WATER HEATER AND METHODS FOR OPERATING THE SAME

Abstract

A water heater includes at least one heating system for heating water. Control circuitry is configured to determine electrical parameters of individual components of the at least one heating system. The electrical parameters are utilized to determine operating conditions of the water heater. The operating conditions can be utilized to control at least some aspect of the water heater.

Description

FIELD OF THE DISCLOSURE

The present disclosure generally relates to water heaters and, more particularly, to controls for water heater systems.

SUMMARY OF THE DISCLOSURE

According to a first aspect of the present disclosure, a water heater includes a tank for holding water, a resistance heating element, a heat pump including a compressor that compresses refrigerant of the heat pump, and a fan that draws air to a heat exchanger of the heat pump, voltage detection circuitry that communicates a first signal indicative of a system voltage, current detection circuitry that communicates a second signal indicative of a current drawn by the heat pump and the resistance heating element, and control circuitry. The control circuitry is configured to determine a first current to the compressor and calculate a second current to the fan based on the first current and the current drawn when the compressor and the fan are both on.

Embodiments of the first aspect of the present disclosure can include any one or any combination of the following features:

the second current is at most 10% of the first current;

the control circuitry is configured to determine a blockage condition of the fan based on the second current;

the control circuitry is configured to calculate a third current to the resistance heating element and calculate the second current based further on the third current;

the calculation of the second current includes determining a peak current of the current drawn;

the current drawn is an alternating current (AC) signal, and the calculation of the second current includes detecting a current spike of the AC signal adjacent the peak current;

the current detection circuitry is configured to provide the second signal up to a current threshold, and the control circuitry is configured to estimate the current drawn when the current drawn is greater than the current threshold;

the control circuitry estimates the current drawn by summing a plurality of readings of the second signal; and

the control circuitry is configured to calculate an instantaneous root-mean-square (RMS) current of the current drawn.

According to a second aspect of the present disclosure, a water heater includes a tank for holding water, at least one heating system including at least a heat pump having a compressor and a fan that draws air to a heat exchanger of the heat pump, current detection circuitry that communicates a signal indicative of a current drawn by the at least one heating system, and control circuitry configured to determine a first current to the compressor and a second current to the fan based on the signal.

Embodiments of the second aspect of the present disclosure can include any one or any combination of the following features:

the second current is at most 10% of the second current;

the control circuitry is configured to determine a blockage condition of the fan based on the second current;

the at least one heating system includes a first heating system having the heat pump and second heating system having a resistance heating element, wherein the control circuitry is configured to calculate a third current to the resistance heating element and calculate the second current based further on the third current;

the calculation of the second current includes determining a peak current of the current drawn;

the current drawn includes an alternating current (AC) signal, and wherein the calculation of the second current includes detecting a current spike of the AC signal adjacent the peak current;

the current detection circuitry is configured to provide the signal up to a current threshold, and wherein the control circuitry is configured to estimate the current drawn when the current drawn is greater than the current threshold;

the control circuitry estimates the current drawn by summing a plurality of readings of the signal; and

the control circuitry is configured to calculate an instantaneous root-mean-square (RMS) current of the current drawn.

According to a third aspect of the present disclosure, a method for determining current to a fan of a heat pump of a water heater using a single current sensor that detects current drawn by a combination of the fan and a compressor of the water heater. The method includes communicating, via the current sensor, a signal indicative of a current drawn by the heat pump, determining a first current to the compressor, and determining a second current to the fan based on the first current and the current drawn when the compressor and the fan are both on.

Embodiments of the third aspect of the present disclosure can include any one or any combination of the following features:

determining a peak current of the current drawn, detecting a current spike of an AC signal adjacent the peak current, and determining an operating condition of the fan based on the current spike.

According to a fourth aspect of the present disclosure, a water heater includes a tank for holding water, at least one heating system for heating the tank, voltage detection circuitry that communicates a first signal indicative of a system voltage, and control circuitry configured to sum a plurality of instances of the first signal, determine a level of the system voltage based on the sum, communicate an output to control the water heater based on the level.

Embodiments of the fourth aspect of the present disclosure can include any one or any combination of the following features:

the output includes a power configuration including at least one of a frequency and a phase;

the control circuitry is configured to classify the system voltage as one of 240 volts split phase, 208 volts three phase, and 120 volts single phase based on the sum;

the voltage detection circuitry includes magnitude detection circuitry that provides an indication of a voltage magnitude and frequency detection circuitry that provides an indication of a frequency of the system voltage;

the control circuitry is configured to determine a frequency of the system voltage via a switch that deactivates at zero voltage points of the system voltage;

current detection circuitry that communicates a second signal indicative of a current drawn by the at least one heating source;

switching circuitry controlling electrical power to the at least one heating system, wherein the control circuitry is configured to control the switching circuitry to interrupt power to the at least one heating system in response to the current drawn exceeding at least one current threshold;

the control circuitry is configured to adjust the at least one current threshold based on the output;

the at least one heating system includes a first heating system having a resistance heating element and a second heating system having a heat pump each configured to heat the tank, wherein the control circuitry is configured to set a first current threshold for operation of the resistance heating element and a second current threshold for operation of the heat pump, and wherein the output is a control signal to limit activation of the switching circuitry; and

the control circuitry is configured to determine the level based on a sequence of the instances of the system voltage.

According to a fifth aspect of the present disclosure, a water heater includes a tank for holding water, a resistance heating element, a heat pump for heating the tank, voltage detection circuitry that communicates a first signal indicative of a system voltage and control circuitry configured to sum a plurality of instances of the first signal, determine a level of the system voltage based on the sum, and communicate an output based on the level.

Embodiments of the fifth aspect of the present disclosure can include any one or any combination of the following features:

the output includes a power configuration including a voltage magnitude and at least one of a frequency and a phase;

the control circuitry is configured to classify the system voltage as one of 240 volts split phase and 208 volts three phase; and

the output includes an indication of a low-voltage condition of the supply voltage;

According to a sixth aspect of the present disclosure, a method for operating a water heater that has at least one heating system includes communicating, by voltage detection circuitry, a first signal indicative of a system voltage, summing a plurality of instances of the first signal, determining a level of the system voltage based on the sum, communicating, by control circuitry of the water heater, an output based on the level to control the water heater.

Embodiments of the sixth aspect of the present disclosure can include any one or any combination of the following features:

classifying the system voltage as one of 240 volts split phase, and 208 volts three phase, and 120 volts single phase based on the sum;

determining a frequency of the system voltage by monitoring a switch that deactivates at zero voltage points of the system voltage;

determining the level based on a sequence of the instances of the system voltage;

controlling switching circuitry to interrupt power to the at least one heating system in response to a current drawn by the at least one heating system exceeding a current threshold; and

adjusting the current threshold based on the output.

According to a seventh aspect of the present disclosure, a water heater includes a tank for holding water, a resistance heating element, a heat pump, current detection circuitry that communicates a first signal indicative of current drawn by the heat pump and the resistance heating element, voltage detection circuitry that communicates a second signal indicative of a system voltage and control circuitry configured to activate the resistance heating element for a first activation period, monitor the first signal during the first activation period, deactivate the resistance heating element to end the first activation period, determine a calculated resistance of the resistance heating element based on the second signal and the first signal monitored during the first activation period, calculate a first current drawn by the resistance heating element using the second signal during the during a second activation period subsequent to the first activation period and the calculated resistance.

Embodiments of the seventh aspect of the present disclosure can include any one or any combination of the following features:

the control circuitry is configured to recursively calculate the calculated resistance following each period of activation of the resistance heating element;

the control circuitry is configured to: compare a calculated first resistance value to a subsequently-calculated second resistance value and adjust the calculated resistance by a fixed increment based on the comparison;

the control circuitry is configured to increment the calculated resistance when the subsequently-calculated second resistance value is greater than the calculated first resistance value;

the control circuitry is configured to calculate a degradation level of the resistance heating element based on the comparison of the resistance values;

the control circuitry is configured to determine a second current drawn by the heat pump during the second activation period and when the heat pump is activated;

the heat pump includes a compressor and wherein the second current is drawn at least by the compressor; and

the heat pump includes a fan and wherein the second current is drawn by a combination of the compressor and the fan.

According to an eighth aspect of the present disclosure, a water heater including a tank for holding water, a resistance heating element, current detection circuitry that communicates a first signal indicative of current drawn by at least the resistance heating element, and control circuitry configured to activate the resistance heating element for an activation period, monitor the first signal during the activation period, deactivate the resistance heating element to end the activation period, and determine a calculated resistance of the resistance heating element based on a system voltage and the first signal monitored during the activation period.

Embodiments of the eighth aspect of the present disclosure can include any one or any combination of the following features:

voltage detection circuitry that communicates a second signal indicative of the system voltage;

a heat pump configured to heat the tank, wherein the current drawn includes a first current to the resistance heating element and a second current to the heat pump;

the control circuitry is further configured to store, in a memory, the calculated resistance, during a subsequent second activation period, calculate the first current using the system voltage during the second activation period and the resistance;

the control circuitry is configured to determine the second current by subtracting the first current from the current drawn;

the heat pump includes a compressor and wherein the control circuitry is configured to determine the second current during the second activation period and when the heat pump is activated;

the control circuitry is configured to recursively calculate the calculated resistance following each period of activation of the resistance heating element;

the control circuitry is configured to compare a calculated first resistance value to a subsequently-calculated second resistance value and adjust the calculated resistance by a predetermined value based on the comparison of the resistance values;

the control circuitry is configured to increment the calculated resistance by a fixed increase when the subsequently-calculated second resistance value is greater than the calculated first resistance value;

the control circuitry is configured to calculate a degradation level of the resistance heating element based on the comparison of the resistance values.

