Exhaust fans are essential to the maintenance of safe and comfortable air conditions in contexts like material handling, pneumatic conveying, general ventilation and circulation. Agricultural, automotive, supply and distribution, food processing and packaging, printing and all other manner of commercial and industrial businesses make use of exhaust fans to some extent. Exhaust fans distinguish themselves from other air quality control fans in that they are almost always permanently affixed, if not built into the structure of the buildings in which they function.
Fans of varying performance, configuration and energy consumption are necessary to cover the range of air circulation needs throughout all of industry and commerce. Organizations like the Air Movement and Control Association create the potential for some regularity within the industrial fan market; depending on the number value the agency assigns a fan model, assumptions can be made by buyers about the product’s qualities. Not all manufacturers submit their products to this rating system, though.
All fans, exhaust or otherwise, fall under two categories of fan construction: radial and axial. Axial fans are generally more recognizable by most people because they appear in light-duty settings more frequently than radial fans. In the context of exhaust fans, the ratio of axial fans to radial fans is difficult to tell. Depending on the application, either configuration may be appropriate. Axial fans are characterized by curved, vertical blades that spin around an axis.
Commercial and residential ceiling fans, oscillating fans and nearly all other varieties of light duty fans for consumer or light industrial use are axial in their configuration. These fans work by creating negative and positive areas of pressure as their blades spin. This creates air movement. Radial fans also create uneven air pressure, but their blades are configured horizontally with respect to flat surfaces, as opposed to vertically like axial fans.
Instead of creating an area of negative pressure behind its fan blades, a radial fan creates a negatively pressurized area to the side of its center of gravity and then expels the air at the tips of its blades through a chute. This allows for some flexibility of airflow control in duct systems with right angles.