Energy Smart® Electric Water Heater Operation

Energy Smart® Electric Water Heater

The Energy Smart® Electric water heater control circuit consists of an electronic control board, a fusible link high limit switch, two thermistor temperature sensors, an upper element, and a lower element. The electronic control board has a computer chip, temperature control knob, and a mode switch. Thermistor temperature sensors are mounted to the surface of the tank and sense water temperature through the tank wall.

Energy Smart® water heaters prevent dry firing of the elements, as shown in the photograph. Dry firing occurs when the element is energized without being completely submerged in water, causing it to burn out immediately. A dry fired element is the most common reason for a new water heater to fail.

To prevent dry firing, the controls pulse the upper element on and off for a period of time when the unit is initially filled and electric power is connected. The element is then turned off for 8 minutes. During this time, the upper thermistor senses the temperature of the tank wall. If the tank is empty, heat from the hot element is conducted through the side of the tank and detected by the thermistor. The control will refuse to energize the elements and will flash a code to let the installer know that the tank is empty. After filling the tank, the unit can be reset and the controls will perform the test again.

Energy Smart® Electric Water Heater Operation

If the thermistor senses that the tank is full, it will energize the upper element until the water in the upper third of the tank reaches the temperature setting. Power will then be transferred to the lower element, heating the bottom two-thirds of the tank.

As with standard electric models, when hot water is drawn from the top of the tank, the dip tube delivers cold water to the bottom, eventually lowering the temperature to below the lower thermistor setting. The bottom element will then be energized. If enough water is drawn to cool the upper third of the tank, the upper thermistor will send power to the upper element. When the upper third of the tank is heated, power will again be switched to the lower element.

Unlike standard water heaters, Energy Smart® models do not cease to function when an element burns out. The electronic controls simply transfer power to the working element.

All Energy Smart® Electric water heaters have four operating modes: Smart, Energy Smart®, Low Temperature, and Vacation/Cabin.

In Smart mode the water heater functions similar to a standard electric water heater. Water is maintained at the temperature set by the user.

In Energy Smart® mode the unit maximizes hot water availability while minimizing cost. The control will automatically adjust water temperature over long periods of time. Every time the lower element is energized, the controls lower the water temperature by three-tenths of one degree, but never lower than 115°F. Every time the upper element is energized the controls raise the water temperature by three degrees, but never above the temperature set by the user. Over time, the water in the tank will vary within a small range that satisfies user requirements, while reducing standby heat loss.

In Low Temperature mode, the water temperature is limited to a maximum of 115°F. This may help meet various code restrictions. Check your local codes for more information.

In Vacation/Cabin mode the unit will maintain the water temperature at 50°F. This prevents freezing while minimizing energy usage.

In addition to four user selectable operating modes, Energy Smart® water heaters constantly monitor and signal the status of 8 critical water heater functions in all four modes.

Changing the mode switch from one mode to another and back, or pressing the reset button available on some models, will reset the control.

Energy Smart® Control Circut

After a reset, the control performs self-diagnostics for about ten minutes before normal operation resumes.

If the water temperature reaches 170°F the high limit switch will trip. Resetting the control, as explained above, will reset the high limit switch. Should the water temperature exceed 180°F, a thermal fuse in the thermistor circuit will cause the control to shut down, disabling the water heater until it is properly repaired.