In this paper, the plant runs eight units of chiller with the same design specification every hour. By contract, the plant must supply 13 205 RT per hour for 24 hours a day. However, in this plant case scenario, all units of chillers are not able to run at full capacity due to low in �T of CHW and it affected the CHW production. Typically, a chiller plant that has multi-chillers do not operate all units of chiller at the same time. Therefore, a simple binary integer programming model is created to reduce the number of unit of chiller operated per hour while satisfying the cooling demand by the customer and system operational constraints. The model is solved using Solver tool in Microsoft Excel. The model showed after optimization, the number of unit of chiller operated per hour is possible to reduce one despite low in �T of CHW especially during the day and the total CHW production per hour is reduced to 12.5. © 2019 Penerbit Akademia Baru.