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Operation
103 Liebert
®
CRV
™
12.0 OPERATION
Figure 95 Return air temperature and humidity sensor viewed from the rear of the unit
The control system compares the relayed information with the programmed setpoint and proportional
band values and performs one of the following operations:
• Cooling—Direct expansion mode (DX): The compressor is started and the cold refrigerant flows
through the evaporator, thus cooling the air passing through it. For compressor operation see
Liebert iCOM
®
user manual, SL-18835. Liebert recommends using the supply temperature sensor
to control the cooling capacity of the Liebert CRV, but cooling can be managed from any of the
temperature sensors. The supply temperature is an accurate representation of the actual heat
rejection the Liebert CRV needs to perform. Chilled water Liebert CRV models will modulate the
cooling capacity from 0% - 100% and DX models will modulate the cooling capacity from 20% -
100% compressor capacity. To avoid short-cycling the compressor during room heat load changes,
the CRV will not deactivate the compressor until the air temperature is below 150% of tempera-
ture setpoint when in Remote or Supply Air Control or below 200% of temperature setpoint when
operating in Return Air Control.
• Chilled water mode (CW)—The three-way valve is opened and the chilled water flows through
the coil, thus cooling the air passing through it. For valve operation, see the Liebert iCOM user
manual, SL-18835.
• Reheating—Electrical heating (optional): The heating elements heat the air passing over them
during dehumidifcation. The heating control is active only when the unit is in dehumidification
mode. The reheats will only activate when the unit is dehumidifying. The reheats will begin acti-
vation when the control temperature has dropped to -66% of the control’s proportional band and
will deactivate when temperature setpoint has been reached.
• Dehumidification (DX mode)— The temperature of the cooling coil is reduced to remove mois-
ture from the air (refer to Figures 58, 59, 69 and 90).
In dehumidification mode, the air after passing over the coil is reheated (if needed) by electrical
heaters to stabilize the initial temperature.
NOTE
If dehumidification cannot reach its setpoint within a set amount of time, the unit will delay
dehumidification to allow the room temperature to stabilize.