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Keeping the reefers cool on deck

MacGregor and Carrier Transicold have new ideas for improving the way reefers are cooled on the deck of a vessel.

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No of tiers of reefers on deck can be increased from 2 to 4 or more by using forced air ventilation
No of tiers of reefers on deck can be increased from 2 to 4 or more by using forced air ventilation

Ventilation for reefer containers on the deck of a vessel is becoming more of a challenge. As vessel sizes increase, ships are stacking containers up to 24 rows across the vessel, and the stacks themselves can be 10 or more containers high.


That increased density is making it harder to ventilate reefers in the stacks, meaning reefer machinery has to work harder (and use more energy) to maintain the container’s temperature set point. Furthermore, reefer cargo is growing faster than conventional or dry cargo, and lines want to find ways to get more reefer containers on each vessel.

 

To get more reefer containers on board, lines are increasing the percentage of slots with reefer plugs on new build vessels, and in some cases using splitter boxes to power more than one reefer off one outlet. The lower power consumption of newer reefer containers, coupled with remote monitoring technology, makes this easier to manage.

 

Increasing the number of reefers on deck in one bay, or across several bays, creates a ventilation problem that is more difficult to address than for reefer slots under the hatch covers, where mechanical ventilation systems are used. Both Carrier Transicold and Cargotecowned MacGregor have recently filed patents for improved ventilation systems to address this issue.


MacGregor doubles up


Taking Macgregor first, it has come up with a new system for ventilating reefer containers on deck. It could double the number of reefers that can be stacked in a bay on the deck of a container ship (Patent WO2018046789).


In practice, says MacGregor, reefer stacks on deck are typically limited to the two lowermost layers. As noted above, as the width and height of container stacks has increased with vessel size, the amount of natural ventilation space has declined. Furthermore, lines want to stack more reefers on deck but “this is contingent on improving the ventilation of the environs of the container”, noted MacGregor.


To solve the problem, MacGregor has come up with a system for controlling the airflow around containers on deck using forced ventilation. It consists of temperature sensors, ventilators, and control and interface units that measure the ambient temperature and operate a forced air cooling system automatically. Air from fans is directed using channels and nozzles of various shapes.


The whole system can be separate from the ship, or integrated into the design of the vessel and controlled from the bridge.


Directional approach


Another new patent from Carrier Transicold (US Patent US2019225418) tackles the same issue but with a different approach. Instead of forcing more air around the containers, Carrier Transicold has developed a system using controllable directional louvers on reefer containers to manage the way air is directed into and away from the condenser air intake ports.


Carrier Transicold describes a reefer where the condenser air outlet is configured to direct exhaust air from the condenser unit away from the condenser air inlet, while the internal reefer air outlet ports are configured to direct conditioned air exhausted from the container itself towards the condenser air inlet. According to the patent, the position of the ventilation louvers is controllable, and can be further assisted with the use of attachments that clip on to the ventilation ports.

 

The obvious issue with this approach is how it would work in a dense reefer stack, where a large part of the problem is hot air from one or more reefer containers entering the air intake of other containers. Carrier Transicold has addressed this issue in its patent, which covers scheduling of reefer operations to avoid what it calls “re-ingestion” of hot air. This is achieved by using a decentralised control algorithm with “low sensing and communication requirements in which each local controller determines when to turn its corresponding refrigerated storage container on and off within a given time window, in order to minimise waste heat ingestion from neighbouring refrigerated storage containers”.

 

Different options for determining the operation of adjacent reefer machinery are discussed. These include measuring the difference between ambient air temperatures and condenser inlet air temperature to determine a “pseudo-data element for potential exhaust air ingestion. With this data the controller can determine whether to turn on the condenser unit at different threshold temperatures, and different reefer units can be run in a sequence that minimises the amount of hot exhaust air from neighbouring units”.

 

Carrier Transicold believes the system could reduce energy usage while at the same time being cost-effective to implement. “The autonomous reefer schedule logic, based on the quality of air at the unit’s condenser inlet, in addition to the cargo space temperature, minimises potential waste heat ingestion, and thereby reduces energy usage for refrigeration,” the patent notes. “The decentralised control logic only requires one additional sensor for condenser inlet temperature, rendering the solution practical with low implementation cost. The control logic can be easily integrated with the individual unit legacy controller or implemented as a standalone local controller for each reefer.”


Only a few years ago, such a system would likely have been regarded as overly complex and costly to implement. However, the whole reefer industry is now focusing on remote reefer monitoring, minimising energy consumption and data-based reefer management. This type of system aligns well with that trend.

 

 

 

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