Cold plate refrigeration uses frozen eutectic plates inside the body compartment to absorb heat as a means of maintaining desired temperature levels. Those passive plates are "refrozen" each day during a 10 to 12 hour electrical plug in of the on board refrigerant compressor. Probably the greatest misconception or user mistake made with any variation of cold plate system is that frost or ice on the eutectic plate surface means it's cold and that's good. Not so, just the opposite is true. Frost and ice act as insulation blankets and actually prevent the plates from performing their assigned task of absorbing BTU's of heat from air inside the body space.
Cold plate systems have three basic variations in design. The original passive plate design with no air circulation inside the body and plate recharge only while plugged into a stationary electrical source. The newer "plate/blower" medium temp. cold plate systems are designed to incorporate fans which circulate air over the frozen plates to improve desired temperature maintenance and consistency through out the entire body space. These plate blower systems offer improved plate defrost capabilities as well. The third basic design variation adds a nose or under-body side-mounted diesel generator set providing continuous power to the refrigeration compressor. This permits a continuous recharge of the eutectic plates over the route operating day, maintaining desired temperature over a longer time.
Satisfactory product quality assurance using cold plate refrigeration absolutely requires high and consistent levels of product handling standards. It also requires education, training, daily supervision, and management commitment. Cold plate systems simply do not have the ability to overcome careless, sloppy product handling and route operating practices.
All but the smallest capacity over-the-road mechanical refrigeration systems today are directly powered by a diesel engine. The basic systems use a diesel engine to drive a refrigeration compressor which circulates refrigerant through an evaporator unit coil. A high volume forced air is blown over those coils. This continuous "heat exchange" may be operated indefinitely and, depending on equipment performance specifications, maintains any desired operating temperature from -20 degree F to plus 45 degree F for dairy or ice cream products.
Modern over-the-road mechanical refrigeration offers virtually unlimited ability to guarantee delivered product integrity and quality. Advances in refrigeration compressor design have provided improved operating efficiency and increased capacity. Innovations in diesel engines and electronic controls now permit automatic engine starts and stops, and lower operating speeds as determined by power requirements of the compressor in maintaining temperature settings. Power plant "cycling" and RPM reduction extends operating life, while reducing noise levels and fuel consumption.
Communication, global positioning systems (GPS) and sensor technologies offered by original equipment mechanical refrigeration manufacturers (OEM's) combined with third-party providers now permit complete (real time if desired) in-route monitoring and proof of product temperature, location and any unauthorized product access. In addition to providing quality assurance to customers, those same capabilities will answer many of the new federal food product protection requirements mandated by Congress and Homeland Security.
The "bottom line" is cold plate refrigeration in any of the basic variations is cheaper to purchase, maintain and operate than its mechanical refrigeration counter part. However cold plate systems are finite in ability to absorb heat BTU's and can not overcome sloppy route and product handling practices. Whereas over-the-road mechanical systems almost certainly cost more to purchase, operate and maintain. But, their ability to maintain desired temperature settings is virtually unlimited. And mechanical systems may be specified with the luxury of sufficient spare capacity to overcome or compensate for poor route operating practices. With diesel power now the standard, mechanical refrigeration has joined cold plates in the long-life transportation asset class.