AUTOMATIC POWER TRANSFER SWITCHING FOR A WATER HEATER

Abstract

A water heater includes power distribution circuitry receiving primary power and secondary power. The water heater includes a heat exchange system including at least one component powered via the primary power and configured to transfer heat between a refrigerant and water. The water heater includes at least one heater operably coupled with and configured to heat at least one portion of the heat exchange system. The water heater includes switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry.

Claims

1. A water heater, comprising: power distribution circuitry receiving primary power and secondary power; a heat exchange system including at least one component powered via the primary power and configured to transfer heat between a refrigerant and water; at least one heater operably coupled with and configured to heat at least one portion of the heat exchange system; and switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry.

2. The water heater of claim 1, wherein the switching circuitry includes a first switch electrically activated via the primary power to electrically couple the primary power with the at least one heater.

3. The water heater of claim 2, wherein the switching circuitry includes a second switch electrically activated via the secondary power to electrically couple the secondary power with the at least one heater.

4. The water heater of claim 3, wherein the switching circuitry includes a timer electrically interposing the power distribution circuit and the first switch to delay primary power to the first switch following the primary power being available.

5. The water heater of claim 4, wherein the timer includes a timer coil and a timer normally-open circuit closing in response to primary power energizing the timer coil longer than a threshold time.

6. The water heater of claim 5, wherein the first switch includes a first coil and a first normally-closed circuit opening in response to the first coil being energized following the delay, wherein the timer normally-open circuit provides the primary power to the first coil in response to closing of the timer normally-open circuit.

7. The water heater of claim 6, further comprising a first intermediate node electrically interposing the timer normally-open circuit and the first coil.

8. The water heater of claim 6, wherein the second switch includes a second coil and a second normally-closed circuit opening in response to the second coil being energized in the second condition.

9. The water heater of claim 8, further comprising a second intermediate node electrically interposing the first normally-closed circuit and the second coil.

10. The water heater of claim 9, further comprising a controller powered by the primary power and configured to communicate a control signal to operate the at least one heater in the first condition.

11. The water heater of claim 10, further comprising: a control relay electrically activated in response to the control signal and electrically interposing the switching circuitry and the at least one heater, wherein the control relay includes a relay coil and a relay normally-closed circuit opening in response to the control signal energizing the relay coil.

12. The water heater of claim 10, wherein the relay normally-closed circuit is closed when the primary power is unavailable.

13. The water of claim 12, further comprising: a third intermediate node coupled to the first normally-closed circuit, the second normally-closed circuit, and the relay normally-closed circuit.

14. The water heater of claim 1, where the heat exchange system includes at least one of piping and a heat pump, and wherein the at least one heater includes resistive heating tape coupled to the at least one of the piping, and the heat exchange system to warm the heat exchange system when primary power is unavailable.

15. The water heater of claim 1, wherein the secondary power is back-up power and the switching circuitry limits primary power and back-up power from activating the at least one heater simultaneously.

16. A back-up power circuit for a heat exchange system of a water heater, comprising: power distribution circuitry receiving primary power and back-up power and configured to power the heat exchanger via the primary power; at least one heater operably coupled with and configured to heat at least one portion of the heat exchanger; and switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry.

17. The back-up power circuit of claim 16, wherein the switching circuitry includes a first switch electrically activated via the primary power to electrically couple the primary power with the at least one heater.

18. The back-up power circuit of claim 17, wherein the switching circuitry includes a second switch electrically activated via the secondary power to electrically couple the secondary power with the at least one heater.

19. The back-up power circuit of claim 18, wherein the switching circuitry incudes a timer electrically interposing the power distribution circuit and the first switch to delay primary power to the first switch following the primary power being available.

