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This is how cooling vegetables with hot air works

1 June 2015 • 2 min reading time

Vegetables harvested in the hot climate of India quickly lose their freshness. To change this, TNO developed a cheap, economical and clean cooling system that operates independently from electricity networks. But how does it work?

Outside the highly populated cities of southern India, like Bangalore, Chennai and Madurai, there is an extensive rural area of small villages and crop fields. But no less than forty per cent of the harvest withers away before it can reach the supermarket shelves in the cities. This is partly because the tomatoes, aubergines and sweet peppers are exposed to the sun for too long.

An off-grid cooling system

A cold store could be a solution, but air conditioners are too expensive and run on electricity which is not available in many places. Business developer Leon Stille knows the local situation well. During his studies he spent six months in India, and is now working on a new TNO project to develop a cheap off-grid cooling system.

Adiabatic cooling

The basis of the project is a simple and effective cooling system. This system comprises a number of simple devices placed on the roof of a cold store whereby the hot outside air comes in contact with an environmentally friendly solvent via a membrane that separates the air and water. Simple solar collectors desorb the water from the solvent, creating water vapour,which is then condensed and reintroduced into the hot, dry air that is spread throughout the room. By desorbing the water vapour from the air and then reintroducing it, the air temperature drops. This so called adiabatic cooling is a natural process.

Combination of existing techniques

The system runs completely autonomously: little or no water needs to be added and the little amount of steam that is required for the pump is provided by a single solar cell. Stille: “These are all existing methods, but it is the combination of these methods that is unique.” More efficient is the desorbing process. “This project involves many of the TNO knowledge areas, like gas treatment, process development, materials science and system integration. Carbon nanoparticles are an innovation that we have added. This makes the desorption process much more efficient”, Stille says.

“These are all existing methods, but it is the combination of these methods that is unique”

Improving fresh food chain supermarkets

TNO is now developing pilots in cooperation with local and Dutch companies. The consortium, which includes Larive Consulting, seed breeder Rijk Zwaan and the logistics companies Broekman and RBK, aims to improve the entire fresh chain for Indian supermarkets.

Loss of quality reduced

Three store rooms and twotrucks are being equipped with the cooling system, which could result in a quality loss reduction from forty percent to approximately twenty percent. TNO is the driving force. The aim is for local companies to build the systems. India will be the first to get a system that can also be applied in other countries with a hot climate.

Higher quality product

“This project is a great combination of benefits,” says Stille. “We can invest in a new technology and export our knowledge, but the functional advantage is whom you are doing it for. They can purchase this higher-value system for a relatively cheap amount, and get a higher price for their product. This is how we try to take the level of prosperity a step further.”

Project storage spaces

The development and building of the storage spaces started at the end of 2015 and has a term of five years. Stille will be a regular visitor. “I am tremendously motivated by the practice. I hope that over five years I can say: look, this what we as TNO have done.”

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