to form a fuel/air mixture that is then emitted from the blower housing151into the burner box164via a conduit160.

Referring still toFIG.1, burner box164generally includes a chamber166and one or more burners170fluidly coupled to chamber166. The burner(s)170are partially enclosed by a housing168that is coupled to the vestibule115. Generally speaking, the fuel/air mixture is provided to an inlet167of the chamber166via the flow conduit160, and is then communicated from the chamber166to the one or more burners170wherein the fuel/air mixture is combusted to produce flue products. Thereafter, the hot flue products are emitted from the burners and flowed into the heat exchanger assembly120.

The inlet167into chamber166may be at least partially formed by an orifice plate162that is disposed between the flow conduit160and the chamber166so as to adjust the pressure of the fuel/air mixture entering the chamber166during operations. Without being limited to this or any other theory, the pressure of the fuel/air mixture entering the chamber166may be set or adjusted (e.g., via the orifice plate162) such that the fuel/air mixture fills the chamber166and flows generally evenly to the one or more burners170. In addition, the pressure of the fuel/air mixture within chamber166may be set or adjusted (e.g., again, via the orifice plate162) so as to provide an appropriate flow rate through burner(s)170so as to avoid flame lift-off during operations. In some embodiments, the pressure of the fuel/air mixture within the chamber166may be about 3.5 inches of water. The size of the orifice plate162to achieve the desired pressure of the fuel/air mixture within chamber166will depend on various factors such as, for instance, the size of the chamber166, the speed of the premix blower152, the length and size of the flow conduit160, the number, size, and arrangement of the burners170, etc. In some embodiments, the orifice plate162is omitted.

In some embodiments, the orifice plate162may provide central aperture or hole size of between 0.5 and 1.5 inches. For instance, in some embodiments, the orifice plate162may have a central aperture size of about 0.75 inches. In some embodiments, the orifice plate162may have a central aperture size of about 0.90 inches or 1.10 inches.

The housing168may include one or more ports or openings to allow a flow of secondary air into the housing168and therefore mix with the combusted (or partially combusted) fuel/air mixture that is emitted from the burner(s)170. For instance, the housing168(or a portion thereof) may be spaced from the vestibule115so as to form a gap174therebetween. In addition, in some embodiments, additional ports172may also be formed in the wall of housing168. The ports172may be disposed along a side of the housing168that faces inward, and generally toward a center of the combustion compartment112. During operations, secondary air is drawn into the housing168via the gap174(and the ports172, if present), and then mixes with the combusted (or partially combusted) fluid flowing out (and thus downstream) from the burner(s)170and into the heat exchanger assembly120.

Without being limited to this or any other theory, the flow of secondary air may help to complete the combustion of any hydrocarbon fuel that was not combusted within the burner(s)170. In addition, the secondary air entering at the gap174(and the ports172, if present) may form an insulating barrier between the walls of the heat exchanger tube(s) of heat exchanger assembly120(discussed in more detail below) and the hot combustion products within the inlet of the heat exchanger, such that the heat exchanger tubes are protected from the relatively high initial temperature generated via the combustion process.

The size of the gap174(and the ports172, if present) may be chosen to provide a desired flow rate of secondary air during operations, and therefore may be set or adjusted based on a variety of factors such as, for instance, the number, size, and arrangement of the burner(s)170, the flow rate of the fuel/air mixture, etc.

Referring still toFIG.1, heat exchanger assembly120includes one or more heat exchanger tubes that are configured to receive the hot flue products produced from the combustion within burner(s)170of combustion assembly150. In particular, in this embodiment, heat exchanger assembly120includes one or more primary heat exchanger tubes122and one or more a secondary heat exchanger tubes124. The primary heat exchanger tube(s)122include inlet(s)121that form a general inlet for the heat exchanger assembly120and the secondary heat exchanger tube(s)124include outlet(s)123that form a general outlet for the heat exchanger assembly120. Between the inlet(s)121and outlet(s)123, the primary heat exchanger tubes122are coupled to the secondary heat exchanger tube(s)124via a hot header116. Inlet(s)121is/are generally fluidly coupled to the burner(s)170through the vestibule115, and the outlet(s)123is/are fluidly coupled to combustion blower130via a cold header117. In this embodiment, the combustion blower130is disposed within the combustion compartment112along with the combustion assembly150so that the combustion products are communicated from the cold header117, through the vestibule115, into the combustion blower130.

The combustion blower130may generally comprise a centrifugal blower comprising a blower housing131, a blower impeller132at least partially disposed within the blower housing131, and a blower motor133configured to selectively rotate the blower impeller132. The combustion blower130may generally be configured as a modulating and/or variable speed blower capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the combustion blower130may be a single speed blower. The blower motor133may comprise any suitable driver for rotating the impeller154within blower housing131. For instance, in this embodiment, the blower motor133comprises an electric motor.

Generally speaking, during operations, once flue products emitted from burner(s)170enter the inlet(s)121of the primary heat exchanger tube(s)122, they are pulled through the primary heat exchanger tube(s)122, the hot header116, and the secondary heat exchanger tube(s)124to the outlet(s)123and cold header117by the combustion blower130. The combustion blower130then emits the flue products to a flue pipe134for conveyance to the outside environment. The arrows118inFIG.1generally depict the flow path of flue products within the heat exchanger assembly120as generally described above. As the flue products are flowed through the primary heat exchanger tube(s)122and the secondary heat exchanger tube(s)124, an airflow (not shown inFIG.1, but see e.g., airflow182inFIG.3) is directed over the outer surfaces of the heat exchanger tubes122,124so that heat is transferred from the flue products to the airflow.

An orifice plate126may be disposed between the cold header117and the combustion blower130. Without being limited to this or any other theory, the orifice plate126may produce a backpressure within the cold header117and secondary heat exchanger tube(s)124that is to generally slow the flow rate of the hot flue products within the heat exchanger assembly120and therefore promote additional heat transfer from the flue products to the airflow outside of the heat exchanger tubes122,124during operations.

Referring still toFIG.1, an auxiliary heater106may be disposed within the combustion compartment112. During operations, auxiliary heater106may generate heat that is radiated within the combustion compartment112. In some circumstances, the furnace100is intended for installation in an outdoor environment. When installed outdoors, the ambient temperature surrounding the furnace100may fall below an acceptable level for operating one or more components within the combustion compartment112(e.g., such as the blowers152,130and particularly motors155,133). Therefore, if the furnace100has not been operating for an extended period, the temperature within the combustion compartment112may fall below the threshold temperature. To prevent combustion compartments temperature falling below a threshold temperature, auxiliary heater106may be utilized so as to maintain the temperature within the combustion compartment above a predetermined minimum (e.g., −4° F. in some embodiments) such that operation of the various components within combustion compartment112(e.g., again, such as blowers152,130) may be immediately initiated upon receipt of a call for heat within the defined space. In some embodiments, auxiliary heater106may comprise a resistive heater that generates heat via one or more electrically resistive coils when they are energized with electrical current. In some embodiments, furnace100may include a low temperature governor that may prevent operation of the furnace if the temperature surrounding the furnace100and/or within the combustion compartment112should fall below a predetermined minimum value.

