Evaporative coolers for postharvest storage: where to best use them and how well do they work?

Abstract

Passive evaporative coolers have a huge potential to help smallholder farmers to preserve their fresh fruit and vegetables longer after harvest. However, we still lack transparent information on where evaporative coolers perform sufficiently well to significantly extend the postharvest life of the fresh produce. Unsatisfactory evaporative cooler performance is a potential cause for farmers' limited adoption of this technology to reduce their food losses. We present easy-to-use tools that help to better scope regions with the best potential to deploy evaporative coolers. This information should help avoid installing evaporative coolers in areas with environmental conditions that incite insufficient cooling. Concretely, we developed design charts of the achievable temperature depression by evaporative cooling based on the local air temperature and humidity. We quantified for apple, banana, mango, and tomato the resulting additional days in postharvest life gained by storing the produce in an evaporative cooler. We present geographical maps of India, Nigeria, and the entire world that answer how much evaporative cooling can maximally decrease the produce temperature and extend postharvest life for banana fruit. We make these maps available online. We also quantify how well evaporative coolers perform with respect to reducing the temperature and how they should be sized. Our results facilitate installing evaporative coolers only in suitable regions where they successfully help to preserve food longer. Our data also show in which months the cooler can be operated with the best performance. We thereby avoid disillusions and loss of trust in the technology with smallholder farmers, policymakers, farmers, or farmer cooperatives. Further catalyzing the implementation of small-scale evaporative coolers can bring farmers significant gains in postharvest life, reduce food losses, and increase revenues.