GAS-ELECTRIC HYBRID WATER HEATER

Abstract

A system for heating water includes an interior region, a first heat source including a gas burner configured to generate combustion gases; a second heat source including an electric heating element; a temperature or flow or pressure sensor positioned to directly or indirectly sense a temperature or a flow or a pressure of water contained in the interior region; and a mechanical and/or electrical controller coupled to the temperature or flow or pressure sensor, the first heat source, and the second heat source. The controller actuates the first heat source by firing the gas burner in response to a first signal from the temperature or flow or pressure sensor, and/or actuates the second heat source by actuating the electric heating element in response to a second signal from the temperature or flow or pressure sensor.

Claims

1. A system for heating water comprising: an interior region configured to contain water to be heated; a first heat source configured to generate heat for transfer to water contained in or entering or exiting the interior region, the first heat source including a gas burner configured to generate combustion gases; a second heat source configured to generate heat for transfer to the water contained in or entering or exiting the interior region, the second heat source including an electric heating element; a sensor positioned to directly or indirectly detect a temperature or a flow or a pressure of the water contained in or entering or exiting the interior region; and a controller coupled to the sensor, the first heat source, and the second heat source, the controller being configured to: actuate the first heat source in response to a signal from the sensor, and/or actuate the second heat source in response to a signal from the sensor.

2. The system of claim 1, the controller being further configured to: actuate the first heat source in response to a signal from the sensor when hot water demand is above a first threshold, and/or actuate the second heat source in response to a signal from the sensor when hot water demand is below a second threshold, thereby mitigating short cycling and cyclic losses of the first heat source.

3. The system of claim 1, the controller being further configured to: detect when there is no or low hot water demand; and actuate the second heat source to recover a set point temperature or flow of the system.

4. The system of claim 1 comprising a water storage tank at least partially defining the interior region, the water storage tank being configured to contain the water to be heated; and a heat exchanger extending within the interior region defined by the water storage tank; wherein the gas burner is positioned to deliver the combustion gases such that they can enter the heat exchanger for the transfer of heat from the combustion gases to the water contained in the interior region.

5. The system of claim 1, the controller being configured to actuate the first heat source and the second heat source simultaneously.

6. The system of claim 1, the sensor including a thermistor.

7. The system of claim 1, the first heat source having a first recovery efficiency, the second heat source having a second recovery efficiency, and the system having a system recovery efficiency between or greater than the first recovery efficiency and/or the second recovery efficiency.

8. The system of claim 7, the first recovery efficiency, the second recovery efficiency, and the system recovery efficiency each being a first hour rating.

9. The system of claim 1, the system being tankless.

10. A method for heating water comprising: actuating a first heat source to generate heat for transfer to water contained in an interior region of a water heater, wherein actuating the first heat source includes firing a gas burner in response to a signal from a sensor; and actuating a second heat source to generate heat for transfer to the water contained in the interior region of the water heater, wherein actuating the second heat source includes actuating an electric heating element in response to a signal from the sensor.

11. The method of claim 10, wherein the firing of the gas burner is in response to a call for heat when a temperature or a flow or a pressure sensed by the sensor is below a setpoint or prescribed temperature or flow or pressure.

12. The method of claim 10, wherein actuating the first heat source is performed before actuating the second heat source.

13. The method of claim 10, wherein actuating the first heat source is performed after actuating the second heat source.

14. A system for heating water comprising: an interior region configured to contain water to be heated; a primary heat source configured to generate heat for transfer to water contained in the interior region, the primary heat source including a gas burner configured to generate combustion gases; a secondary heat source configured to generate heat for transfer to the water contained in the interior region, the secondary heat source including an electric heating element; a sensor positioned to directly or indirectly sense a temperature or a flow of the water contained in the interior region or entering or exiting the interior region; and a controller coupled to the sensor, the first heat source, and the second heat source, the controller being configured to: actuate the primary heat source in response to a first signal from the sensor when hot water demand is above a primary threshold, and actuate the secondary heat source in response to a second signal from the sensor when hot water demand is below a secondary threshold, thereby mitigating short cycling and cyclic losses of the primary heat source.

15. The system of claim 14, the controller further configured to: detect when there is no or low hot water demand; and actuate the secondary heat source to recover a set point temperature or flow of the system.

16. The method of claim 10, further comprising: mitigating short cycling and cyclic losses of the first heat source by actuating the second heat source.

17. The method of claim 16, further comprising actuating the first heat source when hot water demand is above a first threshold.

18. The method of claim 16, further comprising actuating the second heat source when hot water demand is below a second threshold.

19. The method of claim 16, further comprising: detecting when there is no or low hot water demand; and actuating the secondary heat source by actuating the electric heating element to recover a set point temperature of the system.

20. The system of claim 4, wherein the gas burner of the first heat source is configured to direct the combustion gases downwardly into the heat exchanger for the transfer of heat from the combustion gases to water contained in an upper portion of the water storage tank, the electric heating element of the second heat source is positioned in a lower portion of the water storage tank to transfer heat to water contained in the lower portion of the water storage tank, the sensor is positioned to detect the temperature of water contained in the lower portion of the water storage tank, and the controller is further configured to actuate the electric heating element of the second heat source in response to a signal received from the sensor.

21. The system of claim 20, the controller being configured to actuate the electric heating element of the second heat source in response to the temperature detected by the sensor when the sensor detects a demand for heated water in excess of a pre-determined demand.

22. The system of claim 20, the controller being operable in a plurality of modes, the controller being configured to actuate the electric heating element of the second heat source in response to the temperature detected by the sensor when the controller is in one of the modes, and the controller being configured to not actuate the electric heating element of the second heat source in response to the temperature detected by the sensor when the controller is in another one of the modes.

23. The system of claim 1, the sensor comprising an upper sensor and a lower sensor, and the controller is further configured to: actuate the first heat source in response to a signal from the upper sensor when the upper sensor triggers a call for heat; and actuate the second heat source in response to a signal from the lower sensor when the lower sensor triggers a call for heat.

