What is Offshore Reefer Container Ventilation & Why You Need It

According to UNEP, around 1/3 of the world’s food is lost or wasted every year. Often, inefficient transport systems between growers and consumers are the reasons why.

A significant complicating factor that comes into play with perishable foods is temperature moderation.

Temperature is essentially the single most important factor in preserving the freshness and quality of perishable commodities. This is because the rate of respiration is directly proportional to the rate of deterioration, which typically increases exponentially as temperatures increase.

As a rule of thumb, every 10°C (18°F) increase in temperature translates to the rate of deterioration increasing two to three times over.

Read our article on “Offshore Reefer Container Temperature Range.”

What Is Offshore Reefer Container Ventilation?

Offshore reefer container ventilation is the controlled exchange of air inside a refrigerated shipping container with outside air, designed to remove cargo respiration gases, such as carbon dioxide (CO₂) and ethylene, while maintaining stable temperature and humidity levels. It is a core function of any reefer ventilation system and a critical factor in cold chain logistics for perishable goods, including fresh produce, seafood, dairy, and pharmaceuticals.

In MGS IceStorm’s DNV 2.7-1 certified offshore reefer containers, ventilation is managed by a Thermo King-powered microprocessor that controls fresh air exchange rates in real time, a system known as Ventilation on Demand (VOD).

One of the most reliable ways to maintain temperature-controlled shipping for perishable goods is an offshore reefer container, specifically, a DNV 2.7-1 certified unit like MGS IceStorm’s 10ft Ice Storm or 8ft Ice Wave offshore refrigerated containers.

These containers are engineered to hold a precise internal temperature, regulate humidity, and sustain consistent refrigerated container air circulation from loading to delivery.

Ventilation in reefer containers

Ventilation essentially refers to the replacing of air inside a container with air from the surrounding environment. For the most part, the fresh air intake capacity of most reefer containers varies between 0 and 180 m3/hour (50 Hz).

How Much Ventilation Does Your Cargo Need?

The correct ventilation rate depends on the cargo’s respiration rate, the speed at which it produces CO₂, ethylene, and heat. Below is a reference guide for common cargo types and their recommended fresh air exchange settings:

Ventilation rates are indicative. Actual settings should be confirmed with a cold chain specialist based on cargo volume, voyage duration, and ambient conditions.

Fresh air ventilation removes accumulated respiration gases, primarily carbon dioxide (CO₂) and ethylene, produced by perishable cargo as a natural byproduct of the ripening process.

Left unmanaged, high CO₂ concentrations accelerate spoilage and can cause off-flavours in fresh produce, while elevated ethylene levels trigger premature ripening across an entire cargo load.

Each cargo type has a distinct respiration rate, which determines how aggressively ventilation needs to work. High-respiration cargo like bananas and tomatoes require more frequent reefer container fresh air exchange, while low-respiration goods like hard cheeses or frozen meat need minimal airflow to avoid moisture ingress and temperature fluctuation.

However, each cargo maintains its own unique respiration characteristics to accommodate different perishables.

Fruit, for example, can be divided into climacteric and non-climacteric. Climacteric fruits continue to ripen after harvest, while non-climacteric fruits stop ripening after harvest.

As a result, climacteric fruits have a high level of respiration, for example, pears, mangoes, avocados and bananas. Non-climacteric fruits include citrus, grapes, cherry and watermelon.

Fresh air affects the efficiency of refrigeration installation as the evaporator cooling coil is designed to eliminate humidity from the air inside the container.

However, fresh air also means that the evaporator cooling coil must remove humidity for freshly introduced air.

At temperatures below 10°C, this results in more frequent defrosting periods and frequent interruption of the circulation fans. In turn, less fresh air intake shows that:

• the evaporator cooling coils require defrosting less often
• circulation is interrupted less frequently

Therefore, it is safe to say that the respiration gasses emitted by non-climacteric fruit are much lower than those of climacteric fruit. As such, the need for ventilation of non-climacteric fruit becomes far less.

Controlled Atmosphere (CA) and Modified Atmosphere Packaging (MAP)

For certain high-value or sensitive cargo, standard fresh air ventilation is replaced, or supplemented, by controlled atmosphere (CA) shipping or modified atmosphere packaging (MAP).

Controlled atmosphere (CA) shipping actively manages the levels of oxygen (O₂), carbon dioxide (CO₂), and nitrogen (N₂) inside the container. By reducing O₂ to between 2–5% and elevating CO₂ to 3–8%, CA shipping dramatically slows the respiration rate of fresh produce, extending shelf life by days or even weeks compared to standard refrigeration.

Modified atmosphere packaging (MAP) works at the packaging level, sealing individual products in gas-flushed bags or trays before loading them into the reefer container. The reefer’s ventilation system then maintains the ambient conditions that preserve the integrity of each MAP-sealed unit during transit.

