4. For Chilled Water unit when ALL of the following are considered to be true:
a. The unit has been powered ON for a least 30 min AND
b. Call for cooling is greater than A105.5 'Loss of Cooling - CW Threshold' (default 50%) AND
c. Temperature difference between Return Temp - Supply Temp is less than A105.2 'Loss of Cooling - Delta
RET - Sup' (default 0.55k) AND
d. One or more of the following are true:
• Unit return temperature is above S203 'Std. Sensor High Return Temperature'.
• The above conditions a. - d.) are continuously true for A105.3 'Loss of Cooling - CW Delay' (default
1800 seconds).
When the unit is in this state, the end-user may define the desired unit operation.
3.4 Vertiv™ Liebert® Fluid Economizer
Two types of fluid economizers are offered, GLYCOOL and Dual-Cool. GLYCOOL models are two-pipe systems. This means
that two pipes enter the unit and feed the chilled water/free-cooling coil as well as the compressor(s) and heat exchanger
(eg., Liebert® Paradenser, tube-in-tube condenser or brazed plate heat exchanger). Dual Cool units can be either two pipe or
four pipe systems. A two-pipe unit has two fluid lines dedicated to the secondary cooling source, and the compressor(s) heat
rejection is an air cooled condenser. Four pipe Dual Cool models have two fluid pipes dedicated to chilled water/freecooling
and two pipes for the compressor(s) heat exchanger. Each model offers a primary DX source and a secondary chilled water or
free-cooling coil.
3.4.1 Differential Temperatures/Controls (Comparator Circuit)
Delta T (Temperature Difference) between Room and Fluid
The comparator circuit determines if the glycol / chilled water temperature of the second cooling source is low enough to
provide at least partial cooling capacity. Free-Cooling Fluid Temperature is controlled in the User - Sensor Data menu, Figure
7.10 on page 128. The comparator circuit has four settings (DT Between Room / FC Type, [Service Menu, Setpoints]):
• Disabled
• Contact
• Temp
• Set
The Disabled setting is for standard compressorized and chilled water units that do not have a second cooling source. The
Disabled setting can also be used to disable the second source of cooling. The Contact setting is used when an external input
is being used to determine when the second cooling source is to be activated. The external control communicates to the
Liebert unit via contact closure.
• Closed = activate second cooling source control
• Open = deactivate second cooling source control
The Temp setting is the factory default (12°F [-11.1°C]) on free-cooling and dual cooling units. If the temperature difference
between the second source cooling fluid parameter, Free-cooling Fluid Temperature (User Menu, Sensor Data) and room air
is equal to or greater than the adjustable DT Between Room / FC Fluid (Service Menu, Setpoints) value, then the second
source cooling fluid will be used to provide at least partial cooling.
3 Service Operation
70
Vertiv™ Liebert® iCOM™Installer/User Guide
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