Optional Glycool (Econ-O-Cycle) Cooling - Emerson Liebert iCOM Training And Service Manual

iCOM
Control Training and Service Manual

Optional Glycool (Econ-O-Cycle) Cooling

When Liebert DS units are supplied with the Glycool option, the basic unit is
supplied with an additional coil, piping, valve and an Aquastat Sensor (AQ) which
measures the glycol fluid temperature. The sensor is mounted to the unit supply
fluid line and serves as the control interface in determining the system operation.
Selection between glycool or compressorized operation is controlled by the
microprocessor using this aquastat to sense the glycol temperature.
The Glycool Cooling program establishes two distinct control bands for cooling
control operation. The first band controls the operation of the chilled glycol valve
and the second controls the operation of the compressors, 2 stages, 4 stages or
digital scroll.
The microprocessor checks the return air temperature and the entering glycol fluid
temperature to determine a cooling capacity. In order to reduce compressor
cycling and to prevent chilled glycol valve hunting, Glycool cooling capacity does
not become available until the entering chilled glycol fluid temperature is at least
8°F below the return air temperature or 3°F lower than the return air temperature
for two (2) consecutive hours.
When the microprocessor decides that the return glycol fluid temperature is cold
enough the first cooling band is modulating valve control. A second band is added
to the first band for the compressors as in the normal 2 stage, 4 stage or digital
scroll control method. If the chilled glycol fluid temperature is not cold enough the
valve control band is replaced by the compressor band. If the chilled glycol
cooling capacity is reduced by a rise in the glycol fluid temperature, the control
band shrinks proportionally. This allows the compressor band to move down as
well. The following charts on the next two pages show the Glycool operation at
100% capacity and the Glycool at 50% capacity.
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