Emerson E2 Anti-Sweat Control, Demand Defrost, Wait State, Temperature Termination

defined Pump Down and Run-Off times will be observed as normal.

Electric Defrost

Electric defrost uses electric heaters to defrost the evaporator coil. During electric defrost, the application will turn the Defrost output ON, which will likewise acti- vate the heaters connected to the power module’s defrost relay.

Any user-defined Pump Down and Run-Off times will be observed as normal.

11.4.4.3Defrost Termination

Both the start time and the end time of a defrost cycle are determined by the user. The Pump Down, Defrost, and Run-Off stages all have fixed durations, and when the last stage of the cycle is complete, defrost is terminated.

However, a case controller may be programmed to ter- minate the Defrost stage of the defrost cycle early if the temperature inside the case rises above a fail-safe tempera- ture setpoint. For certain defrost types, defrost heat may also be “pulsed” in order to keep the temperature below the setpoint without terminating defrost.

Temperature Termination

One or more temperature sensors in the case circuit may be designated as termination temperature sensors. The values of these sensors are combined into a single control value, and this value is compared to the setpoint. If the termination control value is greater than the user- defined setpoint, defrost will end, and the defrost cycle will begin the Run-Off period (if applicable).

Termination sensors may be either analog temperature sensors or digital closures (Klixons). Also, Case Circuit applications may use the value of the analog case tempera- ture sensors for use in temperature termination.

Pulsed Defrost

Pulsed Defrost is only available if the circuit is using Electric or Hot Gas defrost.

Pulsed Defrost is similar to Temperature Termination, except when the termination temperature rises above the setpoint, defrost does not terminate. Instead, the output that applies defrost heat is turned OFF. The output will remain OFF until the temperature falls below the setpoint, at which time the output will come back ON.

The Case Circuit application will continue to pulse defrost in this manner until the defrost time has passed. The defrost cycle will then begin the Run-Off period.

11.4.4.4Demand Defrost

If a case is configured with a demand defrost sensor, a case controller may use their inputs as a means of keeping scheduled defrost cycles from occurring when frost levels

are not high enough to require a defrost.

The optical demand defrost sensor may be either an analog or digital type sensor. When this sensor detects no major build-up of frost, the Case Circuit application ignores all scheduled calls for defrost and continues in refrigeration mode. When the sensor detects frost, the defrost inhibit is cancelled, and the case circuit will enter defrost at the next scheduled time.

A demand defrost inhibit only keeps scheduled defrosts from occurring. Any manual calls for a defrost cycle will occur as normal. CCB demand defrost is cur- rently not supported in E2. Demand sensors, if present on the circuit, will be ignored.

Demand Fail-Safe Time

To protect against demand defrost sensors that may not be working properly, a demand fail-safe time may be set up. Demand fail-safe times limit the amount of time a defrost inhibit may last. If a demand defrost sensor does not detect frost for an amount of time equal to the Demand Fail-Safe Time, the defrost inhibit is lifted and the circuit will enter defrost at the next scheduled time.

11.4.4.5Emergency Defrost

When necessary, a user can initiate an emergency defrost cycle from a circuit. Emergency defrost cycles are similar to normal defrost cycles, except an emergency defrost cycle will ignore all calls for termination and remain in defrost for the entire programmed defrost time.

Emergency defrosts are initiated by the user from the Case Control Circuit Bypass screen (see Section 12.6,

Manual Defrost and Clean Mode).

11.4.4.6The WAIT State

When a Case Control Circuit application enters defrost mode, it sends a message out to all case controllers in the circuit to begin defrost at the same time. However, since each case in a circuit will have its own termination sen- sors, it is possible for some cases to terminate defrost while defrosts in other cases continue.

When a case controller terminates defrost, it enters a state of operation called “the WAIT state.” While in the WAIT state, all refrigeration and defrost heat will remain OFF. When the Case Control Circuit application detects that all case controllers have entered the WAIT state, the application will consider the defrost cycle completed, and refrigeration will restart.

11.4.5 Anti-Sweat Control

Acase controller manages its anti-sweat heaters by monitoring the dewpoint in and around the case area. The dewpoint input value is compared to the anti-sweat appli- cation’s control setpoints (the Full ON setpoint and the

Case Control Circuits Software Overview • 11-13