Abstract
A smart cooling-aeration (SCA) system was developed and tested for cooling bulk paddy stored in concrete silos in a south-subtropical depot of Guangzhou, China. Besides lowering the grain temperature with natural cold air during winter months, the cooling-aeration operation was also required to minimize grain moisture content loss, as well as the fan noise nuisance to nearby residents. Based on the grain and ambient air condition, the SCA system used the collected information in Aeration Window Model (AWM) for optimal control of aeration fans. The AWM was based on the CAE adsorptive equation and equilibrium absolute humidity curve. The SCA system was tested in two concrete silos of 650 tonnes in Guangzhou (22°44′N, 113°30′E) from 7 December 2018 to 5 March 2019. The system was set to turn on the fans when the temperature of grain bulk was 3 °C higher than the ambient air temperature and the equilibrium absolute humidity of grain for adsorption was above the absolute humidity of the ambient air. The grain temperature in one silo decreased by 10.3 °C after 97.8 h of aeration. The unit energy consumption by one 5.5-kW centrifugal fan was 0.063 kWht∙°C-1. The grain temperature was lowered by 9.2 °C in 106.5 h in the second silo with the unit energy consumption of 0.031kWht∙°C-1 by a 2.2-kW centrifugal fan. The unit energy consumption for both silos were 52−77% lower than the lowest “typical” value (0.132 kWht∙°C-1) in similar type of silos in the region when cooling aeration is manually controlled. Compared to the 650 tonne paddy rice in the control silo with a 15 kW aeration fan, the grain moisture content, the total milled rice yield and grain processing quality was unchanged by the smart cooling aeration with smaller kW aeration fans.
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