Referring generally now toFIGS.2-4, more particular depictions of furnace100ofFIG.1are shown so as to show the relative arrangement of the various components described above according to some embodiments. It should be noted thatFIGS.2and4generally omit the housing110(except for the vestibule115) so as to best show the various components of the combustion assembly150and heat exchanger assembly120. However,FIG.3provides a schematic representation of housing110about combustion assembly150and heat exchanger assembly120.

Referring specifically toFIG.3, a circulation blower180is disposed within the heat exchanger compartment114along with the heat exchanger assembly120. During operations, the circulation blower180may generate an airflow182that is directed over the heat exchanger tubes122,124, so that heat may be transferred from the heat exchanger tubes122,124to the airflow182as previously described above. In this embodiment, the furnace100is arranged in a so-called “downflow orientation” such that the airflow182is emitted out of bottom side113of the heat exchanger compartment114after flowing over the heat exchanger tubes122,124. In other embodiments, the furnace100may be arranged to emit the airflow182out of a top side111of the heat exchanger compartment114(such that the furnace100is in a so-called “upflow orientation”), or may be arranged to emit the airflow182out of a side surface of the heat exchanger compartment114(such that the furnace100is in a so-called “side-flow orientation”). In this embodiment, the circulation blower180is configured to emit and force the airflow182over the heat exchanger tubes122,124, and thus, circulation blower180is disposed above the heat exchanger tubes122,124within the heat exchanger compartment114so as to produce the downflow orientation previously described above. However, in other embodiments, the circulation blower180may be configured to draw or pull the airflow182over the heat exchanger tubes122,124(and thus may be disposed below the heat exchanger tubes122,124within heat exchanger compartment114so as to produce the downflow orientation previously described above).

In addition, as is also shown inFIG.3, the furnace100may include an electrical switch assembly184that includes one or more switches for energizing one or more of the blower motors155,133, and/or the blower motor (not shown) of the circulation blower180. In this embodiment, the electrical switch assembly184is disposed along an upper surface or top112aof the combustion compartment112. Without being limited to this or any other theory, placement of the electrical switch assembly184outside of the combustion compartment112may shield the electrical switch assembly184from the heat generated within the burner box164(e.g., within burners170) during operations.

Referring specifically toFIG.4, generally speaking, the primary heat exchanger tubes122,124may be round in cross-section. However, portions of the secondary heat exchanger tubes124may comprise elliptical or oval sections125that may include one or more indentations or crimps127. Without being limited to this or any other theory, the elliptical sections125may reduce a projected cross-sectional area of the secondary heat exchanger tubes124so as to reduce a pressure drop for the airflow182(FIG.3) flowing across the heat exchanger tubes122,124during operations. In addition, the one or more indentations127may induce turbulence within the flue products flowing with the secondary heat exchanger tubes124so as to promote mixing of the flue products and enhance heat transfer from the flue products to the airflow (see e.g., airflow182inFIG.3) outside of heat exchanger tubes122,124.

In addition, as also shown inFIG.4, in this embodiment the primary heat exchanger tubes122are generally arranged or wrapped about the secondary heat exchanger tubes124. As a result, the secondary heat exchanger tubes124are disposed within the primary heat exchanger tubes122.

Referring now toFIG.5, a cross-section along section A-A is shown so as to further illustrate the components of the burner box164. In this embodiment, burner box includes two burners170fluidly coupled to chamber166via a pair of ports or apertures169. In particular, burner box164includes a first burner170aand a second burner170b. In this embodiment, the first burner170ais disposed vertically below the second burner170b.

Each burner170a,170bincludes a burner housing176that is disposed within the housing168and coupled about a corresponding one of the ports169. In this embodiment, the burner housings176are hollow cylindrical members that each include a central axis175, a first or inner end176a, and a second or outer end176bopposite first end176a. Inner ends176aare engaged with an outer wall166aof chamber166about the corresponding ports169such that second ends176bproject outward or away from outer surface166aalong the corresponding axis175. Note—FIG.5only depicts the axis175of the burner housing176of second burner170bso as to simplify the drawing.

Each burner170a,170bis generally aligned with a corresponding opening or inlet121of one of the primary heat exchanger tubes122. Because there are a total of two burners170a,170bin this embodiment, there are two corresponding primary heat exchanger tubes122that are generally aligned with the burners170a,170b. In particular, ports169in chamber166are generally aligned with the openings of primary heat exchanger tubes122such that the axes175of burner housings176are generally aligned with the central axes129of the corresponding primary heat exchanger tubes122when housings176are coupled to outer surface166aof chamber166about ports169as shown inFIG.5.

A burner medium178is disposed between the inner ends176aof the burner housing176and the chamber166. The burner medium178may comprise a porous material (e.g., a knitted material, mesh, etc.) that is generally allows the fuel/air mixture to flow therethrough. Without being limited to this or any other theory, flowing the fuel/air mixture through the burner medium178may slow the velocity of the fuel/air mixture as it flows from chamber166into the burner housings176, and may generally promote even distribution of the fuel/air mixture into the burner housings176during operations.

An ignition assembly190is disposed within the burner housing176of first burner170a. In this embodiment, ignition assembly190comprises a direct spark-type igniter that is configured to ignite the fuel/air mixture by emitting an electrical arc or spark between two electrodes. In particular, as shown inFIG.5, ignition assembly190comprises a first electrode192and a second electrode194extending into burner housing176of first burner170a. Each electrode192,194may include a distal or terminal tip192a,194a, respectively, and may be arranged within burner housing176of first burner170a. In some embodiments, terminal tips192a,194amay be arranged within burner housing176of first burner170asuch that the distal tips192a,194aare more proximate to the inner end176athan outer end176bof burner housing176. However, in various embodiments terminal tips192a,194amay be disposed at any position or depth within burner housing176of first burner170a(e.g., such as at a position more proximate outer end176bthan inner end176a, or a position substantially equidistant between ends176a,176b).

While not specifically shown inFIG.5, it should be appreciated that electrodes192,194may each generally be surrounded in an electrically insulating material, except for the distal tips192a,194aand/or a portion or section of the electrodes192,194that includes the tips192a,194a. The electrically insulating material may be configured to withstand the relatively high temperature of the flames formed within the burner housing176without melting, burning, etc.

During operations, one of the electrodes192,194may be energized with electrical current, while the other of the electrodes192,194may be generally electrically coupled to an electrical ground. As a result, an electrical discharge, such as an arc or spark may form between the electrodes192,194. Due to the electrical insulating material surrounding most of the electrodes192,194as described above, the electric discharge occurs at or proximate to the distal tips192a,194awhich are disposed within the burner housing176, proximate to the inner end176aas previously described. Because the concentration of fuel/air mixture may be generally greater closer to the inner ends176aand ports169of chamber166, the generation of a spark (e.g., at distal tips192a,194a) at a location that is generally proximate to the inner end176aof burner housing176of first burner170amay promote a more reliable ignition of the fuel/air mixture during operations.

