2017 ASHS Annual Conference

Evaporative cooling is an ancient technique for removing heat in warm, dry climates and has been employed for cooling of structures for storage of perishables for the last two decades in India. However, at best, these evaporatively-cooled (EC) structures reduce temperatures only by 10 to 12 °C below the ambient temperatures during the warmest part of the day and can actually have temperatures above ambient in the cooler evening hours. As part of a project supported by the Global Center for Food Security Innovation at Michigan State University, we have redesigned these EC structures using novel inexpensive wall materials in a structure designed to be capable of accepting refrigeration at a later date. We compared the performance of a traditional brick-sand-brick (BSB) wall design with two new wall materials: pervious concrete (PC) and mesh-supported fabric (MSF) in 1/10th scale (1m³) prototype structures at the Indian Agricultural Research Institute, Delhi. The low thermal mass and high heat transmittance of the PC (750 W·h·°C^-1 and 4.12 W·m^-2·°C^-1, respectively) and MSF (42 W·h·°C^-1 and 6.6 W·m^-2·°C^-1, respectively) walls permitted faster and more extensive cooling than BSB (5804 W·h·°C^-1 and 2.01 W·m^-2·°C^-1, respectively) walls. This resulted in a 3- to 4-°C reduction in the temperature of 100 kg of simulated 'produce' relative to a BSB structure during warm dry periods. During cool damp periods, however, the advantage of the MSF and PC structures was lost. The new wall materials and designs were less expensive and easier to construct than the traditional BSB design. We estimate that full-sized structure made with PC or MSF would cost 30 to 50% less than the BSB design for EC storages. A full-scale MSF structure has been built and is being evaluated. Data suggest that reducing insolation onto the surface of the structure can improve functionality and reduce EC wall temperatures as much as 5 °C. Future plans call for retrofitting this room with a solar-powered refrigeration system to achieve temperatures as much as 35 °C below ambient. Modeled thermal properties of the room suggest that the evaporative cooling will reduce the size of the refrigeration system and associated solar array by 1/3 relative to a non-EC room.