scope:

Introduction

Coupled generation - in other words, the conversion - of energy into different forms is, in the light of the wide variety of possible plant systems, one of the major technological methods currently used in the rational application of energy. It is widely discussed in the public arena in the context of the efficient use of energy. Many terms, it appears, are being used incorrectly which means that there is an urgent need for clear definition of all of these terms. The present guideline attempts to fill in a number of definition gaps which have so far, even in discussions between specialists, resulted again and again in misunderstandings.

The term "combined heat and power" (C.H.P.) or cogeneration represents all those processes whereby an energy plant, from the energies with which it is supplied, simultaneously generates several types of target energy - in other words, mechanical energy, electrical energy, heat or coldness - and passes them on to the end consumers.

The coupled generation or conversion of two or several target energies of different value can result in savings in primary energy and even to reductions in emissions. This does, however, assume that the generated target energies are also actually used. Not unless there is simultaneous consideration of the situations at the generating and consuming ends will it be possible to come to useful conclusions regarding the efficiency of such coupled generation or conversion.

A list is provided in this guideline of the physical, energy- and system-related terms which are important in the C.H.P. field. On the basis of this, decisions will preferably be made which should make clear which installations, systems and system technologies should be classed as coming within the field of coupled energy generation or conversion. Efforts are made to obtain the most comprehensive description possible and combined systems of energy conversion which include a serial conversion or application chain are included. The guideline deals on the one hand with the various ways in which C.H.P. is applied as a function of the plant technology and of the energy carriers used and on the other hand with consumer characteristics. Finally, in order to demonstrate the wide variety of C.H.P. installations, a number of systems are listed which are to be classed under combined heat and power.

Subsequent parts of the guideline will deal with the various methods used for allocation and assessing the efficiency of the coupled generation or conversion of different target energies. These parts will also be concerned with application of the methods to processes and will show, with the aid of system comparisons, the special characteristics of the C.H.P. installation as compared with other technologies for efficient utilization of energy.

The C.H.P. installation is an important technical option in integrated energy systems where energy generation or conversion and energy utilization are adjusted to each other and jointly optimised. Subsequent parts of the guideline will even cover these topics.