Issue link: https://cp.revolio.com/i/860140
28 | THE DATA CENTER JOURNAL www.datacenterjournal.com running times that only generators can provide. e most reliable solution to all of these challenges is a parallel emer- gency power system in which several gensets connect in parallel, instead of a single large unit. e total of the paralleled system output will meet or exceed the output of a single unit in backing up the data center. More importantly, though, a parallel system offers advantages that are particularly attractive to data centers. One such advantage is redun- dancy. When the facility's backup power capacity is distributed across several nodes, backup doesn't rely on any single unit. Instead, should a unit be taken offline for service, the facility still has the remaining nodes available to provide backup power. is is true even in the simplest par- allel system: two units connected in parallel, or an N+1 configuration. If one unit is offline, the second genset can support critical loads. is redundancy applies to individual buses, as well. Although multiple gensets are employed to back up the entire facility, they can be allocated in groups to the individ- ual buses in the power-distribution system. is redundant bus topology allows multiple parallel generators on a bus that otherwise would have only had a single generator. It allows for growth and N+1 redundancy on each bus. By definition, this redundancy leads to dramatically greater reli- ability for critical loads compared with a single-engine generator. For example, if the reliability of a standby generator is defined at 98 percent, an N+1 configuration can provide reliability of 99.96 percent, and an N+2 configuration has a reliability of 99.999 percent. Incidentally, an N+2 configuration exceeds the Uptime Institute's Tier IV standard. Many data centers, however, opt for much larger parallel configura- tions. e reason? Scalability. Data centers are designed to grow, and as capacity increases, so will backup- power needs. Using a single-engine generator, these facilities must invest in all of their backup power up front—an outsized investment that can tax the budget. A parallel solution allows facility managers to implement only as much backup power as they immediately need, leaving room to grow as capacity— and revenue —increases. is design is particularly easy to implement in solutions that have a generator controller integrating all paralleling controls and that require no costly switchgear. It's essentially a plug-and-play solution. All that facility managers must plan for is the space to install new generators as necessary. Even then, some solutions allow installation flexibility unlike a single-engine generator, in that units can be installed around the campus and even on rooops. Another aspect of backup power that affects system reliability is fuel. It's also a matter for debate. Diesel is oen the fuel of choice because it can be held in quantity on site. For that reason, it's popular among authorities having jurisdiction (AHJs). Diesel does have some drawbacks, though. Without getting into detail, it can and does degrade in relatively short order, especially ultra-low-sulfur diesel (ULSD). If not properly maintained, it can damage a diesel generator. Also, you can only hold so much on site, and refueling can be a challenge in an emergency, such as when trees are down and roads are impassable. en there's natural gas, which is becoming more popular. Not only is it cleaner burning, but because it's utility supplied—and because the natural- gas infrastructure is oen immune to the circumstances leading to power outages—it can keep a backup power system running indefinitely. Addition- ally, natural gas can serve in demand- peak-shaving and demand-response plans, which can yield great saving and rebates on power under utility incentive programs. Bi-fuel genera- tors (those that run on both diesel and natural gas simultaneously) employ the benefits of both fuels. What's important to note, how- ever, is that in a parallel backup power system, you need not limit yourself to a single fuel. Instead, data centers can mix and match. Some units might run entirely on diesel, whereas others run on natural gas or are bi-fuel. is flexibility is particularly well suited to a parallel solution. Should a diesel engine run out of fuel or have to be taken offline for service, its natural- gas or bi-fuel counterparts can pick up the slack. e same goes for natural gas: if the supply is cut off, the diesel and bi-fuel generators can continue running, as bi-fuel generators can run exclusively on diesel, if necessary. Overall, parallel systems can benefit data centers by offering levels of reliability and scalability that are impossible with single-generator solutions. ose working on new construction should consider parallel systems, and existing data centers can benefit from a reevaluation of their backup-power topologies and strate- gies. n about the author: Curt Gibson is Power Solutions Manager at Generac Power Systems