may have a central aperture size of about 0.75 inches. In some embodiments, the orifice plate 162 may have a central aperture size of about 0.90 inches or 1.10 inches.

The housing 168 may include one or more ports or openings to allow a flow of secondary air into the housing 168 and therefore mix with the combusted (or partially combusted) fuel/air mixture that is emitted from the burner(s) 170. For instance, the housing 168 (or a portion thereof) may be spaced from the vestibule 115 so as to form a gap 174 therebetween. In addition, in some embodiments, additional ports 172 may also be formed in the wall of housing 168. The ports 172 may be disposed along a side of the housing 168 that faces inward, and generally toward a center of the combustion compartment 112. During operations, secondary air is drawn into the housing 168 via the gap 174 (and the ports 172, if present), and then mixes with the combusted (or partially combusted) fluid flowing out (and thus downstream) from the burner(s) 170 and into the heat exchanger assembly 120.

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 gap 174 (and the ports 172, if present) may form an insulating barrier between the walls of the heat exchanger tube(s) of heat exchanger assembly 120 (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 gap 174 (and the ports 172, 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 to FIG. 1, heat exchanger assembly 120 includes one or more heat exchanger tubes that are configured to receive the hot flue products produced from the combustion within burner(s) 170 of combustion assembly 150. In particular, in this embodiment, heat exchanger assembly 120 includes one or more primary heat exchanger tubes 122 and one or more a secondary heat exchanger tubes 124. The primary heat exchanger tube(s) 122 include inlet(s) 121 that form a general inlet for the heat exchanger assembly 120 and the secondary heat exchanger tube(s) 124 include outlet(s) 123 that form a general outlet for the heat exchanger assembly 120. Between the inlet(s) 121 and outlet(s) 123, the primary heat exchanger tubes 122 are coupled to the secondary heat exchanger tube(s) 124 via a hot header 116. Inlet(s) 121 is/are generally fluidly coupled to the burner(s) 170 through the vestibule 115, and the outlet(s) 123 is/are fluidly coupled to combustion blower 130 via a cold header 117. In this embodiment, the combustion blower 130 is disposed within the combustion compartment 112 along with the combustion assembly 150 so that the combustion products are communicated from the cold header 117, through the vestibule 115, into the combustion blower 130.

The combustion blower 130 may generally comprise a centrifugal blower comprising a blower housing 131, a blower impeller 132 at least partially disposed within the blower housing 131, and a blower motor 133 configured to selectively rotate the blower impeller 132. The combustion blower 130 may 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 blower 130 may be a single speed blower. The blower motor 133 may comprise any suitable driver for rotating the impeller 154 within blower housing 131. For instance, in this embodiment, the blower motor 133 comprises an electric motor.

Generally speaking, during operations, once flue products emitted from burner(s) 170 enter the inlet(s) 121 of the primary heat exchanger tube(s) 122, they are pulled through the primary heat exchanger tube(s) 122, the hot header 116, and the secondary heat exchanger tube(s) 124 to the outlet(s) 123 and cold header 117 by the combustion blower 130. The combustion blower 130 then emits the flue products to a flue pipe 134 for conveyance to the outside environment. The arrows 118 in FIG. 1 generally depict the flow path of flue products within the heat exchanger assembly 120 as generally described above. As the flue products are flowed through the primary heat exchanger tube(s) 122 and the secondary heat exchanger tube(s) 124, an airflow (not shown in FIG. 1, but see e.g., airflow 182 in FIG. 3) is directed over the outer surfaces of the heat exchanger tubes 122, 124 so that heat is transferred from the flue products to the airflow.

An orifice plate 126 may be disposed between the cold header 117 and the combustion blower 130. Without being limited to this or any other theory, the orifice plate 126 may produce a backpressure within the cold header 117 and secondary heat exchanger tube(s) 124 that is to generally slow the flow rate of the hot flue products within the heat exchanger assembly 120 and therefore promote additional heat transfer from the flue products to the airflow outside of the heat exchanger tubes 122, 124 during operations.

Referring still to FIG. 1, an auxiliary heater 106 may be disposed within the combustion compartment 112. During operations, auxiliary heater 106 may generate heat that is radiated within the combustion compartment 112. In some circumstances, the furnace 100 is intended for installation in an outdoor environment. When installed outdoors, the ambient temperature surrounding the furnace 100 may fall below an acceptable level for operating one or more components within the combustion compartment 112 (e.g., such as the blowers 152, 130 and particularly motors 155, 133). Therefore, if the furnace 100 has not been operating for an extended period, the temperature within the combustion compartment 112 may fall below the threshold temperature. To prevent combustion compartments temperature falling below a threshold temperature, auxiliary heater 106 may 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 compartment 112 (e.g., again, such as blowers 152, 130) may be immediately initiated upon receipt of a call for heat within the defined space. In some embodiments, auxiliary heater 106 may comprise a resistive heater that generates heat via one or more electrically resistive coils when they are energized with electrical current. In some embodiments, furnace 100 may include a low temperature governor that may prevent operation of the furnace if the temperature surrounding the furnace 100 and/or within the combustion compartment 112 should fall below a predetermined minimum value.

Referring generally now to FIGS. 2-4, more particular depictions of furnace 100 of FIG. 1 are shown so as to show the relative arrangement of the various components described above according to some embodiments. It should be noted that FIGS. 2 and 4 generally omit the housing 110 (except for the vestibule 115) so as to best show the various components of the combustion assembly 150 and heat exchanger assembly 120. However, FIG. 3 provides a schematic representation of housing 110 about combustion assembly 150 and heat exchanger assembly 120.

