Here is the setup
Busch Internaional air handler that was converted at some point in it's life from swamp cooling to chilled water (40-45 degrees). It has a makeup air burner but draws outside air for the burner or a CO flush only. It is cooling a motor room with a couple of motors (they have their own dedicated chillers), all the motor drive panels, and various other mcc panels. The supply duct that the blower hangs in is a concrete corridor that is about 8'x50'x15' that is built across the back of the room. It has various supply's across the top.
Right now the humidity and heat is up (imagine that). Supplys are blowing dense fog out about 15'. Room is cool but obviously humid. Supply corridor has a couple inches of standing water. The room is not tight it has two 20'x100' doors above the walls for cranes and multiple overhead doors. Still I cant imagine this setup not being able to shake the humidity out of the air. There are other setups around there moving 120,000+ CFM of 100% outside air stepping it down to 60 degrees with no humidity issues. Yet the custom re-engineered busch unit getting return air is blowing a fog snoop dogg and Willie Nelson would be impressed by.
This morning I cleaned the chilled water coil it was extremely filthy but not jam packed airflow restricting. Filth is compromised of kerosene based coolant, oil, some type of alcohol that mostly gels in the pan. Also had a sucker truck clean out the corridor. It was running with about 90% less fog afterwards. They were happy the fog left and the room smelled fresh and not like swamp butt. I let them know it will probably be back though.
Have a few possible solutions in mind but wanted some other opinions. Kinda thinking design issue but I would like to get the air handler up to snuff before I throw that dart. This is a reoccuring problem that happens only when humidity and heat soar. They do not remember the room being fogged just the supply corridor needing a sucker truck couple times a year and a slight visible fog between coil and blower. I will be there the rest of the week and do my best to supply additional info if desired.