The Bellagio Hotel in Las Vegas presented a unique problem to hvac engineers: keep humidity levels constant before, during, and after the performances of an aquatic circus in the building.

The Montreal-based circus production firm, Cirque du Soleil, presents what's perhaps the "Greatest (Aquatic) Show On Earth" at the Mirage Resorts' Bellagio Hotel in Las Vegas.

Cirque du Soleil, which normally produces nonaquatic acrobatic circuses internationally, combines death-defying high divers and expert swimmers with skilled acrobatic performers at the world's largest $70 million permanent aquatic theater.

Spectators don't notice it, but equally as skillful as the performances is the hvac design by Dupras Ledoux Assoc. (Montreal) and the piping/sheet metal installation work by Hansen Mechanical (Las Vegas), a subsidiary of EMCOR Group Inc. (Norwalk, CT).

Besides the 68,000-sq-ft showroom that includes a 10,000-sq-ft round pool, and 1,350 spectator seats, the hotel/casino itself offers 3,000 luxury rooms, 270 suites, 45,000- and 25,000-sq-ft ballroom/convention spaces, and several restaurants. The 35-story facility is one of the largest hotels in the world, towering above other hotel/casinos on Las Vegas' famed gambling strip. Located on the former legendary Dunes Hotel and Golf Course, the Bellagio sits on a 122-acre site that includes a 12-acre lake that's choreographed with its own ballet of water, music, and lights.

Humidity A Constant Problem

It's inside the aquatic showcase, however, where Dupras Ledoux Assoc. met and solved many relative humidity (rh) challenges in what's one of the largest aquatic showcases in the world. The engineering firm, which is internationally known for its hvac work on the Olympic Village for the 1976 Montreal Olympics and other projects, designed an innovative hvac system that is unlike anything else in North America. The system not only keeps air and water temperatures at a constant 82°F and 84° respectively, but it also controls humidity through the use of four Dry-O-Tron(r) DS-242 dehumidifiers by Dectron Inc. (Roswell, GA).

Properly sizing the hvac was critical because of the humidity variances presented not only by the 10,000 sq ft of pool water surface, but also from many water jets that shoot water streams up to 60 ft high, plus a giant mist curtain used to project laser light shows. Especially critical is keeping a huge 112- by 65-ft decorative glass dome that towers above the 82-ft-high room free of condensation. The Dry-O-Tron units are sized to remove up to 1,050 lbs of moisture every hour.

Another Dry-O-Tron dehumidifier, a DS-60, is used to dehumidify the circus performers' 8- by 25-ft-long practice/warm-up pool in a separate backstage room. Because spectator comfort was a major design consideration, the Dry-O-Tron units were sized to maintain a comfortable 50% rh. Besides heating the pool water, the units can further control space conditions by air conditioning and/or heating the space.

An interesting side benefit of using the dehumidifiers to control humidity was the fact that the condensation that drains from its HyPoxy(r)-coated, aluminum-finned evaporator (dehumidifier) coil can be reclaimed and returned to the pool. "The amount of condensation reclaimed represents one entire pool fill per year," said Mark Palitza, Dectron's regional sales manager who worked on the project. "By choosing this product, the engineer and the Mirage demonstrated a conscientious concern for water conservation, which has a large political, sociological, and environmental impact in this desert region of the United States."

Other Problem Areas

Proper air distribution design was critical as well in keeping the space free of drafts or ventilation noise. Dupras Lecoux's project engineers, Andre Dupras and Luc Fontin headed an engineering team that sized and specified a high-tech air distribution system. The system distributes air to three critical areas: over the pool and stage areas using 300 swivel nozzle jet outlets; at the bottom of the perimeter walls using 159 flush-mount wall supplies (4- by 24-in. diffusers); and from under the seating area using 1,350 displacement seating outlets (6-in. round diffusers).

Besides humidity control, suppressing noise from the hvac and air distribution systems was as critical, to ensure that audiences hear the performer's dialogue during performances. Therefore, the air distribution system choice was manufactured by H. Krantz TKTGmbh (Aachen, Germany), and distributed by Euro-Tech Products Inc. (Denver, NC). 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 ventilation system design surpasses the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommendations for room sound values.

Everyone Is Comfortable

While fairly common in Europe, using the cavity under a theater's seating risers as one large plenum to supply 1,350 step-displacement seating outlets has never been attempted on such a large scale in a North American facility. "This system is unique in the fashion that it uses the heat plume that leaves the body to pull the air (from the seating floor's 1,350 diffusers) and surround the body with cooler, dehumidified air without creating a draft," said Richard Craig, president of Euro-Tech Products. Craig and Claude Agouri, P.E., president of manufacturer representative firm, AirTechni Inc. (Montreal), provided air distribution consultation on the project.

Spectators probably won't notice the perfect humidity in the aquatic environment, but that's good, because they can put all their concentration on the circus acts diving and splashing in front of them as they watch the grandest aquatic circus in the world. ES