How Reefer Containers Work


Why A Reefer’s Airflow Matters So Much

Offshore DNV and ISO reefer containers use a refrigeration unit to freeze or chill their cargos – that’s obvious. But what’s less obvious to the uninitiated or unwary is the crucial importance of airflow.

Get the airflow wrong and you will at best waste increasingly expensive energy…or at worst jeopardise or ruin your perishable cargo.

How A DNV Or ISO Reefer’s Airflow Cools Cargo

It’s all about convection. Warm air inside the container is drawn into the reefer’s refrigeration unit. Inside this cooling engine are two fans. They suck in the warm air, cool it and push it down into the container. Cool air sinks by its very nature – but the downward pressure of the fans speeds up the process and makes it more efficient.

This cooled air is pushed down behind a vertical baffle on the interior front wall of the container. The cold air passes under the cargo, entering the main container space via ventilation slots in the T-bar floor. The air circulates around the cargo, keeping it cool or chilled, according to the thermostatically controlled temperature.

As the air warms up, it rises and gets drawn back to the front of the reefer where it is then cooled again by the refrigeration unit and the process is repeated. It makes sense to re-chill the air inside the container – it will usually be closer to the desired temperature than the air outside the container.

Some cargo such as plants and fruit need fresh air so this must be drawn in. Fruits metabolise and ripen – drawing in oxygen and giving off carbon dioxide, moisture, heat and ethylene gas. These must be extracted and fresh air drawn in to avoid oxygen depletion.

So far so good, theoretically. But human nature being what it is, the temptation is to cram as much cargo into the container as possible.

And that is when problems can occur…

Poor Loading (Or Overloading) Disrupts Airflow And Ruins Cargos

Every reefer has important markings (load lines) near the ceiling and on the floor (near the doors). These lines are important; do not cross them when loading your cargo. If you do, you risk stopping the air from circulating properly – putting your perishable cargo at risk.

Furthermore, you must spread your cargo evenly across the container floor. This ensures a good airflow. Fail to do so and the cold air will not reach your entire cargo – it won’t go through your crates or boxes. You will create air ‘chimneys’ – short-cycling of the airflow.

In the unlikely event that your cargo is not large enough to cover the container floor, you will need to cover the floor with approved dunnage or heat-treated plywood. And if you do, you’ll need to leave the appropriate gaps for the cool air to circulate.

You don’t have to be an expert at true laminar airflow or air entrainment. Just use common sense.

How To Stop Moisture And Condensation From Damaging Your Cargo

Reefers are watertight but temperature changes can still leave your cargo susceptible to moisture and condensation. This can damage packaging or lead to mould and bacteria. So we ensure that every reefer is always clean and dry – and you should always do the same with your pallets.

One way to help stop condensation is not to pre-cool the container (as tempting as that might be). If you do, the cool air inside will mix with warm air from outside when you open the doors – causing condensation.

Yes, the reefer’s evaporator can help to deal with the moisture but this uses energy, affecting the cooling capacity of the refrigeration unit. So prevention is always better than cure. Dry containers cool better and use less energy.

Essential Components In A Reefer

These are the key components in your reefer’s cooling system:

  • Interior fans help to circulate the air to promote adequate temperature control and stability.
  • Control unit – enables you to set and adjust the internal temperature, alarm, ventilation and humidity levels.
  • Fresh air vent – lets in air from outside to avoid oxygen depletion, allows gases such as ethylene from fruit ripening to escape.
  • Evaporator – gets rid of moisture, helping to keep your reefer dry to preserve your cargo.
  • Condenser – cools the air. Condensers can be water cooled but are usually air cooled.
  • Power cable – reefers need three-phase, 380-460V electrical power.
  • Voltage transformers – optional dual voltage transformers allow your reefer to run on voltages down to 200V instead of the usual voltage.
  • Gensets – generators that supply power when mains electricity is not available.

Many of our reefers are used for storage in challenging locations. Our experienced team can advise you on the best units to specify for your intended sites. For instance, we would recommend Carrier Transicold for Africa because of the massive and widespread support network. Spares are readily available in any condition: new, refurbished or used.

Lease Or Buy DNV And ISO Reefers From Cargostore

Cargostore is the world’s largest supplier of DNV reefers. We can help you to source quality DNV and ISO reefers in a challenging market.

Our refrigerated container range includes:


We can also supply highly specialised refrigerated containers such as:

Cargostore is one of the world’s fastest-growing suppliers of ISO and DNV containers for onshore, offshore and shipping.

Customers rely on our containers for a wide range of commercial operations, large scale event catering, mining, stability and aid including peacekeeping and humanitarian missions. Our containers are being leased all over the world – notably in Africa and the Middle East.

Find our more here about how to lease shipping containers.

Get Expert Advice On Leasing Containers

Contact Cargostore now in London, Abu Dhabi or Holland to lease containers for shipping and/or storage. You will benefit from:

  • expert technical advice and fast quotes from our highly experienced team
  • seamless transition to a smooth and efficient finance team – fast credit checks and paperwork
  • excellent operational aftercare – proactive assistance for unit repairs and troubleshooting
  • depots worldwide.

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