This research was done by using a mathematical modeling for a heat storage tank by the preparation a mathematical function using MATLAB software for charging and discharging phase of the storage tank . it was applied partial storage strategy on a default building located in the city of Palmyra in the Syrian desert. peak cooling load (420 kW) and storing (1420 kw-h) within a storage tank size of "30m3" So that the store of ice at night and melting using outer fusion technology (External Melt) in thermal and electrical peak hours in the next day . The results showed the feasibility of a thermal modeling of the tank to cover the air-conditioning load cooling load required ,the results also showed the shift of part of the electrical daily load of the chiller about (576 Kw-h) with a clear reduction of mechanical and electrical equipment with the provision of using electrical energy to a summer season about (1376 kW-h/Season) and improving the daily electrical factor (DLF) achieves stability of the electric system. This paper presents the results can be generalized to large projects in the tropics help in thermal and power consumption peak shift.