Microprocessor controlled tankless water heater system

An apparatus for controlling a water delivery system to obtain precise set point temperatures, the apparatus comprising:

• a. a housing having an inlet, an outlet and a passage between the inlet and the outlet to permit a continuous flow of water from the inlet to the outlet;
• b. at least one heating element mounted in said passage of said housing for heating water as it flows through said passage, and electrically connected with electronic control circuitry contained within said housing;
• c. means for selecting a desired temperature of the water and generating a pulse width modulated (PWM) square wave proportional to the desired temperature;
• d. a temperature sensor in fluid communication with the water for sensing an actual temperature of the water at said outlet of said housing and generating a direct current (DC) output voltage signal proportional to the actual temperature;
• e. a first amplifier for receiving said DC output voltage signal from said temperature sensor to remove electrical noises and amplifying said DC output voltage signal;
• f. a second amplifier connected to said first amplifier for receiving said amplified DC output voltage signal and subtracting it from a value proportional to said desired temperature, and generating an output error signal representative of a difference between said desired temperature and said actual temperature;
• g. a comparator also connected to said first amplifier for receiving said amplified DC output voltage signal and comparing it with an internal standard voltage, and generating an over temperature signal when said actual temperature exceeds the internal standard voltage;
• h. a zero crossing detector coupled to an alternating current (AC) power signal for generating DC support voltages, and for detecting a zero crossing signal of the AC power signal;
• i. a microprocessor connected to said second amplifier and said zero crossing detector for receiving said error signal and said zero crossing signal to provide a trigger signal, the microprocessor having an internal timer for providing a timing range;
• j. an external timer connected to said microprocessor for assisting said internal timer to extend said timing range to cover 50 or 60 Hz input power frequency such that said internal timer and the external timer are used to set the proportionality of said PWM square wave;
• k. said microprocessor being programmed for constantly calculating a proportional (P) term, an integral (I) term and a derivative (D) term based on an algorithm to determine operating characteristics of said trigger signal;
• l. said algorithm including a loop equation utilizing a proportional constant K.sub.p, an integral constant K.sub.i and a derivative constant K.sub.d which reflect physical dimensions of said water delivery system and said at least one heating element, said algorithm performing the functions of:
• (i) waiting for an interrupt of said zero crossing signal;
• (ii) calculating said proportional term which is said error signal times said proportional constant K.sub.p ;
• (iii) calculating said integral term which is said integral constant K.sub.i times the integral of said error signal over said timing range;
• (iv) calculating said derivative term which is said derivative constant K.sub.d times the current rate of change of said error signal;
• (v) calculating a new PWM term by adding said P+I+D, such that the result is scaled by said constants;
• (vi) retaining said new PWM term for setting said internal and external timers after a next interrupt of said zero crossing signal;
• (vii) said new PWM term determines said operating characteristics of said trigger signal from said microprocessor;
• and
• m. an optocoupler connected to said microprocessor for receiving said trigger signal and providing full power of said AC power signal into said at least one heating element to heat up the water;
• and
• n. said optocoupler also connected to said comparator and said optocoupler having a triac and a light emitting diode (LED) for receiving said over temperature signal to provide a fail-safe shutdown of said system by preventing the optocoupler from turning the triac on such that with power removed from the triac, said at least one heating element cools within less than one half AC cycle and said outlet water temperature returns to a safe value;
• o. whereby said microprocessor ensures that said characteristics of said trigger signal is quickly determined to quickly force the power levels to a sufficiently high value so that the incoming water can be heated rapidly.

An apparatus for controlling a water delivery system, comprising:

• a. a tankless water heater having an inlet, an outlet and a passage between the inlet and the outlet to permit a continuous flow of water from the inlet to the outlet;
• b. at least one heating element mounted in said passage of said tankless water heater for heating water as it flows through said passage, and electrically connected with electronic control circuitry contained within said tankless water heater;
• c. means for selecting a desired temperature of the water and generating a pulse width modulated (PWM) wave;
• d. a temperature sensor for sensing an actual temperature of the water at said outlet of said tankless water heater and generating a direct current (DC) output voltage signal;
• e. a first amplifier for receiving said DC output voltage signal and amplifying said DC output voltage signal;
• f. a second amplifier for receiving said amplified DC output voltage signal and subtracting it from a value proportional to said desired temperature, and generating an output error signal;
• g. a comparator for receiving said amplified DC output voltage signal and comparing it with a standard voltage, and generating a over temperature signal when said actual temperature exceeds the standard voltage;
• h. a zero crossing detector coupled to an alternating current (AC) power signal for generating microprocessor timing support voltages, and for detecting a zero crossing signal of the AC power signal;
• i. a microprocessor connected to said second amplifier and said zero crossing detector for receiving said error signal and said zero crossing signal to provide a trigger signal, the microprocessor having an internal timer for providing a timing range;
• j. an external timer connected to said microprocessor for assisting said internal timer to extend said timing range such that said internal timer and the external timer are used to set the proportionality of said PWM wave;
• k. said microprocessor being programmed for constantly calculating a proportional (P) term, an integral (I) term and a derivative (D) term based on an algorithm to determine operating characteristics of said trigger signal;
• l. said algorithm including a loop equation utilizing a proportional constant K.sub.p, an integral constant K.sub.i and a derivative constant K.sub.d ;
• m. an optocoupler connected to said microprocessor for receiving said trigger signal and providing full power of said AC power signal into said at least one heating element;
• and
• n. said optocoupler also connected to said comparator and having a triac for receiving said over temperature signal to provide a fail-safe shutdown of said system by preventing the optocoupler from turning the triac on;
• o. whereby said microprocessor ensures that said characteristics of said trigger signal is quickly determined to quickly force the power levels to a sufficiently high value so that the incoming water can be heated rapidly.

