There is an increasing drive towards low energy architecture and developing buildings that work with the climate rather than in spite of it. One technology in the area of low energy building design is that of utilising building thermal mass and/or active thermal storage Systems. Essentially the mass acts as a thermal flywheel and can both attenuate external energy flows and suppress internal environmental energy swings. These active thermal storage systems can take differing configurations and in this paper the results and comparisons for a few differing geometries and configurations are presented. Relationships between slab surface temperature, cooling potential and active core temperature are also presented.