The density can be as much as 5 sq ft per person. Background noise control is also more important than in a movie theater. The stage is a separate problem. Stage lighting, highly variable from one presentation to another, is a major contributor to the cooling load. Scenery can be intricate and delicate, and vary from one scene to another, presenting air distribution problems.
Actors can perform at widely varying levels of exertion.
Lighting loads at stage level can be handled by exhausting air around the lights. Conditioned air is usually delivered, using numerous supply registers, from the low side and backstage with numerous return or exhaust registers at the lights. Low velocities are essential to keep scenery and curtains from fluttering. Air balancing is also needed to avoid chimney effects that might cause the main curtain to billow when it is lowered. Spot cooling may also be needed at the stage manager's and prompter's locations, and at the control board area.