Outside air quantities supplied by an air handler are based on peak occupancy, which happens infrequently in many locations. Furthermore, when the zone is occupied at its maximum rate of occupancy, it’s often satisfactory if it recovers after only a few hours, overnight, or over the course of several days. Auditoriums, church sanctuaries, theaters, and public assembly halls may fit this criterion.
A carbon dioxide sensor interlocked with a damper in the outside air intake can reduce the outside air use to the minimum needed to maintain healthy conditions. Since outside air is more costly to treat than return air (it’s usually warmer and more humid than return air in the summer and colder and dryer in the winter), any reduction in outside air saves energy. No matter what’s done, though, it’s imperative that the building environment remains within the healthy air standards promulgated by the codes.
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Excerpt from Energy Conservation Projects.