Patent ID: 12209774

In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments described in detail in the following description.

Referring first toFIGS.1and2, a water heater10is shown having a housing or a cabinet12. The cabinet12includes a back plate14and a plurality of sidewalls16,18,20,22surrounding an interior cavity24within the cabinet12. The back plate14is able to be mounted to a wall (not shown) in order to mount the cabinet12to the wall. The housing12also includes a cover26or removable or hinged door26configured to allow access to the interior24of the cabinet12.

As shown inFIG.3, the water heater10includes a flow path28that extends from an inlet30of the cabinet12to an outlet32of the cabinet12. In the representative embodiment of the invention, the inlet30is disposed in the bottom sidewall20of the cabinet12and the outlet32is disposed in the left sidewall16of the cabinet12. In varying embodiments of the invention, the inlet30and the outlet32may be disposed in any of the sidewalls16,18,20,22of the cabinet12.

The controller38is further in communication with a user interface40. In the representative embodiment of the invention, the user interface40is disposed within the cabinet12and visible through the cover26, when the cover26is closed. Further yet, it is contemplated that the controller may detect whether the cover26is open/removed or closed. Additional capabilities of the user interface40will be described later and in further detail. In other embodiments of the invention, the controller38may also be in communication with a communication interface41exterior to the cabinet12by way of a Modbus communication protocol.

In the representative embodiment of the invention, the fluid or flow path28extends from the inlet30to the outlet32by way of a number of vertically oriented channels42connected sequentially by way of a number of upper junctions44and lower junctions46configured to navigate the flow path28through the interior24of the cabinet12. The inlet30is connected to the first channel42by way of an inlet channel29and an inlet junction31. As shown inFIG.4, the inlet channel29extends from the inlet30to the inlet junction31. The inlet junction31then transitions the flow path28to the first channel42to direct water through the water heater10. Similarly, the outlet32is connected to the last channel42by way of an outlet junction33. As shown inFIG.4, the outlet junction33transitions the flow path28from the last channel42to the outlet32. In other embodiments of the invention, it is contemplated that an outlet channel may be disposed between the outlet junction33and the outlet32.

As shown inFIGS.3and4, each lower junction46may include a drain port47configured to assist in draining the fluid from the flow path28of the water heater10, if necessary. In the representative embodiment of the invention, each drain port47is configured to drain the two channels42that are connected to the specific lower junction46having that drain port47. By disposing a drain port47in each lower junction46, every channel42is able to be drained via gravity.

The water heater10further includes a number of heating elements48that are disposed in one or more respective channels42of the flow path28. In the representative embodiment of the invention, the heating element48is disposed in each channel42. However, it is contemplated that varying embodiments of the invention may dispose any number of heating elements48including zero in each channel42.

An inlet temperature sensor34is disposed within the cabinet12and along the flow path28at a location between the inlet30and the heating elements48to measure an inlet temperature of the water heater10. In varying embodiments of the invention, the inlet temperature sensor34may be disposed at a location adjacent the inlet30, adjacent a flow meter54, or any other location before the first heating element48. Similarly, an outlet temperature sensor36is disposed within the cabinet12and along the flow path28at a location between the outlet32and the heating elements48to measure an outlet temperature. In the representative embodiment of the invention, the outlet temperature sensor36is disposed adjacent the outlet32. In different embodiments of the invention, the outlet temperature sensor36may be disposed at any location between the outlet32and the final heating element48. The water heater10includes a controller38in communication with the inlet temperature sensor34and the outlet temperature sensor36so as to receive the measured inlet and outlet temperatures, respectively.

The water heater10also includes a number of intermediate temperature sensors50disposed at one or more of the upper junctions44of the flow path28. While the representative embodiment of the invention depicts an intermediate temperature sensor50at each upper junction44, it is contemplated that varying embodiments of the invention may include any number of temperature sensors50including zero disposed at each upper junction44. In an alternative embodiment of the invention, any number of temperature sensors50could also be disposed at each lower junction46. Further yet, other embodiments of the invention could include any number of temperature sensors50disposed at various locations along the flow path28. Each intermediate temperature sensor50measures an intermediate temperature of the fluid within the flow path28at a location between adjacent heating elements48. In turn, the controller38is in communication with each intermediate temperature sensor50to measure the intermediate temperature at various locations along the flow path28. As stated above, the representative embodiment of the invention includes an intermediate temperature50between each heating element48.

