A reefer container is commonly used to ship temperature-sensitive cargo because it can maintain the ideal temperature throughout the journey. The reliability and effectiveness of the container depend entirely on the different parts it is made of, which must work together to protect your product’s quality during transport.
In this blog, we will explore these core reefer container components and determine how they keep your shipment safe
Structural and Insulation Components
The outer shell of a reefer is the first line of defense for your cargo. These structural parts seal the inside environment and prevent outside weather from affecting your cargo.
Insulated Sandwich Panels
The walls, roof, and floor of your container are built with a thick layer of high-density polyurethane (PU) or polyisocyanurate (PIR) foam that is sandwiched between metal sheets. The inside walls are lined with clean, rust-resistant stainless steel, while the outside is covered in aluminum or steel sheets.
This layered design blocks outside heat from entering and gives the container the strength it needs to handle rough handling and heavy stacking during travel.
Door Seals and Vapor Gaskets
The rear doors are lined with multi-layer, heavy-duty rubber gaskets designed to create an airtight, moisture-seal when closed. These gaskets will prevent warm, humid ambient air from leaking into the interior.
Without a proper vapor seal, moisture can enter the container and freeze on the evaporator coils, reducing the system’s cooling efficiency.
The Red Line
Painted or marked clearly along the top of your containers’ interior sidewalls, this load limit line dictates the maximum height your cargo can reach. It serves as an important operational safety boundary for you.
Stacking your goods above this line restricts overhead space, blocking air flow and creating hotspots in your shipments.
Sensor Systems
To keep your cargo safe, your reefer relies on a network of sensors. These sensors act as a container’s eyes and ears, constantly tracking conditions inside to protect your shipments.
Temperature Sensors
These sensors are located at the air inlet and outlet points to track the exact temperature of the air moving through your container. They tell the cooling unit when to blast cold air or when to back off.
This constant monitoring ensures your cargo stays at its ideal temperature throughout the entire journey.
Controlled Atmosphere Sensors
If you are shipping fresh produce, your container needs to breathe. These sensors measure the level of oxygen, carbon dioxide, and humidity inside the space. By tracking these gases, the system can automatically adjust the ventilation to slow the ripening process, so your goods arrive fresh.
Data Logging and Alarms
Think of this as your container’s black box. It continuously records all temperature and atmospheric data, giving you a complete history of the trip. If anything goes wrong, like a sudden temperature jump or power glitch, the system instantly triggers an alarm so you can fix the issue immediately and prevent problems.
The Power Supply
To keep your cooling system running, your container needs a reliable source of electricity. Whether you are moving cargo across land or sea, your reefer relies on some flexible power options to keep things cold.
Plugging into External Power
When your container is packed at a shipping terminal or loaded onto a container ship, it plugs directly into the local electrical grid or the vessel’s central power system. This gives your unit a steady, continuous supply of electricity without burning fuels.
Gensets or Generator Sets
When your container is on the road or on a train, external plug-ins aren’t available. In these cases, you can rely on a genset, which is a portable diesel-powered generator that clips right onto your container to provide power on the go.
Electrical Standards
To protect your equipment from damage, your power source must meet these specific electrical requirements:
- Voltage: Your container runs on a high-voltage system, usually 460V or 380V, depending on the region, to efficiently power the heavy cooling machinery.
- Phase: The system uses phase 3 electrical power, which provides the steady, high-capacity energy needed to start and run heavy-duty industrial compressors smoothly.
- Frequency: Depending on where you are in the world, the power will run either 60 Hz, which is common in North America, or 55 Hz to 50 Hz, which is common in Europe and Asia. Your system is designed to handle either of these frequencies.
- Tolerance: Power grids can fluctuate, so your system allows for a small safety margin of around 10% above or below the target voltage to prevent unexpected power spikes or drops from shutting down your unit.
The Refrigeration Systems
To cool the space, the refrigeration system operates in a continuous thermodynamic cycle, extracting heat from the container’s interior and releasing it to the surrounding environment.
This process relies on a refrigerant – a specialized gas designed to absorb and release heat efficiently as it cycles through the system.
The cycle moves this refrigerant through four core components:
The Compressor
The compressor is the heart of the cycle; it draws in the refrigerant gas at low pressure and compresses it to high pressure and temperature.
