Fresh food comes to our stores and then into our kitchens no matter what the season. That’s no big deal today, but it wasn’t always this way.
People who grew up in cold climes as late as the 1950s can remember when things like firm, flavorful tomatoes simply weren’t available in winter. Women preserved fruits and vegetables at harvest time by “canning” them in glass jars, but when served months later they didn’t taste anything like the good stuff picked from the fields.
Fast trucks with transport refrigeration equipment whisk a great variety of reasonably priced products to market year round. Modern “reefer” units precisely control temperatures to suit the cargo, whether produce, meat, dairy products, candies and beverages, or a host of non-food items like paint and medical supplies.
Long-haul tractor-trailers (and sometimes railroad reefer cars) carry products from packing houses, processing plants and manufacturing centers to distribution warehouses. From there, other big rigs or light- and medium-duty straight trucks carry products to stores. Spec’ing a reefer unit for a truck body is about the same as for a semitrailer, but a few more operational details have to be considered. First, some basics.
Mechanical And Other Reefers
Mechanical refrigeration units powered by a diesel engine constitute the great majority of equipment sold today. The engine spins a compressor and a generator, which supplies electrical power for controls and other functions. The engine sits in the box on the forward wall of the trailer or truck body.
Light trucks with small bodies are often “self-powered” by the truck’s own engine. The reefer’s compressor is mounted on the engine, like an air conditioning compressor. This is generally not a good system for trucks frequently stuck in traffic.
If more than one type of commodity is carried, the trailer or truck body is divided by bulkheads into compartments, and each gets its own evaporator and temperature sensing apparatus. So frozen foods (kept at zero degrees Fahrenheit or less) can be carried with “fresh” foods (usually maintained in the mid-30s or low- to mid-40s, depending on the type) and dry goods (at ambient or below).
Of course, the unit and its compressor run only when needed, whether to cool the load or heat it in cold weather. Electronic controls monitor temps and adjust the output of cold or warmed air, and assist with inspection of the various subsystems in the unit and the trailer or truck body.
Stand By For Clean Air
In a few locales, authorities demand that reefer engines be shut down, along with the truck’s main engine when idle. More of these rules are expected in the future, and can be accommodated by equipping the local facility with power outlets. For the reefer, an electric motor can substitute for the engine. This “stand-by” capability adds perhaps 10 to 12% to the reefer’s cost, and requires a hefty outlay to electrify the facility with 115-, 220- or 440-volt outlets. It also assumes the local power grid can supply ample electricity to the facility.
Steady, reliable power is a requirement for another type of transport refrigeration – the cold plate. One or more of these are installed in the wall(s) of a truck body. The plate contains refrigerant that’s frozen while the truck is parked overnight at its home base. After loading, the plate is unplugged and the truck makes its deliveries. If sized correctly, the plate has enough cooling capacity for the entire run. Compared to a mechanical reefer, the cold plate has almost no moving parts and is less costly to buy – but the supporting infrastructure is expensive.
A third type of transport refrigeration uses super-cold carbon dioxide as the refrigerant. Once filled, pressurized CO2 needs no moving parts to work and no human being or electrical controls to monitor it. Such systems were first used on ocean containers. A small Louisiana company headed by Louis Saia (a scion of the family that founded and later sold Saia Motor Freight) began making a CO2-chilled Pallet Reefer about 10 years ago. These handle shipments of small loads by regular LTL carriers.
And Thermo King, a pioneering reefer supplier, recently began building CO2 systems for trucks, following introduction of a trailer unit several years ago. TK also claims more than four years of commercial CO2 experience in Europe. The system itself costs about 5% less than a mechanical reefer, including a cryogenic tank to carry CO2. But the operator must either have access to a CO2 supply station, or buy one. TK can set up a turn-key station for about $100,000; this stores CO2 at approximately 300 psi and 0 F, and converts it to 130-150 psi and -55 F in the truck’s tank.
Putting Them To Work
Class 2 to 7 delivery trucks with insulated bodies and various types of reefer units are a familiar sight on urban streets. Thermo King and Carrier, the other main supplier of transport refrigeration equipment, build mechanical, engine-driven units to suit varying duties of all truck classes in every region of North America and many countries overseas. They say the spec’ing process starts – as it does with any hauling job – by analyzing the operation.
Sit down with the people you’ll buy from and describe the operation. What’s to be hauled and where, at what temperature(s) and what ambients, in what kind of traffic and street/freeway conditions? How will the truck be loaded, and will the cargo be at the right temperature when it’s put aboard or will the reefer have to cool (or heat) it?
What type and size body will you use? How many doors in the body, and what kind of doors? How many stops per day will the truck make, and how long will the doors stay open each time? Will there be long cruising periods between stops or constant stop-and-go traffic?
As you can imagine, all those operating factors will determine the type and capacity of the reefer unit, which is measured in British Thermal Units. BTU ratings range from a few thousand for small, light-truck units to 65,000 or more for medium-duty trucks.
Reefer size must go up with body size and as desired temperature goes down and outside temperature goes up. A body and unit built for Phoenix will have more insulation and reefer capacity than one made for Chicago. Many and/or lengthy stops with doors open increase the loss of conditioned air, so again the reefer must be bigger. Curtains can contain the cold-air loss, so are another spec’ing consideration.
We won’t get into truck body design, except to say that more insulation means thicker walls, and thinner walls mean less insulation, either of which may or may not work in your operation. Door type also matters, because more or less insulation and sealing capability can be built into roll-up or swing-type doors.
Tell the supplier what you’re going to do with the reefer truck, and he’ll build you what you need. Tell the used-truck sales person what you need and he’ll show you something that’ll work. Just keep this basic info in mind while you shop.
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