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3.6.2 Dehumidification
The Dehumidification Enable parameter (Service Menu, Options Setup) allows for enabling/disabling
the dehumidification function.
A call for dehumidification is calculated in the same way as a cooling request. The components
(valves, compressors) will follow this dehumidification request as soon as it is higher than the request
for cooling.
Dehumidification Low Limit
Low Limit 1 and Low Limit 2 are used to avoid overcooling a room during dehumidification. When a
low limit is reached, a compressor or the liquid cooling source that is used for dehumidification is dis-
abled. It is re-enabled when the return air temperature rises. The Low Limit 1 and 2 settings are in
the Service menu under Setpoints.
Low Limit 1: Low Limit 1 will disable one of two compressors for dehumidification. If only one com-
pressor is set for dehumidification, or if the dehumidification source is chilled water, this limit will
not be visible and will be inactive.
Low Limit 2: Low Limit 2 will disable both compressors for dehumidification. This limit will also
stop dehumidification in single compressor units and in chilled water units.
The limits become active when the return air temperature drops below a temperature value equal to
the sum of the temperature setpoint plus the value set on Low Limit 1 and 2 (the Low Limit settings
are negative values).
A dehumidification source is deactivated if the return air temperature drops below the Deactivation
Temperature, as in this example:
Dehumidification Compressor Quantity
Under Factory Settings in the Advanced menu there is an item called Dehumidification With Comp.
This item will be set to either 1, 2, 1 or 2, or BOTH. This setting determines which compressors are
used for dehumidification. It also determines if Low Limit 1 will be available and impacts how the
reheats will operate during dehumidification. The Dehumidification With Comp field is set when the
cooling unit is built and should not be adjusted without consulting the factory first. Table 6 outlines
which Low Limit settings will be available, based on the Dehumidification With Comp selection.
Low Limit 1 & 2 will be available only on cooling units with two compressors when Dehumidification
With Comp is set to BOTH (see WARNING on page 30).
Temperature Setpoint: 70°F
Low Limit Value: -7°F
Deactivation Temperature: 62°F
NOTE
If a cooling unit is equipped with SCR reheat and the SCR Control Type parameter is set to
Tight mode, then Low Limit 2 will be ignored, see 3.5 - Temperature Control—Reheat.
Table 6 Dehumidification With Comp settings
Available to Set Value Dehumidification With Comp Setting Default Setting On
Low Limit 2 only
[blank] (units without compressors) All Chilled Water Units
1 (Compressor 1 dehumidifies only) Liebert Challenger 3000
™
, Liebert DS
™
,
Liebert Deluxe System/3
™
2 (Compressor 2 dehumidifies only) —
1 or 2 (Compressor 1 and 2 alternate) —
Low Limit 1 & 2 Both (both compressors dehumidify) —