Via communication with the controller38, the user interface40is able to show the measured inlet, outlet, and intermediate temperatures to the user via a display52, such as, but not limited to a liquid crystal display (LCD). The controller38is also able to provide the measured inlet, outlet, and intermediate temperatures to the communication interface41. The controller38is configured to operate the heating elements48based on one or more of the measured inlet, outlet, and intermediate temperatures throughout the flow path28in order to bring the outlet temperature to a predetermined set point water temperature. The display52of the user interface40and the communication interface41are also able to display the predetermined set point water temperature to a user and allow the user to adjust the predetermined set point water temperature. In embodiments of the invention in which the water heater10used in conjunction with a safety application, such as, but not limited to an eye wash or shower application, the predetermined set point water temperature may be set at a certain value, such as 80° F. (26.7° C.), that is not adjustable by the user.

The water heater10further includes a flow rate sensor54disposed along the flow path28to measure the flow rate of the fluid within the flow path28. In the representative embodiment of the invention, the flow rate sensor54is disposed at a location between the inlet30and the first channel42. More specifically, the flow rate sensor54is disposed between the inlet channel29and the inlet junction31. In the representative embodiment of the invention, the flow rate sensor54may be coupled to the inlet channel29via a junction35. In varying embodiments of the invention, the flow rate sensor54may be disposed at any location along the flow path28between the inlet30and outlet32of the cabinet12.

In turn, the controller38is in communication with the flow rate sensor54so as to receive the measured flow rate. The controller38is able to use the measurements of the flow rate sensor54to determine the direction of the fluid flowing through the flow path28. When the fluid is flowing from the inlet30to the outlet32, the controller38determines the fluid is moving in a forward flow. Conversely, when the fluid is still or flowing from the outlet32to the inlet30, the controller38determines the flow fluid of the fluid to be zero. In other embodiments of the invention, when the fluid is flowing from the outlet32to the inlet30, the controller38may be able to determine the fluid is moving in a reverse flow.

In the representative embodiment of the invention, the controller38is configured to enable or disable operation of the one or more heating elements48based upon the measured flow rate. For instance, the controller38would enable operation of the heating elements48if the measured flow rate is greater than a predetermined activation flow rate. Conversely, the controller38would disable operation of the heating elements48if the measured flow rate was less than a predetermined deactivation flow rate. Additionally, the controller38would disable operation of the heating elements48if the measured flow rate was determined to be a zero flow or a reverse flow.

As stated above, the controller38is also in communication with the user interface40. The display52of the user interface40is able to show the user the measured flow rate of the fluid within the flow path28. In the preferred embodiment of the invention, the forward flow is depicted with a positive value, while the reverse flow is depicted with a negative value.

The heating elements48discussed above are monitored by the controller38so that the controller38may determine the current of each heating element48. In the preferred embodiment of the invention, the controller38may compute the current of each heating element48in Amperes, root mean squared (Arms). As the controller38is in communication with the user interface40and the communication interface41, the controller38is able to communicate the current of each heating element48to the user interface40and its display52and the communication interface41. As a result, a user is able to read the current of each heating element48on the display52.

As shown inFIG.3, the water heater10may include one or more of a bimetal thermal switch56, fuse57, contactor58, and solid-state relay60electrically coupled to each other and disposed within the cabinet12. In the representative embodiment of the invention, the bimetal thermal switches are shown as a bank of bimetal thermal switches56disposed in each of the channels42of the flow path28. In other embodiments of the invention, a bank of bimetal thermal switches56may be disposed in any number of channels42of the flow path. Further, the representative embodiment of the invention, shows the fuses57in groups of fuse banks. The purposes of these features are described below.

The controller38is able to monitor the state of the banks of bimetal thermal switches56. Further, the controller38is configured to enable or disable operation of the contactors58and the heating elements48based on the state of the bimetal thermal switch56. For instance, when any of the banks of bimetal thermal switches56opens, the current to the respective contactor58is interrupted and the circuit is open. If the controller38detects that any of the banks of bimetal thermal switches56are open as a result of at least one of the bimetal thermal switches within the bank56being in a fault condition, the controller38is able to report the open circuit and fault condition to the user interface40and communication interface41. In turn, the controller38shuts down the remaining contactors58to disable all the heating elements48. Conversely, if the controller38detects that the banks of bimetal thermal switches56are closed as a result of none of the bimetal thermal switches within the banks56being in a fault condition, the controller38enables the heating elements48. As the controller38is in communication with the user interface40, the controller38is able to communicate the status of each bank of bimetal thermal switch56to the user interface40and its display52.

