Tag Archives: F1050.10−Pools

Saving on Natatorium Energy Costs with Green Options

Photos courtesy Jarmel Kizel Architects and Engineers

Photos courtesy Jarmel Kizel Architects and Engineers

by Ralph Kittler, PE

When it comes to designing indoor swimming pool facilities, it is critical to ensure not only a healthy interior environment, but also energy efficiency. New technologies can provide both optimal natatorium environmental control and curtail utility consumption when specified.

Commercial dehumidifiers and 100 percent outside air ventilation system (OAVS) technology for indoor pools have significantly changed in the last decade. Consequently, a new or retrofitted natatorium HVAC system can potentially save millions of dollars in energy costs over the equipment’s 15 to 25-year lifecycle, depending on the sustainable options specified.

In short, today’s indoor pool HVAC equipment is not your parent’s dehumidifier. Current systems can come with:

  • reduced refrigerant charges of up to 85 percent;
  • lowered fan energy costs;
  • compressor heat recovery for ‘free’ pool-water-heating;
  • exhaust heat recovery for preheating outdoor air;
  • modulating controls for pinpoint temperature and humidity control;
  • glycol heat rejection to dry coolers; and
  • web-based microprocessor monitoring and alarms for maintaining daily pinpoint, real-time control by factory technicians.
In New Jersey, the Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center depends on its dehumidifi er to keep glass shared by the aerobics and aquatic areas free of condensation.

In New Jersey, the Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center depends on its dehumidifier to keep glass
shared by the aerobics and aquatic areas free of condensation.

The design team kept the aquatic center a focal point at HUMC Fitness and Wellness Center with ample use of glass separating it from the other areas.

The design team kept the aquatic center a focal point at HUMC Fitness and Wellness Center with ample use of glass separating it from the other areas.

 

 

 

 

 

 

 

 

The R-22 ban and dehumidifier retrofits
Thousands of units manufactured after the 1970s’ advent of the modern-day mechanical indoor pool dehumidifier will be reaching the end of their useful lifecycle within the next five years.

Most of these aging dehumidifiers operate using the hydrochlorofluorocarbon (HCFC) refrigerant R-22. According to the 1989 international treaty, Montreal Protocol on Substances that Deplete the Ozone Layer, this refrigerant has ozone-depleting potential. As a result of the treaty, R-22 is amid a world-wide manufacturing phase-out. The phase-out—which currently calls for 90 percent next year and 99 percent in 2020—has already spiked prices due to dwindling supplies. Price volatility is demonstrated by contractor charges ranging anywhere from $35 to more than $100 per pound of R-22.

Conventional natatorium dehumidifiers built during last 25 years can range from 45 kg (100 lb) to more than 317.5 kg (700 lb) of refrigerant. Therefore, a dehumidifier that leaks all, or even a substantial portion, of its R-22 refrigerant charge could represent significant cost for refrigerant replacement, not to mention damage the environment. This fact alone should get natatorium owners’ attention. However, the fact a refrigeration circuit will generally have at least one or two refrigerant leaks during its lifecycle should also be considered.

R-410A is the succeeding refrigerant to R-22. It is a less environmental-damaging hydrofluorocarbon (HFC)—due to its lack of chlorine—and used in most new dehumidifiers over the last five years, but it is also expecting a future phase-out and subsequent price increase.

Refrigerant price volatility, as well as the suspected danger to the environment, has prompted many HVAC manufacturers to look toward alternatives, such as substituting up to 85 percent of the refrigerant with glycol for heat rejection. Glycol is significantly less toxic to the environment. It operates under pump pressures versus the high pressures of compressors and refrigerants; thus, it is less likely to leak—when it does, glycol is not a vapor or ozone-depleting chemical.

The glycol-based units still have a small refrigerant charge of typically 10 to 20 percent of conventional dehumidifiers. These refrigeration circuits are necessary for dehumidification and optional natatorium space-cooling, however, they carry dramatically less leak liability and risk because they are ultra-compact and factory-sealed by expert technicians. The glycol is transported through polyvinyl chloride (PVC) piping to dry coolers for heat rejection. It also eliminates the potential of installation errors involving hundreds of pounds of refrigerant, expensive copper piping, and outdoor air-cooled condensers subject to contractor onsite workmanship.

In New Jersey, the new $24-million Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center Powered by the Giants, employs a 70-ton, 23,000-cfm dehumidifier that uses 80 percent less refrigerant to dehumidify its 743-m2 (8000-sf) aquatic space. The dehumidifier substitutes glycol for the estimated 312 kg (690 lb) of R-410A refrigerant used by a similar-sized conventional dehumidifier. Specified by consulting engineer firm, Jarmel-Kizel Architects and Engineers, the 10,405-m2 (112,000-sf) facility’s step toward refrigerant independence complemented HUMC’s sustainable programs, such as its in-house Dierdre Imus Environmental Health Center—a not-for-profit children’s advocacy group dedicated to identifying, controlling, and preventing environmental toxic exposure.

The HUMC’s dehumidifi er’s use of glycol for heat rejection eliminated hundreds of pounds of refrigerant from the center. Compared to refrigerants, glycol is 95 percent less expensive and minimally environmentally-damaging in the event of a leak. Photos courtesy Seresco Technologies

The HUMC’s dehumidifier’s use of glycol for heat rejection eliminated hundreds of pounds of refrigerant from the center. Compared to refrigerants, glycol is 95 percent less expensive and minimally environmentally-damaging in the event of a leak. Photos courtesy Seresco Technologies

Direct-drive plenum fans connect the motor directly to the fan shaft, thus eliminating friction, noise, maintenance, and power transfer ineffi ciencies associated with traditional belt-driven fans. As a result, a direct drive plenum style fan uses considerably less energy.

