Available in passive and active variants, Cocooning Chimneys are appropriate as part of a free air cooling system that uses ambient air to remove heat from a data center. Free air cooling delivers energy-efficient and cost-effective data centers; however, one of the key challenges is providing the correct balance between cold aisle temperature, information technology (IT) equipment fan speed, and hot air return temperature. Cocooning via a vertical chimney ensures hot exhaust air from one rack, a row of racks, or a complete aisle, and it is ducted to the ceiling hot air return plenum without affecting aisle temperatures. T4 has used its vast experience in chimney design and configuration within the Cocooning Chimneys to eliminate the common problems associated with free cooling, including polluted air, pollen, insects, and humidity. It has designed the units to be used alongside airside economizers. Suitable for retrofitting, the chimneys bring ambient air in, filter it, and then mix it with exhaust air to raise the temperature, if required. The air is then passed either through an air-to-air heat exchanger, or through a backup water or DX air coil in order to get the right temperature for the room.