Raised Floor Design and Deployment
A raised floor is constructed on a grounded framework of vertical pedestals and stretchers that support floor tiles (2 feet 2 feet in size). The space below the tiles is called the plenum. The raised floor provides for the following:
- A place for the equipment to sit. The tiles must be strong enough to support the weight of the equipment.
- Grounding for the equipment.
- A means to channel cold air from the HVAC units throughout the plenum in an optimal manner and direct it up to the data center to cool the equipment.
- A place to route network cables and power outlets and cables for equipment on the tiles. Since they are under the floor tiles, the data center looks less congested. The cables are also safe from being accidentally unplugged or kicked around by data-center people. Despite the advantages of raised floors, some data centers do not use them.
The word plenum (pronounced PLEH-num) means "full" in Latin. It is the space between the data center subfloor and the floor tiles and is usually between 11⁄2 to 2 feet in height. The HVAC must be capable of pressurizing the plenum. The open structure in the plenum contains a floor grid system (pedestals and stringers) that must be strong enough to support the tiles and maximum expected weight on the tiles (such as equipment-filled racks), HVAC units, dollies, forklifts, and people in the data center. The plenum contains the power outlets and network cables for equipment in the racks.
The raised floor consists of tiles or floor panels that provide a supporting base for the racks and equipment. They are generally 2-feet squares. Tiles are usually made of metal such as cast aluminum. You must choose tiles whose maximum load specifications exceed your requirements. Cast aluminum tiles can support a load of up to 1,500 pounds, even if they have a 50 percent passthrough. Tiles made of concrete or compressed wood can support only up to 500 pounds and, therefore, should be avoided. Tiles with inadequate strength or ill-fitting size warp or crack under the load and then pose a risk to equipment and people.
Tiles can be solid (that is, with no holes) or perforated (with holes for cold air to enter the data center). Tiles provide a great deal of flexibility in controlling air-flow patterns between the plenum and equipment. Solid tiles redirect air flow and help preserve pressure in the plenum or subfloor. Perforated tiles are used next to equipment racks and below bottom-cooled heavy equipment to redirect some cold air into the room or directly to equipment racks. Figure 4-3 shows the placement of racks, solid and perforated tiles, and aisle locations. Tiles with cutouts are used for passage of cables. Equipment racks are usually arranged in alternating rows: back-to-back or face-to-face.
Figure 4-3 Equipment rack, aisles, and tile location on the data-center floor. Solid tile Perforated tile Equipment rack
Sometimes it is necessary to cut and modify tiles to accommodate odd shapes of the room, edges of the floor, and around columns. The exposed cut edges of the tiles must be capped with protective trims to avoid particles entering the air stream. Exposed edges can damage cables and injure people lifting and repositioning tiles in their slots.
The previous tip was excerpted from Chapter 4, 'Data Center Design,' from the book Administering Data Centers: Servers, Storage, and Voice over IP by Kailash Jayaswal, courtesy of Wiley Publishing. Click here for the complete collection of book excerpts.
This was first published in May 2006