Abstract:
A warm-air furnace is adapted to provide diagnostic enhancements and more robust installation. In an embodiment, sensing equipment aboard the furnace is used to determine a first performance metric during installation of the furnace. That performance metric is then compared with a baseline metric that may have been obtained at a factory in order to obtain a performance variation value. At least partially in response to the performance variation, a notification is provided to a user. The notification may be an indication of poor installation or shipping damage, present failure and/or predicted future failure, for instance.

Description:
BACKGROUND  
     FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to warm air furnaces, and more particularly, to fault detection in a warm air furnace.  
       BACKGROUND OF THE INVENTION  
       [0002]     Many houses and other buildings use warm air furnaces to provide heat. Generally, these furnaces operate by heating air received through cold air or return ducts and distributing the heated air throughout the building using warm air or supply ducts. A circulation fan, operated by an alternating current (AC) permanent-split-capacitor (PSC) motor, directs the cold air into a heat exchanger, which may be composed of metal. The heat exchanger metal is heated using a burner that burns fossil fuels. The burner is ignited with an ignition device, such as an AC hot surface ignition element. The air is heated as it passes by the hot metal surfaces of the heat exchanger. After the air is heated in the heat exchanger, the fan moves the heated air through the warm air ducts. A combustion air blower, or inducer, is used to remove exhaust gases from the building. The inducer is typically operated using an AC shaded-pole motor.  
         [0003]     Because furnaces play a critical role in the comfort and safety of occupants of the building, it is important that the warm air furnace remains functional and that any problems with furnace operation be quickly diagnosed and corrected. Such diagnosis and repair is often difficult due to the complexity of modern heating, ventilation, and/or cooling systems. Therefore, it is desirable to detect faults in the warm air furnace prior to failure.  
         [0004]     Preventive detection and repair may prevent the occupants of the building from either remaining in an uncomfortably cold building or having to leave the building while waiting for a repair technician to fix the warm air furnace. Therefore, a need exists to detect faults in a warm air furnace while the furnace is operating. Some faults occur even prior to installation, thus it is important for the operation of a furnace that its initial installation in the home or building be done correctly and with an eye toward discovering faults due to installation or shipping. Therefore, a need exists for a system of correctly installing furnaces to correct installation and pre-installation faults.  
         [0005]     The heating system in a building comprises the furnace, duct work, and the building itself. Thus, a particular furnace model may have different optimal operating conditions depending upon its building of residence. In addition, the individual operating conditions of the furnace-home combination may alter the expected life of replaceable components of the furnace. Therefore, a need exists for a system of discovering baseline optimal values for the furnace-home combination and detecting changes in those values.  
       SUMMARY  
       [0006]     The present invention provides an apparatus for warm air furnace diagnostic enhancements and a method for using those enhancements for baselining and more effective troubleshooting. Generally, various embodiments may meet a number of objectives, including: ensuring a more robust furnace installation at a customer premises; dynamically identifying elements of the furnace that may be subject to future fault; and identifying and/or diagnosing current faults. Of course, some embodiments may meet other objectives or have other uses.  
         [0007]     In an exemplary embodiment, a warm air furnace (“furnace”) is equipped with a Flash based microcontroller or EEPROM memory with a microcontroller to retain data in a non-volatile state. Prior to shipment from a manufacturing facility, factory test values for the furnace are measured to create a factory baseline. The measurement may involve passing the furnace through a predetermined furnace test cycle, and obtaining measures during the test cycle, for instance. As examples of potential measurements taken, key baseline furnace performance indicia to retain includes but is not limited to flame current, hot surface ignition (HSI) current, inducer current, fan current, pressure switch open and close times, and heat exchanger rates of temperature rise. These data are stored in the memory of the furnace and are accessible by a technician at installation.  
         [0008]     During installation, measurements may be taken of the performance indicia and compared to the factory baseline. Variations from the factory baseline may indicate improper installation or damage during shipment. Alternatively, the variations may indicate that a maintenance schedule of the installed furnace should be revised or reconsidered. Thus, according to an embodiment, the furnace may determine that a variation is outside of a predetermined range of acceptable variations and, as a result, modify the maintenance schedule to recommend more immediate maintenance. An indication may be provided to a technician or furnace user of the modified maintenance schedule.  
