Abstract:
Water heater apparatus is provided with features that allow for a horizontally compact water heater installation comprising upper and lower vertically stacked electric individual water heaters served by a single electrical branch circuit. Each of the upper and lower water heaters has a water storage capacity not exceeding 55 gallons, and the combined water storage capacity of the upper and lower water heaters is greater than 55 gallons. The electric heating elements of the two water heaters are non-simultaneously controlled so that at no time do the two water heaters heat water at the same time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the filing date of provisional U.S. patent application Ser. No. 61/539,565 filed Sep. 27, 2011. The entire disclosure of the provisional application is incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The challenge of designing an energy efficient, economical residential electrical water heating system which effectively utilizes available building floor space has been heightened by the U.S. Department of Energy&#39;s recent amendment of their existing energy conservation standards for residential water heaters. In formulaic fashion, this amendment effectively requires that any residential water heater having a water storage capacity greater than fifty five gallons must incorporate therein a heat pump. While such incorporation is designed to increase the efficiency of an over-fifty five gallon water heater, installation with suitable airflow for all replacement applications may not be practical or cost effective. In view of this heightened efficiency requirement it would be desirable to provide multiple water heaters to meet the hot water requirements. It is to this goal that the present invention is primarily directed. 
     In representatively illustrated embodiments thereof, this invention provides specially designed water heater apparatus with features that allow for an installation comprising upper and lower vertically stacked electric individual water heaters served by a single electrical branch circuit. Each of the upper and lower water heaters has a water storage capacity not exceeding 55 gallons, and the combined water storage capacity of the upper and lower water heaters is greater than 55 gallons. The electric heating elements of the two water heaters are non-simultaneously controlled so that at no time do the two water heaters heat water at the same time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view through two vertically stacked electric water heaters embodying principles of the present invention and served by a single electrical branch circuit; 
         FIG. 2  is a schematic electrical circuit diagram of the stacked water heaters; 
         FIG. 3  is a schematic electrical circuit diagram of a single element electric water heater useable in place of the lower water heater in  FIG. 1 ; 
         FIG. 4  is a schematic electrical circuit diagram of a double element electric heater useable in place of the lower water heater in  FIG. 1 ; 
         FIG. 5  is a schematic electrical circuit diagram of first and second vertically stacked single element electric water heaters which are electronically controlled and served by a single electrical branch circuit; 
         FIG. 6  is a schematic electrical circuit diagram of vertically stacked single element and double element electric water heaters which are electronically controlled and served by a single electrical branch circuit; and 
         FIG. 7  schematically depicts an alternative electronic control scheme for vertically stacked water heaters that are served by a single electrical branch circuit. 
     
    
    
     DETAILED DESCRIPTION 
     Schematically depicted in  FIG. 1  is a specially designed electric water heater assembly  10  which comprises vertically stacked upper and lower electric water heaters  12  and  14  and is served by a single branch electrical circuit portion  16  of an electrical distribution panel  18 . Branch circuit  16  comprises two power wires or leads L 1  and L 2 , and a ground wire or lead G. Each of the water heaters  12  and  14  has a metal tank  20  adapted to hold a quantity of water  22  to be heated. According to an aspect of the present invention, the volume of each of the tanks  20  is no more than fifty five gallons, and the total volume of the two tanks  20  is greater than fifty five gallons. As subsequently described herein, the upper and lower electric water heaters  12  and  14  are non-simultaneously controlled in a manner such that neither water heater operates while the other one is performing its water heating function. Thus, the electrical branch circuit  16  need only be sized to accommodate one of the two water heaters  12  and  14  (the larger one if they do not have equal water heating capacities). Importantly, this combination of design aspects in the present invention adheres to both the letter and spirit of the DOE energy efficiency standard amendment. Specifically, neither of the water heaters has a water storage capacity exceeding fifty five gallons, and the two stored water quantities (which together exceed fifty five gallons) are never heated at the same time. 
     Still referring to  FIG. 1 , each the tanks  20  is enclosed within an outwardly spaced metal jacket  24 , with suitable insulation  26  being disposed within the space between the jacket  24  and the tank  20 . The upper end of each jacket  24  has a centrally disposed upward projection  24   a , and the lower end of each jacket  24  has a complementarily shaped central recess  24   b . The upper and lower water heaters  12  and  14  are vertically stacked as shown in  FIG. 1  by placing the lower water heater  14  on a suitable horizontal support surface such as a floor  28  and then placing the upper water heater  12  atop the lower water heater  14  in a manner such that the upper projection  24   a  of the lower water heater  14  is interlockingly received in the lower recess  24   b  of the upper water heater  12 . This horizontally aligns and stabilizes the upper and lower water heaters  12  and  14 . 
