Running a refrigerated trailer comes at a price, but several proven strategies can help fleets save some cold, hard cash.
“Door switches is one that is overlooked quite a bit,” says Paul Kroes, strategic insights leader for Thermo King Americas, describing such switches as a feature that has the single-biggest impact on reducing reefer run time.
Some operators are under the misconception that refrigeration units should continue to run when doors are open, but that simply pulls in warm air that will continue to circulate through the trailer once the journey resumes, he said in a presentation for the Technology and Maintenance Council of the American Trucking Associations. A door switch will turn off the transport refrigeration unit each time the door opens.
The layout of the trailer interior will make a difference of its own. Chutes, return air bulkheads, and insulated bulkheads all help to ensure air is evenly distributed.
There are also structural issues to consider when spec’ing the refrigerated trailer itself.
While most people are familiar with R values in home insulation, reefer insulation is measured by an inverse number known as a K-factor. Blown urethane, for example, has a typical R-value of 7.14 per inch, compared to a K-factor of .14. Styrofoam has a K-Factor of .275, while fiberglass is typically measured at .33, wood is at 1.00, steel is at 310, and aluminum is at 1,500.
The higher the K-Factor, the more heat will transfer through the material. An inch of aluminum might transfer 1,500 BTU per hour, compared to urethane that will transfer 0.14 BTU per hour, explains Tim Schmeits, director of engineering – Everest SS Great Dane.
Trailer walls are constructed with a mixture of material, though, including things such as plastic liners, freon-blown urethane, aluminum posts, and aluminum skins.
“We’ve got to take all of these materials into consideration,” Schmeits says.
The final Ua values consider all the pieces together. And the higher the Ua, the more work the related cooling unit will need to do.
Increasing Ua values
Several common design features all conspire to increase the Ua values – such as closer upright spacing that requires additional uprights, cargo tracks, additional crossmembers or roof bows, lower fifth wheel heights, and meat rails.
To compound matters, any insulating value that is achieved will steadily degrade.
“The foam in that sidewall, or roof, or floor is going to degrade over time,” Schmeits says, referring to factors such as outgassing of the blowing agent gas, and the damage from normal wear and tear. “It’s also going to degrade from moisture intrusion into that foam.”
But while plastic liners are permeable, they can be enhanced with metal foil, he says, referring to one strategy that will help.
“Incorporating a metallic foil into the liner creates an impermeable layer to virtually eliminate the opportunity for water intrusion. Not only is this important on the interior of the trailer, but also below the floor insulation,” Schmeits says. The lower layer protects against road splash and spray.
“Incorporating a metallic foil in the liner also significantly reduces the outgassing and extends the life of the trailer, as well as the life of the cooling unit due to lower hours of operation.”
The good news is that interior trailer liners are stronger than their predecessors. This offers fleets more opportunities to incorporate changes such as lower scuff bands in the name of saving weight, or lowering the overall heat transfer rate to place less wear and tear on the refrigeration unit itself.
The value of telematics
As important as the structural features are, operating and maintenance decisions are increasingly being driven by telematics data.
Product-specific setpoints improve the integrity of the cargo inside, but also lower the short cycling, extending the lives of starters, relay boards, and batteries, Kroes says as an example.
Through telematics, operations teams can also keep a closer eye on factors as diverse as the reefer status, the real temperature of a load, and locations. From the standpoint of compliance and security, this will help to prove that temperatures were maintained, and records all door openings.
But there are cost savings to be realized, too. Telematics data can lead to proactive maintenance activities before small issues spiral out of control. And the data ensures the most fuel-efficient mode is always used.
Alerts from critical components such as ABS and lighting can identify if a trailer has an issue before it hits the road. And the warnings triggered during a journey can help maintenance teams identify an issue and even order a part if needed.
Each operation will have unique needs to address.
“A trailer traveling through a mountain region hauling an average weight of 30,000 lb. is living a completely different lifecycle than a trailer moving throughout the southeast with an average weight of 15,000 lb.,” Schmeits explains.
“Looking at your fleet’s diagnostic data, fault codes, and miles traveled with an issue allow you to understand broader patterns and trends, and ultimately change your maintenance program. Usage information from miles traveled to load/unloaded miles can help you reallocate your fleet to areas where there is more need and inform your next purchasing decisions on new trailers.”
The data streams have power needs of their own, of course, which can strain the charging system, reduce battery life, and increase operating hours overall. It’s why Kroes refers to solar panels as one of the most “profound innovations” to address the related issues.
Tapping into the power of the sun, components last longer thanks to reduced runtime, alternator offloading, and starter engagement, he says. Employees spend less time responding to low-battery alarms, too.
“The technology has matured to the point that it’s durable enough,” Kroes says.
And like any other piece of equipment, reefers benefit from preventive maintenance.
“One of the big ones is obviously cleaning out the coils,” Kroes says. But he warns that steam cleaners and high-pressure washes can damage the coils. Air pressure tends to be the best method where it’s allowed.
When it comes to the engine itself, one of the goals will be to minimize vibration caused by things like cracked frames and brackets or misaligned belts. “You can get some serious wear and tear,” Kroes says, referring to the value of a belt tension gauge.
Today’s fuels are also conspiring against the system. Ultra Low Sulfur Diesel includes lower levels of lubricants and aerodynamics that help to protect legacy fuel systems, Kroes explains. Fuel additives have been introduced to address the issue, but they also lead to more water that contributes to oxidation and microbial contamination.
Here, it’s important to clean the fuel inlet screens at the transfer pump inlet, and to use new copper gaskets at every preventive maintenance interval. Kroes also recommends performing clarity tests at every preventive maintenance interval.
It’s yet another example of the benefits that come with a clear maintenance strategy.