Strategies for cooling a server room: Flooring, cabling, budget

There's no one best way to handle cooling a server room. Your customer's existing facilities, installed hardware and budget will be the biggest factors in how you help keep server room cooling costs down.

By Yuval Shavit, Features Writer

Cooling a server room has always been important, but these days it's even more so. Modern hardware like blade servers can take up a tremendous amount of energy per unit, and energy costs are skyrocketing. Server room operators are hit twice -- once to power their machines, and then again to cool them. If your client is thinking of upgrading its server room or data center, now is a good time to revisit the space and make sure it's being cooled as efficiently as possible.

Setting up an energy-efficient server room is difficult, and your approach will have to differ from client to client. Larger companies with existing data centers often like to standardize, and their established methods won't always be the best for the project you're working on, said Don Beaty, president of DLB Associates, an engineering consultancy in Ocean, N.J. If a company runs cabling for its data centers under a raised floor, for instance, you may have to set the new server room up the same way, even if overhead cables work better for it.

All those constraints can make upgrading an existing data center more difficult than starting from scratch, said Peter Sacco, president of PTS Data Center Solutions in Franklin, N.J. About 80% of the projects PTS works on are those "brownfield" rooms, he said, and those require experience and creativity to work around the client's needs.

Every company's IT department has a different list of what's standardized, so your first step should be to talk with your client to determine what's flexible and what isn't, said Beaty, who also chairs the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Technical Committee.

Different approaches, but no silver bullet

There are several ways of cooling a server room. Many rooms use a raised floor with perforated floor tiles. With a raised floor, cold air is pushed through this area, which is often one or two feet deep, and then moves up through the servers and collects at the ceiling. But installing a raised floor can be expensive, especially if you need to provide ramps to make the area handicap-accessible, Beaty said. If your client is in an office building that doesn't have a specialized server room, the ceiling may not be high enough to put a raised floor in.

If your client's server room does have a raised floor, you'll also need to consider where to run the various cables the servers need. In the past, companies tended to put them under the raised floor to keep the room neater. Many companies and cooling consultants now suggest putting them overhead, above the servers, so that they don't interfere with the flow of air under the raised floor. But even that isn't always the right answer, Sacco said. Cables under a raised floor can actually help with cooling a server room by slowing down the airflow under the raised floor and thus pushing that cold air through the tiles and toward the servers, he said.

Cost is another consideration; the approach that yields the best server room cooling may be out of your client's budget, Sacco said. This can be especially true when the server room contains high-density blade servers. Hardware vendors are pushing blades as the latest technology, and companies sometimes buy them without considering how they'll approach cooling a server room full of those machines, he said. Racks have gone up from taking just a couple kW in the 1990s to 25 kW or more today for a rack of blade servers, and every watt increases the amount of heat in the room. It's no longer enough just to calculate the average amount of heat a data room will produce and buy enough air conditioners for it, but more sophisticated approaches and technologies come at a premium. About 87% of Sacco's clients have bought blades, he said, and most have given up on buying more and gone back to standard racks, largely because of the cooling costs.

Many companies are trying to "go green" in their data centers, for the sake of their public image as well as their energy bills, Beaty said. More efficient cooling equipment is a part of that, but it can also cost more up front. A good way to lower your client's capital and ongoing costs is to buy only what the data center needs. Installing an air conditioning unit that's too powerful will cost more, and it will run at a lower efficiency. Air conditioning units have an optimal operating range, and you can lose up to 25% of the unit's efficiency by having it either under- or overworked.

Blades are definitely a part of the data center's future, and energy density will likely go up before it goes down. In the next installment of our Hot Spot Tutorial, we'll look at how to cool a server room with high-density hardware.

This was last published in June 2008

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