Natatoriums are typically the most corrosive environment that facility staff will maintain. The design architect, HVAC engineer, and pool consultant need to reduce the factors that lead to corrosion, but all the designers involved and the facility personnel need to be keenly aware of the cause of natatorium corrosion. The primary drivers of corrosion in the natatorium are:
Water Chemistry
The reaction of chlorine and biological material in the pool causes the creation of a handful of organic compounds called chloramines. These chloramines are liberated from the pool water into the air and are very corrosive.
Condensation
Pool environments are typically maintained around 80-85 deg. F and between 50-60% relative humidity (RH) for occupant comfort. Any surface below the resulting dewpoint (between 60-65 deg. F) can form condensation. Combined with the chloramines in the air, this moisture corrodes almost every type of metal in its path.
Proper pool chemistry can reduce chloramines, but they will always be present at some level. Splashing, spray, and some condensation will also occur in this very wet environment. So, designers need to take measures to reduce corrosion:
Outdoor Air Ventilation
Exhausting chloramine laden air and replacing it with fresh outdoor air dilutes the concentration of corrosive compounds. However, the more you increase outdoor air, the higher your energy bills will be. Minimum ventilation rates should always be provided per code and the recommendations of ASHRAE Standard 62.1.
Air Distribution
Proper HVAC air distribution should wash the building envelope and reduce stagnant areas where condensation can occur.
Material Selection
Even stainless steel will corrode in the worst natatoriums. Plain carbon steel should never be left unprotected. Epoxy coated galvanized steel, aluminum, fiberglass, and treated 316 series stainless steel are all appropriate materials in the pool environment. Surfaces should be cleaned frequently without abrasives.
Dehumidification Capacity
Hundreds of pounds of water evaporate off the surface of the pool every hour. The actual rate depends on many factors and is always varying. The HVAC engineer must consider these factors and properly size the dehumidification capacity of the pool heating-cooling units to maintain the design RH and space dewpoint.
The potential for corrosion will always exist in a natatorium. The key to successful design and operation of these facilities is recognizing the causes and minimizing that potential. If you need assistance in evaluating your current natatorium or designing a new facility, please do not hesitate to contact Douglas C. Barnhart, PE at (717) 845-7654 or dcb@ba-inc.com.