Fan systems are vital to the operation of many industries and buildings. Fans often serve over a wide range of operating conditions because of changes in ambient conditions, occupancy, and production demands. The importance of fans often causes system designersto be concerned about under-performing systems. Designers tend to compensate for uncertainties by adding capacity. However, peak requirements may only occur for a few days or weeks each year, and normal operating conditions could be well below the design conditions. Although your fan may be the right size some of the time, it may be the wrong size most of the time. An oversized fan operates below its most efficient point and creates problems such as high capital costs, high energy costs, decreased reliability, high system pressures and flow noise. In this course we will discuss the ways that airflow is controlled in fan systems and we will definethe main opportunities to improve performance in fan systems. We will also explore common fan system problems.