Fluid heating control system

• US 6,246,831 B1
• Filed: 06/16/1999
• Issued: 06/12/2001
• Est. Priority Date: 06/16/1999
• Status: Expired due to Term

• Current Assignee: A. O. Smith Corporation
• Original Assignee: David Seitz
• Inventors: Everett, Louis J., Seitz, David E., Neumann, Rodney H., Harman, Thomas Lamson, Sharp, David Paul
• Primary Examiner(s): Walberg, Teresa
• Assistant Examiner(s): DAHBOUR, HENRY
• Application Number:
  US09/334,337
• Time in Patent Office: 727 Days
• Field of Search: 392/465, 392/466, 392/479, 392/480, 392/481, 392/484, 392/485, 392/486, 392/487, 392/488, 392/489, 219/483, 219/497
• US Class Current: 392/486
• CPC Class Codes: F24H 15/104 Inspection; Diagnosis; Trial operation
• CPC Class Codes: F24H 15/12 Preventing or detecting fluid leakage
• CPC Class Codes: F24H 15/174 Supplying heated water with desired temperature or desired range of temperature
• CPC Class Codes: F24H 15/212 Temperature of the water
• CPC Class Codes: F24H 15/246 Water level
• CPC Class Codes: F24H 15/335 Control of pumps, e.g. on-off control control of compressors of heat pumps F24H15/38
• CPC Class Codes: F24H 15/37 of electric heaters
• CPC Class Codes: F24H 15/395 Information to users, e.g. alarms
• CPC Class Codes: F24H 15/407 using electrical switching, e.g. TRIAC
• CPC Class Codes: F24H 15/414 using electronic processing, e.g. computer-based
• CPC Class Codes: G05D 23/1931 to control the temperature of one space
• CPC Class Codes: H05B 1/0283 For heating of fluids, e.g. water heaters
• CPC Class Codes: H05B 2203/021 Heaters specially adapted for heating liquids
• CPC Class Codes: H05B 3/10 Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor

Abstract

An improved system, method and apparatus for control of an instantaneous flow-through fluid heater system is disclosed. The control incorporates a logic control method providing modulation of power in small steps to a plurality of heating elements retaining responsiveness to closed-loop control needs without inducing light flicker. Further, the life of the coils of heating circuit electromechanical relays are extended by energizing the coils with a pulse-width-modulated drive decreasing in duty cycle and thus the latent coil heat when an increase in mains voltage is sensed. The life of the contacts of same relays are extended by inhibiting heating element triac drive immediately upon sensing loss of relay coil power, such as by an over temperature limit switch opening, thus ensuring that relay contacts open with zero heating element current. In addition to the software “watchdog timer” internal to the microcontroller, a redundant fail-safe circuit external to the microcontroller prevents a program lockup condition from leaving any heating element triac or relay drive in an energized state. A combination of control hardware and program provide self-diagnostic detection of an inoperative thermistor, stuck relay, or a failed triac or heating element. An improved means of sensing water level is disclosed incorporating a low-level, high frequency signal, allowing detection of non-conducting distilled water and the reliable detection of water in the presence of main-frequency currents as would exist in ungrounded sheathed heating elements with electrical leakage or as would exist with bare-elements.

Claims

1. A fluid heater powered by an alternating current (AC) electric power source, said heater comprising:

a housing having at least one chamber, said housing having a fluid inlet and a fluid outlet;

a plurality of electrically powered heating elements, each of said plurality of heating elements positioned within a respective one of said at least one chamber for heating a flowing fluid;

a power controller for controlling the connection of each of said plurality of heating elements to the AC power source such that each of said plurality of heating elements is connected for at least one half cycle of each of the plurality of power cycle patterns defining a power level, the plurality of power levels at which said plurality of heating elements operate are selected from the group consisting of 0/2x, 12.5/2x, 25/2x, 37.5/2x, 50/2x, 62.5/2x, 75/2x, 87.5/2x and 100/2x, wherein a numerator of each of these fractions represents the number of half cycles of an x Hz AC power source within one second during which said plurality of heating elements are powered, wherein the operation of each of said plurality of heating elements is sequentially timed to substantially reduce switching frequencies which otherwise would cause visually perceptible lighting flicker from the AC power source;

one or more fluid temperatures sensors each responsive to fluid temperature at a selected location within the at least one chamber; and

a logic circuit for controlling a desired temperature of the flowing fluid from the fluid outlet, said logic circuit receiving temperature information from the one or more fluid temperature sensors and providing temperature information to said power controller.

