Data center designs continue to evolve, and, recently, more facilities are built with slab floors and overhead cabling, often in line with Open Compute Project (OCP) recommendations. Rather than install expensive, inflexible ducting to supply cooling from overhead diffuser vents, engineers are seeing efficiency gains by flooding the room with cold supply air from either perimeter cooling units, CRAC/CRAH galleries, or other cooling methods (rooftop cooling units, fan walls, etc.).
Hot-aisle containment (HAC) then separates the cold supply air from the hot exhaust air, and a plenum ceiling returns the exhaust air back to the cooling units. As such, this design is also gaining popularity due to its simplicity and flexibility.