         [0009]     Even with proper installation, the installation baseline measures may differ from the factory baseline measures—for example, air flow rates may depend upon duct-work configuration and building size, likewise, customized furnace options may also cause installation baseline measures to differ from their factory based counterparts. In a further embodiment, an installation baseline is created during installation by measuring the baseline furnace performance indicia and storing those indicia in the memory of the furnace. The installation baseline is useful for predicting wear-out of key system components and for helping in diagnosis of fault conditions. According to the embodiment, the baseline installation indicia are then compared with later obtained indicia and with the run-time counter. The maintenance schedule of the furnace may then be modified based on the comparison.  
         [0010]     In yet another embodiment, the apparatus compares the stored factory baseline and installation baseline and further compares those figures to later obtained measures to determine the performance of the furnace. In another embodiment, periodic measurements are taken of the performance indicia and of run-time counters to help predict system degradation. Such time-series information is also useful for determining whether a particular problem is due to acute failure or to a gradual decline in performance.  
         [0011]     According to the preferred embodiment, the warm are furnace includes a data storage and a processor. The data storage may be used to store furnace performance data as well as instructions that are executable by a processor. Sensing circuitry is also provided for obtaining furnace performance data during operation of the warm air furnace. These various elements of the furnace may be communicatively linked through a data bus. The instructions stored in data storage may be machine language programs for obtaining readings from the sensing circuitry, storing the readings in data storage, comparing the various readings, and updating a maintenance schedule based upon the comparisons, for instance.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Presently preferred embodiments are described below in conjunction with the appended drawing figures, wherein like reference numerals refer to like elements in the various figures, and wherein:  
         [0013]      FIG. 1  is a block diagram of a warm air furnace with diagnostics.  
         [0014]      FIG. 2  is a block diagram of a control system for a warm air furnace with diagnostics.  
         [0015]      FIG. 3  is a flow chart of a method of operation of the warm air furnace.  
     
    
     DETAILED DESCRIPTION  
       [0000]     Exemplary Warm Air Furnace and Control  
         [0016]      FIG. 1  shows a simplified block diagram of a warm air furnace  100 . The warm air furnace  100  includes a controller  102 , a gas valve  104 , a burner  106 , an ignition element  108 , a circulator fan  112 , a heat exchanger  114 , and a combustion air blower  116 , which is also referred to as an inducer. The warm air furnace  100  may include additional components not shown in  FIG. 1 , such as sensors for detecting temperature and pressure, and filters for trapping airborne dirt. Furthermore, warm air furnaces have various efficiency ratings. Additional components may be necessary to achieve different levels of efficiency.  
         [0017]     The warm air furnace  100  depicted in  FIG. 1  is fueled by natural gas. However, the warm air furnace  100  may be fueled by other fossil fuels, such as oil and propane. Different fuel sources may require different components in the warm air furnace  100 . For example, a warm air furnace fueled by oil may include an oil pump.  
         [0018]     The warm air furnace  100  may be connected to a thermostat, an exhaust vent, warm air or supply ducts, cold air or return ducts, and a gas supply. The warm air furnace  100  may also be connected to an alternating current (AC) power supply. The warm air furnace may have at least one AC load. For example, the ignition element  108  may be an AC hot surface ignition element, the fan  112  may include an AC motor, such as an AC permanent-split-capacitor (PSC) motor, and the inducer  116  may include an AC motor, such as an AC shaded-pole motor.  
         [0019]     Generally, the warm air furnace  100  operates as follows. The thermostat sends a “heat request” signal to the controller  102  when the thermostat is adjusted upwards. The controller  102  may perform a safety check, which may include checking a pressure switch located within the warm air furnace  100 . (The pressure switch is not shown in  FIG. 1 .) Once the safety check is completed, the controller  102  may activate the inducer  116  by turning on an inducer motor, such as an AC shaded-pole motor. After turning on the AC shaded-pole motor, the controller  102  may verify that the pressure switch in the warm air furnace  100  closes. If the pressure switch closes properly, the controller  102  may then activate the ignition element  108 .  
