Patent ID: 12253284

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 a 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 described above, a gas-fired furnace is generally configured to combust fuel and air and thereby generate heat that may be delivered to a comfort zone of an indoor area via a circulation fan or blower of the furnace. Particularly, the furnace may be configured to provide a temperature rise between a temperature of an inlet airflow of the furnace and a temperature of a conditioned airflow of the furnace. The temperature rise is targeted to a predefined temperature rise range in which the furnace is designed to operate. Thus, the temperature rise range of the furnace may depend upon the configuration of the furnace. For instance, a first exemplary furnace having a first configuration may have a temperature rise range between 30 degrees fahrenheit (° F.) and 60° F., while a second exemplary furnace, having a second configuration that is different from the first configuration, may have a temperature rise range between 40° F. and 70° F.

The temperature rise produced by the furnace may vary during operation in response to changes in the amount of airflow through the furnace produced by the circulation fan. Generally, at a given rate of combustion within the furnace, the temperature rise provided by the furnace between a temperature of the inlet airflow and a temperature of the conditioned airflow may increase in response to a decrease in the amount of airflow circulated through the furnace. In other words, a decrease in the airflow rate provided by the circulation fan results in less volume of air available to absorb the heat generated within the furnace over a given period of time. Conversely, the temperature rise provided by the furnace may decrease in response to an increase in the amount of airflow circulated through the furnace (i.e., an increase in the airflow rate provided by the circulation fan) as more airflow is available to absorb the heat generated within the furnace over a given period of time.

In some applications, if the temperature rise provided by the furnace decreases below a lower end of the temperature rise range of the furnace, the temperature of the conditioned airflow may not be warm enough to adequately heat the comfort zone. Additionally, if the temperature rise provided by the furnace increases above the temperature rise range of the furnace, the temperature of the conditioned airflow may exceed a maximum permissible conditioned airflow temperature of the furnace. The maximum permissible conditioned airflow temperature of the furnace may vary depending upon the application and the configuration of the furnace, but in some applications may correspond to a temperature equal to an upper end of the temperature rise range of the furnace plus a fixed margin which may, in some applications, range approximately between 100 degrees fahrenheit (° F.) and 200° F. As an example, the maximum permissible conditioned airflow temperature for a furnace having a temperature rise range of 30° F. and 60° F. would be 160° F. when the fixed margin is equal to 100° F. Additionally, a conditioned airflow temperature exceeding the maximum permissible conditioned airflow temperature of the furnace may eventually result in damage to the furnace due to overheating of the furnace and/or heat-related discomfort to occupants of the comfort zone of the indoor area. A conditioned airflow temperature produced by the furnace that is in excess of a target conditioned airflow temperature (e.g., as requested by a controller of the furnace) may result from improper installation of the furnace, a malfunction of the circulation fan or other component of the furnace, and/or a clogged filter or air cleaner of the furnace.

In conventional furnaces, the furnace includes a temperature limit switch, such as a spring-operated bimetallic switch. The switch opens automatically to shut off the burner in response to a temperature of the bimetallic switch reaching a predefined set-point temperature. Using a bimetallic switch to trigger shutoff has drawbacks. For example, the performance of the bimetallic switch may be orientation specific, requiring the switch to be installed within the furnace in a particular orientation for the switch to function as intended, limiting the flexibility in which the components of the furnace may be internally positioned, as well as the ways in which the furnace may be oriented in the indoor space. Additionally, a bimetallic switch is a separate component that adds cost to the furnace.

Accordingly, embodiments disclosed herein include systems and methods for operating a furnace whereby a temperature limit switch, such as a spring-operated bimetallic switch, is rendered superfluous in preventing the furnace from exceeding its designed temperature rise range. Particularly, embodiments disclosed herein include systems and methods for operating a furnace that includes operating a gas-fired furnace to produce a conditioned airflow, monitoring one or more parameters indicative of an airflow rate of the conditioned airflow, and deactivating a burner assembly of the furnace in response to the one or more parameters indicating that the airflow rate is less than a minimum airflow rate. Embodiments disclosed herein also include systems and methods for operating a furnace that includes operating a gas-fired furnace to produce a conditioned airflow, monitoring a parameter that is indirectly indicative of a temperature of the conditioned airflow, and deactivating a burner assembly of the furnace in response to the parameter indirectly indicating that the temperature of the conditioned airflow exceeds a threshold. As will be described in more detail below, use of the embodiments disclosed herein may allow for the operation of a furnace in a manner that prevents the furnace from exceeding a maximum permissible conditioned airflow temperature thereof without needing to rely on a temperature limit switch, such as a spring-operated bimetallic switch.