Both CA shipping and MAP are increasingly relevant in temperature-controlled shipping for premium produce exporters, pharmaceutical distributors, and high-value seafood shippers operating in demanding offshore environments.

MGS IceStorm’s offshore reefer containers support CA and MAP cargo requirements through microprocessor-controlled ventilation settings, adjustable O₂/CO₂ management, and Thermo King-powered container refrigeration units (CRU), giving operators full control over atmosphere from port to platform.

What is ‘return air’ in reefer containers?

Return air refers to the air that has been circulated through the reefer and returned to the refrigeration unit for re-cooling. In low-temperature mode, the majority of common refrigeration units control ‘return temperature’ using a two-point switching method.

So, as long as the ‘return air’ temperature is above the nominal value, the refrigeration unit will cool at full power.

Consequently, once the nominal temperature is reached, the refrigeration unit switches itself off. It leaves only the fans responsible for circulating the air in the reefer container running.

When the ‘return air’ temperature rises to approximately 0.5°C above the nominal value, the refrigeration unit starts up again, and the entire process is repeated.

Do note that the supply air temperature must always be lower than the nominal temperature.

Reefer container ventilation settings

The advanced technology from our partnership with Thermo King ensures that the 8ft & 10ft offshore reefer container by MGS maintains a refrigerated container temperature setting that ranges from -30c to +20c with a humidity controller to meet the requirements of different perishables.

Humidity and Airflow Balance in Reefer Containers

Ventilation and humidity are interdependent. Increase fresh air exchange too aggressively and you risk pulling dry ambient air into a high-humidity cargo load, causing dehydration and weight loss in fresh produce.

Reduce ventilation too much, and moisture accumulates, encouraging mould growth and condensation on packaging.

Getting the humidity and airflow balance right means matching ventilation rate to both cargo type and ambient conditions:

• High-humidity cargo (fresh fruit, vegetables, cut flowers): Recommended relative humidity of 85–95%. Ventilation must be carefully managed to maintain moisture without allowing condensation.
• Low-humidity cargo (hard cheese, cured meats, dried goods): Dehumidification range of 65–85% required. MGS IceStorm containers dehumidify within this range automatically.
• Pharmaceutical and chemical cargo: Often requires sealed or near-zero ventilation with precise humidity ceilings to preserve product integrity and meet regulatory requirements.

MGS IceStorm’s offshore refrigerated container airflow system uses T-bar aluminium flooring to direct conditioned air evenly along the base of the cargo load, ensuring uniform temperature distribution from floor to ceiling, not just at the evaporator.

Ventilation on Demand (VOD): How MGS Manages Airflow Automatically

One of the most significant advancements in reefer ventilation system design is Ventilation on Demand (VOD), a feature standard across MGS IceStorm’s DNV 2.7-1 certified Ice Storm and Ice Wave offshore reefer containers.

Rather than running ventilation at a fixed rate throughout a voyage, VOD continuously monitors respiratory gas levels inside the container and triggers fresh air exchange only when CO₂ or ethylene concentrations reach a set threshold. This means:

• Less energy consumption: the system doesn’t ventilate unnecessarily.
• Reduced temperature fluctuation: fewer cold-air disruptions from outside air intake.
• Lower risk of evaporator coil icing: the primary cause of defrost cycles and cargo temperature variance.
• Better cargo outcomes: targeted ventilation aligned to actual respiration, not a fixed schedule.

VOD is especially valuable on long offshore voyages where ambient temperatures vary significantly, common on routes between Europe, West Africa, and Southeast Asian oil and gas platforms.

Container ventilation control in MGS reefers is managed by a Thermo King microprocessor, with all fresh air exchange events logged automatically for traceability and HACCP compliance.

Why is ventilation important in transporting perishable cargo?

Proper ventilation is the most cost-effective way to prevent condensation in a reefer container, but the calibration matters.

Insufficient ventilation allows moisture and heat from cargo respiration to accumulate, creating conditions for spoilage, mould, and condensation on packaging.

Over-ventilation, on the other hand, draws in excessive outside air, which can freeze the evaporator coils and trigger repeated defrost cycles, raising energy costs and causing short-term temperature spikes that stress cold-sensitive cargo.

This is precisely why microprocessor-controlled ventilation, rather than manual or fixed-rate settings, is the standard in modern offshore reefer container operations. MGS IceStorm’s VOD system eliminates both risks by responding to real-time gas levels rather than a fixed timer.

Frequently Asked Questions

What is the purpose of ventilation in a reefer container?

Reefer container ventilation removes accumulated respiration gases (primarily CO₂ and ethylene) produced by perishable cargo during transit.

It also prevents condensation, balances humidity, and maintains consistent refrigerated container air circulation throughout the voyage. Without adequate ventilation, even a correctly chilled container can experience accelerated spoilage from gas build-up.

