Evaluation of a new heat transfer and evaporative design for a zero energy storage structure

Abstract A passive evaporative zero energy storage structure (ZESS) has been developed as a low cost and eco-friendly cooler for storing perishable fruit and vegetables with moderate respiration rates. Evaporation is influenced by weather conditions (air temperature, relative humidity, and the direction and speed of the outside air) and the porous nature of the heat exchanging and evaporative media (pore space of gravel stone with thermal–hydraulic conductivity and vapor diffusion properties of the porous medium). The ZESS consists of two heat exchanging media (outside wall made of porous volcanic lava stone and inside wall made of solid clay brick), one evaporative medium (sand–zeolite–gravel stone), and one natural humidifier (detachable clay water tank) inside the storage area. The results obtained from the performance tests revealed that the temperature inside the ZESS was 15 °C lower than the outside air temperature, while the inside relative humidity was 20% higher than the outside relative humidity. As a result, the shelf life of stored tomato and eggplant inside the ZESS increased from 7 to 19 days and 4 to 9 days, respectively, with maximum watering of 29 L day −1 . Thus, a ZESS provides an excellent means of short-term preservation of fruit and vegetables soon after harvest.