Indoor waterparks and natatoriums are part of almost every new hotel and resort development today. According to the 2006 Waterpark Resorts Construction Report, the number of indoor waterparks being built is growing more than 30 percent a year.

This is all good news for the HVACR industry, in more ways than one. Not only do the new hotels need cooling and heating, so do the new indoor pool facilities, which can be quite elaborate.

Looking at the numbers, 73 new hotel waterpark additions and expansion projects either broke ground or were constructed last year. A total of 36 hotel indoor waterparks - with 6,004 rooms and nearly 1.1 million square feet of waterpark - opened in 2006, and another 37 hotel indoor waterparks were either under construction or scheduled to open this year.

Just the presence of hundreds of thousands of gallons of water splashed around with wave machines, water cannons, water slides, and patrons can create rainforest-like conditions. Combine that with airborne byproducts of such a facility’s necessary pool water sanitizing chemicals and IAQ becomes vital for patron comfort. To put it another way, such indoor extravaganzas can be a dehumidification/humidity - for lack of a better word - challenge.

Just ask Joe Schmitz, director of waterpark development and operations for the Wilderness Hotel & Resort, located in Wisconsin Dells, Wis. He is responsible for making sure all is running swimmingly at “America’s largest waterpark resort.” The Wilderness has seven waterparks, three being indoors.

“Air handling in the indoor waterpark has been one of the biggest challenges since the evolution of the whole indoor waterpark phase,” said Schmitz.

Generally speaking, there are two different ways to approach the humidity issues of an indoor waterpark. One is a dehumidification unit with a minimal amount of outside air required by code. The other system uses large air changes, 3 to 6 per hour, of 100 percent outside air. To make this latter approach economical, energy recovery equipment is utilized to recapture the heat that is exhausted from the facility. The energy recovery usually takes the form of coil run around loops, plate exchangers, or heat pipes.


With all of the activity, splashing, and spraying at an indoor waterpark, this adds to the normal evaporation. Excess moisture can ruin a facility, as well as cause health problems. In the eyes of Bert Fredericksen, the two key components are control of the humidity and removal of air- borne contaminants.

“Humidity control is necessary to maintain comfort and for protection of the building materials,” explained the vice president and director of engineering of Fredericksen Engineering. The Mequon, Wis.-based firm has participated in a number of projects with major waterpark operators and have been involved in the system selection and coordination.

“Removal of airborne contaminants is a health issue,” he said. “Chloramines are a by-product of the water treatment. If these are not removed, bathers’ lungs can be irritated. Old timers used to call this swimmer’s cough.”

There is no one perfect answer or system in achieving this humidity-free indoor environment. There is no canned HVAC solution. Each facility usually provides different humidity challenges, said Fredericksen.

“Each building and climate must be evaluated on its own,” he said. “Unfortunately, all too often the choice is driven by first cost. We would prefer to see more attention paid to the energy impact of the choice.”

Can an indoor waterpark rely strictly on an outside air supply and exhaust?

“Yes, but this is actually a form of dehumidification in that you are using relatively dry outside air to replace the humid indoor air,” answered Fredericksen. “Somewhat, unfortunately, this is a common method of dealing with indoor waterparks. Contractors are installing 100 percent outdoor air systems that use air-to-air heat exchangers to reclaim as much energy as possible from the exhaust airstream. This concept does work, but it is very energy intensive.”

The Big Splash Indoor Waterpark at the Ramada Hotel Resort in Ocean Shores, Wash., presented a different set of humidity challenges. Because the indoor creation is connected through a corridor to the hotel, it was important to maintain a negative pressure inside the park; otherwise, chlorine could have penetrated the walls and damaged the structure. Worse yet, odors could have been pulled into the hotel.

The park required 16,000 cfm, with a minimum of 3,000 cfm outdoor air and up to 100 percent outdoor air. For optimal efficiency, heat recovery was incorporated into the air-handling unit, designed and supplied by Des Champs Technologies. The air-handling components also needed a special coating to ensure their lifespan, as they had to be suited to the moist seacoast environment of the Pacific Northwest.


In the case of the 70,000-square-foot Wild Waterdome, one of the three indoor waterparks under the Wilderness Resort’s roof, outside air supply and exhaust are used to control humidity. The mechanical system was designed by Kilgust Mechanical, based in Madison, Wis., and a wholly owned subsidiary of EMCOR Group, headquartered in Norwalk, Conn.

According to Jason Beren, P.E., vice president of operations, there were some “unique challenges” because the project meant enclosing an existing outdoor wave pool.

“The occupancy of the Wilderness Resort and the Wild Waterdome varies through the week and year,” he said. “Therefore, the system needed to be able to operate at different levels to match the activity level.”

A goal of the project was to make people feel like they were outside, even in the summertime. Therefore, as long as the conditions - temperature and humidity - were about the same inside as it was outside, the guests would be comfortable. Large sliding glass walls are opened in the summer to allow the guests to move back and forth from the outdoor pool areas to the indoor Wild Waterdome. In the summer, the building is essentially open to the outdoors.

While the Foiltech Roof is great for gaining heat in the winter, a greenhouse-type condition exists in the summer. Beren said the team had to account for a large amount of solar gain this roof created.

“In the wintertime, this solar gain is beneficial in providing daytime heating. However, in the summer, this heat needs to be removed,” he said. “With no cooling, we needed to ensure that the combination of energy recovery units and a summer ventilation system could control the temperature and humidity.”

According to Beren, the summer ventilation system takes advantage of prevailing winds and the “stack effect” of hot air rising. The natural openings consist of windows, overhead doors, and sliding glass walls to introduce outside air to the facility down low. Six large propeller fans at the peek of the facility are designed to assist the natural flow.

