The Pros and Cons of Underground Data Centers

cavern-entrance

The entrance to the Cavern Technologies data center in Lenexa, Kansas, which houses its customer servers more than 75 feet underground. The company is among a growing number of data bunkers storing data for high-security clients. (Photo: Cavern Technologies)

ORLANDO, Fla. - The data bunker industry is growing, as more customers seek out ultra-secure underground hosting for their IT operations. Operators of subterranean server farms say these environments are similar to above-ground facilities, but they often must address misperceptions about underground sites, many of which are housed in former limestone mines.

The emergence of underground data centers was the focus of a session at last week's Data Center World Fall conference, in which several experts discussed the advantages and challenges of underground data centers, and offered tips to consider when evaluating a data bunker.

"The underground data center space is experiencing rapid growth due to the efficiency and speed to market it offers," said John Clune, the president of Cavern Technologies, which operates a data center in a limestone mine in Lenexa, Kansas. "One of the bigger challenges has been the perception of underground data centers. People are imagining a tight cubbyhole with a guy with a light on his helmet. The reality is that we've got 18 foot ceilings."

Cavern Technologies is among a cluster of underground facilities in the Midwest, which also includes SubTropolis,  The Mountain Complex and SpringNet Underground in Missouri; and the InfoBunker and U.S. Secure Hosting in Iowa.

Tips from Data Bunker Veterans

Not all underground data centers are created equal, and potential customers need to shop carefully and be mindful of the differences between traditional and underground facilities, according to architect Kerry Knott of Bell/Knott & Associates. Knott has worked on a number of underground business parks and data centers in Kansas and Missouri, and offers some insights into evaluating a data bunker.

"Data center buildouts are a good use for these kind of facilities," said Knott. "Once the data center is built, if you take someone in there blindfolded, they'd never know they were underground. You've got the same equipment; it's just been an underground facility."

But there are some differences. Here are some pros and cons to consider with facilities built in limestone mines:

Speed to Market: Clune says Cavern was recently able to deploy 5,000 square feet of data center space for a client in just 60 days. "The speed to market is impressive in the underground," said Clune. One factor is that there's no need to build or adapt a shell, as the underground space has already been created and all that is needed is the framing and buildout of the data halls. Another benefit is permitting from local officials. "In every underground I've worked with, we have had a blanket permit" once the initial underground space is created,  said Knott. "It’s one of the advantages of underground structures. That could be an 8 to 10 week savings." Another benefit is that construction can continue year-round, with no weather delays.

Construction Costs: Underground data centers can also be cheaper, Knott said, since there's no expense to construct a concrete shell. Subterranean structures also offer potential savings on disaster-proofing, especially in the Midwest. "To build a tornado-proof building above ground can cost an extra $100 a square foot," said Knott, who added that customers often inquire about other types of disasters. "People are concerned about collapse, and they're worried about earthquakes," he said. "An underground space, unlike the building above ground, doesn't move and doesn't need to be reinforced. An earthquake doesn't affect the enclosure at all, but you do have to brace the improvements."

Facility History and Origin: Recently-built underground facilities are usually appropriate, but those that were mined in the 1960s and earlier may not be. "To be an acceptable space for a data center, it has to have been mined for commercial development," says Knott. "The limestone has to be preserved in the proper thickness and have structural integrity. The room size is also important, because the columnar support will be rock columns that may be 25 to 30 feet in diameter."

The size and placement of these columns impacts the technical space. "Optimizing the layout within the property is essential," said Knott. "It's tough to get 90-degree corners with underground columns, so you have to be creative, since almost all your equipment is square. With the restrictions of the columns and placement of the corridor, you have to work with what you have. It can be awkward if these are haphazardly shaped."

Cooling and Ventilation: Underground spaces are naturally cool, but that doesn't mean they'll stay that way once you fill them with servers. "Heat rejection is the biggest concern and the biggest challenge," said Knott. "Most underground spaces have their own fresh air and ventilation system, but that's generally for comfort rather than the kind of heat we're putting into the space with the data center. Your options are to drill (ventilation) holes up through the top or horizontally to the exterior."

Placement of Mechanical Equipment: Some mechanical and electrical equipment requires ventilation and must be housed in an exterior yard. There are several options to address this, which customers must consider if their goal is disaster avoidance, as this equipment will be more exposed. "Generators and air-cooled chillers can be placed against an exterior wall or protected with an outside wall," said Knott. "You can also build another underground chamber to house them." Another issue to consider is fire suppression systems, and what happens with water in the event the system is ever discharged in part of the facility.

Staff Considerations: There won't be any daylight in an underground data center, but that's not different from many above-ground data centers, Knott says. A bigger concern for staff might be parking, as underground facilities can be large, and that sometimes means that parking areas are a significant distance from the data center.

john-clune-cavern

John Clune, President of Cavern Technologies, a Midwestern underground data center, talks about the pros and cons of underground data centers. While the underground temperature is a consistent 68 degrees, the data center engineers do have to accommodate for waste heat from servers and other gear. (Photo by Colleen Miller.)

cavern-datacenter

One of the data halls at Cavern Technologies in Kansas, which offers few clues that the facility is 75 feet below ground. (Photo: Cavern Technologies)