A closed thermochemical heat storage system based on pure salt hydrate, namely SrBr2·6H2O is developed and its performance, numerically investigated. This paper focuses on system development as an addition to existing micro-combined heat and power (cogeneration). The originality of this work lies in the fact that it models the coupled heat and mass transfer with chemical reaction on a 3D geometry to be closed to reality. Besides, a reaction front model is also developed, in order to determine optimal parameters (bed porosity, bed thickness kinetic behaviour) and thermal power, required for system efficiency. Then, sensitivity of permeability and thermal conductivity on the reaction efficiency is numerically demonstrated, leading to some recommendations for future prototype development. Results exhibit a theoretical reactor energy storage density of 115 kWh m−3, storage capacity of 61 kWh, thermal efficiency of 78% (at 90% of reaction conversion) and COPth of 0.97, highlighting system performances. An average output temperature of 52 °C is numerically obtained. A comparison simulation-experiment is then performed and discussed, showing encouraging results, even if limited at lab-scale. Performances are quite similar, consolidating the idea that, waste heat from cogeneration can be re-used with 78% of efficiency.