Emerson Liebert iCOM User Manual download pdf (Page 36)

Operation

Reheat During Dehumidification

Hot gas reheat or hot water reheat will start as described in 3.4 - Temperature Control—Reheat,

when the temperature decreases during the dehumidification process.

The parameter Electric Reheat Operation defines how the heaters react in case the temperature

decreases during the dehumidification process. This parameter does not impact SCR reheat

operation. 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—This setting applies only to two-compressor units with BOTH compressors selected for

dehumidification. The electric reheats are prevented from turning on until Low Limit 1 is reached. At

this condition, one stage of dehumidification is disabled and the reheats are activated. At Low

Limit 2, both stages of dehumidification are disabled. When Delayed is selected on units with a single

compressor selected for dehumidification (Dehumidification With Comp Setting: 1, 2, and 1 or 2), the

reheats will operate in the same manner as they do for Staged as described below. Delayed is the

default setting for Liebert DS units.

Staged—This setting applies to one or two compressor units. Electric heaters will stage as described

in 3.4.1 - Electric, Hot Gas and Hot Water Reheat. Staged is the default setting for Challenger

3000 units. On two compressor units with staged reheat selected and Dehumidification With Comp

set to BOTH, the control allows for operating two compressors and reheats simultaneously. It is

important that electrical service to the unit be sized and wired for this option if selected.

3.6 Control Types

3.6.1 Temperature and Humidity Control Types

The Liebert iCOM has three Temperature and Humidity Control Types:

• Proportional

•PI

• Intelligent

Each control type affects the timing and intensity of the cooling/heating and

humidifying/dehumidifying operations. The Control Type parameter is in the Service menu under

Setpoints.

Proportional—If Proportional Control is selected, the percent cooling/heating requirement is

determined by the difference between the air temperature sensor reading and the temperature

setpoint. As the air temperature rises above the temperature setpoint, the percent cooling required

increases proportionally (from 0 to 100%) over half the programmable temperature proportional band

(See 3.2.1 - Temperature Proportional Band). The percent heating requirement (0 to -100%) is

determined the same way when the air temperature falls below the setpoint. The

humidifying/dehumidifying operations are controlled in the same manner as the cooling/heating

operations; however, the humidity sensors, setpoints and proportional bands are utilized. The

Proportional 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 air temperature/humidity

has been above or below the setpoint. If the actual air temperature/humidity is above the setpoint, the

percent requirement is slowly but continuously increased until the total is sufficient to bring the

return room air back to the setpoint. This control type is commonly selected on free-cooling and dual-

cool 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.

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Emerson Liebert iCOM User Manual Page 36

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