24. The system of claim 23, the controller being configured to actuate the second heat source in response to the signal from the lower sensor when the controller is set to operate in a selected mode.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0007] FIG. 1 illustrates an embodiment of a control logic that can be used according to an aspect of the invention.

[0008] FIG. 2 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0009] FIG. 3 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0010] FIG. 4 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0011] FIG. 5 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0012] FIG. 6 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0013] FIG. 7 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0014] FIG. 8 illustrates another embodiment of a control logic that can be used according to an aspect of the invention.

[0015] FIG. 9 illustrates schematically an embodiment of a water heating system according to an aspect of the invention.

[0016] FIG. 10 illustrates an embodiment of a method according to an aspect of the invention.

[0017] FIG. 11 illustrates another embodiment of a method according to an aspect of the invention.

[0018] FIG. 12 illustrates an embodiment of a control circuit according to an aspect of the invention.

[0019] FIG. 13 illustrates another embodiment of a control circuit according to an aspect of the invention.

[0020] FIG. 14 illustrates another embodiment of a control circuit according to an aspect of the invention.

[0021] FIG. 15 illustrates another embodiment of a control circuit according to an aspect of the invention.

[0022] FIG. 16 illustrates another embodiment of a control circuit according to an aspect of the invention.

[0023] FIG. 17 is a temperature-time chart illustrating an aspect of the invention.

[0024] FIG. 18 schematically illustrates an embodiment of a gas-electric hybrid water heater according to aspect of this invention.

[0025] FIG. 19 schematically illustrates a side view of another embodiment of a gas-electric hybrid water heater according to an aspect of this invention.

[0026] FIG. 20 is a chart illustrating temperature readings over time at positions within a water heater operating in standby mode.

[0027] FIG. 21 is a chart illustrating setpoint and differential temperatures according to aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

[0029] Generally, the invention relates to a hybrid water heater system configured to simultaneously or non-simultaneously fire a gas burner and an electric heating element(s). The system makes it possible to use pre-configured input rates to improve the overall efficiencies of gas water heater products including by driving the recovery efficiency and the Department of Energy's uniform energy factor (UEF) efficiency ratings. The hybrid or dual-powered gas-electric water heater uses gas and electric heating, preferably at predetermined inputs, to simultaneously or non-simultaneously heat water to temperatures dictated by the control(s). The input rates can be configured in such a way that the water heater utilizes higher thermal efficiency of the electric heating element or elements. By firing at least one electric heating element and the gas burner together, recovery efficiency can achieve higher (e.g., from non-condensing to condensing) performance from a gas-fired system with or without condensing, resulting in higher efficiency performance overall.

[0030] By using one or more electric elements having a higher recovery efficiency than gas inputs, and by strategically firing them either simultaneously or non-simultaneously, a higher recovery can be achieved as compared to a gas-fired water heater alone with or without condensing according to embodiments and aspects of the invention.

[0031] According to exemplary embodiments of the invention, a system for heating water is provided. The system may be a tank-style water heater, a tankless water heater, a boiler, or any other system used to heat water.

[0032] The system includes an interior region configured to contain water to be heated. The interior region may be a tank, a conduit, or any region configured to contain water or water flow.

[0033] The system includes a first heat source configured to generate heat for transfer to water contained in the interior region, the first heat source including a gas burner. The gas burner can be configured for combustion of any combustible gas, such as natural gas or propane.

[0034] The system includes a second heat source configured to generate heat for transfer to the water contained in the interior region, the second heat source including an electric heating element(s). The electric heating element(s) can be an immersion heating element, an electric coil, or any other electric element configured to transfer heat to water.

[0035] The system includes a temperature and/or flow sensor positioned to directly or indirectly sense a temperature and/or a flow of the water contained in (and/or entering/exiting) the interior region. For example, a demand for heat signal can be based on a temperature and/or flow threshold(s). Additionally, or alternatively, a demand for heat signal can be based on a pressure indication from one or more pressure sensors. For example, because pressure drop can be the result of flow, a flow sensor could be supplemented by, or replaced with, a pressure sensor or a pressure switch. It will be understood that a temperature and/or flow sensor(s) can be utilized, and that a pressure switch and associated algorithm can be utilized to actuate the various heat sources as a response to any of the sensors independently, or a sequence, or a calculation from them over time.

[0036] The sensor(s) can be configured to sense temperature and/or flow and/or pressure by directly sensing water temperature and/or water flow and/or a pressure, by indirectly sensing water temperature such as by sensing a temperature of a surface containing the water, or by any other way of detecting water temperature and/or flow. Accordingly, the sensor(s) need not be in a tank or interior region; specifically, it can also be on the outside of a tank wall or otherwise outside of the interior region. Also, a sensor or sensors can be used to detect a temperature rate of decay.

[0037] A flow-activated sensor, switch, or meter can be used to determine the order of operation of the electric heating element(s) and/or gas burner based on predetermined flow rates. Activating the electric heating element(s) can be based on a signal from a gas pressure switch, for example, which normally signals the gas valve to open the flow path for gas to travel through the feed and pilot ultimately lighting the gas burner (standard gas heater operation). When the valve turns on flow for the burner (not the pilot), that pressure can activate the pressure switch.

[0038] The signal from a gas pressure switch can also be used to turn on one or more electric heating elements. For example, the system can actuate the second heat source by actuating the electric heating element in response to a signal from the temperature sensor and a signal from the gas pressure switch.

[0039] The system includes a mechanical and/or electrical controller coupled to the temperature or flow or pressure sensor(s), the first heat source, and the second heat source. Either mechanical or electric controls, or any combination of the two, can be used. For example, a mechanical snap disc could be utilized as a sensor that is external to the tank.

[0040] The controller is configured to actuate the first heat source by firing the gas burner in response to the signal from the temperature or flow or pressure sensor(s); to actuate the second heat source by actuating the electric heating element in response to the signal from the temperature or flow or pressure sensor(s); or to actuate both the first heat source, by firing the gas burner in response to the signal from the temperature or flow or pressure sensor(s), and the second heat source, by actuating the electric heating element(s) in response to the second signal from the temperature or flow sensor(s). The first and second heat sources can both act in response to a signal from the same sensor(s) and/or controller. Also, a signal could also turn on the electric element(s) instead of the gas burner and vice versa, and both could heat simultaneously.

