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Answers to Your Tier 4 Questions

What exactly is Tier 4?

Tier 4 refers to a set of emissions requirements established by the EPA to reduce emissions of particulate matter (PM), oxides of nitrogen (NOx) and air toxics from new, non-road diesel engines. As part of this clean air initiative, the EPA proposed New Source Performance Standards (NSPS) to define the acceptable levels of emissions in large stationary generator sets. Standards set forth by NSPS are intended to regulate national emissions and are designed to be progressively tightened over time to achieve a steady rate of air quality improvement without unreasonable economic disruption.

What is the difference between Tier 4 interim and Tier 4 final?

Tier 4i, or interim, refers to the NSPS emissions standard that became effective on Jan. 1, 2011, for all new, high-horsepower diesel generator engines. The Tier 4i standard significantly cuts NOx emissions, and expands operational flexibility to also include non-emergency use with the achievement of Tier 4i certification.

Tier 4F, or final, refers to the NSPS emissions standard that will become effective on all large stationary generator sets (gensets) in 2015. Requiring a significant reduction in PM, Tier 4F represents the highest level of clean air regulations proposed to date. The EPA began issuing Tier 4F certification in January 2014. Cummins Power Generation was the first generator set manufacturer to apply for and receive Tier 4F certification.

What are the specific Tier 4i and Tier 4F emissions restrictions for high-horsepower, stationary gensets?

Allowable emissions are dependent upon the size of the generator.

How does the EPA interpret emergency operation versus non-emergency?

The EPA defines “stationary emergency applications” as those in which the generator set operates only during periods of an outage of the normal utility power supply (with the exception of limited-duration operation for testing and maintenance). All other uses, such as prime power, rate curtailment and storm avoidance constitute non-emergency use.

How are emissions regulations defined for emergency and non-emergency?

The EPA does not impose a limit on the number of hours that a generator may operate in emergency situations. However, the EPA does limit operators to run their emergency gensets 100 hours per year for maintenance and exercise purposes. And while emergency run time is unlimited, Tier 2 emissions levels are also in effect during emergency usage.

My manufacturer requires that I periodically operate my gensets for maintenance and testing. Does this count against the 100 hours of yearly non-emergency operation?

Yes. All maintenance, testing and non-emergency uses count toward the 100-hour yearly limit.

Storm avoidance operation is important in our business. How does Tier 4 affect us?

Storm avoidance is an effective tool for large stationary genset operators to mitigate potential risks of incoming storms, rolling blackouts or other unforeseen natural disasters. Only gensets that are EPA Tier 4i or Tier 4F-certified are permitted to operate with no limits for such circumstances. Those seeking best available technology or lowest emissions possible may opt for an EPA Tier 4F certification.

If I need generators for rate curtailment or prime power, what’s required to comply with Tier 4?

Essentially, large, stationary gensets must be Tier 4i or Tier 4F-certified for all non-emergency applications. Rate curtailment, where the operator elects to run during a utility’s peak demand period in exchange for rate reduction, and prime power, where the operator elects to run the genset as a primary source of power, are common non-emergency uses. Non-emergency operation is only legal when using a Tier 4i or Tier 4F-certified genset.

There seem to be a lot of different ways to interpret the Tier 4 standard. What are the differences among certified, compliant, and verified?

Before we talk about the differences among these classifications, it’s important to realize first that Cummins provides fully EPA certified Tier 4i and Tier 4F gensets.

Certified — Means that the complete genset system (engine and exhaust aftertreatment) has been tested by the EPA on-site at the manufacturer’s location, and therefore does not require additional testing once installed. Cummins has a comprehensive, full line of 4i and Tier 4F certified high-horsepower stationery gensets.

Compliant — Means the manufacturer has tested and internally validated compliance with 4i or 4F, but the unit must be tested by the EPA once installed to verify compliance. This may also be referred to as “verified.” It’s important to understand that in this case the OEM has not engaged with the EPA for certification; site verification is not a substitute for official EPA Tier 4 certification.

Will my Tier 4i-certified generator set need to be re-certified or modified to meet Tier 4F in 2015?

No. The EPA’s 2015 4F classification will apply only to new gensets installed after the standard’s effective date. The Tier 4i certification has been in effect since 2011. As a result, all new gensets installed since that date that meet Tier 4i certification are acceptable for usage into the foreseeable future.