Referring now toFIGS.1,2, an embodiment of a gas-fired furnace100is shown. As discussed herein, a furnace (e.g., furnace100) may be referred to as being “gas-fired”, where the “gas-fired” furnace is configured to be in fluid communication with a gas flow for thermodynamic heat transfer and where the gas-flow comprises products of a combustion reaction from a burner. In some embodiments, furnace100may comprise a component of an HVAC system that includes an indoor unit comprising furnace100and an indoor refrigerant heat exchanger or evaporator, an outdoor unit comprising an outdoor fan and an outdoor refrigerant heat exchanger or condenser, and a refrigerant loop extending between the indoor and outdoor refrigerant heat exchangers. Furnace100may configured as an indoor furnace that provides conditioned air to a comfort zone of an indoor space. However, in general, the components of furnace100may be equally employed in an outdoor or weatherized furnace to condition an interior space. Moreover, furnace100may be used in residential or commercial applications.

In some embodiments, furnace100may generally include a fuel supply valve102, an air and fuel (air/fuel) mixing unit110, an intake manifold120, a partition panel130, a burner assembly140, a plurality of heat exchangers150, a hot collector box160, and a first fan or draft inducer170. Mixing unit110may be coupled end-to-end with intake manifold120. Additionally, burner assembly140may be positioned between intake manifold120and heat exchangers150, where heat exchangers150may extend from burner assembly140to hot collector box160.

The air/fuel mixing unit110of furnace100may be configured for the introduction of fuel and air to allow at least partial mixing of fuel and air before a combustion reaction process. Air/fuel mixing unit110may receive air via an air inlet112and fuel via fuel supply valve102to allow at least partial mixing of the fuel and air. For example, the fuel may be natural gas available from the fuel supply valve102attached and operatively engaged with the air/fuel mixing unit110. Fuel supply valve102may be configured to be adjusted, such as electrically or pneumatically, so as to obtain a desired and/or predefined air-to-fuel ratio. As will be discussed further herein, fuel supply valve102may be configured for staged operation and/or modulation type operation, and may be operatively connected to a controller190(shown schematically inFIG.2) of furnace100. For example, staged operation may comprise two flame settings, whereas modulation type operation may be incrementally adjustable over a large range of outputs, such as, for example, from 40% to 100% output capacity. While furnace100is shown inFIGS.1,2as comprising a premix furnace configured to mix air and fuel within air/fuel mixing unit110, in other embodiments, furnace100may not include air/fuel mixing unit110and may instead be configured to mix the fuel and air within burner assembly140.

The intake manifold120of heat exchanger100may generally include a flow distributor122extending from an inlet of intake manifold120coupled with air/fuel mixing unit110. Intake manifold120may also include a plurality of heat exchanger supply tubes124extending from flow distributor122to an outlet of intake manifold120coupled with heat exchanger150.

The burner assembly140of furnace100may include a plurality of burners142and at least one igniter144(shown inFIG.2). Each burner142of burner assembly140may be received in one of the supply tubes122of intake manifold120. Igniter144of burner assembly140may be positioned at an opening of each burner142and may be configured to induce a combustion reaction by igniting a gas flow passing in and/or by burners142, where the gas flow comprises a mixture of the air and fuel. Particularly, the gas flow may initially take the form of air and fuel that is at least partially mixed and/or uncombusted (i.e., not yet ignited or undergone a combustion reaction) in air/fuel mixing unit110. As the gas flow travels through intake manifold120and heat exchanger150, burners142and igniter144of burner assembly140may initiate a combustion reaction. Combustion may occur at least partially within an interior space of each burner142so that heat is generated and forced out of the open end of the burner142and into the heat exchanger tube150. In some embodiments, igniter144may comprise any of a pilot light, a piezoelectric device, and/or a hot surface igniter. Igniter144may be controlled by controller190of furnace100.

In some embodiments, the heat exchanger150of furnace100has a first end152coupled to intake manifold120and a second end154coupled to hot collector box160. Heat exchanger150may comprise an exterior surface156and a plurality of heat exchanger tubes158extending between the first end152and the second end154. In some embodiments, each heat exchanger tube158is a bent, S-shaped tube that extends through a tortuous path to enhance the surface area available for heat transfer with the surrounding circulation air. However, in other embodiments, the configuration of heat exchanger150may vary. In some embodiments, a finned condensing heat exchanger165may extend from hot collector box160to draft inducer170. However, generally, furnace100may be operated with or without a condensing heat exchanger as a “condensing” or “non-condensing” furnace, respectively.