20. A water heater, comprising: power distribution circuitry receiving primary power and secondary power; a heat exchange system powered via the primary power and configured to transfer heat between a refrigerant and water; at least one heater operably coupled with and configured to heat at least one portion of the heat exchange system; and switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry, wherein the switching circuitry limits primary power and back-up power from activating the at least one heater simultaneously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the drawings:

[0008] FIG. 1 is a side elevational view of an exemplary water heating system having a water heater external to and supplying hot water for a client facility;

[0009] FIG. 2 is a functional block diagram of a heat pump incorporating heaters according to one aspect of the present disclosure;

[0010] FIG. 3 is a functional block diagram of control circuitry for a water heater constructed according to one aspect of the present disclosure;

[0011] FIG. 4 is a functional block diagram of an automatic transfer switch circuit for a water heater;

[0012] FIG. 5 is an electrical diagram of a portion of an automatic transfer switch circuit for a water heater;

[0013] FIG. 6 is an electrical diagram of a portion of an automatic transfer switch circuit for a water heater;

[0014] FIG. 7A is an electrical diagram of the automatic transfer switch circuit of FIG. 6 in a first state with main power applied;

[0015] FIG. 7B is an electrical diagram of the automatic transfer switch circuit of FIG. 6 in a second state following unavailability of main power and availability of back-up power; and

[0016] FIG. 7C is an electrical diagram of the automatic transfer switch circuit of FIG. 6 in a third state following a return of main power and unavailability of back-up power.

[0017] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles described herein.

DETAILED DESCRIPTION

[0018] The present illustrated embodiments reside primarily in combinations of method steps and apparatus components related to automatic power transfer switching for a water heater. Accordingly, the apparatus components and method steps have been represented, where appropriate, by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Further, like numerals in the description and drawings represent like elements.

[0019] The terms including, comprises, comprising, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by comprises a . . . does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0020] In general, the present water heating arrangement may provide for maintained operation of on-board electric heat tape, heat trace, oil heaters, thermal blankets, or other resistive heating elements during power outages to limit freezing of water lines and/or other heat exchanging components. The water heating arrangement also provides for enhanced power savings by limiting back-up power usage to specific components. Further, the water heating arrangement limits conditions in which main power and back-up power simultaneously provide power to components of the water heating arrangement, thereby limiting over-current current back-feed and/or shorting scenarios.

[0021] Referring generally to FIGS. 1-7C, reference numeral 10 generally designates a water heater 10. The water heater 10 includes power distribution circuitry 12 that receives primary power and secondary power. The water heater 10 includes a heat pump 14 powered via the primary power and configured to transfer heat between a refrigerant and water. At least one heater 16 is operably coupled with and configured to heat at least one portion of the heat exchange system. Switching circuitry 18 electrically interposes the power distribution circuitry 12 and the at least one heater 16 to selectively power the at least one heater 16 via the primary power in a first condition of the switching circuitry 18 and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry 18.

[0022] Referring now to FIG. 1, a water conditioning system 20 includes a water heater 10 that produces hot water and a tank 22 that stores the hot water. In the present example, the water heater 10 is disposed in a region 24 external to a client facility 26 and provides hot water to the tank 22 in an interior 28 of the client facility 26, though other arrangements of the water conditioning system 20 may be provided. For example, the water conditioning system 20 may be wholly disposed in the interior 28 of the client facility 26. Accordingly, the illustrated example is merely exemplary and non-limiting.

[0023] The water heater 10 provides the hot water to the client facility 26 via a heat pump 14 in the water heater 10. Cold, cool, or otherwise main water from the facility is supplied to the water heater 10 via a supply line 32 (e.g., pipe(s), tube(s)). The cold water is heated by the water heater 10 and is returned to the client facility 26 via a return line 34. The water conditioning system 20 may include one or more sensors, such as thermal sensors and/or flow sensors, input devices configured to set one or more temperature setpoints for the water conditioning system 20, and output devices that control an amount of heat applied to the water based on data from the sensors and the temperature setpoints. In this way, the water conditioning system 20 may be controlled to provide a target temperature for the water according to the temperature setpoint(s).

[0024] With continued reference to FIG. 1, the water heater 10 includes one or more control panels 36, such as a high-voltage panel and/or a low-voltage panel, that provide and control power to components of the water heater 10. Power and/or communication is provided between the client facility 26 and the water heater 10 via one or more conduits 38 extending between the client facility 26 and the water heater 10. For example, three-phase 480 alternating-current voltage (VAC) power, 110/115/120 VAC power, Dec. 24, 1948 direct-current (DC) voltage power, and/or low-power communication (e.g., Ethernet, TCP/IP, Modbus, RS485, other industrial communication protocol) may be provided between the control panel(s) 36 and the client facility 26 via wiring disposed in the conduits 38.

