阅读说明：本技术 用于预测热水器罐故障的系统和方法 (System and method for predicting water heater tank failure ) 是由 R·O·诺贝勒 N·沃克 王尧隽 于 2020-05-01 设计创作，主要内容包括：一种储水式热水器,其包括被配置为容纳流体的罐、至少部分置于所述流体中的通电阳极和电子处理器。所述电子处理器被配置为接收所述通电阳极的电流测量值；确定电流测量值是否超过最大阈值；当电流测量值超过最大阈值时,记录一段持续时间内的多个罐电位测量值；根据记录的罐电位测量值确定罐故障的预测时间；并且输出对应于罐故障的预测时间的警报。(A storage-type water heater includes a tank configured to hold a fluid, an energized anode disposed at least partially in the fluid, and an electronic processor. The electronic processor is configured to receive a current measurement of the powered anode; determining whether the current measurement exceeds a maximum threshold; recording a plurality of tank potential measurements over a duration of time when the current measurement exceeds a maximum threshold; determining a predicted time for a tank fault based on the recorded tank potential measurements; and outputs an alarm corresponding to the predicted time of canister failure.)

1. A storage-type water heater, comprising:

a canister configured to contain a fluid;

an energized anode disposed at least partially in the fluid; and

an electronic processor configured to

Receiving a current measurement of the powered anode,

determining whether the current measurement exceeds a maximum threshold,

recording a plurality of tank potential measurements over a duration of time when the current measurement exceeds a maximum threshold,

determining a predicted time of tank failure based on the recorded tank potential measurements, an

An alarm corresponding to the predicted time of canister failure is output.

2. The water heater as recited in claim 1, wherein the electronic processor is further configured to determine a predicted time of tank failure based on at least one characteristic of the water heater.

3. The water heater as recited in claim 2, wherein the at least one characteristic affects a degradation rate of the metal and/or the liner.

4. The water heater as recited in claim 3, wherein the at least one characteristic includes at least one selected from the group consisting of a tank temperature setpoint, a temperature differential setpoint, a water inlet temperature, and a duty cycle of the water heater.

5. The water heater of claim 2, wherein the electronic processor is further configured to determine a predicted time of tank failure based on a calculation of when a trend line for a plurality of tank potential measurements is expected to fall below a tank potential threshold.

6. The water heater as recited in claim 5, wherein the tank potential threshold is determined based on at least one selected from the group consisting of: the duty cycle of the water heater, the tank temperature set point, the slope of the trend line, and the conductivity of the water in the water storage tank.

7. The water heater as recited in claim 5, wherein the tank potential threshold is determined based on at least one selected from the group consisting of: duty cycle, total dissolved solids level, tank temperature set point, slope of trend line, and conductivity of water in the tank.

8. The water heater as recited in claim 1, wherein the predicted time to tank failure is less than one year.

9. The water heater as recited in claim 1, wherein the electronic processor determines a predicted time of tank failure based on a trend line of recorded tank potential measurements.

10. A storage-type water heater, comprising:

a canister configured to contain a fluid;

an energized anode disposed at least partially in the fluid; and

an electronic processor configured to

Receiving a current measurement of the powered anode,

determining whether the current measurement exceeds a maximum threshold,

determining a predicted time of tank failure based on the maximum threshold and an adjustment factor, and

an alarm corresponding to the predicted time of canister failure is output.

11. The water heater as recited in claim 10, wherein the electronic processor is further configured to determine the adjustment factor based on at least one characteristic of the water heater.

12. The water heater as recited in claim 11, wherein the at least one characteristic affects a degradation rate of the metal and/or the liner.

13. The water heater as recited in claim 12, wherein the at least one characteristic includes at least one selected from the group consisting of a tank temperature setpoint, a temperature differential setpoint, a water inlet temperature, and a duty cycle of the water heater.

14. The water heater as recited in claim 11, wherein the electronic processor is further configured to adjust the adjustment factor based on at least one selected from the group consisting of: a duty cycle, a total dissolved solids level, a tank temperature set point, a slope of a trend line for a plurality of tank potential measurements, and a conductivity of water in the storage tank.

