User manual

Operation
22
Reheat During Dehumidification
The parameter Electric Reheat Operation defines how the heaters react in case the temperature
decreases during the dehumidification process. The Electric Reheat Operation parameter is in the
Advanced menu under Factory Settings and should not be adjusted without factory approval.
No—No electric reheat allowed during dehumidification process.
Delayed—Not applicable to Liebert PEX units.
Staged—This is the standard setting for Liebert PEX units. Electric heaters will stage as described in
3.3.1 - Electric Reheat.
3.4 Control Types
3.4.1 Temperature and Humidity Control Types
The Liebert iCOM control has three Temperature Control Types: Proportional, PI and Intelligent.
Each control type affects the timing and intensity of the cooling/heating and humidifying/dehumidify-
ing operations. The Control Type parameter is in the Service menu under Setpoints.
Proportional – If Proportional Control is selected, the percent cooling/heating requirement is deter-
mined by the difference between the return air temperature sensor reading and the temperature set-
point. As the return air temperature rises above the temperature setpoint, the percent cooling
required increases proportionally (from 0 to 100%) over half the programmable temperature propor-
tional band (See 3.2.1 - Temperature Proportional Band). The percent heating requirement (0 to -
100%) is determined the same way when the return air temperature falls below the setpoint. The
humidifying/dehumidifying operations are controlled in the same manner as the cooling/heating oper-
ations; however, the humidity sensors, setpoints and proportional bands are utilized. The Propor-
tional control type is commonly selected on compressorized units.
PI – If PI Control is selected, the percent cooling/heating requirement is calculated by adding together
two individual terms – proportional and integral. The proportional term is calculated in a manner
similar to the previously described Proportional control. The integral term (sometimes called “reset
action”) is calculated by measuring how much and for how long the return air temperature/humidity
has been above or below the setpoint. If the actual return air temperature/humidity is above the set-
point, the percent requirement is slowly but continuously increased until the total is sufficient to
bring the return room air back to the setpoint.
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.
!
WARNING
If the electrical service to the unit is not properly sized, it could trip the building circuit
breakers (or fuses) or, in extreme cases, damage the building wiring. This Warning applies
only when the Dehumidification With Comp is set to BOTH and the Electric Reheat
Operation is set to Staged. Consult factory before making any changes to the default settings.
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 - ).