2. The fluid heater according to claim 1, wherein a plurality of power levels at which said plurality of heating elements operate are selected from the group consisting of 0/120, 15/120, 30/120,45/120, 60/120, 75/120, 90/120, 105/120 and 120/120, wherein a numerator of each of these fractions represents the number of half cycles of an AC power source within one second during which said plurality of heating elements are powered.

3. The fluid heater according to claim 2, wherein said plurality of heating elements are connected to the AC power source for generating desired fluid heating power levels by dithering between a smaller one and a larger one of said plurality of power levels such that an average power pattern generated by said plurality of heating elements over a period of time is substantially equal to a desired fluid heating power pattern.

4. The fluid heater according to claim 3, wherein said period of time is less than 15 seconds.

5. The fluid heater according to claim 4, wherein the smaller one of said plurality of power pattern is determined by dividing the desired fluid heating power pattern by twice the period of time and using the integer portion of the result thereof.

6. The fluid according to claim 5, wherein the larger one of said plurality of power patterns is the next larger one after the smaller one of said plurality of power patterns.

7. The fluid heater according to claim 1, wherein the said plurality of heating elements are connected to the AC power source for substantially the same number of even and odd half-cycles of said plurality of power cycle patterns, thereby minimizing a DC component in the AC power.

8. The fluid heater according to claim 7, wherein each of said plurality of power cycle patterns has four cycles.

9. The fluid heater according to claim 1, wherein said at least one chamber is an integer multiple of two chambers.

10. The fluid heater according to claim 9, wherein said at least one chamber is four chambers.

11. The fluid heater according to claim 1, wherein said at least one chamber is an integer multiple of three chambers.

12. The fluid heater according to claim 1, wherein said at least one chamber is at least two chambers each having at least one heating element positioned therein.

13. The fluid heater according to claim 1, wherein said at least one chamber is four chambers each having at least one heating element positioned therein.

14. The fluid heater according to claim 1, wherein said logic circuit receives a signal representing a temperature setpoint, and wherein said logic circuit sends a desired power pattern to said power controller which controls the connection of said plurality of heater element s such that the temperature of the heated fluid from the fluid outlet is maintained at substantially the setpoint temperature.

15. The fluid heater according to claim 14, wherein said one or more temperature sensors include a plurality of temperature sensors each located at one of the fluid inlet, the fluid outlet and the at least one chamber, said plurality of temperature sensors being connected to said logic circuit such that said logic circuit calculates a deviation from the setpoint temperature using temperature information from said plurality of temperature sensors.

16. A fluid heater powered by an alternating current (AC) electric power source, said heater comprising:

a housing having at least one chamber, said housing having a fluid inlet and a fluid outlet;

a plurality of electrically powered heating elements, each of said plurality of heating elements positioned within a respective one of said at least one chamber for heating a flowing fluid;

a power controller for controlling the connection of each of said plurality of heating elements to the AC power source such that each of said plurality of heating elements is connected for at least one half cycle of each of a plurality of power cycle groups, defining a power level wherein the connection of each of said plurality of heating elements is sequentially timed to substantially reduce switching frequencies which otherwise would cause visually perceptible lighting flicker from the AC power source;

a logic circuit for controlling a desired temperature of the flowing fluid from the fluid outlet, said logic circuit receiving temperature information from the one or more fluid temperature sensors and providing temperature information to said power controller;

said logic circuit calculates a deviation by determining a calculated setpoint and subtracting the sum of temperatures measured by said plurality of temperature sensors;

the calculated setpoint is equal to the sum of the integers from 1 to the number of chambers divided by the number of chambers times T_rise plus T_in times the number of chambers, where T_in is the fluid inlet temperature, and T_rise is the difference between the desired fluid outlet temperature and T_in;

the deviation is equal to the calculated setpoint minus the sum of the temperatures measured by said plurality of temperature sensors; and

if the deviation is a positive value then said logic circuit causes said power controller to increase power to said plurality of heating elements, and if the deviation is a negative value then said logic circuit causes said power controller to decrease power to said plurality of heating elements.

