SYSTEM AND METHOD FOR HEATING ELEMENT FAILURE DETECTION

Abstract

According to one aspect of the invention, a water heater is provided comprising an electric heating element circuit; a circuit coupled to the electric heating element circuit and configured to supply current to the electric heating element; a sensor coupled to the circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and a controller coupled to the circuit. The controller is configured to perform a spike test on the operation of the electric heating element circuit by comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit; and identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit. The controller is also configured to perform a signature test on the operation of the electric heating element circuit by in response to identifying the negative spike, supplying or continuing to supply the current to the electric heating element for a first predetermined time period: terminating the supply of current after the first predetermined time period; and determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; and in response to identifying the positive spike terminating the supply of current to the electric heating element for a second predetermined time period; and determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

Description

FIELD OF THE INVENTION

This disclosure relates to heating element failure detection for water heaters.

BACKGROUND OF THE INVENTION

Conventional water heaters often include heating elements. In many cases, for example, an electrical heating element includes a looped electric conductor encapsulated in electrical insulation and surrounded by a water-tight metal jacketing. Over time, the metal jacketing and the electrical insulation of such an element can deteriorate. For example, the metal jacketing of the heating element can break open and damage and/or remove the insulating material surrounding the electrical conductor. If heating elements deteriorate, the operation of the water heater can be compromised and/or damage can be caused to the electronic power system components of the water heater.

It is therefore desirable to reliably identify a failure of a heating element to reduce or prevent compromise to the operation of the water heater and/or prevent damage to the power components of the water heater.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a water heater is provided comprising an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element; a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and a controller coupled to the electric heating element circuit. The controller is configured to perform a spike test on the operation of the electric heating element circuit by comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit; or identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit. The controller is also configured to perform a signature test on the operation of the electric heating element circuit by in response to identifying the negative spike, supplying or continuing to supply the current to the electric heating element for a first predetermined time period: terminating the supply of current after the first predetermined time period: and determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; or in response to identifying the positive spike terminating the supply of current to the electric heating element for a second predetermined time period; and determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

According to another aspect of the invention, a water heater is provided comprising an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element; a sensor coupled to the electric heating element circuit and configured to detect a rate of change of circuit temperature associated with operation of the electric heating element circuit; and a controller coupled to the electric heating element circuit, the controller being configured to: perform a spike test on the operation of the electric heating element circuit by comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; and identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit; or identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit.

According to another aspect of the invention, a water heater is provided comprising an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element; a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and a controller coupled to the electric heating element circuit, the controller being configured to detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit; detect whether the electric heating element circuit may have failed or failing operation caused by a shorted circuit; perform a signature test on the operation of the electric heating element circuit by: in response to detecting that the electric heating element circuit may have failed or failing operation caused by an open circuit, supplying or continuing to supply the current to the electric heating element for a first predetermined time period; terminating the supply of current after the first predetermined time period; and determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; or in response to detecting that the electric heating element circuit may have failed or failing operation caused by a shorted circuit, terminating the supply of current to the electric heating element for a second predetermined time period: and determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

According to another aspect of the invention, a water heater is provided comprising an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element; a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and a controller coupled to the electric heating element circuit, the controller being configured to compare a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; detect a positive spike or a negative spike in the rate of change of the temperature associated with the operation of the electric heating element circuit, indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit or an open circuit, respectively; if a negative spike is detected, terminate the supply of current to the electric heating element after a first predetermined time period; if a positive spike is detected, immediately terminate the supply of current to the electric heating element for a second predetermined time period: and confirm failed or failing operation of the electric heating element circuit if a temperature increase occurs during the second predetermined time period or if a temperature drop occurs during a third predetermined time period after the first predetermined time period.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.

The foregoing and other aspects of the present disclosure will become apparent to those skilled in the art to which the present disclosure relates upon reading the following description with reference to the accompanying drawings, in which:

FIG. 1A is a perspective view of an embodiment of a water heater, according to an aspect of the disclosure.

FIG. 1B is a perspective view of the water heater in FIG. 1A without the outer shell, according to an aspect of the disclosure.

FIG. 2A is a perspective view of the upper control assembly in FIG. 1B, according to an aspect of the disclosure.

FIG. 2B is a perspective view of the upper control assembly in FIG. 2A without the protective cover, according to an aspect of the disclosure.

FIG. 2C is another perspective view of the upper control assembly in FIG. 2B, according to an aspect of the disclosure.

FIG. 3A is an isolated perspective view of the lower control assembly, according to an aspect of the disclosure.

FIG. 3B is another isolated perspective view of the lower control assembly in FIG. 3A, according to an aspect of the disclosure.

FIG. 4 is a schematic side view of the lower portion of the water heater showing an embodiment of a thermal path, according to an aspect of the disclosure.

FIG. 5 is a circuit diagram of an embodiment of the overall water heater control system, according to an aspect of the disclosure.

FIG. 6 is a flowchart of the overall operation of the water heater, according to an aspect of the disclosure.

FIG. 7 is a flowchart of a “spike” test, according to an aspect of the disclosure.

FIG. 8 is a flowchart of a “signature” test, according to an aspect of the disclosure.

FIG. 9 is a flowchart depicting use of dynamic thresholds during burn-out detection, according to an aspect of the disclosure.

FIG. 10 illustrates a time/temperature plot that uses dynamic thresholds during burn-out detection whenever a heating element first turns ON or transitions between states, according to an aspect of the disclosure.

FIG. 11 illustrates a time/temperature plot that uses dynamic thresholds when a positive spike in the temperature of the power supply components is detected, according to an aspect of the disclosure.

FIG. 12 illustrates a time/temperature plot that uses dynamic thresholds to detect a first positive spike and a “signature” test that uses fixed values to confirm the positive spike determination by monitoring for another positive spike, according to an aspect of the disclosure.

FIG. 13 illustrates a time/temperature plot that uses dynamic thresholds to detect a first negative spike and a “signature” test that uses fixed values to confirm the negative spike determination by monitoring for another negative spike, according to an aspect of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present disclosure will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It is to be appreciated that the various drawings are not necessarily drawn to scale from one figure to another nor inside a given figure, and in particular that the size of the components are arbitrarily drawn for facilitating the understanding of the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It may be evident, however, that the present disclosure can be practiced without these specific details. Additionally, other embodiments of the present disclosure are possible, and the present disclosure is capable of being practiced and carried out in ways other than as described. The terminology and phraseology used in describing the present disclosure is employed for the purpose of promoting an understanding of the disclosed embodiments and should not be taken as limiting.

Although this disclosure relates to various forms of water heating appliances that may include one or more electric heating element circuits (which electric heating element circuits can include, for example, the heating element(s) and the interconnection circuitry that supplies electric power from a power source to the heating element(s), including but not limited to wiring, terminals, and wire-to-wire connections, conductors, etc.), embodiments selected for illustration in this disclosure are electric water heaters such as storage water heaters. A typical electric storage water heater, for example, has two electrical heating elements, one arranged in the upper section of the tank and the other one arranged in the lower section of the tank. The heating elements are controlled by controllers, such as thermostats, for example, which monitor the water temperature in the tank. When the water is too cold, the thermostats turn the heating elements ON. When the temperature of the water reaches a temperature setpoint, the thermostats turn the heating elements OFF. Once the water is heated, the thermostats cycle the heating elements ON and OFF over time to maintain the water at the desired temperature.

When an electrical heating element of the water heater deteriorates, one of two undesirable conditions can occur. In a first condition (open condition), the circuit (which may include a loop of the heating element) remains open and current cannot flow through the heating element (no heat is produced) even when the heating element is powered by the controller. In a second condition (short condition), a deteriorated portion of the electric heating element circuit (such as the broken part of a loop) touches the inner wall of the metal sheathing surrounding the heating element and shorts to ground, thereby causing a large current to flow through the heating element sheathing to ground that can damage the electronic power components of the water heater. Both conditions can occur rapidly, within fractions of a second, and the short condition may cause irreparable damage to the electronic components of the water heater.

One aim of the present disclosure is to implement a rapid and reliable detection of an electric water heating element that might have become open or shorted in a failed or failing condition, and to control the heating elements and the power components of the heater based on this determination. By detecting sudden spikes (e.g., a statistically significant change such as an increase and/or decrease) in the temperature of the components of the electrical power circuit, the solution rapidly and efficiently detects an electric water heating element that might have become open or shorted, and adjusts control of the power supply system of the water heater based on this determination. As a result, the water heater can continue to produce hot water using the remaining (undamaged or undeteriorated) heating element, while the damaged heating element is isolated from the power supply components and the user is notified of the burned-out element so that the burned-out element can be repaired.

Although specific examples are described throughout the disclosure, it is noted here that the disclosure is not limited to these specific examples.

Referring now to specific figures illustrating various embodiments of the disclosure relating to exemplary structural features of a water heater, FIGS. 1A and 1B show a water heater 100 with failed electric heating element circuit detection that is described in detail below. Referring to FIG. 1A, the water heater 100 includes a tank 108 configured to store water to be heated. The tank 108 has a wall with an external surface and an internal surface defining an interior. The tank 108 generally includes a heater shell including a jacket 106 generally filled with insulation (e.g., fiberglass, foam, etc.) that forms an insulating layer around the interior contents (e.g., the tank) of the water heater, primarily keeping heat inside water heater 100, as well as protecting the interior components of the water heater 100 from kinetic shocks. To complete the insulation effect, two covers, an upper cover 102 and a lower cover 104, are placed over cut-outs cut in the water heater jacket 106. These cut-outs exist to expose control components, to facilitate use and configuration of the water heater 100, as well as to increase efficiency in performing maintenance on the water heater 100.

