How Is Indoor Pool Dehumidification Properly Designed?

Everything in a natatorium design flows from the evaporation rate. I calculate it from pool surface area, the temperature difference between water and air, air velocity over the water, and an activity factor — a calm residential-style pool, a busy recreation pool with a slide, and a therapy pool with high water temperature and agitation are three very different loads that happen to share a building type. Hot tubs, spray features, and spectator areas each get their own line in the load calculation. The dehumidification unit is selected for the worst-case hour, not the average day, and I include the outdoor air latent load on top of the pool evaporation — summer ventilation air in a humid climate is a major load of its own. Heat recovery is standard in my designs: the refrigeration circuit that wrings moisture from the air rejects heat that goes back into the pool water or the space, turning the dehumidification penalty into pool heating. I show the owner this energy balance explicitly, because it's the argument that justifies proper equipment over a cheap exhaust fan and a prayer.

The supply air has one critical job beyond comfort: keep every interior surface above the space dew point. I lay out supply to wash exterior glazing, curtain walls, and cold wall surfaces with warm, dry air, using long-throw diffusers or duct socks that reach the glass without blasting bathers. Returns go high, pulling the warmest, most moisture-laden air back to the dehumidifier, and the whole space gets enough air movement that no pocket sits stagnant against a cold surface. Stratification is the enemy — a tall natatorium with a cold roof deck will condense at the ceiling while the deck level reads fine on the thermostat. I design for full mixing or targeted destratification, and I verify with the envelope consultant that the coldest interior surface temperature in the design condition still sits above the design dew point. That single check, done during design, prevents the most expensive natatorium failures I know of.

A natatorium is a corrosive, wet industrial environment wearing a recreation building's clothes, and the design has to respect that. The envelope and the mechanical systems are one coordinated defense — the best dehumidifier in the world cannot save a leaky, uninsulated envelope, and the best envelope cannot survive without dehumidification. I lock these decisions in during schematic design with the architect, because nearly all of them are structural or envelope commitments. • Hold space air ~2°F above water temperature at 50 to 60 percent relative humidity • Wash all glazing and cold surfaces with warm, dry supply air; verify coldest surface stays above dew point • Run the pool enclosure slightly negative to adjacent spaces to contain humid, chlorinated air • Specify coated coils, corrosion-resistant drain pans, and non-corroding ductwork materials • Place the vapor retarder on the warm side with airtight construction and thermal breaks at structure • Recover dehumidification heat to the pool water or space air to offset operating cost