Abstract:
A water heater is provided having an insulated tank having a water inlet and a water outlet, and further defining an interior volume to contain a quantity of water. A primary heating arrangement applies heat energy to the water so as to heat the water. In addition, the primary heating arrangement is configured to maintain the water during standby periods between upper and lower set point temperatures. A supplemental heating arrangement is operative to supply additional heat energy to the water in order to lessen energy usage by the primary heating arrangement during the standby periods. In accordance with a preferred embodiment, the supplemental heating arrangement includes at least one photovoltaic panel and a supplemental heating element. Control electronics are operatively interposed between the at least one photovoltaic panel and the supplemental heating element.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/099,529, filed Jan. 4, 2015, the entire disclosure of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to water heaters. More particularly, the present invention relates to a water heater in which a primary heating arrangement (e.g., electric or gas) is supplemented by a photovoltaic heating arrangement. 
         [0003]    Typical water heaters have a tank in which a quantity of heated water is maintained for use as needed. Generally speaking, such water heaters fall into one of two categories, i.e., electric or gas, depending on the type of heat source used to bring the water in the tank up to the desired temperature. Electric water heaters, for example, are often configured having two electric heating elements near the top and the bottom of the tank, respectively. Typically, the heating elements are energized by AC voltage (such as 240 VAC or others) which is turned on and off as necessary to maintain the desired temperature. 
         [0004]    In this regard, electronic or bimetallic thermostats are used to regulate the water temperature by sensing the water temperature and allowing the voltage to be applied to the heating element(s) when heat is needed. Heat loss over a period of time (i.e., standby loss) or usage of the water heater capacity determines the demand for hot water. Thus, tanks that exhibit greater heat loss in the idle state are less efficient than those that exhibit less standby heat loss because more electric (or gas) energy is required to maintain the desired temperature. Efforts have thus been made to increase efficiency by providing better insulation for the tank. However, even very well insulated water heaters experience some standby loss. 
         [0005]    The present invention recognizes the foregoing considerations, and others, of the prior art. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect, the present invention provides a water heater comprising an insulated tank having a water inlet and a water outlet, and further defining an interior volume to contain a quantity of water. A primary heating arrangement applies heat energy to the water so as to heat the water. In addition, the primary heating arrangement is configured to maintain the water during standby periods between upper and lower set point temperatures. 
         [0007]    A supplemental heating arrangement, operative to supply additional heat energy to the water in order to lessen energy usage by the primary heating arrangement during the standby periods, is also provided. In accordance with a preferred embodiment, the supplemental heating arrangement includes at least one photovoltaic panel and a supplemental heating element. Control electronics are operatively interposed between the at least one photovoltaic panel and the supplemental heating element. 
         [0008]    In many cases, the primary heating arrangement may comprise at least one primary heating element adapted to be energized by AC power. For example, the primary heating arrangement may comprise first and second heating elements located near the top and bottom of the tank, respectively. Typically, first and second thermostats will be respectively associated with the first and second heating elements. For example, the thermostats may comprise bimetallic thermostats or thermistors depending on the embodiment. According to some embodiments, the primary heating arrangement may comprise an electronic processor-based control system operative to control individually the first and second heating elements. In addition, the control system can operate the supplemental heating arrangement in response to tank conditions. The control electronics of the supplemental heating arrangement may comprise a maximum power point tracking (MPPT) controller. 
         [0009]    According to an exemplary embodiment, the second heating element may comprise a primary resistive element and the supplemental heating element. The supplemental heating arrangement may further comprise a high temperature limit switch operative to disconnect application of photovoltaic energy if a predetermined threshold temperature is reached. 
         [0010]    Another aspect of the present invention provides a water heater comprising a tank defining an interior volume to contain a quantity of water. A primary heating arrangement, comprising at least one primary resistive element energized by AC power, applies heat energy to the water so as to heat the water. In this case, the primary heating arrangement further includes at least one thermostat to detect water temperature. 
         [0011]    The water heater also has a supplemental heating arrangement operative to supply additional heat energy to the water in order to lessen energy usage by the primary heating arrangement. The supplemental heating arrangement includes at least one photovoltaic panel, a supplemental heating element, and control electronics operatively interposed between the at least one photovoltaic panel and the supplemental heating element. A main controller is in electrical communication with the primary heating arrangement and the control electronics of the supplemental heating arrangement so as to control selectively heating at the at least one primary resistive element and the supplemental heating element. 
         [0012]    In some embodiments, the control electronics of the supplemental heating arrangement are contained in a separate housing from the main controller. Embodiments are also contemplated wherein the control electronics of the supplemental heating arrangement are integrated into the main controller. 
