Emerson Liebert iCOM User Manual download pdf (Page 41)

Operation

31 Liebert

iCOM

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.

Example: If the “P” deviation is 50% within the “I” time (e.g., 5 min), the call for cooling will be

doubled, giving 100% in 5 minutes.

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.

3.3.1 Setting Up PI Control

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.

NOTE

k is the unit of measure used when U404‚ Temperature Indication, is set to degrees Celsius.

K is the conversion from degrees Fahrenheit to degrees Celsius without the -32°F offset. If the

proportional band is 20°F, then (20/1.8) = 11.1K

Table 6 PI control troubleshooting

Problem Solution

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.

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 195 196

Comments to this Manuals

No comments

Emerson Liebert iCOM User Manual Page 41

Comments to this Manuals

Related products and manuals for IP phones Emerson Liebert iCOM