In an upgrade of its Ultra and Extra series trailer units, Carrier Transicold boosts the refrigeration performance available to truckload carriers and wholesale grocery distributors. The two single temperature units are the first of Carrier Transicold's new X series refrigeration systems. Soon to follow in the series will be the top-of-the-line Ultima XTC and the Ultra XTC.
The Ultra XT is the higher performance of the two new units. It is designed for truckload and grocery applications with the capacity to handle deep frozen loads. The Extra XT is intended for longhaul or distribution use at medium or frozen temperatures.
The new X series units are developments of previous single temperature refrigeration systems. For instance, the new Ultra XT offers capacity of 64,000 Btu/hr at 35° F compared to 46,000 BTU/hr in its previous version. All the X series are designed for higher performance combined with lower life cycle costs and longer component life, says Mike Murdock, trailer product manager for Carrier Transicold.
The Extra XT with its 37-cid, six-cylinder compressor is rated for 32,000 Btu/hr at 0° F and 51,000 Btu/hr at 35° F. Deep frozen rating is 18,500 Btu/hr at -20° F. Ratings for the Ultra XT with its larger 40-cid, six-cylinder compressor are more robust, starting at 21,000 Btu/hr at -20° F and increasing to 33,000 Btu/hr at 0° F and 64,000 Btu/hr at 35° F. This increased capacity allows the Extra XT to pull a trailer down to temperature before loading 33% faster than the previous Extra unit; the Ultra XT pulls down 43% faster. Both units are equipped with the UltraFresh 2 temperature control system.
The new unit series makes improved use of components with a long track record at Carrier Transicold. These include the 2.2-liter Kubota engine in the Ultra XT, Carrier's 05G six-cylinder compressor, and the Carrier Transicold microprocessor controller. The Extra XT uses a slightly smaller 1.9-liter, four-cylinder engine, also by Kubota. Components are combined into a refrigeration system with 18% fewer parts and a 23% smaller refrigerant charge, Murdock says.
Reducing the total number of parts in the units leads to longer system life and lower maintenance costs, Murdock says. Among the parts eliminated are a solenoid valve and the radiator fan that previously was located on the streetside of the engine. Integrating the engine radiator with the condenser coil eliminates the need for the engine fan and its drive belt and allows the condenser fan to draw air through both the engine radiator and the condenser coil. In addition, the alternator now mounts directly to the engine, allowing elimination of mounting brackets.
Units are encased in Carrier Transicold's patented composite skins and grilles. The unit skin and doors are formed by fusing two composite sheets together. Murdock says that the fused joint between the two sheets is actually stronger than any other part of the material.
The big changes in the X series are made in the refrigeration circuit, changes that allow the unit to function more efficiently and more economically. Tubing in the evaporator coil has been reduced to 7 mm in diameter, which reduces the total system volume. This change along with a smaller receiver tank and the solenoid valve deleted from the circuit allows the unit to operate with a refrigerant charge that is six pounds less than that required by previous Ultra and Extra units.
Although tubing in the evaporator coil is smaller, it actually has more surface area for heat exchange. To accomplish this, the interior surface of the evaporator tubes is scored with a crosshatch pattern. In addition, the units reject more heat than their predecessors, because the redesigned condenser section pod is contoured to allow higher airflow across the coils.
Additional efficiency is accomplished by increasing airflow through the evaporator section. The Ultra XT and Extra XT eject air from the evaporator housing at 3,350 cubic feet per minute. Carrier Transicold uses a centrifugal fan and an evaporator outlet positioned in the middle of the trailer front bulkhead to move air at the optimum volume and velocity. The increase is 12% greater than airflow in previous units, while operating with a smaller differential in air speed and volume between high-speed and low-speed operation.
Improved refrigeration efficiency results from making full use of compressor capability, Murdock says. Carrier Transicold has redesigned the control algorithms in its microprocessor controller to ensure that unit operation conforms as closely as possible to load conditions and temperature requirements. This optimizes compressor speed for maximum pulldown and for shorter recovery after a door opening. The controller also carefully coordinates compressor cylinder unloading to match unit capacity to the thermostat set point and cargo temperature sensitivity.
Improving refrigeration system efficiency allows Carrier Transicold to operate the unit engine at lower speed, saving fuel, reducing maintenance requirements, and extending engine life. Engines in the Ultra and Extra units previously operated at 1,900 rpm in the high-speed mode. With the improvements in refrigeration function, high-speed rpm has been reduced to 1,700, and the engines operate at 1,350 at low speed.
“Lower speed will result in extended engine life,” Murdock says. “Coupling a low speed engine to a six-cylinder compressor feeding refrigerant to a high efficiency refrigeration circuit gives us the opportunity to provide superior performance without sacrificing major component life.”
Running the engine at a slower speed also helps reduce noise emission. The Ultra XT and Extra XT generate roughly 2 dB(a) less noise than their predecessor units.
