High relative humidity (RH) was causing a recurring problem in a large food-processing facility. The high-speed package-filling machines were jamming because a powdered food product was absorbing too much moisture from the ambient air. The enclosed production area was approximately 60,000 sq ft and served by five large central-station water-cooled air-handling units (AHUs). A room condition of 70°F and 40-percent RH was desired. I was contacted to troubleshoot the problem.
An investigation revealed sources of considerable moisture. After water-drain lines from the collection pans of two of the five central-station AHUs were declogged, an AHU supply fan causing water carryover from a cooling coil was slowed, and conveyor openings were closed, RH was reduced significantly.
However, the RH issue continued to cause problems. Further troubleshooting failed to disclose the source of the extra moisture. One night, I decided to stay in the plant during the evening shift to see what activity took place. To my surprise, at about 9 p.m., I observed a Zamboni-like machine cleaning the production-room floor. The machine applied hot water to the floor and attempted to recover it with a squeegee-like mop. The floor was made of relatively porous concrete. A followup investigation with the machine's operator revealed that the water tank on the machine had to be refilled relatively often. A calculation indicated that a considerable amount of water was being absorbed by the concrete. Solution: The owner applied an epoxy coating to the concrete floor, and the RH problem was resolved.
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