In some embodiments, the ignition assembly190may comprise another type or design of igniter, other than a direct spark igniter. For instance, in some embodiments, the ignition assembly190may comprise a hot surface igniter that initiates combustion by heating a surface (e.g., with electric current) that is exposed to the fuel/air mixture. Upon contacting the hot surface, the fuel/air mixture is ignited so as to initiate combustion thereof. Without being limited to this or any other theory, the direct spark-type igniter disclosed above for ignition assembly190may provide a more robust system compared with a hot surface igniter due to the generally more substantial construction of electrodes192,194as compared to some designs of a hot surface type igniter. As a result, use of a direct-spark type ignition assembly190may help to ensure more reliable ignition operations throughout the life of furnace100.

Referring still toFIG.5, burner housing176may include one or more notches or apertures177so as to promote flame propagation across each of the burners170a,170bduring operations. In particular, in this embodiment, the burner housing176of first burner170aincludes a notch177on a side facing (or most proximate to) the burner housing176of second burner170b. In addition, the burner housing176of second burner170bincludes a notch177on a side facing (or most proximate to) the burner housing176of first burner170a. Thus, the notches177may provide an open flow path that extends in a radial direction between the axes175of the burner housings176. During operations, notches177in burner housings176may allow flames to propagate between the first burner170aand second burner170b. In particular, during an initial ignition of the burners170a,170b, combustion may initiate within the burner housing176of the first burner170a(e.g., as a result of the spark formed between the electrodes192,194as previously described), and then may propagate to the burner housing176of the second burner170bvia the aligned notches177so as to then ignite the second burner170b. In addition, following initial ignition of the burners170a,170b, the aligned notches177may allow flame to propagate between the burner housings176in the event that flames are lost in one of the burners170a,170b. Each notch177may generally be rectangular in shape and extend axially from the outer ends176bof burner housings176toward the inner ends176a(with respect to the corresponding axes175of burner housings176); however, other shapes and designs of notches177are contemplated herein.

Second burner170bmay include a flame rod sensor196disposed within the burner housing176. The flame rod sensor196may comprise an elongate electrically conductive rod that is inserted through an aperture197in the wall of burner housing176of second burner170b. In some embodiments, the flame rod sensor196may extend into burner housing176(e.g., via aperture197) along a generally radial direction with respect to axis175of burner housing176of second burner170b. During operations, the flame rod196may sense electrical current that is conducted through the flames formed within the burners170a,170b. In some embodiments, and electrical current may be conducted through the flames in burners170a,170bfrom one of the electrodes192,194of ignition assembly190. Because flame rod196is inserted within the burner housing176of the second burner170b, the flame rod sensor196may essentially detect whether flame has fully propagated from the first burner170ato the second burner170b(e.g., via the flow path formed by the aligned notches177as previously described above). Accordingly, if flame is detected in the second burner170bvia the flame rod sensor196, then it may be assumed that flame is also present within the first burner170a. Conversely, if flame is not detected in the second burner170bvia the flame rod sensor196, then it may be presumed that either flame has not propagated to the second burner170bfrom first burner170aand/or that flames are not present in either of the burners170a,170b.

In addition, without being limited to this or any other theory, placement of the flame rod sensor196within the burner housing176may also provide an early indication of an upset in the combustion process within burner box164. Specifically, because combustion is initiated within the burner housings176as previously described above, any upsets (e.g., interruptions in fuel and/or air supply from premix blower152) will cause a loss of flame within the burner housings176first (e.g., particularly close to the burner medium178). Therefore, placing the flame rod sensor196within the burner housing176may allow flame rod sensor196to detect (e.g., via loss of flame) an upset to the combustion process relatively quickly, thereby allowing remediation measures to be taken before damage or other negative consequences occur. For instance, as will be described in more detail below, the placement of the flame rod sensor196within the burner housing176may enhance an ability of a controller assembly (e.g., controller assembly250described in more detail below) of furnace100to detect a blockage in the air inlet158of inlet nozzle153because flame rod sensor196is positioned to detect the resulting upset to the combustion process relatively quickly.

Referring still toFIG.5, during operations, fuel/air mixture is provided to the chamber166via inlet167from the premix blower152and conduit160as previously described above (see e.g.,FIG.1). The fuel/air mixture may generally fill the chamber166and flow out through the ports169into the burner housings176of burners170a,170b, where the fuel/air mixture is ignited (e.g., initially by ignition assembly190) so that flames are produced that flow along axes175of burner housings176toward inlets121of primary heat exchanger tubes122(note: the flames produced within burner housings176may not fully extend to inlets121, and may be fully contained within burner housings176themselves). During this process, secondary air is drawn into the housing168through the gap174as well as the apertures172. This secondary air is generally shielded from the interior of the burner housings176and mixes with the combusted (or partially combusted) fuel/air mixture downstream of the outer ends176bof burner housings176so as to complete the combustion of any fuel that was not combusted within the burner housings176and to insulate the walls of the primary heat exchanger tubes122proximate the inlets121as previously described above.

While the burner box164shown inFIG.5includes two burners170a,170b, it should be appreciated that different numbers of burners170may be included within the housing168in other embodiments. For instance, reference is now made toFIG.6which shows a burner box264that may be utilized within the furnace100in place of burner box164previously described. In describing the features of burner box264, the same reference numerals are used to designate features of the burner box264that are the same as the burner box164, and the description below will focus on the features of burner box264that are different form the burner box164.

In particular, burner box264is generally the same as burner box164except that a third burner170cis disposed between the first burner170aand second burner170balong outer surface166aof chamber166so that burner box264includes a total of three burners. The spacing between the burners170a,170bis adjusted so that third burner170cmay fit between the burners170a,170b. An additional primary heat exchanger tube122is coupled to the vestibule115and aligned with the axis115of the burner housing176of third burner170cso as to receive the combusted fuel/air mixture from third burner170cin the same manner described above for the primary heat exchanger tubes122aligned with the burners170a,170b.

In addition, the burner housing176of third burner170cincludes a pair of notches177that are disposed radially opposite one another about axis175and that are generally proximate and aligned with the corresponding notches177in the burner housings176of first burner170aand second burner170bas previously described above. As a result, the notches177of burner housings176of burners170a,170b,170cmay again form a flow path that extends in a radial direction between the burners170a,170b,170cwith respect to the axes175, so that flames that originate within the first burner170amay propagate to the third burner170c, and finally to the second burner170bvia the notches177.

Operations with the burner box264are generally the same as previously described above for the burner box164, and therefore are not generally repeated herein in the interest of brevity. However, it should be appreciated that the fuel/air mixture within the chamber166flows out of all three burners170a,170b,170cwhich may generally increase the amount of heat generated within the burner box264as compared to the burner box164.

Referring now toFIG.7, the placement of inlet nozzle153, premix blower152, and combustion blower130may be chosen such that primary air that is drawn into the air inlet158of inlet nozzle153is first flowed over the motors133,155of blowers130,152, respectively, so as to provide convective cooling for the blower motors133,155, and therefore prevent overheating of the blower motors133,155during operations.

