Performance evaluation of an indirect air cooling system combined with evaporative cooling

This study developed an indirect air-cooling combined with evaporative cooling (IAC + EC) system for temporary storage of fruit and vegetables (FV) to improve the shelf life of fresh produce under hot and humid climatic conditions. The aim of the study was to investigate the effect of IAC + EC in providing optimum storage environment of temperature and relative humidity (RH) for the tomato fruit compared to storage under ambient conditions. The IAC + EC system had a 53-m(3) storage chamber able to store 3.8 tons of tomatoes. Solar energy during the day and a battery bank facility at night powered the cooling system. The structure was constructed and assembled at Ukulinga research center in Pietermaritzburg. The performance of the IAC + EC was evaluated based on the temperature and the RH measured hourly from 05h00–22h00 daily during a period of 28 days. Temperature and RH were measured in the psychometric unit, various positions in the storage chamber and at ambient conditions. There were significant variations (P < 0.001) in temperature and RH between storage and ambient conditions. The temperature inside the storage chamber was on average 7°C–16°C lower while the average RH was 13%–41% higher than ambient conditions. Temperature and RH at the exhaust end of the IAC + EC storage chamber were 16.40 °C and 88.9% compared to 30.9°C and 47.6% under ambient conditions. Such conditions can enhance the shelf life of FV of moderate respiration rates. Inside the storage chamber, temperature was 15.7°C–16.4°C while the RH was 89.6%–93.8% depending on location. The cooler efficiency varied from 88.04% to 95.6%. The IAC + EC system performed at the same level as evaporative cooling under dry and arid conditions. The results in this study are evidence that IAC + EC system can provide optimum storage conditions for FV as well as being a low-cost technology utilizable in hot and sub-humid to humid areas in sub-Saharan Africa.