By James Hogan
Indoor pools have always been more expensive to operate than other comparably sized buildings, because the heating, ventilating and air conditioning (HVAC) system must run continuously to control humidity and protect the building. However, technological advancements, such as new energy-efficient equipment and add-ons for existing indoor pool HVAC units, offer aquatic facility operators the potential to significantly reduce monthly operating costs.
Supply/exhaust vs. mechanical dehumidification
Probably the most important technological energy-saving innovation to emerge for indoor swimming pool facilities was the mechanical dehumidifier, which hit the market in the 1970s. Previously, natatoriums attempted to control relative humidity (RH) with either conventional air-conditioning or supply/exhaust systems, or a combination of both.
Conventional air conditioning is not designed for, and therefore can not handle, the tremendous humidity loads of natatoriums. However, the technology did help somewhat prior to the development of the modern commercial dehumidifier. Another approach is the use of 100 per cent outdoor air to remove humidity. Since it takes a significant amount of energy to heat and cool that much air, this method is quite costly.
The development of the modern dehumidifier changed energy costs drastically. Instead of being exhausted, a large percentage of air is re-circulated through the dehumidifier’s refrigeration process to condense the moisture and return a drier 50-per cent RH air to the space. The heat reclaimed from the refrigeration process is used to provide free pool water heating and/or to heat the space as needed.
Over the last 30 years, mechanical dehumidification has become the HVAC system of choice for the majority of new and retrofitted natatoriums. However, there are still many remaining natatoriums that have not switched to modern dehumidification. That, combined with the fact the last decade has seen many technological innovations in energy-saving add-on equipment for new and existing dehumidifiers, offers many opportunities for natatorium owners to improve operational costs and lower energy use.
Computation fluid dynamics
Natatoriums are significantly more complex for engineers to design efficiently compared to comparable structures, such as gymnasiums. Constant changes in localized air buoyancy present a challenge in temperature and humidity prediction. Designing an HVAC system with rule-of-thumb practices may be sufficient for conventional buildings, but may fail to meet a natatorium’s unique challenges.
Five years ago, natatorium engineers were presented with a new design tool called computation fluid dynamics (CFD), which accurately simulates air flow, temperature and relative humidity through computer modelling.
This tool is invaluable for both new construction and retrofits. Engineers use CFD to confirm airflow calculations are correct, so that any repositioning of grilles and diffusers are first tried virtually, before physical construction is completed. This allows an early confirmation of design and assurance of suitable indoor air quality (IAQ).
Besides IAQ, a CFD analysis also improves energy savings because the facility is more efficient. Therefore, CFD analyses can lead to a building’s Leadership in Energy & Efficiency Design (LEED) credits from the U.S. Green Building Council (USGBC), Washington, D.C. (For more on LEED credits, see pg. 60.)