concern for frozen food warehouses because it increases the costs for annual maintenance and coverage for liability insurance. When humid air mixes with a freezer’s air, commercial facilities normally rely on heated, high-speed freezer entrance doors to control ice and snow accumulation. In dry climates, a freezer entrance door adequately maintains desired temperature conditions, conserving energy, but in Florida, the dewpoint and humidity are extremely high, causing entrance doors to become more prone to ice build-up.
A combination of desiccant equipment and fabric duct air distribution was the solution for the ice build-up problem confronting the 320,000-sq-ft refrigerated warehouse in Bradenton.
Bentzel Mechanical of St. Petersburg installed a Munters desiccant dehumidifier, Model F-30 FreezAire™, with 400 lb/hr of moisture removing capacity. Meanwhile, engineer Gary Evans of Systems Components Corp., in Ocala, designed the air distribution system with fabric
duct made by FabricAir®.
Using a desiccant system and industrial-grade fabric duct to distribute dehumidified air is considered a unique solution in the industry, according to the manufacturers. Utilizing these type of systems together to eliminate ice buildup providing an 80% reduction in semi-daily defrost cycles for each of the freezer/cooler’s 21 evaporator coils and rooftop condensing coils, they said. The manufacturers added that the technology has helped reduce the defrost cycles on the plant’s ammonia refrigeration to only 1/wk.
The payback does not include estimates of additional $50,000 annual savings for ice removal on the 40-by-360-ft trucking dock that was previously performed by in-house maintenance people, said Evans. Ice had regularly accumulated on the floor and ceilings as far as 20 ft from each of the four 14-by-8-ft automatic entry freezer door thresholds, according to Evans.
"With the new desiccant and fabric ductwork system, we reduced relative humidity from
worst case scenarios of 90%, to a constant everyday 40% relative humidity," added Evans.
Bentzel Mechanical installed the 10,000-cfm desiccant system and subcontracted the fabrication of the sheet metal supply and return. The supply ducts connect the rooftop desiccant unit to the 140-ft-long run of 42-in dia fabric duct that runs just above the four freezer doors, according to Bentzel.
The project also included 180 ft of 40-in.-by-24-in. metal return duct with 12 grilles that are spread evenly along the 23 truck door openings, added Bentzel.
The manufacturers said that typical fabric duct distributes air through fabric permeability and/or linear diffusers, and in the Bradenton facility, the permeability is designed to control static pressure. Above each freezer door, an 8-ft section of fabric duct has 120 plastic, narrow-throw air nozzles that bathe the floor and door hardware with dry air, the manufacturers noted. The maintenance department also plans to clean the duct routinely and the process can be done in an estimated four hours, concluded the manufacturers.
Publication date: 10/15/2001