Emerson Liebert ICOM-DO Manuel d'utilisateur télécharger pdf (Page 25)

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Operation

3.2.2 Compressor Control

Depending on its type, a Liebert Precision Cooling unit may have one or two compressors with or

without unloaders or variable capacity.

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 13).

Figure 13 One single-step compressor without unloaders

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 14).

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 14).

Figure 14 Two single-step compressors without unloaders or one compressor with an unloader (two-step)

Temp Setpoint : 70°F

Proportional Band : 8°F

Deadband : 2°F

½ Proportional Band

Cooling

+ 100 %

Cooling

71 72 73 7470

½ Dead-

band

Cool 1

Off

Cool 1

Increasing Temperature

Temp Setpoint : 70°F

Proportional Band: 8°F

Deadband : 2°F

1/2 Proportional Band

Cooling

+ 100%

Cooling

71 72 73 7470

1/2 Dead-

band

Cool 1

Cool 2

Increasing Temperature

Cool 2

Off

Cool 1

Off

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Emerson Liebert ICOM-DO Manuel d'utilisateur Page 25

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