11.3.5 Humidification; Figure 70 Service Menu Setpoint Screen For Humidification - Emerson Liebert CRV User Manual

Temperature Sensor Control: Fan temperature control uses the factory-equipped return, supply or
remote sensors. See Table 33 for applicable control sensor combinations. When operating the fan in
coupled mode, the fan speed follows the call for cooling to reach the temperature setpoint. When the
fans are operating in a decoupled mode, the fans are ramped following the fan control band to achieve
the fan setpoint. The fan setpoint is a calculated value found on line U303 of the User menus, Sensor
Data. U303 is established by lines located in Service menus, Setpoints.
Here (S102 Temperature Setpoint) + (S125 Fan Delta) = Fan control setpoint. As the temperature
sensed at the fan control sensor (S125) deviates from setpoint (U303), the fan modulates between
50 and 100% according to the fan control band. Fan speed increases as the temperature deviates
further from setpoint. The inverse happens as the controlled temperature gets closer to setpoint. The
fan control band is established by using the following formula and control lines:
(U303 Fan Setpoint) + (S128 Fan Control Band)
S129 Fan speed integration time works with the fan control band to slowly speed or slow down the fan
to maintain tight fan control.
Emerson recommends controlling the fan speed using the remote rack temperature sensors. The
remote rack sensors are an accurate representation of the delivery of the Liebert CRV's discharge air
and help ensure that cold aisle temperature is maintained. The Liebert iCOM will ramp fan speed to
100% during a call for reheat or humidification. On DX models of the Liebert CRV, a unique freeze
protection algorithm will increase fan speed if the compressor pressure gets too low. This feature
increases system reliability and helps to provide partial cooling if a low side refrigerant issue occurs.
In a single fan fails, the Liebert CRV will ramp the remaining operating fan to 110% of its rated
output to compensate for the loss of airflow. In addition, an alarm will report which fan failed.

11.3.5 Humidification

The Liebert CRV's humidification is activated when the measured temperature and humidity sensor
has been calculated to exceed the corresponding dew point setpoint. The dew point setpoint is
calculated based on the temperature and humidity of the sensor set to control the control setpoint and
relative humidity.

Figure 70 Service menu setpoint screen for humidification

Example: Temperature Setpoint 72°F / Humidity Setpoint 50% = 52°F Dew Point
NOTE
The Liebert iCOM control monitors the condition of the air discharging from the unit to protect
neighboring electronic equipment. Liebert iCOM will prevent the humidifier from activating if
the discharge air is near its saturation point. This protects against discharging fog from the
unit or condensation forming on the unit's supply air baffles. This protection mode is activated
when the supply sensor reading is below 53°F (11.7°C) or above 55% relative humidity. When
this condition is met, a message will display showing "humidifier" suspended.
The status of the humidifier lockout can be viewed in the Service/Diagnostics menu.
These protections do not apply to the external humidifier output.
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Liebert iCOM Control
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Liebert CRV