[0041] The system can include a water storage tank at least partially defining the interior region, the water storage tank being configured to contain the water to be heated. Alternatively, the system can be a tankless water heater without a water storage tank.

[0042] The system can include a heat exchanger extending within the interior region defined by the water storage tank. A gas burner can be positioned to deliver the combustion gases such that they can enter the heat exchanger for the transfer of heat from the combustion gases to the water contained in the interior region.

[0043] The electric heating element(s) of the system can be positioned for immersion in the water contained in the inlet, outlet and/or within the interior region. Alternatively, it can be positioned such that it is not immersed in the water.

[0044] The controller of the system can be configured to actuate the first heat source and the second heat source simultaneously. Alternatively, the controller can be configured to actuate the first heat source simultaneously, before, and/or after actuating the second heat source.

[0045] The system can include a blower associated with the gas burner. For example, the blower can be incorporated into or used with a gas burner, such as a down-fired gas burner, to urge the flow of combustion gases to or from a heat exchanger such as flue (e.g., push- or pull-types of blowers can be utilized including pull-types that mix external to combustion air for cooling purposes of the exhaust gases).

[0046] The system can include a pilot associated with the gas burner. Additionally, the system can include a gas valve configured to permit or prevent or limit flow of gas to the gas burner. A pressure switch can also be included in the system, with the controller being configured to operate the gas valve in response to a demand for heat signal.

[0047] The temperature and/or flow or pressure sensor of the system can include a thermistor.

[0048] The first heat source of the system can have a first recovery efficiency, the second heat source can have a second recovery efficiency, and the system can have a system recovery efficiency between, or greater than, the first recovery efficiency and the second recovery efficiency. For example, the system's recovery efficiency can also correspond to a weighted average between the first recovery efficiency and/or the second recovery efficiency. To illustrate, 75% of input at 80% recovery efficiency and 25% of input at 98% recovery efficiency would result in the following equation: (0.750.80)+ (0.250.98)=0.845, which is 84.5% recovery efficiency.

[0049] The first recovery efficiency, the second recovery efficiency, and the system recovery efficiency can each be a first hour rating or contribute toward a first hour rating. There could be some level of first hour improvement for the overall system, and first hour rating for the overall water heater (unlike the recovery efficiency of each heat source) could be improved.

[0050] As illustrated above, an electric heating element may have a higher efficiency then a gas burner, and when the two are fired together the higher efficiency of the electric heating element increases the overall efficiency of the water heater as compared to just a first heat source (gas burner) alone. Accordingly, the first and second heat sources may provide different targeted performance benefit(s) in terms of higher efficiency and/or transferring more BTU's into the water.

[0051] The system can include a heat exchanger, for example in the form of one or more flues or coils, through which the combustion gases generated by the gas burner travel. A combustion chamber can be included in the system, in which the combustion gases are generated by the gas burner, with the combustion chamber being coupled to deliver the combustion gases into the one or more flues.

[0052] A method for heating water according to embodiments of the invention includes several steps. The steps can be completed in any order, depending on particular applications or needs.

[0053] The method includes actuating a first heat source to generate heat for transfer to water contained in an interior region of a water heater, wherein actuating the first heat source includes firing a gas burner in response to a signal from a temperature and/or flow and/or pressure sensor(s).

[0054] The method also includes actuating a second heat source to generate heat for transfer to the water contained in the interior region of the water heater, wherein actuating the second heat source includes actuating an electric heating element(s) in response to a signal.

[0055] The firing of the gas burner can be in response to a call for heat when a temperature and/or a flow and/or a pressure sensed by the temperature and/or flow and/or pressure sensor is below a setpoint or prescribed temperature or flow or pressure. A call for heat may relate to the gas valve, which can have a temperature sensor (e.g., thermistor, RTD, thermocouple, etc.) that is in a shank/thermal well of the gas valve that is monitoring the water temperatures and the rate of decay in temperature of the water. As the electro/mechanical controller(s) senses, calculates and/or gas valve sees either a sudden rate of decay or water temperatures below a certain temperature, it can charge a solenoid to open the flow path for gas to travel through a feed and/or pilot ultimately lighting the burner. When the electro/mechanical controller(s) starts the process of lighting a burner based on information or a signal from a temperature sensor (or electro/mechanical controller logic/device) it can be considered a call for heat.

[0056] Power vent water heaters typically light the pilot to light the burner when there is no standing pilot. The gas valve may act after certain control sequences are completed. For example, a blower may turn on and monitor for whether the pressure switch (e.g., a blower pressure switch) is making contact. For example, a blower pressure switch checks that the blower is on and that venting is not blocked, thus allowing for the water heater to fire safely and discharge combustion products correctly. Such sequences prior to lighting the burner can be used as a signal for actuating the electric heating element.

[0057] The first signal from the temperature and/or flow and/or pressure sensor(s) can be the same as the second signal from the temperature and/or flow and/or pressure sensor(s). The first signal and the second signal can alternatively be separate signals. The first signal and the second signal can be the same or simultaneous and can be mechanically activated as opposed to a signal to/from a controller (e.g., a snap disc and a pressure switch for mechanical devices).

[0058] Actuating the first heat source can be performed before actuating the second heat source. Alternatively, actuating the first heat source can be performed after actuating the second heat source, or the first heat source and the second heat source can be actuated simultaneously. For example, actuating the second heat source may be performed by actuating the first heat source, and/or actuating the first heat source may be performed by actuating the second heat source.

[0059] The method can also include igniting a pilot prior to firing the gas burner when actuating the first heat source. Actuating the second heat source can be performed before igniting the pilot. Alternatively, actuating the second heat source can be performed after igniting the pilot.

[0060] The method can include actuating a blower prior to firing the gas burner when actuating the first heat source. Actuating the blower can be performed in response to a signal received from a pressure switch. Actuating the second heat source can be performed before actuating the blower. Alternatively, actuating the second heat source can be performed after actuating the blower.

