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The current work presents energy efficient hot air drying by controlling the relative humidity (RH) including step-down and continuous dehumidification of RH as to specify material based on Weibull and Bi-Di models. The drying characteristics of yam slices of different thickness (6, 12, 18 mm) and longan were investigated using two RH control strategies. Results showed that continuous decrease of RH was energy efficient for longan, while the step-down strategy was more energy efficient for 12 or 18 mm thick yam slices drying. In terms of drying kinetics, the step-down control strategy of RH is more energy efficient for those materials whose drying rate as well as sample’s temperature curves display three distinct stages and sample thickness is relative large. In terms of β and Bi values in Weibull and Bi-Di models respectively, it is observed that the step-down control strategy of RH drying method is more efficient when the β value exceeds 1 and the Bi value was more than 0.1. The current investigation provided an assessment method for the convective hot air drying method by controlling RH to improve drying efficient and save energy consumption.