Referring specifically to FIG. 3, a circulation blower 180 is disposed within the heat exchanger compartment 114 along with the heat exchanger assembly 120. During operations, the circulation blower 180 may generate an airflow 182 that is directed over the heat exchanger tubes 122, 124, so that heat may be transferred from the heat exchanger tubes 122, 124 to the airflow 182 as previously described above. In this embodiment, the furnace 100 is arranged in a so-called “downflow orientation” such that the airflow 182 is emitted out of bottom side 113 of the heat exchanger compartment 114 after flowing over the heat exchanger tubes 122, 124. In other embodiments, the furnace 100 may be arranged to emit the airflow 182 out of a top side 111 of the heat exchanger compartment 114 (such that the furnace 100 is in a so-called “upflow orientation”), or may be arranged to emit the airflow 182 out of a side surface of the heat exchanger compartment 114 (such that the furnace 100 is in a so-called “side-flow orientation”). In this embodiment, the circulation blower 180 is configured to emit and force the airflow 182 over the heat exchanger tubes 122, 124, and thus, circulation blower 180 is disposed above the heat exchanger tubes 122, 124 within the heat exchanger compartment 114 so as to produce the downflow orientation previously described above. However, in other embodiments, the circulation blower 180 may be configured to draw or pull the airflow 182 over the heat exchanger tubes 122, 124 (and thus may be disposed below the heat exchanger tubes 122, 124 within heat exchanger compartment 114 so as to produce the downflow orientation previously described above).

In addition, as is also shown in FIG. 3, the furnace 100 may include an electrical switch assembly 184 that includes one or more switches for energizing one or more of the blower motors 155, 133, and/or the blower motor (not shown) of the circulation blower 180. In this embodiment, the electrical switch assembly 184 is disposed along an upper surface or top 112a of the combustion compartment 112. Without being limited to this or any other theory, placement of the electrical switch assembly 184 outside of the combustion compartment 112 may shield the electrical switch assembly 184 from the heat generated within the burner box 164 (e.g., within burners 170) during operations.

Referring specifically to FIG. 4, generally speaking, the primary heat exchanger tubes 122, 124 may be round in cross-section. However, portions of the secondary heat exchanger tubes 124 may comprise elliptical or oval sections 125 that may include one or more indentations or crimps 127. Without being limited to this or any other theory, the elliptical sections 125 may reduce a projected cross-sectional area of the secondary heat exchanger tubes 124 so as to reduce a pressure drop for the airflow 182 (FIG. 3) flowing across the heat exchanger tubes 122, 124 during operations. In addition, the one or more indentations 127 may induce turbulence within the flue products flowing with the secondary heat exchanger tubes 124 so as to promote mixing of the flue products and enhance heat transfer from the flue products to the airflow (see e.g., airflow 182 in FIG. 3) outside of heat exchanger tubes 122, 124.

In addition, as also shown in FIG. 4, in this embodiment the primary heat exchanger tubes 122 are generally arranged or wrapped about the secondary heat exchanger tubes 124. As a result, the secondary heat exchanger tubes 124 are disposed within the primary heat exchanger tubes 122.

Referring now to FIG. 5, a cross-section along section A-A is shown so as to further illustrate the components of the burner box 164. In this embodiment, burner box includes two burners 170 fluidly coupled to chamber 166 via a pair of ports or apertures 169. In particular, burner box 164 includes a first burner 170a and a second burner 170b. In this embodiment, the first burner 170a is disposed vertically below the second burner 170b.

Each burner 170a, 170b includes a burner housing 176 that is disposed within the housing 168 and coupled about a corresponding one of the ports 169. In this embodiment, the burner housings 176 are hollow cylindrical members that each include a central axis 175, a first or inner end 176a, and a second or outer end 176b opposite first end 176a. Inner ends 176a are engaged with an outer wall 166a of chamber 166 about the corresponding ports 169 such that second ends 176b project outward or away from outer surface 166a along the corresponding axis 175. Note—FIG. 5 only depicts the axis 175 of the burner housing 176 of second burner 170b so as to simplify the drawing.

Each burner 170a, 170b is generally aligned with a corresponding opening or inlet 121 of one of the primary heat exchanger tubes 122. Because there are a total of two burners 170a, 170b in this embodiment, there are two corresponding primary heat exchanger tubes 122 that are generally aligned with the burners 170a, 170b. In particular, ports 169 in chamber 166 are generally aligned with the openings of primary heat exchanger tubes 122 such that the axes 175 of burner housings 176 are generally aligned with the central axes 129 of the corresponding primary heat exchanger tubes 122 when housings 176 are coupled to outer surface 166a of chamber 166 about ports 169 as shown in FIG. 5.

A burner medium 178 is disposed between the inner ends 176a of the burner housing 176 and the chamber 166. The burner medium 178 may 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 medium 178 may slow the velocity of the fuel/air mixture as it flows from chamber 166 into the burner housings 176, and may generally promote even distribution of the fuel/air mixture into the burner housings 176 during operations.

An ignition assembly 190 is disposed within the burner housing 176 of first burner 170a. In this embodiment, ignition assembly 190 comprises 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 in FIG. 5, ignition assembly 190 comprises a first electrode 192 and a second electrode 194 extending into burner housing 176 of first burner 170a. Each electrode 192, 194 may include a distal or terminal tip 192a, 194a, respectively, and may be arranged within burner housing 176 of first burner 170a. In some embodiments, terminal tips 192a, 194a may be arranged within burner housing 176 of first burner 170a such that the distal tips 192a, 194a are more proximate to the inner end 176a than outer end 176b of burner housing 176. However, in various embodiments terminal tips 192a, 194a may be disposed at any position or depth within burner housing 176 of first burner 170a (e.g., such as at a position more proximate outer end 176b than inner end 176a, or a position substantially equidistant between ends 176a, 176b).