[0025] Both main power and back-up power are provided to the water heater 10. For example, a 480 VAC line and an isolated 120 VAC may be provided to the control panel(s) 36. The back-up power may be provided by the facility or another power source. For example, a back-up generator for the client facility 26, an electrochemical cell, a solar panel/solar cell, or any other back-up power source may be provided to supply the back-up power. As will be described further herein, the back-up power circuit may be configured to power limited components relative to the components powered by the main power. More specifically, the secondary power may be configured to power the at least one heater 16 when main power is made unavailable (e.g., during a power outage). Accordingly, in some examples, the secondary power is back-up power, and the primary power is main power.

[0026] Referring now to FIG. 2, a heat exchange system 40 includes piping 42 (e.g., the supply line 32 and the return line 34) carrying the water to/from the heat pump 14 that heats the water. The heat pump 14 heats the water via thermal exchange with a refrigeration loop 44. The refrigeration loop 44 is a closed system that transfers heat from an environment (e.g., air in the region 24 exterior) to the water in the piping 42. The refrigeration loop 44 includes a compressor 46, a first heat exchanger (e.g., a condenser 48), an expansion device (e.g., an expansion valve 50), and a second heat exchanger (e.g., an evaporator 52). In operation, the compressor 46 pressurizes refrigerant gas, increasing its temperature and energy. The high-pressure, high-temperature refrigerant gas then flows into the condenser 48, where it releases heat to the piping 42. For example, the condenser 48 may include condenser coils 54 including closed tubing through which the refrigerant gas passes, and the closed tubing may be disposed in a container 56 through which the piping 42 passes the water. As a result, the refrigerant condenses into a high-pressure liquid and the water is heated. The liquid refrigerant passes through the expansion valve 50, which restricts its flow and reduces its pressure. As it expands, the refrigerant undergoes a phase change, becoming a low-pressure mixture of liquid and vapor, thereby lowering temperature of the refrigerant. The low-pressure refrigerant enters the evaporator 52, which may include one or more blowers 84/fans that draw air across evaporator coils 58. As the air from the environment passes over evaporator coils 58 of the evaporator 52, heat is transferred from the air to the refrigerant thereby causing the refrigerant to warm and evaporate. The refrigerant then flows to the compressor 46 to repeat the refrigeration cycle.

[0027] As demonstrated in FIG. 2, the at least one heater 16, which may be referred to as an auxiliary heater separate from the primary heating elements utilizing the refrigeration loop 44, includes a plurality of heaters 16 operably coupled with one or more components of the heat exchange system 40. For example, various components of the heat pump 14 and the piping 42 may include resistive heating devices overlaying, disposed adjacent to, or contacting the components of the heat pump 14 and/or the piping 42. The heating components may limit heat loss from the heat exchange system 40 and, in some cases, actively warm fluid (water or refrigerant) in the heat exchange system 40.

[0028] In some examples, the compressor 46 includes a crankcase 60 and a compressor motor 62 disposed in the crankcase 60. Oil may be provided in the crankcase 60 to facilitate movement of attachments to the compressor motor 62 (e.g., a piston) by lubricating the crankcase 60. At low environmental temperatures, the oil may at least partially solidify or otherwise become too viscous for efficient operation. Therefore, the heater 16 (e.g., a thermal blanket) on the compressor 46 may limit freezing of the compressor 46. Other components of the heat pump 14 (e.g., the gas to water heat exchanger 48) may be heated via the heater 16. For example, condensate channel trays and/or condensate discharge lines of the heat pump 40 may include one or more of the heaters 16 (e.g., resistive heaters) that can be controlled and powered via the back-up power in the event of a power outage. Water in the piping 42 may be limited from freezing via heat from the heater 16. In some examples, the compressor 46 uses a crankcase heater, the gas to water heat exchanger 48 uses a thermal blanket, and the water pipes 32, 34 are wrapped in heat trace tape under insulation.

