Distributed generation (DG) appears to be the state of the art solution to efficiently meet growing
energy demand, thanks to recent cost reductions for small scale power generation units and to
energy market liberalization and also in view of insufficient capacity and reliability of existing
transmission grid or of high costs and environmental impacts of grid expansion.
In particular, the potentials of efficient small scale power production are related to the
opportunities of cogeneration: meeting significant heat requirements by activities located close to
such plants could thus yield advantages in terms of economic and energy performances. This is
especially true for urban areas, where the effects of cogeneration could be optimised through the
combination of DG and district heating. Reduction in overall fossil fuel consumption and
associated global emissions – especially in terms of greenhouse gases (GHG) – are most
important benefits associated with district heating. However, in public decision making concerns
often arise as regards local air emissions, which are frequently neglected in preliminary feasibility
studies. Models adopted in early design stages, in fact, mainly aim at cost optimisation and
emissions are usually calculated afterwards, often focusing on GHG only. More articulated
approaches, typical of regional and national energy planning, are seldom used for local small
scale projects.
In the present study, a multi-criteria model is developed to support the synthesis of optimal
cogeneration and district heating systems in terms of economic, local and global environmental
performances. The approach is applied to a project of natural gas engine based cogeneration and
district heating in North-Eastern Italy. Optimal sizing and foreseen operation of the system,
including several cogeneration units and serving, among others, a large hospital, will be presented
and compared with the results of economic optimisation models, thus assessing the effect of
pursuing compromise solutions aiming at more satisfactory environmental performances.