         [0020]     The controller  102  may then open the gas valve  104 , which may activate the burner  106 . The burner  106  may mix the natural gas with air and burn the gas mixture. The ignition element  108  may ignite the gas mixture causing a flame  110  to develop. Once the flame  110  has been produced by the ignition element  108  and sensed by a flame sense rod (not shown in  FIG. 1 ), the ignition element  108  may be deactivated. The flame  110  may warm metal in the heat exchanger  114 .  
         [0021]     After the heat exchanger  114  warms for a predetermined time, typically  15  to  30  seconds, the fan  112  may be activated. The fan  112  may direct cold air received from the cold air ducts into the heat exchanger  114 . The heat exchanger  114  may separate the warm air from exhaust gases. The fan  112  may cause the warm air to exit the heat exchanger  114  through the warm air ducts, while the inducer  116  may cause the exhaust gases to exit through an exhaust vent connected to the outdoors.  
         [0022]     The controller  102  may close the gas valve  104  when the thermostat setting has been reached. The inducer  116  may be deactivated after a predetermined time period, such as  30  seconds, to ensure that the exhaust gasses have been removed from the heat exchanger  114 . The fan  112  may be deactivated after a predetermined time period, such as  120  seconds, to ensure the heat from the heat exchanger  114  is delivered to the warm air ducts. When the ignition element  108 , the fan  112 , and the inducer  116  are turned off, the warm air furnace  100  may be in an Idle mode.  
         [0023]     During both the Idle mode and heating mode, it would be beneficial to monitor the warm air furnace  100  and potentially detect a fault condition prior to damaging the warm air furnace  100 . In a preferred embodiment, a current sensing circuit may be used to measure current levels at various points during a warm air furnace  100  operating sequence. In an embodiment, the warm air furnace may be adjoined with a cooling system such as an air conditioner or a humidifier for example.  
         [0024]      FIG. 2  is a block diagram of a monitoring and control device  200  according to an exemplary embodiment. Other monitoring and control devices may be used. The monitoring and control device  200  may be located within the controller  102 , although elements of the monitoring and control device  200  may be distributed throughout the furnace  100 . Alternatively, the monitoring and control device  200  may be located separately or within another component of the warm air furnace  100 . According to the embodiment, non-volatile data storage is included in the monitoring and control device  200  for retaining key performance measures. By comparing key performance data recorded during production testing with data gathered at initial installation, installers can be warned about certain installation problems that can lead to premature failure. By monitoring the degradation of key performance measures and recording run time, warnings can be issued on wear-out of key WAF systems. By retaining all fault conditions over time, intermittent problems can be more readily diagnosed.  
         [0025]     As shown in  FIG. 2 , the monitoring and control device includes a processor  202 , a set of sensing devices  210 ,  212 ,  214 ,  216 ,  220 ,  222 ,  224 ,  226 ,  228 ,  230  communicatively coupled with the processor  202 , an analog-to-digital converter  208  to convert signals from at one of the sensing devices from an analog signal to a digital signal, data storage  204 , an input/output (I/O) port  206 , and furnace control switches  234 . The various elements of the monitoring and control device  200  are inter-coupled via a data bus  232 . In the exemplary embodiment, the data storage  204  stores program code such as machine readable instructions for execution by the processor  202 , stored parameters that provide guidance and user preferences for execution of the program code, and measured data such as indicia received from the sensing devices or calculated by the processor  202 . The processor  202  may be one or more processing units, such as a general-purpose processor and/or a digital signal processor.  
         [0026]     The plurality of sensing devices are now described. A flame current sensor  210  provides an indication of the presence of flame in the furnace. Several types of flame current sensors may be used including A/C flame ionization sensors and photocell flame sensors. A low flame current at initial installation may indicate poor earth ground connection, flame rod movement due to shipping, low AC voltage, or incorrect AC voltage polarity. High flame current at initial installation may indicate over-fire, high AC line, or flame rod movement during shipping. At later points, variance in flame current may be indicative of other problems such as low flame level, damaged flame current sensor  210 , and/or a need for furnace maintenance.  