The mechanical side of Kilgust’s design is based on a total 220,000-cfm capacity produced by four XeteX (Minneapolis, Minn.) ventilation units.


In wintertime operation, the seasonably dry outside air supply is preheated and mixed with the warm, humid pool room air to provide a comfortable relative humidity to the pool area. If return air heat recovery isn’t sufficient, the XeteX units’ direct-fired burners are designed to heat it to temperature set points.

Beren said energy-recovery units were selected over a DX dehumidification system because of the firm’s experience with other large waterparks.

“We have worked with four of the five major indoor waterpark facilities in Wisconsin Dells,” he said. “All of these projects had been with one type of high air change rates and energy recovery. We have used, and still use, DX dehumidification systems with smaller pools or ones with lower evaporation rates.”

According to Beren, the energy-recovery units have a winter effect of theoretically recovering 80 percent of the heat exhausted from the facility. The direct-fired burners are used to heat the outside air at 100 percent combustion efficiency. He said the combination of the energy recovery with the direct-fired burners brings the operational cost within reason.

“In this project we have 220,000 cfm. However, with energy recovery, the system, in effect, only has to heat 44,000 cfm,” he said.

To address the varying levels of activity, variable-frequency drives are in use with the energy-recovery units. The direct digital control (DDC) system provides for scheduling of different operating levels.

“By code in the state of Wisconsin, the system we installed must run 24/7 and at no less that 25 percent,” Beren explained. “During the night time, the system is operated at 30 percent. On light occupancy days, the system is set to run at 60 percent. On busy days in the winter, the system runs at 80 percent. The only time we go to 100 percent is during the summer or on a holiday weekend.”

Fabric duct was also used to help keep within budget, as well as provide flexibility. Kilgust worked with DuctSox to prepare a three-dimensional layout of the ductwork.


Then again, dehumidifiers and dehumidification systems are helping meet the humidity issues inside some indoor waterparks. It’s more complicated than flipping a switch, however. For one thing, operators have to know about dew point.

According to those in the know, if the dew point is above 50°, a DX dehumidification system might be the best answer to cool the air that comes from the pool and, in the process, picks up the latent (or sensible) energy to put into the refrigerant. It then uses electricity to form an energy-rich gas. According to consultants, that energy can be used different ways: to reheat the air that comes from the cold coil, heat the space; or heat the indoor pool water.

“We use DX dehumidification systems in smaller pools or natatoriums, where the activity levels and evaporation rates are lower,” noted Beren.

“We have found that if the equipment is properly manufactured with corrosion-resistant materials, the systems can function for many years.”

Another possible option is desiccant dehumidification, which uses a wheel to absorb moisture while a hot air stream turns it. In this instance, humidity is designed to be absorbed by the vapor phase.

Rather new to the humidity game is gas-phase filtration, a system that most consultants state is not dew point-specific. It uses scrubber beds of activated charcoal filters to absorb pollutants.

In the big picture, no matter how high-tech - or, low-tech - the system is, the general consensus is that an indoor waterpark still must be augmented with fresh air. Without that precious ingredient, health issues could certainly crop up.

Sidebar: Where There Is Water

Pump suppliers are certainly happy with the trend toward indoor waterparks. ITT, for one, has made it known that it is in a good position to ride the rising tide of indoor attractions.

“The outdoor waterpark construction market is still strong, but the real growth is in indoor parks,” stated Bill Linder, a product line sales manager for ITT’s residential & commercial water value center. “And it’s not just in North America. We expect to see tremendous growth of indoor water parks throughout the world in the near future.”

The company said its pumps and water-purifying equipment are installed in some the world’s biggest outdoor water complexes. The new Sun-N-Fun water park in Naples, Fla., includes $250,000 worth of ITT pumps. It said the Boardwalk at Hersheypark in Pennsylvania utilizes 30 ITT pumps to supply water for, what is being dubbed, “the largest water-play structure in the world.”

ITT said it has already sold product for resort-based waterpark projects in the Caribbean, Dubai, and mainland China. According to the manufacturer, 80 ITT brand pumps move 110,000 gallons - or 1 million pounds - of water per minute through the indoor/outdoor complex that is part waterpark and part aquarium at the Atlantis resort on Paradise Island in the Bahamas.

For more information regarding ITT, go to

Sidebar: Words of Advice

Bert Fredericksen offered some words of wisdom for HVAC contractors looking to break into the waterpark explosion.

“If you are not extremely comfortable with controlling humidity, be sure to hire an engineer that is,” suggested the vice president and director of engineering of Fredericksen Engineering, Mequon, Wis.

Jason Beren, of Kilgust Mechanical, Madison, Wis., had some helpful tips, too. For one, the vice president of operations said a contractor needs to pay close attention to the construction details.

“By that, I mean the hangers, rods, screws, and attachments that are exposed to the environment need to be resistant to the corrosive environment, too,” he said, adding that stainless steel 304 can still be attacked by the chloramines, whereas stainless steel 316 is more resistant.

“Know when your work is going to be sequenced in the schedule prior to finalizing your pricing,” he added. “Installing ductwork 60 feet in the air over the top of a lazy river can cause significant cost overruns if you assumed you would be working over flat ground.”

When using energy-recovery units, Beren said one should include some spare burner capacity to account for periodic defrosting.

“Energy-recovery units need to be periodically defrosted,” he said. “Fortunately, upsizing a direct-fired burner is a relatively low cost item.”

In his estimation, the five keys - “How to make the guests’ visits enjoyable,” is how he put it - an indoor waterpark must have are: a diligent water treatment program; high air change rates; energy recovery and variable levels of operation to keep energy costs down; ultraviolet (UV) water treatment; and pool space negative to surrounding spaces.

Publication date:08/13/2007