Abstract:
The invention includes a tankless liquid heater that employs a series of chambers, each having a plurality of heating tubes, with heating elements positioned thereon, and a control unit comprising a switch, controller, and power distributor to control the flow and heating of liquid in the system. In one embodiment, the control unit takes input from a liquid flow sensor that monitors the passage of liquid through the system, a temperature sensor adapted to monitor liquid temperature, and a current leakage sensor adapted to monitor the current leakage in the system. In response to these sensors, the control controller actuates the relay between an closed position, which allows current from the power distributor to pass to a plurality of heating elements, and an open position, which prevents the current from flowing from the power distributer to the plurality of heating elements.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to currently pending U.S. Provisional Patent Application 61/035,893, entitled, “Tankless Liquid Heater”, filed Mar. 12, 2008. 
     BACKGROUND OF THE INVENTION 
     Electric flow-through liquid heaters, which are often described as electric tankless liquid heaters, heat liquids as they pass through the heat exchanger. The objective of such heaters is to heat liquid as it enters and passes through the heat exchanger to the desired set point by the time it is dispensed at the outlet of the heater. In concept, this process is relatively simple to achieve in closed loop systems in which the operating parameters for flow and temperature can be predetermined. Instantaneous and tankless hot liquid heaters are known in the art for the delivery of hot liquid at a point of use. 
     U.S. Pat. No. 3,909,588 issued to Walker et al. discloses an electric liquid heater using electrodes immersed in an electrically-insulated flow-through tank with controls sensing both liquid temperature and heating electrode current. 
     U.S. Pat. No. 4,337,388 issued to July discloses a rapid-response liquid heating and delivery system incorporating liquid heating means, liquid temperature sensing means, and proportional integral derivative (PID) method of closed loop control. 
     U.S. Pat. No. 4,638,147 issued to Dytch et al. discloses a microprocessor controlled flow-through liquid heater regulating heating power by switching combinations of heating elements of different wattages. 
     U.S. Pat. No. 4,829,159 issued to Braun et al. discloses a method of switching electrical heating elements loads to reduce switching transients by energizing all loads neither switched off nor full on in sequence. 
     U.S. Pat. No. 4,920,252 issued to Yoshino discloses a temperature control method for a plurality of heating elements by allocating a required actuating time within one cycle of a predetermined length of time. 
     U.S. Pat. No. 5,216,743 issued to Seitz discloses a thermoplastic heat exchanger for a flow-through instantaneous liquid heater including a control system using temperature comparisons. 
     U.S. Pat. No. 5,479,558 issued to White, Jr. et al. discloses a flow-through tankless liquid heater with a flow-responsive control means. 
     U.S. Pat. No. 5,504,306 issued to Russell et al. discloses a tankless liquid heater system incorporating a microprocessor based control sensing liquid outlet temperature, accepting an option remote temperature-setting means and providing control of heating elements by applying power in fractions of a power line cycle. 
     U.S. Pat. No. 5,866,880 issued to Seitz et al. discloses using a plurality of heating elements wherein each of the elements receives a substantially equal amount of power and the delay between each element being powered is no more than 32 half cycles. 
     SUMMARY OF INVENTION 
     The invention includes a tankless liquid heater that employs a series of chambers, each having a plurality of heating tubes, with heating elements positioned thereon, and a control unit comprising a switch, controller, and power distributor to control the flow and heating of liquid in the system. 
     The novel tankless water heater includes a first hollow chamber. A liquid inlet and a liquid outlet have respective first ends disposed externally of the first hollow chamber and respective second ends disposed internally of the first hollow chamber. At least one and preferably a plurality of straight tubes is disposed within the hollow chamber in parallel relation to one another. At least one curved tube has a return bend formed therein connecting contiguous parallel straight tubes to one another so that liquid fluid flowing through the straight tubes is constrained to reverse flow direction at least once. A first straight tube of the plurality of straight tubes has a leading end connected in fluid communication with the internal second end of the liquid inlet and a second straight tube of the plurality of tubes has a trailing end connected in fluid communication with the internal second end of the liquid outlet. An elongate insert is disposed concentrically within a lumen of each straight tube and a helical, radially outwardly extending flange is formed along a length of each elongate insert. A plurality of annular heating elements is disposed in contacting, circumscribing relation to each of the straight tubes and in longitudinally spaced apart relation to one another so that heat flows by conduction radially inwardly from the annular heating elements into the straight tubes, thereby heating the straight tubes. Each of the annular heating elements is in independent switched electrical communication with a remote source of electrical power so that loss of power to one annular heating element does not affect the other annular heating elements. Each of the annular heating elements is transversely disposed relative to a longitudinal axis of its associated straight tube. A source of unheated liquid fluid under pressure is connected in fluid communication with the external first end of the liquid inlet so that heated liquid fluid flows outwardly from the external first end of the liquid outlet when at least one of the annular heating elements is operating. The insert and the helical, radially outwardly extending flange causes liquid fluid to flow radially outwardly into contacting relation with the heated straight tubes. The liquid fluid does not contact the annular heating elements. 