         [0027]     An inducer current sensor  212  provides an indication of whether the inducer  116  is operating properly. According to an exemplary embodiment, the inducer current sensor  212  measures the current used by the inducer  116 . Likewise, a fan current sensor  214  provides an indication of whether the fan  112  is operating properly. According to the embodiment, the fan current sensor  213  measures the current used by the inducer  116 . In a preferred embodiment, a single sensor may comprise the fan current sensor  214 , inducer current sensor  212 , etc. This may allow a system to be configured with just one current sensor yet obtain a variety of data.  
         [0028]     In the presently described embodiment, the flame current sensor  210 , inducer current sensor  212 , and fan current sensor  214  each measure current level as an analog signal. The A/D converter  208  is used to convert the analog signals from the three current sensors  210 ,  212 ,  214  to digital signals for the processor  202  and data storage  204 . In furnaces using a pressure switch, a pressure switch sensor  216  indicates whether the pressure switch is open or closed. The pressure switch is used as a safety feature to automatically sense change in pressure and open or close an electrical switching element when a predetermined pressure point is reached. The pressure switch sensor  216  may further be used to indicate pressure switch open time and pressure switch close time. A heat exchanger temperature sensor  220  measures a temperature in the heat exchanger  114 . The sensor  220  may further be used to obtain a rate of temperature change in the heat exchanger. An increased temperature rise rate can, for instance, indicate a dirty air filter, excessive duct restriction, fan motor failure, or over fire condition.  
         [0029]     Some elements of a furnace tend to wear out according to the run-time of specific portions of the furnace cycle. For example, elements associated with heating will need maintenance much less often if the furnace system is only used as a fan and/or air conditioner. Thus, several devices are provided for determining the run-time of portions of the furnace cycle. For instance, a heating switch  222  indicates whether the furnace is operating in a heating mode, a cooling switch  224  indicates whether the furnace is operating in a cooling (A/C) mode, a fan switch  226  indicates whether the furnace is operating in a fan-only mode, an igniter switch  228  indicates whether the furnace is operating with the igniter on, and a pressure switch indicates whether the motor and/or ductwork is operating properly. A counter  230  provides timing information for each portion of the cycle. Thus, according to an embodiment, the measurement and control device  200  may determine, using the heating switch  222  and counter  230 , that the furnace has been operating in a heating mode for a specified number of hours, such as 3,000 hours, for instance.  
         [0030]     Alternatively/additionally, the counter  230 , may be configured to keep track of the number of run-cycles that have taken place for each portion of the cycle. Thus, according to an embodiment, the measurement and control device  200  may determine, using heating switch  222  and counter  230 , that the furnace has operated in a heating mode for a specified number of cycles, such as 30,000 cycles. As with run-time, the number of cycles can be coupled with other measurements to determine or indicate a rate of degradation of elements of the furnace system, and thus to predict future failure or indicate present failure.  
         [0031]     The I/O port  206  may allow the monitoring and control device  200  to communicate with a user and/or technician by, for instance, warning the user that the furnace is not functioning correctly or by indicating that the maintenance schedule has been updated. As such, the port  206  may include a speaker, display (LCD) or lights to provide a audible or visual output to the user. Further, the I/O port  206  may provide connectivity for a technician to obtain stored data and alter stored parameters. In an alternative embodiment, data storage  204  includes a removable memory device such as a flash memory microcontroller or EEPROM memory with a microcontroller. In that case, the technician may transfer data to and from the monitoring and control device  200  using the removable memory device. Further, the system may be configured so that a technician may obtain data via a hand-held tool, such as a portable data device or personal data assistant (PDA). It is contemplated that the hand-held tool may be connected via a Honeywell EnviroCOM thermostat or via a wireless interface, for instance.  
         [0032]     The furnace control switches  234  allow the processor  202  to control activity of the furnace. For example, in an embodiment, the processor  202  executes a standard test cycle through the furnace control switches  234 . In the test cycle, the furnace may be placed in various modes such as heating and cooling modes. During the test cycle, performance indicia are measured through the various sensing devices and may be further calculated by the processors  202  and stored in data storage  204 .  