[0029] Referring now to FIG. 3, control circuitry 64 is configured to control operation of the water heater 10. The control circuitry 64 includes a controller 66, such as a programmable logic device (PLD), that may be communicatively coupled to a controller-area-network (CAN 68) via any wired or wireless communication protocol. For example, the controller 66 may be connected over TCP/IP to other control devices of the client facility 26 to allow the controller 66 to share information about the status of the water heater 10 and/or receive information about other systems of the client facility 26. The controller 66 includes at least one processor and a memory. The memory stores instructions that, when executed by the processor, cause the controller 66 to control the water heater 10. For example, a plurality of input and/or output modules 70 may be in communication with the controller 66 via a backplane over which the controller 66 communicates reading and/or writing signals. For example, the input modules 70 may include digital and/or analog inputs or outputs. The modules 70 may also, or alternatively, include thermocouple input cards for receiving temperature information from one or more temperature sensors 72.

[0030] Still referring to FIG. 3, the controller 66 may utilize serial communication or simplified voltage or current detection or control to communicate with various devices for the water heater 10. For example, the controller 66 may read data from one or more of the temperature sensors 72 that may be positioned to detect the temperature of the water, the refrigerant, the heat exchangers of the refrigeration loop 44, the environmental air, or any other aspect related to temperature control of water heated by the water heater 10. Flow rate meters 74 may also be provided to indicate the rate of water flow through the piping 42 and/or refrigerant in the refrigeration loop 44. Pressure sensors 76, switching devices 78 (e.g., relays, contactors, transistors), buttons 80 (or other user interface equipment), or any other input for operating the water heater 10 may be in communication with the controller 66 to allow the controller 66 to monitor operation of the water heater 10. The controller 66 may also, or alternatively, control various outputs of the water heater 10, such as motor drives 82 (e.g., a variable-frequency drive, a servo drive, etc.), motors for blowers 84 or fans of the water heater 10, valves 86 (e.g., the expansion valve 50), one or more timers 88, and indicator lights 90. It is contemplated that these output devices may also include input terminals for feedback to the controller 66, such as contacts that close or open in response to operation of the output device, motor speed information, or the like.

[0031] It is contemplated that the controller 66 may be powered via the main power, such that loss of the main power results in power loss to the input devices and/or the output devices described with respect to FIG. 2. However, as will be described in reference to the foregoing features, the switching devices 78 and one or more of the timer(s) 88 may be arranged (e.g., wired) to selectively receive power from the back-up power in the event of main power loss.

[0032] Referring now to FIG. 4, an automatic transfer switching (ATS) circuit 92 is provided for selectively operating the heaters 16 between the main power and the back-up power. The ATS circuit 92 includes power distribution circuitry 12 that feeds the switching circuitry 18 with both main and back-up power to the water heater 10. The power distribution circuitry 12 may include terminal blocks, busbars, or other electrical fasteners that provide for the distribution of power signals for the water heater 10. The power distribution circuitry 12 maintains electrical isolation (e.g., power back feed) between the main power and the back-up power.

[0033] The power distribution circuitry 12 may also provide power to other circuitry for the water heater 10, such as a control relay 94 that can selectively interrupt activation of the heaters 16 and will be described in detail with respect to FIG. 5. As demonstrated, main power or back-up power may be selectively provided to some of the heaters 16 by passing through both the switching circuitry 18 and the control relay 94, while other heaters 16 may bypass the control relay 94.

[0034] As previously described, the main power may be configured to power the controller 66 and one or more of the input/output devices previously described, while the back-up power may be limited to selective powering of the switching circuitry 18. Therefore, in the event of a main power outage, power to the controller 66, and thus active control of the control relay 94, may be lost. The control relay 94 may therefore be provided with a normally-closed state that allows current to flow through contacts of the control relay 94 to the heaters 16 when main power is lost.

[0035] Referring now to FIG. 5, the main power is configured to power a power supply 96 and a transformer 98 to provide the water heater 10 with 24 VDC and 120 VAC power, respectively. For example, three-phase 480 VAC or another supply voltage may be stepped down and rectified by the power supply 96 to provide low-voltage DC positive bus+ and a DC negative busfor powering components such as the controller 66 and the input/output devices previously described with respect to FIG. 3. The transformer 98 may step the three-phase power down to single-phase 120 VAC or another lower VAC power (e.g., 240 VAC) to provide a first line bus L1 and a first neutral bus N1 to operate higher-voltage components such as the heaters 16. Accordingly, control power at a lower voltage (24 VDC) may be used to control the switching devices 78 to close/open 120 VAC circuits for the heaters 16. However, as described herein, the back-up power (which may be 120 VAC) may activate the heaters 16 when control power (e.g., from the main power) is lost.

