Indoor pools need special monitoring for the constant challenge of humidity control.
Aquatics operators and service technicians should not be expected to maintain dehumidifiers — these are HVAC/R machines requiring EPA-certified technicians. However, with some fundamental knowledge about natatoriums, pool operators and technicians can provide feedback that prevents future costly repairs or user health issues. Natatoriums can malfunction quickly, so the typical six-month or annual dehumidifier check-up by an HVAC/R service contractor isn’t enough to detect potentially damaging problems before they blossom.
An indoor pool is a unique synergy of the following four factors, the degradation of which could result in building deterioration, air quality health problems and uncomfortable environmental conditions for users.
• Building envelope: Indoor pools can experience issues related to construction techniques or building materials. For example, missing or breached vapor barriers can allow damaging condensation to accumulate inside the walls.
• Ventilation: Supply air ducts and vents must fully cover exterior windows with conditioned air to avoid condensation. The system must move air down to the breathing zone for good air quality.
• Dehumidification: Most indoor pool spaces have a dehumidifier to maintain 50- to 60% relative humidity (RH) and cool or heat the air to a set point temperature. Without it, the space probably depends on outdoor air and exhaust.
• Water chemistry: Imbalanced chemistry results in the buildup of respiratory-affecting chloramines and potentially cause surfaces to corrode.
What to look for
Most modern dehumidifiers are complete HVAC machines that heat and cool the space and use compressor heat recovery to heat the water.
So space and water temperatures, and RH are key checkpoints. These parameters are displayed on the microprocessor’s LED keypad readout and in many cases can be accessed remotely. A good rule of thumb is to keep a two-degree difference between the space (higher) and water (lower) temperatures. A common indoor pool set point is 84°F space, 82°F water temperature and a 60% RH. Lowering the space temperature by even two degrees increases the humidity load by 35%, which could surpass the dehumidifier’s capacity.
On many units, LED keypads have red warning lights to indicate an operation stoppage or other problem that an HVAC/R tech should address. The readout menu can be scrolled to find the cause.
On dehumidifiers that have a pool water heating feature, no water should leak from inlets or outlets. Conversely, hundreds of pool-water heating models have been errantly left unconnected to the pool circulation system. Owners should know that water heating connection to the dehumidifier could save hundreds of dollars on utility bills annually.
An overflowing condensate drain pan, or watermark evidence, could point to a potentially damaging drain-line blockage.
In the natatorium, condensation on exterior walls and ceilings should not occur. Window and skylight condensation indicates the glass is not covered with warm dehumidified supply air and its temperature has dropped below dew point.
Premature corrosion on door hardware or room surfaces could indicate a problem.
Natatoriums must operate with a negative building pressure: Approximately 10% more air volume should be exhausted than introduced. A malfunctioning exhaust fan or ventilation design can result in positive pressure and push pool air and odors into connected living quarters. Positive pressurization also can push moisture into poorly sealed voids inside walls and above ceilings where it can produce mold and deteriorate the building. Natatorium building pressure can be easily checked by slightly opening a door and seeing if the air is being pulled in (negative) or pushed out (positive).
What to listen for
Dehumidifier supply air blowers generally run 24/7 to offset pool evaporation, so monthly or bi-monthly air-filter replacements may be needed. If the blower isn’t running, there’s something amiss.
Dehumidifier compressors run at least 10 minutes at a time. Hearing the compressor short-cycle off and on several times within a minute or two warrants an HVAC/R service contractor’s attention. Very noisy ductwork, such as drum head effects and extreme vibrations, could point to a poor ventilation design. Unusual sounds, such as fan belts squealing or worn out motor or blower bearings, also require an HVAC/R contractor.
A final note: Calling the dehumidifier maker rather than an HVAC/R contractor usually won’t help because they rarely perform repairs. However, a factory technician’s review of the data can help HVAC/R service professionals troubleshoot issues.