The left term of the previous equation corresponds to the rate of energy gained by the dried product, and the parcels in the right side are the absorbed radiant energy, the convective heat loss, the evaporative heat loss and the radiation heat loss, respectively. I(t) is the radiation flux density at a certain day time, and may be obtained through meteorological records. When the recording time interval is very large, it may be shortened through appropriate meteorological models. A model developed by Charles-Edwards and Acock (1977) can be adopted, taking into account diurnal variation of radiation and by generating hourly values of global radiation. This model is a full sine wave and was developed to describe diurnal changes in photosynthetically active radiation