HP ML150 Optimizing facility operation in high density data center environment - Page 17

Ceiling return air plenum In recent years, raised floor computer rooms with very high heat density loads have begun to use a ceiling return air plenum to direct exhaust air back to the CRAC intake. As shown on the right of Figure 11, the ceiling return air plenum removes heat while abating the mixing of cold air and exhaust air. Once the heated air is in the return air plenum, it can travel to the nearest CRAC unit intake. The return air grilles in the ceiling can be relocated if the layout of computer equipment changes. Figure 11. Ceiling return air plenum Dual supply air plenums As power and heat densities climb, a single supply air plenum under the raised floor may be insufficient to remove the heat that will be generated. High-density solutions may require dual supply air plenums, one above and one below (see Figure 12). In this configuration, additional supply air is forced downward in the cold aisle. Figure 12. Dual air supply plenum configuration for high-density solutions Perforated tiles Floor tiles range from 18 inches (46 cm) to 24 inches (61 cm) square. The percentage and placement of perforated floor tiles are major factors in maintaining static pressure. Perforated tiles should be placed in front of at least every other rack. In higher density environments, perforated tiles may be necessary in the front of each rack. Perforated tiles are classified by their open area, which may vary 17