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Operation
41 Liebert
®
iCOM
®
for Liebert DSE
™
Dehumidification with Two Compressors (DH Stage 1)
• Compressors C1A and C2A must be On, while compressors C2B and C1B must be Off.
• The C1A digital compressor must be loaded at 100% at all times.
• The C2A digital compressor will adjust its loading based on whether the Call for
Dehumidification is greater than the Call for Cooling: If the CFD is greater than or equal to the
CFC, C2A must use the ramp on line DH05 (“C2A CFC @ 0% / 100% Dehum Ramp”) with the CFD
used to determine ramp %. If the CFD is less than the CFC, then C2A must use the ramp on line
DH06 (“C2A CFC @ 0% / 100% Cooling Ramp”), with the CFC used to determine ramp %.
• If the Low Limit sensor (line S132) temperature becomes less than or equal to the Low Limit 2
border (lines S132 & S133), then dehumidification will be disabled.
• If the reheat stage indicated on the second column of line DH07 is inactive, and the Return Air
Temperature is above the Low Limit 1 reset border, then Compressor C2B can start (or restart) if
the CFC becomes greater than or equal to the value on line DH03 (“C2B Start @ CFC”). Operation
then moves to DH Stage 2.
If Dehumidification is Not Inactive Because of LL2
• If the CFC is greater than or equal to DH02 (“C1B Start @ CFC”), dehumidification will start with
all four compressors (DH Stage 3).
• If the CFC is greater than or equal to DH03 (“C2B Start @ CFC”), dehumidification will start with
three compressors (DH Stage 2).
• If the CFC is less than DH03, dehumidification will start with two compressors (DH Stage 1).
If Dehumidification is Inactive Because of LL2
• When “Dehum Reheat / LL Sensor Set” (line S132) = “Remote Sensor” OR “Return Sensor”: If the
CFC is greater than or equal to the setting on DH04 (“C1A & C2A Restart @ CFC”), and the Low
Limit Sensor (line S132) temperature is greater than or equal to the Low Limit 2 reset border,
dehumidification will start with two compressors (DH Stage 1).
• When “Dehum Reheat / LL Sensor Set” (line S132) = “Supply Sensor”: If the CFC is greater than
or equal to the setting on DH04 (“C1A & C2A Restart @ CFC”), dehumidification will start with
two compressors (DH Stage 1).
• If the conditions (based on the settings on line S132, “Dehum Reheat / LL Sensor Set” to initiate
dehumidification are not satisfied when the CFD becomes high enough, then dehumidification
operation will be prevented until all of the conditions are satisfied, and the CFD is high enough
(based on the value set on line A558).
After starting dehumidification, the control may transition between DH stages, based on different
conditions. The operation for each of dehumidification stages are described in detail in the
subsequent sections.
Dehumidification During Compressor Alarm(s)
When an alarm that prevents the operation of one or more compressors in a tandem bank is active,
dehumidification operation will be altered or prevented, depending on how many compressors are still
operational. When the unit is dehumidifying while a compressor alarm is active, the readout in the
second column of line DH10 (“Dehum Status”) will show “Active,” and the readout on line DH11
(“Compressor Alarm Operation”) will read “Yes.”
When dehumidification is active and only one compressor is disabled by an alarm, the control will
operate based on the rules described in Dehum Operation with One Compressor Out on
Alarm on page 42 , even if only two compressors are required. The control should operate only by the
rules in Dehum Operation with Two Compressors Out on Alarm on page 42 when two of the
compressors are disabled by alarms.
The same criteria for initiating dehumidification as described in Section 4.2.1 will be used when
compressor alarms are present, and Low Limit 2 will still deactivate dehumidification.