A reefer container is a refrigerated shipping container designed to transport temperature-sensitive goods, from frozen meat to fresh fruit to pharmaceuticals. It looks like a standard steel shipping container on the outside but houses a built-in refrigeration unit and insulated walls that can maintain internal temperatures anywhere from -20°F to 80°F. Reefer containers are the backbone of the global cold chain, moving perishable cargo across oceans and overland while keeping it at precise conditions for days or weeks at a time.
How the Refrigeration System Works
The cooling system in a reefer container operates on the same basic cycle as a home refrigerator, just scaled up for industrial cargo. A compressor circulates refrigerant through the system. The evaporator, located inside the container, absorbs heat from the cargo space and cools the air. The condenser, mounted on the exterior, dumps that absorbed heat outside. Internal fans then circulate cold air throughout the container to prevent hot spots and keep the temperature uniform from floor to ceiling and front to back.
This cycle runs continuously, adjusting output to hold whatever set point the cargo requires. A load of ice cream might need -10°F, while a shipment of vaccines might need a steady 36°F to 46°F (2°C to 8°C). Specialized units handling cryogenic loads can reach as low as -85°F, though most standard reefers operate in the -10°F to 60°F range.
Standard Sizes and Capacity
Reefer containers come in two common sizes: 20-foot and 40-foot high cube. The insulation and refrigeration equipment eat into the usable space compared to a dry container of the same exterior length, so internal dimensions matter more than the label on the door.
- 20-foot reefer: Internal dimensions of roughly 5.46 m long × 2.29 m wide × 2.27 m high (about 17.9 × 7.5 × 7.5 feet). Maximum payload is approximately 27,470 kg (about 60,560 lbs).
- 40-foot high cube reefer: Internal dimensions of roughly 11.58 m long × 2.29 m wide × 2.56 m high (about 38 × 7.5 × 8.4 feet). Maximum payload is approximately 29,260 kg (about 64,500 lbs).
The 40-foot high cube is the more popular choice for ocean freight because the extra height accommodates palletized cargo more efficiently. Despite being nearly twice the length, it only carries slightly more weight than the 20-foot version because container floor strength and ship stacking limits cap the load.
Controlled Atmosphere for Fresh Produce
Temperature control alone isn’t always enough. Fruits and vegetables keep breathing after harvest, consuming oxygen and releasing carbon dioxide and ethylene, a gas that accelerates ripening. Left unchecked, this process shortens shelf life dramatically during a multi-week ocean voyage.
Advanced reefer containers solve this with controlled atmosphere (CA) technology. The system adjusts the gas mix inside the container, typically lowering oxygen levels to 2 to 5 percent and maintaining carbon dioxide at 2 to 5 percent. Reducing oxygen slows the cargo’s respiration rate by up to 30 percent, which delays aging and makes the produce less sensitive to ethylene. Elevated carbon dioxide suppresses mold growth and has antibacterial properties when it dissolves into surface moisture on the fruit.
The system monitors gas levels continuously. If the cargo’s own respiration pushes oxygen too low or carbon dioxide too high, the unit automatically draws in outside air to rebalance. Getting this wrong has real consequences: a combination of elevated temperature and carbon dioxide levels above 5 percent can kill fruit outright. For a commodity like bananas, which are shipped green and ripened at destination, controlled atmosphere extends storage life well beyond what refrigeration alone can achieve.
Power Requirements
Reefer containers run on 460/480 volts, 3-phase power, and can operate at either 50 or 60 Hz, which makes them compatible with electrical grids worldwide. The unit draws up to about 29 amps and requires a grounded circuit with a 30-amp minimum breaker.
Each container comes with a roughly 50-foot power cable and a standardized weatherproof plug. At a port or warehouse, the container plugs into shore power. During road or rail transit, a clip-on or underslung generator set (genset) provides electricity when grid power isn’t available. On a container ship, rows of reefer outlets supply power throughout the voyage.
One common complication: standard North American commercial building voltages are typically 208V or 600V, neither of which matches. If you’re connecting a reefer container at a warehouse or facility, you’ll need a step-up or step-down transformer to convert the supply to 460V. For frequent connect/disconnect scenarios, a wall-mounted receptacle with a quick-connect plug is the most practical setup. For permanent installations, direct hardwiring is an option.
Remote Monitoring and Tracking
Modern reefer containers are equipped with IoT sensors that record temperature, humidity, power supply status, and other conditions in real time. This data transmits wirelessly via cellular, Wi-Fi, or long-range radio networks to a central monitoring platform, where it’s matched to a specific container ID and storage location.
The monitoring system performs three core jobs. It logs conditions continuously for regulatory compliance and quality assurance. It triggers automatic alerts when any parameter drifts outside the acceptable range, so a technician can respond before cargo is damaged. And it generates reports that shippers, terminals, and customers can all access, providing a verifiable record of conditions throughout the journey.
At port terminals, the monitoring platform integrates with the terminal operating system, so each reefer’s position in the yard is linked to its live status data. If a container loses power or its temperature spikes, the system flags its exact location. All data is encrypted, access is controlled by role (technicians see different information than customers), and audit trails are maintained as immutable logs, which matters when disputes arise over whether cargo was properly handled.
What Reefer Containers Carry
The range of cargo is broader than most people expect. Frozen goods like seafood, meat, and ice cream need deep-cold settings. Fresh produce, dairy, and flowers travel at standard refrigerated temperatures. Pharmaceuticals and vaccines require tight, stable temperature bands, often between 36°F and 46°F. Some reefers even carry cargo that needs warming rather than cooling: chocolate, for instance, can be damaged by cold during winter transits, so the container maintains a room-temperature set point of 68°F to 77°F.
Humidity control is another factor. Many modern units regulate moisture levels alongside temperature, which helps prevent wilting in leafy produce, condensation damage on packaged goods, or drying out of items like fresh fish. The combination of precise temperature, humidity, and atmosphere management is what allows perishable goods to travel thousands of miles and arrive in sellable condition.