Data center operators all over the globe are coming to terms with the fact that their services need a mighty push to meet emissions regulations, particularly in areas where air quality targets aren’t yet met. A panel of experts from Cummins, EMP Consultants, and Aeolus Consultants spoke to DCD’s Stephen Worn to unravel how stakeholder collaboration, data center compliance complexities, local regulatory thresholds, best available control technology, and global power generation issues, affect the ability to meet challenging emissions standards.

Weaving through the regulatory landscape with collaborative expertise

One of the biggest challenges for data centers today is navigating the tangled web of emissions and air permitting regulations. For years, EPA Tier II certification was sufficient for standby generator sets, but as data centers grow and emissions regulations tighten, particularly in non-attainment zones, securing these permits has become increasingly difficult. To address this, it is necessary to involve a variety of experts, including generator manufacturers like Cummins, after-treatment manufacturers, and consultants.

Jim McDonald, director of environmental impact at Miratech concurs: “It’s all about marrying the right after-treatment systems with the Cummins engine because this will provide specific parameters for the emissions coming out of the engine itself. By optimizing the integration of these systems, we can help data centers meet even the most stringent emissions requirements.”

The partnership between generator manufacturers such as Cummins, emissions after-treatment manufacturers like Miratch, and critical emission consultants like Aeolus is paramount because, as McDonald points out, understanding the Federal Register is a full-time job. In the US, for example, regulations can vary by state and county. The collaboration helps data centers to develop cohesive, site-specific strategies, whilst avoiding frequent revisions to their processes and ensuring they don’t get caught in a regulatory web.

Dan Welch, principal engineer at Aeolus, highlights that California is not a regulatory monolith; each county has its rulebook with subtle differences, hence a cookie-cutter approach to data center operations seldom succeeds.

“It’s been over 30 years since the 1990 amendments to the US EPA Clean Air Act, and still, there are areas not in attainment with their air quality standards. When the National Emission Standards for Hazardous Air Pollutants (NESHAP) was introduced 20 years ago, small operators with relatively small generators suffered the consequences of the state-wide, broad regulation as it didn’t specify internal combustion engine types. That regulation developed over the next few years to adopt new emission standards for different engine types.”

As air quality standards become a focus for states, jurisdictions are imposing stricter permitting requirements to meet these ever-elusive attainment levels.

Ozone non-attainment and emissions restrictions

Under Title V of the Clean Air Act, the EPA has defined annual thresholds for various emissions constituents. If a facility’s emissions go over these thresholds, it’s classified as a “major source” of emissions, subjecting it to fees and monitoring rules. These thresholds apply to the entire facility, rather than each individual generator.

The EPA has also identified certain counties as “non-attainment areas” because pollution levels there exceed the standards set by the National Ambient Air Quality Standards (NAAQS). In these areas, the major source thresholds are reduced.

To prevent the possibility of exceeding major source thresholds, air quality boards issue permits limiting the number of hours generators can run.

For some locations, this works well. However for larger data centers, particularly in non-attainment areas where major source thresholds are lower, permitted hours can get so low that deploying generator sets becomes impractical. This is where consultant collaboration shines, as they work with data centers and air quality boards to analyze and develop after-treatment systems for gensets. Efficiency improvements, like reducing the startup time of the selective catalytic reduction (SCR) system, help minimize NOx emissions, for example.

Rich Scroggins, technical adviser for data centers at Cummins, explains why monitoring fuel consumption is preferred over just tracking run hours for a more accurate assessment of emissions:

“The reason they’re limiting run hours is that it’s used as a proxy for emissions. However, monitoring fuel consumption is better because it more accurately indicates the emissions produced. When you only monitor run hours, it assumes that the generator is always running at full capacity, which is often not the case. Generators typically aren’t fully loaded, especially during tests, so measuring fuel consumption provides a more accurate model of emissions.”

Regional emissions regulations

Maricopa County

McDonald illustrates the regulatory complexities that data centers face using a real-world example from his work in Maricopa County, Arizona:

“Maricopa County is a major data center hub, currently the fourth largest in the US. With expansions in Mesa and Goodyear, the county’s sliding window rule treats any expansions within four years as a single installation, which can trigger stricter facility caps. Due to worsening pollution, Maricopa County’s air quality status is being downgraded from attainment to non-attainment, with stricter emission limits. This downgrade reduces the facility cap from 100 tonnes to 50 tonnes, requiring further restrictions on operating hours.”

“Data centers are federally allowed 100 hours a year for non-revenue-generating runs, like engine tests, typically done monthly to ensure systems are poised in case of an outage. Limiting runtime too much risks reliability. Implementing NOx reduction technologies extends allowable runtime since NOx contributes to ozone formation. These technologies, such as preheating for SCR systems, improve emissions control efficiency.”

“Maricopa County has cooperated with the industry, and so far we’ve had tremendous success in data center expansions while adhering to regulations.”

California

As McDonald mentioned earlier in the talk, integrating several emissions control technologies effectively requires experience and skill. Welch discusses how to make these technologies work together in practice to meet emissions standards:

“The concept of best available control technology (BACT) is key when it comes to emissions regulations for data centers. For backup diesel generators, BACT can vary by jurisdiction and what precedents have been established. You can make a very good argument that putting these add-on controls, especially in relation to SCR, is not very helpful for routine non-emergency operations, because the engines cycle on and off before the catalysts can heat up and effectively reduce emissions.”

Welch explained that once a precedent for certain emissions controls, like diesel particulate filters or oxidation catalysts, is set, it becomes the new standard for other data centers in the area, even smaller facilities. This can create challenges in terms of space constraints and the ability to retrofit older equipment to meet the new requirements.

Oregon’s air toxics regulations

The discussion around BACT requirements segued into the challenges posed by Oregon’s Cleaner Air Oregon initiative, which regulates air toxics emissions beyond just the traditional criteria pollutants. Welch recalled:

“Oregon’s program, adopted about seven years ago, closely mirrors California’s 1987 Community Right to Know legislation, following the 1985 Bhopal incident. It requires characterizing air toxic emissions from existing operations and assessing health risks. For new projects, you must evaluate maximum potential emissions. The question is, what emissions data should be used for this assessment?”

As Welch explained, this regulation, requiring health risk evaluations from a broader range of compounds, can create additional complexities for data center operators, who may need to rely on emissions data and modeling that is not always clear-cut or well-established.

Emissions compliance planning in data centers

In closing, the panelists stressed the need for data center operators to engage with experts early and often when it comes to navigating emissions regulations. By being transparent about expansion plans and leveraging the latest emissions control technologies, data centers can help future-proof their facilities.

Scroggins emphasized the importance of global manufacturers like Cummins staying engaged with local markets and regulations, as requirements can vary significantly between countries and even within the same country. The panel also highlighted the broader pressure on diesel engines, with some jurisdictions adopting regulations considering a wider range of air toxics. However, the experts argued that diesel engines will remain viable for at least the next decade, especially with continued advancements in emissions control technologies and the use of low-carbon fuels.

By collaborating with manufacturers, consultants, and regulators, data centers can navigate the complex web of emissions rules and requirements, ensuring their backup power systems remain compliant and reliable in the years to come.

For more information visit Data Centers | Cummins Inc.