A great number of variables significantly influence the energetic, environmental and economic results of CHP (Combined Heating and Power) and CHCP (Combined Heating Cooling and Power) plants operation, and as a consequence their project activity is rather complex. In order to select the best layout and properly size the machines, detailed data on hourly electric, thermal, and cooling demand are necessary, so that a series of plant life cycle simulations may have to be carried out. Unfortunately, such detailed data are rarely available, because energy consumptions data for existing buildings are usually derived from aggregated monthly or bimonthly gas and electricity bills. Even more difficulties are encountered for new types of buildings, for which no consumptions data are available. In such cases, the most common procedure consists in performing, using case-oriented criteria, an estimate of the thermal and cooling consumption levels, and to refine it during construction, if necessary. This is the case of an existing medium size CHCP pilot plant for office buildings that covers the electrical, thermal, and cooling loads of two office buildings situated in a Mediterranean area (Palermo, Sicily, Italy). Estimated demand profiles were used; the effect on thermal demand of the conversion of the cooling load into thermal one through an absorption chiller was assessed. This is a very significant aspect in all warm climates zones. Cumulative curves were obtained for the aggregate thermal demand, by summing the heat direct applications and the heat consumptions for feeding the absorption chiller. In this paper the existing plant was compared with other plant configurations, varying both for machine sizes and management criterion, in order to affirm whether or not the plant selected by the designer in a simplified manner was or not an appropriate solution. The comparison was performed from an energetic and economic viewpoint.