Reefer containers became popular for their ability to maintain the ideal temperature for perishable products to keep their quality. Their dedication to protecting temperature-sensitive cargo is remarkable. But have you ever asked yourself how a refrigerated container works? Keep on reading and find out how the containers do this.
Main Components of a Reefer Container
To determine how a reefer container works, you must first learn its main components. Each part plays a vital role in making the reefer container effective.
Refrigeration Unit
Most reefer containers use a front-mounted unit from brands like Carrier or Thermo King. This system acts as the heart of the trailer by housing four main components. First, the compressor pressurizes refrigerant gas into high-pressure liquid.
Next, the condenser releases that trap heat into the outside air. Inside the trailer, the evaporator chills the environment by absorbing heat directly from your cargo.
Finally, an expansion valve that regulates the flow to keep everything stable.
Together, these parts cycle refrigerant constantly to maintain temperatures from -30 °C to +30 °C. This range allows one reefer container to handle everything from deep frozen seafood to fresh tropical fruits.
Insulated Walls
Reefer containers are built with 100-160mm thick polyurethane foam. This insulation foam is sandwiched between corrugated steel inner and outer layers. Specifically, these insulated panels are used on the walls, floor, roof, and doors. Together, they can achieve R-values of 40.
This high rating provides excellent thermal resistance against outside weather. Because of this, the cargo stays safe even on equatorial voyages.
Air Circulation System
High-capacity evaporator fans push cold air downward through the container, while ceiling return vents draw warmer air for recooling. These fans can reach speeds up to 10,000 CFM. Meanwhile, the ceiling return vents draw warmer air back for recooling.
This continuous airflow creates a forced convection loop. This specific cycle maintains temperature uniformity within a ±0.25°C range. Additionally, Adjustable vents also support controlled atmosphere (CA) settings. These vents reduce oxygen levels, extending the shelf life of fresh produce.
Temperature Control Panel
This weatherproof microprocessor is mounted directly on the container’s access door. It features a clear LCD for setting and monitoring internal climate conditions.
Specifically, the unit provides real-time data tracking for all interior variables. The system can log over 3,000 unique events during a single trip. These logs include important alarms for temperature deviations or power failures.
Additionally, the panel supports remote monitoring through advanced telematics. This technology integrates GPS with cellular or satellite communication. Such connectivity allows fleet managers to track cargo status from anywhere in the world.
Power Supply
Reefer containers typically require a standard 440V/60Hz three-phase power supply. This power comes from the vessel or terminal outlets during stationary periods.
Specifically, external power is not always available during road or rail transport. In these cases, clip-on generator sets (gensets) provide the necessary electricity. These 20-40Kw diesel units feature multi-day fuel capacity for long distances.
Furthermore, auto start systems and phase converters provide a seamless power transition. This technology maintains the cooling cycle between ship, rail, and truck. Such reliability protects the cargo throughout the entire transit.
T-Bar Flooring
T-bar flooring is made of extruded aluminum rails (around 10 cm high and 4cm wide) spaced evenly about 12 cm apart. This design creates channels that allow cold air to flow beneath pallets and circulate upward through the cargo.
The air then returns through the top vents, forming a continuous airflow loop. This helps prevent uneven cooling or dead zones and supports up to 99% loading efficiency.
How does a Reefer Container Work?
A reefer container will start working the moment you open the power supply. Once the unit has power, you must set the desired temperature for your cargo. This is known as the set point.
Step 1: The System Checks the Cargo
Sensors measure the return air coming from the cargo. The control unit compares this to your set point. It then calculates exactly how much cooling is needed.
Step 2: The Refrigeration Cycle Starts
The compressor pumps refrigerant through the system. This chemical changes from a liquid to a gas. This change allows it to absorb massive amounts of heat.
Step 3: Heat Removal and Evaporation
Fans pull warm air across cold evaporator coils. The refrigerant inside the coils soaks up the heat. The system then pumps that heat to the outside condenser to release it.
Step 4: The T-Floor
The unit forces chilled supply air into the T-bar floor. These aluminum channels act as a pressure chamber. They ensure air reaches the very front of the container.
Step 5: Upward Circulation and Pressure
Air cannot move sideways through the floor, so it is forced upward. It must pass through the pallets and the cargo. This removes field heat and prevents a warm spot.
