Patent ID: 8204633

Claim:
A water heater controller for controlling a water heater to alter electrical demand while providing hot water for normal use, said water heater comprising an upper heater for heating an upper volume of water and a lower heater for heating a lower volume of water; said water heater controller comprising: power control means for controlling power supplied to said upper heater and for controlling power supplied to said lower heater; a processor configured for controlling said power control means, said processor having a memory, said memory storing a load shift algorithm comprising instructions for varying power applied by said power control means, said load shift algorithm specifying a reserve volume capacity of hot water for said water heater, said reserve volume capacity being a minimum volume of hot water reserved for consumer use and not utilized for load shifting; a lower temperature sensor configured for measuring a temperature of said lower volume of water and providing a resulting lower volume temperature measurement to said processor; means for determining a remaining volume capacity of hot water in said hot water heater, said remaining volume capacity being a capability to deliver said remaining volume of hot water on immediate demand; wherein said processor is configured to control said power control means to control a temperature of said lower volume of said water in accordance with said load shift algorithm when said remaining volume capacity exceeds said reserve volume capacity, and said processor is configured to allow recovery when said remaining volume capacity is less than said reserve volume capacity.