Temperature Control-Second Cooling Source; Differential Temperatures / Controls (Comparator Circuit); Figure 19 Chilled Water Valve Control (Example: Cooling) - Emerson Liebert Challenger 3000 User Manual

Chilled water units that contain a motorized ball valve(s) are connected to the control by an analog
output. The analog output is driven proportionally to the call for cooling as shown in Figure 19.
Larger chill water units may contain two motorized ball valves in which both valves are controlled in
parallel.
NOTE
Depending on the valve specifications, the voltage output may be a 0-10VDC or a 2-10VDC that
is scaled automatically within the control.

Figure 19 Chilled water valve control (example: cooling)

100% Fully Open
Requested Position
0% - Closed
3.3 Temperature Control—Second Cooling Source
Certain cooling units are available with a second source of cooling within the unit. These typically are
compressorized models with an additional chilled water or free-cooling coil.
3.3.1

Differential Temperatures / Controls (Comparator Circuit)

Delta T (Temperature Difference) Between Room and Glycol
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. The comparator circuit has three set-
tings (DT Between Room / FC Type, [Service Menu, Setpoints]):
• No
• Contact
• Value
The No setting is for standard compressorized and chilled water units that do not have a second cool-
ing source. The No 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 cool-
ing source is to be activated. The external control communicates to the Liebert unit via contact clo-
sure.
• Closed = cooling enabled
• Open = cooling disabled.
The Value setting is the factory default setting (8°F [4.4°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 Air / FC Fluid (Service Menu, Setpoints) value, then the second source cooling fluid
will be used to provide at least partial cooling.
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 following actions will be performed:
1. The Free-Cooling Status indication will show "On" instead of "Off".
2. The compressor band will be shifted to the right by 100%, and within the first 100% the free-
cooling valve band will take place (see Figure 20).
The cooling portion of the proportional band is doubled, with the first half of the band controlling
the free-cooling valve and the second half controlling the compressors.
½ Proportional Band
0%
Setpoint
Cooling
+ 100%
Cooling
23
Operation
+ Temp