Emerson Liebert iCOM, Manual

Page: 46 / 172

Operation
Liebert
®
iCOM
®
for Liebert DSE
™
38
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
disabled. It is re-enabled when the 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
compressor 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 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 first consulting the factory. Table 9 outlines which
Low Limit settings will be available, based on the Dehumidification With Comp selection.
Low Limit 1 and 2 will be available only on cooling units with two compressors when
Dehumidification With Comp is set to BOTH (see WARNING on page 42 ).
Low Limit defines the sensor and the setpoint used to determine the low limit thresholds for all
cooling and dehumidification modes.
The value of the selected sensor is compared with the setpoint set in S132 + the LL1 / LL2 settings
(S133).
Possible selections are:
• 0 = Supply Sensor (selectable only when S102 Temperature Control Sensor is set to “Supply”)
• 1 = Remote Sensor (selectable only when S102 Temperature Control Sensor is set to either
“Remote” or “Supply”)
Falls back to “Supply” when all Remote Sensors are set to “Disabled”
• 2 = Return Sensor - Default for all configurations, and the only allowable setting when S102
Temperature Control Sensor is set to “Return.”
Defaults: Any time the S132 sensor setting changes (away from the default “Return” or back to
“Return”), the setpoint will take the value that is set in S103 Temperature Setpoint.
Temperature Setpoint: 70°F (21.1°C)
Low Limit Value: -7°F (-3.8°C)
Deactivation Temperature: 63°F (17.2°C)
Table 9 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 or 2 (Compressor 1 and 2 alternate) Liebert DS
™
Low Limit 1 & 2 Both (both compressors dehumidify) —