An apparatus for controlling a water delivery system to obtain precise set point temperatures and used in conjunction with a shower having means for detecting a person presence in a shower or lavatory, the apparatus comprising:

• a. a housing having a water inlet, a water outlet and a passage between the water inlet and the water outlet to permit a continuous flow of water from the inlet to the outlet;
• b. at least one heating element mounted in said passage of said housing for heating water as it flows through said passage, and electrically connected with electronic control circuitry contained within said housing;
• c. a remote controllable temperature selection device for selecting a desired temperature of the water;
• d. said remote temperature selection device further comprising:
• (i) an up temperature button, a down temperature button and a cold button, all electrically connected with electronic selection circuitry contained within said temperature selection device;
• (ii) said electronic selection circuitry further including a microcontroller having an digital-to-analog (D/A) converter for outputting a pulse width modulated (PWM) square wave proportional to said desired temperature and outputting a bit pattern representing said desired temperature;
• (iii) an electrically erasable programmable read only memory (EEPROM) for storing said desired temperature, where each time said desired temperature is changed, it is written into the EEPROM;
• (iv) a light emitting diode (LED or LCD) display receiving said bit pattern for displaying said desired temperature on a digital display;
• and
• e. a temperature sensor in fluid communication with the water for sensing a water temperature at said water outlet of said housing and operable to enable real time sensing of an actual temperature of the water and generating a linear direct current (DC) output voltage signal proportional to the actual temperature;
• f. a filter/amplifier for receiving said DC output voltage signal from said remote temperature sensor to remove electrical noises and amplifying said DC output voltage signal;
• g. a set point subtraction amplifier connected to said filter/amplifier and said temperature selection device for receiving said amplified DC output voltage signal and subtracting it from a value proportional to said desired temperature, and generating an output error signal representative of a difference between said desired temperature and said actual temperature;
• h. an over temperature detection comparator also connected to said filter/amplifier for receiving said amplified DC output voltage signal and comparing it with an internal standard voltage, and generating an over temperature signal when said actual temperature exceeds the internal standard voltage;
• i. a zero crossing detector coupled to an alternating current (AC) power signal for generating microprocessor timing voltages, and for detecting a zero crossing signal of the AC power signal;
• j. a comparator coupled to said zero crossing detector for receiving said zero crossing signal to generate an interrupt on transitions of said zero crossing signal;
• k. a microprocessor connected to said set point subtraction amplifier and said comparator for receiving said error signal and said zero crossing signal to provide a trigger signal, the microprocessor having an internal timer for providing a timing range;
• l. said microprocessor being programmed to prevent trigger signals from being provided to said optocoupler for a period of time immediately after said zero crossing detector has detected a zero crossing of said AC power signal and said microprocessor has provided said trigger signal;
• m. an external timer connected to said microprocessor for assisting said internal timer to select 50 or 60 Hz said timing range such that said internal timer and the external timer are used to set the proportionality of said PWM square wave;
• n. said microprocessor being programmed for constantly calculating a proportional (P) term, an integral (I) term and a derivative (D) term based on an algorithm to determine operating characteristics of said trigger signal;
• o. said algorithm including a loop equation utilizing a proportional constant K.sub.p, an integral constant K.sub.i and a derivative constant K.sub.d which reflect physical dimensions of said water delivery system and said at least one heating element, said algorithm performing the functions of:
• (i) waiting for said interrupt of said zero crossing signal;
• (ii) calculating said proportional term which is said error signal times said proportional constant K.sub.p ;
• (iii) calculating said integral term which is said integral constant K.sub.i times the integral of said error signal over said timing range;
• (iv) calculating said derivative term which is said derivative constant K.sub.d times the current rate of change of said error signal;
• (v) calculating a new PWM term by adding said P+I+D, such that the result is scaled by said constants;
• (vi) retaining said new PWM term for setting said internal and external timers after a next interrupt of said zero crossing signal;
• (vii) said new PWM term determines said operating characteristics of said trigger signal from said microprocessor;
• and
• p. an optocoupler connected to said microprocessor for receiving said trigger signal and forcing full power of said AC power signal into said at least one heating element heat up the water;
• and
• q. said optocoupler also connected to said over temperature detection comparator and having a triac and a light emitting diode (LED) for receiving said over temperature signal to provide a fail-safe shutdown of said water delivery system by preventing the optocoupler from turning the triac "on" such that with power removed from the triac, said at least one heating element cools within at least one half AC cycle and said outlet water temperature returns to a safe value;
• r. whereby said microprocessor ensures that said characteristics of said trigger signal is quickly determined to quickly force the power levels to a sufficiently high value so that the incoming water can be heated rapidly.