The controller38is able to individually engage and disengage each contactor58when the bimetal thermal switches56are in a closed state and not a fault condition. That is, when a thermal overload or fault condition is detected, the bimetal thermal switches56are automatically tripped and put in an open state. When the bimetal thermal switches56are in the open state, the contactors58are automatically disengaged so as to remove power from the heating elements48. The controller38further monitors the status of each contactor58and bank of fuses57and reports the status of each contactor58and bank of fuses57to the user interface40and the communication interface41.

As stated above, the controller38disengages the contactors58when a fault condition is detected. Further, the controller38does not allow the contactors58to reengage until each fault condition has been removed and acknowledged by the user/operator at the user interface40or the communication interface41.

To extend operating life of the contactors58, the controller38does not change the state of the contactors58while current is flowing through it. That is, the contactors58are engaged and disengaged when the solid-state relays60are off to prevent current from flowing through the contactors58when the contactors58are being engaged or disengaged.

The water heater10may also include a cabinet temperature sensor62disposed within the cabinet12and configured to measure the temperature of the interior24of the cabinet12of the water heater10. The controller38is in communication with the cabinet temperature sensor62and receives the measured cabinet temperature from the cabinet temperature sensor62. Via communication with the controller38, the user interface40is able to show the measured cabinet temperature to the user via a display52. The controller38may also provide the measured cabinet temperature to the communication interface41.

In certain embodiments of the invention, a cabinet heater64may be disposed within the interior24of the cabinet12. In such embodiments, the controller38may activate or deactivate the cabinet heater64based on the measured cabinet temperature. For example, the controller38may be configured to activate the cabinet heater64when the measured cabinet temperature is below a predetermined activation temperature, such as, but not limited, to 40° F. Conversely, the controller38may be configured to deactivate the cabinet heater64when the measured cabinet temperatures is above a predetermined deactivation temperature, such as, but not limited, 55° F. It is further contemplated that this feature may be enabled or disabled from either the user interface40or the communication interface41.

Further, the water heater10may include a cabinet pressure sensor66disposed with cabinet12and configured to measure the pressure within the interior24of the cabinet12. The controller38is in communication with the cabinet temperature sensor66and receives the measured cabinet pressure from the cabinet pressure sensor66. Via communication with the controller38, the user interface40is able to show the measured cabinet pressure to the user via a display52. The controller38may also provide the measured cabinet pressure to the communication interface41.

In embodiments of the invention including the cabinet pressure sensor66, the controller38may disable or enable the heating function of the heating elements48in response to the measured cabinet pressure. For example, the controller38may disable the heating elements48when the measured cabinet pressure is below a predetermined deactivation pressure. Conversely, the controller38may enable the heating elements48when the measured cabinet pressure is above a predetermined activation pressure. The predetermined deactivation pressure and predetermined activation pressure may be adjusted by the user at the user interface40or the communication interface41.

Referring again toFIGS.1-3, the cabinet12includes a power opening68disposed in one of the sidewalls16,18,20,22of the cabinet12. The representative embodiment of the invention depicts the power opening68disposed in the top sidewall22of the cabinet12. The power opening68is configured to receive a power connection or wire harness106. The power connection106is electrically coupled to a power distribution block70within the cabinet12. In turn, the power distribution block70distributes power to the above described elements within the water heater10.

The controller38is also able to determine the electrical power supplied throughout the water heater10via the power connection106. For example, the controller38is able to measure the current traveling through the heating elements48to determine the condition of the electrical power supplied throughout the water heater10. In turn, the controller38is able to detect a power down condition in which the water heater10is powered down. Similarly, the controller38is able to detect a brown out condition within the water heater10due to a drop in voltage. Additionally, the controller38is able to detect a remote reset condition of the water heater10, in which the water heater10and its systems are reset. Since the controller38is in communication with the user interface40and the communication interface41, the controller is able to report the power down condition, brown out condition, the remote reset condition, and the state of all onboard power supplies to the user interface10and the communication interface41. The user interface40is then able to display such conditions to the user via the display52.

In varying embodiments of the invention, it is contemplated that the water heater10may include a global positioning system (GPS)72disposed within the cabinet. In such instances, the controller38may communicate with the GPS72to provide the GPS coordinates of the water heater10to the user interface40and the communication interface41.