Direct-drive plenum fans connect the motor directly to the fan shaft, thus eliminating friction, noise, maintenance, and power transfer inefficiencies associated with traditional belt-driven fans. As a result, a direct drive plenum style fan uses considerably less energy.

 

Retrofitting natatoriums
Whether it is an indoor pool for a small hotel or a large community center, specifiers should prepare for the coming deluge of the aforementioned dehumidifiers that will need replacement in the coming years.

A drop-in replacement with today’s technological improvements might appear feasible on paper, but the reality of mechanical room access may not accommodate a machine that is 2.4 x 3 x 9.1 m (8 x 10 x 30 ft) and arrives at the jobsite on a semi-truck flatbed trailer.

This was a situation confronting Ottawa-based consulting engineer firm, Goodkey Weedmark & Associates in nearby Kanata, Ont., during a $500,000-retrofit of the 25-year-old conventional indoor city recreation center into the new Kanata Leisure and Fitness Centre Wave Pool (KLFCWP).

The firm specified one large 2.6 x 3 x 7.3-m (8.5 x 10 x 24-ft) custom-manufactured unit, which was able to fit into a small mechanical room with no shipping door access thanks to a mechanical room’s mezzanine-level large exterior wall outdoor air louver. The dehumidifier manufacturer pre-planned the custom-built unit for breakdown into three 2.4-m (8-ft) long sections for shipping after the factory assembled and tested it under simulated natatorium operating conditions.

Mechanical contractor, T.P. Crawford (Gloucester, Ont.), rigged the three sections through the outdoor air louver, which was enlarged to 2.8 x 3-m (9.1 x 9.8-ft) for more access. The contractor then assembled and installed it inside the mechanical room. The louver’s opening then refitted for a new outdoor air damper/louver to comply with American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 62, Ventilation for Acceptable Indoor Air Quality—the standard’s outdoor air rates that had increased since the original building’s construction in 1986.

Instead of unit breakdown and assembly inside the mechanical room, a less-expensive and more reliable solution for cramped access and space in mechanical rooms has been developed. The solution is modular units designed to fit through 812-mm (32-in.) wide door frames. Once dollied into the mechanical room, the small horizontal footprint modular units are stacked and connections are quickly integrated to operate in tandem. Multiple pairs can equal the capacity of large units, but they consume considerably less floor space of large original dehumidifiers.

While they are mainly a logistics benefit and designed for retrofitting, the redundancy of two compressors, two coils, and two fans also offer energy-efficient staging that the larger unit with one compressor could never achieve. For example, during low-occupancy periods, staging off one of two small compressors instead of operating one large compressor sized for full occupancy can be a significant energy-savings.

Part of a retrofi t that netted the Wulf Recreation Center in Evergreen, Colorado, a 32 percent energy reduction under an energy performance contract, this replacement outdoor air ventilation system saves nearly $5000 in operational costs. Photos courtesy Wulf Recreation Center

Part of a retrofit that netted the Wulf Recreation Center in
Evergreen, Colorado, a 32 percent energy reduction under an energy performance contract, this replacement outdoor air ventilation system
saves nearly $5000 in operational costs. Photos courtesy Wulf Recreation Center

The Wulf Recreation Center’s new outdoor air ventilation system, does not use compressors, but does take advantage of Colorado’s dry, cooler mountainous climate to provide ideal indoor air quality to the pool. The system uses several state-of-the-art technologies including heat recovery, direct drive fans, and an on-board microprocessor controller.

The Wulf Recreation Center’s new outdoor air ventilation system, does not use compressors, but does take advantage of Colorado’s dry, cooler mountainous climate to provide ideal indoor air quality to the pool. The system uses several state-of-the-art technologies including heat recovery, direct drive fans, and an on-board microprocessor controller.

 

 

 

 

 

 

 

 

 

 

 

 

 

Considering outdoor air ventilation systems
Another sustainable consideration for either retrofits or new construction is an OAVS instead of a mechanical dehumidifier; however, the former is only viable in drier, cooler climates, such as mountainous regions or the northern United States. Using outdoor air in these geographical regions can reduce operating costs significantly, versus continually conditioning air with more energy-intensive compressor-based mechanical refrigeration circuits to maintain a natatorium’s desired 82 to 85 F (27.7 to 29.4 C) space temperature and 50 to 60 percent relative humidity (RH).

What make OAVS more conducive today versus a decade ago are many recent technology and control advancements combined with code changes mandating higher minimum amounts of outdoor air for indoor air quality (IAQ) reasons.

For example, today’s technological advancements were one of the reasons energy performance contractor, McKinstry in Seattle, Washington, was able to guarantee a 32-percent reduction as part of the retrofit of the 40-year-old Wulf Recreation Center in Evergreen, Colorado. The 3716-m2 (40,000-sf) center’s $540,000 retrofit—which included lighting, building envelope insulation, and digital controls—is saving the center $18,000 annually. New state-of-the-art indoor pool ventilation garners a significant portion of the savings. The two 6500-cfm outdoor air ventilation replacement systems for the 650-m2 (7000-sf) indoor pool is now saving a minimum of $4995 in operational savings and $12,704 in reduced therms annually, versus the former original gas-fired make-up air system, according to utility bills for the facility and an energy review McKinstry performed as part of its energy performance contract.

