CONTROL UNIT FOR STORAGE TYPE ELECTRIC WATER HEATER

PURPOSE:To control an electric water heater without an expensive water meter by mounting a plurality of temperature detectors on a hot water storage tank to calculate an average temperature within the tank, and calculating a target set value of the heating temperature on the basis of the average temperature drop within the tank in daytime. CONSTITUTION:A heating unit 12 can heat the full water amount within a hot water storage tank 11 to a predetermined maximum heating temperature (85 deg.C, for example) within a midnight power feeding time through a midnight-power time switch 13. A plurality of temperature detectors 21, 21...are mounted at positions equidistantly so that they each can detect the temperatures of water within the tank for approximately equal capacities thereof. The lowermost temperature detector is mounted at a position close to a bottom plate 11d so that it can measure the temperature of supply water from a water supply pipe 11a. The output of the temperature detector is input into average value operating means 31, and connected to a control switch 14 for turning ON and OFF of power to the heating unit 12 via data memory means 32, set value calculating means 33 and power supply control means 34, on the other hand, the output of a timepiece means 35 is applied to the average value calculating means 31 and power supply control means 34.