Keeping the Cold Air Inside

New trailer building materials help control heat transfer better.

At noon on a hot summer day, food ship­pers can expect the roofs of their refrigerated trailers to reach temperatures of 178 degrees. That means the refrigeration units on those trailers have to work that much harder to cool the contents inside.

These harder-working refrigeration units mean less thermal efficiency, leading to increased fuel costs, a loss of excess cooling capacity, problems maintaining internal temperatures—and potential product damage as a result, and eventually, a total breakdown of the equipment.

So what’s a shipper to do? “You could run your trucks at night,” quips Rod Ehrlich, senior vice president and chief technology officer at Wabash National, a trailer manufacturer based in Lafayette, IN.

Not possible, you say? Well, then, “if you operate your trucks during daylight hours, you need to be concerned about radiant heat,” Ehrlich says.
At Wabash, the solution to radiant heat has been to replace the typical aluminum trailer roofing with SolarGuard, a fiberglass-reinforced plastic with special pigments that prevent UV rays from being absorbed by the roof panel. “We had to look at other materials besides metal because metal conducts heat,” says Ehrlich.

Johnson Truck Bodies, Rice Lake, WI, has also eliminated the metal on the outside of its vehicles. “Now, we always use fiberglass as the external liner because it does not transfer heat the way metal does,” says Matt Huerth, senior inside sales manager. “At the perimeter of the roof, where you would traditionally have steel, it’s been replaced with a plastic thermobreak. The sidewalls are all plastic too. They’ve been a highway for heat transfer in the past.”

Together with fiberglass interior liners, the molded, seamless fiberglass exterior panels are almost 900 times more resistant to heat penetration than traditional aluminum skins, company officials claim.

But, outdoor temperatures are just a small part of the problem when it comes to getting the most efficiency out of refrigerated trailers. As refrigerated trailers age, the high-pressure polyurethane foam insulation between the internal and external skins degrades, caused mostly by a breakdown of the liners over time.

“The foam insulation is a very complex chemical, and the foam manufacturers are always coming out with new and different things,” says Chuck Cole, manager of technical sales and product training at Utility Trailers, City of Industry, CA. “We are always watching what they’re doing because it’s such a big part of our business. We’re constantly trying out new foam variations, and we’re still evaluating composite or alternative materials.”
According to Cole, urethane foam is the industry standard, but the real question to ask is how thick it has to be.

Ehrlich agrees. “We have always used urethane foam. The optimal density is 2.1 pounds per cubic feet,” he says.

The liners themselves are now the center of attention in the trailer manufacturing world, with everyone trying to be the first to market with the new, stronger, more durable, longer-lasting liner.

U.S. Liner Co., Cranberry, PA, a division of American Made and one of the leading manufacturers of trailer lining materials, received a patent recently for its Bulitex refrigerated trailer panels. These panels, made of a multi-layered, woven fiber thermoplastic composite, include a proprietary fabric backing that ensures mechanical adhesion by the foam insulation, creating a stronger bond without the use of screws or special adhesives.
A U.S. Liner Co. spokesperson called the new liner composite “an impenetrable, ballistic-grade material that is more than four times tougher than traditional liners.”

Johnson’s liners are “very impenetrable, 10 times more resistant to puncture than traditional liners,” says Huerth.

Earlier this year, Great Dane Trailers, Louisville, KY, introduced its own liner variation, called ThermoGuard. It is a new one-piece, glass-reinforced, thermoplastic liner that company officials say can potentially reduce cooling unit run time by about 1,000 hours over five years.
ThermoGuard linings “will improve fuel economy almost immediately, within two to three years at least,” says Charles Fetz, vice president of research and design at Great Dane. “It’s something that’s taken us several years to develop, but over a long period of time, you will see real benefits.”

“Reefer owners have always been in a race against time to get the most usefulness out of their trailers before the insulation got too old,” says Phill Pines, chief operating officer at Great Dane. “Until now, the only way to compensate for the decreasing insulation performance has been to make sure the cooling unit had enough excess capacity to maintain temperatures over the course of time.”

Now, the options are much greater. “Everybody is making their trailers better,” Utility’s Cole notes. “There’s a much higher content of glass-lined and composite materials that are stronger, more durable and more impervious to damage, moisture and heat transfer.”

To that end, Johnson Truck Bodies devised a seamless fiberglass ArcticTherm interior liner that company officials claim offers a 26 percent improvement in thermal efficiency compared to other liners.

“We keep trying to improve on our processes, including the foaming materials and liners,” says Huerth. “We’ve found that fiberglass gives us another advantage—we can seal floors, walls and ceilings seamlessly in a one-piece liner that has no junctures for water to build up. It gives us both a strength advantage and a cleaning advantage.”

Regardless of what they’re made of, though, “one-piece liners have quickly be-come the industry standard for cleanliness, attractiveness and durability, and there are no seams for water to get into them,” says Great Dane’s Fetz.

Moisture is also a big factor for a number of reasons, least of which is that it causes the insulating materials to break down more quickly. “Water expands when it gets cold, and when it gets inside the linings, it causes a breaking of the foam cells and allows essential gasses to move and escape, he continues. “Getting the trailer sealed up properly against moisture is the key to its long-term longevity.”

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