The evaporation rate (rev) within the controlled solar drying environment is predicted through vapour balance equation in order to estimate the drying rate (rd. The solar drying model of Seginer & Bux is used for the estimation of humidity ratio difference (Δφ) where they suggested three statistical models (multiplicative model, additive model and neural network model). In direct comparison, the available data set was represented with the highest accuracy by the multiplicative model due to its limited number of parameters and small residual error. The humidity ratio difference (Δφ) is thus modelled as a product of power factors and predictors. Based on this model, the solar chimney was dimensioned and modelled.