15. The water heater as recited in claim 10, wherein the predicted time to tank failure is less than one year.

Technical Field

Embodiments relate to a water heater.

Disclosure of Invention

Powered anodes (powered anodes) may be used to protect the storage tanks of water heating systems from corrosion. In such systems, the anode may be composed of a metal such as platinum or Mixed Metal Oxide (MMO) coated titanium and extend into the water contained in the water storage tank. An electric current may then be applied through the anode to prevent oxidation and corrosion of the bare steel. In some such systems, the amount of current required to adequately protect the bare steel depends inter alia on the quality and material of the tank liner, and the conductivity of the water in the tank. In at least one system, the applied current may be adjusted as the tank liner corrodes.

As the tank liner corrodes, the amount of current required to protect the bare steel of the water storage tank increases. However, due to practical limitations, the amount of current applied through the anode may be less than that required for the protection can. This may lead to deterioration of the tank wall of the water storage tank. Although energizing the anode can delay the failure of the water storage tank, eventually the metal will corrode and the water storage tank may begin to leak.

One embodiment provides a storage-type water heater comprising a tank configured to hold a fluid, an energized anode disposed at least partially in the fluid, and an electronic processor configured to receive a current measurement of the energized anode; determining whether the current measurement exceeds a maximum threshold; recording a plurality of tank potential measurements over a duration of time when the current measurement exceeds a maximum threshold; determining a predicted time for a tank fault based on the recorded tank potential measurements; and outputs an alarm corresponding to the predicted time of canister failure.

Other aspects of the present application will become apparent by consideration of the detailed description and accompanying drawings.

Drawings

Fig. 1 is a block diagram of a water heating system of some embodiments.

FIG. 2 is a side view of an electrode that can be used with the water heater of FIG. 1.

FIG. 3 is a block diagram of a control circuit of the water heater of FIG. 1 in some embodiments.

Fig. 4 is a diagram of a control loop of the control circuit of fig. 3 in some embodiments.

FIG. 5 is a graph illustrating tank potential and energized anode current characteristics of a water heater according to some embodiments.

FIG. 6 is a flow chart of a method of tank fault prediction for the water heater of FIG. 1 in some embodiments.

FIG. 7 is a graph 700 of recorded tank potential measurements over time for a water heater of some embodiments.

FIG. 8A is a graph illustrating a relationship between a temperature set point and a tank life, according to some embodiments.

FIG. 8B is a graph illustrating a relationship between a temperature differential set point and a tank life, according to some embodiments.

FIG. 8C is a graph illustrating a relationship between inlet water temperature and tank life, according to some embodiments.

Fig. 8D is a graph illustrating a relationship between duty cycle and canister life, according to some embodiments.

Fig. 9A is a graph illustrating a relationship between a lower duty cycle and a tank potential, according to some embodiments.

Fig. 9B is a graph illustrating a relationship between a higher duty cycle and a tank potential, according to some embodiments.

Detailed Description

Before any embodiments of the application are explained in detail, it is to be understood that the application is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The application is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

Fig. 1 is a block diagram of a water heating system 100 according to some embodiments of the present application. Although shown as a water heater, in other embodiments, the system 100 may be other appliances, such as, but not limited to, an electric stove or other type of water heater (e.g., an electric water heater). The water heating system 100 is configured to manipulate the temperature (e.g., warm) of a fluid (e.g., water). The water heating system 100 includes an enclosed water tank 15 configured to contain a fluid, an exhaust assembly 20, a burner assembly 25, a control circuit 200, an upper temperature sensor 70, and a lower temperature sensor 75. Some of the components and functions of the water heating system 100, both shown and not shown, are commonly used and understood in the art. Accordingly, for the sake of brevity, only the components of the water heater 10 used to understand the present application will be described more fully herein.

The water heating system 100 further comprises a shell 110 surrounding the tank 15, and a foam insulation material 115 filling the annular space between the water tank 15 and the shell 110. The can 15 may be formed using ferrous metal and lined internally with vitreous enamel to protect the metal from corrosion. In other embodiments, the canister 15 may be formed using other materials, such as plastic.