In particular, in some embodiments (e.g., such as the embodiment ofFIG.7) the inlet nozzle153and air inlet158are generally centrally located within combustion compartment112, between the motors155,133such that air is drawn over the motors133,155in route to the air inlet158. As shown inFIG.7, in this embodiment, the air inlet158(and inlet nozzle153in general) is disposed vertically between the motors155,133of blowers152,130, respectively.

In addition, in some embodiments, air inlets are disposed along the outer surfaces of combustion compartment112so as to further channel the incoming air over the motors133,155while the air is in route to air inlet158during operations. For instance, as shown inFIG.7, one or more (e.g., a plurality of) first air inlets202may be formed in a front cover (or door)200of the combustion compartment112that are generally disposed above the motor133. In other words, the motor133is generally disposed between the first inlets202and the air inlet158of inlet nozzle153in the vertical direction (or other linear direction such as horizontal or a diagonal between the vertical and horizontal directions). As a result, during operations, the vacuum created at the air inlet158by premix blower152generates air flows204that flow into the combustion compartment112, through inlets202, over and around motor133, and eventually to air inlet158. In some embodiments, the inlets202are vertically higher than all portions or surface of the motor133; however, in other embodiments, inlets202are disposed vertically higher than a portion of motor133(e.g., such as a majority of motor133in some embodiments).

Also, front cover200of combustion compartment112includes one or more second openings206that are generally disposed below the motor155of premix blower152. In other words, the motor155is generally disposed between the second inlets206and air inlet158of inlet nozzle153in the vertical direction (or other linear direction such as horizontal or a diagonal between the vertical and horizontal directions). As a result, during operations, the vacuum created at the air inlet158by premix blower152generates air flows208that flow into the combustion compartment112, through inlets206, over and around motor155, and eventually to air inlet158. In some embodiments, the inlets206are vertically lower than all portions or surface of the motor155; however, in other embodiments, inlets206are disposed vertically lower than a portion of motor155(e.g., such as a majority of motor155in some embodiments).

Accordingly, due to the relative placement of the air inlet158, motors133,155, and inlets202,206in front cover200, the motors133,155may be subjected to convective cooling via the air flows204,208that is configured to maintain an acceptable operating temperature of the motors133,155during operations. In some embodiments, it is desirable to maintain the temperature of the air flowing through premix blower152and into burner box164as close to ambient as possible.

Also, the flow of air within the combustion compartment112(e.g., air flows204, the flow of secondary air toward and through the gap174, ports172, etc.) may provide convective cooling to burner box164, which thereby maintains a relatively stable temperature within the burner box164during operations. Without being limited to this or any other theory, limiting the temperature increases within the burner box164during operation of the furnace100may allow the fuel/air ratio for producing a reduced amount of NO from the combustion process may be maintained at a relatively constant level. Specifically, the temperature within the burner box164and particularly within the housing168and about the burner(s)170, may affect the density of the air within the fuel/air mixture. The density of the air in the fuel/air mixture may then affect rate of combustion and therefore influence the amount of NO that is thereby produced. Normally, one would expect the temperature of the burner box164to increase relatively quickly during operations due to the combustion occurring within the burner(s)170, which would then require adjustments in the fuel/air ratio to maintain relatively low levels of NOx. However, in the furnace100, the above-described air flow within combustion compartment112may help to slow (or even halt) the temperature increase of and within the burner box164during operations so that the fuel/air ratio may be held substantially stable during operation, while still producing relatively low levels of NOxas described above.

Further, reducing the temperature increase within the burner box164during operations may also reduce an overall noise of the furnace100during operations. Specifically, as the fuel/air mixture, flames, flue products, etc. flow into and through the burner box164, vibrations are produced that may be audible within a certain distance of the furnace100. The temperature within the furnace100(and particular burner box164) may alter the resonant frequencies of components of burner box164such that adjustments in motor speeds (e.g., blower motors155,133), firing rates, etc. may be called for so as to avoid these changing resonant frequencies during operations. However, by reducing the temperature increases within the burner box164via the above-described air flows within combustion compartment112(e.g., air flows204, the flow of secondary air toward and through the gap174, ports172, etc.), the resonant frequencies of burner box164may remain substantially constant or stable so that such adjustments are avoided during operation and the operation of the furnace100can be effectively tuned so as to reduce the overall noise.

During operations with the furnace100, the conditions (e.g., pressure, temperature, fuel/air ratio, etc.) of the combustion process within the burner(s) (e.g., burners170a,170b,170c, etc.) may be precisely controlled via the various structures and features described above so as to produce relatively low levels of NOxin the flue products. In some embodiments, utilizing the features described above within furnace100, levels of NOxbelow 14 ng/J of NOxmay be produced during operations.

Having described various features and components of embodiments of a furnace100, the discussion will now turn to various control systems and methods that may be utilized with various embodiments of furnace100. Referring now toFIG.8, an example controller assembly250for furnace100is shown. In the discussion below, additional and continuing reference is also made toFIG.1which schematically shows the various components of furnace100as previously described above.

Generally speaking, the controller assembly250is coupled to various components of the furnace100as well as various sensors configured to detect various operating parameters within the furnace100. Controller assembly250may comprise a singular controller or control board or may comprise a plurality of controllers or control boards that are coupled to one another. For convenience, and to simplify the drawings, the controller assembly250is depicted schematically as a single controller unit that is coupled to the various components and sensors within furnace100. The controller assembly250may be a dedicated control for the furnace100or some or all functionality of controller250may be integrated with other controllers of an HVAC system, such as a system controller (e.g. a thermostat) or other unit controllers, such as for a packaged unit having both the furnace100and air conditioning capability.

As depicted inFIG.8, controller assembly250comprises a processor252and a memory254. The processor252(e.g., microprocessor, central processing unit (CPU), or collection of such processor devices, etc.) executes machine-readable instructions256provided on memory254(e.g., non-transitory machine-readable medium) to provide controller assembly250with all the functionality described herein. The memory254may comprise volatile storage (e.g., random access memory (RAM)), non-volatile storage (e.g., flash storage, read-only memory (ROM), etc.), or combinations of both volatile and non-volatile storage. Data consumed or produced by the machine-readable instructions256can also be stored on memory254. As noted above, in some embodiments, controller assembly250may comprise a collection of controllers and/or control boards that are coupled to one another. As a result, in some embodiments, the controller assembly250may comprise a plurality of processors252, memories254, etc.

Controller assembly250is communicatively coupled to premix blower152, combustion blower130, circulation blower180, fuel valve156, ignition assembly190, and flame rod sensor196, wherein each of these components is configured as previously described above. In addition, controller assembly250is communicatively coupled to a plurality of sensors disposed within furnace. For instance, controller assembly250is communicatively coupled to a pressure sensor260that is configured to detect a pressure within inlet nozzle153(or another point upstream of the premix blower152). The pressure sensor260may comprise any suitable device that is configured to detect a pressure or value indicative thereof.