FIG. 1B shows the water heater 100 of FIG. 1A without the jacket 106. Specifically, the water tank 108 and wiring harness 110 are exposed. The wiring harness 110 may include various stranded or solid wires that interconnect electrical components from an upper control assembly (not shown in this view), a lower control assembly (not shown in this view), an upper heating element (not shown in this view), and a lower heating element (not shown in this view). Details of these electrical connections are described in more detail with respect to later figures. The water tank 108 can be figuratively divided into an upper half and a lower half. This is because water heater 100 has two heating elements (not shown in this view) referred to as an upper heating element (UE) and a lower heating element (LE), which are located in the upper half of the tank in the region of upper cover 102, and the lower half of the tank in the region of lower cover 104, respectively. Details of the upper control assembly, the lower control assembly, the UE and the LE are now described with reference to the figures.

Regarding exemplary features of an upper control assembly of a water heater, FIGS. 2A-2C depict the upper cover 102, as well as the components of the upper control assembly located beneath the upper cover 102. In FIG. 2A, for example, the upper cover 102 includes a set-point temperature knob 200 for setting the desired set-point (SP) temperature of the water.

In FIG. 2B, the upper cover 102 has been removed, thereby exposing the mechanical and electrical components of the upper control assembly hidden beneath. These components include a printed circuit board (PCB) 208 mounted to the cover 102, aperture 210 for receiving the knob 200, a snap-disc limit switch 212, a temperature sensor 226 for measuring upper tank wall temperature, upper heating element UE 218 with UE electrical terminals 220, and a spring clip 216 for mounting the limit switch 212 to a spud on the water tank 108. In one example, the spud may be a metal cylindrical portion that is formed into the tank wall or welded to the tank wall. The spud may have female treads for receiving and mounting the heating element.

FIG. 2C shows a rear view of the components in FIG. 2B. As shown, PCB 208 includes various electrical components 224 (e.g., microprocessor, power regulators, analog I/O, digital I/O, etc.) that form the controller for the water heater 100. PCB 208 also includes a potentiometer 222 for receiving the shaft of knob 200 and outputting a distinct resistance based on the knob rotational angle, which is then translated by the controller into a desired SP temperature. Each of the components in FIGS. 2B and 2C will now be described in more detail.

The controller on PCB 208 generally detects the desired SP temperature from the potentiometer 222, monitors upper temperature sensor (UTS) 226 and lower temperature sensor (LTS) (not shown) in order to control (e.g., modulate) the power supplied to UE 218 and the LE (not shown) to regulate the temperature of the water in the tank. Although not shown, UTS 226 (e.g., a thermistor) is thermally coupled to (e.g., physically contacting) the upper wall portion of the water tank 108 in order to detect tank wall temperature. In general, the controller controls solid-state switches in a power switching module (not shown) to modulate the power supplied to UE 218 and the LE (not shown) during a heating cycle (typically a time period during which the heating elements are turned ON to heat the water to reach the SP).

Limit switch 212 shown in FIGS. 2B and 2C is a snap-disc implemented for safety purposes in this embodiment. Although not shown, limit switch 212 is thermally coupled to (e.g., physically contacting) the upper wall of the water tank 108 in order to detect tank wall temperature. Limit switch 212 includes upper line power electrical terminals L1_upper and L2_upper that receive the line power (e.g., 240 VAC) from a power source (e.g., dual pole circuit breaker in a circuit breaker panel), and lower line power terminals L1_lower and L2_lower that distribute the line power to a power switch module located in the lower control assembly (not shown) that supplies power to both the UE and LE. When the limit switch “snaps closed,” electricity is free to flow between the L1_upper and L1_lower terminals, as well as between the L2_upper and L2_lower terminals. When the limit switch 212 “snaps open,” the connections between L1_upper and L1_lower and between L2_upper and L2_lower are broken such that electricity is not distributed to the power switch module. This break occurs when the limit switch 212 detects a tank wall temperature in excess of a predetermined safe operating limit temperature (e.g., factory set temperature) of the water heater.

It is noted that UE 218 and LE 400 can be embodied in a high temperature resistive wire, which produces heat when electricity passes through the wire. This heat then is transferred to the water through conduction and convection, by having the wire, coated in electrical insulation and surrounded by a water-tight metal jacket, enclosed in water tank 108 and immersed in the water (not shown).

Spring clip 216 is a mechanism by which the limit switch 212 is physically attached to water heater tank 108. In this example, the spring clip 216 includes circular mounting portion 216A that is forced onto the outer circumference of spud 217 of the water tank. Spring loaded flanges of circular mounting portion 216A fix to the outer circumference of the spud 217, thereby holding spring clip 216 firmly in place against the upper wall of tank 108. Spring clip 216 also includes spring legs 216B that snap onto and firmly press limit switch 212 against the wall of water heater tank 108. Spud 217 is also used for holding UE 218 in place. Specifically, spud 217 may have female threads, whereas UE 218 may have male threads. During assembly, the UE 218 is threaded into spud 217. A similar mounting procedure is performed with another spud (not shown) and LE 400.

Regarding exemplary features of a lower control assembly of a water heater, FIGS. 3A and 3B show an isolated (from the water heater) view of the lower control assembly components. In these views, it is shown that the water heater includes a LE 400 and a thermally conductive (e.g., metal) power switching circuit board 402. LE 400 performs substantially the same tasks as UE 218, and typically has the same or similar physical configuration. The LE 400 is mounted to the wall of the tank 108 and extends into the interior of the tank 108. Similar to UE 218, the LE 400 can be implemented in a high temperature resistive wire, which produces heat when electricity passes through the wire. This heat then is transferred to the water through conduction and convection, by having the wire, coated in electrical insulation and surrounded by a water-tight metal jacket, enclosed in the water tank 108 and immersed in the water (not shown). Similar to UE 218, LE 400 also can have its power cut by the limit switch 212 if unsafe temperatures are detected by the limit switch 212.

The lower control assembly components can also include a power switching module housing 304, which houses a power switching module (not shown) and electrical terminals 306, LE terminals 310 and spring clip base 302 including a circular mounting portion 302A that is forced onto a spud (similar to spud 217 but not shown) of the water tank. Spring loaded flanges of circular mounting portion 302A fix to the outer circumference of the spud, thereby holding spring clip 302 firmly in place against the lower wall of water heater tank 108. Spring clip base 302 also includes brackets 302B and 302C that engage with portions of housing 304 and spring wire 303 that firmly presses housing 304 and a metal power switching circuit board (not shown) against the lower wall of water heater tank 108. A ground screw may also be fixed to ground terminal 308E for mounting a ground wire to spring clip 302.

The terminals 306 of the power switching module 304 may be screw terminals for securing wiring that connects lower control assembly components to upper control assembly components. Other connection methods, however, such as welding or fusing are possible, though screw-clamping is preferred in order to preserve the modularity of the components of the water heater 100. In this example, there are three terminals. A first one of the terminals receives a wire from limit switch 212 that feeds L1 to the power switching module. A second one of the terminals receives a wire to feed L1 to the LE. A third one of the terminals receives a wire to feed L1 to the UE.

The circuit board 402 can be a thermally conductive (e.g., aluminum) circuit board 402 releasably mounted to the external surface of the tank 108. The circuit board 402 includes a thermal path for conducting heat through the circuit board 402. For example, the water heater 100 can include a biased retainer positioned to releasably mount the circuit board 402 to the external surface of the tank 108. The thermal path of the circuit board 402 is thermally coupled to the external surface of the tank 108. The circuit board 402 can include a thermally conductive support layer, a circuit layer, and a dielectric layer interposed between the thermally conductive support layer and the circuit layer. The thermal path of the circuit board 402 can extend through the thermally conductive support layer, the circuit layer, and the dielectric layer.

A thermal interface can be provided between the circuit board 402 and the wall of the tank 108 to maintain thermal coupling between the thermal path of the circuit board 402 and the wall of the tank 108. The thermal interface can be selected from the group consisting of thermal grease, heat paste, thermal gel, thermal tape, thermal putty, thermal gap filler, thermal polymer, and thermal adhesive.

The power switching circuit board 402 is electrically connected to both UE 218 and LE 400, as well as to the limit switch 212. Generally, the power switching circuit board 402 includes, among others, power switching elements (not shown) and a temperature sensor 606 (shown in FIG. 4).

For example, an electronic switch 816/818 (shown in FIG. 5) is mounted to the circuit board 402 and electronically coupled to the lower heating element LE 400. The electronic switch 816/818 is thermally coupled to the thermal path of the circuit board 402 so that heat generated by the electronic switch 816/818 is transferred along the thermal path from the electronic switch 816/818, through the thermal path of the circuit board 402, and to the wall of the tank 108. The temperature sensor 606 is arranged to sense the temperature of the thermal path relating to the temperature of the circuit board 402 and of the electronic switch 816/818. The temperature sensor 606 can be mounted to the circuit board 402 and thermally coupled to the electrical circuit used for driving the heating elements, including but not limited to electronic switch 816/818. For example, the temperature sensor 606 can be thermally mounted to the power switches (e.g. TRIACs, etc.) that supply power to the heating elements, can be mounted to a wire/trace of the circuit board 402 that carries the current to/from the heating elements, or can be mounted to a thermally conductive intermediate component (e.g., the metal circuit board 402, etc.). This arrangement of the temperature sensor 606 allows the temperature of the electronic and electric circuit components to be detected.

