Energy management is an extremely important task, especially in the context of production processes consuming and/or producing huge amounts of different energy carders. In this paper we discuss the design and implementation of an energy management system for an integrated iron and steel plant, using object-oriented technology and a relational database. The aim of this energy management system is to supply current and prognostic information about the energy turnovers in the production units for the people working at the power plant (which is a part of the integrated iron and steel plant), to enable better controlling and adaptation of the conversion and purchase of energy. The prediction of the energy turnovers are calculated on the basis of Zeigler's discrete event system and the abstract class simulator. A major design restriction has been the ability to fine-tune the technological parameters of the prediction models in an easy way, without changes to source code. Flexibility and adaptability are important requirements that drove the design of the whole energy management system.