From cogeneration to trigeneration: profitable alternatives in a competitive market

Trigeneration refers to the combined production of electricity, heat, and cooling. In a competitive energy market framework, the adoption of Combined Heat, Cooling, and Power (CHCP) plants may become profitable with respect to traditional systems, where electricity, heat, and cooling are produced or purchased separately. This paper illustrates and evaluates the possible benefits of adopting different trigeneration alternatives in the design of a new energy system, with the specific focus on comparing different cooling production solutions. For the cooling side of CHCP systems, most of the literature refers to absorption groups fed by cogenerated thermal energy. Here, the trigeneration concept is extended to also include conventional electric chillers, heat pumps, or direct-fired absorption chillers. Comparative analysis of the trigeneration solutions is carried out for a hospital site, by performing time-domain simulations to characterize the out-of-design operation and different regulation strategies of the equipment. Poor effectiveness of using classical energy efficiency indices is discussed. A more effective economic analysis, where buying/selling electricity in a competitive market is specifically considered, is then performed. Finally, a multiscenario analysis is carried out for assessing the impact of electricity and gas price variations on the choice of the most convenient trigeneration solution.