The water heater 100 can also include an optional second temperature sensor 610 (shown in FIG. 4) that may also be implemented in the lower control assembly, thermally coupled to the wall of the tank 108, and configured to sense a temperature corresponding to the temperature of the wall of the tank 108 and relating to the temperature of the water stored in the tank 108. For example, the system could have LTS 606 positioned on the thermally conductive circuit board as described above, and have the second temperature sensor 610 fixed to the tank wall 108 in proximity to the thermally conductive circuit board. Such a configuration allows the controller to directly detect tank wall temperature and therefore water temperature via the second temperature sensor 610, while determining temperature of electronics 604 and electrical connections 608 via LTS 606.

In certain embodiments, the temperature sensor 606 can be a dual-purpose temperature sensor that is also thermally coupled to the wall of the tank 108 to sense a temperature corresponding to the temperature of the wall of the tank 108 and relating to the temperature of the water stored in the tank 108, and thermally coupled to the thermal path of the circuit board 402 and to the electronic switch 816/818 to sense a temperature corresponding to the temperature of the thermal path of the circuit board 402 and the electronic switch 816/818.

The water heater 100 can include multiple heating elements 218/400 and multiple electronic switches 816/818. Each of the electronic switches 816/818 can be electronically coupled to a respective one of the heating elements 218/400, one which is mounted to an upper portion of the wall of the tank 108, and another one is mounted to a lower portion of the wall of the tank 108.

The water heater 100 can also include a controller 820 (shown in FIG. 5) that is electrically coupled to the electronic switch 816/818 and the temperature sensor 606. The controller 820 is configured (e.g., programmed) to control the heating elements 218/400 and the electronic switch 816/818 based on temperature signals received from the temperature sensor 606. The temperature signals received from the temperature sensor 606 can correspond to a sensed temperature of the thermal path of the circuit board 402 or to a sensed temperature of the electronic switch 816/818.

The controller 820 monitors the detected temperature of the temperature sensor 606. This temperature is associated with the temperature of at least one of the lower tank wall, the circuit board 420, the power switching elements, and the electrical connections to the power switching module. The controller 820 uses this detected temperature to supply or terminate power to the heating elements 218 and 400 during the heating cycle in an attempt to reach the SP temperature, and to detect possible faults in the system (e.g., faulty heating elements and electrical components, faulty electrical connections, sensor drift, etc.). The electrical and control aspects of the controller 820, power switching module, heating elements and failure detection are described in more detail with respect to later figures.

Regarding exemplary features of a thermal path, and as described above, the power switching circuit board 402 is made of or includes thermally conductive material such as metal. This allows the power switching circuit board 402 to conduct heat. Although not shown in FIGS. 3A and 3B, the power switching circuit board 402 is held firmly to the tank wall by spring clip 303 and optional thermal paste. This creates a thermal bond between the backside of power switching circuit board 402 and the tank wall, thereby creating a thermal path that includes or is thermally coupled to the solid-state switches and other electronics of the power switching module, electrical connections, power switching circuit board, the lower tank wall and the water in the tank.

An example, of the thermal path is shown as a side view of the lower portion of the water heater in FIG. 4, where the heat contributions of the various components are bi-directionally conducted through the thermal path. For example, heat 612/614 produced by electronics 604 (e.g., power TRIACS, OPTO-TRIACS, resistors, etc.) and electrical connections 608 (e.g., one or more screw terminals) is conducted through thermally conductive power switching circuit board 402 to the tank wall 108 and into the water. Likewise, heat from the water is conducted through the water to the tank wall 108, to the thermally conductive power switching circuit board 402, and to the electronics 604 and the electrical connections 608. Therefore, the overall heat in the thermal path includes combined heat contributions from various sources. This thermal path is beneficial for increased efficiency by introducing the heat produced by the electronic switches back into the tank, rather than being wasted, and allowing a measurement point for a temperature sensor to accurately measure a single temperature that includes the combined heat of the water and the heat produced by the electronic/electrical components (e.g., switches).

For example, in order to monitor the temperature of the thermal path, lower temperature sensor (LTS) 606 is mounted to the thermally conductive power switching circuit board 402. The heat absorbed by the thermally conductive power switching circuit board 402, and detected by the LTS 606 is a sum of the heat contributions of the water and the electronic/electrical components, such as electronics 604 and electrical connections 608.

In general, the thermal path heat absorbed by the thermally conductive power switching circuit board 402 and detected by LTS 606 is processed by the controller 820. In one example, the controller 820 processes the detected by LTS 606 temperature to determine the temperature (e.g., heat contributions) of the individual components, including the temperature of the electronics 604, the temperature of the circuit board 402, the temperature of the electrical connections 608, the temperature of the tank wall 108 and the temperature of the water in the tank. This is performed based on experimental and/or theoretical temperature correlations between the detected temperature and the associated temperatures of the individual components. Such a correlation is affected by various factors that include but are not limited to physical layout of the circuit board (e.g., power switch placement, LTS 606 placement, etc.), physical properties of the circuit board (e.g., the type of metal, thickness of metal, type of dielectric, thickness of dielectric, etc.), power rating of the power switches, thermal connection between the circuit board and the tank wall, size of the water tank, and temperature of water in the tank.

In one example, the overall temperature and the rate of change of the temperature may both be analyzed to determine heat contributions of the individual components during cycling ON/OFF of the water heater. Since the electronics 604 and the electrical connections 608 rapidly heat up and cool off (e.g., short time constant) during cycling ON/OFF of the water heater, and are directly attached to the metal circuit board 402, they contribute significantly to the rate of change of the thermal path temperature detected by LTS 606. In contrast, since the heating elements UE 218 and LE 400 are immersed in the water, the temperature of the water and therefore the temperature of the tank wall remains fairly constant during cycling ON/OFF of the water heater such that the water temperature slowly rises (e.g., long time constant) and contributes significantly to the steady state level of the thermal path temperature. In addition, there may be a known temperature offset between various components. For example, if the temperature sensor 606 detects a temperature Temp 1 during operation of the water heater, the controller 820 may be able to determine the temperature of electronics 604 as Temp 1+TempOffset 1, and determine the temperature of electrical connections 608 as Temp 1+TempOffset 2.

In this way, the controller 820 can distinguish between what is herein referred to as “secondary heat” versus what is herein referred to as the “primary heat” based on conditions, such as rate of change of the detected temperature, the steady state level of the detected temperature, and temperature offsets. In this context, “primary heat” is heat attributable to the heat absorbed by the water and conducting through the tank wall. It, therefore, generally corresponds to, relates to, or is otherwise associated with, the temperature of the water in the tank. In contrast, “secondary heat” is heat attributable to, generated by, or otherwise associated with, electrical/electronic components of the water heater, including but not limited to the resistive losses of the power switches (e.g., TRIACs, TR1, TR2, TR3, etc.) and electrical connections. For example, secondary heat is produced by resistive losses of electronics 604 and electrical connections 608 when driving the heating elements. This secondary heat conducts through the metal circuit board 402 to the LTS 606. The secondary heat described above inflates the heat detected by the LTS 606. In general, when either the LE 400 or UE 218 is driven, LTS Reading=Primary Heat (water heat)+Secondary Heat (Heat Generated by the Electrical/Electronic Components). It is noted that the secondary heat is generally present when the heating elements are being driven. Once the heating elements are shut off, the secondary heat dissipates and the LTS readings are equal to or approach the Primary Heat (water heat).

Secondary heat can generally be characterized by the rate of change of the temperature (e.g., how fast/slow the temperature is increasing/decreasing) or by a temperature difference taken between different time points (e.g. Temp1@Time1-Temp2@Time2). The sensed temperature of the thermal path (e.g., the temperature sensed by LTS 606) is the sum of primary heat and secondary heat because the thermal path is thermally coupled, directly or indirectly, to the electronic components of the water heater and to the tank wall, which will have a temperature corresponding to or relating to the temperature of water stored within the water tank.

This disclosure, according to exemplary embodiments, therefore makes it possible to use a temperature, such as the temperature detected by LTS 606, to parse between, separately determine, compensate for, and/or otherwise differentiate between, primary heat and secondary heat. Thus, according to exemplary embodiments, this disclosure makes it possible to monitor for or determine the presence, absence, change, or degree of secondary heat and to monitor or control operation of the water heater according to the presence, absence, change, or degree of secondary heat. As described herein in connection with various embodiments of the disclosure, this capability to parse between, separately determine, compensate for, and/or otherwise differentiate between, primary heat and secondary heat, and to monitor for or determine the presence, absence, change, or degree of secondary heat, facilitates a variety of beneficial control functions and features.

For example, the controller 820 can perform the various control methods disclosed herein by using upper temperature sensor (UTS) signals along with either the uncompensated (e.g., raw or raw filtered) LTS signals that include primary heat +secondary heat, or the compensated LTS signals where the secondary heat is cancelled out (e.g., subtracted out) or by using a combination of uncompensated and compensated LTS signals. These uncompensated/compensated LTS signals may generally be smoothed by filtering (e.g., low pass filtering) to produce fewer erratic values. Therefore, it is noted that figures and their corresponding descriptions that discuss the use of uncompensated values, could instead use compensated values, whereas figures and their corresponding descriptions that discuss the use of compensated values, could instead use uncompensated values.

Secondary heat generally also has a lower thermal resistance path to the temperature sensor than the primary heat, because the secondary heat sources and LTS 606 are located on the same electronic board assembly. This allows for rapid and accurate detections and determinations of secondary heat values produced by the secondary heat sources, and to distinguish them from the slower heat that is produced by the heating elements and heated water. Specifically, the time constant for the secondary heat sources to heat up the electronic board assembly to steady state temperature is much shorter than the time constant for the heating elements to heat water in the tank to steady state temperature. Thus, relatively rapid increases and decreases in temperature measured by the LTS 606 are generally attributable to the secondary heat sources (e.g., electronic switches), whereas slower increases and decreases in temperature measured by the LTS are generally attributable to the primary heat sources (e.g., the heating elements). In this way, primary heat can be detected and used by the controller 820 to represent, or correlate to, the temperature of the water in the tank, and secondary heat can be detected and used by the controller 820 to represent, or correlate to, the temperature of the electronic switch or switches.