[0061] According to additional embodiments of the invention, a system for heating water can be configured to mitigate short cycling and/or mitigate cyclic losses of the primary heat source. A water heating system might operate under short-cycling when it remains in its start-up cycling, fails to stay on long enough to complete a full cycle, and/or otherwise cycle more than needed or desired. For example, in an electric water heating system, a cycle can include blower fan actuation, heating element actuation and deactivation, and then blower deactivation.

[0062] Aspects of the invention can help to reduce the energy waste and/or the wear-and-tear associated with such short-cycling. For example, a hybrid storage tank water heater that utilizes gas as the primary fuel source and electricity as a secondary fuel source can mitigate short cycling and cyclic losses. Accordingly, this invention also makes it possible to create a burner control and algorithm that utilizes gas combustion to heat water when the hot water demand is above a particular threshold. But if the hot water demand is below a certain threshold, particularly in standby, the algorithm can utilize electricity and electric resistance heating elements to maintain the water temperature.

[0063] By reducing short cycling the system can minimize cyclic losses and reduce fuel consumption for the end user. Reducing short cycling also reduces wear and tear on the water heater which can extend its service life. This is especially beneficial for commercial water heaters that may be oversized for a particular application. Also, this technology can allow end users to participate in demand response programs of local utility providers. A load shedding signal to electrical elements for reduced power draw from the grid can be facilitated by modulating or not utilizing electrical element(s).

[0064] According to exemplary embodiments of the invention, the system includes an interior region configured to contain water to be heated; a primary heat source configured to generate heat for transfer to water contained in the interior region, the primary heat source including a gas burner configured to generate combustion gases; a secondary heat source configured to generate heat for transfer to the water contained in the interior region, the secondary heat source including an electric heating element; and a temperature or flow or pressure sensor positioned to directly or indirectly sense a temperature or a flow or a pressure of the water contained in the interior region.

[0065] The system also includes a mechanical and/or electrical controller coupled to the temperature and/or flow and/or pressure sensor(s), the first heat source, and the second heat source. The controller is configured to actuate the primary heat source by firing the gas burner in response to the first signal from the temperature or flow or pressure sensor of from the controller as a result of an algorithm, when hot water demand is above a primary threshold, and actuate the secondary heat source by actuating the electric heating element(s) in response to the second signal from the temperature and/or flow and/or pressure sensor when hot water demand is below a secondary threshold, thereby mitigating short cycling and cyclic losses of the primary heat source.

[0066] The controller can also be configured to detect, learn, or predict when there is no and/or low hot water demand; and actuate the secondary heat source by actuating the electric heating element to recover a set point temperature and/or flow and/or pressure of the system.

[0067] A method for heating water according to aspects of the invention can also mitigate short cycling and cyclic losses. The method includes actuating a primary heat source to generate heat for transfer to water contained in an interior region of a water heater, wherein actuating the primary heat source includes firing a gas burner in response to a signal from a temperature and/or flow and/or pressure sensor; actuating a secondary heat source to generate heat for transfer to the water contained in the interior region of the water heater, wherein actuating the secondary heat source includes actuating an electric heating element in response to a signal from the controller as a result of an algorithm, temperature and/or flow sensor(s); and mitigating short cycling and cyclic losses of the primary heat source by actuating the secondary heat source.

[0068] The method can also include actuating the primary heat source when hot water demand is above a primary threshold. The method can also include actuating the secondary heat source when hot water demand is below a secondary threshold. Additionally, the method can include detecting when there is no and/or low hot water demand; and actuating the secondary heat source by actuating the electric heating element to recover a set point temperature of the system.

[0069] Referring now to the figures, selected embodiments of the invention are illustrated as non-limiting examples.

[0070] FIG. 1 illustrates an embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for atmospheric control of the gas burner. A temperature sensor (e.g., a thermistor) that is thermally coupled to (e.g., physically contacting) a wall portion of the water tank monitors the temperature of the water in the water heater, or a temperature corresponding to the water temperature, and transmits temperature signals to a controller that is coupled to the first heat source including a gas burner configured to generate combustion gases and the second heat source including an electric heating element. The firing of the gas burner can be in response to a call for heat when a temperature or a flow or a pressure sensed by a temperature sensor or a flow sensor or a pressure sensor is below a setpoint or prescribed temperature or flow or pressure. The controller can compare, based at least in part on the temperature data or the flow rate data, the detected temperature or the detected flow rate to a threshold temperature or temperature setpoint or a threshold flow rate or setpoint, and, responsive to determining that the temperature is lower than the threshold temperature or temperature setpoint, or the flow rate is less than a threshold flow rate or greater than a flow rate threshold, the controller can output a control signal to activate the electric heating element (e.g., simultaneously with the gas burner or while the gas burner continues to operate or while the burner is off).

[0071] FIG. 2 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for atmospheric control. Similar to the embodiment of FIG. 1, in this embodiment, the system is configured for atmospheric control of the gas burner, and the operation is similar to the one described above with reference to FIG. 1. FIG. 2 provides additional detail regarding the timing of the activation of the electric heating element relative to the igniting of the pilot that ultimately fires the gas burner. In the embodiment illustrated in FIG. 2, the controller activates the electric heating element after the pilot is ignited and the gas burner is turned on.

[0072] FIG. 3 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for atmospheric control. Similar to the embodiment of FIG. 1, in this embodiment, the system is configured for atmospheric control of the gas burner, and the operation is similar to the one described above with reference to FIG. 1. FIG. 3 provides additional detail regarding the timing of the activation of the electric heating element relative to the igniting of the pilot that ultimately fires the gas burner. In the embodiment illustrated in FIG. 3, the controller activates the electric heating element before the pilot is ignited and before the gas burner is turned on.