Integral to the savings are the two units’ heat recovery, direct drive fans, and an on-board microprocessor controller for pinpoint outdoor air modulation. Unlike the original supply/exhaust system, heat from the space’s exhaust air is now recovered via a glycol run around loop (GRAL) for pre-heating outdoor air. Using heat recovery helps raise outdoor air temperatures from –17.7 to 7.2 C (0 to 45 F) and reduces heating costs significantly.

As the Wulf Recreation Center demonstrates, an OAVS indoor swimming pool environment can be precisely controlled for much of the year, due partly to the technology advancements of outdoor air modulation controls.

While a well-designed OAVS can provide precise space conditions during drier, colder outdoor weather, this approach is not suitable for every facility. This is because there are periods when the space conditions may become warmer and more humid than desired, such as during mild weather and summer. For facilities where this period of time is short, or where the patrons would not mind elevated conditions during the warmer weather as a trade-off to the higher operating costs of running and maintaining a refrigeration circuit, OAVS is definitely a viable, sustainable option.

Whether an indoor pool is a prime candidate for the OAVS approach can be determined by software available from most dehumidifier manufacturers. The software calculates and models the expected space conditions throughout the course of a year, using local weather data input.

The use of outdoor air-modulating controls is another advantage of the new HVAC technology at the Wulf Recreation Center. By monitoring indoor and outdoor air conditions precisely, only the required amount of outdoor air is introduced to maintain the best possible pool space indoor air quality (IAQ), save energy, and comply with codes. Photo courtesy McKinstry

The use of outdoor air-modulating controls is another advantage of the new HVAC technology at the Wulf Recreation Center. By monitoring indoor and outdoor air conditions precisely, only the required amount of outdoor air is introduced to maintain the best possible pool space indoor air quality (IAQ), save energy, and comply with codes. Photo courtesy McKinstry

The dehumidifi er industry has innovated new designs featuring up to 85 percent less refrigerant than a traditional dehumidifi er. Instead of refrigerants and copper piping, the process uses glycol, heat exchangers, and polyvinyl chloride (PVC) piping, which signifi cantly reduces the environmental impact. Photo courtesy Seresco Technologies

The dehumidifier industry has innovated new designs featuring up to 85 percent less refrigerant than a traditional dehumidifier. Instead of refrigerants and copper piping, the process uses glycol, heat exchangers, and polyvinyl chloride (PVC) piping, which significantly reduces the environmental impact. Photo courtesy Seresco Technologies

 

 

 

 

 

 

 

 

 

 

Specifying high technology
The real game-changer in indoor pool HVAC energy savings has come with technology such as exhaust-air heat-recovery, dedicated duty direct drive fans, and microprocessor operational control and monitoring.

Perhaps the most energy-saving air comfort and efficiency development has been the modulating outdoor air control. These controls monitor indoor and outdoor air conditions precisely and introduce only the amount of outdoor air required to maintain the best possible indoor air conditions. Before these precise controls were developed, natatoriums might have provided more outdoor air than needed during ultra-dry winter conditions that resulted in indoor relative humidity (RH) levels dropping too low below the desired 50-percent RH. Low RH levels create an uncomfortable chilling effect on wet skin and also raise operational costs. Bringing in more outdoor air than needed results in more outside air and pool water heating requirements.

Another option is pool water heating via heat recovery from the refrigeration circuit’s compressors. However, the ‘free’ pool water heating option is sometimes omitted during product specification, especially in value engineering requests. It is also sometimes missed during contractor installation.

There are dozens of dehumidifiers currently operating in natatoriums throughout North America where this energy-saving feature is mistakenly bypassed unbeknownst to the building owner. Consequently, the facility needlessly pays for pool water heating via a separate conventional gas-fired or electric pool water heater originally intended to back-up the dehumidifier’s pool water heating or expedite it during a dump-and-fill.

Selecting a mechanical dehumidifier with pool water heating through heat recovery might raise the upfront capital cost, but the benefit over the long-term will result in thousands of dollars saved in energy costs, depending on the facility size.

ASHRAE 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, has taken the energy recovery requirement a step further by mandating heat recovery or a pool cover. Many states have adopted the standard into local code requirements.

ASHRAE 90.1 calls for a pool cover for commercial indoor pools using conventional pool heaters unless “over 60 percent of the energy for heating comes from site-recovered energy.” The pool water heating option for a compressorized unit easily satisfies this requirement, but could also help satisfy a local code requirement and help eliminate the need for a pool cover.

Using exhaust air to pre-heat outdoor air
ASHRAE 62, Standards for Ventilation and Indoor Air Quality, recommends all commercial buildings bring a prescribed percentage of outdoor air as mandated by local building codes.

For the northern United States and Canadian indoor pools, wintertime heating of cold outdoor air to at least 26 C (80 F) to match the pool air temperature is costly. Fortunately for natatorium operators, their facilities’ humid and warm exhaust air is extremely energy rich and ideal for energy recovery. This recovered energy can be used to preheat the code-required outdoor air via heat-exchangers.

Preheating outdoor air using recovered heat from the exhaust air can cut outdoor air-heating costs by 50 to 75 percent. The payback for this kind of pool dehumidifier option is often only a few months (and rarely more than a few years), which makes it a cost-effective investment.

Remotely located exhaust fans can also be outfitted with heat transfer coils piped to the dehumidifier. Natatorium exhaust air is an energy source specifiers and operators should always consider for heat recovery. Aging dehumidifiers manufactured before this feature was available should be reviewed for a more energy-efficient replacement.

