DALLAS — Are field-built systems better than packaged dehumidification units when it comes to dehumidifying a large indoor pool or natatorium?

That was the decision mechanical engineer, Robert E. (Ed) Cliver, P.E., principal, Estes McClure Associates Inc. (EMA) had to make recently while designing the 21,000-square-foot natatorium at Carrollton-Farmers Branch ISD with a 120- by 75-foot indoor pool in the Dallas suburb of Carrollton, Texas.

Cliver initially designed a generic field-system design 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, Texas-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 Monterrey, Mexico, had used a similar strategy in other schools with success.

However, when the Carrollton-Farmers Branch project ran over budget during the design phase mainly due to structural costs, all trades were requested to “think outside the box.” Project mechanical contractor, H & G Systems, Garland, Texas, and manufacturer’s representative, McMillan Choate & Associates, Dallas, suggested redesigning the natatorium HVAC system with a Dry-O-Tron™ packaged dehumidifier manufactured by Dectron Internationale, Roswell, Ga.

Armed with statistical data from other Dallas-area indoor pools, Mark McMillan, principal, McMillan Choate, revealed that the natatorium’s supply ductwork insulation could be eliminated even though it’s a major factor in preventing condensation in the original field-built system design. Packaged dehumidifiers are designed to maintain a 50 percent relative humidity and deliver conditioned supply air above the dew point, therefore eliminating condensation concerns associated with metal natatorium ductwork. Specifying a packaged dehumidifier with factory-mounted controls, uninsulated duct, along with other minor refinements shaved an estimated $35,000 off of the original mechanical, electrical, plumbing (MEP) portion of the project bid and helped bring the project under budget.

Switching to a packaged dehumidifier also saved over 500 square feet of 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 of $115 per square foot, amounted to an additional $60,000.

The school district also saved on installation costs, according to Kirk Fitzgerald, president of H & G Systems. “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.”

According to Dectron, a packaged unit is simpler to operate by the owner. The field-built system would have been monitored and controlled by the school district’s building automation system. However, the RS-282 Dry-O-Tron that Cliver specified is only monitored by the system, and is controlled by its own factory-programmed microprocessor-based controller. “The Dectron system is much more foolproof to install and operate because all components are interfaced and pre-tested at the factory,” added Cliver. “All the contractor has to do is install it and wire it to the building automation system for monitoring temperature and humidity.”

“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 specified a York International Corp., Norman, Okla., rooftop heating/cooling system for offices and other areas adjacent to the natatorium portion of the building.

The success of the Carrolton-Farmers Branch ISD project prompted EMA to specify a packaged dehumidifier on its next major natatorium project, the 40,000-square-foot Carroll ISD Aquatic Center, Southlake, Texas. However, EMA took equipment packaging one step further by adding Dectron’s on-board 2,200-mbh and 1,750-mbh boilers to the custom-made RS-462 and RS-282 Dry-O-Tron units that serve the 180- by 75-foot pool and 30- by 40-foot warm-up pool, respectively. Installed by Decker Mechanical, Cedar Hill, Texas, the dehumidifier still recovers compressor heat to heat the pool water and space reheat for winter operation. However, the interfaced onboard boiler serves as a backup pool water heater and space heater while eliminating the need for a conventional swimming pool heater.

According to Cliver, this onboard boiler strategy offers three distinct advantages:

1. It frees up precious mechanical room space, especially in this case since the packaged dehumidifier is a rooftop unit;

2. It adds a safety dimension by keeping the boiler’s natural gas combustion process away from pool chemicals; and

3. It uses energy more efficiently.

“We eliminated over 1,000 square feet of mechanical room space at a significant cost savings, by putting these units and the integral boiler on the roof,” added Cliver.

Since the large units had to be custom manufactured to achieve their combined moisture removing capacity of 750 pounds per hour of moisture, Cliver also specified other customizations such as purge fans for quick exhausting during water super-chlorination periods.

The project’s success is also attributed to EMA’s air distribution design, which consists of a perimeter 48-inch-round spiral duct system. The 20-foot-high ductwork washes the walls with dehumidified air and is hidden aesthetically in the open architecture ceiling and trusses.

Although the entire building, including the Trane (Tyler, Texas) Voyager Series rooftops used for areas other than the natatorium, is controlled by a TAC Americas, Carrollton, Texas, building automation system, Cliver set the Dry-O-Tron to control itself with its Dotics 9™ onboard microprocessor controller. The TAC system only monitors the natatorium setpoints.

EMA is now sold on packaged dehumidifiers. “A natatorium is not like a commercial building where you primarily design an air comfort temperature of 72 degrees F with air conditioning,” Cliver explained. “Instead, a natatorium is designed for 84 degrees F air, 82 degrees F pool water, and 50 to 60 percent relative humidity. There are a lot of calculations to be made that culminate with a figure that determines how many pounds of water can be removed per hour.”

Throughout its 29-year history EMA has done hundreds of school HVAC, electrical, and plumbing projects and has worked for more than half of the 1,040 school districts in Texas and 47 colleges/universities. But being selected for school HVAC design work didn’t always guarantee the natatorium portion of the project. Now, according to EMA, the firm is sought after for its winning natatorium and sports facility MEPT designs regardless of whether it’s designing the school’s general HVAC.

With the success of the Carrollton-Famers Branch ISD and Carroll ISD Aquatic Center, EMA was also selected for the recently completed 10,000-square-foot Duncanville ISD natatorium, Duncanville, Texas. Still under construction is the 38,000-square-foot natatorium for Frisco ISD, Frisco, Texas. Currently in the planning stage, the McKinney ISD, McKinney, Texas, natatorium is being designed by EMA.

“The MEPT design we formulated the last few years has made us one of the leading natatorium designers in the state and created a niche that we’re very capable and comfortable doing,” said Cliver.

Publication date: 08/25/2003