According to a ninth aspect of the present disclosure, a method for determining a resistance of a resistance heating element of a water heater. The method includes communicating a first signal indicative of current drawn by at least the resistance heating element, activating the resistance heating element for an activation period, monitoring the first signal during the activation period, deactivating the resistance heating element to end the activation period, and determining a calculated resistance of the resistance heating element based on a system voltage and the first signal monitored during the activation period.

Embodiments of the ninth aspect of the present disclosure can include any one or any combination of the following features:

calculating a current to the resistance heating element using the system voltage during a second activation period subsequent to the first activation period and the calculated resistance.

According to a tenth aspect of the present disclosure, a water heater includes a tank for holding water, a component of at least one heating system that heats the tank, current detection circuitry that communicates a first signal indicative of a current drawn by the component, and control circuitry configured to determine an activation state of the component, determine at least one current threshold based on the activation state, compare the current drawn to the at least one current threshold, determine a threshold duration based on the current threshold, and in response to the current drawn differing from the at least one current threshold for longer than the threshold duration, control the water heater.

Embodiments of the tenth aspect of the present disclosure can include any one or any combination of the following features:

the at least one current threshold includes a first current threshold and a second current threshold greater than the first current threshold, and wherein the control circuitry is configured to select one of the first current threshold and the second current threshold for comparison to the current drawn based on the current drawn;

when the first and second current thresholds are less than the current drawn, the one of the first current threshold and the second current threshold is the greater of the first current threshold and the second current threshold;

apply a first threshold duration when the current drawn exceeds the first current threshold and is less than the second current threshold, and apply a second threshold duration when the current drawn exceeds the second current threshold;

the second threshold duration is shorter than the first threshold duration;

the at least one heating system includes a plurality of heating systems each having a corresponding activation state, wherein the at least one current threshold includes a first current threshold corresponding to a first set of activation states and a second current threshold corresponding to a second set of activation states different from the first set of activation states;

controlling the water heater includes deactivating a component of a most-recently activated one of the plurality of heating systems;

the first heating system includes a resistance heating element, and wherein the second heating system includes a heat pump including a compressor that compresses refrigerant of the heat pump;

the first signal is indicative of current drawn by a total of a first current to the resistance heating element and a second current to the heat pump, wherein the control circuitry is configured to, in response to the current drawn falling below the at least one current threshold after exceeding the at least one current threshold and before exceeding the threshold duration, determining a startup condition of the compressor; and

the compressor includes a motor, wherein controlling the water heater includes determining a locked condition of a rotor of the motor.

According to an eleventh aspect of the present disclosure, a water heater comprising includes at least one heating system including a component, current detection circuitry that communicates a first signal indicative of a current drawn by the component, and control circuitry configured to determine an activation state of the component, determine at least one current threshold based on the activation state, compare the current drawn to the at least one current threshold, determine a threshold duration based on the current threshold, and in response to the current drawn exceeding from the at least one current threshold for longer than the threshold duration, control the water heater.

Embodiments of the eleventh aspect of the present disclosure can include any one or any combination of the following features:

the at least one current threshold includes a first current threshold and a second current threshold greater than the first current threshold, and wherein the control circuitry is configured to select one of the first current threshold and the second current threshold for comparison to the current drawn based on the current drawn;

when the first and second current thresholds are less than the current drawn, the one of the first current threshold and the second current threshold is the greater of the first current threshold and the second current threshold;

apply a first threshold duration when the current drawn exceeds the first current threshold and is less than the second current threshold, and apply a second threshold duration when the current drawn exceeds the second current threshold;

the second threshold duration is shorter than the first threshold duration;

the at least one heating system includes a plurality of heating systems each having a corresponding activation state, wherein the at least one current threshold includes a first current threshold corresponding to a first set of activation states and a second current threshold corresponding to a second set of activation states different from the first set of activation states; and

controlling the water heater includes deactivating a component of a most-recently activated one of the plurality of heating systems of the plurality of heating systems.

According to a twelfth aspect of the present disclosure, a method for operating a water heater includes communicating a first signal indicative of a current drawn by a component of at least one heating system of the water heater, determining an activation state of the component, determining at least one current threshold based on the activation state, comparing the current drawn to the at least one current threshold, determining a threshold duration based on the current threshold, and controlling the water heater in response to the current drawn differing from the at least one current threshold for longer than the threshold duration.

Embodiments of the twelfth aspect of the present disclosure can include any one or any combination of the following features:

the at least one current threshold includes a first current threshold and a second current threshold greater than the first current threshold, and wherein the control circuitry is configured to select one of the first current threshold and the second current threshold for comparison to the current drawn based on the current drawn; and

applying a first threshold duration when the current drawn exceeds the first current threshold and is less than the second current threshold, and applying a second threshold duration when the current drawn exceeds the second current threshold.

These and other features, advantages, and objects of the present disclosure will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a functional block diagram of a control system for a water heater;

FIG. 2 is a functional diagram of a water heater showing heating devices and sensing circuitry for the water heater;

FIG. 3 is an electrical schematic of power distribution circuitry for a water heater;

FIG. 4 is a detailed electrical schematic of voltage detection circuitry of FIG. 3;

FIG. 5 is a graph of temperature and electrical current over time for an exemplary use case in a hybrid operating mode of a water heater;

FIG. 6 is a flow diagram of an operational method for a water heater;

FIG. 7A is a flow diagram of an operational method for a water heater;

FIG. 7B is a flow diagram of an operational method for a water heater;

FIG. 8 shows a first graph of system voltage of a water heater and corresponding count values detected by voltage detection circuitry over time and a second graph of sums of the count values per half-line cycle;

FIG. 9A is a flow diagram of an operational method for a water heater;

FIG. 9B is a table of power configurations determinable by control circuitry of a water heater;

FIG. 10 is a graph of system voltage and current draw over time during operation of a heat pump for a water heater; and

FIG. 11 is a flow diagram of an operational method for a water heater.

The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles described herein.

DETAILED DESCRIPTION

As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

As used herein, the term “coupled” (in all of its forms: couple, coupling, coupled, etc.) generally means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components (electrical or mechanical) and/or any additional intermediate members. Such joining may include members being integrally formed as a single unitary body with one another (i.e., integrally coupled) or may refer to joining of two components. Such joining may be permanent in nature or may be removable or releasable in nature, unless otherwise stated.

As used herein, the terms “the,” “a,” or “an,” mean “at least one,” and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to “a component” includes embodiments having two or more such components unless the context clearly indicates otherwise.

Referring generally to the figures, reference numeral 10 generally designates a water heater. The water heater 10 can alternatively be referred to as a water heater system and can include tank water heaters, “tankless” water heaters, hybrid water heaters, gas-fired water heaters, etc. In general, the water heater 10 of the present disclosure can provide for enhanced electrical parameter detection and control. The detection techniques employed can provide for robust fault detection and response times. For example, high-speed processing technology can optimize or otherwise enhance utilization of detection hardware (e.g., sensors, detection circuitry). The configuration of control circuitry 12 of the water heater 10 can further provide for classification of different states of at least one heating system 14 of the water heater 10.

Referring now to FIGS. 1-4, the water heater 10 can be supplied power via a utility, such as an electrical system for a residence or commercial setting. The electrical system can provide electricity at a standard voltage and frequency. For example, the supplied power (power in) can be 120 volts at alternating current (VAC) at a frequency of 60 Hertz (e.g., 120 VAC 60 Hz), 208 VAC 60Hz, 240 VAC 60 Hz (split phase), 230 VAC 50Hz, or any other AC supplied power (e.g., any AC voltage and frequency). In the present examples, the water heater 10 is configured for two-phase operation at 240 VAC 180 degrees out of phase. However, it is contemplated that the water heater 10 can be configured for a first supplied power (120 VAC), a second supplied power (240 VAC), or a third supplied power (230 VAC 50 Hz).

While the water heater 10 of the present disclosure may use any one of a plurality of heating methods, at least one heating system 14 for the exemplary water heater 10 herein includes a first heating system that is refrigerant-based and a second heating system that is electrical-based. The first heating system can include a heat pump 16. The second heating system can include at least one resistance heating elements 18a, 18b. Other heating systems 14 can be employed, such as gas-based heating systems 14. As will be described further herein, the detection methods and technology employed can provide for electrical parameter detection of the heating systems 14 relative to other portions of the water heater 10. For example, a total current to the heating systems 14 can be monitored separately or independently from current to other peripherals of the water heater 10. By way of example, power to the control circuitry 12, temperature sensing devices, or other peripheral devices of the water heater 10 (e.g., a mixing valve 54, a leak detection circuit) may be on a different circuit than the heating systems 14.

Referring particularly to FIG. 1, voltage detection circuitry 20 and current detection circuitry 22 are provided for detecting system voltage of the water heater 10 and current to the heating systems 14, respectively. In series with the current detection circuitry 22 are loads 24 of the heating systems 14. In this way, a total current to the resistance heating elements 18a, 18b, and components of the heat pump 16 can be monitored separately from current to other devices of the water heater 10. By way of example, the control circuitry 12 is not on a circuit leg common to the current detection circuitry 22 and the heating systems 14. While demonstrated as “electrically upstream” of the heating systems 14, it is contemplated that the current detection circuitry 22 may be located elsewhere in other examples. For instance, the current detection circuitry 22 could be located “electrically downstream” of the heating systems 14 provided the current detection circuitry 22 is on a leg common to the heating systems 14. The current detection circuitry 22 can thus detect current drawn by the heating systems 14. In some examples, the current detection circuitry 22 detects current only to the heating systems 14.