         [0013]    An additional aspect of the present invention provides a method of controlling operation of a water heater having a primary heating arrangement that functions to maintain water temperature during standby periods between a predetermined upper set point temperature and a predetermined lower set point temperature. One step of the method involves providing a solar heating arrangement operative to supply additional heat energy to the water in order to lessen energy usage by the primary heating arrangement, the solar heating arrangement including electronics operative to detect availability of solar energy. According to another step, a determination is made of whether abundance of solar energy at a particular time exceeds a threshold. If the abundance of solar energy exceeds the threshold, raising at least the lower set point temperature. According to a further step, heat energy from the solar heating arrangement is applied to water contained within the water heater if the water temperature is between the upper set point temperature and the lower set point temperature. 
         [0014]    According to exemplary methodology, the primary heating arrangement may be temporarily disabled when heat energy from the solar heating arrangement is applied. In some cases, the primary heating arrangement may be operated to apply heat energy when additional heat energy from the solar heating arrangement is also applied. Exemplary methodology contemplates determining whether one of the upper set point temperature and lower set point temperature has already been raised if the abundance of solar energy does not exceed the threshold. If one of the upper set point temperature and lower set point temperature has already been raised, it can be lowered to a default value. 
         [0015]    Another aspect of the present invention provides a method of controlling operation of a water heater having a primary heating arrangement. According to one step, a solar heating arrangement operative to supply additional heat energy to the water in order to lessen energy usage by the primary heating arrangement is provided. A determination is made of whether solar energy is available at a particular time. If the solar energy is available, heat energy is applied from the solar heating arrangement to water contained within the water heater. While heat energy is being applied from the solar heating arrangement, the primary heating arrangement is selectively operated to also supply heat energy to the water. 
         [0016]    Other objects, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, as well as methods of practicing same, which are discussed in greater detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
           [0018]      FIG. 1  is a diagrammatic representation of a water heater constructed in accordance with an embodiment of the present invention. 
           [0019]      FIG. 2  is a block diagram showing certain aspects of the water heater of  FIG. 1 . 
           [0020]      FIG. 3  is a side elevation of a dual-sheath heating element that can be used in accordance with embodiments of the present invention to allow primary electric heating and photovoltaic supplemental heating. 
           [0021]      FIG. 4  is a diagrammatic representation of a heating arrangement in accordance with a first alternative embodiment of the present invention. 
           [0022]      FIG. 5  is a block diagram of a heating arrangement in accordance with a second alternative embodiment of the present invention. 
           [0023]      FIG. 6  is a flowchart showing an exemplary method by which the embodiment of  FIG. 5  may be operated. 
       
    
    
       [0024]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
         [0026]    Presently-described embodiments provide a water heater having a supplemental photovoltaic (e.g., solar) heating arrangement which at least partially offsets standby losses that might otherwise occur. The energy produced by one or more relatively small and easily-installable photovoltaic panels preferably contributes energy equal to or greater than typical standby loss. Because modern water heaters are generally well-insulated, this can often be achieved by a solar energy contribution which is less than about 5% of the water heater&#39;s total energy consumption. Water heaters constructed in accordance with the present invention may often achieve an Energy Factor (EF) of greater than 1.0. 
         [0027]    Referring now to  FIG. 1 , a water heater  10  constructed in accordance with an embodiment of the present invention is illustrated. Water heater  10  includes an insulated tank  12  capable of containing a fixed volume of water, e.g., 20, 40, or 50 gallons. Heated water is discharged through an outlet  14 , while colder water enters the tank through an inlet  16 . Often, inlet  16  will be configured such that the incoming water will enter and mix with the existing water near the bottom of the tank. 
         [0028]    Referring now also to  FIG. 2 , water heater  10  includes top and bottom heating elements  18  and  20  mounted to the tank. In this regard, each of heating elements  18  and  20  includes a resistive element  22  and  24  that loops into the interior volume of the tank from a respective mounting flange  26  and  28 . Application of AC energy (e.g., 240 VAC) to resistive elements  22  and  24  causes them to heat in conventional fashion. In this case, however, heating element  20  includes a supplemental resistive element  30  to which supplemental photovoltaic energy is applied to offset standby losses in the tank. (One skilled in the art will appreciate that  FIG. 2  is a simplified block diagram in which electrical connections that may actually be two or more lines are shown as a single line.) 
         [0029]    Additional detail regarding a preferred embodiment of heating element  20  can be seen in  FIG. 3 . As shown, resistive element  24  turns back in order to increase its overall length, and thus the heated surface area exposed to the water. In this embodiment, resistive element  30  has a shorter overall length because it is intended to supplement the heating provided by the primary AC heating arrangement. A pair of connection terminals, e.g., terminal  32 , provides electrical connection between resistive element  24  and a source of AC energy. Likewise, a pair of connection terminals, e.g., terminal  34 , provides electrical connection between resistive element  30  and the photovoltaic source. 