Accordingly, secondary heat differentiation is made possible by aspects of this disclosure. For example, one common thermal path of a circuit board can be thermally coupled to electronics including one or more electronic switches, to a temperature sensor, and to a water tank, which allows for easy interconnection of these components and for heat sensing and heat transfer to, from, and/or among these components. This configuration permits heat transfer from the electronics, especially the electronic switch(es), to the temperature sensor (to facilitate sensing the temperature or temperature changes of the electronics) and to the water tank (for dissipation). It also permits heat transfer from the water tank to the temperature sensor (for sensing the temperature of the water tank, generally corresponding to the temperature of water in the tank). Despite these advantages, such a configuration also combines secondary heat generated by and transferred from the electronics (including the electronic switch(es) and perhaps other sources) with primary heat generated in and transferred from the water tank, thus making the raw temperature signal from the temperature sensor undifferentiated as between the secondary heat and the primary heat. In order to parse or differentiate or segment or otherwise derive functional or operational meaning or information about the secondary heat or the primary heat, this disclosure makes it possible to (1) reliably and accurately detect secondary heat or changes in secondary heat, or otherwise differentiate between secondary heat and primary heat in electric water heaters: and (2) use that detected or differentiated secondary heat strategically to enable various electric water heating control functions described herein, such as but not limited to detection of failure or degradation of heating elements, dry fire detection, non-simultaneous heating element or electronic switch operation, detection of switch failure or degradation, etc.

The electrical connections and functionality of the water heater control system are now described in more detail. The electronic control system for the water heater generally includes a processor, power switches (e.g., TRIACs, etc.), and a temperature sensor. The power switches power the electric heating element circuits in response to control signals from the processor. The controller monitors the temperature sensed by the temperature sensor to detect heat produced by the power switches. The controller uses this temperature information to determine if an electric heating element or other component of the electric heating element circuit is burned out (e.g., open or shorted).

For example, FIG. 5 is a circuit diagram of the water heater circuit Line voltage (e.g., 240 VAC) that enters the system from an external power supply 800 (e.g., circuit breaker panel) via an L1 line and an L2 line (e.g., 10 awg solid conductors). Both these lines are connected to the input terminals of limit switch 802 to feed electrical current through limit switch 802, where it is then output and fed to the other components of the water heater circuit. On the L2 side, L2 connects directly to both the UE 804, as well as the LE 806. On the L1 side, however, L1 is fed through power switching module 800 before being fed to the heating elements. Power switching module 800 generally includes electronics 604, LTS 606 and electrical connections 608 mounted to power switching circuit board 402. Electronics 604 generally include OPTO-TRIACs 812/814, power TRIACs 816/818, and resistors. In this example, power TRIAC 816, herein referred to as TR1, is connected between L1 and the LE 806. Likewise, power TRIAC 818, herein referred to as TR2, is connected between L1 and the UE 804. Power TRIACs 816 and 818 are triggered ON/OFF by signals received from OPTO-TRIACs 812 and 814 respectively, which are controlled by controller 820 based on temperature readings from UTS 808 (e.g., thermistor) and LTS 810 (e.g., thermistor). The controller 820 is powered by L1 and L2, includes SP port 826 for receiving the SP temperature from the potentiometer, and may include a communication port 206 for communicating with remote computers and other water heaters.

In order to ensure safe operation of power switching module circuit 800, and maintain compliance with UL standards, the power switching module circuit 800 may require a shutoff mechanism to disconnect power switching module circuit 800 in the event of a failure (e.g., if one of the power TRIACs 816/818 is stuck in the conducting mode). This shutoff mechanism may be required by UL standards to also be independent of limit switch 212. One example of a shutoff mechanism is shown as switching device 824 controlled by controller 820 to enable/disable power to TR1 and TR2. During normal operation, the controller 820 turns ON switching device 824 thereby allowing TR1 or TR2 to power the UE and/or LE. However, if the controller 820 determines that TR1 and/or TR2 have failed in the ON (e.g., conducting) position, the controller 820 turns OFF switching device 824, thereby turning OFF the UE and the LE. In practice, the switching device 824 may be a third TRIAC included in the power switching module 800 installed on circuit board 402, herein referred to as TR3, for example, for cutting power to TR1 and TR2.

In general, the controller 820 in FIG. 5 can include devices such as a microprocessor, memory devices, analog input/output (I/O), digital I/O, power regulation, etc. (not shown), which serve to perform various operations. For example, such operations may include operations related to collecting and recording temperatures from sensors 808 and 810 and acting upon those temperatures to control OPTO-TRIACs 812 and 814, as well as switching mechanism 824.

The memory of the controller 820 generally stores the programming for the controller 820. Specifically, the memory stores instructions that, when executed by the controller 820, cause the controller 820 to provide functionality related to fault detection of the heating elements, current or temperature detection programming, temperature indicator programming, etc. To facilitate these programs, the memory also stores temperature records comprising the time, temperature, and the thermistor that recorded the temperature. For example, the memory stores various values, including but not limited to current and temperature values associated with the operation of the electric heating element circuits and the thermal path including the circuit board 402, current and temperature thresholds (positive and negative), rate of change of the current and the temperature associated with the operation of the electric heating element circuit thresholds (positive and negative), predetermined time periods, etc. The memory further stores additional diagnostic records, for example, the last time the controller 820 received signal data from the upper OPTO-TRIACs, to assist a technician in determining whether there is a problem with the heating elements.

Detailed operation of the circuit shown in FIG. 5 will now be described. During operation, the controller 820 monitors the temperature of the upper tank wall temperature sensor UTS 808 and the lower tank wall temperature sensor LTS 810 via I/O lines 822 and compares these temperatures, as well as the rate of change of the temperature associated with the operation of the electric heating element circuit to thresholds (positive and negative) or to a SP temperature received by the knob potentiometer via input 826, respectively. Based on this comparison, the controller 820 controls the power supplied to one or more of the heating elements 804 and 806 by switching the power TRIACs 816/818 via OPTO-TRIACs 812/814 during the heating cycle.

For example, if during normal operation, the controller 820 determines that the upper tank wall temperature UTS and/or the lower tank wall temperature LTS is below the SP temperature, controller 820 outputs a signal via lines 822 to trigger one of OPTO-TRIACs 812 or 814 to begin conducting. Upon receiving the control signals, one of OPTO-TRIACs 812 or 814 conduct current from L1 to the control gates of one of power TRIACS 816 or 818. This triggers one of power TRIACS 816 or 818 to conduct electrical current from L1 to one of heating elements 804 or 806 which then convert the electrical current into heat to begin heating the water in the tank. The current being conducted is dictated by the control mode chosen by the controller. This allows the controller 820 to turn the heating elements fully OFF or fully ON.

While the heating elements 804/806 are heating the water in the tank, the controller 820 continues to monitor the temperature of the upper tank wall temperature sensor UTS 808 and/or the lower tank wall temperature sensor LTS 810 and compare these temperatures, as well as the rate of change of the temperature associated with the operation of the electric heating element circuit to thresholds (positive and negative) or to a SP temperature received by the knob potentiometer via input 826, respectively. Based on these comparisons, the controller 820 may then control power TRIACS 816/818 to continue or to stop supplying the electrical current to the heating elements.

As discussed above, the controller 820 monitors the temperature sensed by temperature sensor 606 to detect heat produced by the power components (e.g., TRIACs, etc.). This temperature information is used to determine if an electrical heating element or other component of an electric heating element circuit is burned out (e.g., open or shorted). Based on the time since the heating element was turned ON or OFF and the temperature sensed by temperature sensor 606, the controller 820 computes a rate of temperature change (e.g., how fast/slow the temperature is increasing/decreasing) and compares the calculated rate of temperature change to positive and negative thresholds (expected rates of change) to determine if there is a spike in the rate of temperature or change (e.g., statistically significant temperature change, such as increase and/or decrease that crosses (e.g., exceeds and/or decreases below) a threshold within a short period of time, such as 1° F. in 0.1 seconds, for example), in order to protect the temperature-sensitive electronic components (e.g., TRIACs, etc.). The threshold for positive spike in the rate of temperature or change can be dynamic. For example, the controller 820 monitors the rate of change of the LTS 606 (e.g., how much the new temperature reading varies in value from the last temperature reading) and can establish a mean value and standard deviation for this rate of change. If the difference between the new and the previous LTS 606 temperature value is larger than, for example, six times the standard deviation for this rate of change (e.g., a “Positive Dynamic Threshold”), the controller 820 determines that a positive spike has occurred and reacts by shutting off power to the heating element circuit. In one example, a broken part of a heating element loop could touch the inner wall of the water heater tank and short to ground. In such circumstance, current will spike and the detected current and/or the detected temperature will show a rapid or relatively rapid increase. According to this disclosure, the controller is configured to determine that the element is burned out and in a short condition. The controller may then stop and prevent any future power flow to the burned-out element and issue a warning to the user. For example, if a heating element is burned out in the short condition, the controller can open the switch and prevent the switch from closing in the future, thereby isolating the failed or failing heating element and protecting the switches. For example, if the controller 820 detects that the rate of change of the temperature associated with the operation of the electric heating element circuit is above a positive threshold, indicating that an electric heating element or other component of electric heating element circuit may have failed or failing operation caused by a shorted circuit, the controller 820 outputs a signal via lines 822 to trigger one of OPTO-TRIACs 812 or 814 to immediately terminate the supply of current to the electric heating elements if certain conditions discussed below are met. In contrast, if the controller 820 detects that the rate of change of the temperature associated with the operation of the electric heating element circuit is below a negative threshold (e.g., statistically significant temperature decrease is detected), indicating that the electric heating element circuit may have burned out and became open, the controller 820 outputs a signal via lines 822 to trigger one of OPTO-TRIACs 812 or 814 to continue to supply current to the electric heating element circuit for a predetermined time period (e.g., 40 seconds) if certain conditions discussed below are met. Upon receiving the control signals from the controller 820, one of OPTO-TRIACs 812 or 814 conducts or stops conducting current from L1 to the control gates of one of power TRIACS 816 or 818. This triggers one of power TRIACS 816 or 818 to conduct electrical current from L1 to one of heating elements 804 or 806 which then convert the electrical current into heat to continue heating the water in the tank for a predetermined time period, or to stop conducting if certain conditions discussed below are met.