Controller assembly250is also communicatively coupled to a first motor sensor262and a second motor sensor263. The first motor sensor262is configured to detect a speed of the impeller154, output shaft (not shown) of motor155, or both of premix blower152, and second motor sensor263is configured to detect a speed of the impeller132, output shaft (not shown) of motor133, or both of combustion blower130. The motor sensors262,263may comprise any suitable device for measuring a rotational speed of an object (e.g., impeller, shaft, etc.). In some embodiments, the sensors262,263may comprise Hall-effect sensors that utilize magnetic signals for detecting a rotational speed. In some embodiments, the motors sensors262,263may be configured to detect a speed of the impellers154,132, motors155,133, etc. in a number of revolutions per unit time (e.g., revolutions per minute—RPM).

Referring still toFIG.8, controller assembly250may also be coupled to or integrated with a separate device266. The separate device266may comprise an input/output (I/O) unit (e.g., a graphical user interface, a touchscreen interface, or the like) for displaying information and for receiving user inputs. The device266may display information related to the operation of the furnace100and may receive user inputs related to operation of the furnace100. During operations, device266may communicate received user inputs to the controller assembly250, which may then execute control of furnace100accordingly. In some embodiments, the device266may further be operable to display information and receive user inputs tangentially related and/or unrelated to operation of the furnace100. In some embodiments, however, the device266may not comprise a display and may derive all information from inputs from remote sensors and remote configuration tools (e.g., remote computers, servers, smartphones, tablets, etc.). In some embodiments, controller assembly250may receive user inputs from remote configuration tools, and may further communicate information relating to furnace100to device266. In these embodiments, controller assembly250may or may not also receive user inputs via device266. In some embodiments, the controller assembly250and/or the device266may be embodied in a thermostat that may be disposed within the defined space.

Controller assembly250may be communicatively coupled to the various components described above (e.g., blowers152,130,180, valve156, ignition assembly190, flame rod sensor196, sensors260,262,263, device266, etc.) through any suitable communication path or method. For instance, in some embodiments, controller assembly250may be communicatively coupled to these various components via a wired communication path (e.g., electrically conductive wire, fiber optic cable, acoustically conductive cable, electrically conductive pads, traces, contacts, etc.), a wireless communication path (e.g., radio frequency communication, infrared communication, acoustic communication, WIFI, Bluetooth®, near field communication, etc.), or a combination thereof.

In addition, controller assembly250, device266, and various components of furnace100(e.g., blowers152,130,180, ignition assembly190, valve156, sensors260,262,263, etc.) may be coupled to a power source258. Power source258may comprise any suitable source (or collection of sources) of usable power—e.g., such as electrical power). For instance, power source258may comprise one or more batteries, capacitors, etc. In some embodiments, the power source258may comprise electrical power provided from a local utility. Some of the components within furnace100may receive power (e.g., electrical power) directly from power source258or indirectly through other components (e.g., such as controller assembly250). It should be noted that only some of the example connections to power source258are shown for the depicted components of furnace100and controller assembly250so as to simplify figure. In this embodiment, the power source258provides a source of Alternating Current (AC) power.

Various control methods for furnace100are now described herein. In some embodiments, the following methods may be performed utilizing embodiments of furnace100and controller assembly250as described herein. Thus, in describing the following methods, continuing reference is made to the components of furnace100and controller assembly250previously described above and/or generally shown inFIGS.1-8.

Referring now toFIG.9, a method300of starting up furnace100is shown. Initially, method300includes receiving a call for heat at block302. The call for heat may be received by the controller assembly250from another device (e.g., such as device266) or may be generated within the controller assembly250itself (e.g., such as in embodiments where the controller assembly250is or is incorporated within a thermostat or other suitable user input device for furnace100). The call for heat may be derived upon detecting or determining that the temperature within the defined space serviced by the furnace100is below a desired temperature or temperature range.

After the call for heat is received at block302, method300proceeds to perform a pre-purge sequence at block304. Generally speaking, the pre-purge method may be configured to purge fuel and/or flue products from the furnace100prior to initiating subsequent combustion operations. More particular, the pre-purge sequence may sweep or purge flue products out of the heat exchanger assembly120(e.g., heat exchanger tubes122,124, headers116,117, flue pipe134, etc.), and may sweep or purge fuel from portions of the combustion assembly150(e.g., the inlet nozzle153, premix blower152, conduit160, chamber166, housing168, burner(s)170, etc.).

Referring now toFIG.10, an embodiment of a method320for performing a pre-purge sequence for furnace100is shown. The method320may be performed as block304within method300inFIG.9.

Initially, method320includes closing the fuel valve156at block322. For instance, for the furnace100and controller assembly250, the controller assembly250may close the fuel valve156so as to prevent any fuel (e.g., natural gas, propane, etc.) from flowing through the fuel valve156into the inlet nozzle153. As previously described above, the fuel valve156may comprise a negative pressure regulator valve that opens in response to a negative pressure generated by the operation of the premix blower152. In addition, in some embodiments, the valve156may be closable by controller assembly250(e.g., via a suitable actuator that is communicatively coupled to controller assembly250) so as to prevent fuel from flowing out of the valve156into the inlet nozzle153regardless of the pressure at the gas inlet159and/or operating state of the premix blower152.

In addition, method320includes starting the premix blower152at block324and starting the combustion blower130at block326. Specifically, blocks324and326comprise starting the premix blower152and the combustion blower130via the controller assembly250so as to cause the motors155,133to rotate the impellers154,132within the blower housings151,131. As a result, air may be drawn into the air inlet158of inlet nozzle153, flowed through the premix blower152and into burner box164. The air is then emitted from burner(s)170and flows into the primary heat exchanger tube(s)122of heat exchanger assembly120. Thereafter, the negative pressure generated by the combustion blower130may draw the air through the heat exchanger tubes122,124, headers116,117and into flue pipe134which then vents the air into the outer environment. As the air is flowing through the combustion assembly150and heat exchanger assembly120as described above, fuel and flue products present therein (e.g., such as might be retained within the combustion assembly150and/or heat exchanger assembly120at the end of the previous operation of furnace100), may be swept from the furnace10and vented to the outside environment. Without being limited to this or any other theory, purging flue products and fuel from the furnace100prior to initiating an operation thereof may prevent an improper fuel/air ratio within the burner(s)170when combustion is later ignited within the burner(s)170. In addition, in some embodiments, the pre-purge method (e.g., method320) at block304may help to ensure that combustion does not occur within burner(s)170until desired by removing potentially combustible materials from furnace100.

Referring still toFIG.10, in some embodiments, method320may comprise stopping the premix blower152at block328in lieu of closing the gas valve156and starting the premix blower152at blocks322and324, respectively, as previously described above. As previously described above, the fuel valve156may comprise a negative pressure regulator valve that opens in response to a negative pressure generated by the operation of the premix blower152. As a result, by stopping the premix blower152at block328, fuel may not be drawn through fuel valve156and therefore into the burner box164, so that actuating or closing the gar valve156may be unnecessary. In these embodiments (e.g., where the block328is performed in lieu of blocks322,324), the combustion blower130may be started at block326following (or at the same time as) stopping the premix blower152at block328.

