Single Family, Multiple Applications: Thermo King Redesigns Multi-Temp Systems

Following the reengineering of its wide-post SB series trailer refrigeration systems in 2000, Thermo King has announced a complete redesign of its multi-temp units. As of November 2001, all multi-temp systems in the Thermo King line for trucks and trailers carry the Spectrum designation.

All units carry the Spectrum name, because the entire line shares a high degree of parts commonality. This is especially true of the SB wide post units and the Super II narrow post systems, which share the same engines, compressors, and control systems. In addition, the Spectrum line has been designed to use a new line of remote evaporators. These evaporators are the same for all trailer units. Slight modifications have been made to Spectrum evaporators for multi-temp truck applications. With a host unit and two remote evaporators, Spectrum trailer units can provide positive temperature control in three separate compartments.

For large trailer applications, Thermo King now offers the Spectrum SB and the Spectrum DE. The SB is a conventional host refrigeration unit with a single evaporator outlet plus the ability to operate one or more remote evaporators. The Spectrum DE is a nosemount, wide-post refrigeration unit with a split evaporator. With separate plumbing to each side of the split evaporator, the DE can provide dual temperature control in a center-divided trailer without remote evaporators. With the addition of a remote evaporator, the DE can provide three zones of temperature control — two from the host unit and the third from the remote evaporator.

Noise Abatement Standard

The Spectrum SB is built on the new Thermo King SB-series design with Whisper noise abatement as standard equipment. To provide for the increased capacity demands placed on a multi-temp system, the condenser coil in the Spectrum SB is 30% larger than in previous Thermo King wide-post multi-temps. The larger condenser allows the Spectrum SB to increase capacity in the fresh temperature range. The Spectrum SB provides 51,000 Btu/hr capacity at 35° F, 31,000 Btu/hr at 0° F, and 20,000 Btu/hr at -20° F.

For a capacity comparison, the Spectrum DE offers 45,000 Btu/hr at 35° F, 29,000 at 0° F, and 17,200 at -20° F. Although the Spectrum Super II uses the same compressor and an engine with identical horsepower, the smaller narrow-post unit case limits condenser and evaporator coil sizes. As a result, capacity of the Spectrum Super II is 43,500 Btu/hr at 35° F, 27,000 at 0° F, and 16,000 at -20° F.

More Efficient Operation

All three trailer units in the Spectrum series can operate in the Cycle-Sentry start/stop mode. Special programming in the microprocessor control system helps make Cycle Sentry more efficient in multi-temp applications. Until recently, the controller sensed temperature in each temperature zone as though that were the only zone in operation. As a result, the controller might cause the host unit to run to satisfy a demand for temperature change in the medium temperature compartment. However, almost as soon as the thermostat for that zone was satisfied and the unit shut down, the unit would begin running again to satisfy a change in the frozen compartment temperature. With this scenario playing out, a unit could be set for Cycle Sentry, yet remain in running mode almost all the time.

The new Smart Reefer MP-IV controller programming causes the unit to run slightly longer every time it starts to ensure that all temperature zones are satisfied before the unit shuts down. The result is longer runs when the engine is running, but less total run time during a trip.

Two options are available for use with the MP-IV control system. Thermo King's DAS data logger has a 512K memory that can monitor up to six sensors. Rear remote control panels for two-zone or three-zone operation allow unit operation from inside the trailer at the rear. These remote panels allow the operator to set and check temperature in all compartments and to turn the system on or off in each compartment.

Remote Evaporators

Remote evaporators for the Spectrum series are new. The S-series evaporators are available as one-third trailer width for multi-lane trailers or one-half width for center divided trailers or conventional latitudinal divided compartments. The new remote evaporators replace the TLE-series that was introduced in 1998. That thin-line series of evaporators was only 6.75 inches deep compared to nine inches for previous Thermo King remote evaporators. The new evaporators are roughly one inch deeper than the TLE-series — 7.9 inches — while still mounting close to the ceiling for increased trailer cube and protection from damage during trailer loading.

Thermo King says it puts the extra evaporator thickness to good use. The evaporator coil in the new system is 30% larger than the coil in the TLE-series. In addition, the impellers have more blades. The result is higher airflow through the evaporator and higher thermal capacity. Although modified slightly for trucks, the S-series evaporators are essentially the same for truck or trailer application. Capacity of S-series evaporators is 29,600 Btu/hr at 35° F, 18,400 at 0° F, and 11,950 at -20° F. Air flows through the systems at 1,200 cubic feet per minute.

Two new Spectrum trailer units have improved maintenance requirements. The SB and the DE have been upgraded to EMI-3000 maintenance standards, which allows service intervals to be extended to 3,000 hours. The extended interval is standard on the wide-post units and optional on the Spectrum Super II.

Thermo King's new truck multi-temps are called the Spectrum TS and are based on the company's line of truck units with scroll compressors. The microprocessor controller provides the same tight temperature control available with Spectrum trailer units. The new remote evaporators provide 35% more capacity and 25% more airflow than previous Thermo King remotes for truck units. The DAS data logger is available as an option.

Truck units have a new remote control panel designed to fit into the radio slot on the truck instrument panel. The panel is easy to operate, even in gloves. Text and graphical information on a simple interface is available in multiple languages. Once engaged, the controller prompts the user to complete any intended operation.

All Spectrum units are compatible with Thermo King's new wireless data transmission system, R:Com. This system allows tracking of units while at a terminal and downloading of data from the unit data logger.

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