Swimming pools are generally very high energy users. Evaporation from the pool surface has the effect of cooling the water. To sustain a comfortable water temperature (80°F to 84°F), that evaporative cooling has to be compensated by adding heat to the water. The natatorium air will quickly become laden with water vapour if there is inadequate air exchange with outside. This condition is very undesirable because it is uncomfortable for swimmers and results in water condensing on walls, windows, and the ceiling. In cold outdoor conditions and especially where the natatorium is under even the slightest positive pressure, condensation will migrate into the structural pores and cracks. There it will freeze and work to break apart the building envelope.
To prevent rapid structural deterioration, this facility is equipped with large exhaust fans and 100% outside air makeup air units, running continuously. Humidity is kept down by the constant introduction of drier outside air, and the fans are sized to maintain a negative pressure in the natatorium (larger exhaust than supply). From an energy standpoint:
• The pool water is continually being heated to compensate for evaporation.
• The makeup air is continually heated for introduction into the space.
• The exhaust air, containing all the makeup air heat and the latent heat from the pool is being thrown away.
A heat recovery dehumidifier, though expensive, offers a packaged solution. Humid natatorium air is drawn into the unit and cooled for dehumidification. The water condensed from the air stream is returned to the pool. The heat recovered from the dehumidification is re-introduced to either the makeup air stream or to the pool water as needed. Once the humidity problem is solved, air exchange can be greatly reduced to satisfy occupant ventilation requirements only. The amount of cold outside air brought in through a heat recovery dehumidifier is only a fraction of that for a 100% makeup system.
Two well-known manufacturers are Dectron (Dry-o-Tron) and Desert Aire. The annual savings for this measure are relatively large at $8,150, but the cost is also high at $136,245. This gives a simple payback greater than 22 years. We recommend this measure based on the combined benefits of energy savings and lower space humidity (less humidity damage).