Why Is NetApp's New Data Center So Efficient? Big Fans and Hot Air

NetApp just finished building a new data center in RTP, and it is one of the most efficient in the world. I mostly focus on innovation around storage and data management, so I was surprised by how much room there is for interesting innovation in data center design.

The big problem of data centers is getting the heat out. In a typical data center, for every kilowatt you put in to run your equipment, you have to spend another kilowatt on air-conditioning to pull the heat out. In other words, it actually takes 2 kW of energy to run 1 kW of equipment. This is a Power Utilization Effectiveness (PUE) of 2.0.

NetApp's new data center has a PUE of 1.2, which cuts the total power requirement almost in half. At current electricity prices, we'll save over $7 million a year. We use many techniques to achieve this, but I have two favorites: big fans and hot air.

First for the big fans: our data center moves enough air to fill the Goodyear Blimp in three seconds. To get a mental picture of this, imagine an endless series of blimps flying out of the building – every three seconds another blimp. The harder you blow, the faster you cool.

The hot air technique is more subtle. Most data centers cool air to 55 or 60 degrees, but our team figured out how to get effective cooling with 74-degree air. Less cooling equals less energy. The trick is to manage airflow carefully. Rack mounted equipment sucks air in the front and blows it out the back maybe twenty degrees hotter. Most data centers have rows and rows of racks in a big open room, so the air gets all mixed up. It works better to deliver cooler air directly to the front of the rack and collect the hot air from the back. In our previous data center, we experimented with plastic shower curtains to separate the “cool aisles” at the front of the racks from the “hot aisles” at the back, and it worked wonderfully. In the new data center, we went a step further and used drywall to build airtight cool aisles, which we pressurize to speed airflow through the equipment and ensure that the hot air can’t get back around to the front. The hot aisle can get up to 95 degrees, which is uncomfortable, but that’s okay – it’s optimized for equipment and energy, not for people.

In RTP, the outdoor temperature is 74 degrees or less 67% of the time, which means we can usually use outside air with no cooling at all. Our data center has more cooling capacity than the Empire State Building, but our goal is to leave it off.

It didn’t take exotic technology to achieve this result. The design and airflow are unusual, but we used ordinary air conditioning units, heat exchangers, and so on. In fact, we reduced the cooling capacity by about 20% so this technique is not only cheaper to run but also cheaper to build. If you want to learn more, we welcome visitors.

Comments

[paulmon]

Dave, curious how you the data center deals with humidity when using outside air. Dehumidifying tends to require similar energy levels to air conditioning.

[Joe Miller, Facilities Operations Manager, NetApp RTP]

Paul,
By design, our elevated supply air temperatures require less dehumidification than a traditional data center. Although our building automation systems do provide positive control to maximum humidity limits, the majority of the time ambient conditions are such that dehumidification is not required when using outside air for free cooling.

[paulmon]

Joe, this data center design is something I've wished would take adoption in Canada. Granted our power is VERY cheap compared to many parts of the US, not using the power is still the responsible thing to do. Considering our average temps are below 60F for 7 months of the year there is no reason why this isn't doable, aside from the lack of capital to invest in such a solution.

I've been saying for years that the solution to a hot data center isn't to cool it better, it's to engineer it to allow it to run hot, ideally so hot that no cooling is required. Unfortunately the hardware isn't there yet to allow for that. It seems the style of data center you've recently deployed is a good happy medium.

[Joerg Hallbauer]

Since most cabling is done on the back of computer equipment, I have to wonder how the poor guys who have to work in those 94 degrees isles feel about this great idea?