         [0030]    Referring again to  FIGS. 1 and 2 , water heater  10  in this embodiment includes an electronic controller  36  that operates resistive elements  22  and  24 . In this regard, respective electronic thermostats (e.g., thermistors)  38  and  40  detect the water temperature near heating elements  18  and  20 . This temperature information is fed to controller  36  and used to selectively turn resistive elements  22  and  24  on and off. In particular, controller  36  operatives respective electrical switches  42  and  44  that connect or disconnect AC energy to resistive elements  22  and  24 , respectively. Switches  42  and  44  may be any suitable type of normally open switching device that may be operated by controller  36 , such as a suitable solid state or solenoid controlled switch. Controller  36  includes a DC power supply  46  also in electrical communication with the AC power source through an electrical cut-off (ECO)  47 . As one skilled in the art will recognize, ECO  47  removes electrical power from the water heater in the event of an over-temperature condition. Typically, an ECO, once opened, must be manually reset. 
         [0031]    Preferably, controller  36  includes a processor implementing instructions (e.g., firmware) that will turn on resistive elements  22  and  24  at different times in order to achieve the desired results. For example, if hot water in the tank has been used, controller  36  may first turn on resistive element  22  while leaving resistive element  24  off. This heats water near the top of the tank (where hot water discharges) so that some hot water is available more quickly. After the water at the top of the tank has been heated, resistive element  22  turns off and, depending on the temperature detected at thermostat  40 , resistive element  24  may be turned on. When the desired temperature at the bottom of the tank is also reached, both of the AC resistive elements will be off. Without any supplemental heating as described herein, the tank temperature will gradually decrease due to escaping heat. Once the temperature drops by a predetermined amount (e.g, 15-20 degrees F.), resistive heating is again applied to bring the water temperature back up to target. If no water is used, this cycle of heating and slow cooling repeats in “saw tooth” fashion. 
         [0032]    In accordance with the present invention, such standby losses can be at least partially offset using supplemental photovoltaic energy. Specifically, the illustrated embodiment utilizes one or more photovoltaic panel(s)  48  mounted at a suitable location for exposure to solar energy. For example, photovoltaic (PV) panel  48  may be placed on a homeowner&#39;s roof in an orientation likely to receive the most energy from the sun. The energy yielded by photovoltaic (PV) panel  48  is preferably conditioned using a suitable solar controller  50  for application to resistive element  30 . According to a preferred embodiment, for example, controller  30  may be a maximum power point tracking (MPPT) controller. Such controllers operate as DC-to-DC converters to optimize matching between PV panel  48  and the resistive load. Although solar controller  50  is shown as a separate device in the drawing, one skilled in the art will appreciate that it can be integrated into PV panel  48 . 
         [0033]    In this embodiment, the supplemental solar heating arrangement operates independently of controller  36 . Thus, the additional heat provided by resistive element  30  will not be dictated by controller  36 , but will reduce the need in standby for controller  36  to turn on resistive elements  22  and  24 . In order to ensure that PV panel  48  does not overheat the water, a high temperature limit switch  52  is provided. Switch  52  is normally closed, but will open in the event that the water temperature reaches a predetermined threshold. For example, switch  52  may be a bimetallic switch, attached to tank  12  at a suitable location, that opens mechanically when the temperature threshold is reached. In this embodiment, switch  52  is configured as an ECO which must be manually reset once tripped. 
         [0034]    As an example, panel  48  may generate up to 235 W of power with good exposure to sunlight. In this case, controller  50  can operate to provide 8-10 amps of DC current at a nominal 24 VDC. One commercially available solar controller believed to be suitable for this purpose is the PPT 12/24 solar controller from Solar Converters Inc., located in Guelph, Ontario, Canada. As available, the supplemental energy is supplied continuously to tank  12  subject to being cut-off if high-limit switch  52  detects excessive temperature. 
         [0035]    Referring now to  FIG. 4 , a supplemental heating arrangement similar to that shown in  FIGS. 1 and 2  is incorporated into a water heater utilizing traditional bimetallic thermostats. In this regard, the thermostat for top heating element  18  is incorporated into a first switching unit  54  which includes the ECO for the AC power connection. The thermostat for the AC portion of bottom heating element  20  is incorporated into a second switching unit  56 . The respective temperature set points of the top and bottom thermostats, and the manner in which switching units  54  and  56  are interconnected, achieve the desired operation. 
         [0036]    In this regard, AC energy enters first switching unit  54  through a normally closed high-limit switch  58 . The state of the top thermostat determines whether the switch  60  connects between terminals “1” and “4,” or between terminals “1” and “2.” If the switch position is between terminals “1” and “2,” then heating element  18  is energized. If the switch position is between terminals “1” and “4,” heating element  18  is not energized but energy is provided to second switching unit  56 . The state of the bottom thermostat determines whether switch  62  of second switching unit  56  is in an open or closed position. If switch  62  is in the closed position, then resistive element  24  of heating element  20  is energized. 