With continued reference to FIG. 1, switching circuitry 26 electrically interposes power from the supplied power and the heating systems 14, with which the switching circuitry 26 is in series. As will be described further in reference to FIG. 3, the switching circuitry 26 can be configured to interrupt high voltage signals (e.g., line voltage), neutral, or both. The control circuitry 12 is in communication with the current detection circuitry 22, the voltage detection circuitry 20, and the switching circuitry 26. For example, the current detection circuitry 22 and the voltage detection circuitry 20 may electrically couple with the control circuitry 12 via a conductor, such as a tracing of a circuit board and/or wiring, such that electrical signals may be exchanged with the control circuitry 12. In some examples, the current detection circuitry 22 and the voltage detection circuitry 20 can provide output signals on one or more conductors that electrically couple with pins of a microcontroller of the control circuitry 12. By way of example, the output signals, which are input signals to the control circuitry 12, can be a voltage and/or current that is representative of an electrical parameter. For example, the voltage detection circuitry 20 can output signals representative of the system voltage (e.g., frequency and/or magnitude), and the current detection circuitry 22 can output a signal representative of the current drawn by the heating systems 14.

The control circuitry 12 can control the switching circuitry 26 in response to or based on the current drawn and/or the system voltage. For example, the control circuitry 12 can determine an overcurrent condition, an undercurrent condition, an overvoltage condition, an undervoltage condition, or any other electrical condition based on the signals from the current detection circuitry 22 and the voltage detection circuitry 20, and output one or more signals to control the switching circuitry 26 to open or close electrical connection between the supplied power and one or more of the loads 24. While demonstrated as a common block of switching circuitry 26 for a common block of loads 24, it is contemplated that individual portions of the switching circuitry 26 may electrically interpose supplied power and individual loads 24, such that the control circuitry 12 can selectively control the switching circuitry 26 to control power to specific loads 24 based on the current drawn and/or system voltage.

As demonstrated in FIG. 1, the “global” context of the current detection circuitry 22 (e.g., detecting current to multiple loads 24 of the heating systems 14) combined with advanced processing techniques employed by the control circuitry 12 can allow the hardware and software to, in effect, “sense” current drawn by the individual components of the heating systems 14. Thus, while only a “total” current drawn by the heating systems 14 as a whole may be monitored directly, as opposed to current to each load 24 being monitored directly, the advanced processing techniques and methods employed herein can allow the control circuitry 12 to determine multiple states for multiple loads 24 of the heating systems 14 on an individual basis. For example, the control circuitry 12 can logically isolate portions of the signals from one or both of the current detection circuitry 22 and the voltage detection circuitry 20 to determine parameters and/or faults or other conditions of individual loads 24 (e.g., components of the heat pump 16, one or more of the resistance heating elements 18a, 18b).

Referring now to FIG. 2, a functional diagram demonstrates the components of the heating systems 14 relative to a tank 28 of the water heater 10. The heating systems 14 include an electrical-based heating system having a first resistance heating element 18a adjacent an upper portion 30 of the tank 28 and a second heating element 18b adjacent a lower portion 32 of the tank 28. Each resistance heating element 18a, 18b is configured to heat water in the tank 28 and is mounted thereto. In the present example, the resistance heating elements 18a, 18b extend into the tank 28, though it is contemplated that the resistance heating elements 18a, 18b may operably couple to an outer surface 34 of the tank 28 to indirectly heat water in the tank 28 by heating the tank wall. The resistance heating elements 18a, 18b can be electrical elements that generate heat when electrical current passes through the given element due to resistive components of the resistance heating elements 18a, 18b. For example, the resistance heating elements 18a, 18b can be composed of metallic alloys, ceramic materials, or ceramic metals that are configured to generate heat in response to electrical current.

The heat pump 16 includes a compressor 36, a first heat exchanger 38, an expansion device 40 downstream of the first heat exchanger 38, and a second heat exchanger 42 downstream of the expansion device 40. The heat pump 16 can be configured to circulate refrigerant to heat the tank 28 and the water therein. For example, in operation, refrigerant is cycled through a closed-loop system to transfer heat. The cycle begins at the expansion device 40 (e.g., expansion valve), where high-pressure liquid refrigerant is throttled to a low-pressure, low-temperature state. This cooler refrigerant then enters the second heat exchanger 42 (the evaporator), where it absorbs heat from the surrounding environment via air drawn over the evaporator by a fan 44. As the refrigerant absorbs this heat, it evaporates into a low-pressure vapor. The vaporized refrigerant is then drawn into the compressor 36, which increases its pressure and temperature. The high-pressure, high-temperature vapor exits the compressor 36 and flows into the condenser 38, where it releases the absorbed heat to the tank 28. As the refrigerant releases heat, it condenses back into a high-pressure liquid. This liquid then flows back to the expansion device 40, completing the cycle and allowing the process to repeat. By continuously cycling refrigerant through these components, the heat pump 16 effectively moves heat from one location (air) to another (e.g., the tank 28).

The control circuitry 12 is configured to control components of the heat pump 16 based on temperatures of the refrigerant and/or air as measured via heat pump temperature sensors 46 positioned at various points of the heat pump 16. For example, the control circuitry 12 can control the compressor 36 by controlling a first motor 48 that drives the compressor 36. The compressor 36 can be a constant-speed compressor 36. In some examples, the compressor 36 receives only an on command or not an on command (e.g., no speed input). The fan 44 can also be controlled via a second motor 50 that drives the fan 44. The expansion device 40 can include an actuator 52, such as a third motor, that can be controlled via the control circuitry 12. By controlling these devices, the control circuitry 12 can execute a heat pump control algorithm in which water in the tank 28 is heated via the heat pump 16 (e.g., heat transferred from the condenser to the tank 28).

In a first operating mode (“heat-pump only mode”), the control circuitry 12 operates the heating systems 14 such that the resistance heating elements 18a, 18b are not activated, but rather only the heat pump 16 as a heat source is controlled to reach a target temperature. In another operating mode (“hybrid mode”), the control circuitry 12 operates both the heat pump 16 and the first heating element 18a based on heat demand. For example, the first resistance element 18a can be activated on an as-needed basis (e.g., during a warm water demand that cannot be supplied using heated water from the heat pump 16). In “hybrid plus” mode, the control circuitry 12 operates the heat pump 16 and either the first resistance heating element 18a or the second resistance heating element 18b depending on an availability of warmed water. In another operating mode (“electric only” mode) the heat pump 16 is not operated and only one or either of the first and second resistance heating elements 18a, 18b are activated to maintain a heat level.

The control circuitry 12 can operate the water heater 10 in any of heat-pump only mode, hybrid mode, hybrid plus mode, or electric-only mode to heat the tank 28. For example, the heating systems 14 can heat the tank 28 to a target temperature that is based on a temperature setpoint controlled by a user. For example, when a mixing valve 54 is provided for mixing water from an input line 56 from a water utility (“cold water”) and heated water from the tank 28 via an output line 58, the target temperature can exceed the target temperature, such that a temperature of the mixed cold water and warmed water reaches the temperature setpoint. The mixed water can be output via a mixed water line 60. In such an example, the target temperature can be higher than the temperature setpoint. In models in which the mixing valve 54 is omitted, the target temperature can equal the temperature setpoint.

With continued reference to FIG. 2, the temperature of the tank 28 and/or the water therein can be determined using tank temperature sensors 62 that measure temperatures adjacent the upper portion 30 and the lower portion 32. Based on the tank temperature, the control circuitry 12 can activate/deactivate loads 24 of the heating systems 14 to provide the warmed water at the target temperature.

A user interface 64 can be provided in communication with the control circuitry 12 to allow user/technical personnel control of the water heater 10 and for displaying information related to the water heater 10. For example, the user interface 64 can include a display 66 that can indicate different diagnostic conditions, fault conditions, or operating conditions of the water heater 10. By way of example, conditions related to electrical parameter detection (e.g., high or low current, high or low voltage) can be reported via the display 66. The display 66 may be provided with the water heater 10 or with a display remote from the water heater 10. By way of example, the user interface 64 can include an interface of a mobile device executing a software application that allows the water heater 10 and the mobile device to communicate with one another. In this way, the control circuitry 12 can communicatively couple with the user interface 64 via wired or wireless (e.g., Wi-Fi, Bluetooth, etc.) communication.

In general, the control circuitry 12 can be configured to control heating sources based on the refrigerant temperatures, the tank temperature, and the system voltage and current drawn. By utilizing both electrical and temperature monitoring, the control circuitry 12 can provide multiple estimates for operating conditions of the heating systems 14. For example, current to the compressor 36 can be indicative of a condition of the refrigerant, such as one or more temperatures or pressures. The refrigerant temperatures as detected by the heat pump temperature sensors 46 can be compared to the temperatures/pressures estimated based on electrical detection. Based on differences between these values, the control circuitry 12 can determine faults or other conditions of the heating systems 14.

Referring now to FIG. 3, power distribution circuitry for an exemplary water heater 10 is shown. As previously described, the example water heater 10 is a two-phase model (e.g., 240 VAC), though similar circuitry can be provided for a single-phase model (e.g., 120 VAC). For example, the supplied power in the present example can include a first line 68 and a second line 70, each at a voltage level of 120 VAC relative to neutral and 180 degrees apart. In a single-phase model, only the first line 68 can be provided.