     While the illustrated upper and lower water heaters  12  and  14  are representatively depicted as being identical, it will be readily apparent to those of ordinary skill in this particular art that they could be of different storage capacities, heating capacities and/or different physical sizes if desired without departing from principles of the present invention. For example, the upper water heater  12  could be of a smaller diameter than the lower water heater  14 , with the central vertical axes of the two water heaters being horizontally offset from one another. It should be noted that the vertical stacking of the two water heaters  12  and  14  advantageously reduces the footprint of the overall water heater assembly  10  compared to, for example, (1) placing both of the water heaters  12 , 14  on the floor  28 , or (2) using a single water heater (having the same total water storage and heating capacity as the stacked water heater assembly  10 ). 
     Each of the upper and lower water heaters  12  and  14  has a resistance type electrical heating element  30  horizontally extending into the interior of its tank  20  and being controlled by a conventional combination high limit/operating thermostat  32 . As indicated by the flow arrows in  FIG. 1 , during operation of the assembly  10 , water flows into the lower tank  20  via an inlet pipe P 1 , from the lower tank  20  into the upper tank  20  via a transfer pipe P 2 , and then out of the upper tank  20  through an outlet pipe P 3 . As will be readily appreciated by those of skill in this particular art, the plumbing connections between the two water heaters may be accomplished to provide either a serial flow connection therebetween (as illustratively depicted in  FIG. 1 ) or a parallel flow connection between the two water heaters. 
     Circumferentially aligned junction boxes  34  are disposed in peripheral portions of the upper and lower ends of each of the upper and lower water heaters  12  and  14 . Extending downwardly through the insulation  26  between the two junction boxes  34  on each water heater  12  and  14  is a vertical wiring passage  36 . The upper water heater  12  is stacked atop the lower water heater  14  in a manner such that, as schematically depicted in  FIG. 1 , the junction boxes  34  and the wiring passages  36  are circumferentially aligned with one another. 
     As subsequently described in more detail herein, power and ground wiring from the single branch electrical circuit  16  is passed downwardly through the circumferentially aligned wiring passages  36  and is operatively connected to the heating elements  30  and the thermostats  32  in a manner such that the heating elements are non-simultaneously controlled. With reference now to  FIG. 2 , each of the conventional thermostats  32  has an upper high limit section  38  and a lower operating section  40 . Sections  38  and  40  have the indicated wiring terminals  1 - 4 , and each operating section  40  is provided with the indicated single pole, double throw switch  42 . Each electric heating element  30  is electrically coupled to its associated switch terminals  2  and  4  as indicated. 
     According to a feature of the present invention, the two thermostats  32  are electrically coupled in a manner providing the non-simultaneous control of the two heating elements  30  so that only one is operable at a given time. Specifically, as schematically depicted in  FIG. 2 , power leads L 1  and L 2  are respectively connected to terminals  1  and  3  of the high limit section  38  of the upper thermostat  32 , and the ground lead G is connected to the grounding terminal  44  of the upper water heater  12 . Operative control coupling of the upper and lower water heaters  12  and  14  is effected utilizing supplemental power leads L 1   a ,L 2   a  and a supplemental grounding lead Ga. Lead L 1   a  is interconnected between the thermostat operating section terminal  4  of the upper water heater  12  and the thermostat high limit section terminal  1  of the lower water heater  14 . Lead L 2   a  is interconnected between the thermostat high limit section terminal  4  of the upper water heater  12  and the thermostat operating section terminal  3  of the lower water heater  14 . Lead Ga is interconnected between lead G and the grounding terminal  46  of the lower water heater  14 . 
     By tracing the circuitry in  FIG. 2  it can be seen that with the upper thermostat switch  32  interconnecting its associated thermostat operating section terminals  1  and  2  current flow through the upper heating element  30  to satisfy the water heating demand of the upper water heater  12  is permitted, but simultaneous current flow through the lower heating element  30  is precluded by the circuit opening between terminals  1  and  4  of the operating section  40  of the upper thermostat  32 . Conversely, when the water heating demand of the upper water heater  12  is satisfied, the upper switch  32  disconnects the terminals  1  and  2  of the operating section  40  of the upper thermostat  32  and electrically connects the terminals  1  and  4  of the operating section  40  of the upper thermostat  32 , thereby permitting current flow through the lower heating element  30  and blocking current flow through the upper heating element  30 . Accordingly, neither heating element  30  can receive a current throughflow when the other heating element  30  has electrical current being supplied thereto. 
