Paralleled System Backs Up University of Utah Data Center
Smaller generators with integrated paralleling enable modular growth.
SPACE CONSTRAINTS, NOISE CONCERNS, AND RELIABILITY
As part of this project, the university issued an RFP to select a backup power solution.
“The university and hospital use computer systems to automate otherwise manual processes,” said Brent Elieson, associate director, information technology and services at the University of Utah. “While we do have failover hot sites and DR [disaster recovery] sites, it would still be very disruptive to our efficiency if we experienced frequent power outages.”
The university had some specific challenges for its backup power system. The footprint, for instance, was an issue, as space in the yard where the generators were to be installed was at a premium.
Sound requirements were another concern. The University of Utah wanted a quiet unit so as not to bother its neighbors.
Additionally, “The requirements of our systems demand a Tier III level of reliability,” Elieson said. Paralleled systems offer significant reliability advantages. They are often mathematically more reliable than large engine generator solutions because the loss of any one generator would have less impact. This offers significant advantages in reliability for critical loads.
Originally, the specification had required several large, 2 megawatt (MW) generators connected in parallel using traditional switchgear. Such an approach has some drawbacks, largely due to the cost, complexity, space requirements, and integration issues associated with traditional paralleled systems. As a result, Generac power solutions manager Curt Gibson and Generac dealer Energy Management Corp. (EMC) believed that a Generac MPS solution would be an ideal alternative for this application.
An example of this could be comparing a facility with 4 MW of designed load, using 2 MW generators, installing 6 MW of capacity (three generators) to achieve N+1. Using binomial distribution with a 97% probability of the generators running would predict a reliability of carrying the entire 4 MW load to be 99.73%. Using 500 kW generators that reliability is achieved with only 5 MW (N+2) of installed generators at a cost significantly lower, and with a smaller footprint. When the actual load is lower, let’s say 3 MW which is common, 500 kW generators would offer N+4, which provides drastically higher reliability (99.9994%).
“Generac MPS solutions reduce complexity and costs by eliminating the custom paralleling controls,” Gibson said. “That’s often a very attractive differentiator. Eliminating external switchgear also reduces space requirements and reduces the lead time necessary for installing and commissioning the system.”
Gibson and EMC worked with engineering firm SmithGroup and the electrical contractor in Salt Lake City to present the value of an integrated paralleling solution. The 1 MW units are comprised of two 500 kW generators connected in parallel and housed within a single enclosure. The result is a generator that takes up even less space than a single-engine unit with the same output.
MORE SCALABILITY NEEDED
However, one additional hurdle had to be overcome — scalability beyond 9 MW. Under most circumstances, modular power solutions — whether implemented with the generators or otherwise — have been limited to 9 MW. The university expected the data center would require 11 megawatts when complete, so it could accommodate future expansion.
The solution that Gibson and EMC proposed was a unique one: install one MPS system comprised of five units on a single bus now (delivering 5 MW to manage current demand) and install a second MPS system comprised of six units (6 MW) on a second bus in the future. The additional units would be added as necessary to meet capacity demands and minimize capital expenditures as the data center grows.
The five units on the one bus were installed and commissioned in 2011. The other six units are slated to be installed in the near future as needed. A 22,000-gal diesel fuel tank serves the five units, and a separate such tank will be installed with the other six units. While the fuel storage and delivery system was designed by the engineering firm, EMC worked closely with them on all aspects of system integration.
“This solution was very economical and saved us money over what we were expecting to pay,” Elieson said. “The system comes online much faster than we had expected, taking the load off of the UPS and improving the life of the batteries. The units scale very well for our needs and are easy to grow without purchasing additional parallel gear.”
Early completion of the project allowed the university to move into the data center ahead of schedule.
Also, the system met the university’s sound requirements. “The sound package that came with the generators was very good,” Elieson said. “We were concerned about disturbing our neighbors, (and) we were very pleased with how quiet the systems run.”