While not specifically shown in FIG. 5, it should be appreciated that electrodes 192, 194 may each generally be surrounded in an electrically insulating material, except for the distal tips 192a, 194a and/or a portion or section of the electrodes 192, 194 that includes the tips 192a, 194a. The electrically insulating material may be configured to withstand the relatively high temperature of the flames formed within the burner housing 176 without melting, burning, etc.

During operations, one of the electrodes 192, 194 may be energized with electrical current, while the other of the electrodes 192, 194 may be generally electrically coupled to an electrical ground. As a result, an electrical discharge, such as an arc or spark may form between the electrodes 192, 194. Due to the electrical insulating material surrounding most of the electrodes 192, 194 as described above, the electric discharge occurs at or proximate to the distal tips 192a, 194a which are disposed within the burner housing 176, proximate to the inner end 176a as previously described. Because the concentration of fuel/air mixture may be generally greater closer to the inner ends 176a and ports 169 of chamber 166, the generation of a spark (e.g., at distal tips 192a, 194a) at a location that is generally proximate to the inner end 176a of burner housing 176 of first burner 170a may promote a more reliable ignition of the fuel/air mixture during operations.

In some embodiments, the ignition assembly 190 may comprise another type or design of igniter, other than a direct spark igniter. For instance, in some embodiments, the ignition assembly 190 may 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 assembly 190 may provide a more robust system compared with a hot surface igniter due to the generally more substantial construction of electrodes 192, 194 as compared to some designs of a hot surface type igniter. As a result, use of a direct-spark type ignition assembly 190 may help to ensure more reliable ignition operations throughout the life of furnace 100.

Referring still to FIG. 5, burner housing 176 may include one or more notches or apertures 177 so as to promote flame propagation across each of the burners 170a, 170b during operations. In particular, in this embodiment, the burner housing 176 of first burner 170a includes a notch 177 on a side facing (or most proximate to) the burner housing 176 of second burner 170b. In addition, the burner housing 176 of second burner 170b includes a notch 177 on a side facing (or most proximate to) the burner housing 176 of first burner 170a. Thus, the notches 177 may provide an open flow path that extends in a radial direction between the axes 175 of the burner housings 176. During operations, notches 177 in burner housings 176 may allow flames to propagate between the first burner 170a and second burner 170b. In particular, during an initial ignition of the burners 170a, 170b, combustion may initiate within the burner housing 176 of the first burner 170a (e.g., as a result of the spark formed between the electrodes 192, 194 as previously described), and then may propagate to the burner housing 176 of the second burner 170b via the aligned notches 177 so as to then ignite the second burner 170b. In addition, following initial ignition of the burners 170a, 170b, the aligned notches 177 may allow flame to propagate between the burner housings 176 in the event that flames are lost in one of the burners 170a, 170b. Each notch 177 may generally be rectangular in shape and extend axially from the outer ends 176b of burner housings 176 toward the inner ends 176a (with respect to the corresponding axes 175 of burner housings 176); however, other shapes and designs of notches 177 are contemplated herein.

Second burner 170b may include a flame rod sensor 196 disposed within the burner housing 176. The flame rod sensor 196 may comprise an elongate electrically conductive rod that is inserted through an aperture 197 in the wall of burner housing 176 of second burner 170b. In some embodiments, the flame rod sensor 196 may extend into burner housing 176 (e.g., via aperture 197) along a generally radial direction with respect to axis 175 of burner housing 176 of second burner 170b. During operations, the flame rod 196 may sense electrical current that is conducted through the flames formed within the burners 170a, 170b. In some embodiments, and electrical current may be conducted through the flames in burners 170a, 170b from one of the electrodes 192, 194 of ignition assembly 190. Because flame rod 196 is inserted within the burner housing 176 of the second burner 170b, the flame rod sensor 196 may essentially detect whether flame has fully propagated from the first burner 170a to the second burner 170b (e.g., via the flow path formed by the aligned notches 177 as previously described above). Accordingly, if flame is detected in the second burner 170b via the flame rod sensor 196, then it may be assumed that flame is also present within the first burner 170a. Conversely, if flame is not detected in the second burner 170b via the flame rod sensor 196, then it may be presumed that either flame has not propagated to the second burner 170b from first burner 170a and/or that flames are not present in either of the burners 170a, 170b.

In addition, without being limited to this or any other theory, placement of the flame rod sensor 196 within the burner housing 176 may also provide an early indication of an upset in the combustion process within burner box 164. Specifically, because combustion is initiated within the burner housings 176 as previously described above, any upsets (e.g., interruptions in fuel and/or air supply from premix blower 152) will cause a loss of flame within the burner housings 176 first (e.g., particularly close to the burner medium 178). Therefore, placing the flame rod sensor 196 within the burner housing 176 may allow flame rod sensor 196 to 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 sensor 196 within the burner housing 176 may enhance an ability of a controller assembly (e.g., controller assembly 250 described in more detail below) of furnace 100 to detect a blockage in the air inlet 158 of inlet nozzle 153 because flame rod sensor 196 is positioned to detect the resulting upset to the combustion process relatively quickly.

