In a low-pressure centrifugal chiller, what is meant by the term 'high efficiency purge unit?'

Correct Answer: Option D — Those purge units which discharge very little refrigerant with the air being removed.

High-efficiency purge units on low-pressure centrifugal chillers utilize small internal refrigeration condensing circuits to separate and recover refrigerant from non-condensable gases, discharging only clean air while returning condensed refrigerant to the system.