The Set option allows free-cooling whenever the fluid temperature sensed (User Menu > Sensor Data) is colder than the
temperature setpoint. The difference required between the temperature setpoint and the fluid temperature is adjusted on the
following line DT2 Room / FC Fluid value (Service Menu, Setpoints). The second source cooling fluid will be used to provide
cooling if the temperature difference between the second source cooling fluid parameter, Free-cooling Fluid Temperature and
room air is equal to or greater than the adjustable DT Between Room / FC Fluid value.
Sensors used for this delta T are: room/local sensor or the return air sensor; and the glycol sensor.
If this delta T is true, the Free-cooling Status indication will show “On” instead of “Off”. The status is found in the User- Sensor
Data menu, Figure 7.10 on page 28. The primary and secondary source of cooling will stage accordingly. See the next sections
for more information.
Figure 3.17 Second Cooling Source and Two-Step Compressorized Cooling
Minimum Chilled Water Temperature—This feature allows the user to select a minimum chilled water temperature to
prevent simultaneous operation of the chilled water (free cooling) and compressor(s) on units factory-programmed to
operate both sources simultaneously. This feature is enabled in Service>Setpoints, parameter Minimum CW Temp.
If the fluid temperature sensed is below the Minimum CW Temp Value, (Service Menu, Setpoints), and the Delta T
(Temperature Difference) Between Room and Glycol (see Differential Temperatures/Controls (Comparator Circuit) on the
previous page ) is satisfied, the control will operate ONLY the chilled water for cooling. The compressor(s) is locked out. If
cooling does not operate, (i.e., loss of chilled water flow), the control will override this setting and activate a compressor(s).
When this happens, free-cooling will be locked out for one hour.
If the fluid temperature is above the minimum CW value, the control will operate the chilled water (free cooling) and
compressor(s) simultaneously if needed. If the Minimum CW Temp is disabled, the control may operate both sources as load
requires.
3 Service Operation
71
Vertiv™ Liebert® iCOM™Installer/User Guide
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