Common facility operational issues are often blamed on the dehumidifier

by Sally Bouorm | August 1, 2013 10:14 am

[1]

By Ralph Kittler

Canada has thousands of indoor swimming pools. Unfortunately, many of them are more problematic than facility operators would like to admit. Too often, the pool’s dehumidifier is blamed and the real cause of a natatorium problem is never discovered nor addressed. Chlorine odours, mould, condensation, or poor indoor air comfort, generally have causes unrelated to the dehumidifier. Instead, they may be due to building pressurization imbalances, improper vapour barrier, poor ventilation design, unbalanced water chemistry, or unsuitable architectural materials. They can also be related to inadequate maintenance, or perhaps just a slow, unnoticed degradation of operating parameters. Additionally, a few seemingly minor items missed during design and construction can also contribute to facility problems. Natatoriums have many unique design challenges and considerations that are not always obvious to anyone unsure about these facilities’ state-of-the-art requirements.

Without having an engineering background, one of the difficulties facility operators face is finding the true source of the problem, especially if there has been a long, gradual downward performance spiral. Some problems take a while to manifest and are not apparent until environmental conditions become unbearable or a visible deterioration occurs.

Chlorine odours can be a red flag

Any hint of chlorine odours in the facility’s non-pool areas is an indication of an undesirable, but easily corrected, building pressurization problem. Additionally, odours in adjacent spaces signal a natatorium air-side pressurization malfunction.

Under the guidelines of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE[2]) standards for natatoriums, indoor pools are purposely designed with a slight negative building pressure. Negative pressure is created by exhausting more air than what is being introduced to satisfy the local code requirements for outdoor ventilation air.

Negative pressure (exhaust air) is also important because it ensures there is always some natatorium air, presumably containing some pool chemicals, being exhausted so it can be replaced with fresh outdoor air. This continuous dilution of the airborne chemicals helps ensure the best indoor air quality (IAQ) possible.

[3]

However, facility chloramine problems will generally not fully resolve the airborne chemical challenge with this ventilation approach alone as the source might be an underlying water chemistry problem. Further, trying to solve IAQ problems derived from water chemistry issues can be expensive in terms of conditioning excessive amounts of outdoor air. An appropriate balance of outdoor air and exhaust, to keep proper negative pressure, should be all that is necessary for proper IAQ if water chemistry is properly maintained. Persistent chloramine problems have a better chance at being resolved using water sanitation alternatives such as ultraviolet (UV) irradiation, sorghum moss, or a deck-level air capture exhaust system.

Since negative pressure is critical for indoor pools, heating, ventilation, and air conditioning (HVAC) engineers ensure it is accomplished by specifying one or more exhaust fans in the ventilation system. The exhaust fan might be packaged with the dehumidifier, or mounted separately. Building operators should know where the exhaust fans are located.

Chlorine odours and eye irritation in the pool, or in non-pool areas, likely signifies a building pressurization problem, if pool chemistry and daily bather loads have not dramatically changed. In this case, the exhaust fan should be checked first. It may not be working properly or its original rating configuration (i.e. capacity to move air in cubic feet per minute [CFM]) has been changed. All it takes is one person fiddling with the exhaust fan or outside air dampers to create an imbalance of exhaust or outside air that leads to IAQ problems.

For example, a facility with a long history of chlorine odour problems in the pool area might have had someone decide that more outdoor air was needed to resolve the issue. Therefore, they open the outdoor air damper more and unbalance the entire system by creating a positive pressure environment. The IAQ problem remains unresolved and new complaints inevitably arise about pool odours residing in the facility’s other rooms.

As such, it is highly recommended that facility operators develop a solid understanding of the overall ventilation system’s air pattern. Equally important is the facility’s amount of outside ventilation air and exhaust air balance, which will not cure deck-level IAQ issues if the ventilation system is not delivering good quality air to the breathing zone. Therefore, some air delivery modifications might make a significant difference.

Vapour barriers

Another misdiagnosed problem incorrectly associated with the dehumidifier is condensation on or inside a building structure. Instead, vapour barriers (i.e. vapour retarders)—a ubiquitous plastic sheeting that envelopes the entire pool room—could be to blame.

[4]

Indoor pools are warm environments with 50 to 60 per cent relative humidity (RH). This environment has a high pressure relative to the outdoors and cold weather. The vapour barrier is akin to a balloon keeping moisture contained in the environment. A well-sealed building with a good vapour barrier is a critical factor in preventing moisture penetration into the walls and roof. A vapour barrier that is not tight, due to a tear, allows moisture to migrate toward the low pressure of the outdoors. It is the contractor’s responsibility to install the vapour barrier undamaged and per the architect’s specifications. An improperly sealed or torn vapour barrier can allow moisture into areas where it will eventually damage the building envelope or even its infrastructure.

Further, condensation migration in subfreezing climates could produce ice on a natatorium’s exterior wall or roof, which is a serious issue that should be addressed immediately.

Condensation issues

Some facility managers accept natatorium condensation as an inherent nuisance of indoor pools. However, condensation is not acceptable on windows or walls and is many times mistakenly blamed on the dehumidifier.

Condensation can still occur at 30 or 40 per cent indoor RH levels. Window condensation typically points toward an air distribution problem; whereas wall condensation indicates the insulation is deficient or its R-value (i.e. its measure of thermal resistance) is too low. Wall condensation is the more serious problem of the two, as any amount of condensation must be addressed immediately to avoid serious building structure deterioration.