Referring again toFIG.9, in some embodiments, method300may also comprise performing a warm-up sequence at block306. In particular, in some embodiments of furnace100the ignition assembly190comprises a hot surface style igniter as previously described above. As a result, the hot surface may be pre-warmed prior to introducing fuel/air mixture into the burner(s)170so as ensure more reliable ignition within burner(s)170.

Referring now toFIG.11, a method330for performing a warm-up sequence within furnace100is shown. In some embodiments, the method330may be performed as block306within method300inFIG.9.

Initially, method330includes stopping the premix blower152at block332, and stopping the combustion blower130at block334. In particular, blocks332,334may comprise stopping the premix blower152and combustion blower130so as to prevent motors155and133, respectively from rotating impellers154and132, respectively, via controller assembly250.

In addition, method330includes energizing the hot surface igniter for a predetermined period of time at block336. As previously described, when ignition assembly190is a hot surface style igniter electric current may be supplied through a resistive surface so as to generate heat. Thus, when the hot surface is energized as in block336, the temperature of the hot surface begins to increase. The predetermined period of time at block336may be a sufficient amount of time based on the electrical current flowing through the hot surface as well as the design (e.g., material, shape, size, etc.) of the hot surface, such that the hot surface igniter reaches an appropriate temperature to ignite the fuel/air mixture when the mixture is flowed over the hot surface subsequent to the warm-up method320. In some embodiments, the temperature hot surface igniter may be raised above the flash point temperature of the fuel/air mixture (or the flash point of the fuel disposed within the fuel/air mixture) that is to be provided to burner(s)170and hot surface igniter.

It should be appreciated that in some embodiments of method300, the warm-up sequence of block306may be omitted. For instance, in some embodiments, ignition assembly190may comprise a direct spark igniter such that warm-up sequence is not necessary prior to an ignition sequence (see e.g., block308described in more detail below).

Referring again toFIG.9, method300also includes performing an ignition sequence at block308. As generally described above, an ignition sequence within furnace100may be different depending on the design and type of ignition assembly190.

Referring now toFIG.12, a method400of igniting furnace100is shown. In some embodiments, method400may be performed as block308within method300inFIG.9. Initially, method400includes starting the premix blower152at block402and starting the combustion blower130at block404. As previously described, operation of the premix blower152and combustion blower130may initiate the flow of fluid (e.g., initially air) through the combustion assembly150and heat exchanger assembly120. In addition, method400includes opening the fuel valve156at block408. Specifically, in some embodiments, after the energization of blowers152,130, the fuel valve156may be opened so as to start the flow of fuel to the burner box164along with the air flowing into the inlet nozzle153at air inlet158. In some embodiments, the premix blower152may be started in response to or simultaneously with opening the fuel valve156at block408.

Method400also includes energizing the ignition assembly190at block408. The precise method and timing of energizing the ignition assembly190will often depend on the type and design of ignition assembly190that is being utilized within furnace100. As previously described above, in some embodiments, the ignition assembly190comprises a direct-spark igniter. As a result, in these embodiments, energization of the ignition assembly190at block408may occur by conducting electric current to one of the electrodes192,194so as to generate an electrical arc between the tips192a,194aof electrodes192,194. In some embodiments, electric current is not conducted to the one of the electrodes192,194until a sufficient time has passed since opening the fuel valve156and initiating the flow of fuel to the burner(s)170at block406, so that a sufficient volume of fuel (within a fuel/air mixture) is present within the burner(s)170to ensure reliable ignition when a spark is emitted between the electrodes192,194.

In other embodiments, the ignition assembly190may comprise a hot surface type igniter as previously described. In these embodiments, energizing the ignition assembly190may comprise energizing the hot surface with electric current so as to increase a temperature thereof as previously described. However, in these embodiments, the energization of the hot surface igniter may occur before or simultaneously with opening the fuel valve156and initiating the flow of fuel to the burner(s)170. For instance, in these embodiments, the energization of the ignition assembly190may occur during a previous warm-up method (e.g., at block306of method300). Specifically, as previously described, during the warm-up sequence, the hot surface style ignition assembly may be energized with electric current so as to increase a temperature thereof (see e.g., block336in method330ofFIG.11). The ignition assembly190may then remain energized so as to maintain the heat of the hot surface so that ignition may occur once the fuel (and mixed air) reaches the hot surface following opening of the fuel valve at block406. Thus, in some embodiments of method400, energizing the ignition assembly190at block408may occur before blocks402-406.

Referring still toFIG.12, following starting of the premix blower152and combustion blower130at blocks402and404, respectively, opening of the fuel valve156at block406, and energization of the ignition assembly190at block408, method400next includes determining whether flame sensor196is detecting flame at block410. As previously described, flame rod sensor196may detect the presence of flame within one or more of the burners170(e.g., burners170a,170b,170c, etc.) by detecting an electric current that is conducted through the flame.

If flame is detected at block410, method400ends; however, if flame is not detected at block410, method400proceeds to close the fuel valve156at block412. Specifically, as previously described, if the flame rod sensor196detects electric current conducted through the flames within the burner(s)170(e.g., burners170a,170b,170c, etc. inFIGS.5and6), then it may be determined that flames are present in the burner(s)170following energization of the ignition assembly190and opening the fuel valve156. Thus, in this event, the ignition method400may end and normal operations of the furnace100will proceed thereafter. Alternatively, upon determining that no flame is present at block410, method400may recycle to either re-energize the ignition assembly190at block408or to again determine whether flame is present at block410.

Specifically, if the flame rod sensor196does not detect the present of flame within the burner(s)170, then it will be assumed that the fuel/air mixture flowing into the burner(s)170did not ignite as a result of energizing the ignition assembly190at block408. As a result, method400may proceed, in some embodiments, to close the fuel valve at block412and thereby prevent the build-up of un-combusted fuel/air mixture in the burner box164, heat exchanger assembly120, and possibly in the environment surrounding the furnace100(which may present a dangerous risk of an uncontrolled explosion in and around the furnace100). However, in some embodiments, method400may reattempt to ignite the fuel/air mixture with the ignition assembly190at block408and/or to re-determine whether flames are present within the burner(s)170via the flame rod sensor196at block410if no flames are detected at block410.

Referring again toFIG.9, following the performance of the ignition sequence at block308(e.g., method400inFIG.12), method300proceeds to start the circulation blower180at block310. Specifically, once combustion has been initiated, the circulation blower180may be started so as to initiate the transfer of heat from the hot flue products resulting from the combustion to the airflow182provided to the defined space within the heat exchanger assembly120as previously described above. For the furnace100, starting the circulation blower180to initiate airflow182may occur before, during, or after the ignition sequence at block308. For instance, in some embodiments, it may be desirable to delay the initiation of airflow182until the heat exchanger tubes122,124of heat exchanger assembly120have reached a sufficient temperature so as to ensure a sufficiently high temperature of airflow182at the exit of heat exchanger compartment114and therefore avoid flowing uncomfortably cool air to the defined space (which may negatively impact occupant comfort). Thus, in these embodiments, controller assembly250may wait a predetermined period of time after the ignition sequence at block308to start the circulation blower180at block310. In other embodiments, the circulation blower180may be started simultaneously, before, or very soon after the ignition sequence at block308so as to improve heat transfer efficiency of the furnace100.

