The SubZero CRACup is the first shippable AC extension of its kind. Made of high-grade aluminum, it ships flat with four easy-to-connect corners. The extensions are a key element in the separation of hot and cold airflow. Warm exhaust air is directed by the Rack Hat partition into the drop ceiling void. This hot exhaust air can then be equally distributed to numerous AC units with extensions. As a result, warmer air is returning back to the coils, greatly increasing cooling capacity. Additionally, the shared plenum balances the thermal load among the AC units. This is an advantageous design for high-powered racks with hot exhaust, since the hot air is pulled from the hot aisle before it is allowed to mix with the cold air. The higher return air temperature allows the CRACs to operate much more efficiently given the higher return air temperature.