In one example, to turn the heating elements OFF, the controller 820 stops supplying a control signal to OPTO-TRIACs 812/814 which controls the power TRIACS 816/818 to turn OFF. In another example, to turn the heating elements ON, the controller 820 supplies a continuous control signal to OPTO-TRIAC 812 or 814 which controls the power TRIAC 816 or 818 to turn ON.

A shutoff mechanism 824 may be implemented as a third power TRIAC TR3. In one example, TR3 may be triggered by a third OPTO-TRIAC (not shown) via resistor (not shown).

During normal operation, controller 820 controls power TR3 via the OPTO-TRIAC (not shown) to continuously conduct (e.g., L1 power is continuously applied to power TRIACs 816/818). If the level of heat and/or the rate of increase in heat detected by LTS 810 reaches a predetermined threshold, the controller 820 may determine that one of the heating elements or the power switching module circuit 800 has failed (e.g., one of the power TRIACs 816/818 is stuck in the conducting mode). In response to this determination, the controller 820 controls TR3 via OPTO-TRIAC (not shown) to stop conducting (e.g., power is prevented from reaching power TRIACs 816/818), effectively shutting off the power switching module circuit 800.

As discussed above, the controller 820 can detect the temperature, and/or the rate of change of the temperature, of the electronic components that drive the heating elements. The controller 820 monitors the sensed temperature, and/or the rate of change of the temperature, to detect heat produced by the power switches. This temperature information is used to determine if an electric heating element or other component of an electric heating element circuit is or may be burned out (e.g., open or shorted).

Instead of temperature, the controller 820 can detect current of the electronic components that help drive the heating elements. Specifically, a current sensor (not shown) can be electrically or inductively coupled to the electrical circuit. For example, a current sensor can be inductively coupled to a wire/trace of the electrical circuit that carries current to/from the heating elements.

A correlation exists between the current flowing through the electronic or driving components (e.g., power switches, relays, etc.) of the heating element circuit and the temperature those components produce. An increase in current flow results in an increase in temperature, whereas a decrease in current flow results in a decrease in temperature.

As a result of heating element burn out, one of two conditions can occur:

(Exemplary Open Condition) The heating element loop burns out and remains open and current will stop flowing. The detected current and/or the detected temperature will show a rapid decrease. Upon detecting a decrease in the detected current and/or temperature, the controller 820 determines that the element is burned out and in an open condition. The controller 820 may then stop and prevent any future power flow to the burned-out element and issue a warning to the user. For example, if one of the heating elements is burned out in the open condition, the controller opens a switch and prevents the switch from closing in the future, thereby isolating the failed heating element. In the meantime, the controller 820 can still control the other heating element to operate as normal.

(Exemplary Short Condition) The broken part of the failed heating element loop touches the inner wall of the heating element sheathing and shorts to ground. Current will spike and the detected current and/or the detected temperature will show a statistically significant increase. The controller 820 determines that the heating element is burned out and in a short condition. The controller 820 may then stop and prevent any future power flow to the burned-out element and issue a warning to the user. For example, if one of the heating elements is burned out in the short condition, the controller 820 opens a switch and prevents the switch from closing in the future, thereby isolating the failed heating element and protecting the switches and the other power supply components. In the meantime, the controller 820 can still control the other heating element to operate as normal.

FIG. 6 is a flowchart that illustrates the overall operation of detecting a failed or failing electric heating element circuit of the water heater. The electric heating element circuit burn-out test includes two phases. A first phase is referred to herein as a “spike” test as an initial test to detect a possible element burn-out, followed by a second phase which is referred to as a “signature” as a supplemental test to confirm the spike test determination. The term “spike” test simply refers to the detection of a more rapid or larger change (e.g., a statistically significant change) in a sensed condition that may occur, such as a change in temperature or current, or a rate of change in temperature or current, for example. For example, a statistically significant change in the sensed condition can be a more rapid or larger change. The term “signature” test simply refers to a change in a sensed condition, such as a temperature or current, for example, that may signify or be consistent with a condition to be detected, such as an open or shorted circuit. The spike test and signature test can both be performed sequentially, or the spike test or signature test can alternatively be performed independently.

In step 602 of the illustrated embodiment, the controller 820 computes a rate of temperature change. In step 604, the controller 820 compares the calculated rate of temperature change to positive and negative thresholds to determine if there is a spike in the rate of temperature change (e.g., statistically significant temperature increase or decrease).

In step 606, the controller 820 performs a spike test and detects a positive or negative spike in the rate of temperature change. The detected temperature correlates to the operating temperature of the TRIACs powering the electric heating element circuits (because TRIACs produce heat when driving the elements, and this heat is detectable by the temperature sensor). During the spike test, the controller computes a rate of temperature change and compares the calculated rate of temperature change to positive and negative thresholds to determine if there is a spike in the rate of temperature change (e.g., statistically significant temperature increase or decrease). For example, if a heating element burns out and becomes open, the TRIAC no longer draws current and therefore a negative spike (e.g., statistically significant temperature decrease) is detected. In contrast, if a heating element burns out and becomes shorted to ground, the TRIAC draws a large amount of current and therefore a positive spike (e.g., statistically significant temperature increase) is detected.

FIG. 7 illustrates the details of the spike test. In the left portion of FIG. 7, the controller 820 performs a positive spike test. Specifically, in step 702, the controller 820 compares the rate of temperature change to a positive threshold to determine if there is positive spike in the rate of temperature change (e.g., statistically significant temperature increase). If there is a positive spike in the rate of temperature change, in step 704, the controller 820 checks whether the upper heating element is ON. If the upper heating element is ON, in step 706, the controller 820 determines that there is positive spike in the rate of temperature change of the upper heating element, which indicates that the heating element might have burned out and became shorted to ground, and proceeds to the “signature” test step (explained with reference to FIG. 6). If the upper heating element is OFF, in step 708, the controller 820 checks whether the lower heating element is ON. If the lower heating element is ON, in step 710, the controller 820 determines that there is positive spike in the rate of temperature change of the lower heating element, which indicates that the heating element might have burned out and became shorted to ground, and proceeds to the “signature” test step (explained with reference to FIG. 6). If the controller 820 determines that neither the upper heating element or the lower heating element is ON, the controller 820 continues to monitor the circuit for a positive spike in the rate of temperature change of the heating elements (top left portion of FIG. 7).

The right portion of FIG. 7 illustrates a similar processing for the negative spike test. In step 712, the controller 820 compares the rate of temperature change to a negative threshold to determine if there is a negative spike in the rate of temperature change (e.g., statistically significant temperature decrease). If there is a negative spike in the rate of temperature change, in step 714, the controller 820 checks whether the upper heating element is ON. If the upper heating element is ON, in step 716, the controller 820 determines that there is negative spike in the rate of temperature change of the upper heating element, which indicates that the heating element might have burned out and became open, causing the TRIAC to no longer draw current, and proceeds to the “signature” test step (explained with reference to FIG. 6). If the upper heating element is OFF, in step 718, the controller 820 checks whether the lower heating element is ON. If the lower heating element is ON, in step 720), the controller 820 determines that there is negative spike in the rate of temperature change of the lower heating element, which indicates that the heating element might have burned out and became open, causing the TRIAC to no longer draw current, and proceeds to the “signature” test step (explained with reference to FIG. 6). If the controller 820 determines that neither the upper heating element or the lower heating element is ON, the controller 820 continues to monitor the circuit for a negative spike in the rate of temperature change of the heating elements (top right portion of FIG. 7).

Turning back to FIG. 6, if in step 606, during the spike test, the controller 820 detects a possible heating element burnout, then in step 608, the controller 820 performs a “signature” test to confirm that the spike test was not false positive due to noise inherent in the temperature signal. For example, as discussed above, positive spikes are caused by electric shorted electric heating element circuit that results in rapid increase in current flow through the TRIACs. This surge in current flow causes rapid power dissipation increase which causes rapid increase in secondary heat, which as described above, is the heat attributable to, generated by, or otherwise associated with, electrical/electronic components of the water heater, including but not limited to the resistive losses of the power switches (e.g., TRIACs, TR1, TR2, TR3, etc.) and electrical connections. This rapid secondary heat increase is detected by lower temperature sensor (LTS) 606 as a “positive spike.” Even though the controller 820 immediately (e.g., at the moment a positive spike is detected) terminates the supply of power to the electric heating element circuits, the extra power dissipated by the TRIACs prior to terminating power causes secondary heat to rise for a certain period of time. Other events can also cause a rapid or relatively rapid increase in the temperature detected by the LTS 606. For example, in case two water heaters are plumbed in series, the hot water from the upstream water heater may enter the bottom of the downstream water heater while the heating elements of the downstream heater are powered. Or there could be a passive solar loop connected to the water heater that brings hot water suddenly to the cold water input of the water heater. Another potential rapid or relatively rapid increase in the temperature detected by the LTS 606 can be caused by voltage potential suddenly rising due to large household load (e.g., similar to an AC system) turning off in a house supplied by marginal wiring. If this happens while a heating element is turned on, it may look like a spike that would pass the signature test because of the time constant associated with water temperature changes and the amount of current change that is caused by, e.g., a rapid change in applied voltage (220 VAC jumping suddenly to 240 VAC). If the positive spike was not caused by high current flow (e.g., by shorted electric heating element circuit), then the controller 820 will not detect excess heat during the signature test. The secondary heat will diminish as soon as the power is terminated and the signature test will find no temperature increase in secondary heat over the temperature value that was detected prior to the occurrence of the “positive spike.” Alternatively, if the controller 820 detects excess heat during the signature test or temperature increase in secondary heat over the temperature value that was detected prior to the occurrence of the “positive spike,” then the controller 820 confirms burn-out with the “signature” test, then in step 610, the controller 820 prevents supply of current to the burned-out electric heating element circuit.

