The Weyerhaeuser King County Aquatic Center is one of the largest indoor competitive swimming facilities on the West Coast. Opened for the 1990 Goodwill Games, the facility features a main natatorium with full bleachers and an Olympic-sized dive well (pool) and a 50-meter competition pool and a 25-meter recreation pool. This 2,500-seat facility maintains one of the most active competition schedules in the country, hosting more than 50 events annually. It has been the site of Olympic Trials, top national and international competitions, and the Pacific Northwest's premiere events. At full capacity, this mega-facility has housed up to 50 employees, 1,000 swimmers and 2,500 spectators. During normal operation, the facility typically has an occupancy of 150 or less. Willdan implemented an innovative approach at King County Aquatic Center that replaced aging systems and reengineered or reconfigured building system operation to gain energy savings.


System Replacements Improve Air Quality

The 67,000-square-foot, 60-foot-tall natatorium building was conditioned by six major existing HVAC systems, two of which were nearing the end of their useful life and utilized direct fired gas heating and ineffective exhaust air collection—resulting in a significant build-up of chloramines and carbon dioxide at the pool surface.

In addition to replacing the two old HVAC units with new, larger energy-efficient units, Willdan recommended additional modifications to the existing supply ductwork distribution inside the natatorium, the addition of new ductwork, and reconfiguration of the exhaust air collection vents to the pool deck level. This re-working of the ventilation distribution was necessary to create good ventilation effectiveness that can provide improved indoor air quality during their mega events. In addition, the manner in which Willdan installed it allowed the system to operate in a very energy efficient manner.


Trailer-sized Rooftop Units Surpass ASHRAE Code Requirements

Willdan’s innovative engineering solution focused on fixing the air distribution, and then only increasing the total airflow and ventilation airflow required by the new system during times of peak activity. We replaced two aging constant-volume, outside-air heating and dehumidification systems with two new variable volume units. Two new AHUs provided additional outside air for chloramine removal and de­humid­ification during periods of heavy occupancy when needed, and reduced the airflow during times of light occupancy. In addition, the new units were specified with highly efficient plate-to-plate heat reclaim coils, and additional compressorized heat recovery on the final exhaust air. The existing atmospheric pool heating boilers and domestic hot water heater were replaced with new high-efficiency condensing boilers and heat exchangers. In the men’s and women’s locker room areas, 100 percent outside air systems were replaced with new, more efficient systems. Two  new AHUs were provided to separate the locker room spaces from adjoining meeting rooms and allow for the use of return air in the spaces allowed by code.

As part of the contract, Willdan monitors the system for a year, reporting performance and efficiency. While Willdan has successfully minimized the energy used by the new system, the main benefit of this project to the owner is the significant improvements in indoor air quality, and the benefit of maintaining tight relative humidity and temperature tolerances.


Solar Water/Condensing Boiler Heating Systems and Controls

  • $674,687 project cost
  • Washington Department of Commerce Solar Grant $500,000
  • Guaranteed Energy Savings $6,957

Air Heating Upgrades

  • $2,479,112 project cost
  • $373,500 cash incentive from Puget Sound Energy and Seattle City Light
  • $88,512 estimated annual energy cost savings
  • 745,677 kWh estimated annual savings
  • 37,384 estimated annual therm saving