[0036] With continued reference to FIG. 5, part of the exemplary ATS circuit 92 is demonstrated via wiring with a first terminal block 100. Jumpers 102 may be provided for the first terminal block 100 to short terminals of the first terminal block 100 together. In the present example, the at least one heater 16 includes a first heater EH1 for warming the compressor 46, a second heater EH2 for warming the condenser 48, and a third heater EH3 for warming the water lines (e.g., the piping 42). Each of EH1-EH3 are resistive heaters that heat in response to an electrical potential applied across two conductors 110, 112 of the resistive heaters. Each of EH1-EH3 is electrically coupled to ground via a first intermediate node 114 electrically coupled to a first conductor 110 of the two conductors 110, 112. A second conductor 112 of the two conductors 110, 112 is configured to receive power (e.g., a 120 VAC line voltage) from one of the main power and the back-up power. As illustrated in FIG. 5, EH2 and EH3 may be configured to receive the power via second intermediate nodes 116 that electrically couple with the control relay 94. The control relay 94 electrically interposes the first intermediate node 114 and a third intermediate node 118 to which the main or the back-up power is applied. When power (e.g., a 120 VAC neutral) is applied to the first intermediate node 114 and to the second intermediate nodes 116 (e.g., 120 VAC line), current flows through EH2 and EH3 to warm the piping 42 and the expansion valve 50, respectively. Because the control relay 94 does not electrically interpose the third intermediate node 118 and EH1, EH1 is configured to activate in response to power applied to the first intermediate node 114 and to the third intermediate node 118.

[0037] Still referring to FIG. 5, the control relay 94 includes a relay coil 120 and a pair of relay normally-closed circuits 122 that open in response to the relay coil 120 being energized. Accordingly, when the relay coil 120 is not energized, either via control by the controller 66 or loss of main power, the first intermediate node 114 and third intermediate nodes 118 are electrically connected/closed to allow current to flow between the first intermediate node 114 and the third intermediate node 118. The relay coil 120 is electrically controlled via an output signal from an exemplary output module 124 controlled by the controller 66. For example, the controller 66 may be programmed to interrupt warming of the piping 42 and/or the expansion valve 50 during hot weather or in other conditions. Accordingly, the controller 66 may selectively interrupt power to EH2 and EH3 when main power is available.

[0038] When main power is unavailable, the positive bus+ and negative bus-do not transmit power to the controller 66. Accordingly, the exemplary output module 124 is unable to energize the relay coil 120, thereby leaving the relay normally-closed circuits 122 closed. Thus, when main power fails and back-up power is available, power to the first intermediate node 114 and the third intermediate node 118 will operate EH1, EH2, and EH3.

[0039] Referring now to FIG. 6, power switching functionality between main power and back-up power of the ATS circuit 92 is demonstrated via switching circuitry 18. The switching circuitry 18 selectively connects the first intermediate node 114 with either the first neutral bus N1 or a second neutral bus N2 of the back-up power, and further connects the third intermediate node 118 with either the first line bus L1 or a second line bus L2 of the back-up power. The back-up power may be a 120 VAC supply or another power source in common with the power provided via L1 and N1. Accordingly, the back-up power may be a separate power line wired into the control panel(s) 36 and terminated at a second terminal block for distribution.

[0040] The switching circuitry 18 includes a first switch 126, a second switch 128, and a timer 88. The first switch 126 and the second switch 128 may be any form of any electrical switch, such as a relay, a solid-state switch, a transistor, or, as in the present example, a contactor. In this example, the first and second switches 126, 128 are mechanically interlocked contactors each having a coil and contacts for closing or opening circuits. As will be described herein, although the first switch 126 and the second switch 128 may be electrically interlocked (e.g., the second switch 128 will not activate while the first switch 126 is activated), the mechanical interlocking provides additional limitations on electrical events (e.g., shorts, back feed, etc.). For example, the mechanical interlock may include a pin-and-slot locking mechanism or other structure that limits activation of the first switch 126 and the second switch 128 during the same time.