[0073] FIG. 4 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for atmospheric control. Similar to the embodiment of FIG. 1, in this embodiment, the system is configured for atmospheric control of the gas burner, and the operation is similar to the one described above with reference to FIG. 1. FIG. 4 provides additional detail regarding the timing of the activation of the electric heating element relative to the igniting of the pilot that ultimately fires the gas burner and the turning on of the gas burner. In the embodiment illustrated in FIG. 4, the controller activates the electric heating element after the pilot is ignited, but before the gas burner is turned on.

[0074] As illustrated in the embodiments of FIG. 3 and FIG. 4, it may be beneficial to actuate the electric element before actuating the burner, which can provide the water heater system with an improved energy efficiency and earlier positive performance. Such improved efficiency can be provided without compromising access to hot water and while satisfying hot water demand.

[0075] FIG. 5 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for power vent control of the gas burner. The initial operation illustrated in FIG. 5 is similar to the operations and controls described above with reference to FIGS. 1-4 in that the controller receives temperature signals from a temperature sensor. In addition, the controller depicted in FIG. 5 receives signals from the blower pressure switch that checks whether the blower is on and whether venting may be blocked. The firing of the gas burner can be in response to a call for heat when a temperature or a flow or a pressure sensed by a temperature sensor or a flow sensor or a pressure sensor is below a setpoint or prescribed temperature or flow or pressure. The controller can compare, based at least in part on the temperature data or the flow rate data, the detected temperature or the detected flow rate to a threshold temperature or temperature setpoint or a threshold flow rate or setpoint, and, responsive to determining that the temperature is lower than the threshold temperature or temperature setpoint, or the flow rate is less than a threshold flow rate, the controller can generate a control signal to activate the electric heating element and activate (e.g., simultaneously) the gas burner by turning on the blower associated with the gas burner, igniting the pilot, and ultimately turning on the gas burner.

[0076] FIG. 6 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for power vent control of the gas burner. Similar to the embodiment of FIG. 5, in this embodiment, the system is configured for power vent control of the gas burner, and the operation is similar to the one described above with reference to FIG. 5. The difference between the embodiment depicted in FIG. 6 (compared to that of FIG. 5) is that the controller activates the electric heating element after the blower associated with the gas burner is turned on, after the pilot is ignited, and after the gas burner is turned on.

[0077] FIG. 7 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for power vent control of the gas burner. Similar to the embodiment of FIG. 5, in this embodiment, the system is configured for power vent control of the gas burner, and the operation is similar to the one described above with reference to FIG. 5. The difference between the embodiment depicted in FIG. 7 (compared to those of FIGS. 5 and 6) is that the controller activates the electric heating element after the blower associated with the gas burner is turned on, but before the pilot is ignited, and before the gas burner is turned on.

[0078] FIG. 8 illustrates another embodiment of a control logic that can be used according to an aspect of the invention. In this embodiment, the system is configured for power vent control of the gas burner. Similar to the embodiment of FIG. 5, in this embodiment, the system is configured for power vent control of the gas burner, and the operation is similar to the one described above with reference to FIG. 5. The difference between the embodiment depicted in FIG. 8 (compared to those of FIGS. 5-7) is that the controller activates the electric heating element after the blower associated with the gas burner is turned on and after the pilot is ignited, but before the gas burner is turned on.

[0079] FIG. 9 illustrates schematically an embodiment of a water heating system according to an aspect of the invention. The water heating system includes an interior region configured to contain water to be heated, a first heat source including a gas burner configured to generate combustion gases, a second heat source including an electric heating element, a controller, a temperature sensor (e.g., a thermistor) that is thermally coupled to (e.g., physically contacting) a wall portion of the water tank and that monitors the temperature of the water in the water heater, and/or a flow sensor positioned to directly or indirectly sense the flow of the water contained in the interior region.

[0080] FIG. 10 illustrates an embodiment of a method according to an aspect of the invention. In step 102 of the illustrated embodiment, the controller actuates a first heat source (e.g., firing the gas burner) to generate heat for transfer to water contained in the interior region of the water heater, in response to a first signal from a temperature or flow or pressure sensor. In step 104 of the illustrated embodiment, the controller actuates a second heat source (e.g., electric heating element) to generate heat for transfer to the water contained in the interior region of the water heater, in response to a second signal from the temperature or flow or pressure sensor.

[0081] FIG. 11 illustrates another embodiment of a method according to an aspect of the invention. In step 102 of the illustrated embodiment, the controller actuates a primary heat source (e.g., firing the gas burner) to generate heat for transfer to water contained in the interior region of the water heater, in response to a first signal from a temperature or flow or pressure sensor. In step 104 of the illustrated embodiment, the controller actuates a secondary heat source (e.g., the electric heating element) to generate heat for transfer to the water contained in the interior region of the water heater, in response to a second signal from the temperature or flow or pressure sensor. In step 106 of the illustrated embodiment, the controller mitigates the short cycling and cyclic losses of the primary heat source (e.g., the gas burner) by actuating the secondary heat source (e.g., the electric heating element).

[0082] FIG. 12 illustrates an embodiment of a control circuit according to an aspect of the invention. In this embodiment, the system is configured for atmospheric control of the gas burner, and FIG. 12 depicts atmospheric stand-alone hybrid wiring. The system illustrated in FIG. 12 includes a heating element (e.g., gas burner) configured to generate combustion gases, a pressure switch, a relay, a high limit switch, and a power source. The power source can include interconnection circuitry that supplies electric power from the power source to the heating element(s), including but not limited to wiring, terminals, and wire-to-wire connections, conductors, etc.). The pressure switch can be a gas pressure switch, for example, which normally signals the gas valve to open the flow path for gas to travel through the feed and pilot ultimately lighting the gas burner. The relay turns the heating element on and off based on the signal from the pressure switch. The relay can be integrated into the pressure switch, a TRIAC, a solid state relay, or any other type of electrical input switch. The high limit switch acts as a safety device that is configured to cut off the gas supply when the burner temperature exceeds the safe operating range. When the temperature drops back within the safe range, the high limit switch will allow the gas valve to open again. The high limit switch can be the same or separate from the gas control limit switch.

