9.2 Humidity Control
9.2.1 Dehumidification/Humidification Required
The humidity control is based on a calculated percentage requirement for dehumidification or
humidification (i.e., the difference between the return air humidity and the humidity set point). As the
return air humidity rises above the humidity set point, the percent dehumidification required increases
proportionally from 0 to 100% over a humidity band equal to the humidity sensitivity setting. The
converse is true for percent humidification requirement.
9.2.2 Dehumidification Operation, Compressorized Direct Expansion (DX) Systems
Dehumidification with the standard configuration is accomplished by operating the compressor without
the hot gas bypass active. Dehumidification will be disabled if the heating requirement exceeds 125%. It is
re-enabled when the heating requirement reaches 50%.
9.2.3 Humidification Operation
The canister humidifier is activated when the humidity control calculates a requirement of 100%
humidification; and is deactivated when the humidification requirement falls below 50%.
9.3 Load Control Features
The control system monitors the compressor and prevents it from turning on within a 3 minute period of
being off. If this on-off-on cycle occurs too often (e.g., 10 times in one hour) a Short Cycle Alarm will occur.
9.3.1 Communications
The control system uses a two-wire, RS-422 channel to communicate with Liebert Site Products via a
proprietary protocol. A converter board (ECA2) is available to allow communications with a “dumb”
terminal or a computer using RS-232 channel. More details are provided in the Site Products and ECA2
User Manual.
The communications channel provides both monitoring and control options, including:
• TEMPERATURE/HUMIDITY: Current temperature and humidity readings.
• STATUS (%), Cooling/heating and humidify/dehumidify operating status.
• PRESENT ALARMS: Alarms currently activated.
• SET POINTS:
• Temperature Set point
• Temperature Sensitivity
• Humidity Set point
• Humidity Sensitivity
• High Temperature Alarm
• Low Temperature Alarm
• High Humidity Alarm
• Low Humidity Alarm
• ON/OFF STATUS and CONTROL
• SILENCE ALARM
Vertiv | Liebert Mini-Mate2—5 ton User Manual| 70
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