Referring now toFIG.5, a schematic of the water heater10divides the above described elements of the water heater10into a number of systems. For instance, the water heater10includes a plumbing system74, an electrical system76, and an enclosure system78. The plumbing system74incorporates multiple functions including, but not limited to, a temperature sensor function80, a flow sensor function82, an inlet function84, an outlet function86, a vessel function88, and a heating function90. The electrical system76also includes a number of functions including, but not limited to, a power input function92, a thermal overload protection function94, a control function96such as controller38, a contactor function98, a power switch function100, and the user interface40. Meanwhile, the enclosure system78includes a back plate function102in the form of the back plate14to mount the water heater10to the wall and a cover function104in the form of the cover26and the cabinet12to enclose the interior24of the water heater10.

The temperature sensor function80includes the previously discussed inlet temperature sensor34, outlet temperature sensor36, and intermediate temperature sensors50. As discussed above, the control function38monitors the measured temperatures of the temperature sensors34,36,50of the temperature sensor function80.

The flow sensor function82includes the previously discussed flow sensor54. As described above, the flow sensor54detects both the direction and flow rate of the water flowing through the flow path28within the plumbing system74.

The inlet function84is disposed at the inlet30of the cabinet12and connects the flow path28of the plumbing system74to a water source (not shown). In addition, the inlet function84may also direct water from the water source to the power switch function100to cool a heat sink of the power switch function100. For example, as shown inFIG.3, the solid-state relays60are disposed adjacent the inlet channel29. As a result, the colder water in the inlet channel29assists in cooling the solid-state relays60. The inlet temperature sensor34of the temperature sensor function80is included within the inlet function84.

The outlet function86is disposed at the outlet32of the cabinet12and connects the flow path28of the plumbing system74to an external plumbing hardware (not shown) to deliver the water heated by the water heater10. Such external plumbing hardware may include a tepid valve. The outlet temperature sensor36of the temperature sensor function80is included within the outlet function86.

The vessel function88includes the flow path28, while the heating function90includes the heating elements48disposed along the flow path28. As such, the heating of the water traveling through the flow path28occurs within the vessel function88and by the heating elements48of the heating function90.

As previously discussed, the user interface40allows a user/operator to adjust various parameters of the water heater10, such as set point temperatures, activation flow rates, etc. The user interface40also provides operating information to the user/operator such as temperatures, flow rates, error signals, etc.

The power input function92accepts the power connection106and distributes the power therefrom to the controller38and contactors58of the contactor function98through electrical circuit protection and step-down transformers.

The thermal overload protection function94monitors whether the bimetal thermal switches56are open or closed due to a thermal overload. The thermal overload protection function94works with the controller38to enable the contactor function98under normal operating conditions, while disabling the contactor function98when a thermal overload condition is detected at the vessel function88.

That is, the contactor function98connects the power input function92to the power switch function100based on the state of the thermal overload protection function94while under the command of the controller38. As a result, the thermal overload protection function94provides another means of protection when the controller38can no longer control the heating elements48properly.

The power switch function100controls the electrical energy being provided to the heating elements48. In the representative embodiment of the invention, the power switch function100includes the above described solid-state relays60. The controller38determines the amount of electrical energy provided by the power switch function100to the heating element48. The heating elements48then convert the electrical energy provided by the power switch function100to thermal energy in order to heat the water within the flow path28.

As described above, the controller38manages the user interface40, the communication interface41, monitors the thermal overload protection function94, monitors the temperature sensor function80, monitors the flow sensor function82, controls the contactor function98, and controls the power switch function100. The controller38determines the amount of electrical energy provided by the power switch function100based on the data received by the temperature sensor function80and the flow sensor function82.

As previously discussed, the user interface40includes a display52that is configured to display statistics of the water heater10to a user. The display52is able to cycle through a number of screens.FIGS.6-14illustrate various screens of the display52. As shown inFIG.6, a main screen108displays the set point water temperature. The set point water temperature may be displayed in units such as degrees Fahrenheit and degrees Celsius. As stated above, the user would be able to adjust the set point water temperature via inputs53on the user interface40. Further yet, it is contemplated that the user would be able to adjust the units of the set point water temperature via the inputs53. The main screen108may also display the outlet temperature measured by the outlet temperature sensor36. The outlet water temperature may be displayed in units such as degrees Fahrenheit and degrees Celsius. The main screen108may also display the water flow rate measured by the flow rate sensor54. The water flow rate may be displayed in units such as gallons per minute (GPM), liters per minute (LPM), or liters per second (LPS). Finally, the main screen108may also display the power delivered to the water by way of the heating elements48. WhileFIG.6illustrates the power being displayed in kilowatts, other embodiments of the invention may use other units of measurement.

