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Keeping Mildew at Bay

Michael Valenti

The senior citizens residing at the CTA River Apartments in Tampa, Fla., are breathing easier, thanks to an innovative retrofit of their 16-story building's air-conditioning system. The apartment building is owned by the Hillsborough Classroom Teachers Association of Tampa.

Customized ductwork carries 13,000 cubic feet of cool, dried air through the CTA River Apartments in Tampa, Fla.

The original air-conditioning system at the CTA River Apartments was plagued by an inherent pressure problem caused primarily by bathroom exhaust fans that drew in Florida's muggy summertime air through windows and doors to offset the structure's negative pressure. This influx of moist, tropical air into the hallways fed continuous and plentiful condensation on the air-conditioning system's fan coil cooling units. The result was persistent mildew and poor indoor air quality.

An early attempt to correct the problem involved installing chilled water fan coil units to spot-cool the hallways, lobby, and other common areas to help the building's 200-ton chiller made by Carrier Corp. of Syracuse, N.Y. Unfortunately, this strategy actually spurred mildew growth and made the common areas uncomfortably cool.

Building management approached a Tampa neighbor, the consulting engineering firm of Carastro & Associates, and mechanical contractor Southeast Mechanical Contractors of Tampa Inc. to design environmental, mechanical, and electrical upgrades that ultimately cost $2.3 million and took 14 months.

At the heart of the air-conditioning retrofit portion of the work is an RK-150 Dry-O-Tron dehumidifier, manufactured by Dectron Internationale, based in Rosewell, Ga. The Dry-O-Tron, mounted on the roof, removes up to 500 pounds of moisture per hour from outdoor air, which it conditions to meet the indoor air temperature requirements of the building and then sends through ductwork to cool the interior. The Dry-O-Tron removes moisture using its HyPoxy-coated aluminum-finned evaporator coil.

Typically, the Dry-O-Trons are brought to rooftops by helicopter, but local copter companies refused to lift the dehumidifier to the top of the 160-foot-tall CTA River Apartments because the building was occupied. Lewis Balsizer, the marketing and sales manager at Southeast Mechanical, rented a 200-foot construction crane to lift the dehumidifier. The work with the crane, including setting it up and tearing it down, took three days.

By feeding 13,000 cubic feet per minute of dry, conditioned air into the CTA River Apartments through ductwork, the Dry-O-Tron eliminates moisture and thus reduces mildew formation. This influx of cool, dry air also satisfies current American Society of Heating, Refrigerating, and Air Conditioning Engineers' standards, makes the common areas comfortable, and imparts a positive pressure throughout the building. The reduction on the air conditioning load offsets added energy costs that the Dry-O-Tron incurs.

Carastro & Associates also designed a reheat coil option in conjunction with the Dry-O-Tron. The company specified a model W1514 natural gas-fired hot water boiler from Raypak of Westlake Village, Calif., to heat the outside air as it enters the building during cool periods.

Ernie MacFerran, vice president of Carastro & Associates, designed an air delivery system to supply all floors with an equal amount of cool air, regardless of their distance from the Dry-O-Tron. The duct trunk line starts at 30 x 40 inches at the building's roof and is progressively reduced in size per floor, down to 12 x 12 inches on the second floor. Each floor is equipped with dampers adjusted exponentially to even out the varying duct velocity and guarantee equitable air distribution.

In addition to installing, piping, and ducting the dehumidifier, Southeast Mechanical and its subcontractors replaced approximately 1,000 apartment fan coils with new coils made by McQuay International in Minneapolis. They also removed 16 hallway fan coils, replaced the hot and cold domestic water system, installed a sprinkler system fire alarm network, and made electrical improvements and other upgrades.

Work was done on two levels at once, but only on half of each floor at a time. Carastro & Associates assigned a staff member to monitor daily progress and solve any field problems immediately. While the tenants were transferred to hotels, Southeast Mechanical erected temporary walls within each tenant space to separate work areas from apartment possessions. These security barricades were inspected daily.

It seemed that no request was too small for the renovators. James Gremer, the CTA River Apartments' assistant building manager, asked if the new dehumidifier could be painted peach to match the building. "Few manufacturers could custom match an unusual color like our peach exterior, and when I arrived, I couldn't believe how closely it matched," recalled Gremer.