In some embodiments, the gas flow may follow a combustion flow path (indicated by arrow172) that may be in a direction beginning at the air/fuel mixing unit110and ending at the draft inducer unit170. For example, combustion flow path172may follow from the air/fuel mixing unit110, through intake manifold120, past burners162and through heat exchanger tubes158of heat exchanger150. Combustion flow path172may continue through hot collector box160and condensing heat exchanger165, and may exit past draft inducer170towards a designated venting environment (not shown inFIGS.1,2). It is understood that there may be more or less components of furnace100in fluid communication with combustion flow path172.

In some embodiments, the gas flow described above may be introduced into furnace100by operating in an induced draft mode by pulling the gas flow through furnace100via draft inducer170, or by operating in a forced draft mode by pushing the gas flow through furnace100. Draft inducer170may comprise a blower or fan which is in fluid communication with combustion flow path172and is down-stream of heat exchanger150. Draft inducer170may pull and/or extract the gas flow out from heat exchanger150by creating a relatively lower pressure at one end of combustion flow path172. Embodiments using a forced draft mode may be accomplished by placing a blower or fan at the inlet of air/fuel mixing unit110and forcing the gas flow into and through air/fuel mixing unit110and along combustion flow path172.

As shown particularly inFIG.2, in addition to partition panel130, furnace100may also include a first side panel132, and a second side panel134. Panels130,132, and134may be disposed in a configuration such that fluids (e.g. air) that contact an exterior surface of a component of furnace100(e.g. fluid passing over the exterior surface156of heat exchanger150for thermodynamic heat transfer) are segregated from the gas flow circulating along combustion flow path172.

Furnace100may further include a second or circulation fan180. Circulation fan180may be configured to receive an inlet airflow182and force or drive the inlet airflow182into contact with the exterior surface156of heat exchanger150. In other embodiments, circulation fan180may draw the airflow182across the exterior surface156of heat exchanger150. In response to the inlet airflow182contacting heat exchanger150, heat may be transferred from the gas flow circulating within heat exchanger150to the inlet airflow182, thereby heating inlet airflow182. Following contact with heat exchanger150, the airflow may exit furnace100as an outlet or conditioned airflow184, which may have a temperature that is greater than a temperature of the inlet airflow182. Conditioned airflow184may be delivered to a comfort zone of an indoor space.

In some embodiments, circulation fan180may comprise a centrifugal blower comprising a blower housing181, and a blower motor183configured to selectively rotate a blower impeller185of the circulation fan180that is at least partially disposed within blower housing181. In other embodiments, circulation fan180may comprise a mixed-flow fan and/or any other suitable type of fan. Circulation fan180may be configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, circulation fan180may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of the motor183of circulation fan180.

As shown particularly inFIG.2, furnace100may comprise controller190for controlling one or more components of furnace100. Generally speaking, controller190is coupled to various components of furnace100as well as various sensors configured to detect various operating parameters within furnace100. For example, in some embodiments, controller190of furnace100may communicate with and/or otherwise affect control over fuel supply valve102, igniter144of burner assembly140, draft inducer170, and/or circulation fan180. Additionally, controller190may control draft inducer170to provide an adequate gas flow along combustion flow path172for a desired firing rate through burner assembly140.

Controller190may comprise a singular controller or control board or may comprise a plurality of controllers or control boards that are coupled to one another. For example, controller190may comprise a distinct control board positioned on a panel (e.g., panels130,132, and/or134) of furnace100and/or a control board positioned within the motor183of circulation fan180. For convenience, and to simplify the drawings, controller190is depicted schematically inFIG.2as a single controller unit that is coupled to various components within furnace100. Particularly, controller190may comprise a processor192and a memory194. Processor192(e.g., microprocessor, central processing unit (CPU), or collection of such processor devices, etc.) executes machine-readable instructions196provided on memory194(e.g., non-transitory machine-readable medium) to provide controller190with all the functionality described herein. Memory194may 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 instructions196can also be stored on memory194. As noted above, in some embodiments, controller190may comprise a collection of controllers and/or control boards that are coupled to one another. As a result, in some embodiments, controller190may comprise a plurality of processors192, memories194, etc.

