SUMMARY: Pools require 24/7 Temperature & Humidity Control. In many cases the heating and cooling is okay but the dehumidification is a problem. Using a small dehumidifier may be the best option as opposed to replacing the entire HVAC system.
Unlike a space where comfort is the goal, an indoor pool is an environmental application, requiring constant attention 24 hours a day, 7 days a week. One can’t adjust the thermostat when the pool is unoccupied in the same manner as a bedroom when the occupant is on vacation.
In summary, you design the pool space to be 2⁰-3⁰ above the water temperature for minimal evaporation and maximum comfort. Assuming the pool is about 82⁰, that gets you about 85⁰ and 50-60% RH. Essentially what happens is whenever the adjacent areas are less than that 85F, there will be heat loses and condensate will collect on colder surfaces. Should the air temperature drop below the water temperature, the pool will effectively heat the space at the expense of the pool. If the water temperature drops too much, the chemistry will get out of balance. So, the space requires heat most days (considering the ambient temperatures for the entire year).
Keep in mind as you add heat, you will increase the humidity in space (rising dew point).
When considering the outdoor conditions, it is observed that the temperature and dew points are typically lower than in the pool area. It is not uncommon to see the outdoor air used for dehumidification. If you consider the range for outdoor air (0DB-100DB) vs what is required in the pool area, one will see times where it is difficult to keep the right equilibrium.
There are very few days that you truly need cooling.
So, that brings us to dehumidification. If you increase the air temperature, you increase the dew point. This increases condensation on cold surfaces which left untreated can create mold, rust,etc.
So, what to do if you have heat, don’t need cooling, and the dehumidification is subpar?
Use a single packaged dehumidifier. As an example, the Novelaire DES/DX300 will deliverer about 8#/hr and neutral temperature air. Because humidity is consistent in a space, as opposed to air temps which are warmer towards the top of a space it can be mounted above or adjacent to the space. It is single phase power and uses a simple dehumidistat. Installation is relatively simple, only requiring 4 flex duct connections. This type of unit is perfect for residential and small motel pools. There are other options as the application require.