Boilermakers Pool to Reduce Moisture, Produce Heat
With the opening of its $17.1 million natatorium late last year, Purdue University's swimming program went from practicing in an outdated facility to having the most state-of-the-art aquatic center in the Big Ten Conference. The previous facility—a 1940s era pool in the basement of an athletic field house—was hot, muggy and unattractive.
With the opening of its $17.1 million natatorium late last year, Purdue University’s swimming program went from practicing in an outdated facility to having the most state-of-the-art aquatic center in the Big Ten Conference.
The previous facility—a 1940s era pool in the basement of an athletic field house—was hot, muggy and unattractive. In stark contrast, the new facility, designed by Scholer Corp., a Lafayette, Ind.-based A/E firm, has been touted as a “masterpiece of design” with high-tech humidification.
The 79,000-sq.-ft. natatorium is used for athletic competition, recreation and educational purposes. It features a 50-meter pool, a diving pool, 12-person spa, locker rooms and permanent seating for 600 spectators, with additional temporary seating space for 600. “I think this pool brings Purdue’s aquatic facility up to the premier [Big Ten] facilities, such as Indiana University and the University of Minnesota,” says Steve Ford, Scholer’s vice president and the project architect.
HVAC is the key
At the heart of this facility, the HVAC system includes five heat-recovery dehumidifiers, custom manufactured to include options that went beyond the typical commercial dehumidification operation. Each unit removes 215 lbs. of moisture per hour to maintain 50% relative humidity, while simultaneously heating the pool water to 82°F through a patented heat-recovery process, according to Tom Yee, vice president and mechanical engineer at Scholer. Yee also specified factory-installed steam coils that use steam generated at the university’s central plant to supplement the natatorium’s 84°F space heating.
Some of the customized dehumidification system features include: 100% outside air purging for use during routine super-chlorination periods; an economizer for free cooling; and air-cooled condensers for air conditioning. HVAC controls are also compatible with the campus energy-management system.
To ensure indoor air quality, higher efficiency 60% bag filters were installed. A side effect of the filters was that they create more resistance, meaning it was necessary to upgrade fan motor horsepower.
Another unusual variable was that equipment sizing was difficult because of the pool’s varying moisture, cooling and heating loads. Yee arrived at the total moisture-removing capacity of 1,075 lbs. per hour and air movement of 140,000 cfm by accounting for the natatorium’s worst-case scenario: 1,400 spectators watching combined diving and swimming events, with spa activities also occurring. To deal with these variable conditions, an automatic control system was installed to modulate valves and dampers to maintain water temperature, space temperature and space humidity set points.
Distributing the air
As far as the air distribution design itself, both under-deck and overhead ductwork was employed, with the latter hanging just below the facility’s half-barrel-shaped roof. Under-deck fiberglass reinforced plastic ductwork bathes the perimeter walls and windows with warm, dry air from the dehumidifier to eliminate condensation. Exposed overhead, custom-fabricated 65-in. x 40-in. flat oval aluminum duct is mounted approximately 40 ft. high—65 ft. high in the diving area—to supply general heating and cooling. Beside spectator comfort, conditioned air prevents stagnation and stratification.
Several other factors also affected the air distribution scheme. Chilling effects, for example, were a concern due to supply air velocities. As a result, the system was designed to minimize velocities at the pool deck level. Additionally, to prevent an increased rate of water evaporation, the air stream was directed away from the pool surface. Furthermore, despite the fact that the dehumidification system is designed for total-heat recovery, some air had to be exhausted to deal with odor and moisture containment. Therefore, exhaust fans were installed to create the slight negative pressure needed to prevent odors and moisture from penetrating the building’s non-pool areas.
A final HVAC challenge was chloramine collection. Scholer devised a dual return-air system consisting of under-deck duct that returns 25% of the air at the pool deck where chloramines concentration is the greatest.
Other notable HVAC aspects include the system’s three shell-and-tube heat exchangers, ranging from 1.3 to 1.8 million BTUs, which back up pool heating in the event of system shutdown. Separate air handlers cool auxiliary areas.
The air distribution design also surpasses ASHRAE standards, introducing some 7,000 cfm minimum of outside air per unit.
To the eyes of Purdue students and faculty, the new Aquatic Center is unquestionably more aesthetically appealing, but more importantly, its behind-the-scenes operations support important project goals: good IAQ and energy conservation.