In the representative embodiment of the invention, the inputs53are in the form of a four-button keypad. In other embodiments of the invention, the inputs53may be in the form of a keypad having any number of buttons. In yet other embodiments of the invention, the display52may be in the form of a touch screen with the inputs53integrated into the display52.

In the representative embodiment of the invention, the display52may be changed from the main screen108to other display screens. A menu screen110may be used to navigate the display52through the number of display screens. As shown inFIG.7, the menu screen may list a menu of elements within the water heater10(e.g., Bimetal Status, Contactor Status, Fuse Status, System Status, Temperature Sensors, Flow Sensor, Current Sensors, etc.). The user uses the inputs53to navigate the menu and select which display screen the user would like to proceed to in order to analyze the status of specific elements of the water heater10. As such, the user is able to transition between the main screen and the screens described below via the inputs53of the user interface40.

For instance, the user may select “Bimetal Status” to proceed to a bimetal status screen112. As shown inFIG.8, the bimetal status screen112is configured to illustrate the status of each bank of bimetal thermal switches56(e.g., Bank 1, Bank 2, Bank 3, Bank 4, etc.). Each status is configured to indicate whether that specific bank of bimetal thermal switches56is functioning normally, in a fault condition, or not active.

Similarly, the user may select “Contactor Status” to proceed to a contactor status screen114, which is shown inFIG.9. In the representative embodiment of the invention, the contactor status screen114is configured to show the status of each bank of contactor58(e.g., Bank 1, Bank 2, Bank 3, Bank 4, etc.). Each status is configured to indicate whether the specific bank of contactors58is functioning normally or not active.

Upon selection of “Fuse Status”, the display52proceeds to a fuse status screen116. As shown inFIG.10, the fuse status screen116depicts the status of each bank of fuses57(e.g., Bank 1, Bank 2, Bank 3, Bank 4, etc.). Each status depicts whether the specific bank of fuses57is functioning normally or in a fault condition.

Selection of “Temperature Sensors” from the menu screen110transitions the display52to the temperature sensor screen118shown inFIG.11. The temperature sensor screen118is configured to show the measured temperatures from the input temperature sensor34, the output temperature sensor36, and each of the intermediate temperature sensors50(e.g., T1, T2, T3, T4, T5, etc.). WhileFIG.11depicts the measured temperatures as being shown in degrees Fahrenheit, it is contemplated that the user can adjust the units of the measured temperatures between degrees Fahrenheit and Celsius.

Upon selection of “Flow Sensor” from the menu screen110, the display52transitions to the flow sensor screen119shown inFIG.12. The flow sensor screen119is configured to show the measured flow rate of the fluid through the flow rate sensor54(e.g., Flow). WhileFIG.12depicts the measured flow rate as being shown in gallons per minute, it is contemplated that the user can adjust the units of the measured flow rate between a number of units, such as, but not limited to, gallons per second, liters per minute, or liters per second.

The user may select “System Information” from the menu screen110to transition the display52to the system information screen120. As shown inFIG.13, the system information screen120includes information regarding the water heater10. Such information includes the model, serial number, and manufacturing information of the water heater10.

Finally, the user may select “Current Sensors” to transition the display to the current sensor status screen122, which is shown inFIG.14. In the representative embodiment of the invention, the current sensor status screen122depicts the current being drawn by each bank of heating elements48(e.g., Bank 1, Bank 2, Bank 3, Bank 4, etc.).

Other screen alternatives a screen that displays the inlet temperature measured by the inlet temperature sensor34, the intermediate temperatures measured by the intermediate temperature sensors50, and the outlet temperature measured by the outlet temperature sensor36. The temperatures may be displayed in units such as degrees Fahrenheit and degrees Celsius. Such a screen could also display the status of the bimetal thermal switches56and allow a user to clear the fault condition of any bimetal fuse56.

The display52may also be configured to display another screen in which a user is able to toggle the water heater10between a test mode and a normal operating mode. Features of the test mode will be described in further detail below. In the test mode, the controller38allows each contactor58to be engaged or disengaged from the user interface40or the communication interface41. Further, the controller38allows each bimetal fuse56to be set to a fault state from the user interface40or the communication interface41during the test mode.

In addition, it is contemplated that the controller38may include a real-time clock/calendar (RTCC) having time and calendar values. The time and calendar values are communicated to the user interface40and the communication interface41. In addition, the time and calendar values may be modified by the user interface40and the communication interface41.

