When an HVAC designer is engineering the air handler, the maximum occupancy is used to establish the outside-air requirements. This can place an unnecessary load on the air handler for large assembly areas such as classrooms, libraries, or dining areas when they aren’t full. Another example is school gymnasiums, used for athletics during the day and occasionally for assembly of the student body. It isn’t necessary to provide the small gathering with the same volume of outside air as the full occupancy.
An adjustable outside-air damper on the air handler reduces the energy needed, for conditioning the excess of outside air. In most cases, two settings suffice, one for normal occupancy, the other for maximum capacity. If the air-conditioning is a multiple-stage system, the damper controls can be interlocked with the air handler so that when the unit is at or near full capacity—a good indication that the people load is maximum—the damper is fully open to provide the design outside air.
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Excerpt from Energy Conservation Projects.