"There’s increasing interest in an innovative yet old-school solution to the problem: evaporative cooling."
Food loss due to lack of effective storage is a global problem. In Sub-Saharan Africa alone, approximately 23 percent of available food is lost or wasted, resulting in up to 15 percent less income for approximately 470 million farmers and other value chain actors.
There’s increasing interest in an innovative yet old-school solution to the problem: evaporative cooling. The mechanics of the process are familiar to everyone: When sweat evaporates from your skin, it takes heat with it and you feel cooler. This same principle can be used to create storage devices to keep fruits and vegetables cool. In a dry climate, a storage container can be made with a double earthenware wall, with the space between the walls filled with wet sand. The container walls will “sweat,” and the inner chamber – where fruits and vegetables can be stored – will be cooled to as many as 10 degrees C below the ambient temperature.This process offers an effective, affordable way to keep fruit and vegetables from spoiling.
An Inexpensive, Scalable Solution
Along with temperature reduction, evaporative cooling devices provide protection from animals and insects, and increased humidity inside the storage chamber. This significantly improves the shelf-life of common fruits and vegetables, leading to reduced spoilage (money saved), increased access to nutritious food (improved health), and less need to purchase new food (time saved). The devices are easy to make using affordable, locally available materials, like clay pots, bricks, sand, charcoal, wood, dry grass, gunny or burlap sack, and twine. And because they don’t require electricity, they are an environmentally sound refrigeration solution that’s perfect for areas where access to electricity is limited.
Evaporative cooling devices can also be scaled to meet the needs of the user. For individual or family use, a clay pot-in-pot design is a great choice. Commonly known as a “Zeer pot,” this design was popularized in 1995 by Mohammed Bah Abba in Nigeria. But farmers and communities wishing to pool their resources may require something larger. In the early 1980s, Susanta K. Roy and D.S. Khuridiya developed larger capacity evaporative cooling chambers made primarily from brick – commonly known as “zero energy cool chambers” or “ZECCs” – for use by farmers in India. These chambers can store several metric tons of fruits and vegetables.
However, while evaporative coolers can address post-harvest storage issues for many fruits and vegetables, they aren’t a universal solution. They are most effective in arid regions where the weather is hot and dry most of the year. Just as sweat will not cool your body when it is humid, an evaporative cooling device will not cool your vegetables in humid weather. Additionally, these types of evaporative cooling devices cannot reach temperatures low enough to safely store meat, dairy and many medicines.
A Missed Opportunity
In a recent report from the Global Knowledge Initiative, evaporative cooling technologies are listed among 22 investable innovations with the potential to transform food systems in emerging markets, and as a “quick win” that can be adopted with minimal training and low up-front costs.
Yet in spite of the benefits that evaporative cooling devices can provide for post-harvest vegetable storage, they are not widely used. What can be done to increase the effective production, dissemination and usage of this technology?
Researchers at MIT D-Lab have identified five areas where work is needed. The following sections explore those areas in detail.
Conducting further research on evaporative cooling device designs
Recent results from a research study conducted by MIT D-Lab and the World Vegetable Center in Mali demonstrated that designs that are simpler and easier to construct than the common pot-in-pot configuration can still provide significant benefits for improving vegetable storage. Research on the design constraints for effective product performance at various scales (household, individual farmer and cooperative levels) is needed to identify the most practical, cost-effective and easily disseminated designs.
Scoping regions where evaporative cooling is suitable
Before contemplating the use of evaporative cooling devices, several key factors that are not widely understood need to be considered:
- Local weather: The most benefit is provided in hot and dry climates.
- Access to water: Water must be added for evaporative cooling to work.
- What needs to be stored: While vegetables can benefit, meat, medicine and dairy require lower temperatures than evaporative cooling devices can provide.
- Cost of construction: The cost of building an evaporative cooling device with locally available materials must be affordable relative to the value that it will provide.
Resources are needed to provide guidance for local organizations or individuals, to determine if evaporative cooling is a good fit for a particular context. Systematic mapping would also be helpful, highlighting specific areas where evaporative cooling devices can provide the most value at the community, regional or country level.
Developing scalable dissemination strategies
In recent years, organizations such as Practical Action, Movement e.V., the World Vegetable Center, the Horticulture Innovation Lab, Technoserve, and the Postharvest Education Foundation, among others, have made efforts to demonstrate evaporative cooling technologies in appropriate communities. However, there is a lack of proven approaches for achieving scalable dissemination of these technologies. The approaches that have been used at varying scales can be grouped into two major categories:
- Dissemination of information directly to users for self-construction and use, conducted through digital channels (best practices guides, videos, etc.), extension agents and training workshops.
- Training and support to local entrepreneurs for the construction and sales of evaporative cooling devices to users.
Systematic evaluation of a range of dissemination approaches in various contexts is needed. Building evidence of successful and scalable approaches for disseminating these technologies will provide a template for replication by local organizations operating in similar contexts.
Researching user behavior and impact
While there have been several studies that illustrate the benefits of evaporative cooling devices, much more can be done to encourage communities and development organizations to invest in and scale their dissemination, including:
- Providing stronger evidence that demonstrates the shelf-life improvements of common vegetables through the use of evaporative cooling devices.
- Conducting research that demonstrates how these technologies are being used.
- Publicizing the impact of evaporative cooling systems on families and farmers, including reduced food spoilage, reduced time and money spent traveling to the market, increased nutrition due to availability of vegetables, and increased income for smallholder farmers that are able to sell vegetables at higher prices.
Creating a community of practice
As evidence is gathered about the use, dissemination and impact of evaporative cooling devices, a growing number of people across geographies and professions are working to increase the use of evaporative cooling for produce storage. But more platforms or forums are needed for key stakeholders (practitioners, enterprises, farming cooperatives, researchers, governments and funders) to share learnings, raise awareness and take action to advance the dissemination of these beneficial technologies.
A Call to Action
Evaporative cooling technology has the potential to improve the lives of people in communities around the world where fruit and vegetable loss is a problem and climate conditions are right for this solution. Investment in developing and researching these technologies and dissemination approaches is critical for increasing confidence among users and development sector actors in the scalability of this work. The sector should be working toward a broad understanding of where and how this technology can be applied, gathering examples of success stories and resources that others can learn from and replicate, and fostering a community of individuals and organizations that can serve as ambassadors for these solutions. Embracing this approach – and mobilizing significant and targeted investment – will result in the dissemination of evaporative cooling technologies at a large scale.
Please contact Eric Verploegen at MIT D-Lab and join the Evaporative Cooling Facebook group to connect with other folks working to disseminate these technologies.