The sorption property data for different types of molecular sieves (synthetic zeolites) are presented in equation form. The variation of the isosteric heat of sorption with water loading is derived using Othmer's method. It is found that heat of sorption can be up to 50% greater than the latent heat of vaporization. Heat of sorption data, together with equilibrium isotherms are curve fitted and are incorporated into a numerical model of the nonlinear heat and mass transfer processes that occur in desiccant wheels. Using the numerical model, the influence of different assumptions for heat of sorption and equilibrium equation of molecular sieve on predicted optimum performance of rotary dehumidifier is evaluated. (c) 2006 Elsevier Ltd. All rights reserved.