Don’t let the disparity of manufacturers fool you into thinking reefers are a spec you need spend little time on.
Reefers are complex and rather costly machines that require a diligent by-the-numbers approach when it comes to spec’ing the right one for your operation. Spec the wrong one and you will be eating the cost of spoiled goods every time it fails to do the job.
In fact, recent research conducted by the University of Florida in cooperation with the U.S. Department of Agriculture, found that 46 percent of the reefer owners surveyed had claims, averaging one claim in a little over two years. That’s an alarming number but don’t point the finger at the reefer manufacturers. Both Thermo King and Carrier Transicold have been around for years and their products are well proven. More than likely the problem stems from the user. Reefers tend to be one of the most misunderstood components on a truck.
A reefer unit is basically a big refrigerator on wheels but there is a distinct science behind keeping things cold. The cargo in a trailer is kept cold by removing heat from it. The heat that can destroy a shipment of chocolate ice cream or frozen food meals can invade a trailer from a variety of areas. It can be conducted through the trailer walls, an increasingly likely threat as the industry moves from 96-inch wide trailers with three to four inches of insulation to trailers 102 inches wide with maybe an inch-and-a-half of insulation to improve cargo space and reduce weight. Heat can also find its way into a trailer through gaps in door openings and cracks in door seals. Even a structural member or a steel bolt can become a channel for heat if it passes through from outside to inside.
To remove this unwanted heat, the reefer employs mechanical power to compress and liquefy a gaseous compound that through a heat exchanger called the evaporator basically sucks out heat from the air inside the trailer. The refrigerant compound is passed through a condenser and the heat it has picked up from the cargo compartment removed by dropping the refrigerant’s pressure and blowing outside air across the condenser’s face. What keeps the load at its desired temperature is the reefer’s ability to recirculate cooled air inside the trailer.
The most basic spec you will need to understand when comparing reefers is cooling capacity. This is simply the reefer’s ability to cool under varying circumstances and is measured by the number of British Thermal Units (Btu’s) it can remove in one hour at certain interior temperatures (35F for fresh, 0F for frozen and -20F for deep frozen are the customary interior temperatures reefer dealers will quote) while outside air is 100F. Obviously it takes more capacity to cool a thin-walled 53-foot trailer than a 45-foot trailer with thick walls. In fact, thirty years ago the typical reefer needed to produce about 11,000 Btu/hr to maintain loads at the deep frozen level. Today reefers are pumping out more than twice that to meet the challenges of keeping cargo frozen with the longer, wider and thinner-walled trailer designs.
Hauling a variety of goods within the same trailer at different temperatures can be handled by the same reefer but separate evaporators need to be placed in each compartment and set to run at different temperatures.
It goes without saying that the more information you provide the reefer supplier about your specific application the more informed his spec’ing advice will be. What kind of products are you going to haul, for how long a period, what are the set points of the products you’ll be transporting and where are they going to run – these are all key considerations.
A reefer dealer will use the following formula to calculate the cooling capacity your trailer operation requires: Thermal integrity of the trailer x outside temperature – inside temperature = cooling capacity.
To put this in real world terms, consider the example of a Canadian fresh produce hauler who does local runs with a trailer that has a box loss of 200 Btu/hr/F. Multiply that by 45F, which is the difference of an average warm day (80F) less the temperature the load needs to be cooled down to (35F). In this example, the operation calls for a reefer unit capable of delivering 9000 Btu/hr at an ambient temperature of 80F.
One of the most important advances in reefer technology is the ability to constantly monitor and record the reefer’s operation and the temperature of the load and relay that information to headquarters. Many carriers have avoided costly shipper claims by being able to prove the load was always in the right temperature range while in their care. As the service expectations of shippers increase expect more of them to demand that their carriers spec such capability.
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