Burner assembly 25 is configured to provide heat to the fluid of canister 15 by combustion by the burner. In the illustrated embodiment, the burner assembly 27 is located at the bottom of the canister 15. The burner assembly 27 is configured to receive combustion gas from the gas line and air from the air supply line. The air and gas are combined in the assembly 27 and subsequently combusted by the burner. The burner assembly 27 includes additional components for operation (e.g., fans/blowers, thermocouples, control valves, etc.), which are not described herein for the sake of brevity. Exhaust assembly 20 is configured to force exhaust gases (resulting from combustion by burner assembly 25) out of system 100 via a blower (not shown).

The upper temperature sensor 70 is located at the upper portion of the water tank 15 to determine the upper temperature of the water stored in the upper portion of the water tank 15. The lower temperature sensor 75 is located at the lower portion of the water tank 15 to determine the lower temperature of the water at the lower portion of the water tank 15. In some embodiments, the upper temperature sensor 70 and the lower temperature sensor 75 may be coupled to an outer or inner surface of the water tank 15. The upper temperature sensor 70 and the lower temperature sensor 75 may be a thermistor type sensor, a thermocouple type sensor, a semiconductor type sensor, a resistance temperature detector, or the like. The upper temperature sensor 70 and the lower temperature sensor 75 can be coupled to the control circuit 200 (and in particular the electronic processor 160 of fig. 2) to provide temperature information (e.g., a sensed upper temperature and a sensed lower temperature) to the control circuit 200. In some embodiments, water tank 15 may include one or more additional temperature sensors located at various locations around water tank 15. For example, the water tank 15 may be divided into three or more sections, and temperature sensors may be located at the respective sections. In some embodiments, the water heating system 100 may include one or more additional sensors configured to measure one or more characteristics (e.g., temperature, pressure, voltage, etc.) of the water heating system 100.

Water heating system 100 includes an electrode assembly 165. The electrode assembly 165 (and control circuit 200) may be similar to that described in U.S. patent No. 7,372,005 and U.S. patent No. 8,068,727, the entire contents of which are incorporated herein by reference. Electrode assembly 165 is attached to water heating system 100 and extends into can 105 to provide corrosion protection to the can. As described above and in more detail below, the electrode assembly 165 is used by the control circuitry of the water heating system 100 to predict tank failure due to corrosion of the liner of the tank 105. An example electrode assembly 165 that may be used with water heating system 100 is shown in FIG. 2. Referring to fig. 2, the electrode assembly 165 includes an electrode wire 170 and a connector assembly 175. The electrode wire 170 comprises titanium and has a first portion 180 coated with a metal oxide material and a second portion 185 uncoated with a metal oxide material. During manufacture of the electrode assembly 165, a sheath tube 190 (comprising PEX or polysulfone) is placed over a portion of the electrode wire 170. The electrode wire 170 is then bent twice (e.g., at two forty-five degrees) to hold the sheath tubing 190 in place. A small portion 195 of the electrode wire 170 near the top of the tank is exposed to the tank to allow hydrogen gas to exit the jacket tube 190. In other constructions, the electrode assembly 165 does not include the sheath tube 190. The connector assembly 175 includes a threaded spud 196 that secures the electrode rod assembly to the top of the water tank 15 (not shown) by mating with the threads of the opening 197. Other connector assemblies known to those skilled in the art may be used to secure electrode assembly 165 to can 105. The connector assembly 175 also includes a connector 198 (described below) for electrically connecting the electrode wire 170 with a control circuit. The electrical connection of electrode assembly 165 to the control circuitry makes electrode assembly 165 an energized anode. The electrode wire 170 is electrically isolated from the can 105 to allow a voltage potential to be generated between the electrode wire 170 and the can 105. Other electrode assembly designs may be used with the present invention.

