Operation
Intelligent – If Intelligent Control is selected, the return air temperature/humidity is controlled at or near the setpoint. The percent temperature/humidity adjustment required is calculated based on logic that is programmed into the control. These rules simulate the actions that a human operator would take if manually controlling the system. This control type is commonly selected on chilled water units.
NOTE
The actual return air temperature sensor reading is always displayed on the Status menu. The value displayed for the return air humidity sensor reading depends on the Humidity Sensor Control Type (see 3.7.2 - Humidity Sensor Reading Control Types).
3.7.2Humidity Sensor Reading Control Types
The Liebert iCOM control has three humidity sensor control types: Relative, Compensated and Pre- dictive. The humidity sensor control adjusts how the Temperature and Humidity Control determines the percent requirement for humidification/dehumidification. The humidity sensor control type parameter, Humidity Control Type, is in both the User and Service menus under Setpoints.
Relative—The actual return air humidity sensor reading is sent to the Temperature and Humidity Control to determine if and how much humidification/dehumidification is required. The actual return air humidity reading is displayed on the Status menu. Unnecessary dehumidification can result when overcooling occurs during a dehumidification cycle. This is because a higher than normal relative humidity (RH) reading is caused by overcooling the room. This extends the dehumidification cycle. Later, when the dehumidification ends and the return air temperature rises to the setpoint, the RH reading falls. The final RH reading will then be lower than actually desired. If significant overcooling occurred, the RH could be low enough to activate the humidifier.
Compensated—The actual return air humidity sensor reading is sent to the Temperature and Humidity Control where the Humidity Setpoint is adjusted based on how much the return room air temperature deviates from the desired temperature setpoint. The adjusted humidity setpoint is used for humidification percent requirement determination. For every 1°C deviation from the temperature setpoint the humidity setpoint is changed by 3% RH, inversely proportional: if the temperature increases, the humidity setpoint is decreased, and vice versa. The recalculated humidity setpoint is shown as the Actual Humidity Setpoint (User Menu, Sensor Data). As the humidity setpoint is auto- matically adjusted, the high and low humidity setpoints (User Menu, Set Alarms) are adjusted accordingly. The unadjusted humidity sensor reading is displayed on the Status menu.
Predictive—The actual return air humidity sensor reading is adjusted before it is sent to the Tem- perature and Humidity Control. The humidity sensor reading is adjusted based on how much the return room air temperature deviates from the desired temperature setpoint. For every 1°C deviation from the temperature setpoint, the humidity sensor reading is changed by 3% RH, directly propor- tional: if the temperature increases, the humidity reading is increased and vice versa. The adjusted humidity sensor reading is displayed on the Status menu. Units are shipped from the factory with Predictive humidity control set as default.
If Compensated or Predictive humidity sensor control is selected, overdehumidification is avoided. When overcooling occurs, causing an increase in the relative humidity sensor reading, the humidity control program predicts what the RH will be when the dehumidification cycle ends and return air temperature returns to the setpoint. This allows the dehumidification cycle to end at the proper time. The Compensated and Predictive humidity sensor control can reduce energy consumption by mini- mizing compressor and reheat operation, and eliminating unnecessary humidifier operation.
NOTE
The historical humidity sensor graphs will display the real (unadjusted) sensor readings, no matter which Humidity Control Sensor Type is selected. The graphical sensor data is in the User menu under Graphics.
