Determination and assessment of indices for the energy performance of district heating with cogeneration plants

The integration in a district heating network of renewable energies, waste heat or cogenerated heat is one of the key point of the 2012/27/EU Energy Efficiency Directive issued by the European Union (EU), to contribute to lower primary energy consumptions in final energy uses. The availability of an adequate set of indices that can efficaciously be used to evaluate the performance of hybrid district heating systems, in which traditional, cogenerative and renewable energy sources are integrated, becomes therefore a key aspect to assess the effectiveness of these systems. The aim of this paper is presenting a comparative analysis of different performance indices, applied to a real small-scale district heating network in operation in Turin, Italy, fed by a natural gas cogeneration plant and some boilers. All calculations are based on the experimental data of the real plant and show as the commonly employed indices for the assessment of performance of CHP units can overestimate to a great extent the real performance of the whole system, as do not take into account the heat transportation losses and the pumping electrical requirements. The results of these analyses are presented in detail in the paper.