Design Right to Ensure Spa Air Quality
By Harry Topikian
Spa area patron complaints can run the gamut from chemical odors, uncomfortable rainforest-like conditions, visible mold and mildew to building deteriorations and foamy, unsanitary spa water. Most of these problems typically stem from improper building and ventilation design or poor installation and maintenance.
There are no statistics to draw from, but based on calls to mechanical equipment manufacturers concerning spa room problems, it's estimated that at least half of all spa rooms never operated correctly right from the ribbon cutting, or have degraded into inoperable conditions due to poor maintenance. The end result is that many spa management companies are exposing their customers to uncomfortable or unhealthy conditions that eventually will affect patronization.
A common problem in spa room building construction is the absence, poor positioning or breach of a vapor retarder, which is a plastic sheet, foil-backed or extruded plastic sheet, or vapor retardant paint/coating that envelops the entire room. The architect or engineer might specify a seamless vapor retarder, but they are at the mercy of the contractor whether it's installed properly without any leaking. A breach, such as an unsealed seam, can lead to building deterioration from condensation infiltration or worse yet, mold and mildew inside walls.
Another common design problem is the improper positioning of the return air grille within 20 feet of the spa. Since the 100°F to 105°F heat of spas, in comparison to 80°F pools for example, tend to leach more human body oils and other organic solids, it doesn't take long for this residue to coat the grille, the ductwork interior and the HVAC unit parts when the return grille is positioned too closely. A return air design with slightly more cubic feet of measurement (cfm) airflow than the supply air is important for keeping the room under negative pressure. This prevents spa and chemical odors from infiltrating the non-aquatic areas of the facility. Since some of the return air must be exhausted in order to bring in a code-compliant percentage of outdoor air, the best design solution is to put a dedicated grille directly over or near the spa to exhaust the contaminants directly outdoors. Then the mandatory return air grille for the HVAC equipment can be positioned elsewhere in the room.
As for maintenance, spa water should be tested three times daily in addition to draining and refilling after every 40 users. The combination of high heat, excessive evaporation rates due to jet agitation, high counts of human body organic compounds and other factors exclusive to spas makes water chemistry 10 times more critical than a swimming pool. A spa with excellent water balance in the morning can quickly turn into a cesspool by 1 p.m.
Air distribution into the space is also critical, especially for exterior windows, skylights and walls. Condensation will appear on glass and walls when air distribution is insufficient or poorly diffused. Some equipment manufacturers offer computational fluid dynamics (CFD) computer-aided modeling to analyze problematic spa and pool spaces to correct air distribution.
Another key is dehumidification. Conventional air conditioning can dehumidify somewhat, but it can't handle the huge humidity loads of spa rooms where dozens or maybe hundreds of pounds of moisture per hour must be removed. Mechanical dehumidification equipment is the only method that can maintain the indoor air comfort of 50 percent relative humidity (RH).