As described above, an HVAC system including an indoor unit and an outdoor unit may include furnace100as a component of the indoor unit thereof. The HVAC system may include a system controller, which may be disposed in a thermostat of the HVAC system and may be generally configured to affect control over the indoor and outdoor units of the HVAC system. For example, the system controller may request a target firing rate of the burner assembly140of furnace100in response to an ambient temperature of a comfort zone conditioned by the HVAC system falling below a user-defined set point temperature. In some embodiments, controller190may comprise a controller of furnace100that is separate and distinct from, but in selective communication with, one or more controllers or control boards of the HVAC system (e.g., the system controller of the HVAC system, etc.). However, in other embodiments, controller190may comprise a plurality of controllers or control boards of the HVAC system that are coupled to one another. For example, in some embodiments, controller190may comprise both a controller or control board of furnace100and the system controller of the HVAC system disposed in the thermostat thereof. Thus, in some embodiments, one or more controllers or control boards of controller190may affect control over components of the HVAC system other than furnace100(e.g., the outdoor unit of the HVAC system, etc.).

In some embodiments, controller190may be configured to receive information related to a speed and a torque of circulation fan180whereby controller190may continuously determine the speed and the torque of the motor183of circulation fan180. Additionally, controller190may be configured to estimate an airflow produced by circulation fan180by monitoring one or more parameters of the motor183of circulation fan180, such as a speed and a torque of motor183. The one or more parameters of motor183may be measured parameters of motor183and/or parameters determined from measured parameters of motor183. For example, motor183may comprise one or more sensors configured to measure one or more parameters of motor183, such as current, a counter or back electromotive force (EMF) of motor183, a voltage supplied to motor183, etc. The measured parameters of motor183measured by the one or more sensors thereof may be communicated to controller190. Controller190may be configured to determine one or more parameters of motor183, such as the speed and torque of motor183, based on the parameters of motor183measured by the one or more sensors of motor183and communicated to controller190. Additionally, in some embodiments, controller190may be configured to determine one or more parameters of the motor183of circulation180, such as a speed and a torque of motor183, required to achieve a desired or targeted airflow rate of circulation fan180. For example, the controller190may monitor and adjust one or more measured parameters of motor183(e.g., a current and/or voltage supplied to motor183) to ensure a speed and torque of motor183required to achieve the targeted airflow rate is maintained.

Prior to installation of furnace100, the furnace100(or another test furnace, including a test circulation blower, similar in configuration to furnace100) may be tested at an air plenum test facility at a range of known airflows (i.e., independently measured by equipment of the test facility) to thereby create a motor map or discrete value look-up table correlating airflow produced by circulation fan180with the motor speed and torque of motor183of circulation fan180. As a non-limiting example, a motor map may include airflow along an X-axis thereof, motor power (which may be calculated from a determined motor torque) along a Y-axis thereof, and a plurality of curves each corresponding to a fixed speed of the motor of circulation fan180. In this manner, an estimated airflow may be “looked-up” from the motor map from a known motor speed and torque. However, additional functional relationships for airflow may be used to correlate determined motor speed and torque with estimated airflow.

Further, controller190may also be configured to determine a minimum airflow rate corresponding to an estimated rate of conditioned airflow184of furnace100which corresponds to a maximum permissible conditioned airflow temperature (e.g., maximum permissible conditioned airflow temperature of conditioned airflow184) of furnace100. Particularly, prior to installation of furnace100, the furnace100(or another test furnace similar in configuration to furnace100) may be tested at a test facility by activating the burner assembly140of furnace100and operating circulation fan180at a range of airflows (either independently measured by equipment of the test facility or estimated from the motor map). As the circulation fan180is operated at a range of airflows, the temperature of conditioned airflow184of furnace100may be independently measured by equipment of the test facility to thereby estimate the airflow rate of conditioned airflow184which corresponds to the maximum permissible conditioned airflow temperature of furnace100.

In some embodiments, the inlet airflow provided to the furnace (e.g., furnace100) during testing may be at a fixed nominal inlet airflow temperature. The nominal inlet airflow temperature using during testing may be a temperature that is near, at, or above a maximum inlet airflow temperature the furnace is expected to receive during operation following installation to ensure that the temperature of the inlet airflow received by the furnace during operation does not substantially exceed the nominal airflow temperature used during testing.

In certain embodiments, during operation of the furnace, a controller (e.g., controller190) may monitor a temperature of the inlet airflow (e.g., inlet airflow182) and may compare the inlet airflow temperature with the nominal inlet airflow temperature used during testing and adjust the maximum permissible conditioned airflow temperature in response to the monitored inlet airflow temperature exceeding the nominal inlet airflow temperature. For example, the controller may decrease the maximum permissible conditioned airflow temperature in proportion to the difference between the monitored inlet airflow temperature and the nominal inlet airflow temperature (e.g., reduce the maximum permissible conditioned airflow temperature 5° F. in response to the monitored inlet airflow temperature exceeding the nominal inlet airflow temperature by 5° F., etc.). The temperature of the inlet airflow received by the furnace may be determined using a dedicated temperature sensor positioned in a flowpath of the inlet airflow. Alternatively, the controller may monitor an indoor temperature determined by, for example, a thermostat of an HVAC system comprising the furnace in order to estimate the temperature of the indoor airflow received by the thermostat.

