As data center deployments accelerate globally, operators are confronted with growing regulatory and infrastructural challenges that impact onsite power generation. Air quality regulations are limiting data centers’ ability to generate power onsite.

In the coming years data centers are expected to be deployed where utilities are constrained, giving operators incentives or even mandates to increase their onsite power generation.

How can data center designers, constructors, and operators find the right solutions, in a global market where the right approach can mean different things in different areas? That’s where choosing the right partnerships comes into play, it’s a vital component for the success of data center facilities.

How did we get here?

Today, diesel generator sets in standby applications must be certified by the EPA to meet Tier II level emissions in the US. Emissions certification is based on levels of several emissions constituents, most notably oxides of nitrogen (NOx) and particulate matter (PM), over a standard test cycle.

For typical emergency standby applications, Tier II certification has been sufficient, and emissions after-treatment has not been required. Beyond that, there are two regulatory factors in the US impacting the deployment of on-site power generation solutions: Major source thresholds and non-attainment areas.

Under Title V of the Clean Air Act, the EPA has defined annual, cumulative thresholds for various emissions constituents above which an installation would be considered a major source of emissions, which would subject it to fees and monitoring requirements. The threshold applies to a site, not an individual generator set.

The EPA has also identified counties, known as non-attainment areas, in which concentrations of regulated pollutants exceed levels set by the National Ambient Air Quality Standards (NAAQS).

Air quality officials in non-attainment areas are required to take steps to reduce pollutant levels, one of which is to reduce the major source threshold. Thresholds vary depending on the level of non-attainment. The default major source threshold for NOx is 100 tons per year but in some cities, the threshold is as low as 25 tons per year.

So why are data centers unique?

With data center installations needing to scale up to address the increasing demand for data, so has the need to increase the amount of power and backup power to support these facilities. These large installations could contribute to total site emissions that would exceed the major source threshold.

To address this, air quality boards issue permits to operators limiting the number of hours a generator set can run to make sure they don’t exceed the major source threshold.

Compliance strategies:

For large sites in non-attainment zones, the permitted operating hours could be so low that it is impractical to deploy Tier II-certified generator sets. In these instances, there are steps operators can take to make sure cumulative emissions levels comply with the permitted allowance. The most common of these are deploying emissions after-treatment systems, reducing testing hours, and monitoring fuel consumption rather than operating hours.

Reducing emissions through exhaust after-treatment

The most common emission after-treatment equipment to reduce NOx is called selective catalytic reduction (SCR). Diesel exhaust fluid (DEF) is injected into the exhaust stream and runs through a catalyst and reacts with the exhaust, reducing NOx output. On average an SCR from any reputable manufacturer will reduce NOx by 90 percent. Adding more catalysts to the system can lead to reduction levels of up to 99 percent.

Reducing emissions levels through optimized exercise schemes

Standby diesel generator sets spend more of their operating hours in testing than in live operational settings, so reducing testing is a tactic for reducing site emissions.

The conventional recommendation has been to run standby generator sets once a month, with at least 30 percent load. With many modern fuel systems, it isn’t necessary to run tests with load, and running no load saves on emissions.

Data center operators should work with their generator set manufacturer to identify an optimized test regimen that minimizes run hours while maintaining confidence that the generator sets will start and pick up load when required. In some cases, generator testing is defined in a customer’s Service Level Agreement so operators should work with their customers to make sure the SLA reflects the optimized test regimen.

Optimizing run hours through fuel consumption monitoring

Some regulators allow monitoring fuel consumption rather than run hours as a proxy for monitoring emissions – this results in a more accurate measure of real emissions.

That is an advantage for the operator because it's a more accurate measure of how much NOx is being put into the air. The permitted operating hours are calculated assuming that the generator is running at 100 percent load which is almost never the case, especially when most of the hours are just for testing purposes with the generator set running at 30 percent load or unloaded. The amount of NOx emitted to the atmosphere in grams per hour (as opposed to the normalized value in grams per horsepower-hour as stated on most data sheets) is lower when running at a lighter load.

Constrained grids: Increasing the demand for onsite power

While emissions regulations have been pushing data centers to reduce their use of onsite power, constrained grids in many regions are pushing data centers to increase their use of onsite power.

Many utilities have offered financial incentives for their customers to participate in grid support programs but data centers have been reluctant to do so as burning fuel and operating their generator sets was considered an operational risk that can’t be justified. Operating generator sets in a grid support program imposes an additional layer of emissions regulations.

In the United States, for example, running a generator set in non-emergency operation (which would include grid support programs) requires the engine to be EPA Tier IV certified. Tier IV certification requires a 90 percent reduction in NOx below Tier II levels and also requires the generator set to shut down if the emissions performance is out of compliance.

This makes the emissions after-treatment system a single point of failure which has been unacceptable to data centers, however as data centers are increasingly planned for locations with constrained grids, participating in demand response programs is becoming a mandatory condition of their connection agreement in some cases, so there is a renewed interest in Tier IV certified generator sets.

Navigating the regulatory landscape

With the myriad of emissions regulations confronting data center operators, it is important to partner with companies like Cummins who have experience deploying generator sets in many different jurisdictions.

Cummins offers the technical knowledge needed to reduce emissions. At the local level, Cummins maintains strong relationships with air quality boards, emissions consultants, and after-treatment suppliers – critical partners in obtaining air permits. The key for data center operators is to begin these conversations as early in the siting process as possible.

What does the future hold?

While there are many attractive low-carbon technologies on the horizon, diesel generator sets are going to be the primary source of backup power for data centers for a long time. The challenges of emissions permitting and constrained grids are only going to get more acute. This will make emissions reduction strategies and securing air permits an even more substantial part of deploying data centers.

Constrained utilities will become more prevalent over the next decade driving data centers to run their onsite generators more frequently in a regulatory environment that will tend to limit their operation. Companies like Cummins, with their technical expertise, experience, and industrial relationships will be key partners to the data center industry in navigating the muddy waters of regulations.

For more information visit Data Centers | Cummins Inc.