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Better circulation due to air distribution mats in reefers

Temperature differences in reefer containers aren’t a new problem. Over the years, various solutions were thought of, and pieces of cardboard are extensively worked with to optimise air flow in the containers. In 2016, Wageningen UR started research to scientifically show which way is effective.

“That it’s warmest close to the door and that it would be good for the products if more cold air were to reach the door, is hardly a new idea,” says Leo Lukasse of the Wageningen UR. He was involved in both the research in climate chambers in Wageningen and in field research last year. The most favourable form of the air distribution mat to have the best effect on air distribution was determined during the ‘laboratory research’ stage. “The form that turned out to be the most favourable, is the one now used by Otflow,” Leo sums up the results. “This research is part of GreenCHAINge fruit and vegetables, and partly financed by Topsector Tuinbouw & Uitgangsmateriaal.”

Field test with grapes
To also test the results in practice, a field research was started. This requires cooperation of companies from the sector. Leo says this doesn’t always go smoothly, but he calls this research ‘an example.’ “The sender, transporter and receiver have to cooperate in a field research in the cold supply chain. Things often go wrong, but this time, all of the links cooperated.”

Six containers were loaded with grapes in South Africa, their destination was the Netherlands. Transport time was 24 days. In three containers, the floor was partially taped off with an Otflow air distribution mat. The other three containers functioned as the control group. Each container was equipped with 31 data-loggers that registered temperatures every ten minutes. “The field test confirmed what we had already seen in climate chambers,” Leo concludes. “Temperatures near the door were more favourable in containers equipped with Otflow.”

Major temperature difference
“Grapes in particular often have quality problems due to temperature deviations in the containers,” Leo explains. Besides, the choice to use a grape transport was a practical one: these trade parties wanted to cooperate. In the conclusions, the difference in quality wasn’t perceptible. “It’s a shame we couldn’t observe a visible effect,” Leo admits. “Of course, it could be that effects are larger under other circumstances.” For example, a product of a lower quality, a higher ambient temperature, a different variety or a longer transportation time could lead to a larger difference in quality.

However, the general conclusion was confirmed: the Otflow results in a better air circulation so that temperatures near the door are lower in containers than in containers without Otflow. That difference can be up to 30 per cent. “You could generalise the results of the research to other products that don’t have much of their own heat production and are loaded cold.” Potatoes, onions, lily bulbs and citrus are just a few examples. It’s different for bananas. “Bananas have a high heat production and they are loaded hot. We’d have to do more research,” the researcher says. He expects the results for similar products could deviate.

Research concluded, now it's the market’s turn
Leo mentions that the sector often looks at banana transports, in which it’s common to tape off the floor between the last pallets and the door using cardboard. Yet according to him it’s not a good idea to copy these methods without thought. “Bananas are loaded hot, so you first have to blow as much air as possible through the product to cool it. That’s why banana exports place a piece of cardboard on the floor between the last pallet and the door.”

For the bananas, which mostly cause the risks of high temperatures themselves rather than the outdoor temperature, this is a good idea. “I’ve also seen it used with, for example, citrus and pineapple, but I wonder why. I expect it barely has an effect in these fields, and if it does, I think it’s a negative effect,” Leo says. For these products, outdoor temperature is a larger risk. Good air circulation around the product is more important.

For all traders who have problems caused by high temperatures near the doors, Otflow could be a good solution according to Leo. “These traders should look into it,” he concludes. “It’s fun to see a technique that we’ve researched being taken up by Otto de Groot, who made a company out of it. Now it’s the market’s turn to take it further.”

More information:
Wageningen UR
Leo Lukasse

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