This squeezing action prepares the gas to release its trapped heat.
The Condenser
This component regulates the transfer of heat from the container to the surrounding environment. The hot, high-pressure refrigerant gas flows into a set of tubes while fans blow the air across them to direct an airflow over the condenser coils.
As the outside air absorbs the heat, the refrigerant gas cools down and condenses into a liquid under high pressure, effectively removing the extracted heat from the system.
Expansion Valve
This component controls the flow of refrigerant into the evaporator by lowering its pressure. It acts like a narrow nozzle, forcing the high-pressure liquid into a low-pressure area. As the pressure decreases, the temperature of the refrigerant drops, turning it into an icy-cold mixture.
The Evaporator
This is where the actual cooling happens inside your container. The icy cold refrigerant travels through coils located inside the cargo area, and a fan blows the warm air from your cargo across these cold coils. The refrigerant absorbs heat from your goods, cools the air, and evaporates back into a low-pressure gas.
This cycle continues until the system maintains the exact set temperature needed for your cargo.
Air Flow System
Cooling will only be effective when it is evenly distributed. If the airflow is blocked, hotspots or uneven cooling occur, even if your refrigeration system is functioning properly. To prevent this, reefer containers rely on a specialized distribution network.
T-Shaped Floor
Also known as T-bar, this unique floor design consists of raised aluminum T-slots. Instead of blowing cold air from the ceiling like a standard building AC, a reefer forces cold air down through the bottom of the container.
The T-shaped channels act as a pipeline network, guiding cold air under the pallets and forcing it to circulate upward through and around the cargo before returning to the refrigeration unit at the top.
Fresh Air Vents
Not all cargo needs to be completely sealed off. For living, breathing shipments such as fresh fruits and vegetables, the fresh air vents regulate the intake of outside air and the release of built-up gases (like carbon dioxide and ethylene).
These vents can be manually or automatically adjusted to prevent cargo from suffocating and keep the internal temperature remains stable.
Final Thought
A reefer container is an advanced climate-controlled temperature system. High-quality insulation, continuous refrigeration cycle, and specialized T-shaped flooring work in harmony to create an effective and efficient system. Guided by real-time sensors and flexible power options, it maintains precise, uninterrupted temperature tolerances to preserve cargo quality from origin to destination.
Frequently Asked Questions:
How do reefers stay powered during a long journey?
While at a port terminal or on an ocean vessel, reefers are plugged directly into the ship’s or port’s electrical grid. However, while traveling on land via truck or rail, they rely on portable, diesel-powered generators called Gensets (generator sets) that clip onto the container to provide continuous power.
How does airflow work inside a reefer container?
Unlike standard air conditioning units that blow air from above, reefers pump cold air down into the floor. The air travels through specialized aluminum T-bar flooring and flows upward through the cargo. This ensures a consistent, bottom-up airflow that regulates temperature across the entire shipment.
What is the main component that keeps a reefer container cold?
The heart of any reefer is its integrated refrigeration unit, which is securely bolted onto the front end of the container. This all-in-one machinery housing contains the compressor, condenser, evaporator, and electronic control system that actively regulates the internal climate.
What does the compressor do in a reefer container?
The compressor is considered the engine of the refrigeration cycle. It compresses the refrigerant gas, raising its temperature and pressure, and pumps it through the system to drive the cooling process.
What is the difference between the condenser and the evaporator?
They perform opposite jobs. The condenser is located on the outside of the container and releases heat from the refrigerant into the outside air. The evaporator is located inside the cargo hold; it absorbs heat from the air inside the container, keeping your goods cold.
You may also find this blog post useful
How Does a Reefer Container Work?
A Guide to Reefer Container Temperature Monitoring and The Challenges You May Encounter
Different Types of Reefer Containers
How are Reefer Containers Powered?
About The Author
Evan Wang
I am Evan Wang, the General Manager, Marketing Director, and SEO Expert at Sunnyda Cold Room. I have over 20 years of experience in the refrigeration industry, and my expertise is in commercial refrigeration solutions.
I’d be delighted to share practical ideas about refrigeration products, project selection, export trade, SEO, and marketing.
Let’s connect!
