Control system and method for operating a lower resistive heating element of an electric water heater to kill bacteria

Abstract

A controlled system and method for operating a lower resistive heating element of an electric water heater is described to kill bacteria in a lower portion of a water holding tank of an electric water heater. A controller having a timer circuit operates the lower resistive heating element bypassing the control of the thermostat associated with the upper and lower resistive heating element to maintain the lower resistive heating element active during a predetermined sanitizing time period whereby the temperature in the lower portion of the tank is maintained at a predetermined temperature sufficient to kill bacteria. The controller is programmed to override a load shedding function during the predetermined sanitizing time operiod.

1 . A safety system for operating a lowermost resistive heating element of an electric water heater to kill bacteria in a lower portion of a water holding tank of said electric water heater, said system comprising a controller having a computer with a memory for receiving instructions to perform a programmed function, a timer circuit associated with said programmed function, a temperature sensor connected to said tank lower portion feeding temperature signals to said controller, said lowermost resistive heating element having a pair of terminals to which is secured two leads from a supply voltage to energize said lowermost resistive heating element, said controller operating switch means to energize said lowermost resistive heating element independently of thermostats associated with an uppermost resistive heating element and said lowermost resistive heating element during a continuous predetermined sanitizing time period as programmed in its memory sufficient to maintain water temperature in said lower portion of said tank to a predetermined temperature sufficient to kill bacteria to sanitize said tank lower portion. 
     
     
         2 . The safety system as claimed in  claim 1  wherein said predetermined temperature is in the range of 140 degrees F. sufficient to kill the Legionella bacteria. 
     
     
         3 . The system as claimed in  claim 1  wherein said switch means is an open thermostat contact connected between a live lead of said supply voltage and one of said pair of terminals, said controller causing said open contact to close to energize said lower resistive heating element, the other of said terminals being connected to an associated lead of said supply voltage from a high limit switch. 
     
     
         4 . The safety system as claimed in  claim 3  wherein said thermostat of said uppermost resistive heating element will switch over said supply voltage to said terminals of said lowermost resistive heating element through a lower thermostat of said lower resistive heating element during normal operating time periods of said water heater when said power switch is in a normally open condition. 
     
     
         5 . The system as claimed in  claim 1  wherein there is further provided a second temperature sensor connected to an upper portion of said tank to feed temperature signals of water temperature within said tank upper portion to said controller, said controller monitoring said water temperature in said upper portion of said water holding tank during a predetermined time period if said temperature signals from said temperature sensor connected to said tank lower portion does not attain said predetermined temperature sufficient to kill bacteria and generating a servicing signal indicating that the water heater requires servicing. 
     
     
         6 . The system as claimed in  claim 1  wherein said controller has a communication link with a power provider and wherein said controller will override a power shedding function from said power provider if said controller is operating said lowermost resistive heating element during said continuous predetermined sanitizing period. 
     
     
         7 . The system as claimed in  claim 6  wherein said predetermined sanitizing time period is an off-peak time period or a period dictated by local health regulations. 
     
     
         8 . A method of operating a lowermost resistive heating element of an electric water heater to kill bacteria in a lower portion of a water holding tank of said electric water heater, said electric water heater having an uppermost resistive heating element, each said lowermost and uppermost resistive heating elements being controlled by a thermostat control having a temperature sensor, said method comprising the steps of:
 i) providing a controller having a computer with a memory for receiving instructions to perform a programmed function and having a timer circuit associated therewith;   ii) controlling a supply voltage to a pair of terminals of said lowermost resistive heating element to energize said lowermost resistive heating element;   iii) sensing the temperature of water in said lower portion of said water holding tank, and   iv) energizing said lowermost resistive heating element by said controller independently of said thermostats and during a continuous predetermined sanitizing time period, as programmed in said memory of said controller, sufficiently to maintain water temperature in said tank lower portion to kill bacteria to sanitize said lower portion of said water holding tank.   
     
     
         9 . The method as claimed in  claim 8  wherein said step (iv) comprises connecting said supply voltage on and off during said predetermined sanitizing period of time to maintain the water temperature in said tank lower portion to about 140 degrees F. to kill the Legionella bacteria. 
     
     
         10 . The method as claimed in  claim 8  wherein said step of sensing comprises securing a temperature sensor on an outer surface of said water holding tank at said lower portion thereof and establishing a connection with said controller to receive temperature signals therefrom to monitor the temperature of water in said tank lower portion. 
     
     
         11 . The method as claimed in  claim 8  wherein there is further provided the step of securing a further sensor on an outer surface of said water holding tank at an upper portion of said water holding tank to sense the water temperature in said upper portion to monitor the operating condition of said water heater and to detect proper operation of said resistive heating elements