Raised Floors—Unnecessary Cost or Unparalleled Performance?

When constructing a new data center, companies nowadays are invariably faced with the decision of whether or not to use a traditional raised floor.

Those of us who have been around for a while recall early large mainframe equipment that required bulky cables, which could only realistically be placed under a raised floor. Other data center systems and services that required bottom-fed access were also typically concealed under the raised floor. Most importantly, the raised access floor was used to deliver cooled air to the front of the equipment racks.

But times have changed. Convergence has reduced cabling loads and bundles of optical fiber cables can now be installed in overhead trays or below the raised floor. The smaller footprint of today's computing equipment allows for installation in standard EIA-310 racks. Equipment is also more powerful and cooling requirements have increased. Rather than traditional perimeter cooling, close-coupled cooling brings cooling closer to the equipment, often in line within rows for increased energy efficiency.

While these innovations have made it possible to potentially do away with raised floors, is the decision really that straight-forward? There are several criteria to consider.

Cooling System

Will CRAC units be perimeter, in-row, overhead or a hybrid solution? Reconfiguring floor tiles to maximize airflow patterns and ensure cold and hot air separation is easier than changing overhead duct work. Plus, overhead ducting can complicate cable tray routing and other systems. Locating chilled water pipes overhead is also more problematic should a leak ever occur.

Equipment Requirements

How will power be brought to the rack? If overhead power is used, all the devices must be able to connect. Large enterprise devices like disk arrays and tape libraries might require power cords to exit the bottom of the rack, and some of these large power cords can be rather unsightly or present a trip hazard in a non-raised-floor environment. Some equipment may also have different airflow needs (i.e., top or side vented), which is easier to accommodate when the underfloor space is used as a cooling plenum. 

Electrostatic Discharge and Grounding

The simple act of walking across a floor can generate a detrimental static charge. Raised-floor tiles are designed to properly direct these charges to ground-and they resist static electricity in the first place. Non-raised-floor environments require anti-static solutions such as special tiles with conductive adhesives and copper ground straps. Furthermore, best practices require bonding equipment racks to ground to keep high-frequency noise away from critical processing equipment-a task that is typically easier in a raised-floor environment since the floor's support grid provides an ideal low impedance path.

System Location

Some services like floor drains and water pipes are naturally predisposed to be in a certain location. With a raised floor, drains can be strategically placed to accommodate condensation lines. They also provide a way to get rid of water should a leak occur. While power and communication cables are equally at home underfloor or overhead, some prefer to keep work on ladders to a minimum due to safety concerns.

Change Management

While floor choice doesn't impact changes within the racks, when an entire rack or row needs to be repositioned, a raised-floor's fixed systems (i.e., cooling and power) can typically stay in place. In a non-raised environment, changing rack or row placement could require changing overhead infrastructure, including air ducts, cable tray and power bus systems.

Space Considerations

A raised floor can require additional space and either ramps or a sunken slab to accommodate difference in floor height with surrounding areas. In spaces with very low ceilings, a raised floor may not be possible if the minimum vertical clearance of 8'-6" cannot be maintained. A non-raised-floor environment does offer more flexibility regarding rack and row placement since they do not need to line up with tiles. While this may allow for more racks, air management challenges could be created.

Kosten

The potential cost of a raised floor (typically $20-$25 per square foot) should also be considered. But without a raised floor, the cost of installing an anti-static floor ($7-$12 per square foot) should be factored into the equation. In fact, all factors should be considered before determining if the cost differential alone is enough to make a decision.

There is no single flooring solution that will satisfy every need. While doing away with a raised floor can be justified in some situations-especially where space and cost are a primary concern-it's important to be fully aware of all the limitations this decision could create. There are few, if any, limitations to what type of IT equipment and cooling systems can be accommodated using a raised-floor system.