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New low-sulfur diesel may hinder data center generators

An EPA ruling that limits the amount of sulfur in diesel fuel may weaken the performance and reliability of the generators backing up your data center.

A federal rule limiting the use of sulfur in diesel fuel is taking effect, and it could limit the performance of the generators that back up your data center.

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In 2004, the Environmental Protection Agency (EPA) passed the Clean Air Nonroad Diesel Rule. But this June, its requirements took effect; now the amount of sulfur allowed in the diesel fuel for offroad engines -- such as agricultural equipment, some construction vehicles and backup generators -- has decreased. Previously the amount was unregulated and typically more than 3,000 parts per million (ppm). Now it must be less than 500 ppm.

I don't think the impact is going to be so huge that there will be thousands of generators across America that will no longer be sufficient.
Eric Gallant,
senior account managerLee Technologies

By June 2010, that cap drops again, to less than 15 ppm. The EPA wants to reduce the amount of sulfur in diesel fuel because the particles from high-sulfur fuel can cause pollution and acid rain.

Using ultralow-sulfur diesel fuel could affect how your generators run, said Eric Gallant, a senior account manager at Lee Technologies, a data center consulting and services company in Fairfax, Va.

Generator inefficiencies
A central issue is that ultralow-sulfur diesel fuel has less energy content, so generators may be unable to respond to sudden changes in load, said Gallant. In rare cases, a generator that is accustomed to operating at maximum capacity may have a lower maximum capacity, which could limit the ability of a generator to back up a data center.

Further, the lower energy content causes the fuel to be slightly less efficient, which means you'll need more diesel fuel to get the same amount of energy from it. Add to that the likelihood that fuel suppliers will charge more for ultralow-sulfur fuel because they have to remove the sulfur from it, and it could equal even higher fuel costs for data centers.

Perhaps more importantly, Gallant said the process by which fuel suppliers remove the sulfur also removes some of the lubricating properties of the fuel.

"There's a higher possibility of some kind of electrical discharge accident, causing a fire and hurting somebody," he said. "This comes down to a safety issue."

Gallant predicted that despite the drawbacks, most diesel fuel suppliers will not wait until 2010 to bring the sulfur level below 15 ppm. They'll do it now so they don't have to deal with the incremental change today, and then again in 2010.

But not everyone is concerned about the change. At Equinix Inc., a major data center hosting company in Foster City, Calif., Jay Park, director of systems engineering, doesn't think the change will significantly affect performance. Some fuel additives can help restore the lubricating properties of the fuel, although Park said that Equinix might incur minor additional maintenance costs for the fuel system because of the lower lubrication of the engine.

Concerning reduced energy capacity, Park said it is minor -- on the order of 1% to 2% at most. "The diesel engines usually have this much excess capacity above the generator set-rated capacity," he said. "Additionally, the maximum design operating loads on our systems are well below levels affected by this fuel change."

Gallant agreed. "I don't think the impact is going to be so huge that there will be thousands of generators across America that will no longer be sufficient," he said. "You're just not going to get as much out of diesel fuel per gallon, and you won't get as much out of your diesel engine."

Once data center operators switch to low-sulfur fuel, Gallant recommended that they consider the following issues:

  • Budget. Review your budget for the extra cost of the new fuel, which will get less mileage per gallon, so to speak, as well as have a higher cost per gallon.
  • Load transmission. Consider how electrical loads are brought to the generator. If loads can be put on more gradually, engines will respond better than by doing a step load, for example (where sources of uninterruptible power supply (UPS) are suddenly transferred to a generator.
  • Testing. During your first year of using the new fuel, test it more regularly. All diesel fuel has some microbial growth in it. The change in fuel might cause some sediment and contamination to break loose and float in the tanks, affecting fuel performance.
  • Guidance. Plenty of data centers out there aren't even aware of the new rule. Your fuel provider can be a good source of guidance on this front.
    "People who own generators need to ask providers, ' What are you doing to handle this?' " Gallant said. But even providers, he noted, "aren't aware of all the changes."

Let us know what you think about the story; e-mail Mark Fontecchio, News Writer.

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