D-EIMWC00804-14EN
Centrifugal Chillers
53
Oil Analysis
Interpreting Oil Analysis Data
Oil wear metals analysis has long been recognized as a useful tool for indicating the
internal condition of rotating machinery and continues to be a preferred method for
Daikin centrifugal chillers. Daikin Service or a number of laboratories specializing in oil
testing can do the test. To accurately estimate the internal condition it is essential to
properly interpret the oil wear test results.
Numerous test results from various testing laboratories have recommended action that
has prompted unnecessary concern by customers. Polyolester oils are excellent solvents
and can readily dissolve trace elements and contaminants. Most of these elements and
contaminates eventually end up in the oil. Also, the polyolester oils used in R-134a
chillers are more hygroscopic than mineral oils and can contain much more water in
solution. For this reason, it is imperative that extra care be used when handling
polyolester oils to minimize their exposure to ambient air. Extra care must also be used
when sampling to ensure that sample containers are clean, moisture-free leak proof and
non-permeable.
Daikin has done extensive testing in conjunction with refrigerant and lubricating oil
manufacturers and has established guidelines to determine action levels and the type of
action required. Table 1 indicates these parameters.
In general Daikin does not recommend changing lubricating oils and filters on a periodic
basis. The need to change lubricating oil and filters should be based on a careful
consideration of oil analysis, vibration analysis and knowledge of the operating history
of the equipment. A single oil sample is not sufficient to estimate the condition of the
chiller. Oil analysis is only useful if employed to establish wear trends over time.
Changing lubricating oil and filter prior to when its needed will reduce the effectiveness
of oil analysis as a tool in determining machinery condition.
The following metallic elements or contaminates and their possible sources will typically
be identified in an oil wear analysis.
Aluminum
Typical sources of aluminum are bearings, impellers, seals or casting material. An
increase in aluminum content in the lubricating oil may be an indication of bearing,
impeller or other wear. A corresponding increase in other wear metals may also
accompany an increase in aluminum content.
Copper
The source of copper can be the evaporator or condenser tubes, copper tubing used in the
lubrication and motor cooling systems or residual copper from the manufacturing
process. The presence of copper may be accompanied by a high TAN (total acid
number) and high moisture content. High copper contents may also result from residual
mineral oil in machines which have been converted to R-134a. Some mineral oils
contained wear inhibitors which react with copper and result in high copper content in
lubricating oil.
Iron
Iron in the lubricating oil can originate from compressor castings, oil pump components,
shells, tube sheets, tube supports, shaft material and rolling element bearings. High iron
content may also result from residual mineral oil in machines which have been converted
