Using large diameter ceiling fans to improve indoor comfort

by Sally Bouorm | October 1, 2011 11:31 am

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By Nina Wolgelenter

Over the last few decades, several factors have changed the way aquatic facilities condition indoor air. Contributing elements to these changes include the type of chlorine used in the water, the water supply provided by the municipality and fluctuations in heating, ventilation and air conditioning (HVAC) needs. Combined, these elements significantly augment the air quality and, subsequently, the comfort of the facility regardless of the season or location.

Without proper ventilation, HVAC systems can contribute to poor indoor air quality (IAQ) concerns; however, with the introduction of highly evolved ventilation systems, along with high-volume low-speed (HVLS) fan technology, a more favourable, cost-effective environment can be created for swimmers, coaches and spectators alike.

In large natatoriums it is often difficult to achieve uniform temperatures and distribute ventilation with traditional air handling systems due to the sheer size of the space. The addition of large fans decouples air distribution from the HVAC system, allowing for low-energy air circulation, which increases the effectiveness of the ventilation supplied to the space.

The design and operation of indoor aquatic facilities is an exercise in energy conservation and proper engineering. To keep up with modern standards, both new and existing facilities often need to be renovated. To contend with high-energy costs, facility managers are researching opportunities for energy conservation by finding ways to incorporate HVAC efficiencies into their facilities.

Texas-size upgrades

The swimming centre at the University of Texas (UT Austin), built after the 1972 Summer Olympics, set the bar for large, indoor natatoriums with its 2.7-m (9-ft) deep competitive pool and adjacent dive pool. Three decades later, the facility was in need of upgrades with respect to its air quality control. The unique criterion involved in maintaining a quality environment for this facility resulted in an innovative system that controlled the chloramines in the space while taking advantage of waste energy to maintain comfort.

“Air movement was a big challenge due to the large Olympic-size swimming areas and the parameters that were established to accommodate the athletes,” explained Shawn Allen, a mechanical engineer and LEED AP with Jose I. Guerra, Inc., who served as principle on the project.

The potential for chloramine bubbles to form at the breathing zone (water surface) was a given; therefore, creating a way to disperse this gas was established in the initial stages of the project.

During renovation, the ventilation system was completely revamped using computational fluid dynamics (CFD), a computer simulation of airflow, and building information modelling (BIM) to help determine the best system that would provide comfort, as well as improved air quality.

“Through the use of CFD and BIM we were able to produce a model of the space and establish air flow patterns and velocity profiles that optimize air movement while minimizing evaporation and negative cooling effects on athletes,” said Allen.

As a result, the facility incorporated carbon gas-space filtration and increased the amount of outside air that was brought into the space rather than simply recirculating existing air. Fans were also installed throughout the pool complex to aid this process, said UT Austin’s facility director, Charles Logan.

“We have a daily setting for these fans, but at night when the facility isn’t being used, three things happen: release valves open in the building; fans operate at full speed; and 100 per cent outside air is brought in to flush out the air that circulated throughout the day,” Logan explained.

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[2] each, which is roughly three cents per hour. This achieved the design’s air velocity criteria with an extremely low operating cost.

Standard practices

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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.

Effective air movement

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Effective air movement does not occur simply through fan rotation alone. The type of blades—or airfoils—and the angle at which they are placed play an important role. An angle approaching 30 degrees or more will increase drag and therefore require a larger motor, and consequently, move less air. This results in increased energy costs and lower aerodynamic efficiency. At the same time, a flat airfoil, which is almost horizontal, typically will not move much air either. To achieve efficient air movement and avoid excessive drag, a fan with 10 moderately-pitched, narrow-aerodynamic airfoils should be used. Similar to wings on an aircraft, airfoils allow for a much smaller energy-efficient motor. To further enhance airfoil efficiency, winglets[5] are added at the tips to help eliminate wingtip vortices (tubes of circulating air) that can induce drag and lower overall airfoil efficiency.

Humidity control

Humidity control is crucial within all natatoriums regardless of location and size. The mix of chemicals, condensation buildup and bather loads also create indoor air quality concerns that can be addressed in a variety of ways including:

• extensive ductwork;
• exhaust systems; and
• air handling units.

These systems create a constant exchange of inside and outside air. Condensation is inevitable; however, HVLS fans work with ventilation systems to ensure fresh air reaches the occupant level with steady, constant motion. Regardless of the method used to exchange air, it is important to keep it moving around the water to dissipate chloramine gases. To reduce humidity, air is passed through air handlers and cooled to 12.7 C (55 F), which causes the humidity to condense out of the air, albeit energy usage increases. However, UT Austin, with guidance from Allen, designed a heating system that utilized waste heat from a nearby cogeneration plant.The system works by returning air from the pool deck to one of five separate units where it passes over a carbon impregnated filter bank to remove chloramines. Air is then cooled by a chilled-water coil, below saturation temperature, to induce condensation and remove water from the air. Once the air is cooled, it passes over a hot water reheat coil to return the air temperature back to the discharge air set point, which is modulated by thermostats in each individual space. Air leaves each unit free of chloramines, dry and at any range of temperature established by space requirements. Reheat for the units are accomplished indirectly via superheated waste steam from the university’s combined heat and power plant.

To make this work, the total volume of air movement was established based on the calculated evaporation rate of water in the facility. The vapour pressure of the pool water and air at design temperature was also taken into consideration.

The system works by returning air from the pool deck to one of five separate units where it passes over a carbon impregnated filter bank to remove chloramines. Air is then cooled by a chilled-water coil, below saturation temperature, to induce condensation and remove water from the air. Once the air is cooled, it passes over a hot water reheat coil to return the air temperature back to the discharge air set point, which is modulated by thermostats in each individual space. Air leaves each unit free of chloramines, dry and at any range of temperature established by space requirements. Reheat for the units are accomplished indirectly via superheated waste steam from the university’s combined heat and power plant.

Taking the LEED

HVLS fans can also be tied in with a facility’s automation system, allowing facility managers to control all of the ventilation systems together. This is important for aquatic buildings that operate as both recreational facilities with a known number of participants, and as competitive facilities where the number of occupants can increase dramatically over a short time.

Designing aquatic facilities with consideration of its occupants is essential to creating a quality environment. By lowering effective temperatures and increasing ventilation efficiency with silent, gentle-air circulation, HVLS fans enhance aquatic environments for all those using the space.

Proper application of these fans can also help a project earn points under the Canada Green Building Council’s (CaGBC’s) Leadership in Energy & Environmental Design (LEED), a green building certification system providing third-party verification that a building utilized environmentally friendly building practices during construction.

 

 

Nina Wolgelenter is a senior writer for Big Ass Fan Co., a designer and manufacturer of high volume/low speed (HVLS) ceiling and vertical fans in Lexington, Ky. She has a background in environmental education and journalism. Her work on energy conservation, sustainability and the impact of HVLS technology across various industries has been published in magazines, newspapers and online media outlets. She can be contacted via nwolgelenter@bigassfans.com[6].

 

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