Circulating good indoor air quality

by Catherine Howlett | May 1, 2013 4:55 pm

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by Nina Wolgelenter and Christian Taber, LEED AP
What is invisible to the eye is often still prevalent to the other senses. Indoor aquatic facilities, despite being open and vast, often harbor poor indoor air quality (IAQ), which can result in occupational asthmatic-related issues, throat, nasal, and eye irritation, and other health-related symptoms.

There are several factors that contribute to a natatorium’s struggle to maintain good air quality––ones that have changed over the decades. Despite numerous facilities being more than 30 years old, many of today’s IAQ issues revolve around the type of chlorine used, community water supplies, and tighter building envelopes that trap contaminants indoors, making these facilities unable to perform at the levels expected of them. One constant, however, is the need for air movement to help move the chloramine gases and keep their concentration levels to a minimum in the breathing zone—152 to 203 mm (6 to 8 in.) above the water—where the swimmers have no choice but to breathe in the contaminated air. Further, additional air movement helps reduce condensation and mold buildup, both inevitable in damp environments.

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Large-diameter, low-speed fans are popping up more frequently in both new and renovated aquatic facilities, or are simply being installed in existing spaces to increase the effectiveness of ventilation with HVAC systems and provide the much-needed air circulation. The HVAC system ventilates the building by treating the fresh air brought in. However, the ventilation does not always reach the occupants, and is not always efficiently or effectively used.

Dating back to the early 1990s, air circulation was deemed the solution to an increased chloramine problem in an Illinois aquatic center, as no amount of ‘shocking’ was able to reduce the high concentration of chloramines in the pool. (Shocking is a way of super-chlorinating a pool for a short time to help burn the combined chlorine in the water, reactivating the existing chlorine.) Air circulation was suggested by way of numerous floor fans and opening the doors during the shocking process to ventilate the space. According to an article published by the Professional Pool Operators of America (PPOA), fresh air should be forced over the water’s surface to eliminate chloramines and other various chlorination byproducts. (See K. Williams’ 1995/1996 article, “The Basics of Breakpoint Chlorination,” from the Professional Pool Operators of America (PPOA) Pumproom Press.)

Presently, small-diameter, high-speed floor fans are being replaced with ceiling-mounted, large-diameter, low-speed fans as large as 7 m (24 ft) to help circulate the air year-round. This reduced chloramine buildup at the water’s surface and the inevitable condensation issues leading to mold and mildew growth. Regardless of the method used to treat the air, it is important to keep it flowing––without creating a draft––around the space to reduce condensation.

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According to the Centers for Disease Control and Prevention (CDC):

The buildup of these irritants in the air is partially due to poor air turnover. The poor movement of fresh air over the pool surface, combined with the use of air recycling devices to control heating costs, leads to poor air exchange.

Even with energy-efficient air-handling units (AHUs) recirculating the air, chloramines are still trapped at the water surface, unable to escape. Air-handling systems must bring a great deal of fresh air and exhaust full blast when the pool is busy. If not exhausted, the chloramines continue to build. If the AHU does not effectively remove chloramines, then a heavily used pool will likely have an air quality problem.

The existing problems that make up poor IAQ can be resolved by combining prevention measures. Improving air movement in the environment and increasing the effectiveness of the air exchange process will reduce irritant levels in the air as well as help with the high cost of conditioning systems.

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Proper ventilation levels vary based on local code, system/space requirements, and engineering calculations. Figure 1 converts a minimum recommended value into air exchanges per hour (volume of air in space/volume of outdoor air provided in one hour). American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 62, Ventilation for Acceptable Indoor Air Quality, requires a minimum of 2.4 L/s/m² (0.48 cfm/sf) of floor area for swimming pools.

Air movement at work
The University of Texas at Austin is home to one of the first large-scale university aquatic facilities built in the United States. Modeled after the facility used for the 1972 Olympics in Munich, Germany, the Texas Swim Center recently met the challenges of improving IAQ with an impressive ventilation system upgrade and the addition of large-diameter, low-speed fan technology. Using computational fluid dynamics (CFD) modelling—a computer simulation of airflow—engineers and facility managers were able to define a system that provides comfort as well as improves air quality.

“We used a carbon gas-space filtration, and increased the amount of outside air we bring in, not just re-circulated the air we have in there,” says Charles Logan, the university’s swim center director.

To aid this process, four 7-m large-diameter, low-speed ceiling fans were installed from the 14-m (45-ft) high ceiling throughout the pool complex.

“We have a daily setting for these fans, but at night when we don’t have anybody in the facility, three things happen,” Logan explains. “[Air] release valves open up in the building, the fans are turned up to full speed, and 100 percent outside air is brought in to flush out all the air that circulated throughout the day.”

This is in contrast to air re-circulators that move around the contaminated air in the space with virtually no way for it to escape.