     Representatively, but not by way of limitation, the water heaters schematically depicted in  FIGS. 1 and 2  are of substantially identical size and construction, with the lower water heater  14  having capped-off power and ground leads L 1   b , L 2   b  and Gb connected as shown to its heating element  30  and thermostat  40 . As will be appreciated, these leads may be operatively connected to the thermostat and heating element of another water heater upon which the water heater  14  is to be stacked. Water heater  12  would, as manufactured, also have these capped off leads which may be operatively coupled to a water heater upon which it could be stacked. In the stacked water heater assembly shown in  FIGS. 1 and 2 , the lead sets L 1 , L 2  and G, L 1   a , L 2   a  and Ga, and L 1   b , L 2   b  and Gb may be conveniently run downwardly through the aligned wiring passages  36  as shown in  FIG. 1 . 
     An alternate bottom electric water heater embodiment  14   a  is shown in  FIG. 3 . Water heater  14   a  is identical in construction to the previously described water heater  14  with the exceptions that it is not provided with the bottom interconnecting leads L 1   b , L 2   b  and Gb, and its thermostat  32   a  does not utilize a terminal  4  on its operating section  40   a.    
     A second alternate bottom electric water heater embodiment  14   b  is shown in  FIG. 4 . Water heater  14   b  has upper and lower electric heating elements  30  and  48  which are respectively controlled by a conventional combination high limit/operating thermostat  32  and a thermostat  50  having a single pole single throw switch  52 . The upper thermostat  32  and heating element  30  are operatively interconnected as shown by power leads L 1   c  and L 2   c , and the upper thermostat  32  is connected to the thermostat  32  of the upper water heater  12  (see  FIG. 2 ) by the leads L 1   a , L 2   a  and Ga. As can be seen this wiring connection provides non-simultaneous control of the water heaters  12  and  14   b , and further prevents non-simultaneous operation of the heating elements  32  and  48  in the lower water heater  14   b.    
     Schematically illustrated in  FIG. 5  is an alternate embodiment  10   a  of the previously described stacked water heater assembly  10 . In assembly  10   a  the previously described combination high limit/operating thermostats  32  shown in  FIG. 1  are replaced by high limit switch structures  54  and  56  respectively disposed within the tank portions of the upper and lower water heaters  12  and  14 , and the switching capability useable to provide non-simultaneous control of the upper and lower water heaters  12  and  14  is provided by an electronic control panel  58  incorporating therein a suitable preprogrammed microprocessor  60 . Power lead L 1  is connected to the upper and lower high limits switches  56 , and the heating elements  30  are also connected as shown to the high limit switches  54  and  56 . Further, the high limit switches  54  and  56  are respectively connected as illustrated to two control panel switches  62  and  64  which are also electrically connected as shown to the power lead L 2 . Switches  62  and  64  may alternatively be relays, or other electronic devices, that can switch the resistive load of the heating elements. In response to temperature signals  66  and  68  respectively received from upper and lower tank water temperature sensors  70  and  72 , the control panel  58  electronically controls the switches  62  and  64  in a manner providing non-simultaneous control of the upper and lower water heaters  12  and  14  shown in  FIG. 5 . 
     A second alternate embodiment  10   b  of the water heater assembly  10  is schematically shown in  FIG. 6  and is substantially identical to the previously described assembly  10   a  in  FIG. 5  with the primary exceptions that the lower water heater  14  is provided with upper and lower heating elements  30   a  and  30   b  coupled to their associated high limit switch  56  as shown, and three switches  86 ,  88  and  90  are included in the control panel  58  and coupled to the high limit switches  54 , 56  and the electric heating elements  30 ,  30   a  and  30   b  as shown. Switches  86 , 88  and  90  may alternatively be relays, or other electronic devices, that can switch the resistive load of the heating elements. In response to temperature signals  66  and  68  respectively received from upper and lower tank water temperature sensors  70  and  72 , the control panel  58  electronically controls the switches  86 ,  88  and  90  in a manner providing non-simultaneous control of the upper and lower water heaters  12  and  14 , and further providing non-simultaneous energization of the lower water heater heating elements  30   a  and  30   b.    
     Shown in  FIG. 7  is a third alternate embodiment  10   c  of the previously described stacked water heater assembly  10 . Embodiment  10   c , by way of non-limiting example, comprises vertically stacked upper and lower water heaters  76  and  78  electrically coupled by the previously described lead sets L 1 , L 2  and G, and L 1   a , L 2   a  and Ga, and each having dual electrical resistance heaters  30  extending through the interiors of their tank portions. The upper and lower water heaters  76  and  78  are non-simultaneously controlled by upper and lower control structures  80  and  82  which may communicate with one another via a communication line  84 . Representatively, the upper control structure  80  may be a master unit, and the lower control structure  82  may be a slave unit, with the master unit  80  having the capability of sensing whether the upper and lower water heaters  76  and  78  have single or multiple heating elements and responsively adjusting the control functions and sequences associated with the operative control of the upper and lower water heaters  76  and  78 . Master unit  80  also determines which element to turn on in a way that only one element is turned on at any given time. 
     The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.