Their high energy density and low heat losses between storage and recovery times make thermochemical processes a promising way to achieve long-term (seasonal) storage. Among the available reactor configurations, open systems using a packed bed of reactive solid are simple and efficient. This paper reports on the local operation and reactive bed behavior of such systems. Mass transfer changes within the reactive bed, which is the main limitation of such systems, was investigated using several state variables (reaction advancement, pressure drop across the salt bed and bed temperatures). Results from two experimental set-ups were analyzed: a small bench for mass transfer characterization, and a prototype at a larger scale. Both used SrBr2/H2O as reactive pair. A salt bed temperature analysis evidenced a reaction front moving within the reactive layer from the moist air inlet to its outlet. A mass transfer study showed marked changes in the reactive bed permeability during the reaction (by one order of magnitude) and with the reactive bed density (from 10(-9) to 10 m(2) when density range from 300 to 600 kW h m(-3)). During the reaction an asymmetric time course of the bed permeability was also highlighted: as f(X) in dehydration and f(1/X) in hydration. (C) 2016 Elsevier Ltd. All rights reserved.