[0083] FIG. 13 illustrates another embodiment of a control circuit according to an aspect of the invention. In this embodiment, similar to the embodiment of FIG. 12, the system is configured for atmospheric control of the gas burner. FIG. 13 depicts atmospheric control wiring. The system illustrated in FIG. 13 includes a gas heating element (e.g., gas burner) configured to generate combustion gases, a number (in this case seven) of electric resistance heating elements, a pressure switch, a relay, a high limit switch, and a power source. In addition to the elements illustrated in FIG. 12, the system depicted in FIG. 13 includes a plurality of additional switches, each of which is associated with one of the seven electric resistance heating elements. The remaining components illustrated in FIG. 13 are the same or similar to the ones depicted in FIG. 12.

[0084] FIG. 14 illustrates another embodiment of a control circuit according to an aspect of the invention. The illustrated, exemplary control circuit for the electric heating element includes a high limit switch that can be the same or separate from the gas control limit switch. The relay shown could be integrated into a pressure switch, a TRIAC, a solid state relay or other type of electrical input switch. More specifically, the system illustrated in FIG. 14 includes a first heating element (e.g., gas burner) configured to generate combustion gases and a second heating element (e.g., one or more electric resistance heating elements), a pressure switch, a relay, a high limit switch, and a power source. In addition, the ability to modulate an element could be possible with a TRIAC and/or solid state relay. Other than the electric heating element, the remaining components illustrated in FIG. 14 are the same or similar to the ones depicted in FIG. 12.

[0085] FIG. 15 illustrates another embodiment of a control circuit according to an aspect of the invention. The illustrated, exemplary control circuit is configured for firing the gas burner and utilizes a standing pilot control logic/structure/hardware. Similar to the embodiment of FIG. 14, the system illustrated in FIG. 15 includes a first heating element (e.g., a gas burner configured to generate combustion gases) and a second heating element (e.g., an electric resistance heating element), a pressure switch, a relay, a high limit switch, and a power source. Other than the electric heating element, the remaining components illustrated in FIG. 15 are the same or similar to the ones depicted in FIG. 12. In addition, FIG. 15 illustrates portions of the atmospheric control logic of the gas burner depicted in detail and described above with reference to FIGS. 1-4. The gas valve illustrated in FIG. 15 can operate in response to a temperature sensor or a flow sensor or a pressure sensor.

[0086] FIG. 16 illustrates another embodiment of a control circuit according to an aspect of the invention. The illustrated, exemplary control circuit is configured for activating the electric heating element and utilizes electrical signals received from a controller and utilizes standing pilot control logic. Similar to the embodiment of FIG. 15, the system illustrated in FIG. 16 includes a first heating element (e.g., a gas burner configured to generate combustion gases) and a second heating element (e.g., an electric resistance heating element), a relay, a high limit switch, and a power source. The difference between the control circuit illustrated in FIG. 16 (compared to FIG. 15) is that the control circuit illustrated in FIG. 16 does not include a pressure switch. The gas valve and the electric heating element illustrated in FIG. 16 can operate in response to a temperature sensor or a flow sensor, as opposed to a pressure switch. The remaining components illustrated in FIG. 16 are the same or similar to the ones depicted in FIGS. 12 and 15

[0087] FIG. 17 is a temperature-time chart illustrating an aspect of the invention. Specifically, FIG. 17 depicts a commercial water heater top Negative Temperature Coefficient (NTC) sensor or thermistor in standby. FIG. 17 shows that standby decay rates can be learned through empirical testing. This data can be used to develop an algorithm so that the burner control can sense when there is no hot water demand. In this case, the burner control would use electric resistance heating elements to recover the tank temperature. Immersed electric resistance heating elements are known to be 98% efficient and do not incur the cyclic losses associated with combustion systems. For example, a combustion system typically uses energy in pre-purge, ignition, and post purge operations. Additionally, combustion systems may not reach optimum combustion efficiency for some time after the ignition has occurred.

[0088] Optionally, the water heating systems described herein can be thermally managed/activated (e.g., by bi-metal/snap disc, thermistor, thermocouple and/or algorithm for decay of outlet/tank location), flow activated (e.g., switch or meter or pressure switch related to flow) with strategic flow rates determining electric and/or gas burner order of operation, load-shedding grid enabled (e.g., uniform non-stacked or well-mixed tank or normal stack, heating water at certain times of day when electrical rates or availability are at optimum), and/or modulated (e.g., electrical tank for load shedding needs).

[0089] FIG. 18 illustrates an embodiment of a gas-electric hybrid water heater according to an aspect of this invention. As illustrated, this embodiment includes a water inlet for cold water to be heated, a water outlet for heated water, an electric element, a signal for the element, a mechanical and/or electric control, temperature/flow signal(s), a gas valve/control, a signal for the gas valve, and a gas burner in a combustion chamber. A flue for receiving combustion gases from the gas burner can be included but is not shown.

[0090] As mentioned previously, in selected embodiments of the invention, a system for heating water can be configured to mitigate short cycling and/or mitigate cyclic losses of the primary heat source. It can also be configured to deliver heated water at times of high demand. FIGS. 19-21 illustrate these and other benefits of water heater systems that can be achieved according to aspects of this invention.

[0091] FIG. 19 schematically illustrates a side view of another embodiment of a gas-electric hybrid water heater according to an aspect of this invention. In this embodiment, the water heater is a top-fired residential or commercial water heater having a combustion assembly (not shown) at the top, above the water storage tank, for directing hot combustion gases downwardly into a flue that extends into and through an interior of a water storage tank. Other configurations are of course contemplated.

[0092] In the illustrated embodiment, gas combustion heat in combustion gases is forced downward through a main combustion chamber flue. The flue can optionally have a single-pass/single-flue configuration (as illustrated), a single-to-multi-flue configuration in one pass, or a single down-fired combustion chamber flue extending into a multi-pass flue system.

[0093] In such an embodiment, the hottest water region is toward the top of the water storage tank. For example, it may be primarily the top or so of the water storage tank that is heated to a setpoint temperature in such systems.

