Book - School of Science and Technology

690 Combined heat and power (CHP)Figure 24.2 Components of a CHP systemand,perhaps,. Supplementary heat and power sources.Figure 24.2 illustrates,in schematic form,how the various components of a simplesystem might be arranged. Similar groupings of components have been built for manyyears and the concept of independence from public supplies has always appealed toplanners. When local generation has been employed,it has usually been for one of tworeasons,either to ensure a continuity of supply where essential to the functional use of thebuilding and process or to provide complete security of an electrical supply in allcircumstances,including national disaster or insurrection.Prime moversAt this stage,it would be as well to consider the form and availability of the heat rejectedby some of the normally encountered prime movers since it is an essential to the design ofCHP systems that the marked differences in these characteristics are not only appreciatedbut put to use. The more important are:. the heat to power ratio at both full and part load. the level or levels of heat rejected. the energy input rate throughout the working range.The first of these characteristics has the greatest influence on selection of equipmentsince the exercise will be centred on matching the heat-to-power ratio of the plant to thebuilding energy-demand profiles. However,it is not enough to ensure that a match exists