In some embodiments, a conditioned airflow temperature map of furnace100which correlates or maps the conditioned airflow temperature of furnace100(reflecting the temperature of the inlet airflow182as well as the temperature rise of the airflow through the furnace100) to the airflow produced by circulation fan180may also be produced during testing. For example, referring briefly toFIG.3, an exemplary conditioned airflow temperature map200of a gas-fired furnace (e.g., furnace100) is shown. Conditioned airflow temperature map includes an airflow rate in cubic feet per minute (CFM) of the circulation fan180of furnace100along an X-axis thereof (which may be estimated from a determined speed and torque of the motor183of circulation fan180utilizing a motor map), and conditioned airflow temperature (e.g., temperature of conditioned airflow184of furnace100) along a Y-axis thereof in degrees fahrenheit (° F.). Additionally, conditioned airflow temperature map200includes a curve202corresponding to the estimated conditioned airflow temperature as a function of the airflow rate produced by circulation fan180. In this manner, an estimated conditioned airflow temperature may be “looked-up” from conditioned airflow temperature map200from a determined speed and torque of the motor183of circulation fan180. As shown inFIG.3, the airflow rate of circulation180is negatively correlated with the temperature of conditioned airflow184.

Referring again toFIGS.1,2, the minimum airflow rate of furnace100determined during testing may be stored in the memory of controller190prior to the installation of furnace100. In some embodiments, the motor map and the conditioned airflow temperature map created during testing may also be stored in the memory of controller190prior to the installation of furnace100.

In this manner described above, controller190of furnace100may apply determined motor speed and torque values to the motor map and conditioned airflow temperature map stored in the memory of controller190to thereby determine or look-up an estimated conditioned airflow temperature of furnace100based on the determined motor speed and torque of circulation fan180. In some embodiments, the motor map and minimum airflow rate may be stored in the memory of controller190, and controller190may apply determined motor speed and torque values to the motor map stored in the memory thereof to determine whether the airflow rate produced by circulation fan180falls below the minimum airflow rate of furnace100.

In some embodiments, furnace100may not include a temperature limit switch (e.g., a spring-operated bimetallic switch) for preventing furnace100from exceeding a designed temperature rise range of furnace100. Instead, as further described below, controller190may be configured to prevent furnace100from exceeding the temperature rise range of furnace100without needing to rely on a separate temperature limit device or switch (e.g., a spring-operated bimetallic switch).

Furnace100may be operated to provide heat to one or more areas and/or comfort zones of an indoor space by transferring heat from hot combustion gases flowing along combustion flow path172generated by furnace100to a conditioned airflow184that may be delivered to the comfort zone of the indoor space. For example, controller190of furnace100may “turn on” or activate the burner assembly140of furnace100by opening fuel supply valve102and operating igniter144and draft inducer170of furnace100to thereby combust fuel and air in burner assembly140and/or heat exchanger150and induce a flow of combustion gases along combustion flow path172. Additionally, as combustion gases are circulated along combustion flow path172, controller190may operate circulation fan180to receive an inlet airflow182and circulate (e.g., blow or pull) air over the external surface156of heat exchanger150. Circulation fan180may also be operated by controller190to circulate the conditioned airflow184from furnace100to the comfort zone of the indoor space. In some embodiments, controller190may also cease activation or deactivate furnace100by “shutting off” or deactivating the burner assembly140by closing the fuel supply valve102and cease the operation of igniter144and draft inducer170to thereby cease the flow of combustion gases along combustion flow path172. Controller190may also cease the operation of circulation fan180following the deactivation of burner assembly140.

Referring now toFIG.4, a method250for operating a furnace is shown. In some embodiments, method250may be practiced with furnace100. Thus, in describing the features of method250, continuing reference will made to the furnace100shown inFIGS.1,2; however, it should be appreciated that embodiments of method250may be practiced with other systems, assemblies, and devices. Generally speaking, method250includes monitoring one or more parameters indicative of an airflow rate of a conditioned airflow of a gas-fired furnace, and deactivating the furnace in response to the one or more parameters indicating that the airflow rate of the conditioned airflow is less than a minimum airflow rate.