Direct drive plenum fans with VFD
Another example of a new energy savings technology is the introduction of dedicated duty direct-drive plenum fans with variable frequency drives (VFD). These plenum fans are a different style of fan that delivers air more efficiently than the traditional centrifugal-style typically seen in traditional dehumidifiers.

Compared to traditional belt-driven fans, a direct-drive plenum fan with a VFD can amount to as much as 15 percent in fan motor energy reduction. Considering a pool dehumidifier’s fans typically operate 24/7, the savings over the equipment’s lifecycle can be significant. The payback is instantaneous since direct-drive plenum fans with VFDs have comparable price to belt-driven systems.

Unlike belt-driven fans, the direct-drive concept connects the motor directly to the fan shaft. Thus, it eliminates friction, noise, maintenance, and power-transfer inefficiencies associated with belt drives.

Remote monitoring
All the aforementioned energy-saving technologies are worthless unless they stay well-tuned, maintained, and monitored. Unmonitored systems can limp along well below their intended optimal operating conditions, unbeknownst to the building owner.

Some dehumidifier manufacturers have solved this dilemma with the development of on-board monitor/control microprocessors that can send the entire unit’s vital operating statistics to the factory via the Internet. These programs sometimes offer a free daily monitoring service and even have smartphone applications where an authorized user can get e-mail alerts or access a unit from anywhere. The manufacturer can alert the facility manager of any issues and help the local service contractor troubleshoot, set up, or adjust the unit to ensure optimal performance. In the event of an alarm, troubleshooting can be assisted by a factory engineer, which ensures a quick resolution to any problem.

Conclusion
Many of the aforementioned advancements in indoor pool dehumidification over the past decade are manufacturers’ catalog items, but they also must be understood and specified by the consulting engineers and contractors. Once the building is operating, specifiers as well as building owners can rest assured the facility is operating at an optimal efficiency and is using the least amount of energy possible in providing IAQ.

Ralph Kittler, PE, is a co-founder and vice president of sales/marketing at Seresco Technologies, an Ottawa-based manufacturer of conventional and reduced-refrigerant natatorium dehumidifiers, and outdoor air ventilation system natatorium HVAC systems. He has 24 years of experience in the HVAC industry and a degree in mechanical engineering from Lakehead University (Thunder Bay, Ont.). Kittler is an American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) Distinguished Lecturer and sits on the association’s Technical Committee 9.8 and 8.10. He can be reached via e-mail at ralphkittler@serescodehumidifiers.com.

Avoiding Problems in Aquatics Facilities: Atypical design for atypical buildings

Photo © BigStockPhoto/Nikita Sobolkov

Photo © BigStockPhoto/Nikita Sobolkov

by Jason S. Der Ananian, PE, and Sean M. O’Brien, PE, LEED AP

If an office building in a cold climate is designed to run at a slight positive pressure while omitting air barrier details at the building enclosure, the likely consequences include higher energy costs and potentially isolated condensation events or freezing pipes during very cold weather, with problems developing in five to 10 years. If this was a natatorium, however, the resulting damage may include human-sized icicles at roof eaves, concealed corrosion of metal framing components, widespread efflorescence on exterior concrete and masonry, and premature failure of the building enclosure components—often within months.

Few, if any, building types present the risks and challenges found in indoor swimming pool facilities. With far higher interior moisture loads than typical buildings and a potentially corrosive interior environment, natatoriums put structural and enclosure systems to the test, especially in cold or even mixed climates.

The authors’ firm has investigated dozens of natatoriums throughout the country and witnessed firsthand the swift and severe nature of failures that can result from improper design and construction. In some cases, the design included the primary components necessary for moisture control, but lacked transition details or did not adequately define the system’s continuity. Others were well-designed but poorly constructed, or poorly designed but built exactly as shown on the drawings. Still others may have functioned well from an enclosure standpoint, if not for significant shortcomings in the mechanical systems’ design or operation.

The watercube—Beijing's National Aquatic Center—may be an extreme example, but even the most basic of natatoriums can present challenges for design professionals when it comes to thermal and moisture control. Photo © BigStockPhoto/Liang Zhang

The watercube—Beijing’s National Aquatic Center—may be an extreme example, but even the most basic of natatoriums can present challenges for design professionals when it comes to thermal and moisture control. Photo © BigStockPhoto/Liang Zhang

Problems are often found in natatoriums that are part of a larger athletic complex where designers fail to make the distinction between ‘typical’ enclosure systems and more specialized systems required for pools, or fail to prevent moisture migration between the pool and adjacent spaces.

Moisture loads and controls in natatoriums
The air in a natatorium often contains nearly three times the moisture per unit volume as a typical, non-humidified building. This greatly increases the importance of controlling moisture transport through the building enclosure. Typically, three forms of moisture transportation can contribute to problems:

  • water leakage;
  • water vapor diffusion; and
  • airflow.

Water leakage, which occurs when water finds a path into the building, is controlled through water management and waterproofing systems that are beyond this article’s scope. Water vapor diffusion, or the movement of water vapor driven by vapor pressure differentials, is typically a slow process that can result in long-term moisture accumulation or condensation within the building enclosure cavities; it is controlled by a vapor retarder.

Airflow is the main contributor to water vapor and heat transport in the enclosures of most buildings. Unless it is controlled by an effective air barrier system, air will flow through the building enclosure cavities where it can condense on cooler surfaces as it travels toward the exterior.

