Across the Sahel, a semi-arid region of west and north-central Africa that stretches from Senegal to Sudan, many small farmers, market vendors and families lack an affordable and effective solution for storing and conserving vegetables. As a result, harvested vegetables run the risk of spoiling before they can be sold or eaten.
However, as described in a recent report "Evaporative cooling technologies for improved vegetable storage in Mali" of the MIT Technology Initiative (CITE) and MIT D-Lab of MIT (Massachusetts Institute of Technology), There are low-cost and low-tech solutions for communities in need of product cooling that are based on an ancestral method that exploits the air-cooling properties of water evaporation. Made of simple materials such as bricks or clay pots, burlap sacks or straw, these devices have the potential to address many of the challenges faced by rural households and farmers who need better vegetable storage after harvest.
The study was carried out by a team of researchers led by Eric Verploegen of D-Lab and Ousmane Sanogo and Takemore Chagomoka of the World Vegetable Center, which is dedicated to continuous work with horticultural cooperatives and farmers in Mali. To obtain information on the use and preferences of evaporative cooling devices, the team conducted interviews in Mali with users of the refrigeration and storage systems and with stakeholders throughout the vegetable supply chain. They also implemented sensors to monitor the performance parameters of the product.
Despite the potential of evaporative cooling technologies to meet a critical technological need, there is little consumer information available on the range of solutions available.
"Evaporative cooling devices for better plant storage have been around for centuries, and we want to provide the kind of information on these technologies that will help consumers decide what products are right for them given their local climate and their specific needs." , says Verploegen, the evaluation lead.
Simple chambers cool vegetables through the evaporation of water, in the same way that the evaporation of perspiration cools the human body. When water (or perspiration) evaporates, take the heat with it. And in less humid climates such as Mali, where it is hot and dry, the technologies that take advantage of this cooling process are promising for the effective conservation of vegetables.
The team studied two different categories of plant cooling technologies: large-scale vegetable cooling chambers built with bricks, straw and sacks suitable for agricultural cooperatives, and devices made from clay pots for individuals and small farmers. Over time, they controlled changes in temperature and humidity within the devices to understand when they were most effective.
"As predicted," says Verploegen, "the real-world performance of these technologies was strongest in the dry season, we knew this was true in a laboratory testing environment, but now we have data documenting that it can be achieve a temperature drop of more than 8 degrees Celsius in a real world use scenario. "
The decrease in temperature, together with the increase in humidity and protection against pests provided by the devices, resulted in a significant increase in the shelf life of commonly stored vegetables, such as tomatoes, cucumbers, eggplants, cabbages and peppers spicy
"The large-scale plant cooling devices made of brick had a significantly better performance than those made with straw or sacks, both from the point of view of technical performance and from the perspective of ease of use," says Verploegen. "For small-scale devices, we find quite similar performance in different designs, which indicates that the design constraints are not very rigid, if the basic principles of evaporative cooling are applied, a reasonably effective device can be made using materials locally available This is an exciting result, meaning that in order to scale the use of this process to keep fresh vegetables, we can look for ways to disseminate information and designs instead of developing and distributing physical products. "
The results of the research indicate that evaporative cooling devices would provide great benefits to small farmers, sellers of vegetables in a market and individual consumers who, due to financial or energy constraints, have no other options.
However, evaporative cooling devices are not suitable for all environments: they are best suited for communities where there is access to water and vegetable storage is needed during hot and dry weather. And users must commit to attending the devices. The sensor data used in the study revealed that users were more inclined to irrigate the cooling devices in the dry season and to reduce the use of the devices when the rainy season began.
For more information
Eric Verploegen, MIT D-Lab Research Engineer