Compressor Control; Figure 13 One Single-Step Compressor Without Unloaders; Figure 14 Two Single-Step Compressors Without Unloaders Or One Compressor With An Unloader - Emerson Liebert Challenger 3000 User Manual

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

Temp Setpoint : 70°F
Proportional Band : 8°F
Deadband : 2°F
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
Cooling
Cool 1
Off
½ Dead-
band
70 71 72
0%
½ Proportional Band
Cooling
1/2 Dead-
band
70 71 72
Cool 1
0%
Off
1/2 Proportional Band
Cool 1
On
73 74 75
Increasing Temperature
Cool 2
On
Cool 1
On
73 74 75
Cool 2
Off
Increasing Temperature
19
Operation
+ 100 %
Cooling
+ 100%
Cooling