There is a indoor pool and normally water is heated to temp 40 deg c. Total water quantity is 15000 ltrs. Out door temp is 44 deg c. The indoor a/c results in high amount of condensataion in supply grilles. FCUs are used to cool the area with 10% of fresh air. There is no possibility of untreated outside air coming in. This area now requires a redesigning. Can anyone suggest what are factors to be considered while calculating load and how exactly a good designing can be done.

Swimming pools are quite complex to design and there is no simple and quick answer but the general procedure is as follows

1. you need to calculate rate of evaporation based on pool usage, water temperature and air humidity inside the pool enclosure. You can find formulas in ASHRAE hvac applications book.

2. Relative humidity inside the swimming pools should be kept at 60% to prevent excessive water evaporation in order to save money on water heating.

3. Minimum amount of fresh air is dictated by the local code. Actual amount of fresh air depends on outside air humidity and relative humidity you try to keep inside the pool enclosure. You need to calculate the balance between water evaporation, absolute humidity brought in by fresh air and absolute humidity taken out via exhaust air. This should balance out at 60% indoor relative humidity. This calculation should be performed for both winter and summer conditions.

4. depending of your location you might need to dehumidify outside air to prevent relative humidity going much more above 60% and you might need to cool that air in order to keep temperature at 2-3 degrees above the water temperature. In Europe, typically you need to heat the air. Dehumidification should be done with heat pumps and heat transferred to water heating.

5. Heat pumps should be used to transfer heat from the discharge air towards pool water heating.

6. Supply air temperature should be kept above dew point temperature of the pool air to prevent condensation on grilles and diffusers.

7. Supply air should be blown across glass areas to prevent condensation on glass surfaces during the winter.

8. Skylights are not good idea and they should be avoided if possible.

9. If you need to heat the pool it is a good idea to use underfloor heating because it works well with heat pumps.

I don't think that fan coil units are appropriate solution for swimming pool.