Fig. 3 is a block diagram of a control circuit 200 for the water heating system 100. The control circuit 200 may be mounted to (and/or integrated into) the water heating system 100 (e.g., on a surface of the tank 15). In some embodiments, the control circuit 200 is located separately from the water heating system 100. As shown in fig. 2, the control circuit 200 includes an electronic processor 160, a memory 204, and an input/output device 206. The control circuit 200 receives power from an AC power source (not shown). In one embodiment, the AC power source provides 120VAC at a frequency of about 50Hz to about 60 Hz. In another embodiment, the AC power source provides about 220VAC at a frequency of about 50Hz to about 60 Hz. In some embodiments, the control circuit 200 also includes a power regulator 223 that converts power from the AC power source to a nominal voltage (e.g., a DC voltage) and provides the nominal voltage to the control circuit 200 (e.g., the electronic processor 160, the input/output device 206, etc.).

The memory 204 stores algorithms and or programs for controlling and processing component information from the exhaust assembly 20, the burner assembly 25, and other components of the water heating system 100, and receiving and providing information to a user of the water heating system 100. The memory 207 may also store operational data of the water heating system 100 (e.g., characteristics of the exhaust assembly 20 and/or the burner assembly 25, historical data, usage patterns, etc.) to assist in controlling the water heating system 100.

The electronic processor 160 is coupled to the memory 204, the upper temperature sensor 70, the lower temperature sensor 75, and the input/output device 206. The electronic processor 160 receives an upper temperature signal (e.g., an upper temperature) from the upper temperature sensor 70 and a lower temperature signal (e.g., a lower temperature) from the lower temperature sensor 75. In addition, the electronic processor 160 accesses programs, algorithms, and/or thresholds stored in the memory 204 to control the water heating system 100 accordingly.

The input/output devices 206 include one or more devices configured to output information to a user regarding the operation of the water heating system 100, and may also receive input from a user. In some embodiments, the input/output device 206 may include a user interface for the water heating system 100. The input/output device 206 may comprise a combination of digital and analog input or output devices as needed to effect control and monitoring levels of the water heating system 100. For example, the input/output device 206 may include a touch screen, speakers, buttons, and the like, to output information and/or receive user input regarding the operation of the water heating system 100 (e.g., a temperature set point for delivering water from the water tank 15). The electronic processor 160 controls the input/output device 206 to output information to a user in the form of, for example, graphics, alarm sounds, and/or other known output devices. The input/output device 206 is also used to control and/or monitor the water heating system 100. For example, the input/output device 206 may be operatively coupled to the electronic processor 160 to control the temperature setting of the water heating system 100. For example, using the input/output device 206, a user may set one or more temperature set points for the water heating system 100.

The input/output device 206 may be configured to display conditions or data related to the water heating system 100 in real time or substantially real time. For example, but not limiting of, the input/output device 206 may be configured to display measured electrical characteristics of one or more components of the water heating system 100, temperatures sensed by the temperature sensors 150,155, and the like.

The input/output device 206 may be mounted on the housing of the water heating system 100, remotely from the water heating system 100 in the same room (e.g., mounted on a wall), in another room of a building, or even outside of a building. The input/output device 206 may provide an interface between the electronic processor 160 and a user interface, including a 2-wire bus system, a 4-wire bus system, and/or wireless signals. In some embodiments, the input/output device 206 may also generate an alert regarding the operation of the water heating system 100. The input/output devices 206 may also include transceivers, antennas, etc. to wirelessly communicate with one or more networks (e.g., to receive and/or store field data as described below).

In some embodiments, the input/output device 206, memory 204, and/or other components of the control circuit 200 are modular and separate from the electronic processor 160. In other words, some components of the control circuit 200 may be separately fabricated as an add-on device that is connected to the electronic processor 160. In some embodiments, the control circuit 200 may be communicatively coupled to an external device (e.g., a wireless control panel, a smartphone, a laptop computer, etc.) through, for example, a remote network, a transceiver, etc.

Control circuitry 200 includes a control loop 250 coupled to electronic processor 160 to control and measure characteristics of electrode assembly 165. Additional control loops 250 may include one or more sensors for measured electrical and/or thermal characteristics of electrode assembly 165. For example, fig. 4 illustrates a control loop 250 of some embodiments. The electronic processor 160 outputs a Pulse Width Modulation (PWM) signal at P0.1. The PWM signal controls the voltage applied to the electrode line 170. A 100% duty cycle results in full voltage being applied to electrode line 170 and a 0% duty cycle results in no voltage being applied to electrode 170. A ratio between 0 and 100% will result in a corresponding ratio between zero and full voltage applied to the electrode wire 170.

