User manual

Operation
Liebert
®
iCOM
®
30
3.3 Temperature Control—Second Cooling Source
Two types of secondary source cooling models 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) heat exchanger (eg., Liebert Paradenser
™
,
tube-in-tube condenser or brazed plate heat condenser). Dual-Cool units can be two-pipe or four-pipe.
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/free-cooling 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.
3.3.1 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 94. The comparator circuit has four settings
(DT Between Room / FC Type, [Service Menu, Setpoints]):
• Disabled
•Contact
•Value
•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 setting (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.
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 94. The primary and secondary source of cooling will
stage accordingly. See the next sections for more information.