Shipping containers are known to withstand the toughest conditions–from massive storms, high winds, and intense heat–to keep their contents safe and secure.
Most cargo ships have facilities to support and carry reefer shipping containers in the form of power points on the deck of the ship. However, before we get ahead of ourselves, let’s delve into what reefers are, and how they function.
What is a reefer container and how does it work?
Reefer containers are essentially large fridges used to transport temperature-controlled cargo items like fruits, meat, fish, seafood, vegetables, and dairy products.
For the most part, reefers are designed to transport chilled or frozen perishable products but can also transport non-food products like flowers, pharmaceuticals and film.
The first reefer was basically modified from the cooling space of a truck in the 1960s.
Nowadays, modern reefers enable automated temperature adjustment from anything between -35 °C and +15 °C degrees. As such, they possess the ability to maintain the cargo at the standardised temperatures in transit from Point A to Point B.
Technically, reefers containers are engineered as bottom air delivery units to distribute chilled air from the floor through specific T-shaped decking. As a result, they possess the advantage of releasing a consistent and uniform flow of air across the shipment, strong enough to ensure a perfect air exchange with the perishable goods.
Reefers can sustain or even lower the temperature of a shipment in the most difficult conditions–with the ability to maintain temperatures of up to 30°C when necessitated– regardless of outside temperatures.
However, the airflow requirements of each commodity typically vary as there is no one size fits all.
For instance, for chilled cargo, air typically has to flow through the cargo at all times, so heat and gases are removed; thus, the cartons used should have ventilation.
On the other hand, for frozen cargo, the air is required to flow around the cargo. As such, there shouldn’t be any gaps between the cargo and the walls. Therefore, the cargo has to be block stowed.
When reefer containers are loaded onto ships, the power supply is typically provided from the power generated by the diesel generators of the vessel.
If the vessel’s generator capacity isn’t enough to support the extra power consumption of the reefers, mobile power packs are usually installed on the ship.
What is a reefer container made of?
Most reefer’s inner walls are made out of stainless steel, with floors made of stainless steel or aluminium. This reduces the actual possibility of water damage. Additionally, the walls, floor and ceiling of a reefer container are typically supplemented with about 100mm of polyurethane insulation.
The floor of the reefer is usually either flat or equipped with a gridiron. The main advantage of a flat floor is the ease of transferring goods to the container with trolleys with wheels, than it would be on a gridiron floor.
However, the downside is its ‘slipperiness’ and the fact that the gridiron floor allows for better air circulation.
The main components of a reefer container include:
- Control unit: This component enables ship crews to set and adjust the internal atmosphere of a reefer, including the temperature, alarm conditions, as well as ventilation and humidity levels.
- Interior fans: Interior fans are usually located inside the reefer to help circulate air to promote adequate temperature control and stability.
- Fresh air vents: Fresh air vents allow air to enter from outside, and any gases from within the container, like fruit-ripening ethylene gas, to leave.
- Condenser: Air-cooled condensers pull cooled air from the top of the refrigerated container and discharge it under the cargo. Subsequently, they push the air to the back doors before it converts naturally and rises, then flows back over the shipment to the return air inlet on the reefer unit. Since air moves under the shipment, proper loading and covering as much of the floor as possible is vital to avert a “chimney” effect and short-cycling.
- Unit evaporator: Excess moisture in a reefer container can easily damage products, quicken food spoilage and even break down packaging, therefore leaving contents vulnerable. So, in some instances, a reefer container will need to warm the air to maintain consistency of the interior temperature, which is achieved either by employing hot gas heat or electrical heating elements. A unit evaporator helps maintain moisture inside the container by either heating or cooling the air that circulates past it from the fan.
- Voltage transformers: Voltage transformers allow reefers to operate on voltages of up to 200V 3ph.
Here are some additional pointers:
- As a side note, reefer containers are typically available with the lengths of 10′ (3M), 20′ (6M) and 40′ (12M) – like conventional shipping containers. However, reefers also come in a high cube model that is around 30 cm higher than a conventional container, as well as an extra-large model that’s 45′ long.
- Most voltage units are dual voltage and designed to operate on 190/230 or 380/460 volts A.C, with 3 phase, 50-60 hertz power.
