Why must air in an occupied space be kept moving?

Keeping air in an occupied space moving is essential primarily to eliminate stratification, which refers to the layering of air at different temperatures within a room. When air is stagnant, warmer air tends to rise while cooler air settles at the lower levels. This can create uncomfortable conditions for occupants, as people often feel warmer near the ceiling and cooler near the floor. By ensuring continuous air movement, the temperature throughout the entire space can be balanced, which enhances overall comfort.

In addition to maintaining a uniform temperature, moving air can aid in optimizing other aspects of indoor air quality and comfort, but the primary factor in this context is addressing stratification. As around the options, conserving energy, eliminating noise, and reducing humidity are all essential considerations in HVAC design and operation; they are not as directly related to the specific concern of preventing stratification in the air within an occupied space.