The energetic feasibility of CHP compared to the separate production of heat and power

At present, promotion of combined production of heat and power (CHP) plays a significant role in most national energy strategies, aiming at primary energy savings and CO2-reduction. However, it is not correct to state that rational use of energy and reduction of CO2-emission are intrinsic to CHP. The amount of energy savings and CO2-reduction by using CHP strongly depend on the performances of the CHP plants (efficiencies, valorization of electricity and heat, number of running hours) and of the characteristics of the reference situation with separate production of heat and power. Especially nowadays, as performances of separate systems for the production of electricity and heat [electricity production by combined cycle plants (efficiency > 50%) and heat production by high efficiency boilers (efficiency > 90%)] are strongly improving, the required performances of CHP plants being preferable to separate systems for the production of heat and power, have to be tightened. In this paper, a calculation methodology for evaluating the primary energy consumption and CO2-emission for both options (CHP and separate production of heat and power) is presented. Based on calculations with this methodology and with practical figures of performances of CHP plants and separate systems for production of heat and power, the boundary conditions that have to be met by CHP systems for being less energy consuming and less CO2-producing are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.