To support its technology, a factory may consume heat and power. We can produce them inside the factory or buy them from an outside plant. For production of these energies, we use a CHP energy system consisting of a steam boiler and a backpressure turbine. Using a steady-state, bottom-up approach, a network of energy modules and mixed integer linear programming (MILP), we have developed a software package KOM9. Depending on the unit costs of different kinds of energies, we found the cost region diagram. This diagram gives an energy plant operator a recommendation for use of an optimum energy consumption of particular composition. This yields the minimum energy expense and, at most, 65.6% in cost saving. Regardless of an inexpensive production of the power, we show that sometimes it may not be optimal to operate the turbine. This is the case when refuse steam for heating purposes is available.