Fan function
Like a traditional ceiling fan, HVLS fans increase air velocity to create a more comfortable environment for building occupants. However, unlike a conventional ceiling fan, one HVLS fan is capable of covering an area as large as 2,787 m2 (30,000 sf). In warmer months, when spectator comfort is a concern, these fans improve personal comfort with an evaporative cooling effect. They do not lower the air temperature in a space, however, the perceived cooling effect can make a person feel eight degrees cooler. As a result, facility managers in air conditioned spaces are able to raise the thermostat without sacrificing comfort, reducing cooling costs by 10 to 15 per cent annually.
HVLS fans are also capable of destratifying (mixing air to eliminate layers of temperature) a space in the winter, reducing energy consumption by as much as 30 per cent. Heated air from a forced air system (37.7 to 51.6 C [100 to 125 F]) is less dense than the ambient air (24 C [75 F] and higher) in an aquatic facility. Hot air naturally rises to the ceiling, however, by slowing the speed of a HVLS fan by 10 to 30 per cent of its maximum rotations per minute (RPM), warm air can be redirected from the ceiling to the occupant level to not only increase employee/patron comfort, but also reduce heat loss through the roof.
To maintain the integrity of the original building envelope at the UT Austin facility, the ceiling was lowered by 3 m (10 ft) to lessen the amount of space that required conditioning, as well as to accommodate four, 7.3-m (24-ft) diameter fans, which were installed 14.6-m (48-ft) above the water surface.
“The result was exactly what we needed as far as air movement at the pool surface,” said Allen. “We knew we wanted to bust the (chloramine) bubble without creating too much velocity and air movement at the deck where swimmers were exiting the water, as a breeze would have chilled them. The idea was to keep the air velocity below 0.3 m/s (60 fpm) at the deck but for the air to move fast enough to sweep the chloramines off the water’s surface.”
By pushing the chloramines to within a reasonable zone, the air handling system picks them up and passes the contaminated air through a carbon filter to kill off the gases.
Using a traditional overhead HVAC system with a ceiling height of 14.6 m (48 ft) would have been very challenging—and energy intensive—to achieve this type of air movement without creating a draft at the water’s surface. Since HVLS fans operate at approximately 50 per cent of their maximum RPM, they only consume 320 watts each, which is roughly three cents per hour. This achieved the design’s air velocity criteria with an extremely low operating cost.
Standard practices
The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) lays out the necessary conditions in terms of air movement, humidity build up and ideal temperatures within pool and spa facilities. Integrating HVAC systems along with air handling systems can go a long way in creating uniform temperatures in indoor aquatic facilities.
Air versus water temperatures
According to ASHRAE, the ideal air temperature within an aquatic facility should be maintained two to four degrees above the water temperature, but not above the comfort threshold of 30 C (86 F). If the water temperature exceeds the air temperature, some form of air movement is necessary for cooling. While ventilation systems, along with extensive ductwork, are often designed to help supply enough air to the facility, the addition of HVLS fans help to distribute the necessary air flow to all parts of the room.
Ductwork
For the UT Austin aquatic facility, airflow was established using large circulator fans. This allowed the facility to forego ductwork altogether, which significantly lessened material and labour costs. A primary concern in many of today’s upgrades is the failure to deliver airflow at the pool deck and water surface, as it can lead to indoor air quality (IAQ) issues. To circumvent this, the large fans work to destratify the air, mixing warm air accumulating at the ceiling with cool conditioned air to create uniform temperatures throughout the facility. With ductwork alone, the entire facility would require conditioning, which would significantly increase operating costs, while not ensuring uniform temperatures.
