Emerson iCOM Digital Scroll Compressors, Digital scroll capacity modulation, 10-100% variable

Operation

Digital Scroll Compressors

A compressor with a suction cutoff unloader can only modulate its capacity between two distinct lev- els: fully loaded and half loaded. A digital scroll compressor can modulate its capacity anywhere between 10-100%. This variable capacity modulation allows cooling units to control an environment more precisely.

Digital scroll capacity modulation is achieved by energizing and de-energizing a solenoid valve on the compressor. When the solenoid valve is de-energized, the compressor capacity is 100%. When the sole- noid valve is energized, the compressor capacity is zero. Therefore, the capacity of the compressor depends on how long the solenoid is de-energized for. If the solenoid is de-energized for 10-seconds, then energized for 5 seconds during a 15-second cycle, the resulting capacity will be 66% as shown in Figure 15.

Figure 15 Digital scroll capacity modulation, 10-100% variable

On single and dual digital scroll compressor systems, the first compressor is started at 25% calculated output from the temperature proportional band and stopped at 10%. On dual digital scroll compressor systems, the second compressor is started at 35% and stopped at 20%, see Figure 16. When a com- pressor is started, the solenoid is energized longer than it is de-energized to match the call for cooling. When the call for cooling increases to 100%, the solenoid is de-energized for the entire 15 second cycle.

Figure 16 Single and dual digital scroll compressor activation points

Comp 2

Off

½ Proportional Band

Increasing Temperature

20