Initially, method250includes operating a gas-fired furnace (e.g., furnace100) to produce a conditioned airflow at method block252. The operation of the furnace at block252may be performed at a test facility prior to the installation of the furnace, or at an indoor space (e.g., a home, etc.) following the installation of the furnace. In some embodiments, method block252may include activating a burner assembly and a first fan of the furnace (e.g., burner assembly140and draft inducer170of furnace100) to combust fuel and air and circulate combustion gases along a flow path (e.g., combustion flow path172) extending through a heat exchanger of the furnace (e.g., heat exchanger150). For example, controller190may open fuel supply valve102and activate burner assembly140and inducer fan170of furnace100to thereby combust fuel and air, which may be circulated through heat exchanger150along combustion flow path172. Method block252may also include operating a second fan of the furnace (e.g., circulation fan180) to circulate air across the heat exchanger to produce a conditioned airflow. For example, controller190may operate circulation fan180to circulate air over the external surface156of heat exchanger150and provide a conditioned airflow184that may be delivered to a comfort zone of the indoor space.

Method250proceeds at method block254by monitoring one or more parameters indicative of an airflow rate of the conditioned airflow. In some embodiments, the one or more parameters may comprise one or more parameters of a motor of the second fan (e.g., motor183of circulation fan180). The one or more parameters of the motor may be determined from one or more other parameters of the motor that are measured. For example, method block254may include determining a speed and a torque of a motor of a circulation fan (e.g., motor183of circulation fan180) of the furnace. In some embodiments, block254comprises determining a speed and a torque of the motor183of the circulation fan180of furnace100as the circulation fan180provides the conditioned airflow184exiting furnace100. As described above, motor183of circulation fan180may communicate one or more measured parameters of motor183to controller190, and controller190may be configured to determine the speed and torque of motor183based on the measured parameters of motor183. The one or more measured parameters of motor183used to determine the speed and torque of motor183may comprise a current and/or voltage supplied to motor183, a counter or back EMF of motor183, etc. Method block254may include controller190continuously determining speed and torque values of the motor183of circulation fan180during the operation of furnace100. In some embodiments, block254may include controller190determining other parameters of motor183, such as a shaft or output power of motor183.

Method block254may optionally include estimating an airflow rate of the conditioned airflow produced by the circulation fan (e.g., circulation fan180of furnace100) based on the determined speed and torque of the motor of the circulation fan (e.g., motor183of circulation fan180). For example, method block254may optionally include estimating the airflow rate as circulation fan180of furnace100produces the conditioned airflow184. In this optional step, the airflow rate of the conditioned airflow produced by circulation fan180may be estimated by controller190of furnace100as furnace100is operated to produce the conditioned airflow184. For example, controller190may periodically estimate the airflow rate of circulation fan180based on the determined speed and torque of motor183of circulation fan180and a motor map stored in the memory of controller190.

Method250continues at method block256by deactivating the burner assembly of the furnace (e.g., burner assembly140) in response to the one or more parameters indicating that the airflow rate is less than a minimum airflow rate. The minimum airflow rate may be predefined and may comprise an airflow rate produced by the circulation fan that corresponds to a temperature of the conditioned airflow (e.g., the temperature of conditioned airflow184) equaling a maximum permissible conditioned airflow temperature of the furnace. For example, as described above, the minimum airflow rate may be determined from testing of the furnace at a test facility prior to installation where the airflow rate produced by the circulation fan is negatively correlated with the temperature of the conditioned airflow of the furnace. In some embodiments, the minimum airflow rate may be saved in the memory of a controller (e.g., controller190) prior to the installation of the furnace.

The maximum permissible conditioned airflow temperature of the furnace (e.g., furnace100) may comprise a temperature in excess of an upper end of a predefined temperature rise range of the furnace. Particularly, the maximum permissible conditioned airflow temperature of the furnace may comprise a temperature above which damage due to overheating may result to the furnace and/or heat-related discomfort may occur to occupants of the indoor area heated by the furnace. In some embodiments, the maximum permissible conditioned airflow temperature of the furnace may comprise a temperature equal to an upper end of the designed temperature rise range of the furnace plus an additional fixed margin or safety factor. For instance, in an example where the fixed margin is equal to 100° F. and the designed temperature rise range of the furnace is between 30° F. and °60 F, the maximum permissible conditioned airflow temperature of the furnace may comprise 160° F. However, in other embodiments, the maximum permissible conditioned airflow temperature of the furnace may vary.

