Energy Smart® Electric Water Heater Operation
Energy Smart® Electric Water Heater
The Energy Smart® electric water heater includes an Energy Smart Module (ESM) User Interface, which allows homeowners to easily adjust the temperature, operating mode, and view diagnostic information, without requiring any tools or removal of water heater components. The ESM is connected to an Electronic Thermostat (ET) above the upper element. Additionally, the SmartPort located at the top of the water heater on the electrical junction box is connected and may be used for future utility demand response and remote thermostat applications.
Upon initial installation (and restart, in the case of power outage), the Energy Smart®; water heater prevents dry firing of the elements. Dry firing occurs when the element is energized without being completely submerged in water, causing it to burn out (see photo). A dry fired element is the most common reason for a new water heater to fail.
To prevent dry firing, the Energy Smart® control pulses the upper element on and off for a period of time when the unit is initially filled with water and electric power is connected. The element is then turned off for about 4 minutes. During this time (total of 8 minutes), the upper thermistor (temperature sensing component, functionally equivalent to a traditional thermostat) 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 display an error code in the Energy Smart Module display, to let the installer know that the tank is not completely full of water. After completely filling the tank, the unit can be reset and the controls will perform the test again. 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. The water heater will operate normally, in the homeowner’s chosen operating mode.
Energy Smart® Water Heater Operating Modes
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 three operating modes: Energy Smart®, Standard, and Vacation.
In Standard mode the water heater functions similar to a standard electric water heater. Water is maintained at the temperature set by the user in the ESM display panel. This may be set between 80°F and 150°F
In Energy Smart® mode the unit maximizes hot water availability while minimizing cost. The homeowner may set the desired temperature between 115°F and 150°F. The control will automatically adjust water temperature over long periods of time. Every 3rd time the lower element is energized (i.e., there is a short draw of hot water), the controls lower the water temperature by one degree, but never lower than 115°F. Every time the upper element is energized (i.e, there is a long draw of hot water) 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 Vacation mode the unit will maintain the water temperature at 60°F. This prevents freezing while minimizing energy usage. This is an easy way to conserve energy and reduce costs while away from home for extended time periods. Upon returning home, the homeowner can simply press the Vacation mode button to deactivate this mode, and return the water heater to the previous Operating Mode and Temperature settings.
Energy Smart® Diagnostics
In addition to three user selectable operating modes, Energy Smart® water heaters constantly monitor the status of critical water heater functions in all modes. Feedback is provided on the following:
- Dry fire
- Upper element
- Lower element
- Upper thermistor
- Lower thermistor
- Electronic thermostat
- Energy Smart Module user interface
- Water temperature exceeding high limit
- Communications between ET and ESM
Reporting of any abnormal condition with the above functions is via an error code displayed in the LCD screen of the ESM user interface. Unlike other electric water heaters, if one element or thermistor fails in the Energy Smart water heater, the remaining working element will continue operating to provide hot water. Similarly, the Energy Smart water heater will continue to provide hot water in the event of a communications error or total failure of the ESM user interface.
The Energy Smart® electronic control includes safety features to protect homeowners. If the water temperature reaches 170°F the protective high limit Energy Cutoff switch will trip. Resetting the switch, as explained in the Use & Care guide, is easily accomplished by pressing a clearly indicated button on the Electronic Thermostat.
Additional safety features are built in, including a factory installed Temperature and Pressure Relief Valve, a tamper resistant drain valve, and a lockout feature on the ESM user interface to prevent children from modifying the water heater temperature and mode settings.