Referring still to FIG. 5, during operations, fuel/air mixture is provided to the chamber 166 via inlet 167 from the premix blower 152 and conduit 160 as previously described above (see e.g., FIG. 1). The fuel/air mixture may generally fill the chamber 166 and flow out through the ports 169 into the burner housings 176 of burners 170a, 170b, where the fuel/air mixture is ignited (e.g., initially by ignition assembly 190) so that flames are produced that flow along axes 175 of burner housings 176 toward inlets 121 of primary heat exchanger tubes 122 (note: the flames produced within burner housings 176 may not fully extend to inlets 121, and may be fully contained within burner housings 176 themselves). During this process, secondary air is drawn into the housing 168 through the gap 174 as well as the apertures 172. This secondary air is generally shielded from the interior of the burner housings 176 and mixes with the combusted (or partially combusted) fuel/air mixture downstream of the outer ends 176b of burner housings 176 so as to complete the combustion of any fuel that was not combusted within the burner housings 176 and to insulate the walls of the primary heat exchanger tubes 122 proximate the inlets 121 as previously described above.

While the burner box 164 shown in FIG. 5 includes two burners 170a, 170b, it should be appreciated that different numbers of burners 170 may be included within the housing 168 in other embodiments. For instance, reference is now made to FIG. 6 which shows a burner box 264 that may be utilized within the furnace 100 in place of burner box 164 previously described. In describing the features of burner box 264, the same reference numerals are used to designate features of the burner box 264 that are the same as the burner box 164, and the description below will focus on the features of burner box 264 that are different form the burner box 164.

In particular, burner box 264 is generally the same as burner box 164 except that a third burner 170c is disposed between the first burner 170a and second burner 170b along outer surface 166a of chamber 166 so that burner box 264 includes a total of three burners. The spacing between the burners 170a, 170b is adjusted so that third burner 170c may fit between the burners 170a, 170b. An additional primary heat exchanger tube 122 is coupled to the vestibule 115 and aligned with the axis 115 of the burner housing 176 of third burner 170c so as to receive the combusted fuel/air mixture from third burner 170c in the same manner described above for the primary heat exchanger tubes 122 aligned with the burners 170a, 170b.

In addition, the burner housing 176 of third burner 170c includes a pair of notches 177 that are disposed radially opposite one another about axis 175 and that are generally proximate and aligned with the corresponding notches 177 in the burner housings 176 of first burner 170a and second burner 170b as previously described above. As a result, the notches 177 of burner housings 176 of burners 170a, 170b, 170c may again form a flow path that extends in a radial direction between the burners 170a, 170b, 170c with respect to the axes 175, so that flames that originate within the first burner 170a may propagate to the third burner 170c, and finally to the second burner 170b via the notches 177.

Operations with the burner box 264 are generally the same as previously described above for the burner box 164, and therefore are not generally repeated herein in the interest of brevity. However, it should be appreciated that the fuel/air mixture within the chamber 166 flows out of all three burners 170a, 170b, 170c which may generally increase the amount of heat generated within the burner box 264 as compared to the burner box 164.

Referring now to FIG. 7, the placement of inlet nozzle 153, premix blower 152, and combustion blower 130 may be chosen such that primary air that is drawn into the air inlet 158 of inlet nozzle 153 is first flowed over the motors 133, 155 of blowers 130, 152, respectively, so as to provide convective cooling for the blower motors 133, 155, and therefore prevent overheating of the blower motors 133, 155 during operations.

In particular, in some embodiments (e.g., such as the embodiment of FIG. 7) the inlet nozzle 153 and air inlet 158 are generally centrally located within combustion compartment 112, between the motors 155, 133 such that air is drawn over the motors 133, 155 in route to the air inlet 158. As shown in FIG. 7, in this embodiment, the air inlet 158 (and inlet nozzle 153 in general) is disposed vertically between the motors 155, 133 of blowers 152, 130, respectively.

In addition, in some embodiments, air inlets are disposed along the outer surfaces of combustion compartment 112 so as to further channel the incoming air over the motors 133, 155 while the air is in route to air inlet 158 during operations. For instance, as shown in FIG. 7, one or more (e.g., a plurality of) first air inlets 202 may be formed in a front cover (or door) 200 of the combustion compartment 112 that are generally disposed above the motor 133. In other words, the motor 133 is generally disposed between the first inlets 202 and the air inlet 158 of inlet nozzle 153 in 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 inlet 158 by premix blower 152 generates air flows 204 that flow into the combustion compartment 112, through inlets 202, over and around motor 133, and eventually to air inlet 158. In some embodiments, the inlets 202 are vertically higher than all portions or surface of the motor 133; however, in other embodiments, inlets 202 are disposed vertically higher than a portion of motor 133 (e.g., such as a majority of motor 133 in some embodiments).

Also, front cover 200 of combustion compartment 112 includes one or more second openings 206 that are generally disposed below the motor 155 of premix blower 152. In other words, the motor 155 is generally disposed between the second inlets 206 and air inlet 158 of inlet nozzle 153 in 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 inlet 158 by premix blower 152 generates air flows 208 that flow into the combustion compartment 112, through inlets 206, over and around motor 155, and eventually to air inlet 158. In some embodiments, the inlets 206 are vertically lower than all portions or surface of the motor 155; however, in other embodiments, inlets 206 are disposed vertically lower than a portion of motor 155 (e.g., such as a majority of motor 155 in some embodiments).

Accordingly, due to the relative placement of the air inlet 158, motors 133, 155, and inlets 202, 206 in front cover 200, the motors 133, 155 may be subjected to convective cooling via the air flows 204, 208 that is configured to maintain an acceptable operating temperature of the motors 133, 155 during operations. In some embodiments, it is desirable to maintain the temperature of the air flowing through premix blower 152 and into burner box 164 as close to ambient as possible.