In some embodiments, method block256comprises deactivating or shutting-off a burner assembly of the furnace whereby combustion of air and fuel in the furnace ceases. For example, controller190of furnace100, having the minimum airflow rate and a motor map of circulation fan180stored in a memory thereof, may determine (based on the determined speed and torque of the motor183of circulation fan180) that the airflow rate of conditioned airflow184produced by circulation fan180is less than the minimum airflow rate. Controller190may close fuel supply valve102and cease the operation of igniter144and draft inducer170to cease the gas flow through furnace100along combustion flow path172in response to determining that the airflow rate of conditioned airflow184is less than the minimum airflow rate. Controller190may also deactivate or cease the operation of circulation fan180of furnace100following the deactivation of burner assembly152to cease the production of conditioned airflow184.

In some embodiments, a controller (e.g., controller190of furnace100) may issue an alert to a user of the furnace (e.g., a homeowner, an installer of the furnace, and/or a technician equipped to service the furnace) notifying the user that the burner assembly (e.g., burner assembly140) of the furnace has been deactivated in response to the one or more parameters indicating that the airflow rate of the conditioned airflow produced by the circulation fan of the furnace (e.g., circulation fan180) has fallen below the minimum airflow rate of the furnace so that the user may have the furnace serviced (e.g., replacing a filter of the furnace to reduce an obstruction to the circulation of airflow through the furnace, etc.). In some embodiments, the controller may place the furnace into an idle mode whereby operation of the furnace, including the burner assembly and/or the circulation fan thereof, is prevented for a predetermined period of time to allow for the burner assembly to cool before operation of furnace100may be resumed. Following the predetermined period of time, the controller may permit the activation of the furnace, including the combustion of air and fuel in the furnace, to satisfy a demand for heating of the indoor space.

In some embodiments, method250may optionally include operating a motor of the second fan at a speed or a torque that corresponds to a target rate of the conditioned airflow. For example, controller190of furnace100may operate the motor183of circulation fan180at a speed or a torque that corresponds to a target rate of conditioned airflow184. The target rate of conditioned airflow may correspond to a target firing rate of the burner assembly of the furnace called by a system controller of an HVAC system comprising the furnace. For example, the system controller may request a target firing rate in response to an ambient temperature of a comfort zone conditioned by the HVAC system falling below a user-defined set point of the HVAC system.

Method250may also include increasing the speed or the torque of the motor of the second fan in response to the one or more parameters indicating that the airflow rate produced by the second fan is less than the target airflow rate. Additionally, the burner assembly of the furnace may be deactivated only in response to both the airflow rate being less than a predetermined minimum airflow rate, and either a speed or a torque of the motor of the second fan being at or above a predefined threshold. For example, controller190may continuously increase the speed or the torque of the motor183of circulation fan180in response to the one or more parameters indicating that the airflow rate of conditioned airflow184is less than the target rate until either the speed or the torque of the motor183of circulation fan180equals or exceeds a predefined threshold. The predefined threshold may comprise a designed maximum speed or torque of the motor183of circulation fan180. In response to the speed or the torque of the motor183of circulation fan180being at or greater than the predefined threshold, and the airflow rate of circulation airflow184being less than the minimum airflow rate, controller190may deactivate burner assembly140to cease the combustion of fuel and air in furnace100.

In some embodiments, method250may further optionally include estimating a temperature of the conditioned airflow of the furnace (e.g., the temperature of the conditioned airflow184of furnace100) based on the estimated airflow rate of the conditioned airflow (e.g., conditioned airflow184). For example, a controller (e.g., controller190of furnace100) may periodically determine or estimate the temperature of the conditioned airflow of the furnace based on a conditioned airflow temperature map of the furnace stored in the memory of the controller. As described above, the conditioned airflow temperature map may be created during testing of the furnace at a testing facility prior to installation. In some embodiments, the conditioned airflow temperature map may be pre-stored in the memory of the controller prior to installation of the furnace. Additionally, in some embodiments, the minimum airflow rate may be determined from the conditioned airflow temperature map of the furnace, where the minimum airflow rate corresponds to the point along the curve of the conditioned airflow temperature map where the estimated conditioned airflow temperature equals the maximum permissible conditioned airflow temperature of the furnace.

Referring now toFIG.5, another method270for operating a furnace is shown inFIG.5. In some embodiments, method270may be practiced with furnace100shown inFIGS.1,2. Thus, in describing the features of method270, continuing reference will made to the furnace100shown inFIGS.1,2; however, it should be appreciated that embodiments of method270may be practiced with other systems, assemblies, and devices. Generally speaking, method270includes monitoring a parameter that is indirectly indicative of a temperature of a conditioned airflow produced by a gas-fired furnace, and deactivating the furnace in response to the parameter indirectly indicating that the temperature of the conditioned airflow exceeds a threshold.

