How it Works - Refrigerated Trailers

Reefer units are often misunderstood, and this misunderstanding can lead to misguided performance expectations. Today, we will outline some facts that will help us better understand how reefer units work and clarify their operation.

One of the most important elements to keep in mind when thinking about reefers is that they are designed to maintain temperature of the product inside them, not cool. Although it may happen if given enough time, reefers are not designed to for example, bring a field load from upwards to 100°F ambient temperature down to 45°F storage temperature. Reefers are solely designed to remove any increased heat, keep temperature of products stable, and control humidity by condensing moisture in the air.

Common ways that heat enters reefer trailers is through the walls (trailers are insulated to prevent this). Heat can also flow around gaps in door openings, through cracked door seals, through trailer floors, or out of the ceiling. A steel bolt or a structural member will act as a conductor if it passes from outside the trailer to inside. Most newer reefer trailers have internal structures for rub-rails and E-tracks that are separated and insulated from the outside walls. If you ever have to make repairs or add accessories to your trailer, remember to never drill bolt holes through the walls. This will maintain the thermal integrity of your reefer unit.

The product that is loaded into the reefer is another source of heat. Some products respirate (create heat) at a faster rate than others. For more on this, check out our publication, Interactions between Refrigerated Trailers and Products.

To accomplish the items that are mentioned at the beginning of this post (remove increased heat, keep product temperatures stable, and control humidity), reefers require 4 components:

- Thermal integrity in the trailer to prevent the inflow of additional heat
- Sufficient BTU capacity to remove the expected amount of heat
- Sufficient airflow
- Sufficient air velocity to move the air through the trailer, over and through the load.


Regular scheduled reefer maintenance and proper loading and stacking procedures will assist in succeeding the 4 above components. We know what the typical occurrences are: loads are often too warm when they are loaded, drivers don’t shut their reefers off before opening doors, and debris often blocks airflow. These occurrences often greatly increase the potential for temperature issues upon delivery.

Reinforcing proper loading procedures (including PULPING product upon pickup) can eliminate and significantly reduce the potential for temperature related issues upon delivery. For more comprehensive loading directions, check out our Carrier Loading Guidelines!!

Do you have anything to share regarding reefer units? What are your experiences?

Stay tuned for a future “scientific” examination of how reefer units work!!!!

References:

Understanding reefers – how hard can it be?. http://www.landlinemag.com/Archives/2001/Mar2001/Your_Equipment/reefers.html. Accessed on Feb. 2, 2011.