Chapter 8 Operation - Liebert CR020 User Manual

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Chapter 8 Operation

Unit operation is completely automatic. This chapter explains how the unit operates.
1. The air, sucked in by the fans, which operate continuously, enters the unit.
2. The air is immediately filtered.
3. The temperature sensor or temperature & rel. humidity sensor (check type installed, see Figure 8-1 for its position),
verifies the state of the inlet air, and relays this information to the control system.
4. The treated air is then dispersed out of the unit.
5. The control system compares the relayed information to the set point and proportional band values programmed
into its memory: it then commands the air conditioner to treat the air as follows:
Cooling
Direct expansion mode (DX)
The compressor is started and the cold refrigerant flows through the evaporator, thus cooling the air passing over it.
Chilled water mode (CW)
The three-ways valve is opened and the chilled water flows through the coil, thus cooling the air passing over it.
Heating
Electrical heating (optional): the heating elements heat the air passing over them. There is one heating steps activate
in case of dehumidification if supply air temperature is too low.
Dehumidification
Under the DX mode, the compressor starts and the air flow on the evaporator surface is reduced (increasing
modulation capacity of compressor), thereby causing dehumidification.
Note: If, during dehumidification, the ambient temperature drops below a specified level, dehumidification will be
stopped if necessary.
In dehumidification mode, the air after passing over the coil it's reheated (if needed) by electrical heater to re-stabilize
the initial temperature.
Humidification
The humidifier creates steam, which is distributed into the air stream via the steam distribution pipe, refer to
Appendix 1 Humidair Humidifier.
Chapter 8 Operation
Figure 8-1 Sensor position
Liebert.CRV Series Air Conditioner User Manual