Also, the flow of air within the combustion compartment 112 (e.g., air flows 204, the flow of secondary air toward and through the gap 174, ports 172, etc.) may provide convective cooling to burner box 164, which thereby maintains a relatively stable temperature within the burner box 164 during operations. Without being limited to this or any other theory, limiting the temperature increases within the burner box 164 during operation of the furnace 100 may allow the fuel/air ratio for producing a reduced amount of NO_xfrom the combustion process may be maintained at a relatively constant level. Specifically, the temperature within the burner box 164 and particularly within the housing 168 and 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_xthat is thereby produced. Normally, one would expect the temperature of the burner box 164 to 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 NO_x. However, in the furnace 100, the above-described air flow within combustion compartment 112 may help to slow (or even halt) the temperature increase of and within the burner box 164 during operations so that the fuel/air ratio may be held substantially stable during operation, while still producing relatively low levels of NO_xas described above.

Further, reducing the temperature increase within the burner box 164 during operations may also reduce an overall noise of the furnace 100 during operations. Specifically, as the fuel/air mixture, flames, flue products, etc. flow into and through the burner box 164, vibrations are produced that may be audible within a certain distance of the furnace 100. The temperature within the furnace 100 (and particular burner box 164) may alter the resonant frequencies of components of burner box 164 such that adjustments in motor speeds (e.g., blower motors 155, 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 box 164 via the above-described air flows within combustion compartment 112 (e.g., air flows 204, the flow of secondary air toward and through the gap 174, ports 172, etc.), the resonant frequencies of burner box 164 may remain substantially constant or stable so that such adjustments are avoided during operation and the operation of the furnace 100 can be effectively tuned so as to reduce the overall noise.

During operations with the furnace 100, the conditions (e.g., pressure, temperature, fuel/air ratio, etc.) of the combustion process within the burner(s) (e.g., burners 170a, 170b, 170c, etc.) may be precisely controlled via the various structures and features described above so as to produce relatively low levels of NO_xin the flue products. In some embodiments, utilizing the features described above within furnace 100, levels of NO_xbelow 14 ng/J of NO_xmay be produced during operations.

Having described various features and components of embodiments of a furnace 100, the discussion will now turn to various control systems and methods that may be utilized with various embodiments of furnace 100. Referring now to FIG. 8, an example controller assembly 250 for furnace 100 is shown. In the discussion below, additional and continuing reference is also made to FIG. 1 which schematically shows the various components of furnace 100 as previously described above.

Generally speaking, the controller assembly 250 is coupled to various components of the furnace 100 as well as various sensors configured to detect various operating parameters within the furnace 100. Controller assembly 250 may 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 assembly 250 is depicted schematically as a single controller unit that is coupled to the various components and sensors within furnace 100. The controller assembly 250 may be a dedicated control for the furnace 100 or some or all functionality of controller 250 may 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 furnace 100 and air conditioning capability.

As depicted in FIG. 8, controller assembly 250 comprises a processor 252 and a memory 254. The processor 252 (e.g., microprocessor, central processing unit (CPU), or collection of such processor devices, etc.) executes machine-readable instructions 256 provided on memory 254 (e.g., non-transitory machine-readable medium) to provide controller assembly 250 with all the functionality described herein. The memory 254 may 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 instructions 256 can also be stored on memory 254. As noted above, in some embodiments, controller assembly 250 may comprise a collection of controllers and/or control boards that are coupled to one another. As a result, in some embodiments, the controller assembly 250 may comprise a plurality of processors 252, memories 254, etc.

Controller assembly 250 is communicatively coupled to premix blower 152, combustion blower 130, circulation blower 180, fuel valve 156, ignition assembly 190, and flame rod sensor 196, wherein each of these components is configured as previously described above. In addition, controller assembly 250 is communicatively coupled to a plurality of sensors disposed within furnace. For instance, controller assembly 250 is communicatively coupled to a pressure sensor 260 that is configured to detect a pressure within inlet nozzle 153 (or another point upstream of the premix blower 152). The pressure sensor 260 may comprise any suitable device that is configured to detect a pressure or value indicative thereof.

Controller assembly 250 is also communicatively coupled to a first motor sensor 262 and a second motor sensor 263. The first motor sensor 262 is configured to detect a speed of the impeller 154, output shaft (not shown) of motor 155, or both of premix blower 152, and second motor sensor 263 is configured to detect a speed of the impeller 132, output shaft (not shown) of motor 133, or both of combustion blower 130. The motor sensors 262, 263 may comprise any suitable device for measuring a rotational speed of an object (e.g., impeller, shaft, etc.). In some embodiments, the sensors 262, 263 may comprise Hall-effect sensors that utilize magnetic signals for detecting a rotational speed. In some embodiments, the motors sensors 262, 263 may be configured to detect a speed of the impellers 154, 132, motors 155, 133, etc. in a number of revolutions per unit time (e.g., revolutions per minute—RPM).

Referring still to FIG. 8, controller assembly 250 may also be coupled to or integrated with a separate device 266. The separate device 266 may 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 device 266 may display information related to the operation of the furnace 100 and may receive user inputs related to operation of the furnace 100. During operations, device 266 may communicate received user inputs to the controller assembly 250, which may then execute control of furnace 100 accordingly. In some embodiments, the device 266 may further be operable to display information and receive user inputs tangentially related and/or unrelated to operation of the furnace 100. In some embodiments, however, the device 266 may 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 assembly 250 may receive user inputs from remote configuration tools, and may further communicate information relating to furnace 100 to device 266. In these embodiments, controller assembly 250 may or may not also receive user inputs via device 266. In some embodiments, the controller assembly 250 and/or the device 266 may be embodied in a thermostat that may be disposed within the defined space.

