By Ralph Kittler
Recent technological advancements in dehumidifier design are now being applied to 100 per cent outdoor air-based ventilation-only systems (OAVOS) for environmental control in natatoriums, and as a result, many facility operators are considering this equipment again for conditioning indoor swimming pool environments.
An indoor swimming pool environment can be precisely controlled for much of the year using an OAVOS approach. This method is not suitable for every facility, however, as there are certain times of the year (mild weather and summer) when the space conditions might get more hot and humid than could be desirable. For facilities where this period of time is short or where the patrons would not mind elevated conditions during the warmer weather, this is definitely an option again.
When the weather is drier and colder, a well-designed OAVOS can control the space conditions quite precisely. It is important to properly model a system’s year-round performance and establish what the local climate can deliver and whether or not it is acceptable for the operator and patrons.
If the indoor conditions cannot be maintained in an acceptable range during milder/warmer periods of the year, the facility operator would need to use a compressorized mechanical dehumidifier to control their space precisely year-round at the conditions desired. Until fairly recently an OAVOS had high operating costs and did not provide stable space conditions, even in cold weather.
An early conditioning method
Long before the development of modern compressorized dehumidifiers in the ’70s, indoor swimming pools were conditioned using simple, 100 per cent OAVOS. These systems generally moved a constant volume of outdoor ventilation air through the pool area year-round. Most did not modulate the amount of outdoor air, nor did they recovery any energy from the exhaust air. As a result, there were dramatic variances in space conditions in addition to seasonal and high energy costs.
For instance, during this time a typical indoor swimming pool would have had a space too dry in the middle of winter and too warm and humid than patrons would have liked in the summer. As energy prices increased, heating large amounts of outdoor air during winter operation started the move towards more energy-efficient alternatives to controlling indoor pool conditions. Thus, the compressorized dehumidifier was born.
A compressorized dehumidifier provides precise, year-round temperature and humidity control, while even contributing to pool water heating. While the initial cost for these systems was higher, their energy savings and precise condition control capabilities made them the product of choice for indoor swimming pools.
Standards change over time and now natatorium designers are seeing building codes calling for increased amounts of outside air as a minimum requirement to providing the best possible indoor air quality (IAQ). With this trend of increasing the volume of outside air in a facility, people have been looking at OAVOS again.
Indoor swimming pool environments are typically maintained at 27 to 29 C (82 to 85 F) and 50 to 60 per cent relative humidity (RH). There may not be too many days during the summer in Canada where the outside air is not able to control the space.
An important tool and critical first step to help establish whether or not an OAVOS is a consideration is the ability to model the year-round space conditions. Software has been developed by manufacturers that can model what the space conditions would be throughout the course of a year using local weather data. This information will help a facility operator decide if this approach to environmental control is something to consider.
Natatorium environmental control has seen many technological developments in recent years, including chloramines source capture removal, waterside ultraviolet germicidal irradiation (UVGI), exhaust air heat recovery, dedicated-duty, direct-drive fans, and microprocessor operational control and monitoring. Depending on the system, it may even have Internet connectivity. These new innovations have been game-changers for the outdoor air ventilation approach.
Perhaps the most notable air comfort and efficiency development for the OAVOS approach has been the introduction of modulating controls. These controls monitor indoor and outdoor air conditions precisely and introduce only the required amount of outdoor air to maintain the best possible IAQ. Before these controls were developed, natatoriums with an OAVOS provided more outdoor air than necessary during the winter, which resulted in indoor RH levels to drop too low. Low RH levels create an uncomfortable chilling effect on wet skin and also raise operational costs. Bringing in more outdoor air than needed means more outside air must be heated and the pool water heating requirements also increase dramatically.
New natatorium projects as well as heating, ventilation, and air conditioning (HVAC) retrofits must decide between OAVOS and mechanical dehumidifiers. Computer modelling can help determine the level of comfort an OAVOS will maintain throughout the year and in seasonal weather conditions common to the natatorium’s respective geographical location. Armed with the best information computer modelling can provide, a facility operator can then make the best business decision for occupants based on comfort and economy trade-offs.
