This report describes the optimization of large scale MIP models to plan economically the operation of energy systems. A number of measures were implemented to accelerate the optimization procedures included in the program package "Energy Management System". This program package is designed to economically plan the operation of any single and combined energy system (electric power system; district heating and its combinations) a week or a day in advance. Between 1 and 2 % savings in operation costs (fuel and start up costs of thermal units and costs for contracted energy) can be expected based on the experience up to now.