Although critical for moisture control in natatoriums, non-humidified buildings can often provide moderate (although not necessarily optimal) performance and avoid condensation without air barriers in the enclosure, and vapor retarders may only be necessary in extremely cold climates. This is reflected in most building codes, which, until recently, made no mention of continuous air barriers and often do not require vapor barriers in warm or moderate climates (Climate Zones 1 through 4, as defined in American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings.

However, it is important to realize the building code is intended for non-humidified/‘general-use’ buildings, and does not specifically cover special buildings such as natatoriums and museums—both of which require atypical interior conditions. The authors’ firm has investigated many natatoriums that complied with building enclosure requirements outlined in the applicable building code, yet still suffered from significant moisture problems. Relying solely on the building code for design guidance is unlikely to result in a durable, functional natatorium.

CS_DECEMBER_2013.indd

Air and vapor flow through natatorium enclosures
High moisture levels in natatorium environments greatly increase the risk of interior surface condensation on cold components, such as windows, doors, roof penetrations, and drains. These conditions also provide an ideal environment for condensation to collect within walls and roofs due to air leakage and vapor diffusion.

Humid air from natatorium spaces that migrates into the exterior walls condense once reaching a surface below the air’s dewpoint temperature. Condensation concealed within wall or roof assemblies may go unnoticed by the building owner until these assemblies are severely degraded. For a natatorium in cold climates, the risk of condensation exists for most of the year, often eight to 10 months. Moisture levels can be significantly reduced by covering the pool when swimmers are not present, but problems may still occur when the natatorium is actively being used.

A properly designed natatorium building should include both a vapor retarder and, more importantly, a continuous air barrier system in the walls and roofs to minimize moisture migration through the enclosure (they may or may not be formed from the same material). Although the terms ‘vapor barrier’ and ‘air barrier’ are often used interchangeably, the two systems have differences in the way they control moisture and the construction necessary for them to be effective. Figure 1 highlights these differences.

Controlling air and vapor flow
Vapor retarders minimize water vapor’s flow through materials by diffusion. Water vapor can flow through the internal pore structure of apparently solid materials such as wood, concrete, and gypsum board. If the air within a building has higher moisture content than the exterior environment, the vapor drive is toward the exterior, tending to ‘push’ water vapor from the inside to the outside.

In cold and mixed climates, this water vapor may condense within the wall or roof as the temperature drops. In this case, a vapor retarder on the interior—or ‘warm’—side of the insulation helps prevent water vapor from reaching colder temperatures, minimizing the risk of condensation in the wall. Conversely, a vapor retarder on the wrong side of the wall, outboard of the primary insulation where it experiences low temperatures, can act as a collection point for condensation and lead to more significant problems than if no vapor retarder was installed. Since the driving force behind water vapor diffusion is relatively minimal, vapor barriers can contain small holes, such as fastener penetrations, and do not require sealed laps to be effective. Even if larger discontinuities exist, damage due to moisture migration in these areas will tend to be localized.

Tracer smoke exfiltration at roof eave. Images courtesy SGH

Tracer smoke exfiltration at roof eave. Images courtesy SGH

Moving air carries both heat and moisture. The magnitude of moisture migration via airflow can be 50 to 100 times that associated with water vapor diffusion alone. Air flows from high to low pressure regions. In buildings, such differentials can result from mechanical system operation, wind, stack effect, or a combination thereof. These pressure differences can exert significant force on air barrier systems, making it necessary for air barriers to have continuous structural support. Even small holes or discontinuities in the air barrier can allow significant air leakage and greatly reduce the system’s effectiveness, especially in buildings with high moisture levels. Complicating matters, a small hole on the interior can lead to air leakage into many other locations, as opposed to creating localized damage as with discontinuous vapor retarders.

The air barrier in a building is more than just a single material. It comprises interconnected components including airtight materials in walls, roofs, doors, windows, curtain walls, and other enclosure elements. To maintain the system’s continuity, airtight transitions are needed between all components, including interior partitions separating the natatorium from adjacent spaces.

The goal of a well-designed and properly installed air barrier is to eliminate uncontrolled airflow through the building enclosure. Uncontrolled airflow results in increased heating and cooling loads; it can also transport moisture or chlorinated air to areas where moisture or odor exposure is undesirable. Critical transitions, such as the roof-to-wall intersection, must be carefully detailed, as poor transitions can greatly reduce air barrier performance and mechanical system effectiveness in controlling building pressure.

The air barrier’s construction is just as important as its design. Success requires coordination between multiple trades at multiple points in the schedule, such as roof-to-wall intersections and window/curtain wall perimeters. Designers must take into account the potential for sequencing conflicts during construction.

Interior partitions that separate interior high-humidity zones from adjacent, non-humidified or even unconditioned interior zones are an oft-overlooked component of the natatorium air barrier system. Natatoriums are commonly part of a larger complex of buildings. Since spaces like offices, storage rooms, and gymnasiums are not usually designed to function under high-humidity conditions, moisture-laden airflow into those spaces through unsealed interior partition walls may lead to significant damage to interior components. Additionally, leakage into adjacent spaces may cause damage to exterior components, if those spaces are located near exterior walls not designed to tolerate high humidity.

Even in the absence of condensation, airflow to and from adjacent spaces can also minimize the mechanical system’s ability to control air pressure within the natatorium (discussed in more detail later in this article). Unless a space is specifically designed to tolerate high humidity, it must be completely air-sealed and isolated from any adjacent spaces that may function as moisture sources.

Natatorium investigation reports reviewed by the authors’ firm almost always cite “improper design/construction of the vapor retarder” as a primary cause of moisture problems. However, in natatoriums, even the absence of a vapor retarder rarely produces the same level of damage as an improperly designed/built air barrier system. This common confusion between air barriers and vapor retarders often results in poorly designed natatoriums and short-term failure of building enclosures.