If the spike test indicates a possible open heating element failure (e.g., negative spike in rate of temperature change), during the signature test, the controller 820 keeps the TRIAC ON for a predetermined time period (e.g., 40 seconds) and then turns the TRIAC OFF after this time period. If another negative spike does not occur, then the controller 820 determines that the heating element is burned out and open (e.g., the heating element was not producing heat during the time period). However, if another negative spike occurs, then the controller 820 determines that there was a false positive in the spike test (e.g., the heating element is still producing heat during the time period), indicating that the heating element is still operating properly.

If the spike test indicates a possible shorted heating element, during the signature test, the controller 820 immediately turns OFF the TRIAC. The controller 820) records the temperature at turn off and compares the recorded temperature to another temperature reading over a short period of time (e.g., 5 seconds). If the difference between the temperature at turn off and the temperature over the later time is greater than a threshold or if the temperature exceeds a threshold temperature (e.g., the temperature increased after turning the TRIAC OFF), then the controller 820 determines that the heating element is shorted (e.g., the high short circuit current flow that occurred before turning off the TRIAC led to a temperature increase at a later time due to thermal lag). However, if the difference between the temperature at turn off and the temperature at the later time is less than the threshold (e.g., the temperature has not increased), then the controller 820 determines that there was a false positive in the spike test (e.g., a high short circuit current did not flow before turning off the TRIAC), indicating that the heating element is still operating properly.

In either scenario (open or shorted heating element), if the controller 820) confirms burn-out, in step 610, the controller 820 prevents supply of current to the burned-out electric heating element. However, if the controller 820 detects a false positive, the controller 820) can resume normal operation and continue to supply current to the electric heating element while monitoring for temperature increases or decreases.

FIG. 8 illustrates the details of the signature test. In the left portion of FIG. 8, the controller 820 performs a signature test following a positive spike test for the upper or lower heating elements, which indicates a possible shorted heating element. Specifically, in step 802, the controller 820 immediately turns OFF the TRIAC, thereby interrupting power supply to the heating elements and turning the heating elements OFF. In step 804, the controller 820 records the temperature at turn off and compares the recorded temperature to another temperature reading over a short period of time t1 (e.g., 5 seconds, for example). In step 806, if the difference between the temperature at turn off of the TRIAC and the temperature over the period of time t1 is greater than a predetermined temperature threshold or if the temperature exceeds a threshold temperature (e.g., if the temperature has continued to increase after turning the TRIAC OFF), then, in step 808, the controller 820) determines that the heating element is shorted (e.g., the high short circuit current flow that occurred before turning off the TRIAC led to a temperature increase at a later time due to thermal lag). In step 810, the controller 820 terminates the supply of current to the burned-out electric heating element and continues to run the water heater without the burned-out heating element. However, if the difference between the temperature at turn off and the temperature at the period of time t1 is less than the temperature threshold (e.g., the temperature has not increased), then, in step 812, the controller 820) determines that there was a false positive in the spike test (e.g., a high short circuit current did not flow before turning off the TRIAC), and continues to supply current to both heating elements.

The right portion of FIG. 8 illustrates a similar processing for a signature test following a negative spike test (negative spike in rate of temperature change) for the upper or lower heating elements, which indicates a possible open heating element. Specifically, in step 814, the controller 820 keeps the TRIAC ON, which continues to power the heating element ON, for a predetermined time period t2 (e.g., 40) seconds, for example), saves the filtered predicted temperature, and then, in step 816, turns the TRIAC OFF after the predetermined time period t2. In step 818, the controller 820 checks whether there is another temperature drop (e.g., another negative spike) during another predetermined time period t3 (e.g., 3 seconds, for example). If the controller 820 does not detect another negative spike in temperature during the predetermined time period t3, then the controller 820 determines that the heating element is burned out and open (e.g., the heating element was not producing heat during the time period t3). In step 822, the controller 820 terminates the supply of current to the burned-out electric heating element and continues to run the water heater without the burned-out heating element. However, if another negative spike occurs during the predetermined time period t3, then, in step 824, the controller 820 determines that there was a false positive in the negative spike test (e.g., the heating element is still producing heat during the time period), and continues to supply current to both heating elements.

In general, since electronics 604 and electrical connections 608 rapidly heat up and cool off during cycling ON/OFF of the water heater (e.g., they have short time constants), and are directly attached to thermally conductive circuit board 402, they contribute significantly to the rate of change of the detected temperature. These factors, among others, may be considered when attempting to perform early detection of failed heating element. For example, controller 820) may be programmed with an algorithm that uses these factors and data to distinguish secondary heat generated in the thermal path from the primary heat radiating from the water in the water tank. In another example, controller 820 may be programmed with an algorithm that determines the rate of change of the temperature associated with the operation of the electric heating element circuits as a difference between temperature readings at different time points.

As discussed above, the memory of the controller 820 can store various values, including but not limited to current and temperature thresholds (positive and negative) and thresholds (positive and negative) related to rate of change of the current and the temperature. Usually, these values are constants recommended by the manufacturers of the different thermo-sensitive components or determined based on experimental and/or theoretical temperature correlations between the detected rate of temperature change and the associated temperature limits of the individual power components. Because both the open and the short conditions due to a failed heating element can occur rapidly, within seconds, and because the electronics 604 and the electrical connections 608 of the power supply circuit can rapidly heat up in response, it is beneficial to quickly identify a failure of the heating elements to prevent damage to the electronic components (power TRIACs, relays, etc.) of the water heater.

One way to ensure rapid detection of initial temperature spikes (increases or decreases) in temperature is to utilize dynamic thresholds (positive and negative), to which the controller 820 can compare the calculated rates of change of the temperature associated with the heating elements or the power supply circuit. The thresholds are dynamic in the sense that they need not be saved as constants in the memory of the controller 820. Instead, the positive and negative dynamic thresholds may change over time based on a dynamic value of a test signal reflecting the rate of change of the temperature associated with the operation of the electric heating element circuits. The test signal can be a live plot of the difference between the new temperature reading and the previous temperature reading. If there was no variation in the LTS 606 temperature reading, the test signal would be a steady value of zero with a standard deviation near zero. However, the difference (or variation) between the LTS 606 temperature reading and the LTS 606 previous temperature reading may not actually be zero. The positive and negative thresholds are dynamic positive and negative thresholds that closely follow (e.g., almost mirror) the rate of change of the temperature associated with the operation of the electric heating element circuits.

In certain embodiments, the positive and negative dynamic thresholds can be determined, preferably in real time, based on a prediction methodology. For example, derivative methods can be used to predict low and high raw temperature values using test signals.

In certain embodiments, the positive dynamic threshold value can be calculated using the mean value of the test signal and standard deviations that are calculated for the test signal. One way of calculating the positive and negative dynamic thresholds can include the use of a multiplier applied to the standard deviations that are calculated for the test signal. The standard deviation times the multiplier is added or subtracted from the mean value of the test signal to create a dynamic positive or negative threshold value.

Any combinations of the described various methods of calculating the positive and negative dynamic thresholds can be used, so long as the calculated dynamic thresholds follow as close as possible (e.g., almost mirror) the rate of change of the temperature associated with the operation of the electric heating element circuits, which allows the controller 820 to rapidly react to, and address, sudden changes in temperature, depending on the circumstances.

It might be desirable to add additional percentages to the calculated intermediary positive dynamic threshold value or limit the minimum value of the positive dynamic threshold value to a certain (predetermined) amount, for safety margins. Other methodologies for calculating the positive and negative dynamic threshold values might be utilized, as would be known to those skilled in the art.

The calculated dynamic thresholds can be used during the spike test, instead of or in addition to, the constant values of the thresholds stored in the memory of the controller 820 and illustrated in FIGS. 6-8. Accordingly, predetermined thresholds, dynamic thresholds, or some combination of predetermined and dynamic thresholds can be utilized in the spike tests.

FIG. 9 illustrates the details of the use of dynamic thresholds during burn-out detection. In step 902, the controller 820 determines whether a heating element is in a process of turning ON. It is known that any time a heating element turns ON (e.g., due to demand of hot water), there will typically be a big positive spike in the test signal, indicating a statistically significant rise in temperature. If the controller 820 determines that the heating element is in a process of turning ON (path “Yes” after step 1202), in step 904, the controller 820 uses fixed values POSITIVE_CONST and NEGATIVE_CONST for the positive threshold and the negative threshold, respectively. These fixed values are saved as constants in the memory of the controller 820. If the value of the test signal is above the fixed test value, the controller 820 detects a burn-out event. The controller 820 will use the fixed test values whenever a heating element first turns ON or transitions between states (e.g., going from lower element ON to upper element ON). If the controller 820 determines that the heating element is not in a process of turning ON (path “No” after step 902), in step 906, the controller 820 checks whether the heating element is ON. If the heating element is not ON (path “No” after step 906), in step 904, the controller 820 uses the fixed value POSITIVE_CONST for the positive threshold.