The first line 68 and the second line 70 provide the supplied power to a converter 72 and to the switching circuitry 26. The supplied voltage can be conditioned via conditioning circuitry 74 upstream of the converter 72 and the voltage detection circuitry 20. For example, the conditioning circuitry 74 can include circuit components to reduce reactive power, such as a varistor, resistors, and capacitors. The converter 72 converts the supplied power at high 120 VAC signal(s) to a low-voltage direct-current (DC) bus for powering various peripherals of the water heater 10. For example, the temperature sensors 46, 62, the control circuitry 12, the mixing valve 54, or other low-voltage equipment can be powered by the low-voltage circuitry. The converter 72 can include voltage regulator 76, a step-down transformer 78, and a conditioner 80 for providing “clean” voltage or voltages. For example, a filtered 12 VDC and/or 5 VDC voltage can be provided for the peripheral devices and for an operating voltage for the switching circuitry 26 (e.g., a voltage of the activation signals from the control circuitry 12).

With continued reference to FIG. 3, the current detection circuitry 22 can electrically interpose the supplied power and the switching circuitry 26 to monitor current supplied to the heating systems 14, less any ancillary currents (e.g., due to heat). A thermal limiter 81 can electrically interpose incoming power and the current detection circuitry 22 and serve to interrupt current to the sources of heating for the tank 28 when a sensed temperature exceeds a temperature threshold. The thermal limiter 81 can be placed on the tank 28, for example, and be configured to mechanically open the circuit in response to the thermal energy of the tank. The current detection circuitry 22 includes a transformer 82 that produces a secondary current proportional to the current drawn based on a predefined coil ratio of the transformer 82. For example, the transformer 82 can have a 1:1000 coil ratio from the primary side (L168) to the secondary side. A first voltage divider circuit 84 is provided for providing a low voltage representative of the secondary current, and therefore representative of the current drawn by the heating systems 14. A first voltage limiter 86 includes a Schottky diode that is operable to clamp the low voltage signal between a voltage range readable by the control circuitry 12, and a filtering capacitor 88 is provided to filter out high-frequency noise from the low voltage analog signal.

By way of example, the low voltage analog signal can be a voltage between 0 and 3.3 volts DC that is read by the control circuitry 12. The value of the voltage is representative of, or proportional to, the current drawn by the heating systems 14. For example, there may be a linear relationship between the lowest readable voltage (e.g., 0 V) and the highest voltage (e.g., 3.3 V) that is proportional to a linear relationship between a lowest level of current drawn (e.g., 0 amperes) and a highest level of current drawn that is readable by the control circuitry 12. The highest level of current drawn may be higher than a highest “readable current” based on the sizing of resistors of the first voltage divider circuity 84. Thus, while the level of current that can be drawn by the heating systems 14 may exceed the highest readable current, the proportional scaling of the input voltage may be modeled to the highest current level that can be directly read. As will be described further herein with respect to the details of the control circuitry 12, the level of current drawn by the heating systems 14 can be estimated or determined even at current levels higher than the highest current level directly readable by the low voltage analog signal by tracking a sum of readings.

With continued reference to FIG. 3, the switching circuitry 26 can include individual switches 90-98 for interrupting specific loads 24. For example, a first switch 90 may be configured to interrupt supplied power to each of the fan 44, the resistance heating elements 18a, 18b, and the compressor 36. The first switch 90 can therefore serve as a redundancy switch that controls each load 24, such that the redundancy switch can be deactivated when an inoperable condition for the heating systems 14 is detected (e.g., very low supply voltage, a maintenance condition). A pair of second switches 92 are configured to control the supplied power to the fan 44. A third switch 94 electrically interposes supplied power and the first resistance heating element 18a. A fourth switch 96 electrically interposes supplied power and the second resistance heating element 18b. A fifth switch 98 electrically interposes the first switch 90 and the compressor 36, thereby controlling supplied power to the compressor 36. It is contemplated that, while demonstrated as loads 24 operable on two-phase power, the switching circuitry 26 can, in any model (e.g., single-phase), be configured to interrupt the supplied power to the loads 24.

The switches 90-98 can include any type of electrical switching circuitry 26, such as a transistor or relay, that can be selectively activated by the control circuitry 12 in response to electrical signals. In the present example, the switches 90-98 are relays such that, when a control signal is applied to a coil of the relay, normally-open contacts of the relay are closed causing current to flow to the subject load 24. It is contemplated that the signal from the controller 102 may control a transistor that closes a relay that closes a circuit to a target load 24. In any event, the signals from the controller 102 can control the switching circuitry 26 to selectively interrupt or close an activation circuit for a respective load 24 or for one or more of the loads 24.

The control circuitry 12 includes a controller 102 having a processor 104 and a memory 106. The memory 106 can store instructions that, when executed by the processor 104, cause the controller 102 to perform tasks related to control of the water heater 10. The processor 104 may include any computing unit capable of executing instructions, such as a central processing unit (CPU), microcontroller unit (MCU), digital signal processor 104 (DSP), application-specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). The processor 104 may be a single-core or multi-core unit and can be implemented as part of a system-on-chip (SoC) or as a standalone component.

The memory 106 can include any type of storage medium capable of storing data or instructions for execution by the processor 104. This includes volatile memory, such as random-access memory (RAM), and non-volatile memory 106, such as read-only memory (ROM), flash memory, electrically erasable programmable read-only memory (EEPROM), or magnetic or optical storage. The memory 106 may store executable program code, configuration data, sensor readings, or any other type of information necessary for the controller 102 to perform operations related to control of a water heater 10. The memory 106 and processor 104 may be integrated into a single package or exist as separate components interconnected by a bus or other communication means.

The controller 102 may be implemented as a discrete hardware device or as part of a larger system, such as a computer, embedded device, or Internet of Things (IoT) node. It may also include auxiliary components, such as communication interfaces, power management units, and analog-to-digital converters (ADCs) to interact with external devices or sensors. The processor 104 may execute firmware, software, or both, enabling the controller 102 to perform specific functions, such as processing input signals, executing control algorithms, or managing system resources for a water heater 10. For example, the current detection circuitry 22 and the voltage detection circuitry 20 can communicate with the control circuitry 12 via ADCs at the controller 102.

With continued reference to FIG. 3, the controller 102 can receive input signals (e.g., the low voltage analog signal indicative of current drawn and low voltage signals indicative of system voltage) and communicate output signals to the switches 90-98 in response to the input signals to selectively activate the loads 24. During a period of activation of the corresponding loads 24, the input signals can be monitored to detect aberrant electrical conditions or electrical conditions indicative of states of the heating systems 14.

With reference to FIG. 4, a detailed view of the voltage detection circuitry 20 is shown demonstrating frequency and magnitude detection. For example, the voltage detection circuitry 20 includes a magnitude detection circuit 108 and a frequency detection circuit 110. The magnitude detection circuit 108 operates similarly to the current detection circuitry 22 by using a second voltage divider circuit 112, a second voltage limiter 114, and one or more filtering capacitors 88 to provide a low voltage analog signal to the controller 102 representative of a magnitude of the system voltage.

The frequency detection circuit 110 includes a pulse node 116 that is active whenever the system voltage is non-zero. The pulse node 116 is configured to control a frequency switch 118 that closes a circuit to the controller 102 when the system voltage is non-zero. In the present example, the frequency switch 118 is a transistor 120, and the gate of the transistor 120 is energized based on the system voltage. When the gate is energized, a signal to the controller 102 is changed. For example, a neutral, ground, or zero voltage signal can be provided through the frequency switch 118 to the controller 102. Based on the timing of when the zero voltages are detected at the controller 102, the controller 102 can determine a frequency of the system voltage. The frequency and the magnitude can be stored in memory 106. As will be described in detail later in reference to FIGS. 6-11, the control circuitry 12 can determine various parameters of the heating systems 14 using the current drawn, the voltage frequency, and the voltage magnitude.

With continued reference to FIG. 4, each line 68, 70 of power is rectified via a half-wave rectifier 122 that has a common output node 124. In electrical series with each half-wave rectifier 122 is a limiting resistor 126 that is sized to provide the detectable range for the magnitude detection circuit 108. For example, the resistors can “step down” the power draw of the voltage detection circuitry 20 and cooperate with the second voltage divider circuit 112 to provide the low voltage analog signal to the control circuitry 12. Each half-wave rectifier 122 can rectify a given line voltage (e.g., one for the first line 68, the other for the second line 70).

Referring now to FIG. 5, an exemplary heating cycle in hybrid mode is demonstrated via a first graph 128. In this example, the tank temperature is initially above a first temperature threshold T_a for activation of the heat pump 16. Over time, or as warmed water is drawn from the tank 28, the tank 28 temperature drops below the first temperature threshold T_a, triggering activation of the heat pump 16. In an exemplary operation, the fan 44 is activated prior to the compressor 36. For example, and with brief reference to FIG. 3, the controller 102 can communicate a signal to one or more of the second switches 92 to activate the fan 44 (e.g., the combination of second switch 92 can control the speed of the fan 44). These activation signals can follow activation of the redundancy switch 90.

The motor for the fan 44 (the second motor 50) can, in some examples, be less powerful than the motor for the compressor 36 (the first motor 48). In some examples, the second motor 50 can be available between zero Watts (W) and 100 W. In some examples, the second motor 50 can be operable up to 50 W. In some examples, the second motor 50 will draw between about 15 and 30 W during use. Conversely, the first motor 48 can operate in the range of 200 to 1000 W when in use. In some examples, the first motor 48 can operate in the range of 300 and 800 W when in use. Accordingly, the power draw of the second motor 50, and thus the fan 44, can be less than 20% of the power draw of the first motor 48 (the compressor 36). Exemplarily, the second motor 50 is less than 10% of the power of the compressor 36. In some examples, the second motor 50 is configured to draw about 5% or less of the power draw of the first motor 48.

