Heat transfer to silos in sunlight

Abstract

Silos located outside for the storage of milk products are usually insulated. In a re-evaluation of the design of silos under. New Zealand's temperate conditions it was decided to determine whether the omission of insulation would result in an unacceptable temperature rise in the stored product. The criterion of acceptance was taken as the USA 3-A Standard, which limits the temperature rise to less than 1·67°C (3°F) over an 18-h storage period. An equation was developed to calculate the thermal energy input from sunlight into a silo, and the thermal energies at different times of the day and at different times of the year are presented. The solar heat input was combined with convective heat loads, assuming New Zealand summer ambient conditions. A greater than acceptable temperature rise occurred with a single skin silo. The insulated silo easily met the 3-A Standard, as did a silo with cladding but no insulation. In the light of this analysis, consideration should be given to installing silos with a double skin construction, i.e. cladding but no insulation, in New Zealand.