FIG. 10 illustrates a time/temperature plot that uses dynamic thresholds during burn-out detection whenever a heating element first turns ON or transitions between states (e.g., going from lower element ON to upper element ON). When a heating element turns ON (e.g., due to demand of hot water), there will typically be a big positive spike in the test signal, indicating a statistically significant rise in temperature. If the controller 820) determines that the heating element is in a process of turning ON (path “Yes” after step 902 in FIG. 9), the controller 820 uses fixed values “Positive Start Test Value” and “Negative Start Test Value” for the positive threshold and the negative threshold, respectively. These fixed values are saved as constants in the memory of the controller 820. If the value of the test signal is above the one of the “Positive Start Test Value” and “Negative Start Test Value,” the controller 820 detects a burn-out event. Turning back to FIG. 9, if the heating element is ON (path “Yes” after step 906), in step 908, the controller 820 calculates a positive dynamic threshold value. In step 910, the controller 820 checks whether the calculated positive dynamic threshold value is lower than the fixed value POSITIVE_CONST stored in the memory of the controller 820. If the calculated positive dynamic threshold value is lower than the fixed value POSITIVE_CONST (path “Yes” after step 1210), in step 912, the controller 820 replaces the fixed value POSITIVE_CONST with the calculated positive dynamic threshold value, which will be used instead of the fixed value POSITIVE_CONST for the positive threshold. If the calculated positive dynamic threshold value is not lower than the fixed value POSITIVE_CONST (path “No” after step 910), in step 914, the controller 820 repeats the processing and remains in a “running state” control mode, monitoring for a positive spike in the temperature of the power supply components. By updating the fixed, constant value POSITIVE_CONST stored in the memory with the calculated positive dynamic threshold value, which follows closely in real time and almost mirrors any changes in the temperature associated with the heating elements and the power supply components, the controller 820 is able to react to any undesirable temperature spikes within a very short time frame and shut down the power components, thereby protecting the temperature-sensitive TRIACs and other electronic components of the heater.

FIG. 11 illustrates a time/temperature plot that uses dynamic thresholds when a positive spike in the temperature of the power supply components is detected. During the “running state” control mode, the controller 820 monitors for a positive spike in the temperature of the power supply components.

FIG. 12 illustrates a time/temperature plot that uses decision block 806 in FIG. 8 when the controller 820 performs a “signature” test to confirm the positive spike determination during the spike test, which indicates a possible shorted heating element. As shown in FIG. 12, the time/temperature plot uses dynamic thresholds to detect a first positive spike (referenced as “Spike” in FIG. 12). During the “signature” test, the time/temperature plot uses fixed values (e.g., predetermined thresholds) to evaluate if temperature continued to rise after cutting power to the heating element circuit. The signature test considers the filtered LTS 606 temperature reading, not the new or the previous LTS 606 temperature reading, as is the case for the test signal. If the filtered LTS 606 temperature reading continues to rise after shutting off power to the heating element circuit, then the controller 820 determines that a significant amount of heat has been generated by the circuit board (and the lower temp sensor) by a larger than normal current surge, likely caused by a short circuit to ground somewhere in the heating element circuit, a failed heating element wire shorting to heating element metal sheathing, or a wire on the heating element terminal block became dislodged and shorted to the tank body. The occurrence of another (e.g., subsequent) positive spike confirms that the temperature continues to increase after the heating element was turned off, which indicates a high current (or high power) event has occurred that generates unexpected heat into the circuit board 208. Because the positive spike indicates a possible shorted heating element, during the signature test, the controller 820 immediately turns OFF the TRIAC, thereby interrupting power supply to the heating elements. The controller 820) records the temperature at turn off (“Filtered Lower Temperature,” as shown in FIG. 12) and compares the recorded temperature to subsequent temperature readings over a short period of time t1 (e.g., 5 seconds, for example). If the difference between the temperature at turn off of the TRIAC and the temperature over the period of time t1 is greater than a predetermined temperature threshold or if the temperature exceeds a threshold temperature (e.g., if the temperature has continued to increase after turning the TRIAC OFF), then the controller 820 determines that the heating element is shorted (e.g., the high short circuit current flow that occurred before turning off the TRIAC led to a temperature increase at a later time due to thermal lag). In this scenario, the controller 820 terminates the supply of current to the burned-out electric heating element and continues to run the water heater without the burned-out heating element. As illustrated in FIG. 12, during the signature test, the filtered lower temperature continues to increase after the positive spike is detected. If there was no high temperature (or high current), there would be no such continued increase. By using the calculated positive dynamic threshold value to detect the first positive spike (referenced as “Spike” in FIG. 12), which follows closely in real time and almost mirrors any changes in the temperature associated with the heating elements and the power supply components, the controller 820 can react to any undesirable temperature spikes, and detect even a small positive spike, within a very short time frame and shut down the power components, thereby protecting the temperature-sensitive TRIACs and other electronic components of the heater.

Conversely, if the difference between the temperature at turn off and the temperature over the period of time t1 is less than the temperature threshold (e.g., the temperature has not increased), then the controller 820 determines that there was a false positive in the spike test (e.g., a high short circuit current did not flow before turning off the TRIAC), and continues to supply current to both heating elements.

The controller 820 can perform similar processing to the above-described calculations of the positive dynamic threshold value to calculate a dynamic negative threshold value.

For example, FIG. 13 illustrates a time/temperature plot that uses dynamic thresholds to detect a first negative spike. After the first negative spike is detected, the controller 820 performs a “signature” test that uses fixed values (as shown in the right portion of FIG. 13) to confirm a negative spike in the temperature of the power supply components. Negative spike, for example, can be confirmed by using the Test Signal and generating an action that should create a second negative spike that exceeds another (e.g., more challenging) threshold. When a good heating element circuit is turned off, a substantial amplitude negative spike should occur. If no spike in excess of the threshold occurs, then the assumption is that the heating element circuit opened (creating the first negative spike) and therefore another spike cannot be produced. Because the negative spike indicates that the heating element might have burned out and became open, during the signature test, the controller 820 keeps the TRIAC ON, which continues to power the heating element ON, for a predetermined time period t2 (e.g., 40) seconds, for example), saves the filtered predicted temperature, and then turns the TRIAC OFF after the predetermined time period t2. After the TRIAC is turned OFF, the controller 820 checks whether there is another temperature drop (e.g., another negative spike) during another predetermined time period t3 (e.g., 3 seconds, for example). If the controller 820 does not detect another negative spike in temperature during the predetermined time period t3, then the controller 820 determines that the heating element is burned out and open (e.g., the heating element was not producing heat during the time period t2). In this scenario, the controller 820 terminates the supply of current to the burned-out electric heating element and continues to run the water heater without the burned-out heating element.

Conversely, if another negative spike occurs during the predetermined time period t3, then the controller 820 determines that there was a false positive in the negative spike test (e.g., the heating element is still producing heat during the time period t2), indicating that the heating element is still operating properly, and continues to supply current to both heating elements. Alternatively, because negative changes or decreases in temperature of the power supply components may be caused by different, sometimes unrelated to the power components, events (e.g., influx of cold water in the heater tank or line voltage power dip), which may not be as critical for the electronic components as large increases in temperature, the controller 820 can calculate a dynamic negative threshold value using a different methodology. For example, turning back to FIG. 9, after determining in step 906 that the heating element is ON, in step 916, the controller 820 checks whether a filtered predicted test signal (“FPTS”) is higher than or equal to a runaway temperature (“RA”). Depending on the results of the determination in step 916, the controller 820 sets the negative threshold value to one of two constant values, NEGATIVE_CONST_1 and NEGATIVE_CONST_2, which are both saved in the memory of the controller 820.

If the heating element is not ON (path “No” after step 906), in step 904, the controller 820 uses the fixed value NEGATIVE_CONST, which is saved as constants in the memory of the controller 820, for the negative threshold value. If the value of the filtered test signal is below the fixed negative test value NEGATIVE_CONST, the controller 820 detects a burn-out event.

In general, if a fault is detected in either of scenarios described above, numerous solutions could be implemented. In one example, an alert could be output to the user or a maintenance technician. In another example, operation of the water heater could be modified to compensate for the fault without turning OFF both heating elements. For example, if a degrading thermal path or heating element is detected, the power supplied to the failed heating element may be reduced or terminated, while the undamaged heating element continues to operate normally, which can avoid ultimate failure of the electronic power supply components of the water heater.

As described in the flowcharts of FIGS. 6-9, the water heater control system of the present disclosure provides a solution for detecting failure of the heating elements of a water heater. By detecting temperature spikes (increase and/or decrease) in the secondary heat produced by the components of the electrical power circuit, the solution rapidly and efficiently detects an electric water heating element that might have become open or shorted, and adjusts control of the power supply system of the water heater based on this determination.

The above-described methods for detecting failure of the heating elements of a water heater can be implemented for tank-based electric water heaters (as described above and illustrated in the figures), as well as to tankless electrical water heaters that may also be susceptible to element burn-out.