As will be described further in detail in reference to the foregoing figures, first and second motors 48, 50 are inductive loads 24 and therefore have a lagging power factor. A run capacitor and/or a starting capacitor can be provided for running and/or starting the motors 48, 50. The result of running these inductive loads 24 is that the instantaneous current to the motors 48, 50 can vary based on the instantaneous voltage (e.g., the instantaneous magnitude of the system voltage). Accordingly, the current draw shown in the first graph 128 in FIG. 5 is somewhat “noisy” as the run capacitors can discharge sequentially during running of the fan 44 and the compressor 36.

As shown, a “fan section” (P1) of the first graph 128 indicates a low level of current drawn relative to current drawn by both the fan 44 and the compressor 36 in the “compressor section” (P2) in which the fan 44 and the compressor 36 are on. It is contemplated that the fan 44 may be activated for a set time prior to activation of the compressor 36 (e.g., the controller 102 turning on the fifth switch 98). For example, a one-minute or 90-second timer may start when the fan 44 starts to allow some heat to be drawn from the air into the evaporator 38 prior to energizing the compressor 36. Following the timer, the compressor 36 can be activated and the heat pump 16 can begin to heat the tank 28 via the condenser.

In response to the tank temperature falling below a second temperature threshold T_b lower than the first threshold T_a, the control circuitry 12 can communicate a signal to activate the first heating element 18a. The tank temperature falling below the second temperature threshold T_b is indicative of warm water being drawn from the tank 28 at a rate higher than the tank temperature can maintain the target temperature. As shown, activation of the first resistance heating element 18a can cause the tank 28 temperature to begin to increase. When the tank 28 temperature rises above the second threshold T_b, the first element 18a can be deactivated. For example, to active the first resistance heating element 18a, the controller 102 can communicate a control to the third switch 94 to cause the supplied power to be provided to the first resistance heating element 18a, and the controller 102 can withhold the same signal to deactivate the third switch 94 to cause the first resistance heating element 18a to become deactivated.

The resistance heating elements 18a, 18b can be electrical elements having an operable range of between 2 kW and 8 kW. In some examples, the resistance heating elements 18a, 18b can be operable in the range of 3 kW and 6 kW. Exemplarily, the resistance heating elements 18a, 18b can be operable in the range of 3 kW and 5 kW. The power draw of each resistance heating element 18a, 18b is dependent on the resistance. As will be described further herein, the control circuitry 12 can periodically calculate the resistance of each resistance heating element 18a, 18b.

With continued reference to FIG. 5, the first graph 128 includes a “first element section” (PE) corresponding to an activation period for the first element. Following the activation period, the tank 28 temperature continues to rise due to thermal energy from the heat pump 16, residual thermal energy from the activation period of the first resistance heating element 18a, and/or a decrease of warm water draw.

When the temperature rises above the first temperature threshold Ta, the control circuitry 12 can deactivate the heat pump 16. In the present example, this is preceded by a delay (T), though it can occur imminently. The delay can allow the tank 28 to store additional thermal energy to limit reactivation of the heat pump 16 for future uses. It is contemplated that delays such as the one illustrated may be incorporated at some or all of the various control points shown in the first graph 128. For example, shut-down or activation sequences can be started and finished to define a starting or ending period for the loads 24 of the heating systems 14. In the present example, the shut-down sequence of the heat pump 16 takes place after the first temperature threshold T_a has been met for predefined duration.

The exemplary hybrid mode use case shown and described with respect to FIG. 5 demonstrates different levels of current drawn for different stages of activation for the heating systems 14 of the water heater 10. Because the control circuitry 12 can determine a status of the heating systems 14 (e.g., heat pump 16 ON, first resistance element 18a ON), the control circuitry 12 can compare the current drawn, as determined based on the signals from the current detection circuitry 22, to expected current levels for a given condition. Further, as will be described further herein, using known or values electrical parameters of the loads 24 determined via diagnostic testing or pre-programmed, the control circuitry 12 can parse out, or divide, the current drawn into different allocations. For example, with the heat pump 16 and one of the resistance heating elements 18a, 18b on, the control circuitry 12 can measure the total current drawn and allocate an amount of current to each load 24 (e.g., the resistance heating elements 18a, 18b, the compressor 36, the fan 44) with enhanced accuracy.

Referring now to FIG. 6, and generally to FIGS. 1-11, a water heater 10 includes a tank 28 for holding water, a resistance heating element 18a, 18b extending into the tank 28, a heat pump 16, current detection circuitry 22 that communicates a first signal indicative of current drawn by the heat pump 16 and the resistance heating element 18a, 18b, voltage detection circuitry 20 that communicates a second signal indicative of a system voltage, and control circuitry 12. The control circuitry 12 is configured to activate the resistance heating element 18a, 18b for a first activation period, monitor the first signal during the first activation period, deactivate the resistance heating element 18a, 18b to end the first activation period, determine a calculated resistance of the resistance heating element 18a, 18b based on the second signal and the first signal monitored during the first activation period, and calculate a first current drawn by the resistance heating element 18a, 18b using the second signal during the during a second activation period subsequent to the first activation period and the calculated resistance.

The resistance checking technique can additionally or alternatively be employed when the heat pump 16 is in use. For example, and with reference to FIG. 5, the control circuitry 12 can perform the resistance detection based on electrical values captured and stored (e.g., in the memory 106) during the period PE (e.g., when both the heat pump 16 and one of the elements 18a, 18b are in use), and those values can be used to update the value of the resistance. The update to the resistance can occur following ending of the period PE and based on electrical parameters recorded during the period PE. For example, the control circuitry 12 can determine first values of the current drawn and the system voltage during the period PE, then, following the period PE (e.g., when the heat pump 16 is running), determine second values of the current drawn and the system voltage. The control circuitry 12 can calculate a difference in the first value of the current drawn and the second value of the current drawn and use the first value of the system voltage to determine a new estimate for the resistance (e.g., apply Ohm’s law). The new estimate of the resistance can be compared to the previous resistance value that was utilized by the control circuitry 12 during the previous period PE for determining current allocation (e.g., current to the heat pump 16 vs. current the element 18a, 18b). Based on this comparison, the stored resistance value can be updated (e.g., assigned to the new estimated value or iterated upward or downward according to the new estimate).

The resistance checking technique employed by the present water heater 10 can be employed each time the given resistance heating element 18a, 18b is activated as the sole heat source and/or when it is not the sole heat source. For example, while the resistance diagnostic can be performed during operation of the compressor 36, by performing the test without operation of the heat pump 16, the current drawn can be entirely allocated to current to the given resistance heating element 18a, 18b. When the resistance diagnostic is executed during operation of the heat pump 16, the current drawn by the heat pump 16 after the heating element 18a, 18b is deactivated and prior to deactivation can be compared to one another to determine a difference in the current drawn, which can be used along with the system voltage to determine a new resistance value. During the test, the system voltage can be monitored. The control circuitry 12 can divide the system voltage (e.g., an RMS voltage) by the current drawn to calculate the resistance of the resistance heating element 18a, 18b.

While the test can be a standalone diagnostic method performed periodically, it can also, or alternatively, be performed during normal operation. For example, when the resistance heating element 18a, 18b is being used to heat the water in the tank 28, an existing resistance value (calculated from a prior activation period) can be used to determine the current to the resistance heating element 18a, 18b. Following this activation period of the resistance heating element 18a, 18b, the actual current drawn by the resistance heating element 18a, 18b while the heat pump 16 was off and the system voltage during the subsequent activation period can be used to re-calculate the resistance. If the re-calculated resistance is different than the existing value, the control circuitry 12 can update the resistance value. In some examples, the new resistance value is assigned to the calculated resistance. However, in some examples, the control circuitry 12 increments the resistance value up or down depending on the difference between the new resistance compared to the previous resistance value. For example, the resistance can be adjusted by a fixed percentage or quantity commensurate with the difference in resistance. For example, if an original calculated resistance is 14.4 ohms, and a new value is 14.0 ohms, the control circuitry 12 will determine the calculated resistance to be between 14.0 and 14.4. If the increment is 1/8, or 12.5% of the difference, the new resistance can be determined to be 14.35. The increment can include an increase to a greater value (positive increment) or a negative increment (decrement).

As the resistance heating element 18a, 18b age, in some cases, the resistances of the given elements 18a, 18b can change. For example, the resistance may decrease or increase over time. The control circuitry 12 can track the change in resistance and determine a degradation level of the resistance heating element 18a, 18b based on comparisons of new vs. old resistance calculations. For example, when the change reaches a specific percentage of an original calculated resistance (e.g., at commissioning of the water heater 10 or at installation of a new resistance heating element 18a, 18b), the control circuitry 12 can determine a degradation level and communicate a signal to indicate replacement or maintenance.

The control circuitry 12 can calculate a current to the heat pump 16 based on the current drawn and current to the electrical resistance element 18a, 18b. For example, the control circuitry 12 can subtract the current to the electrical resistance element 18a, 18b from the current drawn when the current drawn is determined while the heat pump 16 and one of the electrical heating elements 18a, 18b are in use. For example, by using accurate resistance values, a more exact level of current to the resistance heating element 18a, 18b can be determined, thereby resulting in a more accurate estimate of current to the compressor 36, the fan 44, or a combination of both.

