Performance evaluation of a medium size charcoal cooler installed in the field for temporary storage of horticultural produce

Abstract

Evaporative cooling has been used over time as an effective method for controlling the environment in structures. However, documented scientific information on performance of commercial scale storage systems is limited. Based on preliminary laboratory data a medium size charcoal cooler was constructed with a volumetric capacity of 27 m3 and wall thickness of 100 mm at Kikoo village in Kibwezi district in the Eastern Province of Kenya. The area is known for irrigated horticultural farming under extreme environmental conditions. The developed cooler had a sisal stem ceiling covered with 50 mm thick dry reeds. The cooler was constructed to provide temporary storage for fruits and vegetables, destined mainly for exporting to international markets, as a remedy to minimize loss of quality before collection. The performance of the charcoalcooler was evaluated on the basis of the temperature and the relative humidity with three scheduled daily watering regimes, once at 8:00 h, twice at 8:00 and 12:00 h and three times at 8:00, 12:00 and 14:00 h. These watering regimes aimed at reducing the amount of water used and at the same time to ensure that the charcoal was not completely dried. Temperature and relative humidity were measured in the cooler, adjacent grading room and outside the structure to give the ambient conditions. The cooler had the lowest temperature and the highest relative humidity irrespective of time and watering schedule. Triple watering of the cooler showed the highest temperature decrease and relative humidity increase, differences reaching 11 ̊C and 38% respectively, compared to single and double watering. Triple watering also maintained the relative humidity in the cooler within the recommended range of 80 to 95% for horticultural produce. The cooler temperature however remained far above the recommended range of 0 to 10 ̊C for fruits and vegetables. A watering interval of two hours from 8:00 h onwards would be the most appropriate watering regime, considering the extreme environmental conditions and scarcity of water.