Thermochemical energy storage (TCES) systems are excellent alternatives for seasonal heat storage due to their high energy densities. In the present work, an open TCES system employed for space heating application based on strontium bromide-water vapour reactive pair is considered. A simplified one-dimensional numerical model of the reactive bed is developed and validated. Further, the effect of variation of the energy density of the reactive bed on the performance of the system is investigated. The global reaction advancement rate is observed to decrease substantially with the increase in the energy density of the reactive bed, for both hydration and dehydration processes. The ratio of the energy storage/extraction rate to the power consumed to blow the moist air through the reactive bed, during both hydration and dehydration processes, is found to decrease with an increasing energy density of the reactive bed.