         [0000]     Exemplary Operation  
         [0033]      FIG. 3  provides a flow chart illustrating a method of operation that may be used to modify a maintenance schedule of the warm air furnace  100 . The method measures current consumption and other indicia at several points in the warm air furnace  100  operating sequence. The measured indicia are then compared with baseline measures obtained before shipment of the furnace from a factory setting. Depending upon the results of the comparison, a maintenance schedule for the furnace  100  may be modified and/or immediate maintenance recommended.  
         [0034]     Initial installation data can be used to predict wear-out of key system components and to help in diagnosis of fault conditions. For example, increased temperature rate of rise can indicate dirty air filter, excessive duct restriction, over fire condition, or fan motor failure. Decreased HSI current can indicate a failing igniter element. Increased motor currents can indicate bearing wear, winding fault or locked rotor conditions. Pressure switch close or open time increase can indicate increased vent restriction, or inducer motor performance change.  
         [0035]     Before installation, a baseline performance metric for the furnace  100  is obtained  302 . This metric may be obtained in the factory where the furnace is manufactured, for instance. The baseline performance metric is preferably a set of indicia measured by the measurement and control device  200 . These indicia may include, for instance, factory test values for flame current, HSI current, inducer current, fan current, pressure switch open and close times, and heat exchanger rate of temperature rise. The furnace is then installed at a customer premises at  304 . During installation, the measurement and control device  200  is used to determine an installed performance metric at  306 . As with the baseline performance metric, the installed performance metric may include a set of indicia measured by the measurement and control device  200 . In order to obtain the indicia, the measurement and control device  200  may initiate a furnace test cycle. At predetermined portions during the test cycle, the measurement and control device  200  may obtain and record the indicia.  
         [0036]     The test cycle may include passing the current through an idle mode, safety check mode, inducer start mode, inducer run mode, ignition mode, and burn mode for instance. When the warm air furnace  100  is in the idle mode, the ignition element  108 , the fan  112 , and the inducer  116  may be deactivated. During the idle mode  302 , a low current value may be supplied to the warm air furnace  100  due to the lack of current consumption by the ignition element  108 , the fan  112 , and the inducer  116 . The measurement and control device  200  may take an “Idle” current reading during the Idle mode. Alternatively, the current sensing circuit  200  may take periodic Idle current readings during the Idle mode. If the Idle current reading is above a baseline amount, there may be a problem with the warm air furnace  100 . A fault may be caused by shorted or damaged low voltage transformer in the AC power supply  202 . Following the idle mode, the furnace may pass through a safety check mode. In the safety check mode, the pressure switch may be checked to ensure that it is operating properly. If the pressure switch open and close times vary from a baseline measure, then there may be a need for immediate maintenance.  
         [0037]     Next, the furnace may be placed in the inducer start mode, and an inducer current is read during a first period after the inducer motor begins operation. If the inducer start current reading at installation is above a baseline reading, there may be a problem with the warm air furnace  100 . For example, either shorted wiring or motor windings in the inducer  116  may have caused the fault. After a wait period, an inducer run mode may be entered and another inducer current may be read. This second inducer period may be several seconds after the inducer start mode. If the installation inducer run current reading is above or below the corresponding baseline value, there may be a problem with the warm air furnace  100 . For instance, if the inducer run current reading is well above the baseline reading, motor windings may be beginning to short, motor bearings may be beginning to seize, or a rotor in the AC shaded-pole motor may be locked due to an obstruction. If the inducer run current is below the baseline amount, an excessive vent restriction, deteriorating wiring connections, failing or failed motor windings, or a damaged controller  102  may have caused the fault.  
         [0038]     The furnace may then be placed in an ignition mode by activating the ignition element  108 . At that point, an ignition current reading may be taken. If the reading is above or below the baseline amount, there may be a problem with the warm air furnace  100 . If the ignition current reading is above the baseline amount, shorted wiring or ignition element  108  may have caused the fault. If the ignition current reading is below the baseline amount, deteriorating wiring connections or ignition element  108 , an open ignition element  108 , or a damaged controller  102  may have caused the fault.  
