A big rig with a refrigerated trailer. The CARB transport refrigeration unit regulatory concept would limit the GWP of refrigerants in TRUs to 5.
A semi-truck with a refrigerated trailer. Photo credit: Vitpho for Shutterstock.

CARB ‘Regulatory Concept’ Would Set a Refrigerant GWP Limit of 5 for Transport Refrigeration Units

In its current form, the regulation would apply to transport refrigeration units built after December 31, 2032.

The California Air Resources Board (CARB) is considering a “potential regulatory concept” that would require transport refrigeration units (TRUs) built after December 31, 2032, to use a refrigerant with a maximum GWP of 5.

The GWP limit was discussed during a public TRU regulation concepts development workshop hosted by CARB on May 22. It would apply to truck, trailer, domestic shipping container and railcar TRUs but not to TRU generator sets, removable refrigeration units for trailers and containers.

A work in progress: The concept is part of a larger CARB regulatory push to transition diesel-powered TRUs to zero-emission technologies, such as electricity, hydrogen and liquid nitrogen.

  • The impetus for the transition is Executive Order N-79-20, issued by California Governor Gavin Newsom in 2020, which set a goal for 100% zero-emission off-road vehicles and equipment in California by 2035. 
  • A 2022 amendment to CARB’s Transport Refrigeration Unit Airborne Toxic Control Measure (TRU ACTM) requires all truck TRUs operating in California to be zero-emission by December 31, 2029.
  • “CARB will use stakeholder input gathered to refine a potential regulation, but a regulation has not yet been formally proposed or adopted,” Lynda Lambert, Information Officer II at CARB, told NaturalRefrigerants.com. “If CARB does proceed with the requirement, any staff analysis and rationale for proposing such a requirement will be included in the staff report, which is not expected until 2026.”

A massive drop: If this concept were to become a regulation, it would represent a major change from the current GWP limit of 2,200 for newly manufactured TRUs, which went into force December 31, 2022.

  • CARB estimates that, of all the non-truck TRU operations in California, 82% are trailer TRUs, 16% are TRU generator sets, and 2% are domestic shipping container and railcar TRUs.
  • Under the American Innovation and Manufacturing (AIM) Act’s “Technology Transitions” rule, intermodal refrigerated transport containers “with exiting fluid temperature from a chiller equal to or above –50°C (–58°F)” cannot use a refrigerant with a GWP exceeding 700 from January 1, 2025.

NatRef alternatives: While the majority of transport refrigeration units use f-gas refrigerants, natural refrigerant alternatives using CO2 (R744) and hydrocarbons such as propylene (R1270) are available.

  • German manufacturer ECOOLTEC’s TM182, a propylene/CO2 TRU powered by electricity, went on sale in Europe in 2023. In April, U.K. supermarket chain Tesco took delivery of two trucks equipped with the TM182.
  • Carrier Transicold’s NaturaLINE marine container refrigeration unit uses CO2, with the company saying it “delivers sustainability and efficiency equal to our best-in-class performer.”
  • In 2021, Italian gas provider SIAD debuted the COOL FreeToGo, a TRU that used the evaporation of liquid CO2 as opposed to the traditional vapor compression cycle, to provide cooling.

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