A model for compressed hot air storage in a sedimentary porous rock composed of spherical rock is presented. During charging, the rock loses moisture and a dry spherical shell develops around a moist zone. The transient heat conduction, convection and mass transfer that take place during charging and discharging are simulated using a moving-grid numerical methodology for both the wet and dry zones. A process of evaporation/condensation moves the boundary between the two zones. The model is verified using data from a concrete drying experiment. A parametric study is conducted to demonstrate the sensitivity of the system to various parameters. (C) 2004 Elsevier Ltd. All rights reserved.