Combined heat and power production is an old and well-known technique for the rational use of energy and, thanks to more than fifty years of experience, the state of art can be considered very advanced from a technological point of view. Trigeneration, that is combined electric, heat and cooling energy production, is however a quite recent technology and is becoming economically viable thanks to the commercial spread of absorption chillers. In fact, a well-projected trigeneration plant can achieve better results than a cogenerative one. The CHCP plant benefits over CHP will be underlined, showing the effects of regularisation of annual thermal load curves generated by consumption for feeding the absorption chiller, that leads to a more effective choice of the prime mover. Traditional evaluations of CHP or CHCP plants are finalized to calculate thermodynamic efficiency, and not to examine the primary energy savings that is possible to obtain. However, lack of considerations on the methodology used for plant management can deeply influence the obtained results. It is furthermore recognised that a cogeneration or trigenerative plant must be managed in order to strictly follow thermal demand, since it is possible to sell to the public grid the excess electric energy. This study starts from the results on a energetic consumption research in the hotel sector, and in particular from the complete data on thermal and cooling consumption in several European hotels. The authors propose a general and innovative criterion on plant management and determine, on the base of the examined case-studies, some correlations which allow to size the main components of the plant, using only few data which are easy to obtain.