Controller assembly 250 may be communicatively coupled to the various components described above (e.g., blowers 152, 130, 180, valve 156, ignition assembly 190, flame rod sensor 196, sensors 260, 262, 263, device 266, etc.) through any suitable communication path or method. For instance, in some embodiments, controller assembly 250 may 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 assembly 250, device 266, and various components of furnace 100 (e.g., blowers 152, 130, 180, ignition assembly 190, valve 156, sensors 260, 262, 263, etc.) may be coupled to a power source 258. Power source 258 may comprise any suitable source (or collection of sources) of usable power—e.g., such as electrical power). For instance, power source 258 may comprise one or more batteries, capacitors, etc. In some embodiments, the power source 258 may comprise electrical power provided from a local utility. Some of the components within furnace 100 may receive power (e.g., electrical power) directly from power source 258 or indirectly through other components (e.g., such as controller assembly 250). It should be noted that only some of the example connections to power source 258 are shown for the depicted components of furnace 100 and controller assembly 250 so as to simplify figure. In this embodiment, the power source 258 provides a source of Alternating Current (AC) power.

Various control methods for furnace 100 are now described herein. In some embodiments, the following methods may be performed utilizing embodiments of furnace 100 and controller assembly 250 as described herein. Thus, in describing the following methods, continuing reference is made to the components of furnace 100 and controller assembly 250 previously described above and/or generally shown in FIGS. 1-8.

Referring now to FIG. 9, a method 300 of starting up furnace 100 is shown. Initially, method 300 includes receiving a call for heat at block 302. The call for heat may be received by the controller assembly 250 from another device (e.g., such as device 266) or may be generated within the controller assembly 250 itself (e.g., such as in embodiments where the controller assembly 250 is or is incorporated within a thermostat or other suitable user input device for furnace 100). The call for heat may be derived upon detecting or determining that the temperature within the defined space serviced by the furnace 100 is below a desired temperature or temperature range.

After the call for heat is received at block 302, method 300 proceeds to perform a pre-purge sequence at block 304. Generally speaking, the pre-purge method may be configured to purge fuel and/or flue products from the furnace 100 prior to initiating subsequent combustion operations. More particular, the pre-purge sequence may sweep or purge flue products out of the heat exchanger assembly 120 (e.g., heat exchanger tubes 122, 124, headers 116, 117, flue pipe 134, etc.), and may sweep or purge fuel from portions of the combustion assembly 150 (e.g., the inlet nozzle 153, premix blower 152, conduit 160, chamber 166, housing 168, burner(s) 170, etc.).

Referring now to FIG. 10, an embodiment of a method 320 for performing a pre-purge sequence for furnace 100 is shown. The method 320 may be performed as block 304 within method 300 in FIG. 9.

Initially, method 320 includes closing the fuel valve 156 at block 322. For instance, for the furnace 100 and controller assembly 250, the controller assembly 250 may close the fuel valve 156 so as to prevent any fuel (e.g., natural gas, propane, etc.) from flowing through the fuel valve 156 into the inlet nozzle 153. As previously described above, the fuel valve 156 may comprise a negative pressure regulator valve that opens in response to a negative pressure generated by the operation of the premix blower 152. In addition, in some embodiments, the valve 156 may be closable by controller assembly 250 (e.g., via a suitable actuator that is communicatively coupled to controller assembly 250) so as to prevent fuel from flowing out of the valve 156 into the inlet nozzle 153 regardless of the pressure at the gas inlet 159 and/or operating state of the premix blower 152.

In addition, method 320 includes starting the premix blower 152 at block 324 and starting the combustion blower 130 at block 326. Specifically, blocks 324 and 326 comprise starting the premix blower 152 and the combustion blower 130 via the controller assembly 250 so as to cause the motors 155, 133 to rotate the impellers 154, 132 within the blower housings 151, 131. As a result, air may be drawn into the air inlet 158 of inlet nozzle 153, flowed through the premix blower 152 and into burner box 164. The air is then emitted from burner(s) 170 and flows into the primary heat exchanger tube(s) 122 of heat exchanger assembly 120. Thereafter, the negative pressure generated by the combustion blower 130 may draw the air through the heat exchanger tubes 122, 124, headers 116, 117 and into flue pipe 134 which then vents the air into the outer environment. As the air is flowing through the combustion assembly 150 and heat exchanger assembly 120 as described above, fuel and flue products present therein (e.g., such as might be retained within the combustion assembly 150 and/or heat exchanger assembly 120 at the end of the previous operation of furnace 100), may be swept from the furnace 10 and vented to the outside environment. Without being limited to this or any other theory, purging flue products and fuel from the furnace 100 prior to initiating an operation thereof may prevent an improper fuel/air ratio within the burner(s) 170 when combustion is later ignited within the burner(s) 170. In addition, in some embodiments, the pre-purge method (e.g., method 320) at block 304 may help to ensure that combustion does not occur within burner(s) 170 until desired by removing potentially combustible materials from furnace 100.

Referring still to FIG. 10, in some embodiments, method 320 may comprise stopping the premix blower 152 at block 328 in lieu of closing the gas valve 156 and starting the premix blower 152 at blocks 322 and 324, respectively, as previously described above. As previously described above, the fuel valve 156 may comprise a negative pressure regulator valve that opens in response to a negative pressure generated by the operation of the premix blower 152. As a result, by stopping the premix blower 152 at block 328, fuel may not be drawn through fuel valve 156 and therefore into the burner box 164, so that actuating or closing the gar valve 156 may be unnecessary. In these embodiments (e.g., where the block 328 is performed in lieu of blocks 322, 324), the combustion blower 130 may be started at block 326 following (or at the same time as) stopping the premix blower 152 at block 328.

Referring again to FIG. 9, in some embodiments, method 300 may also comprise performing a warm-up sequence at block 306. In particular, in some embodiments of furnace 100 the ignition assembly 190 comprises 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) 170 so as ensure more reliable ignition within burner(s) 170.

