Can computational fluid dynamics modeling save your data center?

Computational fluid dynamics offers a way to understand the cooling needs of your data centre. Software to do the modelling, however, is of variable quality.


Carl Pappalardo the IT systems engineer for Northeast Utilities, had good reason to commission a computational fluid dynamics (CFD) analysis of his company's data center: His data center's raised floor had begun to look like Swiss cheese. Shortly after building a new 15,000-square-foot data center two years ago, Pappalardo noticed that there were "a lot of holes in the floor for cable cutouts and power."

"As I walked around the room, it felt too cold, and my thought was that I wasn't using my cooling efficiently," he said. "I was thinking that all these holes couldn't be good."

He suspected that valuable cold air from CRAC units was escaping from the cable cutouts instead of coming up through only designated perforated floor tiles. So Pappalardo opted for CFD analysis to analyze the flow of fluids, which includes both liquids and gases and indicates whether cold air from air conditioners flows where it should. Performed by the data center consultancy SubZero, the CFD analysis identified the data center's hot and cold spots and ways to improve data center cooling.

Diagnosing data center airflow woes

Computational fluid dynamics has been around since the early 20th century -- often to analyse airflow around aircraft and space shuttles for aerodynamics -- but only over the past few years has CFD emerged as a data center issue. As the cooling infrastructure of data centers has increased in complexity, some large end users and many data center consultants have turned to CFD to understand server room airflow and its importance: in a survey of end users earlier this month, the Uptime Institute reported that 47% used CFD to improve site infrastructure energy consumption.

As a result of Northeast Utilities' CFD analysis, Pappalardo realized that his data center needed some changes. In addition to penetrating the raised floor where the perforated tiles were, the air also came up through the cable cutouts. That dropped air pressure where Northeast Utilities needed it most: in the hot aisle where it could cool IT equipment. By filling up those cable cutouts, Northeast was able to increase the air pressure by 33% where he needed it. He said the move eliminated hot spots and reduced cooling costs, although the company hasn't yet done a full study of how much money it saved.

"Air mixing is the enemy," said Pete Sacco, a data center consultant and founder of PTS Data Center Solutions , who uses CFD software with every room he helps design. "You need to do cooling to and from the load as efficiently and quickly as possible with as little mixing as possible. Eking every bit of cooling out of my investment is the most important thing I can do as a data center operator."

To boot, by doing a CFD analysis, Sacco has found construction errors such as poor sealing of data center walls, which was causing cold air to leak out.

And now some use CFD software in other areas of IT as well. Ernesto Ferrer, a CFD engineer and data center consultant at Hewlett-Packard said he uses the software to help customers design data centers, but they also use CFD to model the airflow within the equipment they sell. Just as in a data center, air within a server or other piece of IT equipment should have good flow through the system. That ensures that the air cools off the electronics and leaves the box as quickly as possible.

In addition, some data center experts now use CFD technology to analyze airflow outside data centers. Why? It can help determine whether and where air-side economizers should be installed. Air-side economizers bring outside air into data centers to cool the IT equipment, and can lead to cost savings by reducing the amount of mechanical refrigeration needed.

CFD software: Price and quality

But Sacco warned that not all CFD software is made equal. He uses software from Future Facilities, a London-based data center design company. But it comes at a steep price: about $US100,000 per licensed seat. That's about three times as much as

TileFlow, software from US company Innovative Research that SubZero uses in its analyses. But Sacco said that more expensive software is worth it for him.

"For the price, for the environment it's set up for, [TileFlow] does a marginally good job," Sacco said. "But they segregate calculations between below and above the raised floor, and it doesn't always come up with accurate readings."

Sacco also considered Flovent, CFD software from Flomerics Group. Flovent is good, he conceded, but is designed for a large range of applications, whereas the Future Facilities software is built specifically for data centers.

Another well-known data center CFD software product is CoolSim from Applied Math Modeling Inc. In the end, users need to decide which software works for them based on details, usability and price.

Renting vs. buying CFD tools

Many data center pros are unwilling to shell out the money for the software as well as for the training to learn how to use CFD tools. Most will just hire a consulting firm to do the work.

But some end users license the software themselves or have plans to. Many are large organizations – banks and financial firms, for example – that can afford the software and the staff to learn it. Amsterdam-based ABN AMRO bank is one such user.

Allan Warn, a data center manager at ABN AMRO, said that over the past eight years the 15,000-square-foot London data center he oversees grew in power from 300 kilowatts to 1.3 megawatts, all in the same footprint. Last year the company had a CFD analysis done and discovered that modeling supported what it already knew: where the hot spots were and that the company had done a decent job of putting IT equipment in the right place so it wouldn't overheat.

For future modeling, ABN AMRO will buy Six Sigma software. They'll drop a bunch of hypothetical servers into a hypothetical CFD data center and gauge the outcome, then play around until it's clear that a new deployment of servers won't burn up the data center.

"We want to use the tool to tell us exactly where to put the equipment without overloading it," he said. "We want to be able to put it in and be able to cool it, not cook it."

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