Contractors who have worked on indoor pools know the biggest challenge they pose lies in maintaining IAQ.

According to the Centers for Disease Control and Prevention (CDC), chloramines are most concentrated just above the surface of the water. The gas they release is heavier than air, which means that the bulk of the chloramines settle right where they can cause the most problems for swimmers.

Therefore, it’s no surprise that a misunderstanding of the impact water and air temperature have on pool evaporation rates is one of the most common issues with indoor pools as far as dehumidification goes.

“Owners and contractors think they can change these values just as they would do in comfort cooling applications,” said Paul Stewart, director of sales, market and service, Desert Aire. “The problem is that deviating from the design conditions can be a source of condensation and mold issues. A great example is when someone decides to raise the water temperature from the design temperature. Raising the water temperature increases the evaporation rate, and that adds more dehumidification load.”

According to Ralph Kitler, former vice president of sales and co-founder of Seresco Technologies Inc., a Dehumidified Air Solutions (DAS) brand, and current vice president of sales for DAS, the only way to deal with air quality issues is if the HVAC technician focuses on air distribution.

“With every job I’ve been to that has air quality problems, the air distribution was lacking to some degree,” he said. “For the HVAC designer to have the best outcome, they need to focus very heavily on how they distribute the air. That good air needs to get to where the people are, for one thing. If you don’t do that, it doesn’t matter how much outdoor air you introduce. If that good air isn’t getting to where it is needed, you can be on 100 percent outdoor air mode, and that air isn’t getting to the people. You have to absolutely design the air distribution correctly.”

One of the most important items to address when making sure an indoor pool is properly ventilated is that the contractor understands the formula in the ASHRAE 62.1 ventilation standard.

“This provides a very prescriptive method for establishing the correct volume of ventilation air,” said Stewart.

Next, the system must have an exhaust fan that can exhaust and maintain a negative pressure in the space to prevent chloramines from migrating to other areas of the facility.

Once those two items are taken care of, it’s important to address the building envelope issues that indoor pools experience due to the construction technique of the pool or building materials. But what are pool experts recommending HVAC contractors do to remedy these issues?

“The remedy for building envelope issues must start with the contractor to understand the powerful impact of moisture,” said Stewart. “Every surface must be resistant to the high dew point environment of an indoor pool and to recognize that chemical off-gassing will occur. In addition, moisture will drive through and around the building’s components, so materials must have a moisture barrier, and all cracks must be filled. Moisture’s vapor pressure impact is like salmon swimming upstream — humidity moves from high to low. Moisture in the air condenses when it reaches dew point temperature, so preventing moisture migration through walls and spaces is the best prevention.”


As far as ventilation issues go, contractors are ensuring supply air ducts and vents fully cover the exterior windows with conditioned air to avoid condensation.

“The design engineer needs to be aware of this specific requirement, and it happens frequently where the exterior windows aren’t adequately covered because the engineer is unaware of it,” said Kitler. “It’s pool design 101, but it does get overlooked frequently.”

Stewart said a good rule of thumb is that duct diffusers provide 3 to 5 cfm of supply air per square foot of windows.

“If the building design incorporates a significant number or size of windows, the dehumidification system’s supply air capacity may need to be increased,” he said. “This will provide the means to move more conditioned air and avoid condensation.”

Furthermore, the importance of proper ventilation and ventilation equipment was illustrated in a 2017 case study titled “Engineer’s HVAC Design Saves Recreation Center Energy and Operational Costs.” In it, the Grapevine, Texas-based Recreation Education and Community (REC) Center utilized an HVAC design from the engineering firm The Ballard Group, located in Lakewood, Colorado, which will save the center an estimated $918,000 in operational and energy costs over the heating, cooling, and dehumidification units’ life cycles. 

This is due to the design options and high-efficiency equipment choices, such as an energy-recovery indoor pool dehumidifier, condensing boilers, high-efficiency chillers, and other energy-efficient equipment selected, according to Bert Baiotto, principal, who led the design team for The Ballard Group.

“In a water park type of atmosphere, it’s critical to assure there’s enough tonnage (refrigeration) to keep the relative humidity in check,” said Baiotto. “Because of the higher design water temperatures, and the higher evaporative effect of the water features, the natatorium required approximately 125 percent more dehumidification capacity than a typical community indoor pool of similar size.”

Overall, while the natatorium IAQ has improved, Seresco’s manufacturer’s representative, Texas Air Systems in Irving, Texas, is working with Chad Hester, the Building Owners and Managers Institute System Maintenance Administrator (BOMI-SMA) and facility manager for the city of Grapevine, to do more. To garner even better IAQ, the two are reviewing the space periodically for possible tweaks. Together, they plan to increase the natatorium exhaust fan control set point to increase the critically important negative.

Hester said variances in atmospheric pressure, outdoor wind direction/velocity, adjacent interior positive pressure spaces, and simultaneous door openings sometimes skew the tightly kempt tolerance.

Finally, according to Stewart, the air handling component of achieving dehumidification, heating, and cooling must also include ventilation.

“The common indoor air quality refrain of ‘dilution is the solution’ applies to poolrooms,” he said. “With more actively used pools, such as competitive swimming pools, the design must take the extra step of adding a low exhaust system. This system captures the chloramines at the pool deck level because they are heavier than air, and then exhausts them without routing them back to the dehumidifier. This is the same concept used in grease hoods in a kitchen application. You put the hood above the stove, not in the food prep area. If planned for in advance, the low exhaust system can include energy recovery technology and can be integrated with the full HVAC design.”  

Publication date: 4/23/2018