The present work aims to analyze the performance characteristics of the series Combined Heat and Power (CHP) system based on Organic Rankine Cycle (ORC) under influence of the heating plant parameters without considering the chemistry of the geothermal water considered as heat source. For evaluation, energetic and exergetic criteria along with the heat transfer capacities have been determined, and also the working fluid R134a has been used. The results showed that increasing the heat demand or the return temperature and only the high supply temperatures lead to destruct the net power generated by the ORC-CHP system. While, influence of the last parameters on the total exergy efficiency and losses is different; whereas raising the heat demands optimizes these exergetic indicators, variation of the supply temperature leads to an optimum for these performances. Since increasing the return temperature has purely negative impacts on all exergetic and energetic criteria, the latter can be improved by reducing this temperature with attention to the heat transfer capacities. Thus, reduction of the return temperature about 5 degrees C lowers the exhausted stream losses by app. 25% and enhances the power generation by app. 52% and the total exergy efficiency by 9%. (C) 2013 Elsevier Ltd. All rights reserved.