Controlling interior surface condensation
Interior moisture levels in natatoriums are high, with dewpoint temperatures ranging between 12.8 and 18.3 C (55 and 65 F). Natatoriums in cold (and even mild) climates are susceptible to condensation on interior surfaces that drop below the ambient dewpoint during the winter. As such, interior surfaces in natatoriums must be kept warm, often as high as 18.3 C, to prevent condensation.

This infrared image of an exterior natatorium wall was taken during the winter in a heating climate. The orange/yellow regions indicate higher apparent surface temperatures and locations of air barrier breaches.

This infrared image of an exterior natatorium wall was taken during the winter in a heating climate. The orange/yellow regions indicate higher apparent surface temperatures and locations of air barrier breaches.

Opaque walls and roofs can typically be designed with continuous insulation and high R-values to meet this criterion. Windows, doors, and curtain walls must be high-performance thermally broken systems designed for high-humidity applications, although even the best fenestration likely experiences surface condensation or frost during the coldest times of the year.

Surface condensation can degrade adjacent construction materials and cause ‘fogging’ on glass surfaces. Several design strategies are effective at reducing the risk of interior surface condensation, including:

  • using high-performance fenestration systems;
  • aligning fenestration systems with the insulation;
  • avoiding installing highly conductive materials against fenestration; and
  • providing air curtains or directed flows of warm air over components or using electric heat-trace cables to deliver supplemental heat directly to glazing and framing systems (often the only way to completely eliminate condensation in cold-climate natatoriums).

Unlike ‘passive’ condensation control systems, such as thermally broken window frames, mechanical and electrical systems require regular maintenance to remain operational.

Natatoriums often include skylights to provide occupants with natural light. The increased condensation risk at skylights is due in part to their orientation; mounted in low-slope roofs or near-horizontal applications, skylights tend to lose more heat through radiation to the sky compared to similarly sized windows and doors (especially at night).

Supplemental heating systems can be difficult to install due to the high visibility of skylight systems. A compromise would be to design a high-performance skylight and install a system of gutters around the perimeter, ensuring any condensation is collected and drained (rather than dropping from the ceiling onto occupants). For gutters to be effective, skylights should be fairly steep in slope so condensing moisture flows down the glass surface to the sill gutters, rather than dripping into the space as can occur in low-slope skylights. The maintenance and cleaning of active condensation control or weep systems can be difficult, particularly on skylights located directly above the pool(s).

The photo illustrates the blower door test setup for quantitative air leakage testing with calibrated fans. These blower doors are also used for imposing pressure differential for qualitative testing.

The photo illustrates the blower door test setup for quantitative air leakage testing with calibrated fans. These blower doors are also used for imposing pressure differential for qualitative testing.

Natatorium air pressure control
It is impractical to achieve a perfectly airtight enclosure, and even small amounts of air leakage can result in condensation. Therefore, natatoriums must be maintained at a negative pressure relative to adjacent interior spaces and the exterior to minimize odor migration and potential for airflow-induced condensation in building enclosure cavities during winter. The 2011 ASHRAE Handbook–HVAC Applications recommends maintaining a negative pressure of between 12 and 37 Pa (0.25 and 0.77 psf) in the natatorium to minimize moisture and odor migration.

Interior partition wall openings, including doors, require gaskets to allow the HVAC to more efficiently control building pressures. Maintaining a negative pressure in the natatorium commonly involves balancing the mechanical system to return more air than is supplied into the building while maintaining the minimum required outdoor airflow rate per ASHRAE Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality.

It is important to understand simply providing more exhaust air than outside air is not sufficient to maintain negative pressure. Even with no outside air and significant exhaust flow, if the quantity of air supplied to the natatorium exceeds the amount returned (due to improperly sized or restricted ductwork, the operation of mechanical systems in adjacent spaces, etc.) the natatorium pressure will still be positive.

The HVAC system’s ability to control building pressure relies heavily on the airtightness of the natatorium enclosure. Controlling building pressures in a ‘leaky’ natatorium is difficult compared to a relatively airtight one. For these reasons, testing and balancing of the natatorium HVAC system should occur following the air barrier system’s completion.

Depending on the climate zone in which the natatorium is located, supplemental exhaust fans may also be necessary to maintain pressure control during the coldest times of year, particularly for facilities with high ceilings or in retrofit applications where the existing mechanical system cannot be practically or appropriately modified.

In cold climates, even with a properly balanced natatorium mechanical system, positive pressure may occur near the ceiling due to stack pressure (i.e. buoyancy of air). The authors often find natatoriums running ‘under negative pressure,’ where the slight differential at the pool deck level is insufficient to overcome stack pressure, allowing for high pressures and significant air exfiltration at the roof level where critical details such as roof-wall intersections often occur.

The supplemental exhaust fan (or even the primary mechanical system fan[s]) is best controlled by a pressure sensor located near the pool ceiling that time-averages the pressure differential between the interior and exterior; a control system speeds up or slows down the exhaust fan accordingly to maintain a zero pressure difference between inside and out. Similarly, pressure should be measured near the high point of the natatorium during testing and balancing of the mechanical systems—preferably during cold weather—to

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obtain a more accurate measure of pressure within the space.

