Central ventilation was the distribution system aboard 22nd century Starfleet vessels, responsible for providing a breathable atmosphere for the ship's crew. Central ventilation was fed the appropriate gases by transfer lines which connected to tanks aboard ship containing the desired gas.
In 2152, Doctor Phlox routed carbon dioxide to the central ventilation of Enterprise NX-01 in order to render unconscious members of the crew whom had been taken over by a series of non-corporeal lifeforms known only as "Wisps," thereby forcing the lifeforms to vacate the crews' bodies. Phlox accomplished this by recalibrating the ship's atmospheric recycling manifold to access the carbon dioxide tanks, and purging the osmotic filters. (ENT: "The Crossing")