The Planet has posted details of the new energy-efficient design for Phase 3 of its D6 data center in Dallas. The new design isolates the cold air and hot waste air, preventing the mixing that leads to inefficiency in many data centers. To accomplish this, The cool air from the computer room air conditioning (CRAC) unit goes into the cold aisle near the bottom of each equipment rack. Each of the racks is equipped with a chimney-style containment system that vents the hot waste air directly into the ceiling plenum, where it is returned directly to the CRAC units.
The Planet has a detailed blog post with lots of photos providing a floor-to-ceiling overview of the process. There are additional pictures on The Planet's Flickr set.