Condensation is predictable

Surfaces colder than the ambient dew point temperature will experience condensation, much like a cold can of soda on a summer day. Likewise, indoor pools typically have a high dew point temperature. For example, a 27.7 C (82 F) plus 50 per cent RH will produce a 16.6 C (62 F) dew point temperature. Windows and skylights are notorious for condensation because their low insulating R-values maintain a cold surface.

[5]

Architects and owners love a lot of windows in indoor pools, which should not pose a problem as long as designers understand the need to distribute proper airflow across their surfaces. Warming the window above the dew point temperature with air distribution eliminates condensation. Therefore, it is the HVAC engineer’s responsibility to assure every square inch of window space receives ample supply air.

[6]

Overhead or under-deck ventilation ductwork should span the entire width of windows. A common architectural mistake is the specification of windows with mullions that jut out on the interior rather than the exterior. Interior mullions block air flow across the entire window surface.

There are some control strategies that measure the inside surface temperature of the exterior window. As the window gets colder, the control activates more dehumidification to lower the space’s RH. This strategy drives up energy costs significantly and is ineffective in extremely cold climates. Dew points cannot be lowered enough in cold climates for this strategy to be effective. As such, the answer is effective air distribution across the window.

Spectator air comfort

Spectator air comfort complaints are common in facilities that host swim events. Swimmers feel comfortable in 27.7 C (82 F) space temperatures because they are wet and in bathing suits; however, fully clothed spectators will be uncomfortable at these conditions.

Facility managers that attempt to accommodate spectators by decreasing the space temperature and/or RH levels will trigger unintended consequences. If the dehumidification system was sized and designed to operate at swim event conditioning, deviating from its design temperature will increase the pool’s evaporation rate, which in turn increases energy use and RH. The system simply may not be able to maintain the swim event set points and the environment will be more humid and uncomfortable.

Natatoriums are typically designed to operate at a two-degree temperature differential (between space and water temperatures), such as 27.7 C (82 F) and 26.6 C (80 F), respectively. Therefore, lowering the space temperature by simply two degrees increases the load on the dehumidifier by 35 per cent. As a result, many of today’s natatoriums are being designed with separate systems for the spectator and pool areas.

Although both spaces co-exist, it is possible to create a small microclimate at a lower temperature and RH level in the spectator area. For older pools, retrofitting the spectator section with a separate dehumidifier and supply duct system can provide a resolution to complaints as well as possibly a quick payback in energy savings.

Dehumidifier operation

RH levels above 60 per cent are another indication the natatorium is not operating properly and typically points to two problems:

1. The facility is being operated at conditions for which it was not designed.
2. The dehumidifier is not operating optimally.

There are many instances where a facility operates its space and water temperatures differently from its original design. Facility managers should know the system’s design operating parameters and what type of dehumidifier/ventilation unit the facility has so operation expectations will be realistic. A traditional compressor-based dehumidifier should maintain a 60 per cent or lower RH and a stable space temperature year-round.

A ventilation-only style system, without compressors and a refrigeration cycle, should keep the space RH levels and temperature under control during cooler weather by utilizing drier, outdoor air. However, as outdoor temperatures get warmer, the ventilation-only system can only provide temperatures that are available outdoors.

Most designers typically adhere to the aforementioned two-degree operating differential recommendation. If engineering records or owner’s manuals are not available, the engineer (or company) of record that specified the dehumidifier should be able to provide details on the system installed and the operating conditions for which the facility was designed. Then, both space and water temperatures, as well as the RH can be confirmed with the readouts from the building automation system (BAS), or from the dehumidifier’s onboard or remote monitor.

Owners and operators are also recommended to take an active role in the design of a new facility to ensure the correct operating conditions are met. For instance, a swim event might demand a 26.6 C (80 F) and 25.5 C (78 F) air and water temperature differential, but a facility might also want the flexibility of providing elderly patrons with 31.1 C (88 F) water during an ‘Aqua Fit’ program. A dehumidifier sized and selected solely for family swimming in 27.7 C (82 F) and 26.6 C (80 F) space and water temperatures should not be expected to automatically have the capacity to accommodate the other two swimming environment extremes.

[7]

Natatorium dysfunctions can also be caused by a dehumidifier that is not operating up to the manufacturer’s specifications. Just like an air conditioner or any other mechanical equipment, dehumidifiers need annual servicing by a qualified contractor.

A slow degradation of space conditions can be caused by an improperly adjusted and/or underperforming system that is operating well outside its design parameters. In this regard, some manufacturers today offer dehumidifiers with web-based microprocessors, which relay operating parameters via the Internet to factory engineers for monitoring. This helps to ensure the dehumidifier performs as efficiently as possible, while optimum space conditions are maintained.

The bottom line for facility managers is to know the basics of natatorium design and dehumidification system operation in order to recognize and rectify problems sooner. The end result will be a more comfortable environment for patrons and a long-lasting facility with the lowest possible operating costs.

 

 

 

 

Ralph Kittler, P.Eng., is co-founder and vice-president of sales and marketing of Seresco USA in Decatur, Ga., a subsidiary of Seresco Technologies Inc., an Ottawa-based manufacturer of natatorium dehumidifiers. He has 23 years of experience in the heating, ventilation, and air conditioning (HVAC) industry and a degree in mechanical engineering from Lakehead University in Thunder Bay, Ont. Kittler recently produced a free ‘Professional Development Hour’ (PDH) video available at www.serescodehumidifiers.com that targets the continuing education requirements for engineers, but also serves as an invaluable primer of indoor pool design and operation basics for facility managers. He can be reached via e-mail at ralphkitter@serescodehumidifiers.com[8].

Source URL: https://www.poolspamarketing.com/trade/common-facility-operational-issues-are-often-blamed-on-the-dehumidifier/

---