Should you supplement battery-based uninterruptible data center power supplies with an emergency generator? Vendors say
question has been coming up with increasing frequency as word spreads about summer rolling blackouts and brownouts and drops in service reliability. Two years ago, 50 million people in eight states from Midwest to New York lost power for at least 24 hours in one giant blackout. Amercan Power Conversion and other vendors note that specific localities can have much higher outage rates, either because of building-specific problems or bad weather (lightning strikes in Southeast, for example, or tornadoes in Midwest). In a rolling blackout, power to industrial facilities is often shut down first. New data center managers should check utilities contract to see if data center is subject to such utility disconnects.
A Growing Problem
“Deregulation of power industry has had a real effect on people’s needs to support their systems during shutdowns or to ride through a shutdown,” says Bill Hunt, product line manager for power generation systems group at APC. Despite that, he says, customers typically admit that they’ve considered a backup generator but rejected idea because of design work required.
“A UPS provides clean power, guarding against surges and drops,” says Dan McHugh, project manager at PTS Data Center Solutions. “In order to provide longer-term power, you’d need racks and racks of batteries. A generator allows you to be out two to three days, so you’re not losing money.” PTS is a consulting firm that does design work, construction, or construction management.
Says Hunt, “Our small and medium business customers started to come to us looking for longer runtimes. It used to be seven to 10 minutes, and now they were asking for two hours or more.” A well-designed emergency generator can run for days.
A data center with seven to 12 racks full of equipment needs 20KW to 40KW to stay up. The cost, installed with proper electronics for testing as well as for emergencies, with noise and air pollution controls, is typically $35,000 to $40,000, vendors say?after warning that installation costs can vary enormously.
Vendors say that units up to 20KW, on a concrete ground-level pad, are standard enough in many circumstances to be “ordered on phone,” in Hunt’s words. But anything larger will require some specialized expertise and more careful configuration. Local electrical and HVAC contractors can point data center personnel in right direction.
It is little wonder that data center management worries about cost. But over time, price doesn’t seem as high. “That’s about same as an extra 45 minutes to an hour’s worth of batteries,” says Hunt, “amortized over about 10 years.” As kilowatt requirements rise, generator option gets cheaper by comparison. But site problems, especially lack of space outside building to pour a concrete pad for generator and noise-attenuating enclosure, can inflate cost quickly.
Michael Dauffenbach, industrial sales region manager for Katolight, says generator itself might be only a third or half total cost. “A 15KW gas [typically propane] unit’s list price is about $10,000,” he says, “and diesel is about same.”
As capacity increases, diesel prices rise more slowly than gas. At 250KW, diesels cost about $45,000 and gas $90,000, again, for generator alone. APC doesn’t see propane or natural gas as practical above 150KW. About a quarter of units APC sells run on gas, with rest on diesel fuel.
