LAS VEGAS - On the way to designing the HVAC systems for the new Wynn Las Vegas Hotel, the project’s consulting engineer, architect, and mechanical contractor were confronted with fierce rain storms, rings of fire, and cannon balls of water… and that was without leaving their offices.

It was internationally-acclaimed show innovator Franco Dragone who conceived performers braving the elements of rain and fire indoors at the 3,000-seat Le Rêve, Las Vegas’ newest aquatic theatrical extravaganza at the Wynn. However it was the HVAC design by consulting engineer, Brad Geinzer, principal mechanical engineer, jba Consulting Engineers, Las Vegas, and installation by Hansen Mechanical Contractors, Las Vegas, that would harness the weathering power of Le Rêve’s dramatic effects and provide indoor air comfort. Mitch Trageton, Marnell Architecture, Las Vegas, was the project’s architect.

“This was one of my most technical projects,” admitted Geinzer, whose firm has had a HVAC design hand in other high-tech Las Vegas theatrical venues such as the Caesars Palace Coliseum and multiple Cirque du Soleil showrooms.

The HVAC design challenge begins with the main 8,200-square-foot, 1.1-million-gallon performance pool. While the pool itself presents somewhat of an evaporative nightmare of humidity, the 32,000-square-foot theater-in-the-round also includes an 80-foot-high rainstorm, an authentic boiling effect that sends bubbles and moisture roaring out of the pool, and an ample assortment of water cannons and other aquatic effects, not to mention supplemental staging pools.

All totaled, Geinzer’s dehumidification design must control a very substantial 950 lbs./hr. of moisture produced by the show. The design is anchored by two 32,000-cfm model DB-5362 and two 11,000-cfm model DB-5120 DRY-O-TRON® dehumidifiers manufactured by Dectron Inc., Roswell, Ga., that serve the aquatic staging areas beneath the seats and the general theater dehumidification, heating, and cooling.

More conventional pool designs, such as a community or water park indoor pool, typically offer engineers steadfast statistics on water usage to help size equipment properly. Geinzer didn’t have that luxury. “We knew the concept of the effects they were going to use during our HVAC design phase, but we had no idea how long or how much of the effect would be part of the show,” Geinzer recalled. “Basically they want to leave open the opportunity for creativity, so they designed the theatrical performance as they went along and adjustments in the show continue even today.”

In most natatorium designs, space and water temperatures typically have a two degree differential, such as 84ºF and 82ºF respectively, to minimize evaporation. The Le Rêve pool has an 86ºF water temperature; however, the air supplied above the pool is 105ºF to keep the wet performers warmer. The air is supplied from ductwork and diffusers in a 10-inch-wide pony wall that also serves as a low-rise buffer between spectators and performers. Three 3,200-cfm York, Norman, Okla., air handlers supply the pool surface air heating. “The pony wall serves as an unobtrusive air delivery system for the performers and it also helps prevent this warmer performance area air from entering the seating area,” said Geinzer.

This huge vapor pressure difference required challenging evaporation calculations by jba and was assisted by Matt Miceli, sales engineer at manufacturer’s representative, Engineered Equipment & Systems Co., Las Vegas.

Meanwhile, the audience is bathed in cooler air supplied by the foundation of the seating area, which acts as a plenum. Air is distributed from specially-designed theater seat diffusers, by H. Krantz TKTGmbh, Aachen, Germany. Although it’s used in a variety of applications, the H. Krantz system is ideal for theaters and concert halls because it’s designed to disperse air with such low velocities that the air volume noise is inaudible to the audience.

The seating area has three separate plenums with eight control zones each with temperature controlled by sensors interfaced with the hotel facility’s Invensys Controls America, Carol Stream, Ill., direct digital control (DDC) building automation system.

Outdoor air varies from 30 to 50 percent, depending on the required special effects, occupied rates, and time of day. The design of jba, which also provided life/safety, mechanical, electrical, and low voltage engineering for the entire hotel, took full advantage of Las Vegas’ inherently dry climate to lessen the dehumidification loads of the theater, according to Geinzer.

The DDC presets - programmed by jba and Invensys representative, Yamas Control Systems Southwest Inc., Las Vegas - are extremely valuable during the show’s diverse facets that combine so many elements requiring different temperature, airflow, and relative humidity set-points. For example, one part of the show requires momentary backstage positive pressurization to push a fog effect out to the main performance area. Making calibrations such as this easier is the fact that all the air handlers, dehumidifiers, and exhaust fans have Toshiba America, New York, variable frequency drives controlled by the DDC system. “Working around all these possible show conditions without disrupting audience comfort made the project very challenging,” said Geinzer.

One thing jba has learned from other HVAC designs at other Las Vegas aquatic theater shows is that many stage hands operate above the performance action with props and lighting and must be provided with separate temperature and humidity control for their respective indoor air comfort.

Aside from indoor air quality, jba’s system is also very energy efficient. The DRY-O-TRON’s employ a heat recovery process that is rejected to the theater’s integral water source heat pump loop that in turn is used to efficiently heat the pool water. Plate heat exchangers by Alfa Laval, Richmond, Va., provide primary pool water heating with backup heating from the facility’s central plant only when required. Not having to cool the water-cooled equipment and instead rejecting heat to the loop also saves energy.

The ceiling of the theater also employs four exhaust fans by Greenheck, Schofield, Wis. Two fans provide conventional exhaust functions and keep the theater at a negative pressure to eliminate air infiltration into the general hotel. Two other exhaust fans activate for smoke management purposes to comply with high rise building requirements in addition to theater requirements due to the adjoining high rise guestroom tower.

Aside from humidity, a ring of fire with huge center flames also has an unpredictable effect on airflow throughout the space. Most importantly was acute attention to exhausting products of combustion during the flame effect. According to National Fire Protection Association Code 160 (Flame Effect Before An Audience), airflows, high/low gas pressure, pilot light operation, and other critical factors are combined by a monitoring system and operator before ignition at each show.

Additionally, dozens of life-safety sensors for smoke, heat, and flame detection are mounted throughout the seating/performance area and interfaced with the DDC system.

The Le Rêve is certainly an impressive collaborative effort between architects, consulting engineers, contractors, theatrical designers, and other disciplines to create a unique aquatic theater event.

Publication date: 02/26/2007