Somewhere between the advent of air conditioning and the fear of rising energy costs, the idea of air movement was lost. Air conditioning enabled people to close windows and provide a cool, comfortable temperature in which to live, work and learn. Jump forward a few decades, and the year-round cost of using HVAC systems, whether for summer cooling or winter heating, is making people rethink their reliance on them. The one constant that seems to be overlooked, though, is the use of air movement, which provides comfort on its own or from accompanying mechanical systems. 

It’s not just comfort that gives air movement a secure job. Working with HVAC systems, air movement from large-diameter, low-speed fans provides an energy-efficient alternative for creating an engaging learning environment and helps curtail indoor air quality (IAQ) concerns that plague education facilities of all ages. This increased air circulation turns over the air in a space several times per hour. It provides a more constant, uniform temperature that inhibits mold growth, and the gentle, quiet operation does not add any unwanted acoustics to the environment.

Fan mechanics

Along with understanding the importance of airflow, facility managers should recognize how these effects are achieved mechanically. Properly engineered, large-diameter, low-speed fans use their immense size—not speed—to move a massive amount of air in areas where traditional, high-velocity fans are rendered ineffective. When the airfoil length is doubled, the surface area that those airfoils sweep is quadrupled. As the size gets larger, the amount of air the fan moves increases at a much faster rate than the amount of power needed to turn the fan as the size gets larger. So, all things being equal, the fan will become more efficient.

The pitch, or angle of attack, at which the airfoil is positioned, also helps determine the effectiveness of a fan. An exaggerated pitch—airfoils with an almost vertical angle of attack—will either increase drag (and possibly increase energy draw); a flat, mostly horizontal airfoil typically will not move much air at all. The most efficient angle lies somewhere in between. Operational speed and airfoil size and shape also affect the performance of a fan. Optimal fan design combines the most air movement with the least amount of energy use. The key is finding the optimal combination that produces the most air movement with the least amount of energy.