How much fresh air does a reefer container exchange per hour?

The fresh air intake capacity of standard offshore reefer containers ranges from 0 to 180 m³/hour (at 50 Hz).

The correct setting depends on the cargo’s respiration rate, the ambient temperature, and voyage duration.

High-respiration cargo like tropical fruit typically requires 40–120 m³/hr, while frozen or pharmaceutical cargo may require near-zero exchange.

What is ventilation on demand (VOD) in a reefer container?

Ventilation on Demand (VOD) is an automated reefer ventilation system that triggers fresh air exchange only when respiratory gas levels inside the container (primarily CO₂ and ethylene) exceed a set threshold. Unlike fixed-rate ventilation, VOD responds to actual cargo conditions in real time, reducing energy use, minimising evaporator icing, and improving cargo outcomes. VOD is a standard feature in MGS IceStorm’s DNV 2.7-1 certified Ice Storm and Ice Wave containers.

What is the difference between CA shipping and standard reefer ventilation?

Standard reefer ventilation replaces internal container air with ambient outside air to dilute respiration gases. Controlled atmosphere (CA) shipping goes further; it actively manages the ratio of oxygen, CO₂, and nitrogen inside the container to slow cargo respiration at a biochemical level.

CA shipping extends shelf life significantly beyond what standard ventilation alone can achieve, and is most commonly used for premium fresh produce, pharmaceuticals, and high-value seafood.

How does reefer ventilation affect cold chain logistics?

Ventilation is a core variable in cold chain logistics. Poor ventilation management, whether under- or over-ventilation, causes temperature fluctuation, humidity imbalance, and gas accumulation, any of which can compromise cargo quality or cause regulatory non-compliance.

In offshore cold chain operations, where containers may be exposed to extreme ambient conditions on platforms or vessels, automated ventilation control is essential to maintaining an unbroken cold chain from origin to destination.

What happens if a reefer container is over-ventilated?

Excessive fresh air exchange draws in too much outside air, which can freeze the evaporator coils, trigger repeated defrost cycles, and cause short-term temperature spikes inside the container.

For cargo that is sensitive to temperature variance, such as fresh berries, cut flowers, or injectables, this can cause direct product damage. Over-ventilation also increases energy consumption and operating costs.

Can MGS IceStorm reefer containers be used for CA or MAP cargo?

Yes. MGS IceStorm’s offshore reefer containers support controlled atmosphere (CA) and modified atmosphere packaging (MAP) cargo requirements through adjustable microprocessor-controlled ventilation, Thermo King-powered container refrigeration units (CRU), and a temperature range of -30°C to +20°C.

Operators can configure ventilation settings to maintain the specific O₂ and CO₂ ratios required for CA cargo, with all exchange events logged for full traceability.

Conclusion

In summary, reefer containers are designed to automatically control refrigeration using the supply air sensor to detect and critically manage temperatures within a 0.5°C (0.9°F) range, or better, under most conditions.

Remember, perishable goods need precise temperature control to maintain their quality all the way to their final destination.

As such, reefer unit ventilation settings must be configured according to cargo requirementsreefer unit ventilation settings must be configured according to cargo requirement.

Overall, fresh air ventilation is especially useful for products that produce high levels of ethylene, such as tomatoes and apples. However, excessive ventilation can result in the freezing of the evaporator coils and will necessitate additional defrosting to remove ice build-up.

For more information on reefer containers, their types and efficiency, check out our blog on “What are offshore reefer containers?”

Need a reefer container that gets ventilation right?

MGS IceStorm manufactures DNV 2.7-1 certified offshore reefer containers, the Ice Storm (10ft) and Ice Wave (8ft), built in partnership with Thermo King and Honeywell. Both units include:

• Microprocessor-controlled reefer container fresh air exchange.
• Ventilation on Demand (VOD) with automated gas-level response.
• Humidity control with a dehumidification range of 65–85%.
• Temperature range of -30°C to +20°C.
• Full data logging for HACCP and cold chain compliance.
• DNV 2.7-1, EN-12079, and ISO 10855 certifications.

Available for sale and rental with ready stock and delivery across Europe, Africa, Asia, the Americas, and Oceania.

Get a Quote | View Ice Storm Specs | View Ice Wave Specs

Jason Tan

Business Director

A graduate (Business) from KDU, Jason Tan, is the current Business Director (Sales) for MGS Icestorm and has been associated with the company for the past 10 years.

With over 13 years in the shipping industry, he has had a significant contribution to Malaysia’s oil and gas industry in the engine and boat supply sector.

His expertise includes managing offshore catering business, offshore reefer containers, AI technology, offshore gas tanks, A60 pressurized cabins, etc. His contributions have helped establish MGS, in partnership (joint venture) with Thermo King and Honeywell to produce state of art Offshore Reefer Container products.