[0094] A lower temperature sensor can optionally be positioned somewhere below the hottest water region achieved by the top-fired combustion gas heat. Accordingly, the temperature can be sensed in a cooler portion of the water storage tank, somewhere below the hottest water region and somewhere between the hottest water region and the bottom of the tank.

[0095] As shown in the exemplary embodiment of FIG. 19, a lower electric resistance heating element is position toward the bottom of the water storage tank. Accordingly, one or more lower electric heating elements can be positioned in proximity to one or more lower temperature sensors.

[0096] Such positioning of electric resistance elements and sensors in the water storage tank can be especially beneficial in a commercial water heating system. For example, when a commercial water heater is top-fired, it may be beneficial to position at least one lower electric heating element and/or at least one lower temperature sensor toward a bottom of the water storage tank where the water is cooler. For example, in instances of a dump draw, there may be a large and sustained demand for hot water such that the hot water request comes all at one time. To help satisfy such hot water demands, it is beneficial to provide one or more lower or bottom heating elements that are actuated in order to provide a larger volume of hot water (e.g., to satisfy hot water demand in dump draw circumstances).

[0097] According to embodiments of the invention, the system may include an upper temperature sensor and a lower temperature sensor, and the controller can be configured to actuate a first heat source, such asa top-fired gas burner configured to generate combustion gases, in response to a signal from the upper sensor when the upper sensor triggers a call for heat. The controller can also be configured to actuate a second heat source, such as an electric heating element in a lower portion of the water heater, in response to a signal from the lower sensor when the lower sensor triggers a call for heat. The controller can also be configured to actuate the second heat source in response to the signal from the lower sensor when, or only when, the controller is set to operate in a selected or special mode of operation.

[0098] According to exemplary embodiments of the invention, a lower temperature sensor and lower heating element can be positioned near the bottom of the tank to heat the portion of the water storage tank that is below the otherwise hottest water region toward the top of the water storage tank. This makes it possible to heat a greater volume of water to a setpoint and therefore improve dump draw capability (e.g., when there is an immediate demand for up to or even more than 100 gallons of water heated to setpoint).

[0099] In one embodiment, the control system for such a water heater configuration could include a special mode, such as a Dump Draw Mode, that would actuate or utilize a lower electric element to maintain a set point temperature measured by a lower temperature sensor. Alternatively, a water heater need not include such a special mode and can actuate or utilize a lower electric element in its usual heating control mode.

[0100] FIG. 20 is a chart illustrating temperature readings over time at various positions within a water heater while in standby mode. Specifically, FIG. 20 illustrates temperature readings over time at positions within a water heater, such as a top-fired water heater like the one illustrated in FIG. 19, while it is in standby mode without any draws of hot water. Temperatures ( F.) sensed at six locations (T1-T6) along the height of the water heater are shown over time (hrs), with T1 being toward the bottom of the water heater and T6 being toward the top.

[0101] Most or all of the temperatures shown in FIG. 20 tend to degrade over time until a burner or electrical element is actuated to maintain a set point. Such degradation is considered a standby loss. According to aspects of this invention, such standby loss can be reduced or minimized or eliminated, thereby increasing the energy efficiency of the water heater and improving its ability to deliver hot water on demand.

[0102] FIG. 21 is a chart illustrating setpoint and differential temperatures for a water heater according to an embodiment of the invention. As illustrated in FIG. 21, an electric element of a water heater according to aspects of this invention maintains the water temperature in a temperature band typically below the setpoint temperature and above an electric element differential temperature. If water temperature falls below the electric element differential, then it may be understood that the electric element cannot maintain the temperature within the temperature band below the setpoint temperature and above the electric element differential temperature, or that the electric element cannot keep up with a demand for hot water. In that circumstance, when the water temperature falls below the electric element differential, then the gas burner of the water heater can be actuated or fired by the control system. In this way, the set points for the electric element(s) and for the burner can be independent of one another and can be the same or different. Though those set points can be the same in some embodiments, they are alternatively set to be different, with one being lower than the other.

[0103] As noted above, water heater efficiency or performance is expected to be improved by implementing a gas-electric hybrid water heater according to embodiments of this invention. First Hour Rating (FHR) and UEF (Uniform Energy Factor) tests can be performed to measure improvements in efficiency, those tests being defined in Appendix E to Subpart B of Part 430 of Title 10 of the Code of Federal RegulationsUniform Test Method for Measuring the Energy Consumption of Water HeatersAppendix E to Subpart B of Part 430, Title 10), and a Simulated Use Test can be performed to examine water heater efficiency under certain conditions. Such a test can first determine a water heater's FHR or First-Hour Delivery (FHD) (generally, the amount of hot water a water heater can provide in the first hour of operation). For the remainder of the test, the water heater's usage pattern can be simulated over 24 hours with specific water temperature, air temperature, and use timing. The results of these tests can be combined to determine the overall UEF of the water heater.

[0104] According to aspects of this invention, improvements of efficiency in terms of UEF and FHR are expected to result from the gas-electric hybrid feature of embodiments of this invention. Also, such improvements in UEF are expected especially when one or more lower-placed electric heating elements are used.

[0105] Although the foregoing features may be especially beneficially employed in commercial water heater applications, the benefits and structures are applicable to residential water heater applications as well. Also, the foregoing features may be beneficial in either atmospheric or power vent water heater appliances, and the number of electric heating elements can vary from a single element to multiple elements.

[0106] Aspects of the invention include, but are not limited to, the following:

[0107] 1. A system for heating water comprising: [0108] an interior region configured to contain water to be heated; [0109] a first heat source configured to generate heat for transfer to water contained in or entering or exiting the interior region, the first heat source including a gas burner configured to generate combustion gases; [0110] a second heat source configured to generate heat for transfer to the water contained in the interior region, the second heat source including an electric heating element; [0111] a temperature or flow or pressure sensor positioned to directly or indirectly sense a temperature or a flow or a pressure of the water contained in the interior region; and [0112] a mechanical and/or electrical controller coupled to the temperature or flow sensor, the first heat source, and the second heat source, the controller being configured to: [0113] actuate the first heat source by firing the gas burner in response to a signal from the temperature or flow or pressure sensor, and/or [0114] actuate the second heat source by actuating the electric heating element in response to a signal from the temperature or flow or pressure sensor.