Following the start-up of the furnace100(e.g., via method300), normal operations of the furnace100may proceed until the call for heat has ceased for the defined space (e.g., such as when the temperature within the defined space reaches a target value). During these operations, controller assembly250may monitor the furnace100for a blockage in the air inlet158of the premix blower152. If the air inlet158to the premix blower152were to become blocked during operations, combustion may be extinguished within the burner(s)170and un-combusted fuel may begin to build within and around the furnace100.

Specifically, referring now toFIG.13, a method500of detecting a blocked air inlet158of the premix blower152is shown. As will be described in more detail below, method500includes multiple parallel manners of detecting the blockage within air inlet158that may help to increase the sensitivity and reliability of controller assembly250in terms of detecting a blocked air inlet158of premix blower152during operations. As will be described in more detail below, method500may employ one, a combination of, or all of these parallel manners and techniques for detecting a blocked air inlet158of premix blower152during operations.

Specifically, method500initially includes detecting a pressure downstream of the air inlet and upstream the premix blower152of the furnace at block502. In particular, block502may comprise receiving an output signal from pressure sensor260as generally described above.

Following detecting the pressure at block502, method500includes determining whether the pressure is below a predetermined pressure value at block506. Without being limited to this or any other theory, if the air inlet158is blocked during operation of the premix blower152, the area between the blocked inlet158and the premix blower152within the inlet nozzle153may begin to fall in pressure due to the continued rotation of impeller154within housing151. The predetermined pressure value in block506may correspond to a sufficient reduction in pressure within the inlet nozzle153so as to indicate that the air inlet158has become blocked (e.g., by dust, dirt, or other obstruction).

If it is determined that the pressure detected at block502is not below a predetermined pressure value at block506(i.e., the determination at block506is “no”), then method500recycles back to block502to once again detect the pressure downstream of the air inlet as previously described. If, on the other hand, it is determined that the pressure detected at block502is below the predetermined pressure value at block506(i.e., the determination at block506is “yes”), then method500may proceed to block510to determine that the inlet of the premix blower is blocked.

In addition, method500comprises detecting a speed of the premix blower152at block504, which may comprise detecting a speed of the impeller154or motor155of premix blower152via the sensor262as previously described. Thereafter, method500includes determining whether the speed detected at block504is above a predetermined speed value at block508. Without being limited to this or any other theory, when the air inlet158, becomes blocked, the impeller154is impacting a reduced volume of fluid (e.g., air, fuel, etc.) within the blower housing151so that a drag force operating on impeller154is reduced. As a result, for a given torque supplied from motor155, the impeller154will rotate at an increased speed, as the air inlet158becomes blocked. The predetermined speed value at block508may correspond with an expected increase in speed impeller154that may result from a blockage in the air inlet158of inlet nozzle153.

If it is determined that the speed detected at block504is not above a predetermined speed value at block508(i.e., the determination at block508is “no”), then method500recycles back to block504to once again detect the speed of the premix blower152as previously described. If, on the other hand, it is determined that the speed detected at block504is above the predetermined speed value at block508(i.e., the determination at block508is “yes”), then method500may again proceed to block510to determine that the inlet of the premix blower152is blocked.

Further, method500also includes determining whether a flame is present with in the burner(s)170of furnace100at block509. In particular and without being limited to this or any other theory, if the air inlet158of the inlet nozzle153becomes blocked, the combustion process may stop within the burner(s)170due to a lack of oxygen. Thus, at block509, the flame rod sensor196may be utilized in the manner described above so as to monitor for the presence of flame within the burner(s)170. If the flame rod sensor196should detect flames within the burner(s)170(i.e., the determination at block509is “yes”), then method500recycles back to once again determine whether flame is presented within the burner(s)170at block509. If, on the other hand, flame rod sensor196does not detect a flame within the burner(s)170(i.e., the determination at block509is “no”), then method500may again proceed to block510to determine that the inlet of premix blower152is blocked. As previously described above, the flame rod sensor196may be placed within one of the burner housings176and therefore close to the location where combustion is initiated for the fuel/air mixture within burner box164. As a result, the flame rod sensor196may detect the loss of flame that may result from a blockage in the air inlet158relatively early (e.g., as compared to situations where flame rod sensor196is disposed outside of burner housing176).

Thus, method500allows a block air inlet158of premix blower152to be detected via a pressure measurement upstream of the premix blower152(e.g., via blocks502and506), a speed measurement of the impeller154or motor155of premix blower152(e.g., via blocks504and508), and/or detecting a loss of flames within the burner(s)170(e.g., via block509). Accordingly, a blocked air inlet158may be more reliably detected (e.g., by controller assembly250) during operations via method500. In some embodiments, method500may detect the blocked inlet158at block510via only one of the pressure measurements via blocks502and506, the speed measurements via blocks504and508, and/or the flame loss detection at block509. Alternatively, in some embodiments, method500may detect the blocked inlet158at block510via a combination or all of the pressure measurements via blocks502and506, the speed measurements via blocks504and508, and the flame loss detection at block509.

Regardless of whether the determination at block510is reached as a result of the determination at block506, the determination at block508, and/or the determination at block509, once it is determined that the inlet of the premix blower is blocked at block510, method500proceeds to initiate a shut-down of the furnace10. For instance, the controller assembly250may directly shut down the furnace10by, for example, closing the fuel valve156, and stopping the premix blower152, combustion blower130, and/or circulation blower180. In some embodiments, the controller assembly250may initiate a shutdown of the furnace10by sending a shutdown command to another device (e.g., device266) that then directly initiates a shutdown of one of more components of the furnace10. In addition, in some embodiments method500also includes outputting an error message at block514, which may include an audible alarm, a message displayed on a display or other suitable location, so as to alert a user of the furnace (e.g., an occupant of the defined space) that an error has occurred within the furnace10(e.g., the air inlet158is blocked) and a service technician should be contacted to address the error. The error message at block514may be output by controller assembly250(or another device such as device266).

In addition to detecting a blocked inlet for the premix blower152, during operations with furnace100, controller assembly250may also modulate a speed of the blowers152,130, and/or180so as to counteract voltage fluctuations provided by power source258. For instance, in some embodiments, power source258may comprise a source of electrical power (e.g., AC electric current) from a local utility as previously described. In some circumstances, the electrical power provided by power supply258may include voltage fluctuations that may cause the speeds of blowers152,130,180to also fluctuate. Accordingly, reference is now made toFIG.14, which shows a method600of maintaining a speed for a blower (or multiple blowers) of furnace100in light of a fluctuating input voltage. Method600may generally be applied by the controller assembly250to the control the speed of any of the premix blower152, combustion blower130, and circulation blower180during operations.