The PWM signal is applied to a low pass filter and amplifier, which is composed of resistors R2, R3, and R4; a capacitor C3; and an operational amplifier U3-C. The low pass filter converts the PWM signal to an analog voltage proportional to the PWM signal. The analog voltage is provided to a buffer and current limiter, which consists of an operational amplifier U3-D, resistors R12 and R19, and transistors Q1 and Q3. The buffer and current limiter provides a buffer between the processor 160 and the electrode assembly 165 and limits the current applied to the electrode wire 170 to prevent hydrogen accumulation. The resistor R7, inductor L1 and capacitor C5 act as a filter to prevent transients and oscillations. The result of the filter is a voltage applied to electrode assembly 165, which is electrically connected to CON 1.

As discussed in further detail below, the drive voltage is periodically removed from the electrode assembly 165. The processor 160 deactivates the drive voltage by controlling the signal applied to the driver consisting of resistor R5 and transistor Q2. More specifically, pulling pin P0.3 of processor 160 low causes transistor Q1 to turn off, which effectively removes the applied voltage driving electrode assembly 165. Thus, the processor 160, low pass filter and amplifier, buffer and current limiter, filter and driver function as a variable voltage power supply that controllably applies a voltage to the electrode assembly 165, creating a powered anode. Other alternative circuit designs may also be used to controllably provide voltage to electrode assembly 165.

Input or connection CON2 provides a connection that allows measurement of the electrode return current. More specifically, resistor R15 provides a sense resistor that generates a signal related to the current on can 105. The operational amplifier U3-B and resistors R13 and R1 provide an amplifier that provides an amplified signal at pin P1.1 to the processor 160. Thus, the resistor R15 and the amplifier form a current sensor. However, other current sensors may be used in place of the sensor just described. Further, in some configurations, a similar current sensor is configured to monitor current at CON1 (i.e., at the anode).

As the voltage is removed, the potential at electrode 165 drops to a potential that is offset but proportional to the open circuit or "natural potential" of electrode 165 relative to can 105. A voltage proportional to the natural potential is applied to a filter composed of a resistor R6 and a capacitor C4. The filtered signal is applied to an operational amplifier U3-A, which acts as a voltage follower. The output of the operational amplifier U3-A is applied to a voltage limiter (resistor R17 and zener diode D3) and a voltage divider (resistors R18 and R20). The output is a signal related to the natural potential of electrode assembly 165, which is applied to processor 160 at pin P1.0. Thus, the filter, voltage follower, voltage limiter and voltage divider just described form a voltage sensor. However, other voltage sensors may be used in place of the disclosed voltage sensors.

The control circuit 200 controls the voltage applied to the electrode wire 170, thereby controlling the current through the powered anode. As will be discussed below, the control circuit 200 also measures the tank protection level, accommodates changing water conductivity conditions, and accommodates electrode potential drift in high conductivity water. In addition, when control circuitry 200 for electrode assembly 165 is integrated or in communication with control circuitry for burner assembly 25, the resulting control circuitry may utilize interactions to provide additional control of the water heating system.

The electronic processor 160 is also configured to control the electrode assembly 165 by controlling the voltage applied to the electrode wire 170 to predict can failure, thereby controlling the current through the energized anode. Electronic processor 160 (particularly an electronic processor as described in U.S. patent No. 7,372,005 and U.S. patent No. 8,068,727) measures the level of can protection by disabling the voltage applied to electrode assembly 165 for a predetermined period of time, determines (measures) the electrode potential (voltage) through control loop 250, and reapplies the voltage supply to electrode assembly 165. Based on the determined electrode potential, electronic processor 160 increases or decreases the voltage applied to electrode assembly 165. Increasing the applied voltage causes the can potential measured by the electrodes to increase, while decreasing the applied voltage decreases the can potential measured by the electrodes. Thus, the control circuit 200 can adjust the open circuit potential of the electrodes until the following target potential is reached. Further, as the characteristics of the water heating system 100 change, the control circuit 200 may adjust the voltage applied to the electrodes such that the open circuit potential of the electrodes is equal to the target point potential.

