The most common and most costly of all the refrigerant contaminants is also the most benign - oil. While moisture, acids, and particulates do physical damage to the refrigerant side of chillers, oil merely reduces efficiency and ramps up energy costs. But higher efficiency and lower energy costs are what we're all after.
How prevalent is oil contamination in today's chillers? If the systems you work with aren't very new, odds are that they contain excess oil in the refrigerant, oil that is degrading chiller performance.