Evaporation
Evaporation of water from swimming pools, fountains, and industrial applications can have disastrous effects if not properly controlled.
The high moisture increases energy cost to heat the enclosure and, if not controlled, increases maintenance costs for repairs to structural components, and will cause premature failure of equipment used to heat and cool the structure.
Damage is more evident in a swimming pool enclosure, where the moist air is combined with chlorine from the pool chemicals. The chlorine attacks ferrous metals and will accelerate corrosion to a dangerous level. Chlorine will also deteriorate cement blocks, bricks, and mortar joints, as it permeates the walls of a structure.
Humidity greatly affects the comfort of building occupants, making it almost impossible to work or relax. Ideally, the relative humidity should be maintained between 50% and 60%, as suggested by ASHRAE.
High humidity adversely affects indoor air quality by providing the moisture that fungi, viruses, and bacteria require to breed and grow. Generally, occupants, that suffer from respiratory infections, asthma and allergies will find it especially taxing, and even harmful.
Controlling Moisture
Installing a dehumidification system is the most important step in removing the excessive moisture from an indoor pool enclosure.
A properly sized system will automatically maintain the correct relative humidity. If so equipped, a dehumidification system also recovers and recycles energy back to the air space as a by-product of free heat.
Efficient dehumidification will not take place if the air distribution system is not properly designed. If, for example, the supply air is channeled over the water surface, it will accelerate evaporation, as well as causing bather discomfort.
Another serious problem associated with a poorly designed distribution system is uneven air disbursement over cold outside surfaces. This results in condensation on exterior walls and windows that is both unattractive and damaging.
Condensation forms as the warm, moisture filled air comes in contact with cold surfaces, such as outside walls and windows and interior furnishings. When the moisture in the air reaches the dewpoint temperature on a surface, it condenses.
To prevent condensation from forming, the surface temperature must be much warmer than the air dewpoint temperature.
Controlling Condensation
Since condensation is dictated by temperature and humidity, it makes sense to control both wherever possible.
Properly positioned supply and return ducting controls the majority of condensate problems, but other methods help prevent this problem, especially in new construction.
Glass doors and windows that are exposed to outside air should have the lowest R rating available. Double or triple pane glass panels are best, and they should be insulated or sealed in vinyl-clad frames wherever possible.
Window frames must be sealed to adjacent walls and insulated with non-porous insulating materials. Window and doorframes must have thermal breaks.
Higher than normal pool water temperatures will increase evaporation. Maintain the proper water temperature (80°F to 82°F for public pools). Water temperatures for spas/whirlpools are warmer than general activity pools, and require special attention because of their small size and much higher evaporation rates.
A lower room air temperature (when compared to pool water temperature) also increases evaporation. Maintain the space temperature approximately 2°F to 4°F above the pool water. Not only will the evaporation rate decrease, but bather comfort will improve.
Water agitation and splashing rapidly increases the evaporation. This is evident where large fountains are present. If condensation is difficult to control, it may be necessary to remove or limit fountain activity to a controllable level.
Likewise, wet decks from bathers will accelerate evaporation. Avoid using carpeting or other materials that will retain moisture.
One of the best deterrents to condensate formation is to include a 4 mil vapor barrier in wall and ceiling construction. While this is usually only applicable to new construction, it can have a dramatic effect on the wall or ceiling temperature.
A vapor barrier also prevents moisture migration through the walls and ceiling and from condensing moisture within the wall structure. As the outside temperature decreases, the dewpoint will be reached at a mid-point within the wall.
Moisture migrating through the wall because of no barrier condenses within the wall structure itself, resulting in a loss of structural integrity.
Condensation problems can be avoided with careful evaluation of the swimming pool environment at the design stage. Addressing the issues during construction goes a long way toward maintaining an energy-efficient pool enclosure for many years.
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