The electronic processor 160 may then determine (measure) the electrode current via the control loop 250 (e.g., via current measurement at CON2 described above), and determine the conductivity state of the water of the tank 105 based on the applied current and voltage. For example, the conductive state may be a high conductivity of water or a low conductivity of water. The conductive state represents the level of metal exposure of the water storage tank (e.g., caused by corrosion inside the tank 105 as described above). When the result is less than the empirical setting, then the electronic processor 160 determines that the conduction state is low and sets the target potential (described above) to a first value; otherwise, the electronic processor 160 sets the target potential to a second value indicative of a high conduction state. It should be understood that in other embodiments, the electronic processor 160 may utilize other methods to determine the conductive state of water.

As the storage tank 105 ages, the inner enamel lining deteriorates and more ferrous metal is exposed to the water stored in the tank 105. As the exposed metal surface area increases, the magnitude of the energized anode current must also increase to adequately protect the exposed ferrous metal. However, the maximum amount of current that may be applied to the water heating system 100 may be limited. For example, the current can cause water to ionize, which produces excess hydrogen within the sealed canister, and the hydronium produced by the reaction can cause the heated water to develop an unpleasant odor. Thus, as the liner degrades, the water heater may reach a point where the energized anode is no longer able to adequately protect the exposed metal of the tank 105. The storage tank 105 may then eventually corrode.

The electronic processor 160 is configured to monitor the potential (voltage) of the electrode 165 relative to the can 105 and to monitor the current at the can 105 at the electrode 165. Using data from these measurements, processor 160 can evaluate the protection provided by the energized anode. Thus, when the electronic processor 160 detects that the energized anode is no longer sufficient to protect the tank 105 from corrosion (e.g., when the energized anode current exceeds a threshold that indicates the state of the tank 105 (e.g., the amount of exposed metal in the tank) such that the energized anode is insufficient to resist corrosion, or exceeds a threshold that indicates that the current level will cause an undesirable or dangerous condition in the water), the electronic processor 160 estimates the time remaining until a fault in the tank 105 is reached.

Fig. 5 is a graph 400 of anode current and measured energized anode voltage (referred to herein as tank potential or voltage) characteristics as a function of operating time of the water heating system 100. As shown in graph 400, the tank potential can be steadily reduced after the maximum anode current that can be safely applied to the water heating system 100 is reached. Field data indicates that tank failure typically does not occur until the tank potential value (e.g., absolute value) drops to between about X and X +3 volts. The field data also indicates that such a reduction in the value (e.g., absolute value) of the tank potential (about X +1 volts) may take more than about one and a half years on average. Thus, using only the maximum current may predict a fault for more than a year, which may be premature in some cases. It may be more desirable and accurate to implement a method that will predict the time to failure over the life of the water heater, such as closer to a year or less.

Fig. 6 is a flow chart illustrating a process or method 600 of predicting a tank failure of the water heating system 100, according to one embodiment of the present application. It should be understood that the order of the steps disclosed in method 600 may be varied. Additional steps may also be added to the control sequence and not all steps may be required. The method 600 is described herein with respect to the control circuit 200 (and in particular the electronic processor 160) of the water heating system 100.

As shown in FIG. 6, initially, electronic processor 160 receives a measure of energized anode current (step 605). In some embodiments, this is measured as a current at or through the energized anode. In some embodiments, this is measured as the current at the can 105 provided from the powered anode. At block 610, the electronic processor 160 determines whether the energized anode current measurement is approximately equal to (or exceeds) the maximum energized anode current threshold. The maximum energized anode current threshold corresponds to a maximum amount of current (e.g., approximately Y mA) that may be safely applied to the water heating system 100. When the energized anode current approximately equals or exceeds the threshold, the electronic processor 160 records a plurality of tank potential measurements over a period of time (block 615). After a period of time, the electronic processor 160 determines a predicted time to tank failure (working length) for the water heating system 100 based on the tank potential measurements recorded over time (block 620). For example, as described in more detail below, the electronic processor 160 can determine a trend line based on the recorded tank potential measurements. The trend line may be a curve fit trend line. For example, the electronic processor 160 determines the fault time based on when the trend line is expected to fall below a predetermined tank potential threshold corresponding to a tank potential indicating a significant tank fault (between Y to Y +3 volts as mentioned above with respect to fig. 5) and an estimated tank life collected from the water tank after the maximum current and predetermined tank potential threshold data are reached. Such a water tank may be similar to water tank 15 to ensure a more accurate prediction. The electronic processor 160 then outputs an alarm corresponding to the predicted time of canister failure (block 625). For example, the electronic processor 160 may display a graphic including the predicted time of tank failure on a display for an operator of the water heating system 100. The electronic processor 160 may also be configured to take adaptive action based on this information, such as initiating a discharge of water from a storage tank or sending a signal to a service professional.