17. A fluid heater powered by an alternating current (AC) electric power by source, said fluid heater comprising:

a housing having at least one chamber, said housing having a fluid inlet and a fluid outlet;

at least one electrically powered heating element positioned within said at least one chamber for heating a fluid flowing through said at least one chamber;

a fluid level detection and shutdown circuit including a fluid level electrode positioned in the upper portion of said at least one chamber in contact with the fluid, a capacitor having a first end connected to the fluid level electrode, a resistor having a first end connected to a capacitor second end, said resistor having a second end connected to a square wave frequency source of a higher frequency than the AC power source, and a voltage comparator having an input connected to the second end of the capacitor and the first end of the resistor, such that if a voltage at the comparator input is greater than a predetermined value because the fluid level electrode is in contact with the fluid than an output of the voltage comparator is at a first logic level, and if the voltage at the comparator input is lower than or equal to the predetermined value then the output of the voltage comparator is at a second logic level because said fluid level electrode is not in contact with the fluid, and a logic circuit for disconnecting said at least one heating element from the AC power source if the output of said voltage comparator is at an inconsistent logic level.

18. A fluid heater powered by an alternating current (AC) electric power source, said heater comprising:

a housing having at least one chamber, said housing having a fluid inlet and a fluid outlet;

at least one electrically powered heating element, said at least one heating element positioned within said at least one chamber for heating a flowing fluid;

a power controller for controlling the connection of each of said plurality of heating elements to the AC power source such that each of said plurality of heating elements is connected for at least one half cycle of each of a plurality of heating elements is sequentially timed to substantially reduce switching frequencies which otherwise would cause visually perceptible lightening flicker from the AC power source;

one ore more fluid temperature sensors each responsive to fluid temperature at a selected location within the at least one chamber;

a logic circuit for controlling a desired temperature of the flowing fluid from the fluid outlet, said logic circuit receiving temperature information from the one or more fluid temperature sensors and providing temperature information to said power controller; and

a fluid leak detection circuit for generating an alarm when fluid is detected outside of said at least one chamber, said fluid leak detection circuit including a fluid sensor located outside of and proximate to a lower portion of said at least one chamber, and a fluid sensor detection circuit connected to said fluid sensor.

19. The fluid heater according to claim 18, further comprising:

a watchdog circuit for preventing the connection of said at least one heating element to the AC power source if said logic circuit operates improperly, said watchdog circuit including a timing circuit having an input connected to said logic circuit and an output connected so as to control said at least one heating element when said timing circuit output is at a first logic level and turning off said at least one element when at a second logic level, using a capacitor connected between said timing circuit input and a heartbeat output from said logic circuit, wherein if there is a stream of pulses from said heartbeat output then said watchdog circuit output is at the first logic level, and if there is not a continuous stream of pulses from said heartbeat output then said watchdog circuit output is at the second logic level.

20. The fluid heater according to claim 18, further comprising:

a low power standby circuit, including at least one upper temperature sensor positioned in an upper portion of said at least one chamber, and at least one lower temperature sensor positioned in a lower portion of said at least one chamber such that low power is applied to said at least one heating element so as to create a thermocline to indicate when there is fluid flow in said at least one chamber, said at least one upper temperature sensor and said at least one lower temperature sensor indicating flow or no flow, whereby said logic circuit and said power controller control heating power to said at least one heating element.

