The terms “reefer container” and “reefer” are short for “refrigerated container.” These containers maintain a stable temperature inside while controlling humidity and promoting adequate airflow. The container’s climate control functionality keeps the products inside from spoiling, which may occur from too much heat, excessive moisture, not enough airflow or temperatures that drop too low.
Temperature-sensitive materials, such as food and pharmaceuticals, require careful temperature control during shipping — a feat accomplished through the use of reefers. Cold chains, or the process of storing and transporting goods at proper refrigeration temperatures, include multiple steps to get supplies from their origin to their destination while keeping the perishable goods fresh. Refrigerated containers are a vital part of this chain and offer a solution that typically provides temperature ranges from -30°C to +25°C. Without these reefers, international shipments of temperature-sensitive products would be impossible.
Reefer containers have decades of use transporting delicate materials that could go bad during shipping. The international cold chain allows the U.S. and other countries to keep cold products fresh and in good condition during an ocean-crossing. Reliable temperature-sensitive transportation gives the U.S. and countries around the world the chance to grow their export markets while also meeting the growing demand for fresh and local foods. Refrigerated containers help with this goal, as they are trusted storage and transport containers.
How Does a Reefer Container Work?
1. How Does a Reefer Container Work as a Shipping Container?
When shipping, reefer container operation is typically run on vessel or shore power.
During rail or truck shipping, a generator provides portable power to the reefers. Containers may have a built-in generator, or they may have one externally located.
The floor of the refrigerated container has a “T-floor” to allow for airflow under the cargo. Cold air blows from the refrigeration unit through the vents at the bottom of the reefer and all the way to the back doors. The warm air at the top of the container flows back to the refrigeration unit over the cargo, where it chills for return to the interior. It is vital that proper loading is observed to prevent “chimneys” or short-cycling of this airflow and that the entire floor of the reefer container is covered during transport, at least by approved dunnage or heat-treated plywood covering if cargo pallets are not available to fill the entire container. Careful placing of containers to allow air to flow between them ensures this operation continues without problems.
For fruit transport, the air movement also allows for fresh air to cycle in as carbon dioxide and ethylene gas-filled air moves out of the reefer, preventing premature spoilage of the fruits.
2. How Does a Refrigerated Container Work for Storage?
Refrigerated containers also work for temporary storage as long as they have a power source to operate the cooling unit. Whether it is storage during an emergency, while a damaged reefer undergoes repairs or to keep surplus products while awaiting shipment, refrigerated containers work just as well for storage as they do for shipping.
3. Parts of a Refrigerated Container
To create the ideal environmental conditions, reefers have multiple sections, many of which dry containers lack. The components you will only find in reefers are the fresh air vent, the evaporator section, and the condenser section. These operate together to maintain the temperature inside the container and in most standard reefers are all combined into one single reefer unit which fits onto the end of the insulated reefer container body. They are not intended to cool a warm cargo load (though they will eventually in most cases), but are intended to keep frozen or cold foods or medicines at stable temperatures.
The fresh air vent allows for air to enter from outside and any gases from in the container, such as fruit-ripening ethylene gas, to leave.
The reefer unit evaporator can either heat or cool the air that circulates past it from the fan that draws air from the top of the container. Sometimes, the reefer will need to warm the air to keep the interior temperature consistent. Reefers can maintain temperatures up to 30 degrees Celsius (86 degrees Fahrenheit). Whether it heats or cools the air depends on the desired internal temperature. Sometimes a heater unit can be added to the container so it can perform a heating function in addition to a cooling function.
Condensers may have air or water cooling, though typically the industry is using air-cooled condensers. Air-cooled models pull cooled air from the bottom of the container and discharge it through the center of the reefer. Because air moves through the middle, stacked goods should not block airflow.
Dual voltage transformers are also an option with some containers.
4. Packing a Reefer for Optimum Climate Control
How you pack a refrigerated container determines how well it keeps the products inside at a constant temperature without hot and cold spots.
Inside a reefer, to allow for proper air movement, goods should not hang over any pallets. The boxes should have vents to allow for vertical airflow from the bottom of the container. Align all vent holes in boxes to keep air moving as smoothly as possible, and do not stack boxes until they touch the ceiling, but observe the internal load line limits. Allow for air to move between the roof and the top of the boxes.
Since the goods in a refrigerated container must be kept cool, it’s optimal to use a dedicated cooling facility where the goods are pre-cooled before they are loaded into the reefer. It is often more feasible and energy efficient to pre-cool the goods than to pre-cool the reefer — if a reefer is pre-cooled, the facility in which goods are loaded into it also needs to also be pre-cooled and temperature-controlled. This is often not possible, which is why pre-cooling the reefer before loading goods would be wasted energy. Pre-cooling will also lead to ingress of warm, moist air into the cold reefer container, causing excess development of moisture and unnecessary defrost cycles, further reducing the ability of the reefer container to cool the product after efficiently after loading.
It is also vital that pallets loaded into the container are completely dry in order to avoid these same defrost issues.
What Is a Reefer Container Used For?
Refrigerated containers are used for fresh flowers, fruits, meats, dairy, vegetables, pharmaceuticals, and chemicals/dangerous goods. These goods can stay fresh or frozen as required in climate-controlled reefers that can reach temperatures as low as -60 degrees Celsius (-76 degrees Fahrenheit). Though typically 20 or 40-feet long, the total space inside is less than the exterior due to the refrigeration equipment taking up some of the room inside the container.
Reefer containers play critical roles in food and medicine shipments around the world. Many companies use them for transport. As leaders in the refrigerated container field, we can help you find the best options for shipping whatever you produce. Contact us at Klinge Corporation if you would like durable, trustworthy reefers that have options such as back-up chillers and more to ensure your shipment arrives in good condition.