Calibrate Valve Actuator; Select Humidity Sensing Mode; Set Status Display; Change Passwords - Liebert Himod Operation & Maintenance Manual

3.7.4

Calibrate Valve Actuator

For systems that use a valve actuator for chilled water or GLYCOOL cooling, the actuator timing may
be calibrated or adjusted. This is the time it takes for the valve to travel from full closed to full open.
It is programmable from 0 to 255 seconds. The factory default time is 165 seconds and should not be
changed unless the actual valve travel time is not correct. The full valve travel time is used by the
control to determine the appropriate valve position. For example, if the valve travel time is 165 sec-
onds and 50% cooling is being called for, the valve will open for 83 seconds to achieve 50% open. To
change the valve travel time, first enter the "CALIBRATE ACTUATOR" screen. The display will show
the present period used by the control for valve actuator full travel. Press ENTER and adjust the time
using the UP/DOWN arrows. When the correct time is displayed, press ENTER to store the new time
to memory.
3.7.5

Select Humidity Sensing Mode

The user may select between RELATIVE (direct) and ABSOLUTE (predictive) humidity control. If
relative is selected, the RH control is taken directly from the RH sensor. If absolute is selected, the
RH control is automatically adjusted as the return air temperature deviates from the desired temper-
ature setpoint. This results in a predictive humidity control. The display will indicate % RH for both
methods of control, but the adjusted humidity reading will be displayed if absolute is selected.
With predictive humidity control, the humidity control is automatically adjusted approximately 2%
RH for each degree difference between the return air temperature and the temperature setpoint.
With relative humidity control, unnecessary dehumidification can result when overcooling occurs dur-
ing a dehumidification cycle. This is because a higher than normal RH reading is caused by overcool-
ing the room (about 2% RH for each degree of overcooling). This extends the dehumidification cycle.
Later, when the dehumidification ends and the temperature rises to the setpoint, the RH reading
falls. The final RH reading will then be lower than actually desired. If the overcooling was significant
enough, the RH could be low enough to activate the humidifier.
If absolute humidity control is selected, over-dehumidification is avoided. When overcooling occurs,
causing an increase in the RH reading, the humidity control program "predicts" what the RH will be
when the dehumidification cycle ends and temperature returns to the setpoint. This allows the dehu-
midification cycle to end at the proper time. The predictive humidity control can reduce energy con-
sumption by minimizing compressor and reheat operation, and eliminating unnecessary humidifier
operation.
3.7.6

Set Status Display

The Status Display can be set to display the return air temperature and humidity SENSOR READ-
INGS or the temperature and humidity control SETPOINTS through this selection. When setpoints
are selected, the status display indicates so by also displaying "SETPOINTS." If SENSOR READ-
INGS is selected, the Status Display will show the return air sensor readings.
3.7.7

Change Passwords

Selecting CHANGE PASSWORDS will prompt the user to select one of the following:
• SETPOINT PASSWORD
• SETUP PASSWORD
The display prompts you to enter a three digit password when making changes. The system includes
two (2) passwords, one for setpoints and one for system setup. The system allows the passwords to be
changed by first entering the present password, factory set as "123" for setpoints and "321" for setup.
The password function provides system security, so only personnel authorized to make changes
should know the passwords. If unauthorized changes are being made, the passwords may be compro-
mised and new ones should be selected. The password function can be disabled by setting DIP switch
8 to OFF.
22 Operation with Advanced Microprocessor with Graphics Control