     In a second embodiment, a second hollow chamber includes a liquid inlet and a liquid outlet having respective first ends disposed externally of the second hollow chamber and respective second ends disposed internally of the second hollow chamber. The second hollow chamber has a plurality of straight tubes disposed therewithin, interconnected to one another at alternating ends by a plurality of curved tubes having return bends formed therein so that liquid fluid flowing into the second hollow chamber at the liquid inlet of the second hollow chamber is constrained to reverse direction at least once before flowing out of the second hollow chamber at the liquid outlet of the second hollow chamber. To place the first and second hollow chambers in parallel relation to one another, a source of unheated liquid fluid under pressure is connected to respective external first ends of the liquid inlets of the first and second hollow chambers and heated liquid fluid flows from respective external first ends of the liquid outlets of the first and second hollow chambers. To place the first and second hollow chambers in series relation to one another, a source of unheated liquid fluid under pressure is connected to the external first end of the liquid inlet of the first hollow chamber and the external first end of the liquid outlet of the first hollow chamber is connected in fluid communication with the external first end of the liquid inlet of the second hollow chamber and the external first end of the liquid outlet of the second hollow chamber is in fluid communication with a point of use. 
     A temperature sensor and a flow sensor are coupled to the liquid heating assembly and a control module is in electrical communication with the temperature sensor and the flow sensor. The control module is programmed to control operating circuitry in response to electrical signals generated by the temperature sensor and flow sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a tankless liquid heater in accordance with an embodiment of the present invention. 
         FIG. 2  is an exploded view of the heating tubes of the invention showing the plurality of heating elements disposed thereon. 
         FIG. 3  is an exploded view of a heating tube showing the helical insert disposed therein in accordance with an embodiment of the present invention. 
         FIG. 4A  is a exploded, perspective view of the liquid heating assembly in accordance with an embodiment of the present invention, showing the liquid flow path. 
         FIG. 4B  is a view of the heating tubes of interior of the chambers of a tankless liquid heater in accordance with an embodiment of the present invention, showing the heating tubes and the liquid flow path there through. 
         FIG. 5  is a perspective view of a tankless liquid heater in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram of the control circuit and liquid heating assembly of a tankless liquid heater in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram of the control circuit and liquid heating assembly of a tankless liquid heater in accordance with an embodiment of the present invention. 
         FIG. 8  is an illustrative control circuit diagram for use in an embodiment of the present invention. 
         FIG. 9  is a flowchart showing the control logic of a tankless liquid heater in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. 
     The components of a tankless liquid heater  10  of a first embodiment are shown in  FIG. 1 . As shown, tankless liquid heater  10  comprises liquid heating assembly  11 , power distributer  12 , switch/relay  13 , temperature controller  14 , general controller  15 , heatsink, and a power source (not shown). Liquid heating assembly comprises first chamber  17 , second chamber  18 , primary liquid inlet  19  couple-able to a pressurized liquid source, and primary liquid outlet  20 . First chamber  17  has liquid inlet  21  in liquid communication with primary liquid inlet  19  and liquid outlet  22  in liquid communication with primary liquid outlet  20 . Second chamber  18  has liquid inlet  23  in liquid communication with primary liquid inlet  19  and liquid outlet  24  in liquid communication with primary liquid outlet  20 . The dual chambers of the system shown in  FIG. 1  create a redundant system. Systems with additional repetition or with only a single chamber are also contemplated. Multiple chambers can be stacked in parallel to increase liquid throughput. 
       FIG. 2  is an exploded view of the interior of first chamber  17  and second chamber  18 . Chambers  17  and  18  each comprise liquid inlet  21 , 23 , liquid outlet  22 , 24 , first heating tube  30 , second heating tube  31 , third heating tube  32 , and fourth heating tube  33 . First heating tube  30  has inlet end  34  in liquid communication with the liquid inlet of chamber  17 ,  18  and outlet end  35 . Second heating tube  31  has inlet end  36  in liquid communication with liquid outlet end  35  of first heating tube  30  and outlet end  37 . Third heating tube  32  has inlet end  38  in liquid communication with liquid outlet end  37  of second heating tube  31  and outlet end  39 . Fourth heating tube  33  has inlet end  40  in liquid communication with liquid outlet end  39  of third heating tube  32  and outlet end  41 . Outlet end  35  of first heating tube  30  is connected to inlet end  36  of second heating tube  31  with first conduit  42  which forms a return bend as depicted. Outlet end  37  of second heating tube  31  is connected to inlet end  38  of third heating tube  32  with second conduit  43  which is also in the form of a return bend as depicted. Outlet end  39  of third heating tube  32  is connected to inlet end  40  of fourth heating tube  33  with third conduit  44 , also of return bend configuration as depicted. 
