Cisco Data Center 2011-Texas: Dynamic or Static UPS?
Cisco’s existing production data center in Texas has 1920 batteries protecting IT loads in the event of a utility power failure. Our Texas Data Center 2 (DC2) will have zero. Running at around 3000 rpm to generate 480V (60Hz) of electricity, the dynamic rotary UPS system will provide Texas DC2 with efficient, reliable backup power that’s both planet friendly and a sound investment. And if you read more below, I’ll tell you why.
When considering UPS systems, the first concern is usually protection against blackouts. Utility companies use the System Average Interruption Frequency Index (SAIFI) to report outages, which are defined as zero voltage delivered for more than 5 minutes. Averaging data from this index, a company can expect from one to five outages per year per facility. But what should be of greater concern to IT departments is power quality, affected by problems that include brief losses, sags, surges, transients, harmonic distortions, and imbalances. They are far more common and can be perceived by sensitive network equipment as an outage, or worse, a destructive event. According to a U.S. study conducted by the Electric Power Research Institute (EPRI), 84 percent of all disturbances are less than 2 seconds. And 98.7 percent are less than 10 seconds. All of which would be considered problems with power quality, not outages.
The majority of data centers today are using static UPS systems. They typically consist of banks of lead-acid batteries that store energy to provide line conditioning and backup to network equipment during power disturbances. If the disturbance progresses to an outage, diesel-fueled power generators are switched on. As the generators are rarely used, the main problems with this system are with the batteries. Even with recycling programs, the production and management of toxic battery chemicals do not benefit the environment, and the shortened life span of frequently cycled batteries result in large replacement expenditures every few years.
In response to financial and environmental costs, new technologies like fuel cell and lithium-ion are being developed. But there are some old technologies being revisited, too. Dynamic UPS, also known as Diesel Rotary UPS (DRUPS), uses the same basic flywheel technology first used in the Paleolithic potter’s wheel, and was then updated during the industrial age for use in energy storage. Powered by the utility, the flywheel spins up to speed. When power quality drops, the inertia of the flywheel keeps it spinning and providing power to the system for up to 10 to 20 seconds, covering that 98.7 percent of all problems.
For the remainder, the backup system works just like a static UPS system. The generator comes online and provides power before the wheel spins down. And then the wheel spins up again, much faster than a battery recharges.
Using dynamic UPS for Texas DC2’s power protection will yield several important benefits for Cisco IT. It will reduce our real estate and carbon footprints. It requires less space, doesn’t have the toxic chemicals, and doesn’t require the same cooling conditions that batteries do. With reduced cooling demands and flexible humidity variances, DRUPS supports the use of evaporative cooling, versus the use of chillers. While DRUPS generally has a higher initial investment cost, the longer lifespan of the equipment will result in a long-term cost reduction. Furthermore, DRUPS requires minimal maintenance performed only 3 times a year within 10 years before overhaul is required.
If you would like to hear more about dynamic UPS and are curious about the one we’ll deploy in Texas DC2, visit our Cisco Data Center 2011-Texas chronicle and view the Flywheels for Power Backup video for a walkthrough of the system.