Initially, method600comprises detecting a speed of a blower of furnace100at block602. For furnace100, block602may comprise detecting the speed of the premix blower152, the combustion blower130, and/or the circulation blower180. The speed of the blowers152,130,180may be detected in any suitable manner. For instance, in some embodiments, the speed of the blowers152,130may be detected by the sensors262,263as previously described above. Similarly, another sensor (not shown) similar to the sensors262,263may be coupled to the circulation blower180and communicatively coupled to the controller assembly250so as to allow controller assembly250to detect the speed of the circulation blower180in the same manner as previously described above for the sensors262,263for blowers152,130, respectively.

Next, method600proceeds to determine whether the speed of the blower is below a predetermined lower limit at block604. If the blower speed is below the predetermined lower limit (i.e., the determination at block604is “yes”), then method600proceeds to shut down the furnace100at block612and output an error message at block614. On the other hand, if it is determined at block604that the speed is not below the predetermined lower limit (i.e., the determination at block604is “no”), method600proceeds to determine whether the speed of the blower is above a predetermined upper limit at block606. If the blower speed is above the predetermined upper limit at block606, method600proceeds again to blocks612and614to shut down the furnace and output and error message as previously described. If, on the other hand, the blower speed is not above the predetermined upper limit at block606(i.e., the determination at block606is “no”), method600proceeds to determine an error between a target speed of the blower and the detected speed at block608and then adjust the speed of the blower to reduce the error below a target error value at block610.

In some embodiments, the predetermined lower limit in block604and the predetermined upper limit in block606may correspond with the lowest and highest speeds, respectively, of the blower (e.g., blower152,130,180, etc.) that correspond with expected fluctuations in the voltage supplied from power source258. In some embodiments, the predetermined lower limit in block604and the predetermined upper limit in block606may correspond with the lowest and highest speeds, respectively, of the blower (e.g., blower152,130,180) that correspond with the lowest and highest acceptable voltage values that may be utilized by the blower for operation. Thus, if the speed of the blower is below the predetermined lower limit in block604or above the predetermined upper limit at block606, then it may be determined that the blower (e.g., blowers152,130,180, etc.) is operating outside of its predetermined normal or acceptable range (e.g., such as outside of the blowers rated input voltage range) so that operations with the blower (and the furnace100more generally) must cease and an error flag is triggered (e.g., by the controller assembly250) so as to alert a user of the furnace that a service technician needs to be contacted to determine and address the error within the furnace100before operations may once again commence.

If, on the other hand, the detected speed of the blower between the predetermined lower limit in block604and the predetermined upper limit in block606, then it may be determined that the blower (e.g., blower152,130,180, etc.) is operating within a normal input voltage range. Accordingly, as previously described above, method600may determine an error between the detected speed and the target speed of the blower and then adjust the speed of the blower so as to reduce or eliminate this error at blocks608,610. Specifically, at block608, determining the error between the target speed and the detected speed from block602may comprise determining a difference between a target value (which may be a target speed value for the blower based on the current operational state of the furnace100) and the detected speed from block602. Once the error is determined, it is compared to a target error that may correspond with an acceptable tolerance about the target speed value at block610. The size of the speed tolerance about the target speed value may vary depending on, for instance, the design of furnace100, the capacity demand for the furnace100, or the particular use of the blower (e.g., whether it is the premix blower152, combustion blower130, circulation blower180, etc.).

Next, method600proceeds to adjust the speed of the blower so as to decrease the error determined at block608. In some embodiments, the controller assembly250utilizes a proportional and integral (PI) control scheme to reduce the error between the target speed value and the detected speed value at block602below the target error. Specifically, if the detected speed of the blower from blower602is above the target speed value, due to an increase in the voltage supplied to the blower via the power source258, then block610may comprise reducing the speed of the blower via the controller assembly250so as to reduce the error below the target error and cause the speed of the blower to move closer to the target speed value. If, on the other hand, the detected speed of the blower from block602is below the target speed value, due to a decrease in the voltage supplied to the blower via the power source258, then block610may comprise increase the speed of the blower via the controller assembly250so as to reduce the error below the target error and cause the speed to move closer to the target speed value.

Referring now toFIGS.13and14, in some embodiments, furnace100and controller assembly250may simultaneously perform the methods500and600during operation of the furnace so as to simultaneously monitor for a blocked air inlet158and adjust the speed of blowers152,130,180to account for voltage fluctuations. Thus, for the premix blower152, controller assembly250may be simultaneously monitoring the speed of the impeller154(or motor155) for via blocks504,508to assess whether air inlet158is blocked, and adjusting the speed of the impeller154and motor155of premix blower152to account for voltage fluctuation from power source258. In order to allow these two operations within methods500,600to operate simultaneously on premix blower152without interference, the predetermined speed value from block508of method500inFIG.13may be equal to or higher than the predetermined upper limit of the speed of the premix blower152at block606of method600. As a result, a blocked air inlet158is not detected via method500as a result of speed changes within the premix blower152resulting from voltage fluctuations in power source258. Also, if the speed of the premix blower152should rise above the predetermined upper limit from block606of method600, the furnace100may be shut down via block612and an error message may be output via block614. In these circumstances, the generated error message may indicate that both an improper input voltage as well as a blocked air inlet158may be present within the furnace100so as to alert the service technician to inspect the furnace100for both problems.

Referring again toFIG.8, during operations with furnace100, a speed control of the premix blower152may be adjusted based on an altitude of the furnace100(e.g., above sea-level). For instance, if furnace100is operated in a location that is relatively high above sea-level (e.g., such as in a mountainous region), the air supply from the surrounding environment may be generally less dense, so that a resistance imposed on the impeller154of premix blower152may be decreased. As a result, for a given power input to the premix blower152, the impeller154may rotate at a faster rate than what would be expected when furnace100is operated in lower altitudes (e.g., such as at or near sea-level).

Accordingly, during operations, controller assembly250may decrease an input or controlled speed of the premix blower152(e.g., a speed of impeller154) so as to counteract the expected increase in impeller154speed associated with increased altitudes, and therefore maintain the fuel/air ratio within the desired range for reducing NOxproduction and providing adequate heating performance and capacity as described herein. In other words, controller assembly250may decrease the controlled speed of the premix blower152(e.g., by decreasing the electric power level supplied to the premix blower152) as the altitude of the furnace100increases.

As described above, the embodiments disclosed herein include furnaces and associated methods of operation that allow a furnace to produce relatively low levels of NO in the flue products, while still delivering reliable and satisfactory heating capacity for the associated defined space. At least some of the furnaces disclosed above may comprise a “push-pull” furnace that employs a first blower to “push” pressurized air and fuel to a burner box (where the air and fuel is combusted), and a second blower to “pull” the flue products resulting from the combustion through one or more heat exchanger tubes. In some embodiments, the furnaces of the embodiments disclosed herein may combust fuel at suitable fuel/air ratio so as to produce less than 14 ng/J of NOx, but while still achieving reliable and stable combustion for delivering adequate heating capacity to the defined space during operation.