     Heating tubes  30 - 33  may be made of any conductive material. In a preferred embodiment, heating tubes  30 - 33  are made of quartz. Chambers  17  and  18  may be increased or reduced in size and may contain any number of heating tubes. 
     Each heating tube  30 - 33  includes insert  69  having raised helical ridge  70  formed integrally therewith as depicted in  FIG. 3 . Helical ridge  70  provides additional functionality by creating turbulence within the heating tube and thereby preventing mineral deposits from building up in the tube, and increasing the surface area of the liquid column that is exposed to the heating elements. Liquid fluid at the center of the column is forced into contact with the tube surface. As drawn, the diameter of insert  69  is about half the diameter of the lumen of its associated tube  30 - 33  so that the elongate toroid-shaped space  71  that surrounds insert  69  has a radial extent that is about half the radius of insert  69 . Helical ridge  70  rises a short distance from insert  69  as depicted, and therefore extends into space  71  by only a nominal amount so that most of the gap between helical ridge  70  and the lumen of the tube is unoccupied. This nominal amount is sufficient to induce turbulence into the flow of liquid fluid through the heating tube in order to inhibit mineral deposit build-up. The relative dimensions as depicted and as recited herein are not critical; the only criticality is that helical ridge  70  be sufficiently prominent to induce turbulence but not so prominent as to promote unwanted laminar flow about insert  69 . The term “nominal” means nominal relative to a distance from the elongate insert to an interior wall of the at least one straight tube within which said elongate insert is concentrically mounted. 
     At least one heating element  45  is positioned on each heating tube  30 - 33 . For illustrative purposes, as shown in  FIG. 2 , heating elements  45  are placed at each end and at the center of heating tubes  30 - 33 . However, any number and/or location of heating elements are contemplated by the present invention. The arrangement of heating elements at different positions on the tube allow for controlled heating of liquid at different locations within the tubes. This arrangement also provides a fine degree of control allowing the temperature of the liquid in the system to be changed by as little as 1 degree (higher or lower). 
       FIGS. 4A and 4B  illustrates the liquid flow path through heating assembly  11  using dotted lines. Liquid enters at primary liquid inlet  19 . Entering liquid is then split between liquid inlet  21  of first chamber  17  and liquid inlet  23  of second chamber  18 . After entering each chamber  17 , 18 , liquid passes through first heating tube  30 , first conduit  42 , second heating tube  31 , second conduit  43 , third heating tube  32 , third conduit  44 , and fourth heating tube, before passing out of chamber  17 , 18 . Liquid exits first chamber  17  at liquid outlet  22  and exits second chamber  18  at liquid outlet  24 . Liquid passing out of liquid outlet  22  and liquid outlet  24  combines and then exits through primary liquid outlet  20 . 
     In another embodiment, as illustrated in  FIG. 5 , first chamber  17  and second chamber  18  are arranged in series. In this embodiment, primary liquid inlet  19  connects to first chamber  17  at liquid inlet  21 , liquid outlet  22  of first chamber  17  connects to liquid inlet  23  of second chamber  18 , and liquid outlet  24  of second chamber  18  connects to primary liquid outlet  20 . The separation and re-combination of liquid is eliminated in this design. Once liquid enters through primary liquid inlet  19 , it flows to liquid inlet  21  of first chamber  17 . Once inside first chamber  17 , liquid flows the same as described above and illustrated in  FIG. 4B  and then exits first chamber  17  at liquid outlet  22 . Liquid then continues to liquid inlet  23  of second chamber  18 . Once inside second chamber  18 , liquid flows as described above and illustrated in  FIG. 4B , exits second chamber  18  at liquid outlet  24 , and continues to exit heating assembly  11  at primary liquid outlet  20 . The dual chambers of the system shown in  FIG. 5  create a repetitive system. Systems with additional repetition or with only single chamber are also contemplated. Multiple chambers can be added in series to increase liquid throughput. 