Referring now to FIG. 6, a method M600 for operating a water heater 10 is demonstrated in view of a sequence of activations of the elements 18a, 18b. The method 600 includes activating the resistance heating element 18a, 18b for a first activation period at step M602. For example, and with reference to FIG. 3, the controller 102 can actuate the third switch 94 causing current to be drawn to the first resistance heating element 18a to heat water at the upper portion 30 of the tank 28. At step M604, the current drawn is monitored during the first activation period. For example, the controller 102 can periodically sample a signal from the current detection circuitry 22 that is indicative of the current drawn. At step M606, the resistance heating element 18a, 18b is deactivated. For example, the controller 102 can withhold an activation signal to the third switch 94. The resistance of the resistance heating element 18a, 18b is calculated based on the current drawn and the system voltage at step M608. For example, the controller 102 can execute instructions to divide the system voltage (e.g., the RMS voltage) by the current drawn as monitored during the first activation cycle. In some examples, the system voltage is presumed, or is rounded (120 VAC) to meet standard voltage based on the detected voltage (e.g., 119.2 VAC).

On subsequent cycles of use of the resistance heating element 18a, 18b, the resistance can be updated. If the resistance heating element 18a, 18b is the only heat source (step M612), the method M600 can read a new current and re-calculate the resistance using new current and voltage values at step M614 without subtraction of current to the heat pump 16. If the resistance heating element 18a, 18b is not the only heat source (M612), the method M600 can determine current to the other heating system(s) 14 (e.g., the heat pump 16) by calculating a difference in the current drawn (during and after activation) (M616). This calculation can be performed after the activation period. At step M618, the resistance value is incremented/decremented by a value, such as a percentage (e.g., a fixed increment).

The method M600 can be dynamic, such that the control circuitry 12 can selectively update the resistance or use the existing calculated resistance to determine current to other components of the system. The method M600 can also provide a basis for other methods described herein related to electrical current allocation.

Referring now to FIGS. 7A and 7B, and more generally to FIG. 1-11, the water heater 10 can be configured to adjust one or more trip levels for components of the water heater 10. For example, the trip levels can be current thresholds that are compared to the current drawn. The control circuitry 12 can select one or more current thresholds based on the operational states of the components of the heating systems 14. For example, a set of current thresholds can be assigned by the control circuitry 12 to operation of the fan 44, to the compressor 36, to the elements 18a, 18b, etc. The set of thresholds can include a sequence of thresholds. For example, during of operation of the fan 44 and the compressor 36 and without operation of the elements 18a, 18b, the set of thresholds can include a first current threshold of 5 amps, a second current threshold of 15 amps, and a third current threshold of 25 amps. A plurality of threshold durations, or time periods, can correspond to the plurality of current thresholds, such that the control circuitry can start a timer when a threshold is crossed. The plurality of threshold durations can include a first threshold duration associated with the first current threshold, a second threshold duration associated with the second current threshold, and so on. When the current drawn exceeds the first current threshold, an elapsed time during which the current drawn exceeds the first threshold can be compared to the first threshold duration and, upon exceeding the first threshold duration, cause the control circuitry 12 to interrupt power to the fan 44 and/or the compressor 36 (in this example). The threshold durations can differ from one another based on the level of the corresponding threshold. For example, the first threshold duration can be greater than the second threshold duration, and the second threshold duration can be greater than the third threshold duration. Thus, shorter time can be allotted for higher current draws. This control scheme may limit over-power conditions and/or be applied to the components of the heating systems 14.

The control scheme can be based on the operational status (e.g., activation states) of components of the at least one heating system 14 that heats the tank 28. For example, the control circuitry 12 can be configured to monitor commands to the switching circuitry 26 to “know” what components should be activated and compare the current drawn to the expected current drawn. Thus, the control circuitry 12 can select from a plurality of the thresholds one or more current thresholds based on which components are currently activated. In this way, a first current threshold or a first set of current thresholds can be associated with a first set of activation states (e.g., operating in hybrid plus mode), and a second current threshold or a second set of current thresholds can be associated with a second set of activation states (e.g., operating in hybrid mode). By tracking the activation states of the components, the control circuitry 12 can determine both over-power and under-power conditions. For example, the first threshold can be a minimum threshold that, when not reached but is “expected” to be, causes initiation of a timer programmed in the control circuitry 12. The elapsed time can be compared to the first threshold duration. If the first threshold duration is met, the control circuitry 12 can determine an under-power condition and control the water (e.g., to shut down). For example, one or more components of the at least one heating system 14 can be deactivated.

With continued reference to FIGS. 1-11, a water heater 10 includes a tank 28 for holding water, a resistance heating element 18a, 18b extending into the tank 28, a heat pump 16 including a compressor 36 that compresses refrigerant of the heat pump 16, current detection circuitry 22 that communicates a first signal indicative of a current drawn by the heat pump 16 and the resistance heating element 18a, 18b, and control circuitry 12. The control circuitry 12 is configured to calculate a resistance of the resistance heating element 18a, 18b, determine a first current to the compressor 36 during operation of the compressor 36 and the resistance heating element 18a, 18b based on the first signal and the resistance, compare the first current to a current threshold, and, in response to the first current exceeding the current threshold for longer than a threshold duration, determine a fault of the compressor 36.

Referring briefly back to FIG. 5, a startup condition for the compressor 36 is generally shown in section P2 of the first graph 128. For example, the current drawn may exceed an operating current limit due to the inductive load 24 on the compressor 36 from a cold start. Thus, the startup condition is not a fault of the compressor 36 or the heat pump 16. However, the current spike indicated in section P2 can be effectively ignored, or differentiated, by the controller 102 due to the startup condition not lasting longer than the threshold duration. By way of example, the control circuitry 12 may initiate a timer of 5 seconds following a command to activate the compressor 36. If the current exceeds a threshold current limit (e.g., 15 amperes) for longer than the timer (the threshold duration), the controller 102 can determine a locked rotor condition of the compressor 36 and determine a fault. In response, the controller 102 can operate only the resistance heating elements 18a, 18b regardless of the heating mode including operation of the heat pump 16. If the current spike does not outlast the timer, the controller 102 can continue operation. In this way, the control circuitry 12 can differentiate between a fault condition and a startup condition.

The timer that is started upon exceeding the current threshold can be any timeframe, such as 5 seconds or less, between half of a second (500 ms) and 2 seconds, or the like. In general, the duration can be relatively low (e.g., less than 10 seconds) to allow for the correct determination by the control circuitry 12 as a startup condition or a locked rotor condition.

By way of example, an inrush current of 13 amps can be drawn by the compressor 36 during startup, and the current threshold can be 12 amps. The current threshold can be within 10% of a start-up current drawn by the compressor 36 when the compressor 36 initiates activation. For example, the current threshold can be less than the start-up current and the current for a locked rotor condition. To differentiate between these conditions, the control circuitry 12 can utilize the timer. Whereas the startup current will subside following a delay less than the threshold duration, in the event of a locked-rotor condition, the current drawn will maintain a level exceeding the threshold duration.

At higher current levels (e.g., above 12 amps, above 15 amps, above 20 amps, above 30 amps, above 50 amps), the resolution of the current detection circuit 22 can be limited relative to the resolution at lower currents. For example, the resolution may be 500 mA or 1 Amp at the high current levels. In general, the resolution at the higher currents can be enough to determine between exceeding the current threshold vs. being below the current threshold. However, the current detection circuitry 22 can be limited up to a current threshold. Using the countsum 138 (FIG. 8) of the current drawn, the control circuitry 12 can estimate the current drawn when the current drawn is greater than the current threshold.

As described previously, the current drawn by the compressor 36 can be estimated when the resistance heating element 18a, 18b and the fan 44 are in use at the same time as the compressor 36 using the calculated resistance values and/or calculated currents to the fan 44 (described in relation to FIGS. 10 and 11).

Referring now to FIG. 7A, a method M700 for operating a water heater 10 includes calculating a resistance of the resistance heating element 18a, 18b at step M702. For example, the resistance can be calculated via method M600. At step M704, current to the compressor 36 is calculated based on the current drawn and current to the resistance heating element 18a, 18b at step M706. The compressor 36 current is compared to the current threshold at step M708. At step M710 a determination is made whether the compressor 36 is faulted depending on whether the compressor 36 current is above the current threshold for a threshold duration (e.g., longer than a timer that is started when the current first exceeds the timer). At step M712, the method M700 includes determining a startup condition if the current falls under the current threshold within the timer (e.g., before the timer expires).

In some examples, the timer has a duration of between 500 milliseconds and 2 seconds. In other examples, the timer is 5 seconds. In general, the control circuitry 12 can control the timer to be the time necessary to determine a fault or a startup condition. It is contemplated that the locked rotor conditions can be determined by accounting for current to the fan 44 as well as, or alternatively to, current to the resistance heating element 18a, 18b. For example, as will further be described, the controller 102 can determine current to the fan 44, and this current may be subtracted from the current drawn by the heating systems 14.

Referring now to FIG. 7B, a method M800 for operating a water heater 10 includes communicating a first signal indicative of a current drawn by a component of at least one heating system 14 of the water heater 10 at step M802. For example, the current detection circuitry 22 can communicate the counts 134 indicative of the current drawn by, for example, the fan 44 (though current to any of the components of the heating systems 14 may be monitored). The method M800 includes determining an activation state of the component at step M804. For example, the control circuitry 12 can determine whether the fan 44 is commanded to be ON or OFF. At step M806, at least one current threshold based on the activation state is determined. The method M800 further includes comparing the current drawn to the at least one current threshold at step M808, determining a threshold duration based on the current threshold at step M810, and controlling the water heater 10 in response to the current drawn differing from the at least one current threshold for longer than the threshold duration at step M812.

