Summarises the capabilities of the ICEPAK software to model the ice-filling and ice-melting processes for rectangular ice storage tanks with multiple harvesting icemakers. The ICEPAK numerical model describes the geometry and quantity of ice filling a rectangular storage tank and the ice-melting behaviour of particulate ice stored in the tank and calculates the tank exit water temperature as a function of time. Verification of the accuracy of the model was accomplished during ASHRAE research project RP-707, and the model results compare well with the experimental data for water level, exit water temperature, and quantity of remaining ice mass. ICEPAK is applicable to particulate ice in a tank with a bottom perimeter water outlet, rectangular storage tanks with up to four ice openings/harvester icemakers, for either ice-opening meltwater flows or uniformly distributed meltwater flows over the plan area of the tank.KEYWORDS: year 1995, ice makers, calculating, melting, ice storage, tanks, rectangular, computer programs, geometry, water temperature, accuracy, comparing, designing, energy storage