Liebert iCOM
®
Control
95
Liebert
®
CRV
™
Supply Control
If 75°F (24°C) server entering air temperature is desired at the rack inlet, the supply air must be
colder to account for any thermal pickup of the air as it flows to the cold aisle. If this does not achieve
the cold aisle temperature setpoint, then set the supply sensor setpoint lower. Continue adjusting the
supply sensor until the cold aisle temperature setpoint is achieved.
The supply temperature setpoint may require adjustment because it will be dependent on the
distance of the Liebert CRV to the racks being cooled. This temperature will also be dependent on
rack blanking panels, server population and whether the racks are in a containment system.
Controlling sensor settings shows the flexibility of the Liebert CRV and how the different sensor
configurations can be used to control the Liebert CRV fan speed and cooling capacity. See
for more information on the different coupled and decoupled modes available with the Liebert CRV.
11.3.2 Cooling
The cooling control of the Liebert CRV can be managed from any of the temperature sensors. See
for applicable control sensor combinations. The Liebert CRV controls cooling output by
monitoring a temperature control sensor, set on line S103, compared to the user programmed
temperature setpoint on either line U202 or S202. The degree of cooling is determined by the
temperature control band.
The temperature control band is established using the following formula and control lines:
(S102 Temperature Setpoint) + (1/2(S105 Temperature Deadband) + (S106 Temperature Control Band)
As the temperature sensed by the temperature control sensor deviates from the setpoint on the
control band, cooling is staged On. S107 Cooling integration time works with the cooling control band
to maintain tight temperature control.
Figure 67 Service Menu Setpoint screen for Cooling
Emerson recommends using the supply temperature sensor to control the cooling capacity of the
Liebert CRV. The supply temperature is an accurate representation of the actual heat rejection the
Liebert CRV needs to perform at an optimal level. A chilled water Liebert CRV will modulate the
cooling capacity from 0% - 100% and the DX version of the Liebert CRV will modulate the cooling
capacity of the unit from 10% -100% compressor capacity.
To avoid short-cycling the compressor during room heat load changes, the Liebert CRV will not
deactivate the compressor until the air temperature is below 150% of temperature control band.