- The container refrigeration unit is fitted at the front of the container and serves as a container front wall.
- Operating control power is principally provided by a single-phase transformer that steps down the A.C supply power source to 24 volts, 1 phase control power.
Types of refrigerated shipping containers
- Automatic Fresh Air Management (AFAM) Containers: AFAM reefer containers exploit advanced technology to regulate the air combination and automatically adjust the scale of fresh air exchange.
They work in a manner similar to controlled atmosphere refrigerated containers to control the composition of oxygen and carbon dioxide. The controls of AFAM refrigerated containers can be flexibly adjusted to influence and extend the shelf lives of the cargo they carry.
- Closed Reefer: This is essentially a conventional-type reefer container as it comes with an integral front wall, all-electric automatic cooling and heating unit.
- Modified/ Controlled Atmosphere reefer containers: These insulated shipping containers sustain a constant atmosphere by replacing consumed oxygen by leveraging an air exchange system. Therefore, keeping an ideal atmosphere in equilibrium with perishable products’ deterioration rate.
What is an offshore container?
An offshore container holds waste that can be open or closed.
Also commonly called “skids” within the offshore oil and gas industry, offshore containers are often employed to transport large components to drilling and production rigs.
Offshore reefer containers are largely used in the shipping industry to transport products and consumable items that need refrigeration.
Uses of offshore reefer containers
Reefers are mainly used in the transportation of goods that required a climate-controlled environment that can reach temperatures of as low as -60 degrees Celsius (-76 degrees Fahrenheit) like:
- Fresh fruits like bananas
- Fresh flowers
- Fresh meats
- Dairy products
- Fresh vegetables
- Chemicals/dangerous goods.
How are offshore reefer containers tested?
Offshore reefer containers require testing through specific methods to ensure they’re up to specification, and safe to use.
The main baseline for testing reefers is DNV testing and accreditation, which offers standard defining requirements and recommended practices that cover the transport of offshore containers and portable offshore units.
DNV standards cover areas of design, manufacturing, testing, certification, and periodic inspection based on environmental conditions, human lives, and hazard to the vessel or offshore installation.
DNV standards also cover aspects of safe lifting and handling of reefer containers and units between two floating vessels, as well as between vessels and fixed or floating offshore installations.
How long do reefers last- Is buying a reefer container cost-effective?
Generally, the cost of a reefer container depends on the manufacturer, size and type of container.
However, for the most part, reefer containers are affordable and come with options to have additional built-in features to maximise their efficiency and safety. Some of these features are remote monitoring capabilities, internal gensets, and even explosion-proof modifications.
But there are options to rent reefer containers instead of purchasing them. TK Reefer is one of the renowned companies that offers cost-efficient reefer container rentals.
Overall, reefers have an average shelf life of up to 10 years, depending on the conditions they have been exposed to. And when a reefer container is decommissioned, it takes little to turn it into an isolated container.
Maintenance of reefers
The most common issues reefers face are due to the gathering of ice. In practice, this occurs near the door, especially if the weatherstrips are allowed to get into poor shape.
Consequently, the door will not close tightly because of this. Another common challenge is when the antifreeze agent has run out.
Maintenance and control of reefer containers should be performed only by qualified reefer technicians, welders, boilermakers, and yard-depot controllers. However, here are a few recommended maintenance tips to consider:
- The reefer unit should not be placed in direct sunlight, but instead where it gets adequate airflow.
- Ensure to clean reefer unit coils monthly by hosing, or air cleaning them monthly
- Properly maintain fins to ensure maximum performance, efficient power usage, and optimal reefer unit operation.
- Regularly clean circulating fans to ensure continual internal air circulation;
- Ensure to defrost the reefer unit and ice on the evaporator coil at 9-hour intervals
- Ensure to regularly clean automatic humidity control drains.
The bottom line is a reefer container is an enclosed specialised shipping container unit employed to transport temperature-sensitive cargo.
The most vital component attribute of a reefer container is temperature consistency as it helps keep goods fresh and prevents any spoilage during long journeys.
That being said, reefer containers play an essential role in the global food and medicine supply chain.
If you’re a company looking to purchase some custom reefers for your transportation needs, reach out to us at MGS Icestorm