Power to the plates

Eutectic holdover plates for truck body refrigeration provide exactly what many local and regional delivery fleets need — reliable temperature control at low cost with a minimum maintenance requirement. However, like all good things, plates come with strings attached: in this case, in the form of an electrical power cord, because plates must be connected to a power supply every night to recharge their refrigerating capacity.

A recent development resulting from the cooperation between Johnson Refrigerated Truck Bodies, a subsidiary of Carlisle Corporation, and International Truck and Engine Corporation has the potential to sever strings holding back plate users. The exclusive agreement between the two manufacturers will not eliminate the need to recharge the plates, but it will help extend the range of trucks using holdover plates as their sole method of temperature control.

Holdover plates are popular among local delivery fleets for products such as milk and ice cream, says Greg LaFrance, director of sales and marketing for Johnson. For instance, The Schwan Food Company, the national home delivery marketer of frozen foods, uses holdover plate refrigeration throughout its fleet.

Big ice cubes

Holdover plate refrigeration requires two main components. The plates actually are large, flat steel tanks containing tubing for circulating refrigerant gas. This tubing is surrounded by a salt brine solution that freezes at a specific temperature and thaws at a predetermined rate, much like the plastic containers of gel that home consumers can use for preserving foods in an ice chest. For transportation applications, the plates can be mounted on the ceiling or walls of a truck body or placed in a housing along with electric fans at the nose of the body. Johnson uses holdover plates from Dole Refrigerating.

A separate refrigeration compressor and condensing unit powered by electricity is used to pump refrigerant gas through the plate tubing until the eutectic solution is frozen solid. At that point, the holdover plates have reached maximum refrigerating capacity, which is expended during a delivery route as the plates slowly thaw. In technical terms, the plates do not thaw, but actually absorb heat from the surrounding cargo compartment. At Johnson and other providers of holdover plate refrigeration, compressor/condenser units are supplied by Copeland Corporation.

An entirely passive system, holdover plates require several hours, usually six to eight, for charging. Once the refrigeration compressor is disconnected from the power source, the capacity of the plates has a finite life depending on the temperature required, ambient temperature in the delivery area, and driver actions such as keeping truck body doors closed as much as possible. Other factors such as strip curtains on truck body doors can help maintain cargo compartment temperature. In typical local delivery applications, holdover plate refrigeration is effective for 10 to 12 hours before the plates need recharging.

Weight limits body size

One other factor tends to limit holdover plate applications. They are heavy. This becomes a matter for compromise. If the truck body fits within certain size parameters, the weight of plates remains acceptable. If the delivery pattern of the fleet fits within the time limits plates impose on operations, plates are an extremely economical and environmentally friendly way to refrigerate product.

The development being pursued by Johnson and International has the potential to change both limiting factors, LaFrance says. As supplied by Johnson, the RouteMax truck body concept is targeted at trucks in the Class 5 through Class 7 range for bodies 12 to 22 ft long. RouteMax is a combination of a Johnson molded fiberglass truck body with an International truck chassis, vehicles in the 4000 series or 7000 series equipped with International's new Diamond Logic PowerPack 3 electrical power system.

International introduced PowerPack 3 at the National Truck Equipment Association Work Truck Show in March 2005. Following that introduction, Johnson debuted RouteMax at the 2005 Worldwide Food Expo held October 26-29 in Chicago.

Truck generates power

PowerPack 3 is a patented onboard AC/DC electric power system that essentially turns the truck alternator into a generator, says Brad Bishop, business line manager — truck electronics, for International. Effectively, the system has removed all the voltage regulation from the alternator, allowing it to produce 52 volts. That voltage runs into PowerPack 3, where it is split into two components — 14 volts DC to power the truck electrical system and 110 volts AC to power the refrigeration compressor for RouteMax. PowerPack 3 provides 3,000 watts of power at engine idle.

PowerPack 3 is available in two versions, Bishop says. One version mounts in the truck battery box, an installation that limits the truck to two batteries. The other version allows PowerPack 3 components to mount at some other location on the truck chassis or in the body. The second version comes with 15 ft of cable to provide mounting flexibility. PowerPack 3 was originally designed to provide power for utility trucks, he says.

Power for the system comes from a large Leece Neville alternator. In the application used by Johnson, the system provides 110-VAC, three-phase power. The basic price for PowerPack 3 is $3,000; the system carries a two-year warranty. International will make the system available for dealer sale in November 2005 and will have a retrofit kit available for earlier-model International chassis early in 2006.

Low fuel consumption

Running PowerPack 3 is comparable to using the truck air-conditioner, Bishop says. It is responsible for less than 2% of total vehicle fuel consumption, he says.

In the RouteMax application, PowerPack 3 is used to run the refrigeration compressor as needed to keep the holdover plates frozen. Providing power to the compressor allows RouteMax to extend the range of trucks refrigerated with holdover plates, says LaFrance.

“Actually the system offers three alternatives,” he says. “The system can keep the plates charged for longer duration routes. By running the compressor during a route, it can allow fleets to use fewer or thinner plates in the truck body, reducing overall weight. Potentially, the system can allow fleets to use lower-capacity compressors. We don't see RouteMax as a way to eliminate system plug-in time, but we certainly see it as a way to extend route duration.”

Running longer routes will allow fleets to make use of the inherent advantages of holdover plate refrigeration. “We can document that plates offer an 80% reduction in hourly operating cost and that the initial purchase price can be 40% to 50% less than other refrigeration systems,” LaFrance says. “In addition, plate systems require almost no maintenance with the exception of a periodic defrost cycle.”

RouteMax has the potential to reduce the weight of vehicles with holdover plate refrigeration significantly. One customer with especially heavily plated bodies thinks vehicle weight can be cut by up to 1,000 lb, LaFrance says.

First volume production of RouteMax is set for March 2006. Johnson has an exclusive agreement with International to combine RouteMax with PowerPack 3. For more information, contact Johnson Refrigerated Truck Bodies, Rice Lake, Wisconsin, or International Truck and Engine.

TAGS: Truck Bodies
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