It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. For example, the term “coupled” as used herein refers to any logical, optical, physical or electrical connection, link or the like by which signals or light produced or supplied by one system element are imparted to another coupled element. Unless described otherwise, coupled elements or devices are not necessarily directly coupled or connected to one another and may be separated by intermediate components, elements or communication media that may modify, manipulate or carry the signals. Also, the term “coupled” can refer to direct or indirect mechanical or thermal connectedness. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order or magnitude between such entities or actions. The terms “comprises,” “comprising,” “includes,” “including,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises or includes a list of elements or steps does not include only those elements or steps but may include other elements or steps not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by “a” or “an” does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

Unless otherwise stated, any and all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. Such amounts are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. For example, unless expressly stated otherwise, a parameter value or the like may vary by as much as ±10% from the stated amount or more. The term “substantially” as used herein means the parameter value or the like.

In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various examples for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed examples require more features than are expressly recited in each claim. Rather, as the following claims reflect, the subject matter to be protected lies in less than all features of any single disclosed example. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

In the above detailed description, numerous specific details were set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.

While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present concepts.

Claims

1. A water heater comprising: an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; anda controller coupled to the electric heating element circuit, the controller being configured to: perform a spike test on the operation of the electric heating element circuit by: comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold;identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit or identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit;perform a signature test on the operation of the electric heating element circuit by: in response to identifying the negative spike if identified: supplying or continuing to supply the current to the electric heating element for a first predetermined time period;terminating the supply of current after the first predetermined time period; anddetermining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; orin response to identifying the positive spike if identified: terminating the supply of current to the electric heating element for a second predetermined time period; anddetermining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

2. The water heater of claim 1, wherein the electric heating element circuit comprises a thermally conductive circuit board.

3. The water heater of claim 2, further comprising a plurality of electric heating elements and a plurality of electronic switches, each of the electric heating elements being electronically coupled to at least one of the electronic switches.

4. The water heater of claim 3, wherein the temperature associated with the operation of the electric heating element circuit is at least one of a temperature of a thermal path for conducting heat through the thermally conductive circuit board, a temperature of at least one of the electronic switches, a temperature of electronic components of the water heater, or a temperature of electrical connections of the water heater.

5. The water heater of claim 3, wherein one of the electric heating elements is mounted to an upper portion of a wall of a tank of the water heater, and another one of the electric heating elements is mounted to a lower portion of the wall of the tank.

6. The water heater of claim 3, wherein the controller is electrically coupled to the sensor, the controller being configured to control at least one of the electronic switches based on signals received from the sensor.

7. The water heater of claim 6, wherein the signals received by the controller from the sensor correspond to a sensed temperature of the circuit.

8. The water heater of claim 6, wherein the signals received by the controller from the sensor correspond to a sensed temperature of at least one of the electronic switches.

9. The water heater of claim 3, wherein the sensor is mounted to the thermally conductive circuit board and thermally coupled to at least one of the electronic switches, the sensor being configured to sense a temperature corresponding to a temperature of at least one of the electronic switches.

10. The water heater of claim 1, wherein the negative spike corresponds to a temperature decrease within a fourth predetermined time period.

11. The water heater of claim 1, wherein the positive spike corresponds to a temperature increase within a sixth predetermined time period.

12. The water heater of claim 1, wherein at least one of the positive threshold or the negative threshold changes over time based on a dynamic value of a test signal reflecting the rate of change of the temperature associated with the operation of the electric heating element circuit.

13. The water heater of claim 12, wherein the positive threshold is a dynamic positive threshold that changes based at least in part on the rate of change of the temperature associated with the operation of the electric heating element circuit.

14. The water heater of claim 1, wherein the positive threshold is a dynamic positive threshold that changes over time based on a prediction methodology.

15. The water heater of claim 14, wherein the dynamic positive threshold is calculated using derivative methods to predict low and high raw temperature values in test signals.

16. The water heater of claim 15, wherein the dynamic positive threshold is calculated using at least one of mean values of the test signals and standard deviations from the test signals.

17. The water heater of claim 14, wherein the dynamic positive threshold is calculated by at least one of adding additional percentages to a calculated intermediary positive dynamic threshold value or limiting a minimum value of the positive dynamic threshold value to a predetermined amount.

18. The water heater of claim 1, wherein during the signature test and in response to the negative spike, the controller is further configured to determine if another negative spike occurs within a third predetermined time period, indicating a false positive result from the spike test and no failed or failing operation caused by the open circuit.

19. A water heater comprising: an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;a sensor coupled to the electric heating element circuit and configured to detect a rate of change of circuit temperature associated with operation of the electric heating element circuit; anda controller coupled to the electric heating element circuit, the controller being configured to: perform a spike test on the operation of the electric heating element circuit by: comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; andidentifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit: or identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit.

20. The water heater of claim 19, wherein the sensor is a lower temperature sensor positioned to sense a temperature associated with a lower portion of a wall of a tank of the water heater, the water heater further comprising an upper temperature sensor positioned to sense a temperature associated with an upper portion of the wall of the tank.

21. The water heater of claim 20, wherein at least one of the lower temperature sensor and the upper temperature sensor comprises a thermistor.

22. The water heater of claim 19, further comprising a plurality of electric heating elements and a plurality of electronic switches, each of the electric heating elements being electronically coupled to at least one of the electronic switches.

23. The water heater of claim 22, wherein at least one of the plurality of electronic switches comprises a TRIAC.

24. The water heater of claim 22, wherein the sensor is a dual-purpose temperature sensor thermally coupled to a wall of a tank of the water heater to sense a temperature corresponding to a temperature of the wall of the tank and relating to a temperature of water stored in the tank, and thermally coupled to at least one of the plurality of electronic switches to sense a temperature corresponding to a temperature of the at least one of the plurality of electronic switches.

25. The water heater of claim 19, the sensor comprising a tank wall temperature sensor thermally coupled to a wall of a tank of the water heater, and configured to sense a temperature of the wall of the tank.

26. The water heater of claim 19, wherein the positive threshold is a dynamic positive threshold that changes over time based on a prediction methodology.

27. The water heater of claim 26, wherein the dynamic positive threshold is calculated using derivative methods to predict low and high raw temperature values in test signals.

28. The water heater of claim 27, wherein the dynamic positive threshold is calculated using at least one of mean values of the test signals and standard deviations from the test signals.

29. The water heater of claim 26, wherein the dynamic positive threshold is calculated by at least one of adding additional percentages to a calculated intermediary positive dynamic threshold value or limiting a minimum value of the positive dynamic threshold value to a predetermined amount.

30. A water heater comprising: an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; anda controller coupled to the electric heating element circuit, the controller being configured to: detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit;detect whether the electric heating element circuit may have failed or failing operation caused by a shorted circuit;perform a signature test on the operation of the electric heating element circuit by: in response to detecting that the electric heating element circuit may have failed or failing operation caused by an open circuit: supplying or continuing to supply the current to the electric heating element for a first predetermined time period;terminating the supply of current after the first predetermined time period; anddetermining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; orin response to detecting that the electric heating element circuit may have failed or failing operation caused by a shorted circuit: terminating the supply of current to the electric heating element for a second predetermined time period; anddetermining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

31. The water heater of claim 30, wherein the controller is further configured to perform a spike test to detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit or a shorted circuit, by: comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold.

32. The water heater of claim 31, wherein the controller is configured to detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit by: comparing the rate of change of the temperature associated with the operation of the electric heating element circuit to the negative threshold; andidentifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit.

33. The water heater of claim 31, wherein the controller is configured to detect whether the electric heating element circuit may have failed or failing operation caused by a shorted circuit by: comparing the rate of change of the temperature associated with the operation of the electric heating element circuit to the positive threshold; andidentifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit.

34. The water heater of claim 33, wherein the positive threshold is a dynamic positive threshold that changes over time based on a prediction methodology.

35. The water heater of claim 34, wherein the dynamic positive threshold is calculated using derivative methods to predict low and high raw temperature values in test signals.

36. The water heater of claim 35, wherein the dynamic positive threshold is calculated using at least one of mean values of the test signals and standard deviations from the test signals.

37. The water heater of claim 35, wherein the dynamic positive threshold is calculated by at least one of adding additional percentages to a calculated intermediary positive dynamic threshold value or limiting a minimum value of the positive dynamic threshold value to a predetermined amount.

38. A water heater comprising: an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; anda controller coupled to the electric heating element circuit, the controller being configured to: compare a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold;detect a positive spike or a negative spike in the rate of change of the temperature associated with the operation of the electric heating element circuit, indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit or an open circuit, respectively;if a negative spike is detected, terminate the supply of current to the electric heating element after a first predetermined time period;if a positive spike is detected, immediately terminate the supply of current to the electric heating element for a second predetermined time period; andconfirm failed or failing operation of the electric heating element circuit if a temperature increase occurs during the second predetermined time period or if a temperature drop occurs during a third predetermined time period after the first predetermined time period.

39. A water heater comprising: an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; anda controller coupled to the electric heating element circuit, the controller being configured to: perform a spike test on the operation of the electric heating element circuit by: comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold;identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit;identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit;perform a signature test on the operation of the electric heating element circuit by: in response to identifying the negative spike if identified: supplying or continuing to supply the current to the electric heating element for a first predetermined time period;terminating the supply of current after the first predetermined time period; anddetermining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit;in response to identifying the positive spike if identified: terminating the supply of current to the electric heating element for a second predetermined time period; anddetermining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

40. A method for detecting failed or failing operation in a water heater, the method comprising: performing a spike test on the operation of an electric heating element circuit, including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element, by: comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold;identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit;identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit;performing a signature test on the operation of the electric heating element circuit by: in response to identifying the negative spike if identified: supplying or continuing to supply the current to the electric heating element for a first predetermined time period;terminating the supply of current after the first predetermined time period; anddetermining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit;in response to identifying the positive spike if identified; terminating the supply of current to the electric heating element for a second predetermined time period; anddetermining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.