Ensuring indoor therapy pools are a favorite destination

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Ralph Kittler, P.E., vice president, Seresco USA
Ralph Kittler, P.E., vice president, Seresco USA

There are no substitutes for an indoor therapy pool's benefits of relaxing buoyant freedom of movement, soothing warmth and hydrostatic pressure pain relief. However, some therapy pool environments fall short.

The environmental conditions of a inadequately designed or poorly maintained indoor therapy pool room can quickly produce an unpleasant environment due to its unique mix of humidity, temperature and airborne pool chemicals.       

Not addressing the unpleasant conditions can often lead to additional problems such as building envelope damage, pool water chemical odors in non-pool areas, patient respiratory issues associated with indoor air quality (IAQ) or decreased capabilities of the heating, ventilating, air conditioning (HVAC) dehumidifier, which typically dehumidifies, cools and heats the space.

Particularly ironic is that instead of their intended purpose of improving a patient's well-being, poorly designed or maintained therapy pools can sometimes be an unpleasant experience.

The performance of a therapy pool room relies on proper design for the building envelope and HVAC system. The architectural building design, must be suitable for a warm space with a high dew point. Consequently the building materials selection and installation techniques must accommodate all this. 

While maintenance is often blamed, even newly-constructed therapy pools may have issues because the building design did not have these special needs considered. These architectural factors work in synergy with the HVAC dehumidifier, air distribution system and pool water chemistry for a healthy environment free of mold, toxic chloramines, excessive moisture and other challenges unique to indoor pools. To ensure all HVAC design engineers have the best design guidelines available to them, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), have consolidated all their design guidelines into a an entire chapter dedicated to Indoor Pools in its upcoming ASHRAE Handbook–HVAC Applications. This will help engineers access all of the state of the art approaches to indoor poll designs.

Facility maintenance

Most large pools, such as those in high schools or community recreation centers operate with water and air temperatures of approximately 80°F and 82°F, respectively. Besides their considerably smaller size, therapy pools are unique because their water temperatures can range up to 92°F or greater and a spa vessel can range up to 100°F or more.

Space air temperature, in relation to water temperature, is critical to minimize evaporation and also maintain occupant comfort. ASHRAE recommends a two-degree differential, such as 90°F water and 92°F air temperatures to help keep operating costs down would be good, it will need to still be comfortable to the patrons. With really warm pool water it is not uncommon the have the water warmer than the air. As long as the dehumidification system was designed for this upfront, there no problem operating this way. It is just more expensive compared to running it with air say 2 degrees warmer. Patron comfort trumps operating cost savings. If the differential varies, possibly through set point adjustments by an unknowing facility manager or an HVAC technician unfamiliar with the original operating design, the evaporative rate may surpass the capacity design of the therapy pool room's HVAC system, which could lead to many of the aforementioned therapy pool room challenges.  

For example, lowering the space below its intended design temperature by as few as two degrees increases the humidity load on the dehumidifier by 35 per cent, which could surpass its design capacity sizing. Thus, the humidity could remain well above ideal comfort levels of 50 to 60-percent RH.  Besides poor comfort, uncontrolled high humidity levels can prematurely deteriorate building materials inside the therapy room, as well as its surrounding support structure.

Typically, a therapy pool room has a dedicated commercial dehumidifier that maintain space temperature and humidity levels through heating or cooling, and dehumidifying the space. Dehumidifiers control the space using an on-board cooling coil that condenses moisture out of the return air from the therapy room space as it passes through the dehumidifier. They then provide free pool water heating using what would be waste heat from the compressor,

Uncomfortable therapy pool room conditions are often a result of the system not being able to keep up because the  water/air temperatures are considerably different to what the design had been.

High technology monitoring and control

The modern mechanical dehumidifier that emerged in the 1970s has made the greatest impact for controlling indoor pool space environments. Like most mechanical devices however, it must be maintained to operate efficiently and effectively. Until recently, natatorium operators or managers never knew if the system worked up to original design specifications.

Now however, modern dehumidifiers offer web browser-based software that managers can access through their smartphones, tablets or personal computers to monitor natatoriums in real-time. Through the internet, a manager can check vital stats, such as water and air temperatures, RH and even historical operating conditions using a smartphone 24/7 from anywhere on the globe. Periodic monitoring not only guarantees comfortable operating conditions, but also offers the ability to spot and correct deficiencies the day they occur, instead of six months later during an HVAC service call.   

Dysfunctional therapy pool rooms

Two telltale signs of a dysfunctional therapy pool room is noticeable condensation on windows, walls or ceilings; and strong chemical odors in or outside the space.

Condensation could be a sign of a poor room design such as improper vapor barrier placement or inadequate insulation. Condensation can also occur when the ventilation distribution design doesn't evenly cover room surfaces with conditioned air. Windows, for example, will have condensation in cold weather unless fully covered with supply air from the duct.

Odors inside the therapy pool room could be a result of poor water chemistry, or a build-up of the toxic respiratory irritant chloramines–chlorine molecules that attach to biological water contaminants to form a toxic gas.

Odors infiltrating to adjacent rooms could point to a space pressurization problem. All pool rooms operate under a negative pressure whereas more air is exhausted than is supplied. A positive pressurization however, will push odors into connecting areas of the facility. Worse yet, a positive pressure will push pool air through the building walls, which will accelerate damage to the building's envelope and possibly its structural integrity. Pool chemical odors should be minimally noticeable, if at all, in a properly operating indoor pool room. Odors should never be detected in non-pool areas.

Any hint of a poorly operating therapy pool room should be turned over to a local expert, often a manufacturers' local representative, who can recommend contractors certified in the highly technical field of natatorium and dehumidifier repair.

Choosing a Dehumidifier

There are several considerations when selecting a dehumidifier for a retrofit or a new construction project.  Do you have space indoors, or does the unit need to go outdoors? Outdoor units free up space the mechanical room, but because the cabinet construction needs to be considerably more robust to protect against the outdoor element, they are more expensive. A good dehumidifier will have fully coated coils to protect against corrosion, the pool water heating option, energy efficient direct drive fans, and a web browser-based control and monitoring for keeping the unit operating at its original design specifications for comfort and energy-savings.

A good working dehumidifier will help ensure the therapy pool room is one of the favorite places of your patrons.

Ralph Kittler, P.E., is vice president, Seresco USA, Decatur, Ga., North America's largest manufacturer of mechanical dehumidifiers for indoor pools. Seresco offers a free one-hour video on proper indoor pool room design and operation at www.serescodehumidifiers.com. He can be reached at ralphkittler@serescodehumidifiers.com.

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