https://nacfe.org/research/emerging-technologies/electric-trucks/decarbonizing-truck-and-trailer-refrigeration/

Decarbonizing Truck and Trailer Refrigeration

Zero-Emission Temperature Control in Trucking

Successful freight movement requires the timely delivery of goods from a vendor to a recipient, often using multiple carriers, and many shipments must be kept within a specified temperature range from the point of origin to the final destination. Careful temperature control — the cold chain — has enabled short- and long-distance shipping of temperature-sensitive goods.

Many goods being shipped are sensitive to temperature. These include fresh produce and other perishable foods, pharmaceuticals, electronics, plants and flowers. Other products such as dairy products, chocolate/candy, eggs, meats, fish, frozen foods, paints and other chemicals require temperature control during shipping. This is actually a larger portion of the market than many think. About 15% of the straight trucks and trailers built are refrigerated using a transport refrigeration unit (TRU).

TRU product lines are broken down into two main classes: single temperature which are used for trucks that are either all fresh or all frozen and multi-temperature which can maintain multiple temperature zones in a single truck.

TRUs create cold or warm air which is then pumped into a box that needs to be at a certain temperature to protect its contents. There are several ways to do this, but diesel fuel has been the primary energy source for powering TRUs for the past century.

The primary way to eliminate emissions from TRUs is to replace the diesel-fueled ICE driving the compressor with an electric motor. These so-called electric transport refrigeration units, or eTRUs, are generally powered by either the traction battery when installed on an electric straight truck chassis or by dedicated batteries when installed on a trailer.

There are several benefits of eTRUs compared to conventional TRUs. These include fuel cost savings, noise reduction, and maintenance savings. However, there are also numerous barriers to the expanded use of eTRUs.  These include both operational and cost challenges.

Conclusions

Based on its research and analysis, the study team came to the following conclusions about the state of transport refrigeration today:

• Freight requiring transport in a specified temperature range encompasses about 15% of straight trucks and trailers. Refrigerated and frozen foods, pharmaceuticals, other grocery items and electronics are some of the commodities requiring refrigeration. Other freight, such as fresh produce and paints, require freeze protection during winters. This is a significant — but often unrecognized — portion of North American freight requiring special straight trucks and trailers with diesel-powered transport refrigeration units.
• Regulations and heightened sustainability expectations are converging to require more sustainable solutions for moving refrigerated goods. CARB has been driving regulations that require zero-emission refrigeration and freeze protection for moving goods. This can be a large challenge as today’s diesel eTRUs run off the diesel truck’s engine or from dedicated engines integrated into the TRUs. These have long run times for when the vehicles are in motion or sitting at warehouses or stores to be loaded or unloaded.
• New refrigeration units have been developed to run with zero emissions using electricity. Many forms of eTRUs are available or under development to respond to these expectations and requirements. These include all-electric units some with significant battery storage, systems that accept plug-in shore power as a source and hybrid units that run primarily on electricity but have diesel or other powertrains to support long run times.
• Other allied solutions are emerging to support these eTRUs. Solutions include Increased insulation or even incorporating cold plates into the truck or trailer bodies, solar or axle-mounted generators (eAxles) to deliver more power to the batteries and other innovative solutions.
• Moving and delivering refrigerated goods with zero or significantly lower emissions while maintaining quality is a large challenge. Although independent of electric truck propulsion units, these “cleaner” solutions compete for resources, but also benefit from developments, such as improved battery size, weight and cost. Delivering reliable, durable and cost-effective solutions quickly has many challenges. 
• Activities are underway to plan for and harmonize the connectors and power requirements for charging electric trucks, charging eTRU batteries, and providing shore power when electric reefers are parked or idling. The broad efforts being made to provide charging infrastructure for electric trucks should be expanded to incorporate the requirements of electric transport refrigeration units.