The development of copious amounts of flaky, white powder from indoor coils has been a recognized industry issue for a couple decades now. The first known occurrences were reported on residential heatpump systems that used refrigerant as the heat transfer fluid. Commonalities between reported cases were coils constructed with bare aluminum fins in an air cooling/ dehumidifying application. The problem would surface during the heating season of the year when the dehumidifying coil’s fin surface was dry of condensate and within the first couple years of operation of the equipment.
Large commercial equipment applications, while still rare, have also been reported as well as chilled water systems in a variety of light commercial and terminal products. As additional occurrences have been identified over the last 10 to 20 years, it has now been shown to happen to any type of dehumidifying coil with bare aluminum fins operating in a system that also supplies forced air heating during the winter season.
The incident rates have been low over the years and until recently limited to coastal areas mostly regionalized in the southern United States. With millions of aluminum fin coils shipped in the reported time period, problem jobs only number in the dozens. The phenomenon has been reported across additional geographical areas in the Southeastern and Midwestern United States, Europe and Asia. But, the primary regions have continued to be hot and humid climates or milder climates that had severe cooling seasons prior to development of the problem. Cases have not been reported in dry, arid climates or on coils that are in heating only applications utilizing hot water, hot glycol solution or steam. There are no documented cases with coils that have non-aluminum fins (copper, steel, etc.) or with coils that have fin surface coatings (corrosion resistant or hydrophilic).
System design does not seem to be an important contributing factor. A variety of applications have demonstrated the capability to produce the white flakes such as coils using either chilled water, chilled glycol solution or volatile refrigerant; 100 percent return air, 100 percent outside air or mixed outside and return air.
Once the coil has been installed and operated for a few cooling/heating seasons its vulnerability is drastically reduced. The phenomenon has only been reported within the first one or two heating seasons and has yet to be reported during a cooling season. Theories suggest that the coils might still be producing the white flakes during the cooling season, but the condensate on the fins formed from dehumidifying the airstream prevents the powder from becoming airborne and thus from being detected.
See the attached Engineering Bulletin for the complete details for aluminum fin surface oxidation on air cooling coils.
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See the attached Engineering Bulletin for the complete details for aluminum fin surface oxidation on air-cooling coils.
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