January 29, 2020
By Ralph Kittler
Of late, exposed wood has gained popularity with many indoor pool designers for multiple reasons. The material lends a unique and modern look that can set a facility apart from the rest. As an added bonus, it can even contribute to Leadership in Energy and Environmental Design (LEED) points to a natatorium due to the renewable nature and carbon footprint benefits of its use.
Why wood works
Trees absorb a good amount of carbon dioxide (CO2) during their lifetime—in fact, carbon constitutes nearly 50 per cent of their dry weight. As trees get older and decay, they release CO2 into the atmosphere. Cutting them down and using timber in construction instead can prevent the release of this harmful gas—at least for the building’s lifetime; longer if it is reclaimed when the structure is old.
As a building material, wood offers many environmental benefits—renewability and sustainability, to name a few. Compared to concrete and steel, wood products help to increase a building’s energy efficiency and minimize the energy consumed throughout the life of the product. Research points to the many advantages of using wood as compared to other materials, such as carbon emissions, effect on water quality, and overall environmental impact when measured over the complete life cycle of the structural material. In addition, a study by the Consortium for Research on Renewable Industrial Materials (CORRIM) found the total life-cycle emissions for wood houses are lower by as much as 31 per cent when compared to houses of concrete or steel, even before accounting for the amount of carbon stored in wood products.
According to Make It Wood, an Australian organization that advocates wood as a sustainable building material, “The production and processing of wood uses much less energy than most other building materials, giving wood products a significantly lower carbon footprint. As a result, wood can be used as a low-emission substitute for materials that require larger amounts of fossil fuels to be produced.”
The group further states using 1 m3 (35 cf) of wood, instead of the same amount of brick or concrete, can save approximately 1 tonne of CO2.
The Canadian Wood Council (CWC) says the durability of wood is often a function of water, but that does not mean wood can never get wet. On the contrary, wood and water can co-exist. Wood is a hygroscopic material, which means it naturally takes on and gives off water to balance out with its surrounding environment. Therefore, it can safely absorb large quantities of water before reaching moisture content levels that can cause fungi and decay.
There are some precautions, however, one must take to ensure the material’s durability. General design rules that apply to all natatoriums must be followed when using wood, too. The area needs to be conditioned by a dehumidifier to avoid any condensation and to keep the space at a relative humidity (RH) of 50 to 60 per cent. Additionally, the building envelope needs a continuous and unbroken vapour retarder, on the warm side of the envelope dew point, to ensure the moisture does not travel through it and condense within the structure.
According to the Western Wood Products Association (WWPA), wood cannot become mouldy until its moisture content reaches or exceeds 20 per cent.
Wood Handbook, published by the United States Forest Service’s laboratory, states wood would never have moisture content that high unless RH is at least 90 per cent, at any temperature.
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), has set recommendations on air movement, humidity, and temperatures within pool and spa facilities. Local codes often use ASHRAE standards as their basis, but these must be checked when designing or renovating a space. That said, standard design principles for pools must be followed to ensure the wood does not decay. The designer should get information from the wood supplier regarding what RH level will ensure the wood remains pristine. Suppliers will most likely call for 50 per cent RH. Note: Although the wood will not become mouldy, it will expand and contract as it absorbs and releases moisture; therefore, the design must account for these changes.
Whether or not one is using exposed wood, one of the most important things a designer must keep in mind is the airflow pattern. The goal is to allow good air that comes out of the dehumidifier to flow uninterruptedly to where it needs to go—in this case, the ‘breathing zone’ where people are usually present, plus any special concern areas, such as walls or windows that are likely to get cold.
The overall airflow pattern needs to ensure there are no areas of stratification, where air is not as well-conditioned as in the rest of the room. One must also make sure the overall air within the space is churning and not stagnating. The air within the breathing zone should be turned over, simply for the purposes of occupant health and comfort. It is not necessary the airflow be directed at any (and all) wood present in a natatorium, but it is important no part of the room falls outside the design condition range. Condensation on wood is as unacceptable as moisture on a window or door.
The Desjardins Sports Complex in Rimouski, Que., is a good example of how wood can successfully be used in an indoor facility. Opened in 2019, this building is modern in every sense of the word. From its highly efficient dehumidification system to the homogenous blend of wood elements and glass curtain walls, the structure brings both high-end design and facilities under one roof. The air distribution design in the complex is well executed, too. The project engineer and general contractor, Stantec, integrated the ducts into the building’s cedar ceiling, with air nozzles projecting slightly from the surface to direct air into the breathing zone and along the windows.
Another example is the combat training pool at the Marine Corps Air Station in Cherry Point, N.C., which has an arched wood ceiling design. Ducts run along the ceiling on either side of the natatorium, providing ample diffusion of supply air with some openings pointed up along the ceiling and others directing flow down into the breathing zone. The pool’s design also demonstrates the importance of using air diffusers with sufficient velocity; this ensures the openings can ‘throw’ the air far enough.
The use of exposed wood framing in indoor pools and aquatic centres is nothing new. Also, a growing demand for green buildings has positioned the material as a powerful and valuable solution for sustainable structure. Not only does it offer design flexibility, but can also be esthetically pleasing if implemented properly.
Ralph Kittler, P.Eng., is vice-president of sales national accounts for Dehumidified Air Solutions (DAS), a manufacturer of humidity and temperature control equipment. He has more than 30 years of experience in indoor pool design and dehumidification and is the reviser responsible for Chapter 25 (Mechanical Dehumidifiers) and Chapter 6 (Indoor Swimming Pools) in the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) handbooks. Kittler was also an ASHRAE distinguished lecturer for 12 years on indoor pool design. He can be reached via e-mail at firstname.lastname@example.org.
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