A TRU must be able reliably to deliver adequate air-cooling capacity (measured in Btus), with sufficient airflow (in cubic feet per minute) and at sufficient velocity to circulate air throughout the trailer. The entire volume of air inside a trailer should be exchanged approximately once every minute.

The capacity of a TRU quantifies its ability to cool (or heat) a given amount of space or cargo. TRU capacity can range from less than 20,000 Btu/hr to more than 65,000 Btu/hr depending on the cargo and the operating conditions.

The standard approach used for keeping fresh and frozen foods and other goods cool in transport has been to use a small (around 2.0 liter) auxiliary diesel engine to drive a compressor and power fans required for air distribution within the trailer. The TRU engines are not as strictly regulated as the truck engine, and emit greater amounts of pollutants per unit of work (hp-hr). One study concluded that the TRU engine can emit more NO_x than the truck’s main engine when idling.

Because the engine must be able to cool the temperature of a trailer load rapidly (upon loading, for example), the engines are spec’d to produce more power than required during standard operating conditions, and operate at that higher level regardless of operating need.

To mitigate the situation, manufacturers are developing hybrid diesel-electric units and other alternatives (such as cryogenic units powered by high-pressure CO₂—a major downside of which is the release of the fuel into the atmosphere as carbon dioxide). Fuel-cell driven units are under investigation. Some hybrid units are belt-driven mechanical models that support plug-in operation to grid-based power when the trailer is parked (i.e., “shore power”).

Some all-electric TRU models (eTRU) use a combination of shorepower and a smaller diesel genset for over-the-road use. This is the type of system involved in this demonstration project.

The Shurepower demonstration project uses a modified version of Shurepower’s Truck Electrified Parking (STEP) technology combined with a new Carrier-Transicold TRU featuring Deltek hybrid diesel technology.

The Deltek hybrid, introduced in the fall of 2005, features a high-performance diesel genset that powers an electric, sealed compressor. The compressor assures an extra tight refrigeration system because its electric motor is inside the compressor housing—no shaft seal required. Electric evaporator and condenser fans control the flow of air and electric-resistance heat enables on-demand heating, independent of the cooling system.

All Deltek systems offer the built-in electric standby capability that Shurepower will use.

The demonstration will be located at the Maines Paper & Food Service distribution facility in Conklin, NY—the second-largest food distribution center in the country—and will be the first of project to supply grid power to over-the-road electric hybrid TRU refrigerated trailers.

Shurepower will work with the utility company, New York State Electric & Gas (NYSEG), to provide three-phase power to the site. Designated loading docks, along with parking spaces that serve as staging areas for the trailers, will be electrified.

Ten demonstration trailers manufactured by Great Dane Trailers will be outfitted with Carrier-Transicold TRUs equipped with Deltek hybrid diesel electric technology that can be directly powered by electricity.

Shurepower will provide the design of an under-trailer wiring system to carry electricity from the rear connection point (at the loading bay) to the TRU mounted on the front of the trailer. In addition, truck tractors will be retrofitted to allow for shorepower plug-in capability for sleeper cab comfort.

Partners with Shurepower, LLC in this demonstration project include NYSERDA, Maines Paper & Food Service, NYSEG, Carrier Transicold, Great Dane Trailers, Penske Truck Leasing Company, and the U.S. Environmental Protection Agency.

Resources:

• Electric-Powered Trailer Refrigeration Unit Market Study and Technology Assessment