Fig. 7 is a graph 700 of recorded tank potential measurements over time for a water heater (e.g., water heating system 100). Here, the maximum current is approximately the same over time, while the tank potential (setpoint voltage) decreases over time. Tank potential measurements were recorded when the maximum current was reached (starting at about X +4 volts). Over a period of time (here approximately 60 days of recording), as more tank potential measurements are recorded, trend line 702 is calculated. A projection 704 of trend line 702 may then be calculated from trend line 702 to approximately determine when the tank potential will reach a predetermined tank potential threshold (here, X +1 volts). As shown in graph 700, the predicted time to failure is within 20 days.

In some embodiments, the electronic processor 160 is configured to display a warning to a user that the canister 105 is not adequately protected when the maximum current has been reached. The processor 160 may also display an approximate working length remaining on the water heating system 100 based on data collected from other water tanks that have failed due to tank degradation. For example, field test data shows that based on about 46 tanks, the tank has about 393 days before failure after reaching the maximum current.

In some embodiments, the electronic processor 160 is further configured to determine a predicted time of fuel tank failure based on at least one other characteristic of the water heating system 100. For example, a water heater operating at a high duty cycle, a high set point temperature, a wide temperature differential set point, and a low incoming water temperature may shorten tank life. In particular, these and other factors associated with high temperature cycles directly affect the reliability of the glass on the heat exchanger of the water heater. Processor 160 may use this information to adjust the slope of the trend line to improve the accuracy of the predicted time of tank failure. Extreme temperature cycling increases glass degradation and therefore increases the rate at which the can potential drops. 8A-8D are graphs 800A-800D showing the relationship between temperature set point, temperature differential set point, inlet water temperature, and duty cycle, respectively, and tank life.

In addition to improving the estimation of the rate of potential tank degradation, the accuracy of fault prediction can be improved by evaluating factors over time that raise or increase the tank potential threshold at the time of the fault. Several factors can be used to adjust the tank potential up or down. For example, factors that may increase the likelihood of an earlier tank failure (in other words, a failure at a higher tank potential) include a higher duty cycle, a higher Total Dissolved Solids (TDS) level, a higher tank temperature set point, and a faster decreasing slope of the tank potential trend line (indicating increased glass degradation). Another factor that may affect the fault and tank potential is the conductivity of the water. High conductivity water is likely to reach maximum current more quickly, but is longer at lower tank potentials (less than X +1 volts). Fig. 9A and 9B are each graphs 900A and 900B, respectively, illustrating how a high duty cycle affects the fault point of the tank potential. In the graph 900A of FIG. 9A, the first water heater with a low duty cycle fails at a tank potential of X-50 volts after the maximum energized anode current is reached. In the graph 900B of fig. 9B, the second water heater with a high duty cycle fails at X volts after the maximum energized anode current is reached. Factors that may reduce the likelihood of an earlier tank failure include, for example, a lower duty cycle condition.

In some embodiments, instead of or in addition to recording the tank potential measurements over a duration of time (block 615 of fig. 6), the electronic processor 160 determines an estimated tank life by calculating a time adjustment factor when the energized anode current approximately equals or exceeds a threshold value. Similar characteristics as described above may be used to determine the time adjustment factor.

The present application thus describes, among other things, a method of predicting a tank fault for a water heater.