The dehumidifier for the Grand Haven High School natatorium was installed outside the building at ground level.
The new $6.5 million, 44,000-square-foot addition to Grand Haven High School, Grand Haven, Mich., might appear like a typical natatorium, but the successful state-of-the-art HVAC design and installation by the consulting engineer and mechanical contractor are very unconventional.

The Grand Haven project is the culmination of many original HVAC design concepts developed and implemented at previous indoor swimming pool projects by an engineering team from GMB Architects - Engineers, Holland, Mich. Led by project mechanical engineer, James Harrison, GMB's innovations at Grand Haven include a unique split return air design.

Additionally, the school district realized a substantial cost savings in labor and materials because GMB specified one of the world's largest dehumidifiers, which was custom manufactured by indoor air quality equipment manufacturer, Dectron Internationale, Roswell, Ga.

The 44,000-square-foot natatorium features supply ductwork that follows the contours of the building’s barrel-shaped ceiling. The return ductwork is underground.

Lofty Goals

"One of our primary goals in the construction of the aquatic center was to have a facility that not only met the needs of our swimming and recreation programs, but also created a comfortable, healthy environment for spectators," said Rick Kent, superintendent, Grand Haven Area Public Schools. "Our aquatic center has exceeded all these goals."

Typical natatorium designs often use one large wall grille to collect return air, but GMB has found that this method may not adequately promote air movement to all areas of a large pool enclosure.

At Grand Haven, the design team used the standard wall grille for only 50 percent of the return air. Air movement is substantially increased because the remaining return air is collected with air inlets under concrete bench seating on two sides of the facility. An aluminum duct and a concrete tunnel under the pool deck serve the bench grilles.

"Because our supply air is high at the ceiling level, we used 50 percent of the return air to help draw it down to the participant and spectator level," said Harrison. "With the single return air wall grille method we've seen at other natatoriums, there's too much air stratification, which leads to indoor air discomfort. We've used this return air design on two other natatoriums. Based on the owner/occupant responses, it's really the best way to go."

The Grand Haven facility also features a therapy pool room with a 25-foot wide wall of windows that is kept free of condensation by column ducts on each side.

The Dehumidifier

GMB broke tradition on other natatorium HVAC design concepts as well. Typically, an indoor pool dehumidifier is in a mechanical room or rooftop location. At Grand Haven, however, the dehumidifier is located outside at ground level to save upwards of $30,000 in mechanical room square footage and eliminate an installation on the facility's aesthetic, barrel-shaped roof.

Since part of the return air is underground in the pool area, Rite-Way Plumbing & Heating, Grand Rapids, Mich., kept the return ductwork underground for aesthetic purposes en route to the dehumidifier. The underground return air enters the dehumidifier via a base configuration and curb plenum - a custom modification specified by GMB.

The challenge with an underground duct installation, according to Larry Heemstra, project manager, Rite-Way Plumbing & Heating, is digging the trench deep enough and then structurally supporting the walls to protect workers against dangerous cave-ins.

Typically, a project of this size requires several dehumidifiers working in tandem. However, GMB specified one of the largest dehumidifiers ever manufactured by Dectron, a Dry-O-Tron® RS-362 with airflow of 64,000 cfm and a moisture-removing capacity of 377 pounds per hour. GMB's design also provides 1/2 cfm outside air per square foot of deck and pool area, which is sufficient for the natatorium's 1,000-spectator capacity. The 32-foot-long unit saved the school district thousands of dollars in piping and ducting.

"I approached Paul McWatters [sales engineer at MacAire Inc., a Grand Rapids-based manufacturer's representative for Dectron] to see if Dectron could custom build one really large unit and they came through," said Harrison.

GMB also designed a supply air distribution system that follows the contours of the natatorium's architectural, barrel-shaped ceiling. While the ductwork was designed to add an aesthetic touch, sheet metal subcontractor, Superior Sheet Metal, Rockford, Mich., found it challenging to install. Manufactured by Eastern Sheet Metal, Cincinnati, the galvanized and epoxy-coated spiral ductwork needed dozens of elbows ranging from 15 to 22 degrees to maintain a constant 12-inch gap along the contoured ceiling.

"Installing the ceiling ductwork was very challenging and required super accurate field measurements," said Jerry Marculis, estimator/coordinator, Superior Sheet Metal.

While the Dry-O-Tron dehumidifies and heats the pool water, it also reduces the space heating load in winter with efficient heat recovery from the exhaust air and preheating of the outdoor air. Space heating is handled by the building's hot water heating system, which is comprised of a two Lochinvar Corp. (Nashville, Tenn.) boilers that supply Taco Inc. (Cranston, R.I.) secondary heat exchanger via a 1.5 horsepower Taco pump.

Besides the main pool, the facility also has a separate 2,000-square-foot therapy pool room that features a wall of windows that is 15 feet high and 25 feet wide. Keeping the windows free of condensation was another design challenge for GMB. The pool deck diffuser system would not provide ample window coverage. Instead, air was supplied from two 12-inch round column ducts on each side of the windows.

Grand Haven now has a big-time pool that attracts many local swimming programs and competitions.

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Publication date: 08/09/2004