Step 6: Atmosphere and Humidity Control
Modern reefers also manage humidity and fresh air. The system vents out CO2 and ethylene gas. This prevents fruits and vegetables from ripening too fast during transport.
Step 7: Constant Monitoring
The system check occurs every few seconds. It adjusts the compressor speed to maintain a steady climate/temperature. This keeps the temperature within a tiny range, often 0.5 °C.
Reefer Cargo Loading Guidelines
Cooling your products is not enough. You must stack your cargo the right way to prevent damage. Proper stacking maintains the ideal temperature and protects your goods throughout transit.
To achieve this, you must follow these essential stowage rules.
Set the Correct Temperature
Always verify the temperature on the official shipping manifest. Correct settings prevent chilled goods from freezing or frozen goods from thawing during transport.
Air flow Management
In a reefer container, air serves as the primary heat-transfer fluid. Clear paths allow the unit to pull heat away from the cargo effectively. If paths are blocked, the machine cannot do its job.
Respect the Floor and Red Line
Never load cargo above the red line on the interior walls. This area is the return air plenum. As a result of keeping it clear, the unit can pull warm air back to the evaporator coil. Otherwise, the system may misread the temperature and fail to cool the cargo.
Secure and Stable Cargo
Use dunnage or bracing to stop the cargo from shifting. Stable loads prevent short cycling. This occurs when cold air bypasses the cargo and returns to the unit sensors too quickly.
Proper Headspace
Leave at least 12 cm of space at the ceiling. This gap allows high-velocity air to reach the back of the container. The air can begin its downward path to cool the rear pallets.
No Overhang Beyond Pallets
Keep all boxes aligned with the pallet edges. Otherwise, overhang blocks the vertical air gaps between the T-bar rails. Similarly, this restriction creates dangerous hot spots at the center of the load.
Keep Door and Rear Area Free
The area near the doors is furthest from the fans. You must keep it clear of plastic wrap or cardboard. In addition, debris here can be sucked into the evaporator, which can cause expensive motor damage.
Pre-Cooling Cargo
Reefer containers maintain temperature; they do not lower it. Loading warm cargo leads to frost buildup on the coils. As a result, the unit enters a constant defrost cycle, which stops the cooling process entirely.
Proper Stacking Techniques
The stacking method must match the cargo type to guarantee thermal protection.
For Fresh Produce: Use ventilated stacking. The air must flow through the cartons to remove the heat of respiration from living plants.
For Frozen Cargo: Use a solid block stacking. As a result, air should flow around the load like a protective blanket to stop external heat.
In Summary
Understanding how a reefer trailer works is essential for successful cold chain logistics. When combined with proper loading practice, it helps protect your cargo and maintain product quality throughout transit. In the end, having the right knowledge leads to a more efficient and stress-free shipping operation.
Whether you are a business owner or a logistics provider looking for a high-performance reefer container, we provide the best solutions. Our professional team can also customize the design to fit your specific needs. Check out our catalog or contact us today.
People Also Asked:
How are reefer containers powered?
They plug into a 440V three-phase power supply. Terminal outlets provide power while stationary. During transport, diesel gensets generate the necessary electricity.
What are the sizes of a Reefer container?
Standard units come in 20ft and 40ft high cube sizes. The 40ft high cube provides extra height for more cargo.
How much power does a 40ft reefer container consume per hour?
A typical unit uses 3.5kW to 6kW per hour. Specifically, consumption depends on the outside temperature and cargo set point.
How does airflow work inside a reefer container?
The unit forces cold air through the T-bar floor. This air then rises through the cargo. Finally, it returns to the top vents for recooling.
How reefer container handle extreme hot weather?
Thick polyurethane foam provides an R-value of 40 for insulation. This barrier blocks external heat. Then the condenser fans exhaust heat more frequently.
Why is pre-cooling cargo important?
A reefer container only maintains temperatures. They cannot cool down warm cargo quickly. Loading warm goods leads to ice buildup and potential spoilage.
What are the power sources for a reefer container?
Vessels provide grid power during the voyage. For trucking, clip-on underslung gensets are used. Many warehouses also offer a dedicated reefer plug.
How can I prevent condensation in my refrigerated container?
Only load cargo that is already at the set temperature. Additionally, keep the floor channels clear. Proper circulation stops moisture from gathering on the ceiling.
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