Digital Scroll Advantage For Rack Systems - Emerson Copeland Scroll Introduction Manual

Digital Scroll Advantage for Rack Systems

Digital scroll compressors having modulation capabilities from 10%–100% naturally fit refrigeration rack systems. Rack systems need to
fulfill varying evaporator load requirements due to changing case loads, not to mention variations due to cases undergoing routine defrost.
This can be attained by complementing fixed-speed compressor racks with a digital scroll of the same capacity. The refrigeration load will
be matched by running fixed-speed compressors to handle the base load and the peaks by the digital scroll. This leads to a smooth and
almost constant system suction pressure (see charts below). Compared to fixed-speed scroll racks where unloading is achieved by cycling
the lead compressor, this results in a saw tooth profile of the system suction pressure and will reduce the life of the lead compressor due to
frequent on and off action. Fluctuating suction pressures lead to varying evaporator temperature and humidity conditions—a condition
that is not advisable for refrigerated products.
Time Time
Compressor modulation by cycling compressor on and off Compressor modulation by digital scroll
Saw tooth profile of suction pressure for Smooth system suction pressure
fixed speed compressor
2