Which environments corrode
The coast and salt air, ammonia environments, the cleaning chemicals used in food plants, sulphurous flue gases and the air of animal housing. What they have in common is this: the corrosion advances not where the coil can be seen but on the unreachable surface between the fins, and by the time it is noticed the heat transfer has already fallen.
Three options
An epoxy-coated aluminium fin protects the fin surface and is usually enough for moderately aggressive environments. A fully epoxy-coated coil covers the tubes and the header as well as the fin; it is for environments where the chemical reaches every surface. A copper fin is a solution that rests on the material rather than on a coating.
All three are available as options on Planer coils. Which one is needed depends on the chemistry of the environment and on the plant's cleaning regime; choosing "the best one just in case" is unnecessary cost.
What the coating costs thermally
A coating adds a thin resistance to the path the heat takes. That loss is small but it is not zero, and it is taken into account during selection. Choosing a coated unit by reading the same table as an uncoated one means running short of capacity in the field.
What is needed to decide
The region the plant is in, the chemicals in the environment, the cleaning method, and whether the unit will stand outside or inside. With those four known, the material choice stops being a matter of debate.