Abstract: Various implementations include a corrugated concrete floor system that includes a plurality of elongated pre-cast concrete floor support units disposed in a horizontal arrangement relative to each other for each floor of a building. The concrete floor support units are disposed between floors of a multi-story building. The units define a plurality of supply air plenums and return air plenums that are arranged alternately in the sandwich space between each floor. The supply air plenums are in fluid communication with the building level above them, and the return air plenums are in fluid communication with the building level below them. By having the supply-air plenum and the return-air plenum share the volume occupied by concrete floor support units, the height of the sandwich space is reduced.