Taking the plunge with packaged dehumidifiers: citing packaged systems' economy, footprint, and reliability, one consulting firm now waltzes across Texas with a solid reputation and a knack for natatorium success

Engineered Systems, April, 2004 by Barry Campbell

Plans for the Carollton-Farmers Branch Independent School District's (ISD) new 12,000-sq-ft notatorium (which would feature a 120- by 75-ft indoor pool) were moving along swimmingly. Located in suburban Dallas, the district had secured funds for the natatorium via a bond election.

Initially Robert E. (Ed) Cliver, P.E., principal of Estes McClure Associates Inc. (EMA), had designed a generic field-system that combined an air handler using coils coated with an anti-corrosion enamel, a remote condensing unit, and a reheat system that would use compressor heat to warm much of the pool water to 82[degrees]F. EMA, a Tyler, TX-based mechanical, electrical, plumbing, and technology (MEPT) engineering firm with hundreds of general school HVAC systems completed throughout Texas, New Mexico, Maryland, Virginia, Oklahoma, and even Mexico, had used a similar dehumidifying strategy in past schools with great success.

THE PINCH, THEN THE PACKAGE

The district ran into problems, however, when the project ran over budget during the design phase. The overrun was due mainly to structural costs, but all trades were requested to "think outside the box" in reducing costs. The project mechanical contractor, H & G Systems (Garland, TX) and manufacturer's representative, McMillan Choate & Associates (Dallas), suggested redesigning the natatorium HVAC system with a Dry-O-Tron[TM] packaged dehumidifier manufactured by Dectron Internationale (Roswell, GA).

Armed with statistical data from other Dallas area indoor pools, Mark McMillan, principal of McMillan Choate, revealed that the natatorium's supply ductwork insulation could be eliminated even though it is a major factor in preventing condensation in the original field-built system design.

Packaged dehumidifiers are designed to maintain a 50% rh and deliver conditioned supply air above the dewpoint, therefore eliminating condensation concerns associated with metal natatorium ductwork. Specifying a packaged dehumidifier with factory-mounted controls, uninsulated duct, and other minor refinements shaved an estimated $35,000 off of the original MEP portion of the project bid and helped bring the project under budget.

"The field-built system would have done the job of dehumidifying just fine; it just wouldn't have done it very economically from tire cost perspective," McMillan said. "At the end of the day, they said, 'For the same money, we can have a simpler system that will work better.'"

Switching to a packaged dehumidifier also saved over 500 sq-ft in mechanical room space because the unit was located outside an exterior wall. The space savings over a field built system destined for indoors when rated at market rates (it $115/sq ft, amounted to an additional $60,000.

ADDITIONAL SAVINGS

The school district also saved installation costs, according to Kirk Fitzgerald, president of H & G Systems, the Carrollton-Farmers project mechanical contractor. "The simplicity of having a complicated system packaged with onboard controls actually saves cost on the installation, and will continue to save operating costs during the system life," said Fitzgerald. "The control systems applied to field-built systems are sophisticated as well, but I've observed past systems to be operated improperly by maintenance personnel who do not fully understand all aspects of the system. This will cause excessive energy inefficiency, poor control, and premature failure of components." He added that while a packaged system is generally easier to install, it is still complicated. "If someone who doesn't understand the system puts one in, it can cause some serious problems. That said, we've never had a problem with a package system that we've installed."

"Even though we've designed a lot of field-built systems in the past, we've established a company design standard now that a packaged dehumidifier will be used with an indoor pool now simply because of the finished product's quality, lower first costs, less space used, and ease of design," said Cliver, who also specified a 15-ton York International Corp. (Norman, OK) rooftop heating/cooling system for offices, the spectator area, and other areas adjacent to the natatorium portion of the building.

The rooftop unit was key to spectator comfort. "When it's 85[degrees] in the pool area, the people there watching the events can get hot, so we put cool air in over the area for what is basically constant spot cooling," he said. Using the York unit with a duct system sup plied by Spiral of Texas to cool the spectator area provided more savings, Fitzgerald added. Rather than incur additional installation costs by using a packaged unit to provide the sensible heating/cooling, it made sense to use the rooftop unit.

ADDITION LEADS TO INNOVATION

When the Dectron packaged unit was installed at the pool, H & G added two Ray-Pak boilers onto the machine to provide heating--one for the hot tub, and one for the air in the pool. The firm also took all the equipment that had been slated to be installed indoors and put it outdoors, using a glycol system. The modification was so successful that Dectron began providing (inboard boiler units with its systems.