Vertiv Liebert iCOM DP400/500 Installer/User Manual page 83

Secondary Cooling Temperature Control with 2-Step Compressor
When the fluid temperature meets the set up requirements, secondary cooling provides temperature control as follows. If the
fluid is not cold enough, primary, compressorized cooling operates as normal.
NOTE: The compressor control method is not affected by economizer operation and operates across the assigned
proportional band based on the compressor configuration of your system (1-step, 2-step, 4-step, or digital-scroll). See
Compressor Control by Cooling Requirement
• 70° temperature setpoint
• 8° temperature proportional band
• 2° temperature deadband
In Figure 7.1 on the next page:
The proportional band is divided evenly on each side of the setpoint, and an additional half of the proportional band is
added to the cooling side for 200% cooling.
• At 71° air temperature (cooling demand 0%), the fluid control valve is closed.
• As cooling demand increases from 0% to 100%, the fluid control valve opens incrementally to increase cooling
capacity proportionally until fully open at 75° (cooling demand 100%).
NOTE: If simultaneous operation of economizer cooling and compressor (DX) cooling is enabled, the compressor(s)
may begin operation before the valve is open 100% because the fluid temperature differential is calculated to provide
insufficient cooling.
• At 100% cooling demand, the compressor control method is employed across the additional half of the
proportional band, a single scroll compressor with unloaders in this example:
• The compressor starts unloaded at 77° when the cooling requirement is 150%.
• At 79° when the cooling requirement is 200%, the compressor operates loaded until 77° is reached when
cooling requirement is 150% when it returns to unloaded operation.
7 Configuring Economizer Operation
on page 23, for a description compressor-control methods.
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