In Focus: Truck refrigeration

Thermo King SB-210

As the price of fuel goes up and up, keeping food cold on the road costs more and more. Yet shippers are more and more demanding about temperature conditions.

The first priority in controlling reefer costs today has to be fuel consumption, and experts for both major suppliers of truck refrigeration systems mentioned the use of programmable microprocessors to control the unit.

Carrier Transicold’s product shield feature, found in the advanced microprocessor, provides intelligent refrigeration system management, says Ignacio Aguerrevere, the company’s director of marketing and product development. “Based on customer parameters and inputs from sensors within and outside the trailer, the microprocessor judges when it’s time to use high or normal airflow, and when to use continuous-run mode or auto-start/stop,” Aguerrevere says. Running in start/stop mode – when the box temperature can be controlled tightly enough – saves fuel by running the engine and compressor only under full load conditions, he says.

Jerry Duppler, trailer product manager at Thermo King, says that up until about 1995, units used simple rheostats. “Now, we can provide various fuel economy modes using complex algorithms that help optimize the use of things like stop/start mode versus continuous run to determine the best way to run the unit,” Duppler says.

Thermo King units also employ what Duppler calls “electronic modulation control” to operate an electronic throttling valve on the suction side of the compressor that replaces the simple mechanical throttling valves of yore; this controls capacity and adjusts the evaporator temperature continuously to optimize it for the conditions, which can increase cycle efficiency. There is even an electronically controlled expansion valve that protects the compressor from liquid refrigerant ingestion while eliminating the 10-15 degree Fahrenheit superheat formerly needed, thus effectively increasing the size of the evaporator and giving the compressor less work to do, Duppler says.

Telematics can provide data on operating parameters like run time and mode – start/stop versus continuous or use of high airflow rather than normal – to establish a baseline that shows fleet managers when the operator needs additional training or if the unit needs maintenance, Aguerrevere says.

All ashore
Both companies offer units that can run on shore power. “It’s been around for 40 years, but escalating fuel prices and environmental concerns have increased interest recently,” says Duppler, who adds that exhaust emissions are eliminated and noise pollution is eased.

Running on the grid costs less, using as little as 55 to 60 percent of onboard diesel power, Aguerrevere says. But, according to Duppler, it’s generally impractical except when used by food distribution companies or their carriers, whose units sit at docks equipped with shore power for long periods.

Thermo King shore power-capable units are direct-driven from a unit-mounted electric motor via a simple clutch, which minimizes mechanical losses. Carrier offers both direct drive and Deltek hybrid diesel-electric technology; the latter employs a 440-volt engine-driven generator that drives a compressor with an internal motor. The high voltage minimizes electrical losses, and the unusual design can reduce fuel costs in certain modes, Aguerrevere says.

Deltek technology uses electric resistance heat supplied by the engine-driven generator for the cold, while standard reefers use “hot gas” for heating, Aguerrevere says; this mode bypasses the condenser and expansion valve, and uses the compressor to pump warm, slightly compressed refrigerant into the evaporator. This can become inefficient and even ineffective in extreme cold, he says.

The Deltek design also eliminates the compressor shaft seal, the hot gas parts and many of the mechanical parts like drive belts and clutches, replacing them with maintenance-free electric motors, Aguerrevere says.

Figuring the life
One of a fleet manager’s biggest challenges in a world of escalating fuel and other costs is calculating when it becomes cost-effective to replace a reefer. Both experts agree that the real cost of operation consists of three components: fuel, routine maintenance, and unscheduled maintenance and breakdowns. The third item ultimately may affect relations with shippers and the fleet’s gross income, make drivers unhappy and often add ruined cargo to the equation.

Unfortunately, says Duppler, “There’s no rule of thumb to say when you should replace a unit. You need to understand the total cost of operation.” All three costs rise steadily with age.

Duppler suggests doing the math: “Try to calculate annual costs, figure in resale value, and do a straight payback analysis.” California Air Resources Board regulations are another factor that should influence a decision, Duppler adds: By January 2009, all reefers seven years old and up will be affected. Solutions for those who want to run a unit nine or 10 years would include retrofitting a diesel particulate filter or even replacing the engine with a CARB-approved model. The rules apply the first time a company enters the state – they are not limited to vehicles domiciled there.

Newer units not only give drivers many fewer breakdowns to complain about, but also are much easier for them to operate, Aguerrevere says.

Are there classic errors in spec’ing fleets need to avoid? A common one is buying the van and reefer unit as if they were separate items, Aguerrevere says: “They work together as a system and should be spec’ed jointly, considering the application.” Also, consider future needs, not just today’s, as fleet hauls may change.

Also a big deal to both Thermo King and Carrier is the number of door openings, which can vary, according to Duppler, from “200 a day to closed for four days.” Also consider both temperature and humidity, which is the air’s total energy content; air that is 90 degrees F in Minneapolis puts a lot less load on the unit than air at the same temperature in New Orleans.

Duppler also thinks it’s important to consider solar heat gain, normally more severe in southern climates; some reefer designs have special features to reduce it. Companies also have to balance the cubic capacity needed to optimize for dry freight backhauls with thicker walls and better insulation that will save both fuel and maintenance costs, he says.