Raised Floor v. Slab Floor v. … Fan Wall? An Old Debate, A New Twist

raised-floor

It’s one of the data center world’s oldest debates: What’s best for a data center design: raised floor or slab floor construction?

The arguments have been hashed out for years, but this debate isn’t dying. A post we wrote on the topic in 2011 remains one of our most popular.

We’re not taking sides at Equinix because we use both designs. But it’s a good time to revisit/update the arguments, especially since we can now introduce another variable into the mix. It’s called a “fan wall,” and it’s soon to appear in Equinix data centers.

Cooling efficiency is all.

There wouldn’t be a slab floor v. raised floor debate if both weren’t proven systems for delivering cooling air. The fan wall steps into the mix as another alternative for supplying this cooling air, critical to data center operations.

Here’s a quick primer on how the fan wall system works: It’s actually two walls – an exterior wall covered with air cooling units and an interior wall covered with louvers, both separated by a 5-to-6 foot wide gap, or plenum.

The cooling units feed air into the plenum and fans circulate the air into the data center, capitalizing on pressure and air flow dynamics to cool the entire space and push hot air up, where it’s vented out of the facility. It’s extremely energy efficient and quiet. Conversations on the data center floor can be held at, well, conversation levels.

But while raised floor and slab floor may be louder, proponents of raised floor tout the ease with which cool air can be directed where needed. A data center operator needs only rearrange perforated floor tiles so that the cool air blown through the raised floor plenum vents up at the desired point of cooling. Some argue the overhead ducts in a concrete slab floor system can’t direct the cool air with the same precision.

However, overhead ducts in a slab floor design have also proven extremely effective. Some say they are the superior option as power density increases, since copious amounts of heavier cool air can be efficiently dropped from above – especially when combined with systems that contain the computing equipment’s warm exhaust in certain aisles. In addition, system air balancing can be easier with a slab floor design because there are fewer leakage issues, such as with improperly sealed cable openings on a floor.

Cost

The costs of installing a raised floor can be as high as hundreds of dollars per square foot, and maintenance costs are also lower in slab floors, where there are no problems with what may be accumulating in the gap underneath the raised floor. But once the raised floor is installed, the flexibility to easily direct cool air where needed can mean a cost advantage that draws things closer to even. With a fan wall there is no overhead duct work or sub-floor venting to worry about, which means lower maintenance costs, plus room for more equipment, compared to on-floor computer room air conditioning (CRAC) units. But it’s also best suited for single-or two-story facilities and retrofits can be complicated.

Durability

Slab floor proponents say their design is more durable, because there are no concerns about placing or moving newer, heavier equipment on areas that weren’t designed for the weight. In addition, slab flooring is considered safer in earthquake zones, since a raised floor could collapse. But proponents respond that raised floors can be constructed to handle almost any load. (We won’t review the pros/cons of fan wall durability until we have extended experience with them.)

Ultimately, we think the best data center design is the one that best fits a customer’s needs. We also know minds change as requirements and technology change. So we end this post with the same sentiment that wrapped up our 2011 post: Let the debate rage on.