Emerson Liebert iCOM Manual De Usuario

Proportional Control requires a much tighter proportional band to hold the unit closer to the setpoint, 

which often results in compressor(s) short cycling or valve hunting.

The integration (I) time works with the proportional band in PI Control to stage call for cooling before 

the actual temperature increases far above the temperature setpoint. The “I” portion does this by 

doubling the current “P” deviation for every time the “I” has elapsed.

While this happens, the real temperature “P” deviation will decrease. If the “P” deviation drops to 

40% and the previously calculated “I” was already on 55%, it will shift back to 45% following “P.” 

From this point the “I” will continue to calculate the call for cooling, but will do so more slowly 

because the room temperature has dropped. Opening the valves or staging compressor(s) to 62% may 

decrease the temperature from 40% to 20%, which would drive the “I” down from 62% to 42%. At this 

point, “P” is 20% and “I” is 42% (call for cooling, valve opening, compressor[s] stage). This continues 

until “P” is 0—on the setpoint or within the deadband.

Three to 5 minutes integration time is adequate for most applications. The proportional band setting 

will vary depending on the heat load and compressor/chilled water valve type. Some additional tuning 

of the PI loop in Service > Setpoints after the unit has been started up may be required. Factors such 

as room heat load, chilled water temperature and external heat gains may affect PI control loop 

performance. Use Table 6 as a guide for the PI control settings.

Intelligent—If Intelligent Control is selected, the 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. This logic simulates the actions that a human would take if manually 

controlling the system. This control type is used only on chilled water units.

Unit is too slow to activate 

cooling.

Decrease the proportional band slightly and monitor operation.

Compressor short cycle alarm.

Increase the proportional band slightly and adjust the integration time to 3-5 min. 

Monitor compressor run time. Run must be higher than 3 minutes to avoid short 

cycle from occurring.

Excessive valve oscillation or 

hunting.

Widen the temperature proportional band and/or consider increasing the 

integration time.