3.8Run Diagnostics, 3.7.6Select Humidity Sensing Mode

Operation with Advanced Microprocessor with Graphics Control

3.7.6Select 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 absolute 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.

3.7.7Set 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.

3.7.8Change 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.