[0115] 2. The system of aspect 1 comprising a water storage tank at least partially defining the interior region, the water storage tank being configured to contain the water to be heated.

[0116] 3. The system of aspect 2 comprising a heat exchanger extending within the interior region defined by the water storage tank.

[0117] 4. The system of aspect 3, the gas burner being positioned to deliver the combustion gases such that they can enter the heat exchanger for the transfer of heat from the combustion gases to the water contained in the interior region.

[0118] 5. The system of aspect 1, the electric heating element being positioned for immersion in the water contained in the interior region.

[0119] 6. The system of aspect 1, the controller being configured to actuate the first heat source and the second heat source simultaneously.

[0120] 7. The system of aspect 1, further comprising a blower associated with the gas burner.

[0121] 8. The system of aspect 1, further comprising a pilot associated with the gas burner.

[0122] 9. The system of aspect 1, further comprising a gas valve configured to permit or prevent or limit flow of gas to the gas burner.

[0123] 10. The system of aspect 9, further comprising a pressure switch, the controller being configured to provide a signal to electrical or mechanical control.

[0124] 11. The system of aspect 1, the temperature or flow or pressure sensor including a thermistor.

[0125] 12 The system of aspect 1, the first heat source having a first recovery efficiency, the second heat source having a second recovery efficiency, and the system having a system recovery efficiency between or greater than the first recovery efficiency and/or the second recovery efficiency.

[0126] 13. The system of aspect 12, the first recovery efficiency, the second recovery efficiency, and the system recovery efficiency each being a first hour rating.

[0127] 14. The system of aspect 1 further comprising a heat exchanger through which the combustion gases generated by the gas burner travel.

[0128] 15. The system of aspect 14 further comprising a combustion chamber in which the combustion gases are generated by the gas burner, the combustion chamber being coupled to deliver the combustion gases into the heat exchanger.

[0129] 16. The system of aspect 1, the system being tankless.

[0130] 17. A method for heating water comprising: [0131] actuating a first heat source to generate heat for transfer to water contained in an interior region of a water heater, wherein actuating the first heat source includes firing a gas burner in response to a signal from a temperature or flow or pressure sensor; and [0132] actuating a second heat source to generate heat for transfer to the water contained in the interior region of the water heater, wherein actuating the second heat source includes actuating an electric heating element in response to a signal from the temperature or flow or pressure sensor.

[0133] 18 The method of aspect 17, wherein the firing of the gas burner is in response to a call for heat when a temperature or a flow or a pressure sensed by the temperature or flow or pressure sensor is below a setpoint or prescribed temperature or flow or pressure.

[0134] 19. The method of aspect 17, wherein the signal from the temperature or flow or pressure sensor is the same as the signal from the temperature or flow or pressure sensor.

[0135] 20. The method of aspect 17, wherein actuating the first heat source is performed before actuating the second heat source.

[0136] 21. The method of aspect 17, wherein actuating the first heat source is performed after actuating the second heat source.

[0137] 22. The method of aspect 17, further comprising igniting a pilot prior to firing the gas burner when actuating the first heat source.

[0138] 23. The method of aspect 22, wherein actuating the second heat source is performed before igniting the pilot.

[0139] 24. The method of aspect 22, wherein actuating the second heat source is performed after igniting the pilot.

[0140] 25. The method of aspect 17, further comprising actuating a blower prior to firing the gas burner when actuating the first heat source.

[0141] 26. The method of aspect 25, wherein actuating the blower is performed in response to a signal received from a pressure switch.

[0142] 27. The method of aspect 25, wherein actuating the second heat source is performed before actuating the blower.

[0143] 28. The method of aspect 25, wherein actuating the second heat source is performed after actuating the blower.

[0144] 29. A system for heating water comprising: [0145] an interior region configured to contain water to be heated; [0146] a primary heat source configured to generate heat for transfer to water contained in the interior region, the primary heat source including a gas burner configured to generate combustion gases; [0147] a secondary heat source configured to generate heat for transfer to the water contained in the interior region, the secondary heat source including an electric heating element; [0148] a temperature or flow sensor positioned to directly or indirectly sense a temperature or a flow of the water contained in the interior region or entering or exiting the interior region; and [0149] a mechanical and/or electrical controller coupled to the temperature or flow sensor, the first heat source, and the second heat source, the controller being configured to: [0150] actuate the primary heat source by firing the gas burner in response to the first signal from the temperature or flow sensor when hot water demand is above a primary threshold, and [0151] actuate the secondary heat source by actuating the electric heating element in response to the second signal from the temperature or flow sensor when hot water demand is below a secondary threshold, thereby mitigating short cycling and cyclic losses of the primary heat source.

[0152] 30. The system of aspect 29, the controller further configured to: [0153] detect when there is no or low hot water demand; and [0154] actuate the secondary heat source by actuating the electric heating element to recover a set point temperature or flow of the system.

[0155] 31. A method for heating water comprising: [0156] actuating a primary heat source to generate heat for transfer to water contained in an interior region of a water heater, wherein actuating the primary heat source includes firing a gas burner in response to a signal from a temperature or flow or pressure sensor; [0157] actuating a secondary heat source to generate heat for transfer to the water contained in the interior region of the water heater, wherein actuating the secondary heat source includes actuating an electric heating element in response to a signal from the temperature or flow or pressure sensor; and mitigating short cycling and cyclic losses of the primary heat source by [0158] actuating the secondary heat source.

[0159] 32. The method of aspect 31, further comprising actuating the primary heat source when hot water demand is above a primary threshold.

[0160] 33. The method of aspect 31, further comprising actuating the secondary heat source when hot water demand is below a secondary threshold.

[0161] 34. The method of aspect 31, further comprising: [0162] detecting when there is no or low hot water demand; and [0163] actuating the secondary heat source by actuating the electric heating element to recover a set point temperature of the system.

[0164] While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.