The development of a thermal storage tank that supplies both long-term thermochemical and short-term sensible storage for solar hot water and space heating is reported. The thermochemical storage is based on the absorption of water by aqueous calcium chloride, a non-toxic and inexpensive liquid desiccant. Compared to water storage, the dual purpose tank provides 2.35 times the amount of energy storage per volume. Water, diluted, and concentrated calcium chloride solutions are stored in a single tank. In this paper we summarize numerical modeling and experimental work on a lab prototype that demonstrate the performance during transient charging operation. Reported data include concentration distributions, streamlines, and mass transfer rates over a relevant range of the governing dimensionless parameters. Analysis of the measured results demonstrate that the absorption storage time constant is on the order of 160 days or longer, suggesting that this concept is a promising development for solar thermal space heating systems in need of seasonal storage.