[0041] The timer 88, or timing relay, includes a timer coil 130 that energizes in response to voltage across the timer coil 130. The timer 88 is programmed or otherwise configured with a pre-defined threshold time (e.g., a delay) for which the timer coil 130 is energized before closing a timer 88 normally-open circuit of the timer 88. In this way, the timer 88 may be an on-delay timer, though an off-delay timer may be used in alternative configurations. The threshold time may be in the range of seconds to minutes to hours. In one example, the threshold time may be 5 minutes or longer, which may be an amount of time for switching from back-up power to main power.

[0042] Still referring to FIG. 6, the first switch 126 includes a first coil 134 and a first normally-closed circuit 136 opening in response to the first coil 134 being energized following the delay. The timer 88 normally-open circuit provides the main power to the first coil 134 in response to closing of the timer 88 normally-open circuit. A fourth intermediate node 138 electrically interposes the timer 88 normally-open circuit and one side of the first coil 134. The first neutral bus N1 is electrically coupled with the other side of the first coil 134. Accordingly, when the timer 88 normally-open circuit closes, the first coil 134 is energized by power from the first line bus L1 and the first neutral bus N1. The second switch 128 includes a second coil 140 and a second normally-closed circuit 142 opening in response to the second coil 140 being energized in the second condition. A fifth intermediate node 144 electrically interposes the first normally-closed circuit 136 and one side of the second coil 140. The second neutral bus N2 is electrically coupled with the other side of the second coil 140.

[0043] The first switch 126 includes a first normally-open circuit 146 that electrically interposes the first line bus L1 and the third intermediate node 118. The first switch 126 also includes a second normally-open circuit 148 electrically interposing the first neutral bus N1 and the first intermediate node 114. The second switch 128 includes a third normally-open circuit 150 that electrically interposes the second line bus L2 and the third intermediate node 118. The second switch 128 also includes a fourth normally-open circuit 152 that electrically interposes the second neutral bus N2 and the third intermediate node 118 Accordingly, the first intermediate node 114 and the third intermediate node 118 may be connected, depending on the state of the first coil 134 and the second coil 140, to the main power or the back-up power.

[0044] Referring now to FIGS. 7A-7C, three states 154, 156, 158 of the ATS circuit 92 are exemplarily demonstrated via a power outage sequence. In a first state 154 of the ATS circuit 92, the first coil 134 is energized (following the delay of the timer 88) at least because the second normally-closed circuit 142 is closed due to the second coil 140 being de-energized, thereby closing the first normally-open circuit 146 and the second normally-open circuit 148. Main power is therefore available to the third intermediate node 118 and applied to EH1. EH2 and EH3 are selectively powered in response to control of the control relay 94, as previously described.

[0045] In a second state 156 of the ATS circuit 92, a power outage of the main power has occurred, and back-up power is provided. The second coil 140 is energized because the first normally-closed circuit 136 is closed due to the first coil 134 being de-energized, thereby closing the third normally-opened circuit and the fourth normally-opened circuit. Back-up power is therefore available to the third intermediate node 118 and applied to EH1, EH2, and EH3. Because the control relay 94 is not activated, the relay normally-closed circuits 122 are closed, and the third intermediate node 118 is closed with the second intermediate nodes 116.

[0046] In a third state 158 of the ATS circuit 92, following the return of main power and de-activation of back-up power, the timer coil 130 is energized because the second normally-closed circuit 142 is closed due to the second coil 140 being de-energized. Following the delay, the ATS circuit 92 is configured to return to the first state 154.

[0047] In general, the mechanically interlocked set of contactors and on-delay timing arrangement to automatically switch between main power and back-up power provides for enhanced thermal energy management and limits freezing scenarios that may impact efficient operation of the water heater 10.

[0048] According to an aspect of the present disclosure, a water heater includes power distribution circuitry receiving primary power and secondary power. The water heater includes a heat exchange system including at least one component powered via the primary power and configured to transfer heat between a refrigerant and water. The water heater includes at least one heater operably coupled with and configured to heat at least one portion of the heat exchange system. The water heater includes switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry.

[0049] According to an aspect of the present disclosure, the switching circuitry includes a first switch electrically activated via the primary power to electrically couple the primary power with the at least one heater.

[0050] According to an aspect of the present disclosure, the switching circuitry includes a second switch electrically activated via the secondary power to electrically couple the secondary power with the at least one heater.

[0051] According to an aspect of the present disclosure, the switching circuitry includes a timer electrically interposing the power distribution circuit and the first switch to delay primary power to the first switch following the primary power being available.

