The charcoal cooling blanket

A scalable, simple, self-supporting evaporative cooling device for preserving fresh foods

Abstract

Evaporative cooling is a high-potential technology to help preserve fresh produce after harvest. This passive cooling solution is especially interesting for marginal and smallholder farmers in remote, off-grid areas. However, evaporative coolers are still rarely deployed. We currently lack simple, small-scale evaporative cooling systems that are affordable for marginal and smallholder farmers. As a solution, we present, design, and test an alternative evaporative cooler – a charcoal cooling blanket. The blanket can be made in any size from locally-sourced materials such as charcoal and burlap, or other biodegradable textiles. The blanket's cost scales down quasilinearly with the length of the blanket. The blanket has several compartments to hold the charcoal and is semi-self-supporting. When building a cold storage room or retrofitting sheds to cooling rooms, the blanket acts as a structural component. The blanket is useable throughout the supply chain. Examples are temporary on-farm storage, cooling during transport by truck, or cooling at the local markets. Single-family households can deploy this cooler in rural, peri-urban, or urban areas for last-mile cooling. In our lab experiments, the blanket cooled the air and the fruit temperature by 5 °C below ambient in a moderately humid environment. This temperature was only 2-3°C above the wet-bulb temperature. The humidity inside our 56L cooler was 85-95%. In field experiments, a 600L blanket cooler achieved a temperature reduction of 2-3°C below the outside air temperature. The lower temperature and higher humidity inside the evaporative blanket cooler reduce thermal food degradation and wilting. The materials to construct the blanket have a carbon footprint of 15 kg CO₂-eq/m². The environmental impact of operating a charcoal-blanket storage room of a twenty-foot equivalent unit (33 m³) is 200 times lower than that of a similar-sized commercial refrigeration unit for a 14 days storage period. We also present a business solution leveraging digitalization to accelerate the adaption of this technology. The charcoal blanket lowers the expertise to construct and operate evaporative coolers. It additionally reduces the cost of microscale cooling facilities. With these blankets, we therefore aim to catalyze the deployment of evaporative coolers.