As previously described, the at least one current threshold can include a plurality of current thresholds each having a corresponding threshold duration. The control circuitry 12 can perform steps of the method 800 to apply one or more of the current thresholds based on the components that are commanded to be activated (e.g., activation states of the components of the heating systems 14). In some cases, the threshold durations for greater current levels are shorter than the threshold durations for lower current levels given the same components activated.

The method 800 can provide for robust over-current and over-current detection by allowing for dynamic adjustment of the current threshold or set of current thresholds applied. By monitoring the activation state of each component, different trip levels can be set for different scenarios, thereby providing enhanced feedback for diagnostics and control.

Referring to FIGS. 8-9B, and more generally to FIGS. 1-11, a water heater 10 includes a tank 28 for holding water, at least one heating system for heating the tank 28, voltage detection circuitry 20 that communicates a first signal indicative of a system voltage, and control circuitry 12. The control circuitry 12 is configured to sum a plurality of instances of the first signal, determine a level of the system voltage based on the sum, and communicate an output to control the water heater 10 based on the level.

In some examples, the output is a power configuration for the water heater 10. The power configuration can be a classification of the input power. The classification can include a magnitude of the system voltage, a frequency of the system voltage, and one or more phases of the system voltage. The power configuration can be stored in the memory 106. The control circuitry 12 can control the water heater 10 and/or perform diagnostics on components of the heating systems 14 based on the power configuration. For example, the control circuitry 12 can determine current thresholds for the components based on the power configuration. The control circuitry 12 can deactivate the heating systems 14 in response to the power configuration. For example, the memory 106 can store a voltage target programmed in the controller 102 which the controller 102 compares the power configuration to. By way of example, the voltage target can be programmed as 120 VAC (RMS), and the control circuitry 12 can detect wiring of a different power configuration (e.g., 240 VAC). In response to a difference between the power configuration and the voltage target, the control circuitry 12 can limit operation of the water heater 10 and/or the heating systems 14.

In some examples, the control circuitry 12 can classify the system voltage as one of 240 volts split phase, 208 volts three phase, 120 volts single phase, and 230 volts single phase (50 Hz) based on the sum. The classification can be based further on a pattern, or distribution of the instances of the first signal (e.g., the system voltage). The classification can be based on the frequency detected using the frequency detection circuitry 110 (FIG. 4). The magnitude detection circuitry 108 and the frequency detection circuitry 110 can each be monitored by the control circuitry 12 to determine the power configuration.

In some examples, the control circuitry 12 can control the switching circuitry 26 to interrupt one or more of the loads 24 in response to the current drawn exceeding a current threshold associated with a given operating condition. The current threshold can be dynamically adjusted by the control circuitry 12 based on the system voltage. For example, if the system voltage is 120 VAC 60Hz, the current threshold may be set less than when the system voltage is 240 VAC 60HZ, which can be different than at 208 VAC 60 Hz, which can be different than at 230 VAC 50 Hz. The system can be configured for higher current trip levels at lower operating voltages with the same hardware. For example, a 208 VAC RMS supply can be two 120 VAC signals 120 degrees apart, while a 240 VAC RMS supply can be two 120 VAC signals split-phase (180 degrees apart). The resulting RMS voltage can be the effective voltage for the heating systems 14 (e.g., configured for 240 VAC), but the resulting current to reach the power required will be different (higher for a 208 VAC system). Accordingly, in some examples, the current thresholds and/or trip levels for the heating systems 14 and/or components thereof can be adjusted by the control circuitry 12 based on the supplied power.

Referring now to FIG. 8, second and third graphs 130, 132 are presented demonstrating exemplary counts 134 of an ADC monitoring the current detection circuitry 22. In this example, five data points, or counts 134, are gathered per half line-cycle (10 counts/cycle) of the system voltage. This is to simplify the concept of ADC counting. In some examples, the ADC can sample 128 counts 134 per cycle. In the example of FIG. 8, the 10 counts 134 per cycle represent the values read by the ADC and stored by the controller 102. Using these counts 134, the controller 102 can calculate the system voltage.

While the second and third graphs 130, 132 of FIG. 8 are in reference to current detection, it is contemplated that such summing and tracking of counts 134 can be applied to the input of the voltage detection circuit in a similar fashion as described.

As previously described with respect to FIGS. 3 and 4, the resistors of the first voltage divider circuit 84 can be selected to provide an operable voltage that provides resolution for the output of the current detection circuitry 22 that is specific to lower levels of current drawn. For example, and as demonstrated in the ADC limit 136 of the second graph 130 in reference to the current detection circuitry 22, the first voltage divider 84 can be configured to limit the signal to a maximum. As shown, the instances of the current drawn output to the controller 102 can be capped by the ADC limit 136. Accordingly, for large current values (e.g., above 15 amperes, above 10 amperes, above 50 amperes), the low voltage provided to the controller 102 is maximized with limited resolution, other than the voltage being at least the ADC limit 136. For example, the ADC limit 136 may be logically aligned with a value of current drawn being 15 amperes (e.g., each count 134 that reaches the limit 136 is indicative of 15 amps). Thus, for a current draw of 20 amperes, the maximum voltage per count 134 to the controller 102 would be the same as for 15 amperes. It is contemplated that the ADC limit 136 is not applicable to the voltage detection circuitry 20 in some examples.

To get accurate but lower-precision current value detection at higher current levels, the control circuitry 12 can also track and store a sum of ADC counts 134 (“countsum”). The countsum 138 can be the sum of counts 134 for a designated period. In this example, a countsum 138 is stored and the value reset after each half line-cycle. Thus, while there is a cutoff at the ADC limit 136, the countsum 138 can still be tracked and correspond to specific current levels or current level ranges. In this way, the controller 102 can determine lower-current levels with significant resolution (e.g., 12-bits), and higher current levels with less resolution (e.g., 6 bits). The countsum 138 corresponding to the current drawn can be used by the control circuitry 12 to estimate or determine that the current drawn exceeds a current threshold.

A countsum 138 of the voltage magnitude and/or the current magnitude can be used by the controller 102 to determine characteristic curves for voltages with differing frequencies. For example, certain ranges of countsums 138 can have pre-programmed correlations (e.g., accessed via a lookup table) to system voltages, such as a 208 VAC signal. Due to the different waveforms generated due to different phases, magnitudes, and/or frequencies, the countsum 138, a pattern of the counts 138, and/or the output of the frequency detection circuitry 110 can be used to distinguish the input power. For example, relations of magnitudes and frequencies of the system voltage can be associated with the countsums 138. In this way, the control circuitry 12 can better estimate system voltage, calculate RMS voltage, and thereby determine overvoltage, undervoltage, or variable-voltage faults. Other conditions can be determined by the control circuitry 12, such as power draw of the individual loads 24 of the heating systems 14.

Referring now to FIG. 9A, a method M900 for operating a water heater 10 includes communicating, by voltage detection circuitry 20, a first signal indicative of a system voltage at step M902, summing a plurality of instances of the first signal at step M904, determining a level of the system voltage based on the sum at step M906, and communicating, by control circuitry 12 of the water heater 10, an output based on the level to control the water heater 10 at step M908.

In some examples, the method M900 can include comparing an RMS voltage to a target voltage and determining a low voltage condition based on the comparison. For example, the low voltage condition can be indicative of a reason for higher-than-typical currents in the heating system 14. By determining the low-voltage condition, the control circuitry 12 can communicate an indication of the low-voltage condition. The output can include at least one signal indicating an anomaly, such as a mismatched voltage, an under-voltage condition, an over-voltage condition, or the like. The output can include a signal or an omission of a signal that interrupts power to the heating systems 14. The output can include the power configuration previously described. In some examples, a detailed message can be presented to place the water heater 10 closer to the voltage source. In some examples, the instructions can be to disconnect the water heater 10 from an extension cord or otherwise reduce the length of a power run (cable) from an outlet to the water heater 10 due to a difference between expected voltage and actual voltage. For example, the extension cord may provide resistance that reduces the power available to the water heater 10.

The method M900 can include classifying the system voltage as 240 VAC RMS or 208 VAC RMS based on the sum of the instances of the system voltage (countsum 138). For example, the controller 102 can calculate the countsum 138 for the voltage readings and correlate the countsum 138 with typical voltage supplies (e.g., 240 VAC RMS, 208 VAC RMS, 230 VAC RMS). The method M900 can also include classifying the frequency using the frequency detection circuitry 110. The frequency and magnitude of the system voltage can allow the controller 102 to determine low or abnormal voltage conditions and determine a fault for power delivery.

Referring now to FIG. 9B, a table representative of possible power configurations determined by the control circuitry 12 is illustrated. As illustrated, the control circuitry 12 can distinguish between various power inputs, such as 230 VAC single phase 50Hz, 240 VAC split phase, 120 VAC single phase, and 208VAC two phase (of three phases). In an exemplary operation, the control circuitry 12 can determine 230VAC at 50 Hz and/ or 240 VAC two-phase without using the countsum 138. The countsum 138 can be used to distinguish between 120 VAC single phase and 208 VAC three phase (two phases). A relatively low countsum 138 can be determinative of 120 VAC and a high countsum 138 can be determinative of 208 VAC three phase. For example, the 120-degree phase shift of the two phases for 208 VAC can provide greater power than 120 VAC, which can be detected using the countsum 138. The control circuitry 12 can store the values of the table and thereby classify the output (e.g., the power configuration) based on the countsum and/or the frequency.

