Why Using Diesel Generators At Virginia Data Centers Poses 'A Real Risk' For Operators

Power shortages may force Loudoun County’s data centers to rely on their fossil fuel backup generators this summer. That could be more challenging than many in the industry anticipate.

Virginia’s environmental regulator believes data centers in Loudoun County may have to periodically disconnect from the power grid and crank up their largely diesel-powered backup generators this summer to ease the strain the industry is placing on local transmission infrastructure.

In a county that is home to the so-called Data Center Alley and houses by far the world’s largest concentration of these facilities, the thought of more than 4,000 locomotive-sized diesel generators running simultaneously — perhaps for extended periods of time — has raised the hackles of residents and community groups worried about environmental impacts from noise pollution to air quality.

But Loudoun County’s data center operators should also be concerned, experts say. In a worst-case scenario where data centers are forced to rely extensively on self-generated power, many operators may find it more difficult than anticipated to keep these buildings up and running due to emissions from their own generators, fuel logistics and a range of other factors. And some industry insiders say many operators are not fully aware of the risk. 

“There’s a real risk that they are not going to have the cooling capacity or the power that they need to keep the data center up and running during that kind of situation,” said Brad Cochran, director of air quality services at CPP Wind Engineering Consultants, which has studied the impact of prolonged generator use on data center operations. 

The potential for increased generator usage in Loudoun County emerged in February when Virginia’s Department of Environmental Quality first proposed a measure temporarily easing restrictions on on-site power generation for Northern Virginia data centers.

DEQ officials warned that, largely due to growing demand from the data center industry, local utility Dominion Energy may not be able to provide enough power to meet demand during events that cause power usage to spike, such as storms or heatwaves. When the local grid operator anticipates this kind of demand surge, the DEQ’s proposed variance would have data centers produce their own power.

The measure lapses in July, when Dominion is scheduled to complete transmission infrastructure upgrades that will allow it to deliver more power to key data center hubs.  

While it isn't inevitable that Loudoun County’s data centers will be switching on their generators en masse this summer, the possibility has caused alarm in a region where the industry’s rapidly expanding footprint has led to a growing wave of political and legal opposition to data center development. 

In public hearings on the DEQ’s proposed rule change, residents and environmental advocates voiced concerns about the air quality implications if the hundreds of megawatts of power needed by local data centers were being produced by generators on-site. Indeed, even data center development veterans agree that the generator emissions in such an event would be dramatic.  

“Wait until Dominion has a power outage — that diesel plume you’ll see from space,” said Compass Datacenters Chief Technology Officer Adil Attlassy, speaking at Bisnow’s National DICE Data Center Management, Operations and Cooling Series earlier this month.

Although residents’ fears have grabbed headlines, some industry experts say generator emissions may also pose significant risks to data centers themselves of which many operators are not aware. The concern, however, is less around the particulate matter and other pollutants in diesel exhaust (although that could be an issue at some data centers). Rather, it is the massive amounts of heat generators create that could leave data centers short on power and unable to cool themselves.

According to CPP’s Cochran, combustion exhaust from diesel generators is typically around 900 degrees, while radiator exhaust can be close to 300 degrees. When a data center runs multiple generators for a significant period of time, Cochran says the exhaust creates what engineers call a thermal plume of hot air that in certain circumstances can harm or disable a data center’s critical systems and potentially bring the facility offline. 

One of the greatest areas of concern is the chiller units used to cool data centers, according to Cochran. On hot days — exactly the kind of day where electricity demand spikes and the possibility of generator use is highest — those chillers, usually located on the data center roof, are often already operating near the edge of their capabilities. If a combination of building design and weather factors cause a thermal plume from generator exhaust to crank that temperature up significantly, it could spell disaster for that data center.

In the right conditions, Cochran says heat emissions could create problems for the generators themselves, causing them to produce less power than anticipated or even shut down, leaving the data center short on power. 

“When you've got a line of 50 or 60 three-megawatt generators and the wind happens to be blowing along that line, some of them down the row are just getting blasted with all that hot air,” Cochran said. “You end up having temperatures that are well beyond what they’re designed for.”

While there are design modifications data center operators can make to mitigate these problems, Cochran believes that most are unaware of the risk to their facilities.

Computer modeling of thermal plumes is typically part of the data center design process, but Cochran said these models are generally overly simplistic. He said that because the odds of long-term generator use were considered remote until recently, more detailed risk assessments taking into account various weather and climate conditions weren’t considered necessary. But that is changing.

“When you start talking about running them for potentially hundreds of hours per year, particularly during the hottest days of the year when the grid is being impacted the most, that's a total game-changer in that it’s not what these systems were designed for,” Cochran said.

“When they've evaluated these systems, a lot of times they haven’t used the most accurate models for it because the risk was so low it didn’t really matter how accurate those assessments were," he added. "But now that the risk has gone sky-high and they're potentially even being mandated to do this, so they need a much better indication of how that's going to affect the operation of their data center. They can't swipe it under the rug anymore.”

Ensuring that the massive amounts of diesel fuel needed to power generators can be reliably resupplied is also a looming concern for Loudoun data center operators in the event of an extended widespread loss of grid energy. Experts say fuel tanks typically need to be refilled every 48 hours if a generator is on constant operation.

Access to diesel has been a growing concern for the data center industry over the past two years as power constraints and grid vulnerability have increased in Europe and in certain U.S. markets. Data center giants Equinix and Digital Realty announced plans last summer to stockpile diesel, while operators in vulnerable areas have prioritized building more robust field supply chains in the event of an emergency. 

But getting fuel to data centers becomes significantly more complicated in areas where the facilities are clustered together — and nowhere more than Loudoun County. Experts tell Bisnow there are serious questions about whether the area’s fuel storage represents a significant supply chain pinch point. And the question of whether the region’s fuel storage and delivery infrastructure has the capacity to deliver the volume of fuel needed in the event of an extended loss of grid power remains untested.

“You’re going to get a traffic jam at the entrance to data center campuses with just the fuel trucks coming in,” said Anke Byer, an associate principal at CPP who specializes in data centers

While severe power shortages and widespread generator use may not materialize in Virginia this summer, the preparations by state regulators are just the latest sign of a growing problem for a data center industry that in some locations is growing faster than the power infrastructure needed to support it. There is a broad consensus that the likelihood of prolonged grid outages in major markets is increasingly likely. 

The issue had been most acute in Europe, where energy regulators in the UK warned of possible energy shortages requiring operators to periodically disconnect from the grid, and in Ireland where officials have already encouraged hyperscalers like Microsoft to regularly run off their generators to take strain off the grid. In the U.S., operators have already been forced to run on emergency generators to take strain off the grid during Texas grid failures in 2021 and the California blackouts soon after. 

Now the data center industry’s power usage is growing faster than ever, and it’s not just the new campuses with hundreds of megawatts of capacity. In a trend largely driven by more powerful chips needed to support emergent technologies like artificial intelligence, operators are using far more power per square foot than they were just two years ago and are utilizing more of the energy utilities allot to a given facility far faster than in the past.

This has made predicting demand from data centers far more difficult for utilities, even those like Dominion with a long history of collaborating with the  industry. As emerging technologies and factors like demand for green energy further complicate the demand equation, experts say the current situation in Virginia is a sign of things to come.

“We're asking more of [utilities] — we're asking for larger scale, we're asking for shorter timelines, we're making bigger investments, and we're expecting the electrons that come across those lines to be green,” said Lindsey Bruner, chief operating officer at CleanArc Data Centers. “There's a change in the dynamic there.”