[0052] According to an aspect of the present disclosure, the timer includes a timer coil and a timer normally-open circuit closing in response to primary power energizing the timer coil longer than a threshold time.

[0053] According to an aspect of the present disclosure, the first switch includes a first coil 134 and a first normally-closed circuit opening in response to the first coil being energized following the delay, wherein the timer normally-open circuit provides the primary power to the first coil in response to closing of the timer normally-open circuit.

[0054] According to an aspect of the present disclosure, the water heater includes a first intermediate node electrically interposing the timer normally-open circuit and the first coil.

[0055] According to an aspect of the present disclosure, the second switch includes a second coil and a second normally-closed circuit opening in response to the second coil being energized in the second condition.

[0056] According to an aspect of the present disclosure, the water heater includes a second intermediate node electrically interposing the first normally-closed circuit and the second coil. According to an aspect of the present disclosure, the water heater includes a controller powered by the primary power and configured to communicate a control signal to operate the at least one heater in the first condition.

[0057] According to an aspect of the present disclosure, the water heater includes a control relay electrically activated in response to the control signal and electrically interposing the switching circuitry and the at least one heater, wherein the control relay includes a relay coil and a relay normally-closed circuit opening in response to the control signal energizing the relay coil.

[0058] According to an aspect of the present disclosure, the relay normally-closed circuit is closed when the primary power is unavailable.

[0059] According to an aspect of the present disclosure, the water heater includes a third intermediate node coupled to the first normally-closed circuit, the second normally-closed circuit, and the relay normally-closed circuit.

[0060] According to an aspect of the present disclosure, the heat exchange system includes at least one of piping and a heat pump, and the at least one heater includes resistive heating tape coupled to the at least one of the piping, and the heat exchange system to warm the heat exchange system when primary power is unavailable.

[0061] According to an aspect of the present disclosure, the secondary power is back-up power and the switching circuitry limits primary power and back-up power from activating the at least one heater simultaneously.

[0062] According to an aspect of the present disclosure, the switching circuitry is configured to limit the primary power and the back-up power from activating the at least one heater in response to the primary power becoming available while the back-up power is available.

[0063] According to another aspect, a back-up power circuit for a heat exchange system of a water heater includes power distribution circuitry receiving primary power and back-up power and configured to power the heat exchanger via the primary power. The back-up power circuit includes at least one heater operably coupled with and configured to heat at least one portion of the heat exchanger. The back-up power circuit includes switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry. According to another aspect, the switching circuitry includes a first switch electrically activated via the primary power to electrically couple the primary power with the at least one heater.

[0064] According to another aspect, the switching circuitry includes a second switch electrically activated via the secondary power to electrically couple the secondary power with the at least one heater.

[0065] According to another aspect, the switching circuitry includes a timer electrically interposing the power distribution circuit and the first switch to delay primary power to the first switch following the primary power being available.

[0066] According to yet another aspect, a water heater includes power distribution circuitry receiving primary power and secondary power. The water heater includes a heat exchange system powered via the primary power and configured to transfer heat between a refrigerant and water. The water heater includes at least one heater operably coupled with and configured to heat at least one portion of the heat exchange system. The water heater includes switching circuitry electrically interposing the power distribution circuitry and the at least one heater to selectively power the at least one heater via the primary power in a first condition of the switching circuitry and via the secondary power when the primary power is unavailable in a second condition of the switching circuitry, wherein the switching circuitry limits primary power and back-up power from activating the at least one heater simultaneously.

[0067] It will be understood by one having ordinary skill in the art that construction of the described disclosure and other components is not limited to any specific material. Other exemplary embodiments of the disclosure disclosed herein may be formed from a wide variety of materials, unless described otherwise herein.

[0068] For purposes of this disclosure, 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 any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature or may be removable or releasable in nature unless otherwise stated.

[0069] It is also important to note that the construction and arrangement of the elements of the disclosure as shown in the exemplary embodiments is illustrative only. Although only a few embodiments of the present innovations have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes, and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present innovations. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present innovations.

[0070] It will be understood that any described processes or steps within described processes may be combined with other disclosed processes or steps to form structures within the scope of the present disclosure. The exemplary structures and processes disclosed herein are for illustrative purposes and are not to be construed as limiting.