         [0039]     The controller  102  may then open the gas valve  104  after a warm-up period following activation of the ignition element  108 . Once ignition element  108  has ignited the flame  110 , the ignition element  108  may be deactivated. A third inducer current reading may be taken at this point. After a delay period to allow the heat exchanger  114  to begin heating, the controller  102  may activate the fan  112 , as depicted in box, and a fan start current reading may be taken soon after the fan motor begins operation. If the fan start current reading is above a baseline amount, there may be a problem with the warm air furnace  100 . For instance, either shorted wiring or motor windings in the fan  112  may have caused a fault.  
         [0040]     After a wait period, the furnace may take a fan run current reading during a second period after the fan motor begins operation. The second period may be substantially 30 seconds after the first fan run current reading. If the second fan run current reading is above or below the corresponding baseline amount, there may be a problem with the warm air furnace  100 . If the fan run current reading is above the baseline amount, motor windings in the fan motor may be beginning to short, motor bearings in the fan motor may be beginning to seize, or a fan cage may be locked or obstructed. If the fan run current reading is below the baseline amount, a duct restriction, deteriorating wiring connections, failing or failed motor windings, or a damaged controller  102  may have caused the fault.  
         [0041]     The controller  102  may close the gas valve  104  when the thermostat setting has been reached. The inducer  116  may be deactivated after a predetermined time period, such as 30 seconds, to ensure that the exhaust gasses have been removed from the heat exchanger  114 . The fan  112  may be deactivated after a predetermined time period, such as 120 seconds, to ensure the heat from the heat exchanger  114  is delivered to the warm air ducts. The warm air furnace  100  may return to the idle mode  302  another idle current reading may be taken.  
         [0042]     In this embodiment, the installed performance metric comprises the set of indicia obtained during the test cycle. Once the installation performance metric is determined, the processor  202  is used to compare the installation performance metric with the baseline performance metric.  
         [0043]     According to the exemplary embodiment, the results of the comparison may fall into three categories: limited variance; significant variance, but within threshold; and variance outside threshold. If there is only a limited variance between the metrics  310 , then there will be no modification of a furnace maintenance schedule. If there is a significant variance, but the variance remains within a threshold (such as within 50% of the baseline)  312  then the processor  202  may modify the maintenance schedule to account for the difference between the baseline metric and the installed metric. If instead, the variance is outside of the threshold, then immediate maintenance should be required. Preferably, an installation technician is notified of the need for immediate maintenance. In a further embodiment, the processor is configured it identify at least one component in the warm air furnace that may have caused the fault.  
         [0044]     In some cases, a factory baseline metric may be unavailable. In those cases, recommended operational values for the furnace may be used in place of a measured baseline.  
         [0045]     Although the method outlined by  FIG. 3  uses a comparison between a factory baseline metric and an installed metric. In a further embodiment, a similar test cycle can be performed on a regular basis such as for each operating cycle of the warm air furnace  100 . Alternatively, the testing may be performed on a periodic basis such as daily. In that case, the new readings may be compared to the baseline metric as well as other, previously measured metrics. Further, some tests may be performed more than others based on failure rates of the warm air furnace components. It is also understood that additional current readings may be taken during the operation of the warm air furnace  100 . While the most likely causes of the faults are provided in method  300 , additional warm air furnace components may cause a fault.  
         [0046]     Not every test described in the method  300  needs to be run during every operational cycle of the warm air furnace  100 . For example, some tests may be performed each time the warm air furnace  100  completes an operational cycle, while other tests may be performed less frequently. Additional tests may also be included in the method.  
         [0047]     By maintaining a run-time counter, periodic maintenance intervals can be established. The home-owner can then be notified when a system component has reached a service interval and should be checked. In a further embodiment, the system may be configured to allow a home-owner to trigger a test cycle to diagnose any suspected problems.  
         [0048]     In a further embodiment, error codes that have occurred since a reset of memory are stored in the data storage. Retaining all error code conditions seen by the WAF greatly improves troubleshooting; especially for intermittent faults. The control provides a means to read-out and clear all stored error codes and may have a plug to download data onto handheld device or use wireless communication such as Bluetooth, for instance.  
         [0049]     It should be understood that the illustrated embodiments are exemplary only and should not be taken as limiting the scope of the present invention. For example, the invention may be used to detect faults in other ignition-controlled appliances, such as a water heater. The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the invention.