Data centersaround the world need reliable standby power, and increasingly, they are seeking solutions that not only meet their power requirements but also satisfy their need for accelerated schedules. A compressed timeline was a big part of the project for theCoreSite data center in downtown Chicago but so was a huge logistical challenge.

The CoreSite data center in the Chicago Loop has a long history in communications, having begun life in 1917 as the Chicago headquarters for the Western Union Telegraph Company. Purchased by CoreSite (then known as CRG West), the building was extensively refurbished several years ago.

“We are a network-dense colocation (colo) provider in the heart of downtown Chicago,” said Howard Yates, senior project manager, CoreSite LLC. “We build the power, the infrastructure, and then we lease it to customers who are sensitive to downtime and need access to robust networks.” Diesel generator sets are an important part of that robustness, providing emergency standby power for the data centers.


There were some issues with the three existing 2-megawatt (MW) generator sets. They were leaking oil, and they were not stable enough to be paralleled, which limited their usefulness. One other complicating factor: they were installed on the roof of the seven-story building. The rooftop location allowed CoreSite to make the most of its indoor space for revenue-generating purposes. So CoreSite decided to remove the three large generator sets and replace them — seven stories up, between several tall buildings, in busy downtown Chicago.

To figure out a plan for this replacement, CoreSite turned to Howard Chez and his firm, Howard S. Chez & Associates. An experienced consulting engineer, Chez designed the specifications for the new standby power system.

“We had three 2-MW systems, and we needed that much capacity just to have the reliability that is known to be required in the data center industry,” said Chez. “We wanted to add a fourth unit to be able to be online in case one of the units failed or was down for maintenance or repair.” In fact, the final plan called for the ability to add a fifth generator set as needed in the future. In the early stages of design work, consideration was also given to changing out the 480-Volt infrastructure with a medium-voltage infrastructure, but that idea was ultimately rejected as too costly.

Several firms submitted bids according to the specification that Chez had developed. The winning bid was from Cummins Power Generation and its regional distributor in the Midwest, Cummins NPower. The one-line drawing shows the new system (Figure 1).


Once the final design was settled, in September 2010, the project moved fast. CoreSite wanted the replacement system installed in three months.

“The biggest challenge from our standpoint was the short lead time,” said Robert Alfini, sales engineer and project manager for Cummins NPower. “The order came in September and they wanted it by the end of the year. It was rush, rush, from both the switch-gear standpoint and generators.”

Despite the tight lead times, the work was completed ahead of the final schedule. “Cummins met their deadlines and their commitments, and we completed our project ahead of schedule, with no impact to our customers,” according to CoreSite’s Yates. “Once we received permit approvals and all of the products from Cummins, everything went as planned with a very seamless transition from the old generators to Cummins. We’re very satisfied.”

“All this had to be coordinated properly, it was a fast job, so everything was taken into an account,” Chez said. “We had several meetings with Cummins, the designers, the structural engineer, the mechanical engineer, contractors, and with the owner and staff on-site. It was really like a well-conducted orchestra.”

Permits were obtained to set up the crane, a piece of equipment that took all night to assemble. Trucks were scheduled to bring in the new generators and steel and remove the old generators (Figure 2). LaSalle Street was closed where the crane was assembled. Congress Parkway was also closed and used to stage the new equipment. The old generators were drained of fuel, oil, and antifreeze to lighten them in preparation for moving.

In addition, the old generators’ unusual construction meant that they had to be removed in sections, and the crane could perform only a limited number of lifts, or picks, in the time available.

“They had to figure out how many picks they were going to be able to do in a day,” Chez explained. “They had to start with empty trucks to remove the old generators and then start bringing in new trucks with new generators, steel, and supplies, so it was really a coordinated effort.”

First thing Saturday morning, the old generator sections were lowered to the ground. Then it began to snow, but the lifting of the new units went smoothly. The only hiccup occurred when a motorist ignored the signs indicating that the block of Congress Parkway was closed and turned the corner and drove into one of the generator sets waiting to be lifted into place. The motorist’s car (and perhaps the motorist’s dignity) sustained some damage. The generator set was unharmed, however, and the installation proceeded.


Cummins NPower brought in a rental power unit to provide standby power in the event of an outage during the operation.

“We had a 2-MW rental unit on-site for the duration of the project, during the switch-over from their old units to the new ones, for a period of about five months,” according to Alfini. Temporary wiring was added at each of the boards to connect to the unit.


The new system consists of four 2-MW DQKAB Cummins generator sets double stacked on the roof, about 23.5 feet high, with one DMC 200 Digital Master Control. (Figures 3 and 4). Adjacent to the generators is an outdoor housing enclosing the DMC 200 with a 6,000-A paralleling switch board (Figure 5). The paralleling board contains four generator-paralleling breakers and four 3,000-A feeder breakers feeding four downstream 3,000-A UM-GM open transition transfer pairs. The paralleling board also contains a load-bank breaker feeding a rooftop-mounted load bank for generator testing (Figure 6).

“The stacks were mirror-imaged, so we only had to provide one platform with the enclosure entrance between the two generators,” Chez said.

“This configuration created the smallest possible footprint for paralleling an 8-MW standby power system in the limited space available on the roof,” Kilinskis stated. Incidentally, the building was designed to have additional floors that were never built, so the roof could easily support the weight of the stacked generator sets.

The new installation is basically an N+1 design that ensures an uninterrupted power source from a double-redundant system in the event of a power outage. It also has enough capacity (6 MW), even if one of the four generator sets is offline for maintenance or another reason. And it can be paralleled, so the generator sets can act as a single power source, just as a utility does (see figure 5).

 “I have always found that it has been a good experience working with Cummins, and I was happy to work with them on this project,” said Chez. “I have had experience with them since the ‘80s. Even when they know they are not going to get a job it has never prevented them from providing me technical help on things,” he added. In fact, Chez has decided to buy a residential standby generator for his own home from Cummins Power Generation. “They have a very good quality product and their support is excellent.”


Alfini noted, “The data center industry is pushing companies like ours for faster deliveries and a smaller footprint. What happened with CoreSite was typical in its schedule and the system design, although logistically it was more challenging than most projects.”