Referring now to FIG. 11, a method 330 for performing a warm-up sequence within furnace 100 is shown. In some embodiments, the method 330 may be performed as block 306 within method 300 in FIG. 9.

Initially, method 330 includes stopping the premix blower 152 at block 332, and stopping the combustion blower 130 at block 334. In particular, blocks 332, 334 may comprise stopping the premix blower 152 and combustion blower 130 so as to prevent motors 155 and 133, respectively from rotating impellers 154 and 132, respectively, via controller assembly 250.

In addition, method 330 includes energizing the hot surface igniter for a predetermined period of time at block 336. As previously described, when ignition assembly 190 is 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 block 336, the temperature of the hot surface begins to increase. The predetermined period of time at block 336 may 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 method 320. 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) 170 and hot surface igniter.

It should be appreciated that in some embodiments of method 300, the warm-up sequence of block 306 may be omitted. For instance, in some embodiments, ignition assembly 190 may comprise a direct spark igniter such that warm-up sequence is not necessary prior to an ignition sequence (see e.g., block 308 described in more detail below).

Referring again to FIG. 9, method 300 also includes performing an ignition sequence at block 308. As generally described above, an ignition sequence within furnace 100 may be different depending on the design and type of ignition assembly 190.

Referring now to FIG. 12, a method 400 of igniting furnace 100 is shown. In some embodiments, method 400 may be performed as block 308 within method 300 in FIG. 9. Initially, method 400 includes starting the premix blower 152 at block 402 and starting the combustion blower 130 at block 404. As previously described, operation of the premix blower 152 and combustion blower 130 may initiate the flow of fluid (e.g., initially air) through the combustion assembly 150 and heat exchanger assembly 120. In addition, method 400 includes opening the fuel valve 156 at block 408. Specifically, in some embodiments, after the energization of blowers 152, 130, the fuel valve 156 may be opened so as to start the flow of fuel to the burner box 164 along with the air flowing into the inlet nozzle 153 at air inlet 158. In some embodiments, the premix blower 152 may be started in response to or simultaneously with opening the fuel valve 156 at block 408.

Method 400 also includes energizing the ignition assembly 190 at block 408. The precise method and timing of energizing the ignition assembly 190 will often depend on the type and design of ignition assembly 190 that is being utilized within furnace 100. As previously described above, in some embodiments, the ignition assembly 190 comprises a direct-spark igniter. As a result, in these embodiments, energization of the ignition assembly 190 at block 408 may occur by conducting electric current to one of the electrodes 192, 194 so as to generate an electrical arc between the tips 192a, 194a of electrodes 192, 194. In some embodiments, electric current is not conducted to the one of the electrodes 192, 194 until a sufficient time has passed since opening the fuel valve 156 and initiating the flow of fuel to the burner(s) 170 at block 406, so that a sufficient volume of fuel (within a fuel/air mixture) is present within the burner(s) 170 to ensure reliable ignition when a spark is emitted between the electrodes 192, 194.

In other embodiments, the ignition assembly 190 may comprise a hot surface type igniter as previously described. In these embodiments, energizing the ignition assembly 190 may 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 valve 156 and initiating the flow of fuel to the burner(s) 170. For instance, in these embodiments, the energization of the ignition assembly 190 may occur during a previous warm-up method (e.g., at block 306 of method 300). 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., block 336 in method 330 of FIG. 11). The ignition assembly 190 may 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 block 406. Thus, in some embodiments of method 400, energizing the ignition assembly 190 at block 408 may occur before blocks 402-406.

Referring still to FIG. 12, following starting of the premix blower 152 and combustion blower 130 at blocks 402 and 404, respectively, opening of the fuel valve 156 at block 406, and energization of the ignition assembly 190 at block 408, method 400 next includes determining whether flame sensor 196 is detecting flame at block 410. As previously described, flame rod sensor 196 may detect the presence of flame within one or more of the burners 170 (e.g., burners 170a, 170b, 170c, etc.) by detecting an electric current that is conducted through the flame.

If flame is detected at block 410, method 400 ends; however, if flame is not detected at block 410, method 400 proceeds to close the fuel valve 156 at block 412. Specifically, as previously described, if the flame rod sensor 196 detects electric current conducted through the flames within the burner(s) 170 (e.g., burners 170a, 170b, 170c, etc. in FIGS. 5 and 6), then it may be determined that flames are present in the burner(s) 170 following energization of the ignition assembly 190 and opening the fuel valve 156. Thus, in this event, the ignition method 400 may end and normal operations of the furnace 100 will proceed thereafter. Alternatively, upon determining that no flame is present at block 410, method 400 may recycle to either re-energize the ignition assembly 190 at block 408 or to again determine whether flame is present at block 410.

Specifically, if the flame rod sensor 196 does 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) 170 did not ignite as a result of energizing the ignition assembly 190 at block 408. As a result, method 400 may proceed, in some embodiments, to close the fuel valve at block 412 and thereby prevent the build-up of un-combusted fuel/air mixture in the burner box 164, heat exchanger assembly 120, and possibly in the environment surrounding the furnace 100 (which may present a dangerous risk of an uncontrolled explosion in and around the furnace 100). However, in some embodiments, method 400 may reattempt to ignite the fuel/air mixture with the ignition assembly 190 at block 408 and/or to re-determine whether flames are present within the burner(s) 170 via the flame rod sensor 196 at block 410 if no flames are detected at block 410.

