High efficiency, peak-power reducing, domestic hot water heater

Abstract

There is herein described a peak-power reducing domestic hot water heater comprising: a closed tank having a predetermined water holding capacity, a hot water outlet in a top end wall of said tank, a cold water inlet in a side wall of said tank adjacent a bottom wall thereof, three spaced apart resistive heating elements projecting substantially horizontally in said tank, each of said resistive heating elements having a temperature sensing element to enable a control of their respective activation; a bottom one of said resistive heating elements extending in said tank spaced slightly above said bottom wall and having a lowest power rating, said bottom resistive heating element being turned on when water is flowing into said cold water inlet and drawn out of said hot water outlet during a peak-power demand time period; a middle one of said resistive heating elements extending in said tank at a level which is calculated to be equal or above an average maximum daily water consumption volume drawn out during the peak power demand time periods; and a top one of said resistive heating elements extending between said middle element and said top end wall of said tank and having a highest power rating; said middle and said bottom resistive heating elements being activated simultaneously only when said top resistive heating element is inactive.

We claim: 
     
         1 . A peak-power reducing domestic hot water heater comprising:
 a closed tank having a predetermined water holding capacity, a hot water outlet in a top end wall of said tank, a cold water inlet in a side wall of said tank adjacent a bottom wall thereof, three spaced apart resistive heating elements projecting substantially horizontally in said tank, each of said resistive heating elements having a temperature sensing element to enable a control of their respective activation;   a bottom one of said resistive heating elements extending in said tank spaced slightly above said bottom wall and having a lowest power rating, said bottom resistive heating element being turned on when water is flowing into said cold water inlet and drawn out of said hot water outlet during one of the daily peak-power demand time periods;   a middle one of said resistive heating elements extending in said tank at a level which is calculated to be equal or above an average maximum daily water consumption volume drawn out during the peak power demand time periods; and   a top one of said resistive heating elements extending between said middle element and said top end wall of said tank and having a highest power rating; and   said middle and said bottom resistive heating elements being activated simultaneously only when said top resistive heating element is inactive.   
     
     
         2 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said bottom resistive heating element has a low watt density rating in the range of from about 15 to 30 W/in 2 . 
     
     
         3 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said average maximum daily water consumption volume drawn out during the peak power demand time periods is in the range of about 90 to 130 liters. 
     
     
         4 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said average maximum daily water consumption volume drawn out during the peak power demand time periods is in the range of about 130 to 150 liters. 
     
     
         5 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said tank is a cylindrical tank having a diameter of about 20 inches or less in order to produce an efficient water temperature stratification between hot and cold water in said tank and thereby reduce water temperature diffusion and ensuring a constant hot water supply in a top portion of said tank. 
     
     
         6 . The peak-power reducing domestic hot water heater as claimed in  claim 5 , wherein said bottom heating element has a life rating which is higher than said middle and top heating elements. 
     
     
         7 . The peak-power reducing domestic hot water heater as claimed in  claim 6 , wherein said bottom resistive heating element has a metal sheath made from one of copper, incoloy or stainless steel, and wherein a magnesium oxide surrounds a central coil thereof. 
     
     
         8 . The peak-power reducing domestic hot water heater as claimed in  claim 5 , wherein said middle resistive heating element produces a heat barrier in said water within said tank at the level of said middle resistive heating element in the range of about 140° F. to reduce the propagation of harmful bacteria to said hot water supply in said top portion of said tank. 
     
     
         9 . The peak-power reducing domestic hot water heater as claimed in  claim 8 , wherein said harmful bacteria is legionnela bacteria. 
     
     
         10 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said tank has a water capacity of about 270 liters, said bottom heating element extends at a water level of about 20 liters from said bottom wall, said middle heating element extending at a water level of about 130 liters from said bottom wall and said top heating element extends at a water level of about 220 liters from said bottom wall. 
     
     
         11 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said tank has a water capacity of about 270 liters, said bottom heating element extends at a water level of about 20 liters from said bottom wall, said middle heating element extending at a water level between about 130 liters to about 150 liters from said bottom wall and said top heating element extends at a water level between about 220 liters to about 240 liters from said bottom wall. 
     
     
         12 . The peak-power reducing domestic hot water heater as claimed in  claim 11 , wherein said top heating element is spaced from said top wall of said tank a distance equivalent to a water volume of about 46 liters. 
     
     
         13 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said bottom resistive heating element is a bolt-on resistive heating element. 
     
     
         14 . The peak-power reducing domestic hot water heater as claimed in  claim 1 , wherein said water holding capacity of said tank is one of about 180 liters and about 270 liters. 
     
     
         15 . A method of reducing the kilowatt demand of a domestic hot water heater during peak hour periods without reducing the amount of hot water requested by a user from a hot water tank having a predetermined water holding capacity, said method comprising the steps of:
 providing a hot water tank with three spaced-apart electrical resistive heating elements extending therein in a spaced-apart manner and each having a thermostat to enable a control of their respective activation;   positioning a middle one of said resistive heating elements at a level exceeding an average maximum daily water consumption volume drawn during one of the peak hour periods, and   activating said bottom one of said resistive heating elements when water is flowing into said cold water inlet and drawn out of said hot water outlet during the peak hour periods, and   simultaneously activating said middle and said bottom one of said resistive heating elements only when said top resistive heating element is inactive.   
     
     
         16 . The method as claimed in  claim 15 , wherein said step of providing comprises providing said bottom one of said resistive heating elements with a low watt density rating in the range of from about 15 to 30 W/in 2 . 
     
     
         17 . The method as claimed in  claim 15 , wherein said step of positioning comprises positioning said middle one of said resistive heating elements at a level exceeding an average maximum daily water consumption volume drawn out of the tank during the peak hour periods at a level between about 90 liters to about 130 liters depending on said tank size of predetermined volume. 
     
     
         18 . The method as claimed in  claim 17 , wherein said step of positioning comprises positioning said middle one of said resistive heating elements at a level exceeding an average maximum daily water consumption volume drawn out of the tank during the peak hour periods at a level between about 130 liters to about 150 liters depending on said tank size of predetermined volume. 
     
     
         19 . The method as claimed in  claim 15 , wherein there is further provided the step of operating said middle resistive heating element to maintain a water temperature at its said level at a temperature of about 140° F. to form a temperature barrier to reduce the propagation of harmful bacteria from the bottom of the tank towards a top portion of the tank where hot water is drawn. 
     
     
         20 . The method as claimed in  claim 15 , wherein said water holding capacity of said tank is one of about 180 liters and about 270 liters.