Why not just use ventilation or an air-to-air heat exchanger to control humidity in my indoor pool?

Pool dehumidifiers, while more expensive than heat recovery ventilators, have similar operating costs and provide superior control of the indoor environment. Even with air-to-air heat recovery (at best 50 to 70% effective) ventilation air requires substantial conditioning energy, especially in winter operation. And you must still replace the pool heat lost to evaporation. The cost of conditioning ventilation air (and separately heating the pool) is comparable to the cost of operating a pool dehumidifier that incorporates energy recovery pool heating. Ventilation and air-to-air heat exchangers can provide some control of indoor humidity levels during those periods of the year when outdoor air contains less water than indoor air (typically during the winter months). The indoor humidity is not “controlled” per se, but rather floats to a level determined by the actual outdoor conditions at the time. This can be a reasonable strategy for an “indoor/outdoor” pool in a mild climate, where the pool deck remains permanently open to the outdoors during the summer months and can be opened as needed during good weather or as conditions require. However, in most commercial facilities or anywhere where the pool will be enclosed year round, the ventilation strategy will not provide adequate control. To be comfortable year round, additional dehumidification must be provided in the swing seasons while dehumidification and cooling must be provided in the summer months.