Low-cost cold storage in Kenya using evaporative cooling
A team of researchers from the Massachusetts Institute of Technology (MIT) and the University of Nairobi are designing affordable off-grid cold storage units for perishable crops in Kenya, using evaporative cooling and upcycled shipping containers.
In hot and arid regions, smallholder farmers struggle with getting fresh crops to market. Access to cold storage would help them harvest and sell more produce while expanding consumers’ access to fresh produce. Unfortunately, many smallholder farming communities lack access to the energy resources needed for refrigeration.
To address this challenge, an MIT research team is collaborating with researchers at the University of Nairobi to develop a cost-effective large-scale cooperative storage facility that uses the thermodynamic properties of evaporating water to refrigerate harvests. 
Evaporative cooling is not a new concept. It has been used in many arid regions where people use a double clay pot system to prolong the freshness of fruit and vegetables.  However, clay pot coolers offer limited storage capacity.
There are currently few existing designs that are large enough to effectively store several metric tons of produce while meeting important criteria such as ease of construction, quality of performance, and affordability. For instance, the costs associated with the energy, implementation, and maintenance of solar-powered mechanical refrigeration units may be prohibitive to many smallholder farmers around the world.
The researchers at the University of Nairobi and MIT D-Lab opted for shipping containers as the basis for the evaporative cooling chamber. Indeed, not only do the shipping containers meet the dimensional specifications of the users’ requirements but the use of shipping containers also allows existing and used materials to be upcycled.
The researchers retrofitted a shipping container with a double-layered insulating wall, a solar-powered fan to force air through a central matrix of wet pads, and interior storage crates arranged to maximize convection, cooling rates and ease of use. The researchers are also experimenting with plant-based aspen fibre and corrugated cellulose pads as a mean of evaporative cooling. Both are a cost-effective and environmentally sustainable solution. Lastly, the team has installed a solar-powered electronic control system that allows farmers to automate the chamber’s fan and water pumps, increasing efficiency and minimizing maintenance requirements.
Several analytical models support this design. These models help maximize cooling capabilities while minimizing water and energy usage and inform decisions on material choices. Based on these models, the researchers estimate that a standard 40-foot-long (12.19 metres) shipping container used as an evaporative cooler will be able to store between 6,500 and 8,000 kilograms of produce. Construction costs are estimated at around 7,000 - 8,000 US dollars, which the research team believes is half the cost of mechanically refrigerated options of similar size. The use of local materials and a centralized manufacturing strategy help reduce the production costs.
While the current design has been developed for farmers near Nairobi in Kenya, these evaporative cooling devices could be deployed in other regions in Kenya, West Africa or regions of western India such as Rajasthan and Gujarat.
Photo courtesy of MIT D-Lab