Design goals and fan selection
Which are the relevant air movement goals for your design and how to select fans that meets those goals?
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Which are the relevant air movement goals for your design and how to select fans that meets those goals?
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Fans are effective for comfort cooling, and air circulation. However, fan applications depend highly on the design goals for desired air speed and distribution and any physical environment limitations. Understanding the elevated air movement design goals is the prerequisite in selecting an adequate fan type for a particular space.
Figure T5 outlines the key considerations for defining the fan design goals, including personal control, targeted, variability, and uniformity. “Personal control” design emphasizes the goal of the fan system to provide thermal comfort for a single occupant, while the adjustment of fans is unlikely to affect the others. “Variability” has its advantage in multi-occupant spaces where occupants have the flexibility to adjust fan operation based on their desired thermal comfort needs, or they are free to move around and choose their preferable locations or thermal conditions. In spaces where there are variable or transient occupancies, non-uniform thermal conditions, or spaces with specific thermal requirements due to architectural features or activity levels, “Targeted” air movement may provide more comfort. Lastly, “Uniformity” (i.e., more regular control) emphasizes uniform air speeds and consistent thermal comfort experience applied in multi-occupant spaces where occupants do not have the flexibility to control fan or change their location, especially when occupants will be staying in those areas for extended periods.
Fan selection criteria mainly depend on the design goals of air speed and distribution, the purpose of elevated air movement (i.e., direct cooling across the human body or air circulation), and any limitations of fan usage in space (i.e., floor-to-ceiling height).
Ceiling fans are generally effective for comfort cooling and air circulation in nearly all scenarios and applications. Ceiling fans are recommended due to their effectiveness in air movement, provided that some limitations of implementation have been compromised, including insufficient height clearance for ceiling fan installation, presence of obstructions at the ceiling or on the floor that block airflow, an inadequate arrangement between lighting fixtures and ceiling fans that cause strobing or visual flickering effect, and high renovation cost for ceiling fans integrated design. Installation of ceiling fans is recommended if these limitations do not apply. Alternatively, other air movement devices shall be chosen if these limitations cannot be compromised. Figure T6 presents the fan selection examples (with/without ceiling fans) based on different design intent. In addition, different types of fans can be integrated to maximize occupants’ comfort and to achieve multiple design intent. For example, ceiling fans can provide a uniformly low-speed background air movement for all occupants in a large open space, while individual fans allow additional personal control to improve occupants’ local thermal comfort further whenever it is necessary (e.g., at transient conditions or near the window). An example of such a mixed design intent approach is presented at the bottom of Figure T6.