Further, the controller38may be programmed with a means for locking out a user from the user interface40in order to prevent an on-site user from unintentionally modifying the settings of the water heater10. The controller38then includes a means for reactivating the user interface40for use by a user. For instance, a user password may be entered into the inputs43of the user interface40to toggle the controller38between locking out the user interface40and unlocking the user interface40.

The controller38provides the means to control the outlet water temperature by preferably employing a Feed-forward plus proportional, integral, and derivative (PID) control, PID control, and linear quadratic tracking (LQT) to accurately control the outlet water temperature. As discussed above, the controller38utilizes feedback from the inlet temperature sensor34, the intermediate temperature sensors50, the outlet temperature sensor36, and the flow sensor or flow meter54as part of its means to control the outlet water temperature and align it with the set point temperature. As described above, the controller38monitors the status of the contactors58and bimetal thermal switches56. In addition, the controller38monitors the current draw of the heating elements48.

FIG.15is a block diagram depicting the Feed-forward PID control loop124of the controller38, according to an embodiment of the invention. As discussed above, the set point temperature is the desired outlet temperature for the water heater10. Meanwhile, the actual outlet temperature is measured by the outlet temperature sensor36. As shown inFIG.15, the outlet temperature sensor36may be configured to output a voltage that a Single Order Hold with Analog-to-Digital Converter (SOH/ADC)126is able to quantize. In turn, the output of the SOH/ADC126indexes a look up table (LUT)128that translates the voltage into a measurement of the outlet temperature in degrees Celsius. Similarly, the inlet temperature sensor34may also be configured to output a voltage that a Single Order Hold with Analog-to-Digital Converter (SOH/ADC)127is able to quantize. In turn, the output of the SOH/ADC127indexes a look up table (LUT)129that translates the voltage into a measurement of the outlet temperature in degrees Celsius.

The controller38then takes the outlet temperature measurement and subtracts it from the setpoint temperature to create an error measurement. In turn, a PID controller138calculates a compensating temperature value based on the error measurement. The compensating temperature value is then fed to a power calculator130to determine a power calculation. The power calculation takes into account the flow rate measured by the flow rate sensor54. The controller38may be a computer, chip, PLC, etc.

Likewise, the controller38compares the inlet temperature measurement to the setpoint temperature in order to create a compensating temperature reflective of the difference between the inlet temperature and the set point temperature. The compensating temperature value is then fed to a power calculator131to determine a power calculation, which also takes into account the flow rate measured by the flow rate sensor54.

The controller38determines the flow measurement as a function of time at block140. This value is then fed to a power calculator142to determine another power calculation. While power calculators130,131,142above are described as separate features, it is contemplated that a single power calculator within the controller38may perform all the tasks of each power calculator130,131,142discussed above.

In turn, each power calculation is then sent through a limiter132that keeps the range of power levels within the capability of the water heater10and its heating elements48. The limited power level determined by the limiter132is then sent to a Pulse Width Modulator (PWM) Generator134, which applies the necessary power to the heating elements48in order to align the outlet temperature with the setpoint temperature. The timing of the control loop124of the controller38may be any value established by a user, preferably 250 ms.

In addition to the PID control loop124of the controller38described above, the controller38further determines the state of the heating elements48based on the water flowing through the heater. Once the flow rate sensor54exceeds the predetermined activation level previously discussed, the controller38transitions from an “idle” state to a “rising temperature” state, in which the heating elements48are activated. Once the error measurement between the outlet temperature measurement and the setpoint temperature is within a certain range, the controller38transitions to an “at temperature” state. A preferred example of such a range is ±0.5° C. Upon reduction of the measured flow rate from the flow rate sensor54, the controller38, which would cause the outlet temperature to overshoot the setpoint temperature, the controller38transitions to an “overshoot” state. In the “overshoot” state, the controller38turns off the solid-state relays60to remove power from the heating elements48. Once the solid-state relays60are turned off, the controller38transitions to a “cool down” state and eventually returns to the “idle” state.

The water heater may include three operational modes with increasing maximum set point temperatures. In a tepid safety heater mode, the maximum set point temperature is 95° F. In a temperate heater mode, the maximum set point temperature is 120° F. In a process heater mode, the maximum set point temperature is 160° F. Preferably, these operational modes are determined at the hardware level and are not adjustable from the user interface42or communication interface41.

It is also contemplated that the water heater10may be synchronized with any number of other similar water heaters10in a back-to-back setup. In such instances, the controllers38of each heater10may identify which heater10is the master unit and which heater10is the slave unit.

It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but includes modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.