Emerson iCOM Two Compressors With Unloaders-Four-Step, Two compressors with unloaders four-step

Operation

Two Compressors With Unloaders—Four-Step

The first two-step compressor is started unloaded at 33% calculated output from the temperature pro- portional band and stopped at 17%. At 80% Compressor 1 will be loaded, at 70% unloaded.

The second compressor starts unloaded at 63% and stops at 47%. At 100%, Compressor 2 will be loaded, at 90% unloaded (see Figure 14).

The four stages of cooling are accomplished in the following manner:

•1 stage: One compressor, unloaded - Cool 1

•2 stages: Both compressors, unloaded - Cool 2

•3 stages: One compressor, loaded and one compressor, unloaded - Cool 3

•4 stages: Both compressors, loaded - Cool 4

Figure 14 Two compressors with unloaders (four-step)

Temp Setpoint: 70°F				Cool 3		Cool 4
						On
Proportional Band: 8°F					On
Deadband : 2°F			Cool 2
½ Dead-		Cool 1	On
		On
band
70	71	72	73	74		75	+ 100%
0%	Cool 1			Cool 3
							Cooling
Cooling	Off	Cool 2		Off	Cool 4
		Off			Off

½ Proportional Band

Increasing Temperature

19