A new dimensionless formulation, that locally accounts for heat conduction and mass diffusion in solid sorbent materials occurring in either enthalpy exchangers or desiccant wheels has been developed. Governing equations were fully normalized using classical dimensionless groups for heat and mass transfer. The model was validated using previously published results, including experimental data. The proposed equations are easily adaptable to incorporate additional features such as the influence of a supporting structure or the effects of flow entrance regions. Finally, results of a test-case are presented, indicating a possible optimization to wheel construction and compactness by reducing the felt thickness. (C) 2004 Published by Elsevier Ltd.