21. A heating system using a circulating heated fluid, said heating system comprising:

a closed loop piping system running through an area to be heated, said closed loop piping system having heated fluid flowing therethrough;

a circulation pump for pumping the heated fluid through the closed loop piping system; and

a fluid heater powered by an alternating current (AC) electric power source, said heater including a housing having at least one chamber, said housing having a fluid inlet and a fluid outlet, at least one electrically powered heating element, said at least one heating element positioned within a respective one of said at least one chamber and adapted for heating the flowing fluid, a power controller adapted for controlling the connection of said at least one heating element to the AC power source such that each of said at least one heating element is connected for at least one half cycle of each of a plurality of power cycle groups, wherein the connection of said at least one heating element is sequentially timed so as to substantially reduce switching frequencies which otherwise would cause visually perceptible lighting flicker from the AC power source, and

a logic circuit for controlling a desired temperature of the flowing fluid, said logic circuit connected to and sending temperature control information to said power controller.

22. The heating system according to claim 21 wherein the temperature of said flowing fluid is controllable by its usage.

23. A fluid heater powered by an alternating current (AC) electric power source, said heater comprising:

a housing having an integer multiple of three chambers, said housing having a fluid inlet and a fluid outlet;

a plurality of electrically powered heating elements, each of said plurality of heating elements positioned within a respective one of said at least one chamber for heating a flowing fluid;

a power controller for controlling the connection of each of said plurality of heating elements to the AC power source such that each of said plurality of heating elements is connected for at least one half cycle of each of the plurality of power cycle patterns defining a power level wherein the operation of each of said plurality of heating elements is sequentially timed to substantially reduce switching frequencies which otherwise would cause visually perceptible lighting flicker from the AC power source;

one or more fluid temperatures sensors each responsive to fluid temperature at a selected location within the at least one chamber; and

a logic circuit for controlling a desired temperature of the flowing fluid from the fluid outlet, said logic circuit receiving temperature information from the one or more fluid temperature sensors and providing temperature information to said power controller.

24. The fluid heater according to claim 23, wherein a plurality of power levels at which said plurality of heating elements operate are selected from the group consisting of 0/120, 15/120, 30/120, 45/120, 60/120, 75/120, 90/120, 105/120 and 120/120, wherein a numerator of each of these fractions represents the number of half cycles of an AC power source within one second during which said plurality of heating elements are powered.

25. The fluid heater according to claim 23, wherein said plurality of heating elements are connected to the AC power source for substantially the same number of even and odd half-cycles of said plurality of power cycle patterns, thereby minimizing a DC component in the AC power.

26. The fluid heater according to claim 23, wherein said at least one chamber is an integer multiple of two chambers.

27. A fluid heater powered by an alternating current (AC) electric power source, said heater comprising:

a housing having at least one chamber, said housing having a fluid inlet and a fluid outlet;

a plurality of electrically powered heating elements, each of said plurality of heating elements positioned within a respective one of said at least one chamber for heating a flowing fluid;

a power controller for controlling the connection of each of said plurality of heating elements to the AC power source such that each of said plurality of heating elements is connected for at least one half cycle of each of the plurality of power cycle patterns defining a power level wherein the operation of each of said plurality of heating elements is sequentially timed to substantially reduce switching frequencies which otherwise would cause visually perceptible lighting flicker from the AC power source;

one or more fluid temperatures sensors each responsive to fluid temperature at a selected location within the at least one chamber;

a logic circuit for controlling a desired temperature of the flowing fluid from the fluid outlet, said logic circuit receiving temperature information from the one or more fluid temperature sensors and providing temperature information to said power controller; and

said logic circuit receives a signal representing a temperature setpoint, and wherein said logic circuit sends a desired power pattern to said power controller which controls the connection of said plurality of heater elements such that the temperature of the heated fluid from the fluid outlet is maintained at substantially the setpoint temperature.

28. The fluid heater according to claim 27, wherein a plurality of power levels at which said plurality of heating elements operate are selected from the group consisting of 0/120, 15/120, 30/120, 45/120, 60/120, 75/120, 90/120, 105/120 and 120/120, wherein a numerator of each of these fractions represents the number of half cycles of an AC power source within one second during which said plurality of heating elements are powered.

29. The fluid heater according to claim 27, wherein said plurality of heating elements are connected to the AC power source for substantially the same number of even and odd half-cycles of said plurality of power cycle groups, thereby minimizing a DC component in the AC power.