In a marine or coastal environment, this may be an acceptable condition. Bare copper is fairly resistant to the corrosive effects of salt air. This is why, for many years, copper fin/copper tube (Cu/Cu) coils have been a popular solution for corrosion in marine applications. The all-copper coil will hold up reasonably well against salt air exposure, without the galvanic corrosion inherent with dissimilar metals.
However, what works well in one environment does not necessarily work well in another. Ask anyone who has ever installed a Cu/Cu coil in a sulfur or methane environment. Cu/Cu coils are not a good solution for locations where the unit may be exposed to various aggressive acids and other chemicals. Several specific applications that come to mind include waste water treatment facilities, pulp and paper mills, refineries, chemical plants, meat and dairy processing facilities, and hog and mushroom farms.