     In an embodiment, as shown in  FIG. 6 , control circuit  50  comprises switch  51 , controller  52 , and power distributer  53 . Temperature is measured by temperature sensor  54  coupled to heating assembly  11  along the outflow portion of the liquid flow path. Liquid flow rate is determined by flow sensor  55  coupled to heating assembly  11  along the liquid flow path. Current leakage is measured by current leakage sensor  59  coupled to the wires disseminating current from power distributer  53 . Various types of sensor and sensor placement may used to measure temperature, liquid flow, and current leakage. The temperature and liquid flow sensors may be mounted to heating tubes  30 - 33 , liquid inlets  21 ,  23 , liquid outlets  22 , 24 , primary liquid inlet  19 , or primary liquid outlet  20 , depending on what is being sensed. In the present embodiment, temperature sensor  54  is located on primary liquid outlet  20  and flow sensor  55  is located on primary liquid inlet  19 . The leakage sensor may be mounted along the current flow path. 
     Temperature sensor  54 , flow sensor  55 , and current leakage sensor  59  provide data to controller  52 , which then actuates switch  51  in response to the received data. Switch  51  may be any device capable of allowing and preventing current flow to the heating elements responsive to input from the controller. In the present embodiment, switch  51  is a solid-state relay. 
     Controller  52  may have a minimum flow rate setting and temperature setting. Controller  52  will actuate switch  51  to a closed position to allow current to flow from power distributer  53  to heating elements  45 , when the flow rate detected by flow rate sensor  55  exceeds the flow rate threshold and the temperature detected by temperature sensor  54  is less than the temperature setting. Controller  52  will actuate switch  51  to an open position to prevent current flow to heating elements  45 , when either the flow rate is less than the flow rate threshold or the temperature is greater than or equal to the temperature setting. 
     Controller  52  may also have a maximum current leakage setting. Controller  52  will actuate switch  51  to an open position when the current leakage detected by current leakage sensor  59  exceeds the maximum current leakage setting. 
     Controller  52  may comprise a general controller that takes temperature and other sensor inputs and uses the inputs to actuate switch  51 , as shown in  FIG. 6  and described above, or Controller  52  may comprise, as shown in  FIG. 7 , a general controller  60 , and a temperature controller  61 . In the embodiment shown in  FIG. 7 , general controller  60  is a printed circuit board and temperature controller  61  is a PID controller. 
     Power distributer receives power from a power source (not shown) and supplies power to heating elements  45  as regulated by switch  51 . 
       FIG. 8  is an illustrative control circuit diagram for use in an embodiment of the present invention. 
       FIG. 9  provides a high-level flowchart of the system control. After powering on the system is powered on in operation  71 , the system moves to operation  72 , which includes accessing on board memory to acquire the necessary settings, such as temperature and power settings. In operation  73 , the system performs a system check for sensor operability, liquid temperature, leakage current, and liquid flow. If all sensors are functional (operation  74 ), the heater, in operation  75 , enters standby mode (heating tubes are turned off). In operation  76 , the system ensures that there is a liquid flow and operation  77  ensures liquid flow is sufficient for operation. In operation  78 , responsive to normal operating parameters (e.g. minimal liquid flow=0.5 GPM), the system activates (or turns on) and modulates the switch for the heating tubes to achieve the user-defined temperature. In operations  80 ,  81 , and  82 , the system constantly monitors parameters, such as temperature, current leakage, and liquid flow. In operation  82 , the system determines if liquid flow is sufficient for operation and if the target temperature has been achieved. If the liquid flow is determined to be sufficient, but the liquid temperature is low, then the system keeps the maximum achievable temperature constant throughout the system in operation  84  until the system is manually turned off (operations  85  and  88 )). Responsive to predetermined parameters the system will issue error codes notifying the user of a problem (e.g. low flow error code (operation  86 ) and/or stop/error code (operation  87 ). For example, once liquid temperature exceeds 125 degrees, the system automatically shuts down and resumes operation once the temperature of liquid in the system falls below 125 degrees. As another example, once the current leakage reaches 15 mA, the system automatically shuts down. 
     The liquid heater of a present embodiment provides a more efficient liquid heater than that of the prior art. Each heating tube draws a current of 10 A making each chamber, having four heating tubes, draw 40 A. An embodiment with one chamber, having amperage of 40 A has wattage of 8.8 kW. An embodiment with two chambers, having amperage of 80 A has wattage of 17.6 kW. Tankless liquid heater of the prior art using the same amount of amperage (80 A), draw 5 kW more than the present invention. Example specifications are given in the chart of  FIG. 10 . 
     In addition, the liquid heater of a present embodiment is capable of operating with only one working heating tube. If up to three heating tubes stop conducting heat for any reason, the remaining tubes will receive the current not being used by the broken tubes and no interruption will result. 
     It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between. Now that the invention has been described,