The charcoal cooling blanket: A scalable, simple, self-supporting evaporative cooling device for preserving fresh foods

Abstract

Evaporative cooling is a technology that has potential to help preserve fresh produce after harvest. This passive cooling solution is particularly interesting for marginal and smallholder farmers in remote, off-grid areas. Evaporative coolers are rarely deployed in these scenarios because there is a lack of simple, affordable, and small-scale systems. A charcoal cooling blanket has been designed and tested as an alternative evaporative cooler. The blanket can be made in any size from locally-sourced materials such as charcoal and hessian, or other biodegradable textiles. The cost of the blanket scales quasi-linearly with the length of the blanket. The blanket is semi-self-supporting and has several compartments to hold the charcoal, a material that is commonly used for evaporative coolers. It can be used throughout the fresh-produce supply chain. In laboratory experiments, the blanket cooled air and fruit temperatures by 5 °C below ambient (23 °C) at 40% relative humidity. This temperature was 2–3 °C above the wet-bulb temperature. The humidity inside a 56 l cooler was 85–95 %. In field experiments, a 600 l blanket cooler also achieved a temperature reduction of 2–3 °C below the outside air temperature. The materials to construct the blanket have a carbon footprint of 15 kg [CO2-eq] m−2. The environmental impact of operating a charcoal-blanket storage room of 33 m3 is therefore 200 times lower than that of a similar-sized commercial refrigeration unit for a 14 d storage period, which is a common storage period for many fruits and vegetables.