Patent Application
20060275719
The present invention relates generally to warm air furnaces, and more particularly, to fault detection in a warm air furnace.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
Exemplary Warm Air Furnace and Control
The warm air furnace 100 depicted in
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.
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
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
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.
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.
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.
As shown in
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.
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.
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.
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.
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.
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.
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.
Exemplary Operation
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Although the method outlined by
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.
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.
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.
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.