Shawn Allen, an engineer with José I. Guerra Inc., helped design the new system. He said the total volume of air movement was established based on the calculated evaporation rate of water in the space, taking into consideration the vapor pressure of the pool water and air at design temperature.

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Allen explained air is returned from the pool deck to one of five separate units where the air passes over a carbon-impregnated filter bank to remove chloramines and is cooled by a chilled water coil below saturation temperature to induce condensation and remove water from the air. Once the air is cooled, it is then passed over a hot-water reheat coil, using recovered heat, which brings the air back up to a discharge air setpoint modulated based on each individual space thermostat. The air leaves each unit free of chloramines, dry, and at any range of required temperature as established by space requirements.

Comfort component
In the summer, large-diameter, low-speed fans provide a cooling effect, moderating the environment for spectators and those milling around the deck. In facilities that must contend with extreme cold in the winter, heating system efficiency is also drastically improved by providing destratification—bringing fresh air trapped at the ceiling level down to the occupants. Heated air from a forced air system (i.e. 38 to 52 C [100 to 125 F]) is less dense than the ambient air (i.e. 24 to 29 C [75 to 85 F]) and naturally rises to the ceiling.

Large-diameter, low-speed fans reduce temperature variations between the floor and ceiling, mixing the warm air trapped at the ceiling with the cooler air at the pool level. Slowing the speed 10 to 30 percent of its maximum rotations per minute (RPM), the warm air is redirected from the ceiling to the occupant level, increasing patron comfort and reducing the heat loss through the roof. At the same time, the fans can be tied in with a facility’s automation system, allowing facility managers to control all their systems together, fluctuating along with capacity, which is critical when it comes to keeping swimmers comfortable outside the water as well.

Ductwork
With large-circulator fans assisting the airflow, the university was able to eliminate ductwork altogether, significantly reducing upfront material and labor costs. According to ASHRAE, failure to deliver airflow at the pool deck and water surface leads to IAQ issues—a primary impetus in many of today’s upgrades. To circumvent this issue, large fans destratify the air, mixing the warm air accumulating at the ceiling with the cool conditioned air, resulting in uniform temperatures. (See the 2011 American Society of Heating, Refrigerating, and Air-conditioning Engineers [ASHRAE] Handbook–HVAC Applications.)

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Air versus water temperatures
The 2011 ASHRAE Handbook–HVAC Applications, states the ideal air temperature within a facility should be maintained 1 to 2 C (2 to 4 F) 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 deemed necessary for cooling comfort. Ventilation systems alone are often designed to help supply enough air to a facility, but the addition of large-diameter, low-speed fans helps with the necessary step of delivering airflow to all parts of the room. At the same time, this air movement must be gentle enough to simply mix the air in the space without causing a draft that can chill swimmers exiting the water. With a typical AHU alone, achieving a well-mixed space in an aquatic environment can be very difficult. Large-circulator fans paired with variable speed drives allow air speeds at the occupant level to match the needs of the occupants and the HVAC system.

Natatorium humidity maintenance
Humidity control is crucial within all natatoriums, regardless of location and size. The mix of chemicals, condensation buildup, and patrons themselves creates IAQ concerns that occur in various ways, including corrosion of exposed and even hidden metal structures, as well as mold growth. With condensation buildup inevitable, large-diameter fans work with ventilation systems to ensure fresh air reaches the occupant level with steady, constant motion without causing a draft. (Condensation in this type of environment can occur on any surface below the dewpoint temperature of the air. This would likely include the walls, roof, and floor, but could be on the equipment inside the space as well.) Regardless of the method used to exchange air, it is important to keep it flowing around the solid surfaces to reduce condensation. If the air is cooler than the pool water, it will cause condensation and ‘misting.’

Without the proper precautions, indoor air quality issues are inevitable, but with the appropriate system put into place, aquatic facilities can focus on the athletes, knowing the air they breathe will not harm them.

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Nina Wolgelenter is a senior writer for Big Ass Fan Co., a designer and manufacturer of large-diameter, low-speed ceiling and vertical fans in Lexington, Kentucky. She has a background in environmental education and journalism. Wolgelenter’s work on energy conservation, sustainability, and the impact of advanced fan technology has been published in magazines, newspapers, and online media outlets. She can be contacted via e-mail at nwolgelenter@bigassfans.com[8].

Christian Taber, LEED AP, serves as the senior applications engineer at Big Ass Fan Co. As head of the applications engineering team, he is responsible for assisting customers with energy conservation and thermal comfort-related projects that involve air movement strategies. Taber spent eight years as an engineer at Trane, focusing on building energy simulation. He is an American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE)-certified high-performance building design professional, a certified energy manager, and a committee member of ASHRAE 90.1 and 189.1. Taber is pursuing a PhD in biosystems engineering from the University of Kentucky, and holds a master of science in mechanical engineering and bachelor of science in chemical engineering, both from Iowa State University. He can be reached at info@bigassfans.com[9].

Source URL: https://www.constructionspecifier.com/circulating-good-indoor-air-quality/

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