Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
Combined heat and power (CHP) systems are able to increase the total energy use of primary energy sources. In the CHP system studied in this paper internal combustion engines produce electricity and the hot engine cooling water is used for the heating of buildings. However, there is still waste heat left which can be fed to an organic Rankine cycle (ORC) to produce electricity. The objective of this study is to design an economic optimal ORC system taking into account the variable load for heating and the change in ambient temperature during a year. Also the auxiliary equipment such as pumps and fans are considered. A thermodynamic steady-state model is developed to simulate the changing behavior hour-by-hour of the complete system in different operating conditions. The ORC efficiency strongly varies over a year. The model allows selecting the optimal size of the heat exchangers (condenser and evaporator), the optimal mass flow rates and the maximal power of fans and pumps needed for the considered application.