Referring now to FIGS. 1-11, a water heater 10 includes a tank 28 for holding water, a resistance heating element 18a, 18b extending into the tank 28, a heat pump 16 including a compressor 36 that compresses refrigerant of the heat pump 16, and a fan 44 that draws air to a heat exchanger of the heat pump 16, voltage detection circuitry 20 that communicates a first signal indicative of a system voltage, current detection circuitry 22 that communicates a second signal indicative of a current drawn by the heat pump 16 and the resistance heating element 18a, 18b, and control circuitry 12. The control circuitry 12 can be configured to determine a first current to the compressor 36 and calculate a second current to the fan 44 based on the first current and the current drawn when the compressor 36 and the fan 44 are both on.

In some examples, the second current is at most 10% of the first current. In this way, the fan 44 can operate similar to that previously described with respect to the difference between the first motor 48 and the second motor 50. The control circuitry 12 can be configured to determine a blockage of the fan 44 based on current to the fan 44. For example, in the event of a lower current than expected for the fan 44, the controller 102 can determine that the air resistance for the fan 44 is low. In some examples, following determining a blocked fan 44, the control circuitry 12 can communicate one or more signals to indicate the blocked condition or otherwise control the heat pump 16 to deactivate in response to the blocked condition of the fan 44.

In some examples, the controller 102 subtracts current to the resistance heating element 18a, 18b calculated based on the resistance calculated in method M600. In this way, current to the fan 44 can be estimated.

Referring now to FIG. 10, a fourth graph 140 indicates an exemplary current draw for operating the heat pump 16 in reference to a line cycle of the system voltage. As shown, the actual current drawn during operation of the heat pump 16 is not a smooth sinusoid. In the example shown, current draw rises when following a rise in voltage. The voltage plotted in FIG. 10 is an absolute value, or magnitude, of the AC voltage. This section P3 is demonstrative of the run capacitor for the compressor 36 charging and discharging current. At section P4, the first motor 48 draws current to reach a first peak 142. However, during current draw of the first motor 48, the current for the run capacitor of the fan 44 is drawn to a second peak 144 higher than the first peak 142 in section P5. The second peak 144 is aligned with the maximum of the system voltage. This is due to the capacitor of the second motor 50 charging then discharging. An overlay of a plot of current without operation of the fan 44 is shown in a dashed line demonstrating indicating what the current drawn may look like without the second peak 144 from the fan 44 current (including the first peak 142). Thus, adjacent a maximum of each of the system voltage (e.g., where the first peak 142 would occur) and the current drawn is a current spike that is indicative of the fan 44 in operation. The control circuitry 12 may be configured to distinguish between these conditions using the signals from the current detection circuitry 22 (e.g., the counts 134), or another value based on the counts 134 (e.g., countsum 138).

Using the current detection techniques previously described, the controller 102 can isolate the fan 44 current and classify the blockage condition based on the current spikes. For example, smaller spikes can correspond to lower current and, therefore, less air resistance for the fan 44.

In general, the second peak 144 can be above the expected first peak 142. Thus, the second peak 144 can be adjacent the first peak 142 in terms of timing. The control circuitry 12 estimates the current drawn by summing a plurality of readings of the current drawn, as previously described (countsum 138) and calculating an instantaneous RMS current of the current drawn. For example, the size (e.g., area under the curve) of the peak of the fan 44 current can be representative of current drawn by the fan 44.

By way of example, the spike of current adjacent the first peak 142 to the second peak 144 is indicative of the run capacitor of the second motor 50 charging and discharging. The size and relative maximum current is indicative of a blockage condition. For example, in a blocked condition, the spike of current allocated to the fan 44 can be 200 milliamperes, whereas a typical spike may be 400 milliamperes. Other amperage ranges are possible and, in general, the control circuitry 12 can determine these ranges over time. It is further contemplated that the current spike can take forms other than shown in FIG. 10. For example, the current spike can itself have a “spike” relative to other portions of the spike. In other words, the current spike can have several spikes, with one spike being higher (higher current) than others. The maximum, or approximate maximum, can be considered the second peak 144 by the control circuitry 12.

Referring now to FIG. 11, a method M1100 for operating a water heater 10 includes determining a current drawn by the heating systems 14 at step M1102. At step M1104, current to the compressor 36 is determined. For example, the expected first peak 142 can be calculated. At step M1106, current to the fan 44 is determined as described. For example, the controller 102 can determine the peak current (step M1108) and identify a current spike adjacent the peak current (step M1110). At step M1112, an operating condition of the fan 44 is determined. For example, a blockage condition can be determined by the control circuitry 12 based on a magnitude of the spike in section P5. In some examples, an inoperable condition of the second motor 50 is determined based on the fan 44 current.

In general, the water heater 10 disclosed herein can provide for enhanced detection and monitoring techniques of electrical parameters for heating systems 14 of the water heater 10. The specialized and targeted approach to current and voltage detection can be used to attain precision at lower levels of power and sufficient accuracy in high-power conditions. Further, the present detection techniques can allocate current draw to specific components while requiring hardware for a “global” current detection. In this way, local current detection circuits specific to individual components may be omitted.

Claims

1. A water heater comprising:

a tank for holding water;

a component of at least one heating system that heats the tank;

current detection circuitry that communicates a first signal indicative of a current drawn by the component; and

control circuitry configured to: determine an activation state of the component; determine at least one current threshold based on the activation state; compare the current drawn to the at least one current threshold; determine a threshold duration based on the current threshold; and in response to the current drawn differing from the at least one current threshold for longer than the threshold duration, control the water heater.

2. The water heater of claim 1, wherein the at least one current threshold includes a first current threshold and a second current threshold greater than the first current threshold, and wherein the control circuitry is configured to select one of the first current threshold and the second current threshold for comparison to the current drawn based on the current drawn.

3. The water heater of claim 2, wherein when the first and second current thresholds are less than the current drawn, the one of the first current threshold and the second current threshold is the greater of the first current threshold and the second current threshold.

4. The water heater of claim 2, wherein the control circuitry is configured to:

apply a first threshold duration when the current drawn exceeds the first current threshold and is less than the second current threshold; and

apply a second threshold duration when the current drawn exceeds the second current threshold.

5. The water heater of claim 4, wherein the second threshold duration is shorter than the first threshold duration.

6. The water heater of claim 1, wherein the at least one heating system includes a plurality of heating systems each having a corresponding activation state, wherein the at least one current threshold includes a first current threshold corresponding to a first set of activation states and a second current threshold corresponding to a second set of activation states different from the first set of activation states.

7. The water heater of claim 6, wherein controlling the water heater includes deactivating a component of a most-recently activated one of the plurality of heating systems.

8. The water heater of claim 6, wherein the first heating system includes a resistance heating element, and wherein the second heating system includes a heat pump including a compressor that compresses refrigerant of the heat pump.

9. The water heater of claim 7, wherein the first signal is indicative of current drawn by a total of a first current to the resistance heating element and a second current to the heat pump, wherein the control circuitry is configured to, in response to the current drawn falling below the at least one current threshold after exceeding the at least one current threshold and before exceeding the threshold duration, determining a startup condition of the compressor.

10. The water heater of claim 1, wherein the compressor includes a motor, wherein controlling the water heater includes determining a locked condition of a rotor of the motor.

11. A water heater comprising:

at least one heating system including a component;

current detection circuitry that communicates a first signal indicative of a current drawn by the component; and

control circuitry configured to: determine an activation state of the component; determine at least one current threshold based on the activation state; compare the current drawn to the at least one current threshold; determine a threshold duration based on the current threshold; and in response to the current drawn exceeding from the at least one current threshold for longer than the threshold duration, control the water heater.

12. The water heater of claim 11, wherein the at least one current threshold includes a first current threshold and a second current threshold greater than the first current threshold, and wherein the control circuitry is configured to select one of the first current threshold and the second current threshold for comparison to the current drawn based on the current drawn.

13. The water heater of claim 12, wherein when the first and second current thresholds are less than the current drawn, the one of the first current threshold and the second current threshold is the greater of the first current threshold and the second current threshold.

14. The water heater of claim 12, wherein the control circuitry is configured to:

apply a first threshold duration when the current drawn exceeds the first current threshold and is less than the second current threshold; and

apply a second threshold duration when the current drawn exceeds the second current threshold.

15. The water heater of claim 14, wherein the second threshold duration is shorter than the first threshold duration.

16. The water heater of claim 11, wherein the at least one heating system includes a plurality of heating systems each having a corresponding activation state, wherein the at least one current threshold includes a first current threshold corresponding to a first set of activation states and a second current threshold corresponding to a second set of activation states different from the first set of activation states.

17. The water heater of claim 16, wherein controlling the water heater includes deactivating a component of a most-recently activated one of the plurality of heating systems of the plurality of heating systems.

18. A method for operating a water heater comprising:

communicating a first signal indicative of a current drawn by a component of at least one heating system of the water heater;

determining an activation state of the component;

determining at least one current threshold based on the activation state;

comparing the current drawn to the at least one current threshold;

determining a threshold duration based on the current threshold; and

controlling the water heater in response to the current drawn differing from the at least one current threshold for longer than the threshold duration.

19. The method of claim 18, wherein the at least one current threshold includes a first current threshold and a second current threshold greater than the first current threshold, and wherein the control circuitry is configured to select one of the first current threshold and the second current threshold for comparison to the current drawn based on the current drawn.

20. The method of claim 19, comprising:

applying a first threshold duration when the current drawn exceeds the first current threshold and is less than the second current threshold; and

applying a second threshold duration when the current drawn exceeds the second current threshold.