Construction mockups of air barrier systems
Construction mockups are typically required for projects to verify both aesthetic and technical aspects of the design. As part of this project phase, mockups of the air barrier should include typical transitions (e.g. wall-to-fenestration, wall-to-roof, etc.) for review by the architect or third-party inspector. This work shall be used to:

  • test installation methods;
  • determine construction defects (if any);
  • establish the technical and aesthetic standard of care for the project; and
  • refine, if necessary, installation methods in accordance with the design intent before construction proceeds.

Mockups are also helpful for coordinating between trades.

The mockups should be performed as many times as necessary for approval by the architect and/or third-party inspector. Inspection of the air barrier should not be pushed to the punch list phase—testing of air barrier mockups should be performed before cladding installation to ease identifying and repairing of breaches.

Field testing of air barrier continuity
Performing whole building air infiltration testing can help verify the performance of air barrier installations as well as locate system defects in new and existing buildings. Several agencies and state building codes even require whole building air infiltration testing for new buildings. It is prudent to perform testing before the air barrier system is concealed by cladding materials or interior finishes so defects can be identified and repaired more easily. Removing cladding after construction is complete to locate air barrier discontinuities is often costly and disruptive to building occupants.

This poorly painted steel diving platform stair experienced heavy corrosion due to direct wetting.

This poorly painted steel diving platform stair experienced heavy corrosion due to direct wetting.

Field testing requires the building be positively or negatively pressurized using blower door fans or manipulating the HVAC system to force air to leak through any air barrier discontinuities in the building enclosure. Various quantitative and qualitative techniques are available to identify leakage paths, including tracer smoke and infrared (IR) thermography. The architect should write the field testing requirements of air barriers into the project specifications.

Qualitative air leakage testing
ASTM E1186, Standard Practices for Air Leakage Site Detection in Building Envelopes and Air Barrier Systems, describes various qualitative methods to locate air barrier discontinuities. One such practice is to pressurize or depressurize the building or individual spaces by using fans or by manipulating the HVAC system, and then using a tracer smoke source over the interior or exterior surfaces of the building enclosure.

Placing the tracer smoke source at the building interior and pressurizing the building or space to locate air exfiltration sites reduces the influence of wind or stack effect. In this case, tracer smoke will be ‘pushed’ from the building through any breaches in the air barrier and be identifiable at the building exterior (Figure 2).

Although it is possible for some projects to depressurize the building and locate the source of tracer smoke on the exterior, this method may be difficult because of the influence of wind and the risk tracer smoke rapidly dissipates before it is drawn into the interior through the air leakage site.

IR thermography (per ASTM E1186) is another useful and efficient qualitative method to locate discontinuities in the air barrier. The purpose of the IR scans is to identify locations of elevated heat loss through the building enclosure. Air infiltration or exfiltration through the building enclosure affects the temperature of wall or roof components in the region of air leakage pathways, given the interior and exterior temperature difference; IR scanning equipment can be used to detect local surface temperature differences (Figure 3).

The conditions most conducive to accurate IR scans are low winds with a large temperature difference (at least 16 C [30 F]) between the interior and exterior air temperatures. Using fans or the HVAC system to pressurize or depressurize the building during the IR scans can exacerbate air leakage through discontinuities in the air barrier, making it easier to identify air barrier breaches on an IR image. Since thermal bridges or insulation discontinuities in the enclosure can also result in surface temperature differentials, it is typically necessary to perform multiple scans—from both the interior and exterior, and with the building under positive and negative pressure—to isolate the contribution of thermal bridges and more accurately identify air leakage sites.

Quantitative air leakage testing
Blower door testing per ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization, is intended to characterize the airtightness of the building enclosure. The test results can be used to compare the subject’s airtightness to similar buildings or against criteria set by industry standards and governing building codes; it can also be used to determine how readily the HVAC system can be adjusted to control pressure and reduce leakage. The tests are conducted using calibrated fans (Figure 4) to pressurize or depressurize the building under controlled conditions.

The ASTM E779 test procedure typically requires a range of induced pressure difference (pressurization and depressurization) from 10 to 60 Pa (0.2 to 1.25 psf). The measured air leakage flow rates (cubic feet per minute) are typically normalized using the above-grade building surface area (walls and roof) and calculated as an air leakage rate at 75 Pa (0.3 in. water column) pressure difference.

While quantitative testing is useful from an overall performance standpoint, a qualitative leak assessment should always be done in natatoriums due to the potential for condensation problems even at small leakage sites. On the same note, when the building is extremely airtight, but experiences all the leakage at one large air barrier breach in the enclosure, identifying the location of that breach is critical.

compounds.

Corrosion on painted structural steel can be caused due to exposure to airborne chlorine compounds.

Corrosion issues
Although some pools have begun to employ alternative technologies to treat pool water, such as ozone or ultraviolet sterilization, the majority of swimming pools still use chlorine-based chemicals for pool water treatment. This is primarily due to the higher initial cost of alternative treatment systems, but also the entrenched nature of chlorination as a means of water treatment, which has been in use for more than a century. While an effective disinfectant, chlorine has the unfortunate side effect of being highly corrosive to typical steels and even some stainless steel alloys.

The most common form of corrosion in natatoriums is visible surface corrosion, which affects bare steel or steel with insufficient corrosion protection. This can affect both materials which are directly exposed to pool water (Figure 5) and those which have no direct wetting and are affected by the chlorine compounds in the air only (Figure 6). In both cases, corrosion can be greatly exacerbated by improper maintenance of the pool water chemistry, which can result in higher levels of chlorine compounds in both the water and air.

