Optional 4 - Step Cooling, Two (2) Compressors With Unloaders; Stage Activation On Temperature Increase; Stage Deactivation On Temperature Decrease; Stage Compressorized Cooling - Emerson Liebert iCOM Training And Service Manual

iCOM
Control Training and Service Manual

Optional 4 - Step Cooling, Two (2) Compressors with Unloaders

The basic temperature cooling control band is established at the temperature set
point with the length equal to ½ of the programmed temperature proportional band
divided by the number of cooling stages.
Liebert DS units are supplied with two (2) compressorized cooling circuits. Each
compressor circuit is rated at ½ of the unit total cooling capacity. The two (2)
semi-hermetic type compressors are each supplied with an electrically controlled
suction cut-off cylinder unloader valve. The electrical solenoid valve is used to
unload or reduce the cooling capacity of the compressor. The compressors will
operate in an on/off - loaded/unloaded configuration method to cool the space.
Hot gas bypass option is not available on 4-stage cooling units.

Stage Activation on Temperature Increase

The temperature controller activates the first cooling step (lead compressor
unloaded) when the return air temperature increases to 33% of the cooling
proportional band. The second cooling step (lag compressor unloaded) is
activated when the return air temperature increases to 63% of the cooling
proportional band.
The temperature controller deactivates the unloader for the third cooling step (lead
compressor loaded) when the return air temperature increases to 80% of the
cooling proportional band. The temperature controller deactivates the unloader for
the fourth cooling step (lag compressor loaded) when the return air temperature
increases to 100% of the cooling proportional band.

Stage Deactivation on Temperature Decrease

The temperature controller activates the unloader on the lag compressor when the
return air temperature decreases to 90% of the cooling proportional control band
value. The unloader on the lead compressor activates when the return air
temperature decreases to 70% of the cooling proportional control band value.
The temperature controller deactivates the unloaded lag compressor when the
return air temperature decreases to 47% of the cooling proportional control band
value. The unloaded lead compressor is deactivated when the return air
temperature decreases to the temperature set point value of 17% of the cooling
proportional control band value.
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