Jack Glass does not work alone. This is something he wants to make absolutely clear, that the people who make up the Department of Data Center Planning at Citigroup, a team of mechanical and electrical engineers—natural tinkerers, all of them—are vital because of their curiosity and meticulous attention to the inevitable “little things that can,” in an ominous sense, “get you in a data center.”

Data centers, which house a company’s mainframes, servers, and storage systems, are not Citi’s functional equivalent to a closet. They are not just a place where they stack away files for safekeeping or in case of future review. Data centers are the central mechanism that enables Citi to do what it does. “We don’t have stores, we don’t have trucks, we don’t have, you know, products that people look at and buy; we deliver financial services,” Glass says. “And we do it through technology.” Citi, one of the world’s largest financial services networks, has 21 data centers plus 400 tech rooms that run less-critical business applications. In all, the corporation’s raised floors—beneath which run cables and wiring that serve information technology equipment—add up to over a million square feet. That makes Jack Glass’s job very important.

In 2008, Citi constructed the first LEED Gold-certified data center in the US. The company has two other LEED-certified data centers in Germany and Singapore.

It is rare for someone to win renown by drastically reducing some aspect of his company, trimming it until its impact is as low as possible. Many industries tend to laud expansion and growth. But Glass, who studied engineering at the General Motors Institute (now Kettering University) and was part of a well-known Salomon Brothers project retrofitting 7 World Trade Center before joining Citi, has actually helped slice the number of data centers by more than half. There were 52 in 2005, when Citi adopted a plan to reduce its number of global data centers, and the eventual goal is to trim that number to 19. Meanwhile the data centers’ density—the average watts per square foot—has leapt upward by at least 50 percent.

Data centers entered the public consciousness as prime candidates for efficiency measures after an EPA report to Congress in 2007 estimated that these buildings made up roughly 1.5 percent of total US energy use. (Their impact can be better seen in Citi’s numbers: though data centers account for just one percent of Citi’s real estate, they consume 25 percent of the company’s total energy across its operations.) The EPA predicted that this number would double to three percent by 2011. But, perhaps thanks to data center operators like Glass and the nimble responsiveness of technology, it didn’t. Data centers currently account for about 2 percent of total energy use in the United States.

Citi’s data-center plan has involved reworking old centers, a task that Glass, as someone who lives in an old home he has progressively updated for the past 22 years, enjoys the most. Yet it also has involved shutting down old sites and opening new ones. Citi constructed three large data centers on American soil in the past decade. One, completed in 2008 in Central Texas, is 100,000 square feet and LEED Gold-certified, the first data center to have the honor. Citi has two other LEED-certified data centers: A LEED Platinum structure in Germany with a sleek, modern exterior; a green wall; and free-cooling system in use for 65 percent of the year. And another LEED Gold facility in Singapore with an uninterruptible power supply system that eliminates the need for battery backup.

Glass was part of the working group created to give input on data center-specific guidelines for LEED certification, which, when written, are planned to be released in November 2012. Even more rewarding has been serving as chair of ASHRAE Technical Committee 9.9. The committee, which contains IT manufacturers, air-conditioning manufacturers, data center “owners” like Glass, and consulting engineers, churned out a set of thermal guidelines for data centers in 2004. It was the first set of guidelines of its kind. Before that, people had no uniform guide for data-center temperatures and tended to over-cool. “You were shooting in the dark,” Glass says. The committee is now publishing its third edition of “Thermal Guidelines for Data Processing Equipment,” part of the ASHRAE Datacom Series.

If you were to visit his office in New York City and ask how he goes about planning Citi’s data centers, he would turn and draw two large circles in marker on his dry-erase board. One circle represents Citi’s IT organization; the other is corporate real estate. Glass’s world occupies the space between these two circles, and his mission is to be wherever they touch, which they must anytime a data center needs to be changed or designed. And if you don’t understand where those circles touch, you don’t understand Glass’s department. He draws those circles for every job candidate he interviews, and he needs them to understand that if you work for him, you are neither real estate nor technology but some amalgam of both. Not everyone can do it, and maybe this is why Glass is so proud of the members of his team—because they have proved that they can.

Glass has a sailboat, and he compares data center operations to the meticulous details a sailor mulls through to prepare for any problems that might surface while on the water. On the end of the dock, hands in pockets, surrounded by a group of other sailboat owners and enthusiasts, “you can talk forever about what little improvements you made to make things better,” he says. Making things better—that’s the best part.