User manual

Operation
Liebert
®
iCOM
®
32
GLYCOOL
™
Cooling—Free-Cooling
GLYCOOL units may be programmed to stage cooling components two ways.
• Operate free-cooling or compressor(s) to maintain temperature (factory default).
• Operate free-cooling and compressor(s) simultaneously.
Caution must be taken when operating free-cooling and compressor simultaneously on GLYCOOL
units. Adequate flow must be provided to the unit to prevent high pressure when 100% free-cooling is
required in addition to DX cooling. Running too cold of fluid temperature and compressor(s)
simultaneously may cause refrigerant pressure to drop. Contact technical support at 800-543-2778 for
more information on simultaneous operation setup.
When the unit is configured to operate free-cooling or compressors(s), free-cooling eligibility is based
on the comparator circuit discussed in 3.3.1 - Differential Temperatures / Controls (Comparator
Circuit). If the circuit determines free-cooling will condition the space, the valve will open and close
as temperature deviates from the setpoint. If the comparator circuit determines that free-cooling is
not capable of conditioning the space, control is automatically replaced by compressor(s).
During either free-cooling or compressor operation, the control uses the temperature proportional
band to determine which operation to perform (cooling/heating) and how much capacity to provide.
The Temperature Proportional Band is a user-defined range that is divided into two equal parts for
cooling and heating. The Temperature Setpoint is between these two equal parts. An optional
temperature and heating deadband range can be defined, which is equally divided on either side of
the setpoint and separates the two halves of the proportional band.
When the unit is configured to operate free-cooling and compressor(s) simultaneously, the comparator
circuit determines free-cooling eligibility. Free-cooling and compressor(s) are staged based on
temperature deviation from setpoint. The cooling proportional band is divided into two parts for
simultaneous operation, the first portion is used for free-cooling and the second for DX operation.
Figure 29 illustrates how the cooling proportional band is broken out on a free-cooling unit with two
step compressors.
Cooling Control Band for Simultaneous Operation = (Temperature Proportional Band/2) / 2 +
(Temperature Deadband/2)
If the comparator circuit determines that free-cooling is ineligible for use, the compressor band will
shift to the left.
Figure 30 Free-cooling and compressorized operation
Dual-Cooling Source
Dual-cooling systems operate in the same manner as a GLYCOOL system, except they are
factory-configured to operate free-cooling and compressor simultaneously. If simultaneous operation
is not desired, contact technical support at 800-543-2778 for assistance.