         [0037]    As shown, solar controller  50  supplies energy to supplemental element  30  of heating element  20  on a continuous basis as solar energy is available. This is subject to high-limit switch  52 , which cuts off the supply of solar energy if the water temperature reaches a threshold.  FIG. 4  shows greater detail regarding the specific wiring pattern between PV panel  48  and solar controller  50  for the exemplary PPT 12/24 solar controller mentioned above. One skilled in the art will appreciate that the wiring pattern will likely change if a different solar controller is employed. 
         [0038]    Embodiments are also contemplated in which the solar controller supplies information to and/or operates under the control of the main water heater controller in order to achieve improved results. In some such embodiments, for example, the functionality of the solar controller could be incorporated into the main controller. In other embodiments, a separate solar controller could be provided but it is in operative communication with the main controller. 
         [0039]    In this regard,  FIG. 5  illustrates an alternative embodiment in which a solar controller  150  is in operative communication with a water heater controller  136 . (The reference numbers for these components are increased by one hundred in comparison with their counterparts in  FIG. 2  to indicate they are modified.) Controller  136  controls switches  42  and  44  for the AC resistive elements, and also controls whether solar controller  150  supplies energy for the supplemental element  30 . This is diagrammatically represented by an internal “switch”  64  by which the controller  136  instructs the solar controller  150  to stop working. Thus, controller  136  functions to apply energy from the AC source and the supplemental solar source in order to enhance overall efficiency. 
         [0040]    For example, as illustrated in  FIG. 6 , controller  136  may execute program instructions which dynamically change temperature set points on a temporary basis in order to take advantage of abundant solar energy when it is available. Typically, the set points will increase a moderate amount (e.g., a few degrees) in order to alleviate any concerns about the water getting too hot. For example, the upper set point may not change but the lower set point can be raised if solar energy is abundant. 
         [0041]    According to this example, the process begins at step  70 , and proceeds at step  72  to sample temperature at the top (“T(u)”) and bottom (“T(L)”) of the tank. At step  74 , a decision is made whether T(u) is less than the upper set point “S(u).” If so, the upper heating element is activated at step  76 . If not, the photovoltaic (PV) output is sampled at step  78  to determine at step  80  whether a solar contribution can be made. As should be understood in view of the present disclosure, the maximum power point tracking solar controller  150  controls the load resistance presented to photovoltaic panel  48  to draw the maximum power from panel  48  as illumination to the panel varies. Nonetheless, there will be a point at which controller  50  will not be able to provide the nominal voltage to be provided by the controller, e.g. 12 Vdc or 24 Vdc. Solar controller  150  detects and reports this condition to controller  136 . 
         [0042]    If solar contribution is not available, a determination is made at step  82  of whether T(L) is less than the lower set point S(L). If so, the lower AC element is activated at step  84 . If not, the process loops back to Start. If sufficient solar energy is available, a determination is made at step  86  of whether T(L) is less than a solar set point S(S). If so, solar contribution is allowed (i.e. controller  136  controls controller  150  to apply its output voltage and current to supplemental element  30  with ECO  52 ) as shown at step  88 . In addition, as shown at step  90 , a determination is made of whether AC heating is also required because of demand or the like. 
         [0043]    In the event that a solar contribution is allowed, a determination is made at step  92  of whether solar energy is particularly abundant at the moment. As should be understood in view of the present disclosure, solar controller  150  detects power available from panel  48  and, thus, provides information to controller  136  of the panel&#39;s ability to provide power sufficient to provide the controller&#39;s output voltage level (e.g. 12 Vdc or 24 Vdc). Accordingly, controller  136  may determine if the power available from panel  48  is sufficiently above the minimum needed to provide the desired output voltage to the supplemental element such that the solar set point should be raised. The level at which available solar power from the panel is sufficient to trigger the solar set point increase is selected at the operator&#39;s desire. If so, the process will raise the solar set point S(S) on a temporary basis to take advantage of the additional “free” energy. This is indicated at step  94 , where it is determined whether the solar set point has already been raised. If not, as indicated at step  96 , the set point S(S) is raised. If abundant solar energy is not available, the solar set point remains at the lower level, or is lowered back to its default value (as indicated at steps  98  and  100 ). It will be appreciated that set point S(S) may or may not be equal to S(L) depending on the exigencies of a particular application. 
         [0044]    It can thus be seen that the present invention provides a water heater arrangement that exhibits improved efficiency and energy factor by the use a supplemental photovoltaic heating arrangement. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. For example, while the above description is primarily directed to an electric water heater having a supplemental photovoltaic heating arrangement, those skilled in the art will recognize that principles of the present invention may be used with gas water heaters as well. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention.