4-48 l Operati on
Setback Feature Guidelines (continued)
A recommended way to determine the “Setback Return Temperature” setpoint is to
monitor the actual temperature of this function during pre-drying of your material
at start-up, and while running at your normal maximum material throughput. The
“Setback Return Temperature” setpoint should be set 10 to 20° above maximum
temperature noted in these situations.
The “Setback Temperature (Process)” setpoint you select should be adequate to
reduce the temperature significantly enough to prevent over-drying of your materi-
al. However, keep in mind that the cooler the temperature selected, the longer it
will take for the material to heat back up to its proper drying temperature once the
dryer comes out of Setback mode.
When drying at low temperatures (for example 160 - 180° F {71 - 82° C}), you are
able to setback the temperature only a small amount. The “Setback Temperature
(Process)” should not be set lower than 150° F {66° C}, even if the control will
allow it. It is very likely the dryer will not be able to achieve low temperatures
without adding additional cooling to the process air circuit. The maximum achiev-
able setpoint is dependent on the temperature of the return air coming back to the
dryer. As the return air temperature climbs, the temperature that the dryer is capa-
ble of controlling at climbs. For example, if the return air to the dryer is 110° F
{43° C}, the dryer may not be able to control at a “Setback Temperature
(Process)” setpoint below 150 - 155° F {66 - 68°C}.
NOTE: Selecting too low of a setpoint for Screen 26 may result in nuisance Process
Temperature Loop Break alarms if the dryer is not able to achieve this setpoint
.
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