Raised Flooring Obsolete or Not?

mstansberry writes "In part three of a series on the price of power in the data center, experts debate the merits of raised flooring. It's been around for years, but the original raised floors weren't designed to handle the air flow people are trying to get out them today. Some say it isn't practical to expect air to make several ninety-degree turns and actually get to where it's supposed to go. Is cooling with raised floors the most efficient option?"

Comments

No

[temojen]

It's in lower power chips, more efficient PSUs, and possibly liquid cooling where the radiator is outside the building (or a heat exchanger to heat pump loop in hot climates).

It's complicated, but basically, yes and no

[freeweed]

So long as you have positive air pressure under your floor, you'll get *some* effect from your perf tiles. However, as I'm sure some fluid dynamics folks will jump in with, air flow is a HARD problem. Yeah, so you're getting cold air coming up through your perfs. Well, most of them. Some of them are actually pulling air DOWN. Why?

If you're bored, check out TileFlow. It's an underfloor airflow simulator. You put in your AC units, perf tiles, floor height, baffles, you name it. It will (roughly) work out how many CFM of cold air you're going to see on a given tile. It's near-realtime (takes a second to recalculate when you make changes), so you can quickly add/remove things and see the effect. I spent some time messing with this a couple of years ago, and it's very easy to set up a situation where you have areas in your underfloow with *negative* pressure.

The article basically summed it up for me:

McFarlane said raised floors should be at least 18 inches high, and preferably 24 to 30 inches, to hold the necessary cable bundles without impeding the high volumes of air flow. But he also said those levels aren't realistic for buildings that weren't designed with that extra height.

I'd go with 24 inches MINIMUM, myself. Also, proper cable placement (ie: not just willy-nilly) goes a long way towards helping airflow issues. Like they said though, you don't always have the space.

Of course, with the introduction of a blade chassis or 4, you suddenly need one HELL of a lot more AC :)

Re:Where else?

[craigburton]

Can I suggest fitting one of these in your data centre racks?

http://www.canford.co.uk/commerce/resources/catdet ails/2457.pdf

or maybe even one of these...

http://www.canford.co.uk/commerce/resources/catdet ails/2458.pdf

Raised flooring is useful for several reasons.

[slasher999]

Raised flooring is useful for several reasons, moving cool air through a data center is only one of them. While requiring air to make severe turns to get out of the floor isn't optimal, most cabinets and the equipment in those cabinets is engineered with this in mind. Air is generally drawn in through the front of the cabinet and device and warm air blows out the back. Fans in the equipment pull the air in - the air doesn't have to "turn" on its own again (not that is really did in the first place). Warm air then rises after leaving the device where it is normally drawn back into the top of the AC unit.

Raised flooring also provides significant storage for those large eletrical "whips" where 30A (in most US DCs any how) circuits are terminated as well as a place to hide miles of copper and fiber cable (preferably not too close to the electrical whips). Where else would you put this stuff? With high density switches and servers, we certainly aren't seeing less cable needed in the data centers. Cabinets that used to hold five or six servers now hold 40 or more. Each of these needs power (typically redundant) and network connectivity (again, typically redundant), so we actually have more cables to hide than ever before.

Cabinets are built with raised flooring in mind. Manufactureres expect your cabling will probably feed up through the floor into the bottom of the cabinet. Sure, there is some space in the top of the cabinets, but nothing like the wide open bottom!

Anyhow, there you have the ideas of someone who is quickly becoming a dinosaur (again) in the industry.

Almost the right idea

[Critical Facilities]

Well, you're close. You are correct that the answer lies in a "hot aisle/cold aisle" configuration. The difference is, it works better when the cold air is coming up from below the raised floor tiles.

Why? You must keep in mind, you're not trying to pump "cold" air in, you're trying to take heat out, and as Mother Nature knows, heat rises. So why not harness the natural convection of heat, allow it to flow up to the ceiling, and have some "perf" ceiling tiles and use the space over the ceiling tiles as your return plenum. Thus, you end up with a positive pressure beneath the raised floor, your heat load in the data room, and your negative pressure over the ceiling tiles leading back to your CRAC units.

I assure you it works fabulously in our 2 year old data center at a major financial company. The other advantage to raised floor is, you don't have to worry about water being overhead. No one wants a condensor water, chilled water, or glycol pipe bursting over a row of server racks. But, put your power whips in liquid-tite conduit, use cable racks for the CAT5 and there's no problem if you have a leak. The leak detection ropes pick it up and you can contain it before it becomes a problem.