This paper describes results from a larger project  which investigated the sizing of Thermal EnergyStorage (TES) systems used as part of the cooling system in buildings. The study was based on DOE-2simulations; daily integrated cooling coil energy requirements for office and retail buildings in theChicago, Fort Worth, and Miami climates were examined in relation to climate and operational parameters. Based on these studies, it was concluded that the peak daily integrated coil load, which determines the storage capacity, occurs during multiday periods of severe weather that do not necessarily include the most severe day or the most severe hour in a particular climate. A significant component of the peak daily integrated coil load is due to energy accumulated during periods whenthe building is not cooled, and stored in building materials and furnishings; ultimately the stored energymust be removed by the cooling system in order to satisfy comfort requirements during occupied periods. The magnitude of the stored energy component of the peak depends on the lengths of the uncooled period and of the severe climate period, and on a host of building design parameters relating to its thermal capacity and its interactions with the climate.