Initially, method270includes operating a gas-fired furnace (e.g., furnace100) to produce a conditioned airflow at method block272. Method block272may be similar to the method block252of method250described above. For instance, method block272may include activating a burner assembly and a first fan of the furnace (e.g., burner assembly140and draft inducer170) to combust fuel and air and circulate combustion gases along a flow path (e.g., combustion flow path172) extending through a heat exchanger of the furnace (e.g., heat exchanger150), and operating a second fan of the furnace (e.g., circulation fan180) to circulate air across the heat exchanger to produce a conditioned airflow.

Method270proceeds at method block274by monitoring a parameter that is indirectly indicative of a temperature of the conditioned airflow. As used herein, “indirectivity indicative” refers to a relationship between two variables that is not directly proportional such that the two variables do not correspondingly increase or correspondingly decrease in the same ratio. In other words, the monitored parameter is not directly proportional to the temperature of the conditioned airflow. The parameter may be negatively correlated with the temperature of the conditioned airflow. In some embodiments, the parameter may comprise or be indicative of an airflow rate of the conditioned airflow or a speed and a torque of a motor of a second fan of the furnace (e.g., motor183of the circulation fan180of furnace100). For example, controller190of furnace100may monitor speed and torque of the motor183of circulation fan180and estimate the airflow rate of circulation airflow184based on the monitored speed and torque of motor183as well as a motor map and a conditioned airflow temperature map stored in the memory of controller190. As described above, the airflow rate of the conditioned airflow is negatively correlated with, and thus may be indirectly indicative of, the temperature of the conditioned airflow.

Method270continues at method block276by deactivating a burner assembly of the furnace (e.g., burner assembly140of furnace100) in response to the parameter indirectly indicating that the temperature of the conditioned airflow exceeds a threshold. In some embodiments, the threshold may comprise a maximum permissible conditioned airflow temperature of the furnace. Thus, method block276may comprise deactivating the burner assembly of the furnace in response to the parameter indirectly indicating that the temperature of the conditioned airflow exceeds the maximum permissible conditioned airflow temperature of the furnace. For example, controller190of furnace100may deactivate burner assembly140to cease the combustion of fuel and air in furnace100in response to the parameter indirectly indicating that the temperature of conditioned airflow184exceeds the maximum permissible conditioned airflow temperature of the furnace. As described above with respect to method block274, the parameter may comprise, or be indicative of, an airflow rate of the conditioned airflow or a speed and a torque of a motor of a second fan of the furnace (e.g., motor183of the circulation fan180of furnace100).

Referring toFIGS.4,5, through use of the systems and methods described herein (e.g., furnace100, methods250,270, etc.), a furnace may be deactivated in response to a conditioned airflow produced by a circulation fan of the furnace being less than a minimum airflow rate required to maintain a temperature of the conditioned airflow equal to or less than a maximum permissible conditioned airflow temperature of the furnace.

Specifically, a gas-fired furnace (e.g., furnace100shown inFIGS.1,2) may be operated to produce a conditioned airflow (e.g., producing a conditioned airflow at method blocks252,272of methods250,270, respectively), monitoring one or more parameters indicative of an airflow rate of the conditioned airflow (e.g., monitoring one or more parameters indicative of the airflow rate at block254of method250) and deactivating a burner assembly of the furnace in response to the one or more parameters indicating that the airflow rate of the conditioned airflow is less than the minimum airflow rate (e.g., deactivating a burner assembly of the furnace at block256of method250). Additionally, a gas-fired furnace may be operated by monitoring a parameter that is indirectly indicative of a temperature of the conditioned airflow (e.g., monitoring the parameter at method block274of method270), and deactivating the burner assembly of the furnace in response to the parameter indirectly indicating that the temperature of the conditioned airflow exceeds a threshold (e.g., deactivating the furnace at block274of method270).

In this manner, the furnace may be deactivated once the temperature of the conditioned airflow produced by the furnace exceeds the maximum permissible conditioned airflow temperature of the furnace without needing to rely on a separate temperature limit switch (e.g., a spring-operated bimetallic switch). As described above, the temperature limit switch rendered superfluous by embodiments disclosed herein may add to the overall expense of the furnace while also requiring the furnace to be configured and/or installed in a particular orientation (limiting the flexibility in which the furnace may be internally configured and/or installed in an indoor space) in order to function as intended. Although the elimination of the temperature switch using the methods described above (e.g., methods250,270) is discussed in the context of gas-fired furnaces, methods described herein may be applied to prevent other heating units of HVAC systems, such as electrically powered supplemental or auxiliary heaters, from exceeding a maximum permissible conditioned airflow temperature.

While exemplary embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.