Referring again to FIG. 9, following the performance of the ignition sequence at block 308 (e.g., method 400 in FIG. 12), method 300 proceeds to start the circulation blower 180 at block 310. Specifically, once combustion has been initiated, the circulation blower 180 may be started so as to initiate the transfer of heat from the hot flue products resulting from the combustion to the airflow 182 provided to the defined space within the heat exchanger assembly 120 as previously described above. For the furnace 100, starting the circulation blower 180 to initiate airflow 182 may occur before, during, or after the ignition sequence at block 308. For instance, in some embodiments, it may be desirable to delay the initiation of airflow 182 until the heat exchanger tubes 122, 124 of heat exchanger assembly 120 have reached a sufficient temperature so as to ensure a sufficiently high temperature of airflow 182 at the exit of heat exchanger compartment 114 and therefore avoid flowing uncomfortably cool air to the defined space (which may negatively impact occupant comfort). Thus, in these embodiments, controller assembly 250 may wait a predetermined period of time after the ignition sequence at block 308 to start the circulation blower 180 at block 310. In other embodiments, the circulation blower 180 may be started simultaneously, before, or very soon after the ignition sequence at block 308 so as to improve heat transfer efficiency of the furnace 100.

Following the start-up of the furnace 100 (e.g., via method 300), normal operations of the furnace 100 may 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 assembly 250 may monitor the furnace 100 for a blockage in the air inlet 158 of the premix blower 152. If the air inlet 158 to the premix blower 152 were to become blocked during operations, combustion may be extinguished within the burner(s) 170 and un-combusted fuel may begin to build within and around the furnace 100.

Specifically, referring now to FIG. 13, a method 500 of detecting a blocked air inlet 158 of the premix blower 152 is shown. As will be described in more detail below, method 500 includes multiple parallel manners of detecting the blockage within air inlet 158 that may help to increase the sensitivity and reliability of controller assembly 250 in terms of detecting a blocked air inlet 158 of premix blower 152 during operations. As will be described in more detail below, method 500 may employ one, a combination of, or all of these parallel manners and techniques for detecting a blocked air inlet 158 of premix blower 152 during operations.

Specifically, method 500 initially includes detecting a pressure downstream of the air inlet and upstream the premix blower 152 of the furnace at block 502. In particular, block 502 may comprise receiving an output signal from pressure sensor 260 as generally described above.

Following detecting the pressure at block 502, method 500 includes determining whether the pressure is below a predetermined pressure value at block 506. Without being limited to this or any other theory, if the air inlet 158 is blocked during operation of the premix blower 152, the area between the blocked inlet 158 and the premix blower 152 within the inlet nozzle 153 may begin to fall in pressure due to the continued rotation of impeller 154 within housing 151. The predetermined pressure value in block 506 may correspond to a sufficient reduction in pressure within the inlet nozzle 153 so as to indicate that the air inlet 158 has become blocked (e.g., by dust, dirt, or other obstruction).

If it is determined that the pressure detected at block 502 is not below a predetermined pressure value at block 506 (i.e., the determination at block 506 is “no”), then method 500 recycles back to block 502 to 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 block 502 is below the predetermined pressure value at block 506 (i.e., the determination at block 506 is “yes”), then method 500 may proceed to block 510 to determine that the inlet of the premix blower is blocked.

In addition, method 500 comprises detecting a speed of the premix blower 152 at block 504, which may comprise detecting a speed of the impeller 154 or motor 155 of premix blower 152 via the sensor 262 as previously described. Thereafter, method 500 includes determining whether the speed detected at block 504 is above a predetermined speed value at block 508. Without being limited to this or any other theory, when the air inlet 158, becomes blocked, the impeller 154 is impacting a reduced volume of fluid (e.g., air, fuel, etc.) within the blower housing 151 so that a drag force operating on impeller 154 is reduced. As a result, for a given torque supplied from motor 155, the impeller 154 will rotate at an increased speed, as the air inlet 158 becomes blocked. The predetermined speed value at block 508 may correspond with an expected increase in speed impeller 154 that may result from a blockage in the air inlet 158 of inlet nozzle 153.

If it is determined that the speed detected at block 504 is not above a predetermined speed value at block 508 (i.e., the determination at block 508 is “no”), then method 500 recycles back to block 504 to once again detect the speed of the premix blower 152 as previously described. If, on the other hand, it is determined that the speed detected at block 504 is above the predetermined speed value at block 508 (i.e., the determination at block 508 is “yes”), then method 500 may again proceed to block 510 to determine that the inlet of the premix blower 152 is blocked.

Further, method 500 also includes determining whether a flame is present with in the burner(s) 170 of furnace 100 at block 509. In particular and without being limited to this or any other theory, if the air inlet 158 of the inlet nozzle 153 becomes blocked, the combustion process may stop within the burner(s) 170 due to a lack of oxygen. Thus, at block 509, the flame rod sensor 196 may 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 sensor 196 should detect flames within the burner(s) 170 (i.e., the determination at block 509 is “yes”), then method 500 recycles back to once again determine whether flame is presented within the burner(s) 170 at block 509. If, on the other hand, flame rod sensor 196 does not detect a flame within the burner(s) 170 (i.e., the determination at block 509 is “no”), then method 500 may again proceed to block 510 to determine that the inlet of premix blower 152 is blocked. As previously described above, the flame rod sensor 196 may be placed within one of the burner housings 176 and therefore close to the location where combustion is initiated for the fuel/air mixture within burner box 164. As a result, the flame rod sensor 196 may detect the loss of flame that may result from a blockage in the air inlet 158 relatively early (e.g., as compared to situations where flame rod sensor 196 is disposed outside of burner housing 176).

Thus, method 500 allows a block air inlet 158 of premix blower 152 to be detected via a pressure measurement upstream of the premix blower 152 (e.g., via blocks 502 and