Stainless steels are often used in swimming pools to combat corrosion, but even these specialty metals have their limitations—especially in chlorinated environments. Common alloys such as Types 304 and 316 can work well in areas where the components are frequently cleaned or wetted/splashed, as this tends to prevent chloride compound buildup on surfaces.

Infrequently cleaned surfaces may corrode quickly once a film of chlorides builds up on their surfaces (Figure 7). This is counterintuitive to many designers, since a stainless steel component that never comes into contact with pool water would, at first glance, appear to have little risk of corrosion. Stainless steel ductwork (often specified due to its perceived superior corrosion resistance) is one of the most commonly corroded items, but stainless steel light fixtures or hangers are also at risk.

Some stainless steel components are also susceptible to the more dangerous stress corrosion cracking (SCC). This type of corrosion often produces little to no outward evidence; rather, it affects the steel’s structure, leading to sudden, brittle failure. For SCC to occur, a susceptible grade of stainless steel (most standard chromium-nickel stainless steels, such as Types 304 and 316, fall into this category) must be placed in a corrosive environment and subjected to a tensile load. Hanger rods for overhead components are the most commonly affected, although other formed metal components, which can contain residual tensile stresses from forming operations, can also fail due to SCC.

There have been several examples of structural failures due to SCC in natatoriums, including ceiling collapses in:

An example of the heavy corrosion of stainless steel ductwork that can occur in a 10-year old natatorium.

An example of the heavy corrosion of stainless steel ductwork that can occur in a 10-year old natatorium.

  • Switzerland (1985), due to failure of stainless steel hangers (resulting in 12 reported casualties);
  • Netherlands (2001), due to failure of stainless fasteners; and
  • Finland (2003), due to failed stainless steel hangers.

This risk means using stainless steel in overhead or safety-critical components must be carefully evaluated. In these cases, specialty alloys such as those containing higher levels of nickel and molybdenum (e.g. Types 904L and 254 SMO), which are more resistant to SCC, are likely necessary.1

Although stainless steels tend to be more expensive than painted steel or aluminum, the higher initial cost is typically justified by reduced long-term costs associated with maintenance, repair, or replacement. This is especially true for components at or near the pool deck which are routinely wetted. Most other metals, even those painted or galvanized, will have greatly reduced service lives in these applications.

For larger structural applications, stainless steel is not practical in terms of cost and availability. In these applications, high-performance paints/coatings—often combined with galvanization—are required for long-term performance. As shown in Figure 7, breakdown of applied paints can result in rapid corrosion of the base metal. Even with high-performance coatings, owners should expect some maintenance and eventual recoating of steel components.

Summary of design strategies
Based on the discussion in this article and personal experience in the design, construction, and investigation of natatoriums, the authors present the following summary of design guidelines for indoor swimming pools. (This is not an exhaustive list of all design concerns, but focuses on primary issues with the building enclosure and interior environment.)

  1. Design a continuous air barrier system for the exterior enclosure, including exterior and interior components that separate the natatorium from adjacent spaces.
  2. Design continuous insulation for the enclosure and minimize the incidence of thermal bridges and structural penetrations through the insulation.
  3. Design an appropriate vapor retarder for the enclosure. This can be the same material as the air barrier, depending on the insulation’s location.
  4. Use high-performance fenestration systems aligned with the thermal insulation, combined with active systems such as warm air washes, to minimize the incidence of interior condensation.
  5. Balance mechanical systems to provide negative air pressure within the natatorium for the full height of the space, not just at the pool deck level. Negative pressure levels must be sufficient (or adjustable) to overcome stack pressure down to the local exterior design temperature. Ductwork should be carefully designed and systems balanced/confirmed before filling of the pool. Confirm, through a testing and balancing report, that the airflow into the pool space is less than the airflow back to the mechanical system. Confirm space pressures by direct measurement in addition to measuring supply/return quantities.
  6. Avoid using stainless steel in applications that are deemed ‘safety-critical’ or where components will not be frequently wetted or cleaned. When stainless steel is employed for safety-critical or overhead applications, a specialty alloy is likely necessary.
  7. Avoid specifying stainless steel for ductwork. Non-corrodible fabric ductwork, painted aluminum, or painted galvanized steel are typically better options.
  8. Write tight specifications for air barrier systems, including provisions for field testing of mockups, installed assemblies, and the whole building enclosure. Testing should include both quantitative and (concurrent) qualitative methods to identify overall leakage rates as well as localized breaches in the air barrier system.

Notes
1 For more information, visit www.nickelinstitute.org/NickelUseInSociety/MaterialsSelectionAndUse/~/media/Files/NickelUseInSociety/Architecture/Successful_Stainless_Swimming_Pool_Design.ashx. (back to top)

Sean M. O’Brien, PE, LEED AP, is an associate principal at the national engineering firm Simpson Gumpertz & Heger (SGH), specializing in building science and building enclosure design and analysis. He is involved in both investigation/forensic and new design projects. O’Brien is a member of the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE), co-chair of the New York City Building Enclosure Council (BEC-NY), and a frequent speaker and author on topics ranging from building enclosure design to energy efficiency. He can be reached at smobrien@sgh.com.

Jason S. Der Ananian, PE, is a senior staff engineer at SGH, specializing in building enclosure design and building science. Der Ananian has more than a decade of experience investigating and designing repairs for art storage facilities, natatoriums, museums, and university facilities. A member of ASHRAE, he has published papers on topics including window flashing, whole-building energy simulation tools, and moisture migration in asphalt shingle roofs, along with quality control of air barriers during construction. Der Ananian can be contacted via e-mail at jsderananian@sgh.com.