Emerson iCOM user manual Compressor Control, Compressor Proportional Bands

Operation

3.3.2Compressor Control

Depending on the type of Liebert air conditioning unit you have your unit may contain one or two compressors with or without unloaders.

Compressor Proportional Bands

One Single-Step Compressor Without Unloaders—One-Step

One single-step compressor, Cool 1, is started at 100% call for cooling from the temperature propor- tional band and stopped at 0% (see Figure 12).

Figure 12 One single-step compressor without unloaders

Temp Setpoint: 70°F
Proportional Band : 8°F					Cool 1
Deadband : 2°F					On
	Cool 1
	Off
½ Dead-
band
70	71	72	73	74	75
0%		½	Proportional Band		+ 100%
Cooling					Cooling

Increasing Temperature

Two Single-Step Compressors Without Unloaders—Two-Step

First single-step compressor, Cool 1, is started at 50% calculated output from the temperature propor- tional band, and stopped at 0%. The second compressor, Cool 2, starts at 100% and stops at 50% (see Figure 13).

One Compressor With an Unloader—Two-Step

The two-step compressor is started unloaded at 50%, Cool 1, calculated output from the temperature proportional band and stopped at 0%. At 100% the compressor starts fully loaded, Cool 2, and returns to unload operation at 50% (see Figure 13).

Figure 13 Two single-step compressors without unloaders or one compressor with an unloader (two-step)

Temp Setpoint: 70°F	Cool 2
Proportional Band: 8°F	On
Deadband : 2°F	Cool 1
1/2 Dead-	On
band

70	71	72	73	74	75
0%	Cool 1		Cool 2		+ 100%
Cooling	Off		Off		Cooling

1/2 Proportional Band

Increasing Temperature

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