GLYCOOL Cooling—Freecooling
GLYCOOL units may be programmed to stage cooling components in either of two ways:
• Operate freecooling or compressor(s) to maintain temperature (factory default)
• Operate freecooling and compressor(s) simultaneously
Caution must be taken when operating free-cooling and the 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 Differential Temperatures/Controls (Comparator Circuit) on page70 . 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 freecooling 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. Second Cooling Source and Two-Step Compressorized Cooling on the previous page on the previous page
illustrates how the cooling proportional band is broken out on a freecooling unit with two step compressors.
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 freecooling 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. Second Cooling Source and Two-Step Compressorized Cooling on the previous page on the previous page
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 freecooling is ineligible for use, the compressor band will shift to the left.
3 Service Operation
72
Vertiv™ Liebert® iCOM™Installer/User Guide
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